Lithium-ion battery

A lithium-ion battery, also known as a Li-ion battery, functions as a rechargeable energy storage device by employing the reversible intercalation of Li+ ions within electronically conductive solid materials. These batteries typically exhibit superior specific energy, energy density, and energy efficiency, alongside extended cycle and calendar lifespans, when contrasted with alternative rechargeable battery technologies. Following their commercial introduction in 1991, the subsequent three decades witnessed a threefold increase in the volumetric energy density of Li-ion batteries, concurrently with a tenfold reduction in their manufacturing cost. By late 2024, annual global demand for these batteries exceeded 1 terawatt-hour, with production capabilities surpassing this figure by more than double.

A lithium-ion battery or Li-ion battery is a type of rechargeable battery that uses the reversible intercalation of Li⁺ ions into electronically conducting solids to store energy. Compared to other types of rechargeable batteries, they generally have higher specific energy, energy density, and energy efficiency and a longer cycle life and calendar life. In the three decades after Li-ion batteries were first sold in 1991, their volumetric energy density increased threefold while their cost dropped tenfold. In late 2024, global demand passed 1 terawatt-hour per year, while production capacity was more than twice that.

The development and subsequent commercialization of Li-ion batteries have profoundly influenced technological advancement, a contribution acknowledged by the 2019 Nobel Prize in Chemistry. These batteries have been instrumental in the proliferation of portable consumer electronics, including laptop computers and cellular phones, as well as electric vehicles. Furthermore, their applications extend to grid-scale energy storage systems and specialized military and aerospace sectors. Unlike standardized battery types such as the AA battery, Li-ion battery dimensions are typically not uniform, presenting diverse and unique form factors dictated by specific device requirements and manufacturers. A nominal voltage of either 3.6 V or 3.7 V is characteristic of these batteries.

During the 1970s, M. Stanley Whittingham pioneered the concept of intercalation electrodes and subsequently developed the inaugural rechargeable lithium-ion battery, which utilized a titanium disulfide cathode and a lithium-aluminum anode. This early design, however, encountered safety issues and consequently did not achieve commercialization. In 1980, John Goodenough advanced this research by incorporating lithium cobalt oxide as the cathode material. Akira Yoshino developed the initial prototype of the contemporary Li-ion battery in 1985, distinguishing itself by employing a carbonaceous anode instead of lithium metal. This innovation was later commercialized in 1991 by a collaborative team from Sony and Asahi Kasei, under the leadership of Yoshio Nishi. For their pivotal contributions to the evolution of lithium-ion batteries, Whittingham, Goodenough, and Yoshino collectively received the 2019 Nobel Prize in Chemistry.

Due to the presence of flammable electrolytes, lithium-ion batteries pose potential fire or explosion hazards. Significant advancements have been achieved in the research and production of safer lithium-ion battery designs. To mitigate this risk, solid-state lithium-ion batteries are currently under development, aiming to eliminate the flammable electrolyte component. Furthermore, the recycling of these batteries can generate toxic waste, including hazardous metals, and also presents a fire risk. The extraction of lithium and other constituent minerals also presents substantial challenges; lithium mining, for instance, is water-intensive and often occurs in arid environments, while other minerals utilized in certain Li-ion chemistries, such as cobalt, may be classified as conflict minerals. These environmental concerns have prompted researchers to pursue enhanced mineral efficiency and explore alternative battery chemistries, including lithium iron phosphate Li-ion variants and non-lithium-based systems like sodium-ion and iron-air batteries.

The term 'Li-ion battery' refers to a broad category comprising at least 12 distinct battery chemistries. Lithium-ion cells can be engineered to prioritize either energy density or power density, depending on the application. For instance, handheld electronic devices predominantly utilize lithium polymer batteries, which incorporate a polymer gel electrolyte, a lithium cobalt oxide (LiCoO
§67§) cathode, and a graphite anode, a combination known for its high energy density. Conversely, chemistries such as lithium iron phosphate (LiFePO
§1718§), lithium manganese oxide (LiMn
§2829§O
§3738§) spinel, lithium-rich layered materials based on Li
§4849§MnO
§57^58§ (LMR-NMC), and lithium nickel manganese cobalt oxide (LiNiMnCoO
§6869§ or NMC) are often preferred for their extended lifespan and higher discharge capabilities. NMC and its derivative chemistries are extensively employed in the electrification of transportation, representing a key technology, when integrated with renewable energy sources, for mitigating greenhouse gas emissions from vehicles. Another high-energy lithium-ion chemistry frequently utilized in electric vehicle batteries is lithium nickel cobalt aluminum oxide (NCA).

Historical Development

Early research into lithium-ion batteries includes a CuF
§67§/Li battery developed by NASA in 1965. A significant advancement toward the contemporary Li-ion battery was achieved in 1974 by British chemist M. Stanley Whittingham, who pioneered the use of titanium disulfide (TiS
§1718§) as a cathode material. This material possesses a layered structure capable of intercalating lithium ions without substantial alterations to its crystal lattice. Exxon attempted to commercialize this battery in the late 1970s but encountered challenges due to the expensive and intricate synthesis process. Furthermore, TiS
§2829§ exhibits sensitivity to moisture, releasing toxic hydrogen sulfide (H
§3940§S) gas upon contact with water. More critically, the presence of metallic lithium within the cells rendered the batteries susceptible to spontaneous combustion. Consequently, Exxon ceased development of Whittingham's lithium-titanium disulfide battery.

In 1980, Ned A. Godshall et al., followed shortly by Koichi Mizushima and John B. Goodenough, independently conducted research that led to the replacement of TiS
§67§ with lithium cobalt oxide (LiCoO
§1718§, or LCO) after evaluating various alternative materials. LCO features a comparable layered structure but provides a higher voltage and demonstrates significantly greater stability in ambient air. This material was subsequently incorporated into the first commercial Li-ion battery, although its use alone did not fully mitigate the persistent flammability issue.

Initial endeavors to create rechargeable Li-ion batteries utilized lithium metal anodes, which were ultimately discontinued due to safety concerns. Lithium metal is inherently unstable and prone to dendrite formation, a phenomenon that can induce internal short-circuiting. The eventual resolution involved employing an intercalation anode, analogous to the cathode material, which effectively prevents the formation of metallic lithium during the battery charging process. Jürgen Otto Besenhard first demonstrated the reversible intercalation of lithium ions into graphite anodes in 1974. Besenhard's method involved organic solvents, such as carbonates, but these solvents degraded rapidly, resulting in a limited battery cycle life. Subsequently, in 1980, Rachid Yazami introduced a more stable solid organic electrolyte, polyethylene oxide.

In 1985, Akira Yoshino, affiliated with Asahi Kasei Corporation, discovered that petroleum coke, a less graphitized carbon variant, could reversibly intercalate lithium ions at a low potential of approximately 0.5 V relative to Li+/Li without experiencing structural degradation. The material's structural integrity is attributed to its amorphous carbon regions, which function as covalent linkages to secure the layers. Despite possessing a lower capacity compared to graphite (approximately Li0.5C6, 186 mAh g–1), petroleum coke became the inaugural commercial intercalation anode for Li-ion batteries due to its superior cycling stability. In 1987, Yoshino secured a patent for what would become the first commercial lithium-ion battery, incorporating this anode. His design utilized Goodenough's previously reported LiCoO₂ as the cathode and a carbonate ester-based electrolyte. The battery was assembled in a discharged state, enhancing both manufacturing safety and cost-effectiveness. By 1991, Sony commenced production and sales of the world's first rechargeable lithium-ion batteries, based on Yoshino's design. The following year, a collaborative venture between Toshiba and Asahi Kasei Co. also introduced a lithium-ion battery.

Throughout the 1990s, substantial advancements in energy density were achieved by progressively replacing Yoshino's soft carbon anode, initially with hard carbon and later with graphite. In 1990, Jeff Dahn and two colleagues at Dalhousie University in Canada reported the reversible intercalation of lithium ions into graphite when an ethylene carbonate solvent was present. This solvent, which is solid at room temperature and combined with other solvents to form a liquid, represented the final key innovation of that era, establishing the fundamental design of the modern lithium-ion battery.

In 2010, the global production capacity for lithium-ion batteries reached 20 gigawatt-hours. By 2016, this capacity increased to 28 GWh, with China contributing 16.4 GWh. Global production capacity further expanded to 767 GWh in 2020, with China accounting for 75% of this total. Estimates from various sources place 2021 production between 200 and 600 GWh, while predictions for 2023 range from 400 to 1,100 GWh.

In 2012, John B. Goodenough, Rachid Yazami, and Akira Yoshino were honored with the IEEE Medal for Environmental and Safety Technologies for their pioneering work in developing the lithium-ion battery. Subsequently, Goodenough, Whittingham, and Yoshino received the 2019 Nobel Prize in Chemistry, specifically recognizing their contributions to the advancement of lithium-ion battery technology. Additionally, Jeff Dahn was presented with the ECS Battery Division Technology Award in 2011 and the Yeager Award from the International Battery Materials Association in 2016.

Design Principles

Typically, the negative electrode in a conventional lithium-ion cell is composed of graphite, while the positive electrode generally consists of a metal oxide or phosphate. The electrolyte system employs a lithium salt dissolved in an organic solvent. To prevent internal short-circuiting, a separator physically isolates the negative electrode (which functions as the anode during discharge) from the positive electrode (which acts as the cathode during discharge). Electrical connection to the external circuit is established via two metallic components known as current collectors.

During the charging process, the negative and positive electrodes reverse their electrochemical functions, transitioning between anode and cathode roles. Nevertheless, in discussions pertaining to battery design, the negative electrode of a rechargeable cell is commonly referred to simply as "the anode," and the positive electrode as "the cathode."

When fully lithiated, in the form of LiC₆, graphite exhibits a theoretical capacity of 1339 coulombs per gram (equivalent to 372 mAh/g). The positive electrode material is typically selected from three main categories: a layered oxide (e.g., lithium cobalt oxide), a polyanion (e.g., lithium iron phosphate), or a spinel (e.g., lithium manganese oxide). More experimental materials, such as graphene-containing electrodes, are also being investigated, though their high production costs currently hinder commercial viability.

Given lithium's vigorous reaction with water, which produces lithium hydroxide (LiOH) and hydrogen gas, a non-aqueous electrolyte is invariably employed, and the battery pack is hermetically sealed to rigorously exclude moisture. This non-aqueous electrolyte commonly comprises a mixture of organic carbonates, such as ethylene carbonate and propylene carbonate, containing dissolved lithium ion complexes. Ethylene carbonate is crucial for forming a stable solid electrolyte interphase on the carbon anode; however, as it is solid at ambient temperatures, a liquid co-solvent (e.g., propylene carbonate or diethyl carbonate) is incorporated.

The predominant electrolyte salt utilized is lithium hexafluorophosphate (LiPF
₆), chosen for its favorable combination of high ionic conductivity and robust chemical and electrochemical stability. The hexafluorophosphate anion plays a vital role in passivating the aluminum current collector, which is used for the positive electrode. A titanium tab is ultrasonically welded to this aluminum current collector. Other salts, including lithium perchlorate (LiClO
§1718§), lithium tetrafluoroborate (LiBF
§2829§), and lithium bis(trifluoromethanesulfonyl)imide (LiC
§3940§F
§48_49§NO
§5758§S
§6667§), are frequently employed in research, particularly in tab-less coin cells. However, their use in larger format cells is often precluded by incompatibility with the aluminum current collector. For the negative electrode, copper, typically with a spot-welded nickel tab, serves as the current collector.

Current collector designs and surface treatments can manifest in various configurations, such as foil, mesh, dealloyed foam, wholly or selectively etched surfaces, and coatings with diverse materials, all aimed at enhancing electrical characteristics.

The selection of materials significantly influences the voltage, energy density, cycle life, and safety performance of a lithium-ion cell. Contemporary research endeavors are focused on exploring novel architectures, particularly those leveraging nanotechnology, to achieve performance improvements. Key areas of interest encompass nano-scale electrode materials and innovative electrode structures.

Electrochemistry Fundamentals

In lithium-ion cells, the electrochemical reactions involve electrode materials that are compounds containing lithium atoms. Despite extensive research into thousands of potential materials for lithium-ion batteries, only a limited selection has proven commercially viable. All commercially available lithium-ion cells utilize intercalation compounds as their active materials. Typically, the negative electrode consists of graphite, often augmented with silicon to enhance its capacity. The electrolyte commonly comprises lithium hexafluorophosphate, dissolved within a blend of organic carbonates. Various materials serve as the positive electrode, including LiCoO₂, LiFePO₄, and lithium nickel manganese cobalt oxides.

During cell discharge, the negative electrode functions as the anode and the positive electrode as the cathode, facilitating the flow of electrons from the anode to the cathode via the external circuit. An oxidation half-reaction occurring at the anode generates positively charged lithium ions and negatively charged electrons; this process may also yield uncharged material that persists at the anode. Lithium ions migrate through the electrolyte, while electrons traverse the external circuit towards the cathode, where they recombine with the cathode material in a reduction half-reaction. The electrolyte serves as a conductive medium for lithium ions but does not participate in the electrochemical reaction itself. The discharge reactions diminish the cell's chemical potential, thereby transferring energy from the cell to the external circuit where the electric current primarily dissipates its energy.

Conversely, during charging, these reactions and transport processes reverse direction, with electrons moving from the positive electrode to the negative electrode via the external circuit. To achieve cell charging, the external circuit must supply electrical energy, which is subsequently stored as chemical energy within the cell, subject to some losses, for instance, attributable to a coulombic efficiency below 1.

Both electrodes facilitate the movement of lithium ions into and out of their structures through processes termed insertion (intercalation) and extraction (deintercalation), respectively.

Due to the oscillatory movement of lithium ions between the two electrodes, these batteries are colloquially referred to as "rocking-chair batteries" or "swing batteries," a nomenclature sometimes employed by European industries.

The subsequent equations illustrate the underlying chemistry, where reactions proceeding from left to right represent discharging, and those from right to left signify charging.

The half-reaction occurring at the graphite negative electrode is presented as:

${\displaystyle {\ce {LiC6 <=> C6 + Li+ + e^-}}}$

The half-reaction occurring within the lithium-doped cobalt oxide substrate of the positive electrode is:

${\displaystyle {\ce {CoO2 + Li+ + e- <=> LiCoO2}}}$

The complete reaction is represented as:

${\displaystyle {\ce {LiC6 + CoO2 <=> C6 + LiCoO2}}}$

The overall reaction, however, is subject to certain limitations. Excessive discharge results in the supersaturation of lithium cobalt oxide, which subsequently leads to the formation of lithium oxide, potentially through the following irreversible reaction:

${\displaystyle {\ce {Li+ + e^- + LiCoO2 -> Li2O + CoO}}}$

Furthermore, overcharging the system to 5.2 volts initiates the synthesis of cobalt(IV) oxide, a phenomenon confirmed by X-ray diffraction analysis:

${\displaystyle {\ce {LiCoO2 -> Li+ + CoO2 + e^-}}}$

The energy capacity of an electrochemical cell is determined by the product of its voltage and the total charge it can deliver. Specifically, one gram of lithium corresponds to 13,901 coulombs, derived from Faraday's constant divided by 6.941. Operating at a potential of 3 V, this translates to an energy density of 41.7 kJ per gram of lithium, or 11.6 kWh per kilogram of lithium. While this energy density marginally surpasses the heat of combustion of gasoline, the overall mass of lithium-ion batteries per unit of energy remains considerably higher due to the inclusion of various auxiliary materials during manufacturing.

It is important to note that the operational cell voltages associated with these reactions exceed the electrochemical potential required for the electrolysis of aqueous solutions.

Discharge and Charge Processes

During the discharge phase, lithium ions (Li⁺
) facilitate current flow within the battery cell, migrating from the negative electrode to the positive electrode via the non-aqueous electrolyte and separator diaphragm.

Conversely, during charging, an external electrical power source applies an over-voltage—a potential exceeding the cell's intrinsic voltage—to compel electrons to traverse from the positive to the negative electrode. Concurrently, lithium ions migrate through the electrolyte from the positive to the negative electrode, where they are incorporated into the porous electrode material through a mechanism termed intercalation.

Energy dissipation attributable to electrical contact resistance at the interfaces between electrode layers and at the junctions with current collectors can constitute up to 20% of the total energy flow in batteries under standard operational parameters.

Distinct charging protocols are employed for individual lithium-ion cells compared to complete lithium-ion battery packs.

• A solitary lithium-ion cell undergoes a two-stage charging process:

1. Constant Current (CC)
2. Constant Voltage (CV)

• A lithium-ion battery pack, comprising multiple cells connected in series, is charged through a three-stage procedure:

1. Constant Current
2. Balance (necessary only when cell groups exhibit imbalance during operation)
3. Constant Voltage

During the constant current phase, the charging unit delivers a consistent current to the battery, while the voltage progressively increases until the maximum charge voltage limit for each cell is attained.

In the balance phase, the charger or battery management system modulates the charging current—either by reduction or by cycling the charge on and off to lower the average current—to equalize the state of charge among individual cells until the entire battery pack achieves equilibrium. This equalization process is typically initiated when one or more cells attain their maximum charge voltage prior to others, as performing balancing at alternative stages of the charge cycle is generally less precise. The prevalent method involves passive balancing, wherein surplus charge is dissipated as thermal energy through resistors temporarily connected across the cells requiring equalization. Conversely, active balancing, while less common and more costly, offers superior efficiency by redirecting excess energy to other cells or the entire battery pack through a DC-DC converter or analogous circuitry. Balancing predominantly takes place during the constant voltage stage of charging, with the system alternating between charge modes until the process is finalized. A battery pack is typically considered fully charged only upon the completion of balancing, given that a single cell group with a lower state of charge will restrict the overall usable capacity of the battery to its own diminished level. The duration of the balancing procedure can range from several hours to multiple days, contingent upon the extent of the imbalance within the battery.

In the constant voltage phase, the charger applies a voltage equivalent to the product of the maximum cell voltage and the number of series-connected cells in the battery. Concurrently, the charging current progressively diminishes towards zero, ceasing when it falls below a predefined threshold, typically around 3% of the initial constant charge current.

A periodic topping charge is advised approximately every 500 hours. This charging process should commence when the cell voltage drops below 4.05 V/cell.

Non-adherence to specified current and voltage parameters can induce excessive coulombic heating within the battery. Furthermore, overcharging to voltages exceeding design specifications poses a significant risk of explosion.

Lithium-ion batteries are subject to more stringent temperature limitations during charging compared to their operational limits. While lithium-ion chemistry generally performs effectively at elevated temperatures, extended thermal exposure diminishes battery longevity. Optimal charging performance, including the potential for "fast-charging," is observed within a temperature range of 5 to 45 °C (41 to 113 °F), and charging operations should ideally occur within this span. Charging remains feasible between 0 and 5 °C, though a reduction in charge current is necessary. During low-temperature charging (below 0 °C), the modest temperature increase above ambient, resulting from the cell's internal resistance, proves advantageous. Conversely, elevated charging temperatures can lead to battery degradation; specifically, charging above 45 °C will impair battery performance. At lower temperatures, the battery's internal resistance may rise, leading to slower charging rates and extended charging durations.

Batteries exhibit a gradual self-discharge phenomenon even when disconnected and not supplying current. For lithium-ion rechargeable batteries, manufacturers commonly report a self-discharge rate of 1.5–2% per month.

This self-discharge rate intensifies with increasing temperature and higher states of charge. A 2004 investigation revealed that under most cycling conditions, self-discharge was predominantly time-dependent. Nevertheless, after several months of storage on open circuit or float charge, losses attributable to the state of charge became substantial. Interestingly, the self-discharge rate did not exhibit a monotonic increase with the state of charge, showing a slight decrease at intermediate charge levels. Furthermore, self-discharge rates may escalate as batteries age. Historical data indicates that in 1999, monthly self-discharge was recorded at 8% at 21 °C, 15% at 40 °C, and 31% at 60 °C. By 2007, the estimated monthly self-discharge rate had decreased to 2% to 3%, a figure that remained consistent at 2–3% by 2016.

In contrast, the self-discharge rate for nickel-metal hydride (NiMH) batteries, as of 2017, significantly decreased from up to 30% per month for older, common cell types to approximately 0.08–0.33% per month for modern low self-discharge NiMH variants. Nickel-cadmium (NiCd) batteries, for comparison, typically exhibit a self-discharge rate of about 10% per month.

Cathode

Transition metal oxides (TMOs) are extensively employed as cathode materials in lithium-ion batteries. This widespread use stems from the variable oxidation states of transition metal cations, which enable these metal oxides to reversibly accommodate lithium ions (Li⁺) and facilitate efficient redox (reduction-oxidation) reactions. Although oxygen ions were traditionally presumed to maintain a 2- oxidation state, the contribution of oxygen redox to lithium insertion is now acknowledged as crucial for the performance of lithium-ion battery cathodes. The layered or framework architectures of TMOs permit the insertion and extraction of Li⁺ during charging and discharging cycles. Concurrently, their transition metals and oxygen anions engage in electron transfer, thereby contributing to high energy density and enhanced stability. Three distinct classes of cathode materials have achieved commercialization in lithium-ion batteries: (1) layered oxides, (2) spinel oxides, and (3) oxoanion complexes. All these materials were initially discovered by John Goodenough and his research team.

Layered Oxides

LiCoO₂ served as the cathode material in the inaugural commercial lithium-ion battery, introduced by Sony in 1991. These layered oxides exhibit a pseudo-tetrahedral architecture, characterized by layers composed of MO₆ octahedra. These layers are separated by interlayer spaces that facilitate two-dimensional lithium-ion diffusion. The band structure of Li_xCoO§6_{7§ supports genuine electronic conductivity, as opposed to polaronic conductivity. Nevertheless, an overlap between the Co⁴⁺ t2g d-band and the O^2- 2p-band necessitates that the stoichiometric coefficient 'x' be greater than 0.5; otherwise, oxygen (O§1415§) evolution will occur. This constraint restricts the charge capacity of this material to approximately 140 mA h g⁻¹.}

Several other first-row (3d) transition metals also form layered LiMO₂ salts. Some of these compounds can be synthesized directly from lithium oxide and M₂O§45§ (e.g., where M represents Ti, V, Cr, Co, or Ni), while others, such as those containing Mn or Fe, are prepared via ion exchange from NaMO§6_{7§. LiVO§89§, LiMnO§1011§, and LiFeO§1213§ exhibit structural instabilities, including mixing between M and Li sites, attributable to the minimal energy difference between octahedral and tetrahedral environments for the metal ion M. Consequently, these materials are unsuitable for use in lithium-ion batteries. In contrast, the distinct ionic radii of Na⁺ and Fe³⁺ enable the utilization of NaFeO§1819§ in sodium-ion batteries.}

Similarly, LiCrO₂ demonstrates reversible lithium (de)intercalation at approximately 3.2 V, yielding capacities between 170 and 270 mAh/g. Nevertheless, its cycle life is limited due to the disproportionation of Cr⁴⁺, which leads to the translocation of Cr⁶⁺ into tetrahedral sites. Conversely, NaCrO§6^{7§ exhibits significantly enhanced cycling stability. LiTiO§89§ undergoes Li+ (de)intercalation at a voltage of approximately 1.5 V, which is considered too low for a viable cathode material.}

These challenges restrict the practical application of layered oxide materials for lithium-ion battery cathodes primarily to LiCoO
§67§ and LiNiO
§1718§. Cobalt-based cathodes are characterized by high theoretical specific (per-mass) charge capacity, substantial volumetric capacity, minimal self-discharge, high discharge voltage, and favorable cycling performance. However, their high material cost presents a significant drawback. Consequently, the current trend among lithium-ion battery manufacturers involves transitioning to cathodes with increased nickel content and reduced cobalt content.

Beyond their lower cost compared to cobalt, nickel-oxide based materials leverage the two-electron redox chemistry of nickel. In layered oxides containing nickel, such as nickel-cobalt-manganese (NCM) and nickel-cobalt-aluminum oxides (NCA), nickel cycles between oxidation states +2 and +4 (in a single step between +3.5 and +4.3 V). Cobalt transitions between +2 and +3, while manganese (typically >20%) and aluminum (usually requiring only 5%) maintain +4 and +3 oxidation states, respectively. This mechanism implies that increasing the nickel content enhances the cyclable charge. For instance, NCM111 provides 160 mAh/g, whereas LiNi_0.8Co_0.1Mn_0.1O§78§ (NCM811) and LiNi_0.8Co_0.15Al_0.05O§1718§ (NCA) achieve a higher capacity of approximately 200 mAh/g. NCM and NCA batteries are collectively referred to as Ternary Lithium Batteries.

A notable category includes "lithium-rich" cathodes, which can be derived from conventional NCM (LiMO₂, where M=Ni, Co, Mn) layered cathode materials. These are produced by cycling them to voltages or charges corresponding to a Li:M ratio of less than 0.5. Under these conditions, a novel semi-reversible redox transition emerges at a higher voltage, involving approximately 0.4-0.8 electrons per metal site. This transition primarily involves non-bonding electron orbitals centered on oxygen atoms. Despite considerable initial interest, this phenomenon has not led to commercial products due to the rapid structural degradation, characterized by O2 evolution and lattice rearrangements, observed in such "lithium-rich" phases.

Cubic Oxide Spinels

LiMn₂O₄ adopts a cubic lattice structure, which facilitates three-dimensional lithium-ion diffusion. Manganese cathodes are appealing due to manganese's lower cost compared to cobalt or nickel. A Li-LiMn§4_{5§O§67§ battery operates at 4 V, and approximately one lithium ion per two Mn ions can be reversibly extracted from the tetrahedral sites, yielding a practical capacity below 130 mAh g–1. However, Mn³⁺ is an unstable oxidation state, prone to disproportionation into insoluble Mn⁴⁺ and soluble Mn²⁺. LiMn§1415§O§1617§ can also intercalate more than 0.5 Li per Mn at a lower voltage of around +3.0 V. Nevertheless, this process results in an irreversible phase transition attributed to the Jahn-Teller distortion in Mn3+:t2g3eg1, alongside the disproportionation and dissolution of Mn³⁺.}

A significant advancement over manganese spinel involves related cubic structures of the LiMn_1.5Ni_0.5O₄ type, where manganese exists as Mn4+ and nickel reversibly cycles between the +2 and +4 oxidation states. These materials exhibit a reversible Li-ion capacity of approximately 135 mAh/g at around 4.7 V. While such a high voltage is advantageous for increasing the specific energy of batteries, the widespread implementation of these materials is presently impeded by the absence of suitable high-voltage electrolytes. In 2023, materials with a high nickel content are generally favored due to their potential for two-electron cycling of nickel between the +2 and +4 oxidation states.

LiV₂O₄ (lithium vanadium oxide) operates at a lower voltage (approximately +3.0 V) compared to LiMn§4_{5§O§67§, exhibits comparable durability challenges, incurs higher costs, and consequently lacks practical utility.}

Oxoanionic

Approximately in 1980, Manthiram identified that oxoanions (specifically molybdates and tungstates in that instance) induce a significant positive shift in the redox potential of the metal-ion when compared to oxides. Furthermore, these oxoanionic cathode materials provide enhanced stability and safety relative to their corresponding oxide counterparts. Nevertheless, they are characterized by inadequate electronic conductivity, attributable to the extended separation between redox-active metal centers, thereby impeding electron transport. Consequently, this mandates the utilization of diminutive cathode particles (under 200 nm) and the application of an electronically conductive carbon coating to each particle. Such a requirement diminishes the packing density of these materials.

Despite extensive research into numerous combinations of oxoanions (sulfate, phosphate, silicate) with various metals (primarily Mn, Fe, Co, Ni), LiFePO₄ remains the sole commercialized compound. Initially, its application was predominantly in stationary energy storage owing to its comparatively lower energy density than layered oxides; however, it has gained widespread adoption in electric vehicles since the 2020s.

Anode

Conventionally, negative electrode materials are fabricated from graphite and other carbon materials, though contemporary silicon-based materials are experiencing growing utilization. A 2016 analysis indicated that 89% of lithium-ion batteries incorporated graphite (comprising 43% artificial and 46% natural forms), 7% utilized amorphous carbon (either soft or hard carbon), 2% employed lithium titanate (LTO), and 2% featured silicon or tin-based compositions.

These materials are employed due to their abundance, electrical conductivity, and ability to intercalate lithium ions for electrical charge storage with a modest volume expansion (approximately 10%). Graphite predominates as the material of choice owing to its low intercalation voltage and superior performance. While numerous alternative materials offering higher capacities have been suggested, they typically exhibit elevated voltages, consequently diminishing energy density. A low voltage constitutes a critical prerequisite for anodes; otherwise, any surplus capacity offers no benefit in terms of energy density.

Given graphite's maximum capacity constraint of 372 mAh/g, substantial research efforts have focused on developing materials with superior theoretical capacities and addressing the technical impediments currently hindering their practical deployment. Early investigations into silicon-based anodes for lithium-ion secondary cells are comprehensively reviewed in the extensive 2007 article by Kasavajjula et al. Specifically, in 2000, Hong Li et al. demonstrated that the electrochemical intercalation of lithium ions into silicon nanoparticles and nanowires results in the formation of an amorphous Li–Si alloy. Concurrently, Bo Gao and his doctoral supervisor, Professor Otto Zhou, reported on the cycling performance of electrochemical cells utilizing silicon nanowire anodes, exhibiting a reversible capacity spanning from approximately 900 to 1500 mAh/g.

The application of diamond-like carbon coatings has been shown to enhance the retention capacity by 40% and extend the cycle life by 400% in lithium-based batteries.

Various strategies involving the application of protective layers have been proposed to enhance the stability of lithium anodes. Silicon is emerging as a promising anode material due to its capacity to host substantially more lithium ions, potentially storing up to ten times the electrical charge. Nevertheless, the alloying process between lithium and silicon induces considerable volume expansion (approximately 400%), leading to catastrophic cell failure. Although silicon has been employed as an anode material, the repeated insertion and extraction of ${\displaystyle {\ce {\scriptstyle Li+}}}$ ions can induce material cracking. Such cracks expose the silicon surface to the electrolyte, initiating decomposition and the subsequent formation of a solid electrolyte interphase (SEI) on the newly exposed silicon (e.g., in crumpled graphene-encapsulated Si nanoparticles). The continuous thickening of this SEI consumes available ${\displaystyle {\ce {\scriptstyle Li+}}}$, thereby diminishing the anode's capacity and cycling stability.

Beyond conventional carbon- and silicon-based anode materials for lithium-ion batteries, high-entropy metal oxide materials are currently under development. These materials operate via a conversion mechanism, distinct from intercalation, and consist of an alloy (or subnanometer mixed phases) of multiple metal oxides, each contributing distinct functionalities. For instance, zinc and cobalt can function as electroactive charge-storage components, copper can serve as an electronically conductive support phase, and magnesium oxide can mitigate pulverization.

Electrolyte

Liquid electrolytes utilized in lithium-ion batteries are composed of lithium salts, including LiPF
₆, LiBF
§1718§, LiFSI, LiTFSI, or LiClO
§2829§, dissolved in organic solvents such as ethylene carbonate, dimethyl carbonate, and diethyl carbonate. During discharge, a liquid electrolyte facilitates the movement of cations, serving as a conductive pathway from the negative to the positive electrodes. At room temperature (20 °C (68 °F)), typical liquid electrolyte conductivities are approximately 10 mS/cm, exhibiting an increase of 30–40% at 40 °C (104 °F) and a slight reduction at 0 °C (32 °F). Combining linear and cyclic carbonates, such as ethylene carbonate (EC) and dimethyl carbonate (DMC), yields high conductivity and promotes the formation of a solid electrolyte interphase (SEI). Although EC contributes to a stable SEI, it remains solid at room temperature, liquefying only upon the incorporation of additives like DMC, diethyl carbonate (DEC), or ethyl methyl carbonate (EMC). During charging, organic solvents readily decompose on the negative electrodes. The initial charging process, when suitable organic solvents are employed as the electrolyte, leads to solvent decomposition and the formation of a solid electrolyte interphase. This interphase, while electrically insulating, offers substantial ionic conductivity, effectively functioning as a solid electrolyte. After the first charge cycle, the interphase thickens sufficiently to impede electron tunneling, thereby preventing further electrolyte decomposition beyond the second charge. For instance, ethylene carbonate decomposes at a relatively high voltage (0.7 V vs. lithium), resulting in a dense and stable interface. Composite electrolytes incorporating poly(oxyethylene) (POE) exhibit a comparatively stable interface. These can be either solid (high molecular weight), suitable for dry lithium-polymer cells, or liquid (low molecular weight), applicable in conventional lithium-ion cells. Room-temperature ionic liquids (RTILs) represent an alternative strategy for mitigating the flammability and volatility associated with organic electrolytes.

Solid electrolyte interphase (SEI)

The concept of the solid electrolyte interphase was initially introduced by Peled in 1979. This term characterized the insoluble product layer formed on alkali and alkaline earth cathodes within non-aqueous batteries (NAB). Prior to this, in 1970, Dey and Sullivan observed that graphite, when utilized in a lithium metal half-cell containing propylene carbonate (PC), caused electrolyte reduction during discharge. This reduction rate exhibited a linear correlation with the applied current. They hypothesized the occurrence of the following reaction:

${\displaystyle {\ce {C4H6O3 + 2e- -> CH3-CH=CH2 + CO3^{2-}}}}$

In 1990, Fong et al. subsequently proposed this identical reaction, positing that the carbonate ion interacted with lithium to generate lithium carbonate. This lithium carbonate then formed a passivating layer on the graphite surface. Currently, propylene carbonate (PC) is rarely employed in batteries because its molecules can intercalate into graphite layers, react with the lithium present, produce propylene, and consequently cause graphite delamination.

The solid electrolyte interphase (SEI) possesses insulating characteristics that enable batteries to achieve wider voltage ranges without merely reducing the electrolyte. This capacity of the SEI to enhance the voltage window in batteries was an serendipitous discovery, yet it is now crucial for contemporary high-voltage battery performance.

Solid electrolytes

Recent advancements in battery technology incorporate solid materials as electrolytes. Among these, ceramics exhibit the most significant potential. Solid ceramic electrolytes are predominantly composed of lithium metal oxides, which facilitate lithium-ion transport through the solid matrix more readily due to their intrinsic lithium content. A primary advantage of solid electrolytes is the elimination of leakage risks, a critical safety concern associated with liquid electrolyte batteries. Solid ceramic electrolytes are further categorized into two principal types: ceramic and glassy. Ceramic solid electrolytes are characterized by highly ordered compounds possessing crystal structures that typically feature ion transport channels. Examples of prevalent ceramic electrolytes include lithium super ion conductors (LISICON) and perovskites. In contrast, glassy solid electrolytes exhibit amorphous atomic structures, comprising elements similar to those found in ceramic solid electrolytes, yet they achieve superior overall conductivities, primarily owing to enhanced conductivity at grain boundaries. The ionic conductivity of both glassy and ceramic electrolytes can be augmented by substituting sulfur for oxygen. Sulfur's larger atomic radius and increased polarizability contribute to enhanced lithium conductivity. Consequently, the conductivities of solid electrolytes are approaching those of their liquid counterparts, with most exhibiting values around 0.1 mS/cm and the most effective reaching 10 mS/cm. An efficient and economical method for tailoring specific electrolyte properties involves introducing a third component, termed an additive, in minimal concentrations. The incorporation of small quantities of an additive ensures that the bulk properties of the electrolyte system remain largely unaltered, while the desired property experiences substantial enhancement. Extensive research has categorized various tested additives into three distinct groups: (1) those designed for modifying solid electrolyte interphase (SEI) chemistry; (2) those aimed at improving ion conduction characteristics; and (3) those intended to augment cell safety, such as preventing overcharging.

Alternative electrolyte formulations, such as those employed in lithium polymer batteries, have also emerged as crucial developments. Polymer electrolytes show promise in mitigating the formation of lithium dendrites. These polymers are intended to avert short circuits and sustain electrical conductivity.

Ionic diffusion within the electrolyte occurs due to minor variations in electrolyte concentration. For the purpose of this discussion, only linear diffusion is considered. The alteration in concentration, denoted as c, expressed as a function of time t and distance x, is represented by:

${\displaystyle {\frac {\partial c}{\partial t}}={\frac {D}{\varepsilon }}{\frac {\partial ^{2}c}{\partial x^{2}}}.}$

Within this equation, D represents the diffusion coefficient specific to the lithium ion. Its value is determined to be 7.5×10⁻¹⁰ m§910§/s within the LiPF
§1819§ electrolyte. The parameter ε, which denotes the electrolyte's porosity, has a value of 0.724.

Dry-Processed Electrode Manufacturing

Dry electrode manufacturing constitutes a solvent-free process for electrode preparation, offering an alternative to the conventional slurry coating technique utilized in lithium-ion batteries. In contrast to traditional methodologies that necessitate liquid solvents like N-methylpyrrolidone (NMP) for active material blending, dry electrode technology employs mechanical mixing, dry coating, and subsequent compaction to achieve a dense electrode architecture.

Process

The standard procedure for preparing dry electrodes comprises three distinct stages:

Dry mixing: Active materials, conductive agents, and binders are homogeneously combined in a solvent-free environment.

The dry coating process involves uniformly applying the powder mixture onto the current collector surface through the application of shear force.

Subsequently, the coated layer undergoes compression or calendering to attain the desired thickness and ensure adequate mechanical integrity.

Advantages

The dry electrode manufacturing process obviates the necessity for drying apparatus, NMP recovery systems, and protocols for managing viscous slurries, as it operates completely without solvents. Key benefits encompass substantial reductions in energy consumption and production expenses, the eradication of the toxic solvent NMP, improved environmental sustainability, and the capability to fabricate thicker electrodes with elevated loading capacities.

Polytetrafluoroethylene (PTFE) Fiberization Binder

Polytetrafluoroethylene (PTFE) is commonly employed as a binder in dry electrodes. When subjected to shear stress, PTFE develops an interconnected network of elongated fibers that infiltrates the entire electrode architecture. This fibrous PTFE network imparts superior mechanical strength, flexibility, and particle adhesion to the electrode, effectively mitigating structural weaknesses inherent in the absence of slurry-based processing.

Biomass Additives

Contemporary research has explored the incorporation of biomass additives, including starch, cellulose, and flour, to improve the pore structure and flexibility of electrodes. These substances facilitate intermolecular crosslinking, decrease tortuosity, and enhance electrolyte wettability. For example, the integration of 1 wt.% flour into PTFE dry electrodes substantially augments mechanical strength, expedites lithium-ion transport, and boosts high-rate performance.

Performance Enhancements

By harnessing the synergistic interplay between PTFE fiber networks and biomass additives, dry electrodes exhibit several advantages: reduced bending, accelerated lithium-ion transport, improved rate performance in high-voltage cathodes (e.g., NCM811), enhanced cycling stability attributed to reduced particle cracking, and more uniform electrolyte permeation coupled with improved interfacial stability. These observations suggest that dry electrode technology possesses considerable promise for scalable and sustainable battery production.

Challenges and Prospective Developments

While dry electrode manufacturing offers notable benefits in environmental sustainability and high energy density, it encounters obstacles in industrialization and large-scale production. Primarily, thick electrodes can display localized density inconsistencies during the pressing stage, potentially resulting in diminished cycle life or erratic electrochemical performance. Secondly, PTFE binders are associated with higher material costs, and although biomass additives contribute to pore structure enhancement, their optimal ratios must be determined to achieve a balance between performance and processing stability. Moreover, transitioning laboratory-scale preparation techniques to industrial production requires resolving challenges related to coating uniformity, consistent pressing, and stringent quality control.

Future developmental trajectories involve: investigating cost-effective or biodegradable binder alternatives; formulating thick electrode designs that reconcile high energy density with mechanical robustness; implementing automated quality monitoring systems to facilitate mass production; and employing advanced characterization techniques to optimize pore structure and ion transport characteristics. Such advancements are anticipated to propel the extensive integration of dry-process electrode technology into commercial lithium-ion batteries.

Battery Designs and Formats

Lithium-ion batteries can incorporate multiple structural levels. Compact batteries typically comprise a single cell. Larger battery systems arrange cells in parallel to form modules, and these modules are then interconnected in series and parallel configurations to create a pack. Furthermore, multiple packs can be connected in series to achieve higher voltage outputs.

Batteries can be outfitted with various components, including temperature sensors, thermal management systems (heating/cooling), voltage regulator circuits, voltage taps, and charge-state monitoring devices. These elements are crucial for mitigating safety hazards such as overheating and short circuits.

Electrode Layers and Electrolyte

At the macrostructural level (ranging from 0.1 to 5 mm), nearly all commercially available lithium-ion batteries incorporate foil current collectors, specifically aluminum for the cathode and copper for the anode. Copper is chosen for the anode due to its non-alloying behavior with lithium, while aluminum is utilized for the cathode because it undergoes passivation in LiPF₆ electrolytes.

Cells

Lithium-ion cells are manufactured in diverse form factors, which are broadly categorized into four primary types:

• Coin cells are characterized by a robust design, typically featuring a stainless steel metal casing. Due to their low specific energy (Wh/kg) and limited total energy capacity (Wh) per cell, their application is restricted to devices such as wristwatches, portable calculators, and certain research instruments. It is noteworthy that the coin cell form factor is predominantly employed for primary lithium-metal batteries.
• Small cylindrical cells, characterized by a solid body lacking external terminals, are commonly found in applications such as most e-bikes, many electric vehicle batteries, and older laptop batteries; these cells are typically manufactured in standardized dimensions.
• Large cylindrical cells feature a solid body equipped with substantial threaded terminals.
• Flat or pouch cells possess a soft, planar body and are utilized in devices like cellular phones and contemporary laptop computers; these specific types are lithium-ion polymer batteries.
• Cells encased in rigid plastic, featuring large threaded terminals, are exemplified by those found in electric vehicle traction packs.

Cylindrical cells are fabricated using a distinctive "swiss roll" method, also referred to as a "jelly roll" in the United States. This process involves coiling a lengthy "sandwich" structure comprising a positive electrode, a separator, a negative electrode, and another separator into a single spiral spool. The resulting assembly is then enclosed within a container. A notable benefit of cylindrical cell construction is its expedited production speed. Conversely, a potential drawback is the development of a significant radial temperature gradient when operating at high discharge rates.

Pouch cells achieve the highest gravimetric energy density due to the absence of a rigid casing. Nevertheless, numerous applications necessitate external containment to mitigate expansion at high states of charge (SOC) and to ensure overall structural integrity. Both rigid plastic and pouch-style cells are occasionally categorized as prismatic cells because of their characteristic rectangular geometries. In electric vehicles of the 2020s, three primary battery cell types are employed: cylindrical cells (e.g., those used by Tesla), prismatic pouch cells (e.g., from LG), and prismatic can cells (e.g., from LG, Samsung, Panasonic, among other manufacturers).

Lithium-ion flow batteries have been developed, which operate by suspending either the cathode or anode material within an aqueous or organic solution.

By 2014, the smallest reported lithium-ion cell was a pin-shaped unit manufactured by Panasonic, measuring 3.5 mm in diameter and weighing 0.6 g. A coin cell form factor is also produced for LiCoO₂ cells, typically identified by a "LiR" prefix.

Electrode layers

Cell voltage

The average voltage for lithium cobalt oxide (LCO) chemistry is 3.6 V when utilizing a hard carbon cathode, and 3.7 V when a graphite cathode is employed. The latter configuration exhibits a comparatively flatter discharge voltage curve.

Applications

Lithium-ion batteries are extensively utilized across a diverse range of applications, encompassing consumer electronics, recreational devices, power tools, and electric vehicles.

Additional specialized applications include providing backup power within telecommunications infrastructure. Furthermore, lithium-ion batteries are frequently considered as a prospective solution for grid-scale energy storage, although as of 2020, their cost-effectiveness at scale had not yet been achieved.

Certain submarine vessels have also been outfitted with lithium-ion battery systems.

Performance Characteristics

Given the wide array of available positive and negative electrode materials for lithium-ion batteries, their energy density and voltage characteristics exhibit corresponding variations.

The open-circuit voltage of lithium-ion batteries surpasses that of aqueous battery types, including lead-acid, nickel-metal hydride, and nickel-cadmium. Internal resistance tends to escalate with both operational cycling and chronological age; however, this phenomenon is significantly influenced by the storage voltage and ambient temperature. An increase in internal resistance leads to a reduction in terminal voltage under load conditions, thereby diminishing the maximum achievable current draw. Ultimately, elevated resistance can render the battery incapable of sustaining its intended discharge currents without experiencing excessive voltage drop or thermal instability.

Lithium iron phosphate batteries, utilizing a lithium iron phosphate positive electrode and a graphite negative electrode, exhibit a nominal open-circuit voltage of 3.2 V and a typical charging voltage of 3.6 V. In contrast, lithium nickel manganese cobalt (NMC) oxide positive electrodes paired with graphite negative electrodes yield a nominal voltage of 3.7 V, with a maximum charging voltage of 4.2 V. The standard charging protocol involves a constant voltage application, regulated by current-limiting circuitry. This process entails charging at a constant current until the cell reaches 4.2 V, followed by continued charging at a constant voltage until the current approaches zero. Typically, the charging cycle concludes when the current diminishes to 3% of the initial charge current. Historically, lithium-ion batteries required a minimum of two hours for a complete charge, precluding rapid charging. However, contemporary cell designs enable full charging within 45 minutes or less. A notable demonstration in 2015 by researchers involved a small 600 mAh capacity battery achieving 68 percent charge in two minutes, and a 3,000 mAh battery reaching 48 percent charge in five minutes. The latter battery demonstrated an energy density of 620 W·h/L, employing heteroatoms bonded to graphite molecules within its anode.

The performance of commercially produced batteries has consistently advanced over time. For instance, between 1991 and 2005, the energy capacity per unit price of lithium-ion batteries experienced a greater than tenfold increase, escalating from 0.3 W·h per dollar to over 3 W·h per dollar. Subsequently, from 2011 to 2017, an average annual improvement of 7.5% was observed. Cumulatively, from 1991 to 2018, the cost of all lithium-ion cell types, measured in dollars per kWh, decreased by approximately 97%. Concurrently, during this identical period, energy density more than tripled. Initiatives aimed at enhancing energy density have played a substantial role in reducing overall costs. Furthermore, energy density can be augmented through advancements in cell chemistry, such as the complete or partial substitution of graphite with silicon in anodes. The integration of silicon anodes with graphene nanotubes effectively mitigates the premature degradation of silicon, thereby facilitating the achievement of unprecedented battery energy densities, potentially reaching 350 Wh/kg, and enabling electric vehicle (EV) prices to become competitive with internal combustion engine (ICE) vehicles.

Cells of identical chemical composition and format (shape) can exhibit varying energy densities depending on their size. Jelly roll cells typically achieve a higher energy density compared to coin or prismatic cells of equivalent ampere-hour (Ah) capacity, primarily due to the more compact packing of their internal layers. Prismatic cells are inherently larger and heavier than cylindrical cells, capable of accommodating the equivalent capacity of more than 20 cylindrical cells. Within the category of cylindrical cells, larger dimensions generally correlate with increased energy density, although the precise value is significantly influenced by the thickness of the electrode layers. A notable disadvantage associated with larger cells is a reduction in the efficiency of heat transfer from the cell to its ambient environment.

Round-Trip Efficiency

An experimental evaluation conducted in 2021 assessed the round-trip efficiency of a "high-energy" type 3.0 Ah 18650 NMC cell. This assessment involved comparing the energy input to the cell with the energy extracted from it, spanning a state of charge (SoC) range from 100% (4.2 V) down to 0% (2.0 V cut-off). Round-trip efficiency is defined as the percentage of usable energy recovered from a battery relative to the total energy expended during its charging cycle.

In a separate experimental characterization performed in 2017, a cell demonstrated a round-trip efficiency of 85.5% at a 2C discharge rate and 97.6% at a 0.1C discharge rate.

Lifespan

The operational lifespan of a lithium-ion battery is conventionally quantified by the number of complete charge-discharge cycles required to reach a predefined failure threshold, typically characterized by a reduction in capacity or an increase in impedance. Manufacturers' specifications commonly employ the term "cycle life" to denote the number of cycles until the battery capacity diminishes to 80% of its initial rated value. Furthermore, merely storing lithium-ion batteries in a charged state contributes to capacity reduction (specifically, the quantity of cyclable Li⁺) and an elevation in cell resistance, primarily attributable to the ongoing development of the solid electrolyte interface on the anode. The concept of "calendar life" encompasses the battery's entire operational duration, integrating both active cycling and periods of inactive storage. Numerous stress factors influence battery cycle life, such as temperature, discharge current, charge current, and the range of states of charge (depth of discharge). In practical applications like smartphones, laptops, and electric vehicles, batteries are rarely subjected to full charge and discharge cycles, rendering the definition of battery life solely through full discharge cycles potentially inaccurate. To mitigate this ambiguity, researchers frequently utilize "cumulative discharge," defined as the total ampere-hours (Ah) delivered by the battery throughout its operational life, or "equivalent full cycles," which represents the aggregate of partial cycles expressed as fractions of a complete charge-discharge cycle. Battery degradation during storage is influenced by both temperature and the battery's state of charge (SOC); specifically, a combination of full charge (100% SOC) and elevated temperatures (typically exceeding 50 °C) can precipitate a significant capacity reduction and gas evolution. The total energy delivered over the battery's lifespan can be calculated by multiplying its cumulative discharge by the rated nominal voltage. This calculation enables the determination of the energy cost per kilowatt-hour (kWh), inclusive of charging expenses.

Throughout their operational lifespan, batteries undergo progressive degradation, resulting in a diminished cyclable charge (also known as Ah capacity) and an elevated internal resistance, which subsequently manifests as a reduced operating cell voltage.

Lithium-ion batteries are susceptible to various degradation processes, some of which manifest during active cycling, others during storage, and some continuously. Degradation exhibits a strong temperature dependency: it is minimal at ambient room temperatures but accelerates significantly when batteries are stored or operated in environments with high temperatures (typically exceeding 35 °C) or low temperatures (typically below 5 °C). Consequently, battery longevity is maximized at room temperature. Elevated charge levels also contribute to an accelerated rate of capacity loss. Moreover, frequent charging above 90% and discharging below 10% can similarly expedite capacity degradation. Maintaining the lithium-ion battery's state of charge within the approximate range of 60% to 80% can mitigate capacity reduction.

A research study employed 3D imaging and model analysis to elucidate the primary causes, underlying mechanisms, and potential mitigation strategies for the persistent degradation observed in batteries across charge cycles. The investigation revealed that "[p]article cracking increases and contact loss between particles and carbon-binder domain are observed to correlate with the cell degradation," further indicating that "the reaction heterogeneity within the thick cathode caused by the unbalanced electron conduction is the main cause of the battery degradation over cycling."

The predominant degradation mechanisms observed in lithium-ion batteries encompass the following:

1. A primary mechanism involves the reduction of the organic carbonate electrolyte at the anode, leading to the formation and growth of the Solid Electrolyte Interface (SEI). Within this interface, Li⁺ ions become irreversibly trapped, resulting in a depletion of the active lithium inventory. This phenomenon manifests as an elevated ohmic impedance of the negative electrode and a corresponding reduction in the cyclable ampere-hour (Ah) charge. Under isothermal conditions, the thickness of the SEI film, and consequently its resistance and the loss of cyclable Li⁺, progresses proportionally to the square root of the duration the battery remains in a charged state. The cumulative number of cycles is not an effective metric for characterizing this specific degradation pathway. Furthermore, under conditions of elevated temperatures or mechanical damage, the electrolyte reduction process can escalate to an explosive reaction.
2. Lithium metal plating constitutes another degradation mechanism, leading to a reduction in the active lithium inventory (cyclable Ah charge), and potentially causing internal short-circuiting and battery ignition. Upon the initiation of lithium plating during cycling, a more pronounced rate of capacity loss and resistance increase per cycle is observed. This particular degradation mechanism is exacerbated under conditions of rapid charging and low ambient temperatures.
3. Electroactive material degradation, affecting both positive and negative electrodes, can occur through various mechanisms, including dissolution (e.g., of Mn³⁺ species), cracking, exfoliation, detachment, or volumetric changes during electrochemical cycling. This degradation manifests as both charge and power fade, characterized by increased internal resistance. Specifically, both positive and negative electrode materials are susceptible to fracturing induced by the volumetric strain associated with repeated delithiation and lithiation cycles.
4. Cathode materials can undergo structural degradation, exemplified by Li⁺/Ni²⁺ cation mixing, particularly prevalent in nickel-rich compositions. Such degradation leads to phenomena like "electrode saturation," a reduction in cyclable ampere-hour (Ah) charge, and "voltage fade."
5. Additional material degradation pathways include: The copper current collector on the negative electrode is notably susceptible to corrosion and dissolution, especially at low cell voltages. Furthermore, the degradation of the PVDF binder contributes to the detachment of electroactive materials, consequently reducing the cyclable ampere-hour (Ah) charge.

• In silicon–graphite composite anodes, conductive additives, such as single-wall carbon nanotubes (SWCNTs), are employed to preserve electrical connectivity during the repeated expansion and contraction of silicon. This strategy effectively mitigates the loss of electronic contact and curtails impedance growth throughout electrochemical cycling.

These degradation phenomena are visually represented in the accompanying figure. A transition between dominant degradation mechanisms is often indicated by a "knee point" (a distinct change in slope) within the capacity versus cycle number plot.

To expedite experimental timelines, the majority of lithium-ion battery aging investigations have been conducted at elevated temperatures, typically ranging from 50–60 °C. Under these accelerated storage conditions, fully charged nickel-cobalt-aluminum (NCA) and lithium-iron phosphate (LFP) cells exhibit an approximate 20% loss of their cyclable charge within 1–2 years. This degradation is primarily attributed to anode aging, which is considered the predominant pathway in these scenarios. Conversely, manganese-based cathodes demonstrate a 20–50% faster degradation rate under similar conditions, likely due to the supplementary mechanism of manganese ion dissolution. At an ambient temperature of 25 °C, lithium-ion battery degradation appears to proceed via similar pathways as at 50 °C, albeit at approximately half the rate. Consequently, extrapolating from limited experimental data, lithium-ion batteries are projected to experience an irreversible loss of approximately 20% of their cyclable charge over 3–5 years or 1000–2000 cycles at 25 °C. Lithium-ion batteries incorporating titanate anodes exhibit resistance to solid electrolyte interphase (SEI) growth, resulting in extended cycle life (>5000 cycles) compared to those with graphite anodes. Nevertheless, in complete cell configurations, alternative degradation mechanisms—such as the dissolution of Mn³⁺, Ni²⁺/Li⁺ cation exchange, PVDF binder decomposition, and particle detachment—become prominent after 1000–2000 days, indicating that the titanate anode does not practically enhance overall cell durability.

Detailed Description of Degradation Mechanisms

A more comprehensive elucidation of specific degradation mechanisms is presented subsequently.

Recommendations

The IEEE standard 1188–1996 stipulates that lithium-ion batteries in electric vehicles should be replaced when their charge capacity diminishes to 80% of the nominal value. For comparative analysis across various studies, a 20% reduction in capacity will serve as a consistent benchmark. It is important to acknowledge, however, that the linear degradation model—which assumes a constant percentage of charge loss per cycle or per calendar time—is not universally applicable. Instead, a "knee point," characterized by a change in slope and indicative of a shift in the dominant degradation mechanism, is frequently observed.

Safety Considerations

Concerns regarding the safety of lithium-ion batteries predated their initial commercial release in 1991. The primary causes of lithium-ion battery fires and explosions are predominantly associated with processes occurring at the negative electrode (which functions as the anode during discharge and the cathode during charge). Under standard charging conditions, lithium ions intercalate into the graphite anode. Conversely, excessively rapid charging or low operating temperatures can induce lithium metal plating on the negative electrode. The resulting dendrites are capable of penetrating the battery separator, leading to an internal short-circuit, which subsequently generates high electric current, heating, and potential ignition. Furthermore, alternative mechanisms include an explosive reaction between the negative electrode material (LiC₆) and the liquid organic carbonate solvent, which can transpire even under open-circuit conditions if the electrode temperature surpasses a threshold of 70 °C.

Lithium-ion batteries, particularly those in the 18650 format or larger, integrate safety features such as a current interrupt device (CID) and a positive temperature coefficient (PTC) device. The CID comprises two electrically connected metal disks. An increase in internal pressure causes these disks to separate, thereby interrupting the circuit and ceasing current flow. The PTC device utilizes a conductive polymer; elevated current levels induce heating in the polymer, which consequently augments its electrical resistance and diminishes current flow.

Fire Hazard

Lithium-ion batteries pose a safety risk due to their flammable electrolyte content and potential for pressurization upon damage. Rapid charging of a battery cell can induce a short circuit, resulting in overheating, explosions, and conflagrations. Lithium-ion battery fires may originate from:

1. Thermal abuse, such as inadequate cooling or exposure to external fire;
2. Electrical abuse, including overcharging or an external short circuit;
3. Mechanical abuse, such as penetration or impact; or
4. An internal short circuit, potentially caused by manufacturing defects or material degradation over time.

Consequently, due to these inherent risks, testing protocols are more rigorous than those applied to acid-electrolyte batteries, necessitating a wider spectrum of test conditions and specialized battery assessments. Furthermore, safety regulators have imposed restrictions on their transportation. Several companies have initiated battery-related recalls, notably the 2016 Samsung Galaxy Note 7 recall, which was prompted by battery fires.

The presence of a flammable liquid electrolyte renders lithium-ion batteries susceptible to fire. Defective batteries can precipitate severe conflagrations. Malfunctioning chargers can compromise battery safety by damaging the integrated protection circuitry. Charging at temperatures below 0 °C can lead to the plating of pure lithium onto the negative electrode of the cells, thereby jeopardizing the safety of the entire battery pack.

A short circuit within a battery can induce cell overheating and potential ignition. Smoke emitted during thermal runaway in a lithium-ion battery possesses both flammable and toxic properties. Batteries undergo testing in accordance with the UL 9540A fire standard, while the TS-800 standard specifically evaluates fire propagation between adjacent battery containers.

Approximately in 2010, large-format lithium-ion batteries were adopted to power systems on certain aircraft, replacing alternative battery chemistries. By January 2014, the Boeing 787 passenger aircraft, introduced in 2011, had experienced at least four significant incidents involving lithium-ion battery fires or smoke, none of which resulted in crashes but all possessed the potential for catastrophic failure. UPS Airlines Flight 6 crashed in Dubai following the spontaneous ignition of its battery payload.

In an effort to mitigate fire hazards, research initiatives are focused on the development of non-flammable electrolytes.

Damaging and Overloading

Issues may emerge if a lithium-ion battery sustains damage, is crushed, or is exposed to an excessive electrical load without adequate overcharge protection. An external short circuit can precipitate a battery explosion. These incidents frequently arise when lithium-ion batteries are improperly discarded with general waste rather than being processed through designated disposal channels. Handling practices by recycling facilities can damage these batteries, leading to fires that may escalate into extensive conflagrations. In 2023, twelve such fires were documented in Swiss recycling facilities.

Overheating or overcharging can induce thermal runaway and subsequent cell rupture in lithium-ion batteries. During thermal runaway, internal degradation and oxidation processes can sustain cell temperatures exceeding 500 °C, potentially igniting secondary combustible materials and, in extreme scenarios, resulting in leakage, explosion, or fire. To mitigate these hazards, numerous lithium-ion cells and battery packs incorporate fail-safe circuitry designed to disconnect the battery if its voltage deviates from the safe operating range of 3–4.2 V per cell, or in instances of overcharge or overdischarge. Lithium battery packs lacking effective battery management circuits, irrespective of whether they are assembled by a vendor or an end-user, remain vulnerable to these problems. Furthermore, inadequately designed or improperly implemented battery management circuits can also precipitate issues; verifying the correct implementation of any specific battery management circuitry presents a considerable challenge.

Voltage Limits

Lithium-ion cells are vulnerable to damage from voltage fluctuations beyond their specified safe operating parameters, typically ranging from 2.5 V to 3.65 V, 4.1 V, 4.2 V, or 4.35 V, depending on the specific cell chemistry. Operating outside these voltage limits accelerates cell degradation and poses significant safety hazards due to the highly reactive constituents within the cells. Extended storage periods can lead to the battery's protection circuitry drawing a minimal current, potentially discharging the cell below its critical shutoff voltage. In such instances, standard charging devices may become ineffective, as the battery management system (BMS) might register this as a cell or charger malfunction. Furthermore, charging numerous lithium-ion cell chemistries below 0 °C is unsafe, as it can induce lithium plating on the anode, potentially leading to internal short circuits and other operational complications.

Individual cells necessitate the integration of additional safety mechanisms:

• A shutdown separator, designed to mitigate overheating.
• A tear-away tab, facilitating internal pressure relief.
• A vent, providing pressure relief during severe outgassing events.
• A thermal interrupt, safeguarding against overcurrent, overcharging, and excessive environmental exposure.

These safety mechanisms are essential because the negative electrode generates heat during operation, while the positive electrode can release oxygen. Nevertheless, the inclusion of these supplementary devices consumes internal cell volume, introduces additional potential failure points, and can lead to the irreversible incapacitation of the cell upon activation. Moreover, these features elevate manufacturing costs when contrasted with nickel-metal hydride batteries, which typically only necessitate a hydrogen/oxygen recombination unit and a secondary pressure valve. Internal cell contaminants possess the potential to compromise the efficacy of these safety devices. Furthermore, these safety components are not universally applicable to all cell types; for instance, prismatic high-current cells cannot incorporate a vent or a thermal interrupt. Consequently, high-current cells must be engineered to prevent the generation of excessive heat or oxygen, thereby averting potentially violent failures. Instead, such cells require internal thermal fuses designed to activate prior to the anode and cathode reaching their critical thermal thresholds.

The substitution of lithium cobalt oxide in the positive electrode of lithium-ion batteries with a lithium metal phosphate, such as lithium iron phosphate (LFP), enhances cycle life, extends shelf stability, and improves safety, albeit at the expense of reduced energy capacity. By 2006, these more secure lithium-ion battery chemistries were predominantly deployed in electric vehicles and other high-capacity battery systems where safety was paramount. In 2016, an energy storage system utilizing LFP technology was selected for installation at Paiyun Lodge on Mount Jade (Yushan), Taiwan's highest lodge. As of June 2024, this system continued to operate without incident.

Product Recalls

In 2006, approximately 10 million Sony-manufactured laptop batteries were subject to a recall. These batteries were integrated into products from various manufacturers, including Dell, Sony, Apple, Lenovo, Panasonic, Toshiba, Hitachi, Fujitsu, and Sharp. Investigations revealed that the batteries were vulnerable to internal contamination by metallic particles introduced during the manufacturing process. Under specific conditions, these particles had the potential to puncture the cell separator, leading to hazardous short circuits.

The International Air Transport Association (IATA) estimates that more than one billion lithium metal and lithium-ion cells are transported by air annually. Certain types of lithium batteries may be prohibited from air transport due to inherent fire risks. Furthermore, several postal authorities impose restrictions on the air shipment (including Express Mail Service) of lithium and lithium-ion batteries, whether packaged individually or integrated within equipment.

Non-flammable Electrolytes

As of 2023, the majority of commercially available lithium-ion batteries utilized alkylcarbonate solvents to facilitate the formation of a stable solid electrolyte interphase on the negative electrode. Given the inherent flammability of these solvents, extensive research has focused on developing non-flammable alternatives or incorporating fire suppressants. An additional safety concern arises from the hexafluorophosphate anion, which is crucial for passivating the aluminum-based negative current collector. Hexafluorophosphate reacts with water, producing volatile and toxic hydrogen fluoride. However, attempts to find suitable replacements for hexafluorophosphate have yielded limited success.

Supply Chain

In 2024, the production of lithium-ion batteries exhibited significant geographical concentration, with China accounting for 60% of global output.

During the 1990s, the United States held the position of the world's foremost producer of lithium minerals, contributing approximately one-third of the global supply. By 2010, Chile surpassed the United States as the leading miner, primarily due to the extensive development of lithium brine resources in the Salar de Atacama. As of 2024, Australia and China have emerged alongside Chile as the three principal lithium-mining nations.

Environmental Impact Considerations

The extraction of lithium, nickel, and cobalt, alongside solvent manufacturing and mining byproducts, poses substantial environmental and public health risks. Lithium extraction can result in aquatic mortality due to severe water contamination. This process has been linked to surface water and drinking water contamination, respiratory ailments, ecosystem degradation, and landscape damage. Furthermore, it exacerbates water scarcity in arid regions through unsustainable consumption, requiring approximately 1.9 million liters per ton of lithium. The substantial generation of byproducts from lithium extraction also introduces unresolved challenges, such as large volumes of magnesium and lime waste.

Global lithium mining activities are concentrated in North America, South America, Asia, South Africa, Australia, and China.

Cobalt for lithium-ion batteries is primarily sourced from the Democratic Republic of Congo. Open-pit cobalt mining in this region contributes to deforestation and habitat destruction.

Open-pit nickel mining has resulted in environmental degradation and pollution in developing nations, including the Philippines and Indonesia. In 2024, nickel mining and processing constituted a primary driver of deforestation in Indonesia.

The manufacturing of one kilogram of a lithium-ion battery requires approximately 67 megajoules (MJ) of energy. The global warming potential associated with lithium-ion battery production is highly contingent upon the energy sources utilized in mining and manufacturing operations, presenting challenges in estimation; however, a 2019 study provided an estimate of 73 kg CO2e/kWh. Effective recycling has the potential to substantially mitigate the carbon footprint associated with production.

Solid Waste Management and Recycling

The recycling of lithium-ion batteries represents a nascent but insufficiently developed industry. Notwithstanding their inherent value, global recycling rates persist at low levels; the International Energy Agency reported in 2024 that merely 5% of end-of-life electric vehicle batteries underwent recycling globally. Lithium-ion battery elements, including iron, copper, nickel, and cobalt, are amenable to recycling; however, the extraction of virgin materials frequently proves more economically viable and logistically simpler than collecting, transporting, and processing spent batteries. Nevertheless, since 2018, recycling methodologies have undergone substantial advancements, and the industrial-scale recovery of lithium, manganese, aluminum, and graphite is now achievable.

The accumulation of battery waste poses both technical complexities and public health risks. Given that the environmental impact of electric vehicles is profoundly influenced by the production of lithium-ion batteries, the imperative lies in developing efficacious strategies for waste repurposing. Recycling comprises multiple stages, commencing with battery storage prior to disposal, proceeding through manual testing and disassembly, and culminating in the chemical separation of constituent components. Battery reuse is generally favored over comprehensive recycling due to its lower embodied energy footprint. As these batteries are considerably more reactive than conventional automotive waste streams like tire rubber, substantial hazards are associated with the stockpiling of spent batteries.

Pyrometallurgical Recovery

The pyrometallurgical method employs a high-temperature furnace for the reduction of metal oxide constituents within the battery into an alloy of cobalt, copper, iron, and nickel. This is the predominant and commercially mature recycling methodology, which can be integrated with other analogous battery types to enhance smelting efficiency and optimize thermodynamic conditions. The metal current collectors facilitate the smelting operation, enabling the simultaneous melting of entire cells or modules. The output of this method comprises a metallic alloy, slag, and gaseous byproducts. At elevated temperatures, the polymers used to bind the battery cells are combusted, and the resulting metal alloy can subsequently be fractionated into its individual components via a hydrometallurgical process. The slag is amenable to further refinement or utilization within the cement industry. The process is characterized by relatively low risk, and the exothermic reaction generated by polymer combustion diminishes the requisite energy input. However, a notable drawback is the irrecoverable loss of plastics, electrolytes, and lithium salts during this process.

Hydrometallurgical Metal Reclamation

This method utilizes aqueous solutions for the extraction of target metals from the cathode material. The predominant reagent employed is sulfuric acid. Variables influencing the leaching kinetics encompass the acid concentration, reaction time, temperature, solid-to-liquid ratio, and the presence of a reducing agent. Experimental evidence demonstrates that H₂O₂ functions as a reducing agent, accelerating the leaching rate via the following reaction:

2 LiCoO_{2 (s)} + 3 H§4_{5§SO§67§ + H§89§O§1011§ → 2 CoSO§1213§ (aq) + Li§1617§SO§1819§ + 4 H§2021§O + O§2223§}

Following leaching, metal extraction can be achieved via precipitation reactions, which are regulated by adjusting the solution's pH. Subsequently, cobalt, recognized as the most valuable metal, is recoverable as sulfate, oxalate, hydroxide, or carbonate compounds. Contemporary recycling methodologies are exploring the direct synthesis of cathodes from the previously leached metals. Within these procedures, the concentrations of the diverse leached metals are precisely predetermined to correspond with the desired cathode composition, facilitating the direct synthesis of new cathodes.

Nevertheless, the primary challenges associated with this methodology include the substantial solvent volume demand and the elevated expenses linked to neutralization. While battery shredding is straightforward, the initial co-mingling of cathode and anode materials introduces complexity, necessitating their subsequent separation. Regrettably, contemporary battery designs significantly complicate this process, rendering metal separation within a closed-loop battery system particularly challenging. Consequently, the shredding and dissolution stages might be conducted at distinct geographical sites.

Direct Recycling

Direct recycling involves extracting either the cathode or anode from the electrode, subsequently reconditioning it, and then reintegrating it into a new battery. The incorporation of mixed metal-oxides into the newly formed electrode can be achieved with minimal alteration to its crystal morphology. Typically, this process entails supplementing the cathode with fresh lithium to compensate for lithium depletion resulting from electrochemical cycling degradation. Cathode strips are procured from disassembled batteries, subsequently immersed in N-Methyl-2-pyrrolidone (NMP), and subjected to sonication to eliminate superfluous deposits. Prior to annealing, the material undergoes hydrothermal treatment with a solution comprising LiOH/Li₂SO₄.

This methodology proves highly cost-efficient for non-cobalt-based batteries, primarily because raw material expenses do not constitute the predominant portion of the overall cost. Direct recycling circumvents the laborious and costly purification stages, rendering it particularly advantageous for economical cathodes like LiMn₂O₄ and LiFePO₄. In the case of these more affordable cathodes, the majority of the associated cost, embodied energy, and carbon footprint are attributable to the manufacturing process rather than the raw materials themselves. Experimental evidence indicates that direct recycling is capable of replicating properties akin to those of pristine graphite.

A significant limitation of this method pertains to the operational condition of the decommissioned battery. If a battery remains in a comparatively healthy state, direct recycling offers an economical means to reinstate its performance characteristics. Conversely, for batteries exhibiting a low state of charge, direct recycling might not represent a justifiable investment. Furthermore, the procedure necessitates customization according to the precise cathode composition, thereby requiring configuration for a single battery type at any given time. Finally, amidst an era of swift advancements in battery technology, a battery design considered optimal today may become obsolete within a decade, consequently diminishing the efficacy of direct recycling.

Physical Materials Separation

Physical materials separation facilitates material recovery through mechanical crushing and the exploitation of distinct physical properties of components, including particle size, density, ferromagnetism, and hydrophobicity. Copper, aluminum, and steel casing materials are recoverable via sorting processes. The residual materials, designated as "black mass" and comprising nickel, cobalt, lithium, and manganese, necessitate a secondary treatment for their recovery.

Biological Metals Reclamation

In biological metals reclamation, also known as bio-leaching, microorganisms are employed to selectively digest metal oxides. Subsequently, these oxides can be reduced by recyclers to yield metal nanoparticles. While bio-leaching has demonstrated efficacy within the mining sector, its application in the recycling industry remains in its nascent stages, presenting numerous avenues for further research.

Electrolyte Recycling

Electrolyte recycling encompasses two distinct phases. The initial collection phase involves extracting the electrolyte from spent lithium-ion batteries, utilizing methods such as mechanical processes, distillation, freezing, solvent extraction, or supercritical fluid extraction. This collection presents significant challenges compared to other Li-ion battery components due to the electrolyte's inherent volatility, flammability, and sensitivity. The subsequent phase focuses on separation or electrolyte regeneration. Separation entails isolating the individual constituents of the electrolyte, frequently employed for the direct recovery of lithium salts from organic solvents. Conversely, electrolyte regeneration seeks to maintain the original electrolyte composition by eliminating impurities, typically achieved through filtration techniques.

Recycling electrolytes, which constitute 10–15 wt.% of a lithium-ion battery, offers substantial economic and environmental advantages. These benefits include the reclamation of valuable lithium-based salts and the mitigation of hazardous compound release into the environment, specifically volatile organic compounds (VOCs) and carcinogens.

Electrolyte recycling in lithium-ion batteries receives less attention compared to electrode recycling, primarily due to diminished economic incentives and more significant processing complexities. These complexities include the challenges of recycling diverse electrolyte compositions, eliminating byproducts accumulated from electrolyte decomposition during operational life, and removing electrolyte adsorbed onto electrode surfaces. Consequently, contemporary pyrometallurgical methods for Li-ion battery recycling often omit electrolyte recovery, leading to the emission of hazardous gases during thermal processing. Nevertheless, given the substantial energy consumption and environmental footprint of pyrometallurgical approaches, future recycling strategies are evolving away from this methodology.

Human Rights Implications

The extraction of raw materials essential for lithium-ion battery production can pose significant risks to local communities, particularly land-dependent indigenous populations.

Cobalt obtained from the Democratic Republic of the Congo is frequently extracted by laborers employing rudimentary hand tools and minimal safety measures, leading to a high incidence of injuries and fatalities. Environmental contamination from these mining operations has exposed local populations to toxic chemicals, which health authorities associate with birth defects and respiratory ailments. Human rights organizations have asserted, and investigative reports have corroborated, the prevalence of child labor within these mining sites.

Research examining the interactions between lithium extraction corporations and indigenous communities in Argentina suggests that the state may have failed to uphold indigenous peoples' right to free, prior, and informed consent. Furthermore, these studies indicate that extraction companies typically managed community access to project information and dictated the parameters for project discussions and benefit distribution.

The proposed Thacker Pass lithium mine in Nevada, USA, has encountered opposition, including protests and legal challenges, from several indigenous tribes. These tribes assert that they were not afforded free, prior, and informed consent and that the project endangers cultural and sacred sites. Concerns regarding the potential for increased risks to indigenous women have also been raised by local communities, citing established connections between resource extraction activities and the issue of missing and murdered indigenous women. Activists have maintained an occupation of the proposed mine site since January 2021.

Ongoing Research and Development

Researchers are diligently pursuing advancements in lithium-ion battery technology, focusing on enhancing power density, safety, cycle durability (battery lifespan), recharge efficiency, cost-effectiveness, flexibility, and other critical performance attributes, alongside exploring novel research methodologies and applications. Solid-state batteries are a significant area of investigation, viewed as a potential breakthrough for overcoming existing technological limitations. Presently, solid-state batteries are widely considered the most promising candidate for next-generation energy storage, with numerous corporations actively engaged in their commercialization.

Key research domains for lithium-ion batteries encompass extending operational lifespan, augmenting energy density, bolstering safety protocols, minimizing production costs, and accelerating charging rates, among other objectives. Significant research efforts are dedicated to developing non-flammable electrolytes, aiming to enhance safety given the inherent flammability and volatility of organic solvents commonly employed in conventional electrolytes. Promising strategies under investigation include aqueous lithium-ion batteries, ceramic solid electrolytes, polymer electrolytes, ionic liquids, and highly fluorinated electrolyte systems.

A primary approach to enhancing battery performance involves the integration of diverse cathode materials, a strategy that enables researchers to augment material properties while simultaneously mitigating their inherent drawbacks. For instance, a potential method involves applying a lithium iron phosphate coating to lithium nickel manganese oxide via resonant acoustic mixing. The material produced by this process exhibits enhanced electrochemical performance and superior capacity retention. Comparable investigations have been conducted utilizing iron (III) phosphate. Given the current understanding that both transition metals and anions within cathodes contribute to the redox activity essential for lithium intercalation and deintercalation, the development of cathode materials incorporating various transition metal cations is increasingly considering oxygen redox reactions in lithium-ion battery cathodes. This approach aims to extend capacity beyond the limitations imposed by transition metals, with computational studies employing density functional theory to optimize materials and minimize structural degradation. Progress in comprehending anionic redox mechanisms has facilitated the development of stabilization strategies, such as surface fluorination, which enhance cycling stability and safety.

Anode-free battery

• Anode-free battery
• Blade battery
• Borate oxalate
• Comparison of commercial battery types
• European Battery Alliance
• Flow battery
• Nanowire battery
• Sodium-ion battery
• Thin-film lithium-ion battery
• VRLA battery
• Ultium

• The entry for "Lithium-ion Battery" in the Encyclopædia Britannica.
• NREL. (July 2015). *Degradation Mechanisms and Lifetime Prediction for Lithium-Ion Batteries*.
• NREL. (March 2013). *Impact of Temperature Extremes on Large Format Li-ion Batteries for Vehicle Applications*.