 A lithium-ion battery pack from alaptop computer | |
| Specific energy | 1–270 W⋅h/kg (3.6–972.0 kJ/kg)[1] |
|---|---|
| Energy density | 250–693 W⋅h/L (900–2,490 J/cm3)[2][3] |
| Specific power | 1–10,000 W/kg[1] |
| Charge/discharge efficiency | 80–90%[4] |
| Energy/consumer-price | 8.7 W⋅h/US$ (31 kJ/US$, $115/(kW⋅h), $32/MJ)[5] |
| Self-discharge rate | 0.35% to 2.5% per month depending on state of charge[6] |
| Cycle durability | 400–1,200cycles[7] |
| Nominal cell voltage | 3.6 / 3.7 / 3.8 / 3.85V,LiFePO 43.2 V,Li 4Ti 5O 122.3 V |
Alithium-ion battery, orLi-ion battery, is a type ofrechargeable battery that uses the reversibleintercalation of Li+ ions into electronicallyconducting solids to store energy. Li-ion batteries are characterized by higherspecific energy,energy density, andenergy efficiency and a longercycle life and calendar life than other types of rechargeable batteries. Also noteworthy is a dramatic improvement in lithium-ion battery properties after their market introduction in 1991; over the following 30 years, their volumetric energy density increased threefold while their cost dropped tenfold.[8] In late 2024 global demand passed1 terawatt-hour per year,[9] while production capacity was more than twice that.[10]
The invention and commercialization of Li-ion batterieshas had a large impact on technology,[11] as recognized by the 2019Nobel Prize in Chemistry.Li-ion batteries have enabled portableconsumer electronics,laptop computers,cellular phones, andelectric cars. Li-ion batteries also see significant use forgrid-scale energy storage as well as military and aerospace applications.[12]
M. Stanley Whittingham conceived intercalation electrodes in the 1970s and created the first rechargeable lithium-ion battery, based on atitanium disulfide cathode and a lithium-aluminium anode, although it suffered from safety problems and was never commercialized.[13]John Goodenough expanded on this work in 1980 by usinglithium cobalt oxide as a cathode.[14] The first prototype of the modern Li-ion battery, which uses a carbonaceous anode rather than lithium metal, was developed byAkira Yoshino in 1985 and commercialized by aSony andAsahi Kasei team led by Yoshio Nishi in 1991.[15] Whittingham, Goodenough, and Yoshino were awarded the 2019 Nobel Prize in Chemistry for their contributions to the development of lithium-ion batteries.
Lithium-ion batteries can be a fire or explosion hazard as they contain flammable electrolytes. Progress has been made in the development and manufacturing of safer lithium-ion batteries.[16] Lithium-ionsolid-state batteries are being developed to eliminate the flammable electrolyte.[17]Recycled batteries can create toxic waste, including from toxic metals, and are a fire risk.[18]Lithium and other minerals can have significant issues in mining, with lithium being water intensive in often arid regions and other minerals used in some Li-ion chemistries potentially beingconflict minerals such ascobalt.[19]Environmental issues have encouraged some researchers to improve mineral efficiency and find alternatives such aslithium iron phosphate lithium-ion chemistries or non-lithium-based battery chemistries such assodium-ion andiron-air batteries.
"Li-ion battery" can be considered a generic term involving at least 12 different chemistries; seeList of battery types. Lithium-ion cells can be manufactured to optimize energy density or power density.[20] Handheld electronics mostly uselithium polymer batteries (with a polymer gel as an electrolyte), a lithium cobalt oxide (LiCoO
2) cathode material, and agraphite anode, which together offer high energy density.[21][22]Lithium iron phosphate (LiFePO
4),[23]lithium manganese oxide (LiMn
2O
4spinel, orLi
2MnO
3-based lithium-rich layered materials, LMR-NMC), andlithium nickel manganese cobalt oxide (LiNiMnCoO
2 or NMC) may offer longer life and a higher discharge rate.[24] NMC and its derivatives are widely used in theelectrification of transport, one of the main technologies (combined withrenewable energy) for reducinggreenhouse gas emissions from vehicles.[25][26]
Research on rechargeable Li-ion batteries dates to the 1960s; one of the earliest examples is aCuF
2/Li battery developed byNASA in 1965. The breakthrough that produced the earliest form of the modern Li-ion battery was made by British chemistM. Stanley Whittingham in 1974, who first usedtitanium disulfide (TiS
2) as a cathode material, which has a layered structure that cantake in lithium ions without significant changes to itscrystal structure.Exxon tried to commercialize this battery in the late 1970s, but found the synthesis expensive and complex, asTiS
2 is sensitive to moisture and releases toxichydrogen sulfide (H
2S) gas on contact with water. More prohibitively, the batteries were also prone to spontaneously catch fire due to the presence of metallic lithium in the cells. For this, and other reasons, Exxon discontinued the development of Whittingham's lithium-titanium disulfide battery.[27]
In 1980, working in separate groups Ned A. Godshall et al.,[28][29][30] and, shortly thereafter,Koichi Mizushima andJohn B. Goodenough, after testing a range of alternative materials, replacedTiS
2 withlithium cobalt oxide (LiCoO
2, or LCO), which has a similar layered structure but offers a higher voltage and is much more stable in air. This material would later be used in the first commercial Li-ion battery, although it did not, on its own, resolve the persistent issue of flammability.[27]
These early attempts to develop rechargeable Li-ion batteries used lithium metal anodes, which were ultimately abandoned due to safety concerns, as lithium metal is unstable and prone todendrite formation, which can causeshort-circuiting. The eventual solution was to use an intercalation anode, similar to that used for the cathode, which prevents the formation of lithium metal during battery charging. The first to demonstrate lithium ion reversible intercalation into graphite anodes wasJürgen Otto Besenhard in 1974.[31][32] Besenhard used organic solvents such as carbonates, however these solvents decomposed rapidly providing short battery cycle life. Later, in 1980,Rachid Yazami used a solid organic electrolyte,polyethylene oxide, which was more stable.[33][34]
In 1985,Akira Yoshino atAsahi Kasei Corporation discovered thatpetroleum coke, a less graphitized form of carbon, can reversibly intercalate Li-ions at a low potential of ~0.5 V relative to Li+ /Li without structural degradation.[35] Its structural stability originates from itsamorphous carbon regions, which serve as covalent joints to pin the layers together. Although it has a lower capacity compared to graphite (~Li0.5C6, 186 mAh g–1), it became the first commercial intercalation anode for Li-ion batteries owing to its cycling stability. In 1987, Yoshino patented what would become the first commercial lithium-ion battery using this anode. He used Goodenough's previously reportedLiCoO2 as the cathode and acarbonate ester-based electrolyte. The battery was assembled in the discharged state, which made it safer and cheaper to manufacture. In 1991, using Yoshino's design,Sony began producing and selling the world's first rechargeable lithium-ion batteries. The following year, ajoint venture betweenToshiba and Asahi Kasei Co. also released a lithium-ion battery.[27]
Significant improvements in energy density were achieved in the 1990s by replacing Yoshino's soft carbon anode first withhard carbon and later with graphite. In 1990,Jeff Dahn and two colleagues atDalhousie University (Canada) reported reversible intercalation of lithium ions into graphite in the presence ofethylene carbonate solvent (which is solid at room temperature and is mixed with other solvents to make a liquid). This represented the final innovation of the era that created the basic design of the modern lithium-ion battery.[36]
In 2010, global lithium-ion battery production capacity was 20 gigawatt-hours.[37] By 2016, it was 28 GWh, with 16.4 GWh in China.[38] Global production capacity was 767 GWh in 2020, with China accounting for 75%.[39] Production in 2021 is estimated by various sources to be between 200 and 600 GWh, and predictions for 2023 range from 400 to 1,100 GWh.[40]
In 2012,John B. Goodenough,Rachid Yazami andAkira Yoshino received the 2012 IEEE Medal for Environmental and Safety Technologies for developing the lithium-ion battery; Goodenough, Whittingham, and Yoshino were awarded the 2019Nobel Prize in Chemistry "for the development of lithium-ion batteries".[41]Jeff Dahn received the ECS Battery Division Technology Award (2011) and the Yeager award from the International Battery Materials Association (2016).
In April 2025, CATL unveiled its Shenxing Plus battery, the first lithium iron phosphate (LFP) battery claiming a range of over 1,000 km (620 miles) on a single charge. The company also stated the battery supports 4C ultra-fast charging, allowing for 600 km of range to be added in 10 minutes, marking a significant advance in making long-range, fast-charging LFP batteries viable for the mass market.[42]
Generally, the negative electrode of a conventional lithium-ion cell is made fromgraphite. The positive electrode is typically a metaloxide or phosphate. Theelectrolyte is alithiumsalt in anorganicsolvent.[43] The negative electrode (which is theanode when the cell is discharging) and the positive electrode (which is thecathode when discharging) are prevented from shorting by a separator.[44] The electrodes are connected to the powered circuit through two pieces of metal called current collectors.[45]
The negative and positive electrodes swap their electrochemical roles (anode andcathode) when the cell is charged. Despite this, in discussions of battery design the negative electrode of a rechargeable cell is often just called "the anode" and the positive electrode "the cathode".
In its fully lithiated state of LiC6, graphite correlates to a theoretical capacity of 1339coulombs per gram (372 mAh/g).[46] The positive electrode is generally one of three materials: a layeredoxide (such aslithium cobalt oxide), apolyanion (such aslithium iron phosphate) or aspinel (such as lithiummanganese oxide).[47] More experimental materials includegraphene-containing electrodes, although these remain far from commercially viable due to their high cost.[48]
Lithium reacts vigorously with water to formlithium hydroxide (LiOH) andhydrogen gas. Thus, a non-aqueous electrolyte is typically used, and a sealed container rigidly excludes moisture from the battery pack. The non-aqueous electrolyte is typically a mixture of organic carbonates such asethylene carbonate andpropylene carbonate containingcomplexes of lithium ions.[49]Ethylene carbonate is essential for making solid electrolyte interphase on the carbon anode,[50] but since it is solid at room temperature, a liquidsolvent (such aspropylene carbonate ordiethyl carbonate) is added.
The electrolyte salt is almost always[citation needed]lithium hexafluorophosphate (LiPF
6), which combines goodionic conductivity with chemical and electrochemical stability. Thehexafluorophosphateanion is essential forpassivating the aluminium current collector used for the positive electrode. A titanium tab is ultrasonicallywelded to the aluminium current collector.Other salts likelithium perchlorate (LiClO
4),lithium tetrafluoroborate (LiBF
4), andlithium bis(trifluoromethanesulfonyl)imide (LiC
2F
6NO
4S
2) are frequently used in research in tab-lesscoin cells, but are not usable in larger format cells,[51] often because they are not compatible with the aluminium current collector. Copper (with aspot-weldednickel tab) is used as the current collector at the negative electrode.
Current collector design and surface treatments may take various forms: foil, mesh, foam (dealloyed), etched (wholly or selectively), and coated (with various materials) to improve electrical characteristics.[45]
Depending on materials choices, thevoltage,energy density, life, and safety of a lithium-ion cell can change dramatically. Current effort has been exploring the use ofnovel architectures usingnanotechnology to improve performance. Areas of interest include nano-scale electrode materials and alternative electrode structures.[52]
The reactants in the electrochemical reactions in a lithium-ion cell are the materials of the electrodes, both of which are compounds containing lithium atoms. Although many thousands of different materials have been investigated for use in lithium-ion batteries, only a very small number are commercially usable. All commercial Li-ion cells use intercalation compounds as active materials.[53] The negative electrode is usually graphite, althoughsilicon is often mixed in to increase the capacity. The electrolyte is usuallylithium hexafluorophosphate, dissolved in a mixture oforganic carbonates. A number of different materials are used for the positive electrode, such asLiCoO2,LiFePO4, andlithium nickel manganese cobalt oxides.
During cell discharge the negative electrode is the anode and the positive electrode the cathode: electrons flow from the anode to the cathode through the external circuit. An oxidationhalf-reaction at the anode produces positively charged lithium ions and negatively charged electrons. The oxidation half-reaction may also produce uncharged material that remains at the anode. Lithium ions move through the electrolyte; electrons move through the external circuit toward the cathode where they recombine with the cathode material in a reduction half-reaction. The electrolyte provides a conductive medium for lithium ions but does not partake in the electrochemical reaction. The reactions during discharge lower the chemical potential of the cell, so discharging transfersenergy from the cell to wherever the electric current dissipates its energy, mostly in the external circuit.
During charging these reactions and transports go in the opposite direction: electrons move from the positive electrode to the negative electrode through the external circuit. To charge the cell the external circuit has to provide electrical energy. This energy is then stored as chemical energy in the cell (with some loss, e. g., due tocoulombic efficiency lower than 1).
Both electrodes allow lithium ions to move in and out of their structures with a process calledinsertion (intercalation) orextraction (deintercalation), respectively.
As the lithium ions "rock" back and forth between the two electrodes, these batteries are also known as "rocking-chair batteries" or "swing batteries" (a term given by some European industries).[54][55]
The following equations exemplify the chemistry (left to right: discharging, right to left: charging).
The negative electrode half-reaction for the graphite is[56][57]
The positive electrode half-reaction in the lithium-doped cobalt oxide substrate is
The full reaction being
The overall reaction has its limits. Overdischarging supersaturateslithium cobalt oxide, leading to the production oflithium oxide,[58] possibly by the following irreversible reaction:
Overcharging up to 5.2 volts leads to the synthesis of cobalt (IV) oxide, as evidenced byx-ray diffraction:[59]
The cell's energy is equal to the voltage times the charge. Each gram of lithium representsFaraday's constant/6.941, or 13,901 coulombs. At 3 V, this gives 41.7 kJ per gram of lithium, or 11.6 kWh per kilogram of lithium. This is slightly more than theheat of combustion ofgasoline; however, lithium-ion batteries as a whole are still significantly heavier per unit of energy due to the additional materials used in production.
Note that the cell voltages involved in these reactions are larger than the potential at which anaqueous solutions wouldelectrolyze.
During discharge, lithium ions (Li+
) carry thecurrent within the battery cell from the negative to the positive electrode, through the non-aqueouselectrolyte and separator diaphragm.[60]
During charging, an external electrical power source applies an over-voltage (a voltage greater than the cell's own voltage) to the cell, forcing electrons to flow from the positive to the negative electrode. The lithium ions also migrate (through the electrolyte) from the positive to the negative electrode where they become embedded in the porous electrode material in a process known as intercalation.
Energy losses arising from electricalcontact resistance at interfaces betweenelectrode layers and at contacts with current collectors can be as high as 20% of the entire energy flow of batteries under typical operating conditions.[61]
The charging procedures for single Li-ion cells, and complete Li-ion batteries, are slightly different:
During theconstant current phase, the charger applies a constant current to the battery at a steadily increasing voltage, until the top-of-charge voltage limit per cell is reached.
During thebalance phase, the charger/battery reduces the charging current (or cycles the charging on and off to reduce the average current) while thestate of charge of individual cells is brought to the same level by a balancing circuit until the battery is balanced. Balancing typically occurs whenever one or more cells reach their top-of-charge voltage before the other(s), as it is generally inaccurate to do so at other stages of the charge cycle. This is most commonly done by passive balancing, whichdissipates excess charge as heat viaresistors connected momentarily across the cells to be balanced. Active balancing is less common, more expensive, but more efficient, returning excess energy to other cells (or the entire pack) via aDC-DC converter or other circuitry. Balancing most often occurs during the constant voltage stage of charging, switching between charge modes until complete. The pack is usually fully charged only when balancing is complete, as even a single cell group lower in charge than the rest will limit the entire battery's usable capacity to that of its own. Balancing can last hours or even days, depending on the magnitude of the imbalance in the battery.
During theconstant voltage phase, the charger applies a voltage equal to the maximum cell voltage times the number of cells in series to the battery, as the current gradually declines towards 0, until the current is below a set threshold of about 3% of initial constant charge current.
Periodic topping charge about once per 500 hours. Top charging is recommended to be initiated when voltage goes below4.05 V/cell.[64]
Failure to follow current and voltage limitations can result in an explosion.[65][66]
Charging temperature limits for Li-ion are stricter than the operating limits. Lithium-ion chemistry performs well at elevated temperatures but prolonged exposure to heat reduces battery life. Li‑ion batteries offer good charging performance at cooler temperatures and may even allow "fast-charging" within a temperature range of 5 to 45 °C (41 to 113 °F).[67] Charging should be performed within this temperature range. At temperatures from 0 to 5 °C charging is possible, but the charge current should be reduced. During a low-temperature (under 0 °C) charge, the slight temperature rise above ambient due to the internal cell resistance is beneficial. High temperatures during charging may lead to battery degradation and charging at temperatures above 45 °C will degrade battery performance, whereas at lower temperatures the internal resistance of the battery may increase, resulting in slower charging and thus longer charging times.[67][better source needed]
Batteries gradually self-discharge even if not connected and delivering current. Li-ion rechargeable batteries have aself-discharge rate typically stated by manufacturers to be 1.5–2% per month.[68][69]
The rate increases with temperature and state of charge. A 2004 study found that for most cycling conditions self-discharge was primarily time-dependent; however, after several months of stand on open circuit or float charge, state-of-charge dependent losses became significant. The self-discharge rate did not increase monotonically with state-of-charge, but dropped somewhat at intermediate states of charge.[70] Self-discharge rates may increase as batteries age.[71] In 1999, self-discharge per month was measured at 8% at 21 °C, 15% at 40 °C, 31% at 60 °C.[72] By 2007, monthly self-discharge rate was estimated at 2% to 3%, and 2[6]–3% by 2016.[73]
By comparison, the self-discharge rate forNiMH batteries dropped, as of 2017, from up to 30% per month for previously common cells to about 0.08–0.33% per month forlow self-discharge NiMH batteries, and is about 10% per month inNiCd batteries.[74]
Transition metal oxides (TMOs) are widely used as cathode materials in lithium-ion batteries as the variable oxidation state of transition metal cations allows oxides of these metals to reversibly host lithium ions (Li⁺) and undergo efficient redox (reduction-oxidation) reactions. While Oxygen ions are commonly assumed to remain in a 2- oxidation state, the role of oxygen redox in facilitating the lithium insertion is now recognized as instrumental in the performance of lithium ion battery cathodes.[75] The layered or framework structures of TMOs allow Li⁺ insertion/extraction during charging/discharging, while their transition metals and oxygen anions participate in electron transfer, enabling high energy density and stability. Three classes of cathode materials in lithium-ion batteries have been commercialized: (1) layered oxides, (2) spinel oxides and (3) oxoanion complexes. All of them were discovered by John Goodenough and his collaborators.[76]
LiCoO2 was used in the first commercial lithium-ion battery made by Sony in 1991. The layered oxides have a pseudo-tetrahedral structure comprising layers made of MO6octahedra separated by interlayer spaces that allow for two-dimensional lithium-iondiffusion.[citation needed] Theband structure of LixCoO2 allows for trueelectronic (rather thanpolaronic) conductivity. However, due to an overlap between the Co4+ t2g d-band with the O2- 2p-band, the x must be >0.5, otherwise O2 evolution occurs. This limits the charge capacity of this material to ~140 mA h g−1.[76]
Several other first-row (3d)transition metals also form layered LiMO2 salts. Some can be directly prepared fromlithium oxide and M2O3 (e.g. for M=Ti, V, Cr, Co, Ni), while others (M= Mn or Fe) can be prepared byion exchange from NaMO2. LiVO2, LiMnO2 and LiFeO2 suffer from structural instabilities (including mixing between M and Li sites) due to a low energy difference between octahedral and tetrahedral environments for the metal ion M. For this reason, they are not used in lithium-ion batteries.[76] However, Na+ and Fe3+ have sufficiently different sizes that NaFeO2 can be used insodium-ion batteries.[77]
Similarly, LiCrO2 shows reversible lithium (de)intercalation around 3.2 V with 170–270 mAh/g.[78] However, itscycle life is short, because ofdisproportionation of Cr4+ followed by translocation of Cr6+ into tetrahedral sites.[79] On the other hand, NaCrO2 shows a much better cycling stability.[80] LiTiO2 shows Li+ (de)intercalation at a voltage of ~1.5 V, which is too low for a cathode material.
These problems leaveLiCoO
2 andLiNiO
2 as the only practical layered oxide materials for lithium-ion battery cathodes. The cobalt-based cathodes show high theoretical specific (per-mass) charge capacity, high volumetric capacity, low self-discharge, high discharge voltage, and good cycling performance. Unfortunately, they suffer from a high cost of the material.[81] For this reason, the current trend among lithium-ion battery manufacturers is to switch to cathodes with higher Ni content and lower Co content.[82]
In addition to a lower (than cobalt) cost, nickel-oxide based materials benefit from the two-electron redox chemistry of Ni: in layered oxides comprising nickel (such as nickel-cobalt-manganeseNCM and nickel-cobalt-aluminium oxidesNCA), Ni cycles between the oxidation states +2 and +4 (in one step between +3.5 and +4.3 V),[83][76] cobalt- between +2 and +3, while Mn (usually >20%) and Al (typically, only 5% is needed)[84] remain in +4 and 3+, respectively. Thus increasing the Ni content increases the cyclable charge. For example, NCM111 shows 160 mAh/g, whileLiNi0.8Co0.1Mn0.1O2 (NCM811) andLiNi0.8Co0.15Al0.05O2 (NCA) deliver a higher capacity of ~200 mAh/g.[85] NCM and NCA batteries are collectively called Ternary Lithium Batteries.[86][87]
It is worth mentioning so-called "lithium-rich" cathodes that can be produced from traditional NCM (LiMO2, where M=Ni, Co, Mn) layered cathode materials upon cycling them to voltages/charges corresponding to Li:M<0.5. Under such conditions a new semi-reversible redox transition at a higher voltage with ca. 0.4-0.8 electrons/metal site charge appears. This transition involves non-binding electron orbitals centered mostly on O atoms. Despite significant initial interest, this phenomenon did not result in marketable products because of the fast structural degradation (O2 evolution and lattice rearrangements) of such "lithium-rich" phases.[88]
LiMn2O4 adopts a cubic lattice, which allows for three-dimensional lithium-ion diffusion.[89] Manganese cathodes are attractive because manganese is less expensive than cobalt or nickel. The operating voltage of Li-LiMn2O4 battery is 4 V, and ca. one lithium per two Mn ions can be reversibly extracted from the tetrahedral sites, resulting in a practical capacity of <130 mA h g–1. However, Mn3+ is not a stable oxidation state, as it tends todisporportionate into insoluble Mn4+ and soluble Mn2+.[81][90] LiMn2O4 can also intercalate more than 0.5 Li per Mn at a lower voltage around +3.0 V. However, this results in an irreversiblephase transition due toJahn-Teller distortion in Mn3+:t2g3eg1, as well asdisproportionation and dissolution of Mn3+.
An important improvement of Mn spinel are related cubic structures of the LiMn1.5Ni0.5O4 type, where Mn exists as Mn4+ and Ni cycles reversibly between theoxidation states +2 and +4.[76] This materials show a reversible Li-ion capacity of ca. 135 mAh/g around 4.7 V. Although such high voltage is beneficial for increasing thespecific energy of batteries, the adoption of such materials is currently hindered by the lack of suitable high-voltage electrolytes.[85] In general, materials with a highnickel content are favored in 2023, because of the possibility of a 2-electron cycling of Ni between theoxidation states +2 and +4.
LiV2O4 (lithium vanadium oxide) operates as a lower (ca. +3.0 V) voltage thanLiMn2O4, suffers from similar durability issues, is more expensive, and thus is not considered of practical interest.[91]
Around 1980Manthiram discovered thatoxoanions (molybdates andtungstates in that particular case) cause a substantial positive shift in the redox potential of the metal-ion compared to oxides.[92] In addition, these oxoanionic cathode materials offer better stability/safety than the corresponding oxides. However, they also suffer from poor electronic conductivity due to the long distance between redox-active metal centers, which slows down the electron transport. This necessitates the use of small (less than 200 nm) cathode particles and coating each particle with a layer of electronically-conducting carbon.[93] This reduces thepacking density of these materials.
Although numerous combinations of oxoanions (sulfate,phosphate,silicate) with various metals (mostly Mn, Fe, Co, Ni) have been studied,LiFePO4 is the only one that has been commercialized. Although it was originally used primarily forstationary energy storage due to its lower energy density compared to layered oxides,[94] it has begun to be widely used in electric vehicles since the 2020s.[95]
| Technology | Major producers (2023) | Target application | Advantages |
|---|---|---|---|
| Lithium nickel manganese cobalt oxide NMC, LiNixMnyCozO2 | Ronbay Technology, Easpring, Ecopro,Umicore, L&F,Posco[96] | Electric vehicles,power tools,grid energy storage | Good specific energy and specific power density |
| Lithium nickel cobalt aluminium oxide NCA, LiNiCoAlO2 | Ronbay Technology, Ecopro[96] | Electric vehicles,power tools,grid energy storage | High energy density, good life span |
| Lithium nickel cobalt manganese aluminium oxide NCMA,LiNi 0.89Co 0.05Mn 0.05Al 0.01O 2 | LG Chem,[97]Hanyang University[98] | Electric vehicles,grid energy storage | Good specific energy, improved long-term cycling stability, faster charging |
| Lithium manganese oxide LMO, LiMn2O4 | Posco, L&F[96] | Power tools, electric vehicles[99] | Fast charging speed, cheap |
| Lithium iron phosphate LFP, LiFePO4 | Shenzhen Dynanonic,Hunan Yuneng, LOPAL, Ronbay Technology[96] | Electric vehicles,[95] grid energy storage[94] | Higher safety compared to layered oxides. Very long cycle life. Thermal stability >60 °C (140 °F) |
| Lithium cobalt oxide LCO, LiCoO2 | Easpring, Umicore[96] | Handheld electronics[96] | High energy density |
Negative electrode materials are traditionally constructed from graphite and other carbon materials, although newer silicon-based materials are being increasingly used (seeNanowire battery). In 2016, 89% of lithium-ion batteries contained graphite (43% artificial and 46% natural), 7% contained amorphous carbon (either soft carbon orhard carbon), 2% contained lithium titanate (LTO) and 2% contained silicon or tin-based materials.[100]
These materials are used because they are abundant, electrically conducting and can intercalate lithium ions to store electrical charge with modest volume expansion (~10%).[101] Graphite is the dominant material because of its low intercalation voltage and excellent performance. Various alternative materials with higher capacities have been proposed, but they usually have higher voltages, which reduces energy density.[102] Low voltage is the key requirement for anodes; otherwise, the excess capacity is useless in terms of energy density.
| Technology | Energy density | Durability | Company | Target application | Comments |
|---|---|---|---|---|---|
| Graphite | 260 Wh/kg | Tesla | The dominant negative electrode material used in lithium-ion batteries, limited to a capacity of 372 mAh/g.[46] | Low cost and good energy density. Graphite anodes can accommodate one lithium atom for every six carbon atoms. Charging rate is governed by the shape of the long, thin graphene sheets that constitute graphite. While charging, the lithium ions must travel to the outer edges of the graphene sheet before coming to rest (intercalating) between the sheets. The circuitous route takes so long that they encounter congestion around those edges.[103] | |
| Lithium titanate LTO, Li4Ti5O12 | Toshiba,Altairnano | Automotive (Phoenix Motorcars), electrical grid (PJM Interconnection Regional Transmission Organization control area,[104]United States Department of Defense[105]), bus (Proterra) | Improved output, charging time, durability (safety, operating temperature −50–70 °C (−58–158 °F)).[106] | ||
| Hard carbon | Energ2[107] | Home electronics | Greater storage capacity. | ||
| Tin/cobalt alloy | Sony | Consumer electronics (Sony Nexelion battery) | Larger capacity than a cell with graphite (3.5 Ah 18650-type cell). | ||
| Silicon/carbon | 730 Wh/L 450 Wh/kg | Amprius[108] | Smartphones, providing 5000 mAh capacity | Pure Si can present a capacity density around 4200 mAh/g, but it will undergo a severe volume expansion (>300%), so it often being mixed with graphite.[109]Another approach used carbon-coated 15 nm thick crystal silicon flakes. The tested half-cell achieved 1200 mAh/g over 800 cycles.[110] |
As graphite is limited to a maximum capacity of 372 mAh/g[46] much research has been dedicated to the development of materials that exhibit higher theoretical capacities and overcoming the technical challenges that presently encumber their implementation. The extensive 2007 Review Article by Kasavajjula et al.[111]summarizes early research on silicon-based anodes for lithium-ion secondary cells. In particular, Hong Li et al.[112] showed in 2000 that the electrochemical insertion of lithium ions in siliconnanoparticles and silicon nanowires leads to the formation of an amorphous Li–Si alloy. The same year, Bo Gao and his doctoral advisor, Professor Otto Zhou described the cycling of electrochemical cells with anodes comprising silicon nanowires, with a reversible capacity ranging from at least approximately 900 to 1500 mAh/g.[113]
Diamond-like carbon coatings can increase retention capacity by 40% and cycle life by 400% for lithium based batteries.[114]
To improve the stability of the lithium anode, several approaches to installing a protective layer have been suggested.[115] Silicon is beginning to be looked at as an anode material because it can accommodate significantly more lithium ions, storing up to 10 times the electric charge, however this alloying between lithium and silicon results in significant volume expansion (ca. 400%),[101] which causes catastrophic failure for the cell.[116] Silicon has been used as an anode material but the insertion and extraction of can create cracks in the material. These cracks expose the Si surface to an electrolyte, causing decomposition and the formation of a solid electrolyte interphase (SEI) on the new Si surface (crumpled graphene encapsulated Si nanoparticles). This SEI will continue to grow thicker, deplete the available, and degrade the capacity and cycling stability of the anode.
In addition to carbon- and silicon- based anode materials for lithium-ion batteries, high-entropy metal oxide materials are being developed. These conversion (rather than intercalation) materials comprise an alloy (or subnanometer mixed phases) of several metal oxides performing different functions. For example, Zn and Co can act as electroactive charge-storing species, Cu can provide an electronically conducting support phase and MgO can prevent pulverization.[117]
Liquid electrolytes in lithium-ion batteries consist of lithiumsalts, such asLiPF
6,LiBF
4 orLiClO
4 in anorganicsolvent, such asethylene carbonate,dimethyl carbonate, anddiethyl carbonate.[118] A liquid electrolyte acts as a conductive pathway for the movement of cations passing from the negative to the positive electrodes during discharge. Typical conductivities of liquid electrolyte at room temperature (20 °C (68 °F)) are in the range of 10 mS/cm, increasing by approximately 30–40% at 40 °C (104 °F) and decreasing slightly at 0 °C (32 °F).[119] The combination of linear and cyclic carbonates (e.g.,ethylene carbonate (EC) anddimethyl carbonate (DMC)) offers high conductivity andsolid electrolyte interphase (SEI)-forming ability. While EC forms a stable SEI, it is not a liquid at room temperature, only becoming a liquid with the addition of additives such as the previously mentioned DMC ordiethyl carbonate (DEC) orethyl methyl carbonate (EMC). Organic solvents easily decompose on the negative electrodes during charge. When appropriateorganic solvents are used as the electrolyte, the solvent decomposes on initial charging and forms a solid layer called the solid electrolyte interphase,[120] which is electrically insulating, yet provides significant ionic conductivity, behaving as a solid electrolyte. The interphase prevents further decomposition of the electrolyte after the second charge as it grows thick enough to prevent electron tunneling after the first charge cycle. For example,ethylene carbonate is decomposed at a relatively high voltage, 0.7 V vs. lithium, and forms a dense and stable interface.[121] Composite electrolytes based on POE (poly(oxyethylene)) provide a relatively stable interface.[122][123] It can be either solid (high molecular weight) and be applied in dry Li-polymer cells, or liquid (low molecular weight) and be applied in regular Li-ion cells.Room-temperature ionic liquids (RTILs) are another approach to limiting the flammability and volatility of organic electrolytes.[124]
The term solid electrolyte interphase was first coined by Peled in 1979 to describe the layer of insoluble products deposited on alkali and alkaline earth cathodes in non-aqueous batteries (NAB).[125] However, Dey and Sullivan had noted previously in 1970 that graphite, in a lithium metal half cell usingpropylene carbonate (PC), reduced the electrolyte during discharge at a rate which linearly increased with the current.[126] They proposed that the following reaction was taking place:
The same reaction was later proposed by Fong et al in 1990, where they theorized that the carbonate ion was reacting with the lithium to formlithium carbonate, which was then forming a passivating layer on the surface of the graphite.[127] PC is no longer used in batteries today as the molecules can intercalate into the graphite layers and react with the lithium there to form propylene and acts to delaminate the graphite.
The insulating properties of the SEI allow the battery to reach more extreme voltage gaps without simply reducing the electrolyte.[128] This ability of the SEI to improve the voltage window of batteries was discovered almost by accident but plays a vital role in high voltage batteries today.
Recent advances in battery technology involve using a solid as the electrolyte material. The most promising of these are ceramics.[129] Solid ceramic electrolytes are mostly lithium metaloxides, which allow lithium-ion transport through the solid more readily due to the intrinsic lithium. The main benefit of solid electrolytes is that there is no risk ofleaks, which is a serious safety issue for batteries with liquid electrolytes.[130] Solid ceramic electrolytes can be further broken down into two main categories: ceramic and glassy.Ceramic solid electrolytes are highly ordered compounds withcrystal structures that usually have ion transport channels.[131] Common ceramic electrolytes are lithiumsuper ion conductors (LISICON) andperovskites.Glassy solid electrolytes areamorphous atomic structures made up of similar elements to ceramic solid electrolytes but have higherconductivities overall due to higher conductivity at grain boundaries.[132] Both glassy and ceramic electrolytes can be made more ionically conductive by substituting sulfur for oxygen. The larger radius of sulfur and its higher ability to bepolarized allow higher conductivity of lithium. This contributes to conductivities of solid electrolytes are nearing parity with their liquid counterparts, with most on the order of 0.1 mS/cm and the best at 10 mS/cm.[133] An efficient and economic way to tune targeted electrolytes properties is by adding a third component in small concentrations, known as an additive.[134] By adding the additive in small amounts, the bulk properties of the electrolyte system will not be affected whilst the targeted property can be significantly improved. The numerous additives that have been tested can be divided into the following three distinct categories: (1) those used for SEI chemistry modifications; (2) those used for enhancing the ion conduction properties; (3) those used for improving the safety of the cell (e.g. prevent overcharging).[citation needed]
Electrolyte alternatives have also played a significant role, for example thelithium polymer battery. Polymer electrolytes are promising for minimizing the dendrite formation of lithium. Polymers are supposed to prevent short circuits and maintain conductivity.[115]
The ions in the electrolyte diffuse because there are small changes in the electrolyte concentration. Linear diffusion is only considered here. The change in concentrationc, as a function of timet and distancex, is
In this equation,D is thediffusion coefficient for the lithium ion. It has a value of7.5×10−10 m2/s in theLiPF
6 electrolyte. The value forε, the porosity of the electrolyte, is 0.724.[135]
Dry electrode manufacturing is a solvent-free electrode preparation process that serves as an alternative to the traditional slurry coating method for lithium-ion batteries[136]. Unlike conventional methods requiring liquid solvents such as N-methylpyrrolidone (NMP) to mix active materials, dry electrode technology relies on mechanical mixing, dry coating, and compaction to form a dense electrode structure.
The typical preparation of dry electrodes involves three steps[137]:
Dry mixing: Active materials, conductive agents, and binders are uniformly blended under solvent-free conditions.
Dry coating: The powder mixture is evenly coated onto the current collector surface under shear force.
Compression/Calendering: The coated layer is compressed to achieve the target thickness and sufficient mechanical strength.
The dry electrode process eliminates the need for drying equipment, NMP recovery systems, or procedures for handling thick slurries since it operates entirely without solvents. Its advantages include: significantly reduced energy consumption and manufacturing costs, elimination of the toxic solvent NMP, enhanced environmental sustainability, and the ability to produce thicker electrodes with higher loading capacities[138].
Dry electrodes typically utilize polytetrafluoroethylene (PTFE) as a binder. Under shear stress, PTFE forms a network of elongated fibers that permeates the entire electrode structure[139]. This PTFE fiber network provides the electrode with exceptional mechanical strength, flexibility, and particle adhesion, thereby compensating for structural deficiencies in the absence of slurry mixing.
Recent studies have introduced biomass additives such as starch, cellulose, and flour to enhance the pore structure and flexibility of electrodes. These additives promote intermolecular crosslinking, reduce tortuosity, and improve electrolyte wettability. For instance, incorporating 1 wt.% flour into PTFE dry electrodes significantly increases mechanical strength, accelerates lithium-ion transport, and enhances high-rate performance[140].
Leveraging the synergistic interaction between PTFE fiber networks and biomass additives, dry electrodes demonstrate: reduced bending, accelerated lithium-ion transport, enhanced rate performance in high-voltage cathodes (e.g., NCM811), superior cycling stability due to diminished particle cracking, and more uniform electrolyte permeation with improved interfacial stability[141]. These findings indicate that dry electrode technology holds significant potential for scalable, sustainable battery manufacturing.
Although dry electrode manufacturing excels in environmental friendliness and high energy density, it still faces challenges in industrialization and mass production[142]. First, high-thickness electrodes may exhibit localized density variations during pressing, leading to reduced cycle life or unstable electrochemical performance. Second, PTFE binders carry higher costs, and while biomass additives help improve pore structure, their ratios require optimization to balance performance and processing stability. Furthermore, scaling up laboratory-scale preparation methods to industrial production necessitates addressing issues such as coating uniformity, consistent pressing, and quality control.
Future development directions include: researching low-cost or biodegradable binder alternatives; developing thick electrode designs that balance high energy density with mechanical stability; introducing automated quality monitoring technologies to support mass production; and utilizing advanced characterization methods to optimize pore structure and ion transport properties. These improvements are expected to drive the widespread adoption of dry-process electrode technology in commercial lithium-ion batteries.
Lithium-ion batteries may have multiple levels of structure. Small batteries consist of a single battery cell. Larger batteries connect cellsin parallel into a module and connect modulesin series and parallel into a pack. Multiple packs may be connectedin series to increase the voltage.[143]
Batteries may be equipped with temperature sensors, heating/cooling systems,voltage regulator circuits,voltage taps, and charge-state monitors. These components address safety risks like overheating andshort circuiting.[144]
On the macrostructral level (length scale 0.1–5 mm) almost all commercial lithium-ion batteries comprise foil current collectors (aluminium for cathode and copper for anode). Copper is selected for the anode, because lithium does not alloy with it. Aluminum is used for the cathode, because it passivates in LiPF6 electrolytes.
Li-ion cells are available in various form factors, which can generally be divided into four types:[145]
Cells with a cylindrical shape are made in a characteristic "swiss roll" manner (known as a "jelly roll" in the US), which means it is a single long "sandwich" of the positive electrode, separator, negative electrode, and separator rolled into a single spool. The result is encased in a container. One advantage of cylindrical cells is faster production speed. One disadvantage can be a large radial temperature gradient at high discharge rates.
The absence of a case gives pouch cells the highest gravimetric energy density; however, many applications require containment to prevent expansion when theirstate of charge (SOC) level is high,[147] and for general structural stability. Both rigid plastic and pouch-style cells are sometimes referred to asprismatic cells due to their rectangular shapes.[148] Three basic battery types are used in 2020s-era electric vehicles: cylindrical cells (e.g., Tesla), prismatic pouch (e.g., fromLG), and prismatic can cells (e.g., from LG,Samsung,Panasonic, and others).[22]
Lithium-ion flow batteries have been demonstrated that suspend the cathode or anode material in an aqueous or organic solution.[149][150]
As of 2014, the smallest Li-ion cell waspin-shaped with a diameter of 3.5 mm and a weight of 0.6 g, made byPanasonic.[151] Acoin cell form factor is available for LiCoO2 cells, usually designated with a "LiR" prefix.[152][153]
The average voltage of LCO (lithium cobalt oxide) chemistry is 3.6v if made with hard carbon cathode and 3.7v if made with graphite cathode. Comparatively, the latter has a flatter discharge voltage curve.[154]: 25–26
Lithium-ion batteries are used in a multitude of applications, includingconsumer electronics, toys, power tools, and electric vehicles.[155]
More niche uses include backup power in telecommunications applications. Lithium-ion batteries are also frequently discussed as a potential option forgrid energy storage,[156] although as of 2020, they were not yet cost-competitive at scale.[157]
Somesubmarines have also been equipped with lithium-ion batteries.[158][159]
| Specific energy density | 100 to 250W·h/kg (360 to 900kJ/kg)[160] |
|---|---|
| Volumetric energy density | 250 to 680 W·h/L (900 to 2230 J/cm3)[161][162] |
| Specific power density | 1 to 10,000 W/kg[1] |
Because lithium-ion batteries can have a variety of positive and negative electrode materials, the energy density and voltage vary accordingly.
Theopen-circuit voltage is higher than inaqueous batteries (such aslead–acid,nickel–metal hydride andnickel–cadmium).[74]Internal resistance increases with both cycling and age,[163] although this depends strongly on the voltage and temperature the batteries are stored at.[164] Rising internal resistance causes the voltage at the terminals to drop under load, which reduces the maximum current draw. Eventually, increasing resistance will leave the battery in a state such that it can no longer support the normal discharge currents requested of it without unacceptable voltage drop or overheating.
Batteries with a lithium iron phosphate positive and graphite negative electrodes have a nominal open-circuit voltage of 3.2 V and a typical charging voltage of 3.6 V. Lithium nickel manganese cobalt (NMC) oxide positives with graphite negatives have a 3.7 V nominal voltage with a 4.2 V maximum while charging. The charging procedure is performed at constant voltage with current-limiting circuitry (i.e., charging with constant current until a voltage of 4.2 V is reached in the cell and continuing with a constant voltage applied until the current drops close to zero). Typically, the charge is terminated at 3% of the initial charge current. In the past, lithium-ion batteries could not be fast-charged and needed at least two hours to fully charge. Current-generation cells can be fully charged in 45 minutes or less. In 2015 researchers demonstrated a small 600 mAh capacity battery charged to 68 percent capacity in two minutes and a 3,000 mAh battery charged to 48 percent capacity in five minutes. The latter battery has an energy density of 620 W·h/L. The device employed heteroatoms bonded to graphite molecules in the anode.[165]
Performance of manufactured batteries has improved over time. For example, from 1991 to 2005 the energy capacity per price of lithium-ion batteries improved more than ten-fold, from 0.3 W·h per dollar to over 3 W·h per dollar.[166] In the period from 2011 to 2017, progress has averaged 7.5% annually.[167] Overall, between 1991 and 2018, prices for all types of lithium-ion cells (in dollars per kWh) fell approximately 97%.[168] Over the same time period, energy density more than tripled.[168]Efforts to increase energy density contributed significantly to cost reduction.[169] Energy density can also be increased by improvements in the chemistry if the cell, for instance, by full or partial replacement of graphite with silicon. Silicon anodes enhanced with graphene nanotubes to eliminate the premature degradation of silicon open the door to reaching record-breaking battery energy density of up to 350 Wh/kg and lowering EV prices to be competitive with ICEs.[170]
Differently sized cells of the same format (shape) with the same chemistry may have different energy densities.Jelly roll cells usually have a higher energy density than coin or prismatic cells of the same Ah, because of a tighter/compresses packing of the cell layers. Among cylindrical cells, those with a larger size have a largerenergy density, albeit the exact value strongly depends on the thickness of the electrode layers. The disadvantage of large cells is decrease of the heat transfer from the cell to its surroundings.[162]
The table below shows the result of an experimental evaluation of a "high-energy" type 3.0 Ah 18650 NMC cell in 2021, round-trip efficiency which compared the energy going into the cell and energy extracted from the cell from 100% (4.2v) SoC to 0% SoC (cut off 2.0v). Around-trip efficiency is the percent of energy that can be used relative to the energy that went into charging the battery.[171]
| C rate | efficiency | estimated charge efficiency | estimated discharged efficiency |
|---|---|---|---|
| 0.2 | 86% | 93% | 92% |
| 0.4 | 82% | 92% | 90% |
| 0.6 | 81% | 91% | 89% |
| 0.8 | 77% | 90% | 86% |
| 1.0 | 75% | 89% | 85% |
| 1.2 | 73% | 89% | 83% |
Characterization of a cell in a different experiment in 2017 reported round-trip efficiency of 85.5% at 2C and 97.6% at 0.1C[172]
The lifespan of a lithium-ion battery is typically defined as the number of full charge-discharge cycles to reach a failure threshold in terms of capacity loss or impedance rise. Manufacturers' datasheets typically uses the word "cycle life" to specify lifespan in terms of the number of cycles to reach 80% of the rated battery capacity.[173] Simply storing lithium-ion batteries in the charged state also reduces their capacity (the amount of cyclableLi+) and increases the cell resistance (primarily due to the continuous growth of the solid electrolyte interface on the anode). Calendar life is used to represent the whole life cycle of battery involving both the cycle and inactive storage operations. Battery cycle life is affected by many different stress factors including temperature, discharge current, charge current, and state of charge ranges (depth of discharge).[174][175] Batteries are not fully charged and discharged in real applications such as smartphones, laptops and electric cars and hence defining battery life via full discharge cycles can be misleading. To avoid this confusion, researchers sometimes use cumulative discharge[174] defined as the total amount of charge (Ah) delivered by the battery during its entire life or equivalent full cycles,[175] which represents the summation of the partial cycles as fractions of a full charge-discharge cycle. Battery degradation during storage is affected by temperature and battery state of charge (SOC) and a combination of full charge (100% SOC) and high temperature (usually > 50 °C) can result in a sharp capacity drop and gas generation.[176] Multiplying the battery cumulative discharge by the rated nominal voltage gives the total energy delivered over the life of the battery. From this one can calculate the cost per kWh of the energy (including the cost of charging).
Over their lifespan, batteries degrade gradually leading to reduced cyclable charge (a.k.a. Ah capacity) and increased resistance (the latter translates into a lower operating cell voltage).[177]
Several degradation processes occur in lithium-ion batteries, some during cycling, some during storage, and some all the time:[178][179][177] Degradation is strongly temperature-dependent: degradation at room temperature is minimal but increases for batteries stored or used in high temperature (usually > 35 °C) or low temperature (usually < 5 °C) environments.[180][181] Also,battery life in room temperature is maximal. High charge levels also hastencapacity loss.[182] Frequent charge to > 90% and discharge to < 10% may also hastencapacity loss.[citation needed] Keeping the li-ion battery status to about 60% to 80% can reduce the capacity loss.[183][184]
In a study, scientists provided 3D imaging and model analysis to reveal main causes, mechanics, and potential mitigations of the problematicdegradation of the batteries overcharge cycles. They found "[p]article cracking increases and contact loss between particles and carbon-binder domain are observed to correlate with the cell degradation" and indicates that "the reaction heterogeneity within the thick cathode caused by the unbalanced electron conduction is the main cause of the battery degradation over cycling".[185][186][additional citation(s) needed]
The most common degradation mechanisms in lithium-ion batteries include:[187]
These are shown in the figure on the right. A change from one main degradation mechanism to another appears as a knee (slope change) in the capacity vs. cycle number plot.[187]
Most studies of lithium-ion battery aging have been done at elevated (50–60 °C) temperatures in order to complete the experiments sooner. Under these storage conditions, fully charged nickel-cobalt-aluminum and lithium-iron phosphate cells lose ca. 20% of their cyclable charge in 1–2 years. It is believed that the aforementioned anode aging is the most important degradation pathway in these cases. On the other hand, manganese-based cathodes show a (ca. 20–50%) faster degradation under these conditions, probably due to the additional mechanism of Mn ion dissolution.[179] At 25 °C the degradation of lithium-ion batteries seems to follow the same pathway(s) as the degradation at 50 °C, but with half the speed.[179] In other words, based on the limited extrapolated experimental data, lithium-ion batteries are expected to lose irreversibly ca. 20% of their cyclable charge in 3–5 years or 1000–2000 cycles at 25 °C.[187] Lithium-ion batteries with titanate anodes do not suffer from SEI growth, and last longer (>5000 cycles) than graphite anodes. However, in complete cells other degradation mechanisms (i.e. the dissolution ofMn3+ and theNi2+/Li+ place exchange, decomposition of PVDF binder and particle detachment) show up after 1000–2000 days, and the use titanate anode does not improve full cell durability in practice.
A more detailed description of some of these mechanisms is provided below:
Depending on the electrolyte and additives,[196] common components of the SEI layer that forms on the anode include a mixture of lithium oxide,lithium fluoride and semicarbonates (e.g., lithium alkyl carbonates). At elevated temperatures, alkyl carbonates in the electrolyte decompose into insoluble species such asLi
2CO
3 that increases the film thickness. This increases cell impedance and reduces cycling capacity.[181] Gases formed by electrolyte decomposition can increase the cell's internal pressure and are a potential safety issue in demanding environments such as mobile devices.[178] Below 25 °C, plating of metallic Lithium on the anodes and subsequent reaction with the electrolyte is leading to loss of cyclable Lithium.[181] Extended storage can trigger an incremental increase in film thickness and capacity loss.[178] Charging at greater than 4.2 V can initiate Li+ plating on the anode, producing irreversible capacity loss.
Electrolyte degradation mechanisms include hydrolysis and thermal decomposition.[178] At concentrations as low as 10 ppm, water begins catalyzing a number of degradation products that can affect the electrolyte, anode and cathode.[178]LiPF
6 participates in anequilibrium reaction with LiF andPF
5. Under typical conditions, the equilibrium lies far to the left. However the presence of water generates substantial LiF, an insoluble, electrically insulating product. LiF binds to the anode surface, increasing film thickness.[178]LiPF
6 hydrolysis yieldsPF
5, a strongLewis acid that reacts with electron-rich species, such as water.PF
5 reacts with water to formhydrofluoric acid (HF) andphosphorus oxyfluoride. Phosphorus oxyfluoride in turn reacts to form additional HF and difluorohydroxyphosphoric acid. HF converts the rigid SEI film into a fragile one. On the cathode, the carbonate solvent can then diffuse onto the cathode oxide over time, releasing heat and potentially causing thermal runaway.[178] Decomposition of electrolyte salts and interactions between the salts and solvent start at as low as 70 °C. Significant decomposition occurs at higher temperatures. At 85 °Ctransesterification products, such as dimethyl-2,5-dioxahexane carboxylate (DMDOHC) are formed from EC reacting with DMC.[178]
Batteries generate heat when being charged or discharged, especially at high currents. Large battery packs, such as those used in electric vehicles, are generally equipped with thermal management systems that maintain a temperature between 15 °C (59 °F) and 35 °C (95 °F).[197] Pouch and cylindrical cell temperatures depend linearly on the discharge current.[198] Poor internal ventilation may increase temperatures. For large batteries consisting of multiple cells, non-uniform temperatures can lead to non-uniform and accelerated degradation.[199] In contrast, the calendar life ofLiFePO
4 cells is not affected by high charge states.[200][201]
TheIEEE standard 1188–1996 recommends replacing lithium-ion batteries in an electric vehicle, when their charge capacity drops to 80% of the nominal value.[211] In what follows, we shall use the 20% capacity loss as a comparison point between different studies. We shall note, nevertheless, that the linear model of degradation (the constant % of charge loss per cycle or per calendar time) is not always applicable, and that a "knee point", observed as a change of the slope, and related to the change of the main degradation mechanism, is often observed.[212]
The problem of lithium-ion battery safety was recognized even before these batteries were first commercially released in 1991. The two main reasons for lithium-ion battery fires and explosions are related to processes on the negative electrode (anode when discharging, cathode when charging). During a normal battery charge lithium ions intercalate into graphite. However, if the charge is too fast or the temperature is too low lithium metal starts plating on the negative electrode, and the resulting dendrites can penetrate the battery separator, internally short-circuit the cell, and result in high electric current, heating and ignition. In other mechanisms, an explosive reaction between the negative electrode material (LiC6) and the solvent (liquid organic carbonate) occurs even at open circuit, provided that the electrode temperature exceeds a certain threshold above 70 °C.[213]
Nowadays, all reputable manufacturers[who?] employ at least two safety devices in all their lithium-ion batteries of an 18650 format or larger: a current interrupt (CID) device and a positive temperature coefficient (PTC) device. The CID comprises two metal disks that make an electric contact with each other. When pressure inside the cell increases, the distance between the two disks increases too and they lose the electric contact with each other, thus terminating the electric current through the battery. The PTC device is made of an electrically conducting polymer. When the current through the PTC device increases, the polymer gets hot, and its electric resistance rises sharply, thus reducing the current through the battery.[214]
Lithium-ion batteries can be a safety hazard since they contain a flammable electrolyte and may become pressurized if they become damaged. A battery cell charged too quickly could cause ashort circuit, leading to overheating, explosions, and fires.[215] A Li-ion battery fire can be started due to
Because of these risks, testing standards are more stringent than those for acid-electrolyte batteries, requiring both a broader range of test conditions and additional battery-specific tests, and there are shipping limitations imposed by safety regulators.[65][218][219] There have been battery-related recalls by some companies, including the 2016SamsungGalaxy Note 7 recall for battery fires.[220][221]
Lithium-ion batteries have a flammable liquid electrolyte.[222] A faulty battery can cause a seriousfire.[215] Faulty chargers can affect the safety of the battery because they can destroy the battery's protection circuit. While charging at temperatures below 0 °C, the negative electrode of the cells gets plated with pure lithium, which can compromise the safety of the whole pack.
Short-circuiting a battery will cause the cell to overheat and possibly to catch fire.[223] Smoke from thermal runaway in a Li-ion battery is both flammable and toxic.[224] Batteries are tested according to the UL 9540A fire standard, and the TS-800 standard also tests fire propagation from one battery container to adjacent containers.[225]
Around 2010, large lithium-ion batteries were introduced in place of other chemistries to power systems on some aircraft; as of January 2014[update], there had been at least four seriouslithium-ion battery fires, or smoke, on the Boeing 787 passenger aircraft, introduced in 2011, which did not cause crashes but had the potential to do so.[226][227]UPS Airlines Flight 6 crashed inDubai after its payload of batteries spontaneously ignited.
To reduce fire hazards, research projects are intended to develop non-flammable electrolytes.[228]
If a lithium-ion battery is damaged, crushed, or subjected to a higher electrical load without having overcharge protection, problems may arise. External short circuit can trigger a battery explosion.[229]Such incidents can occur when lithium-ion batteries are not disposed of through the appropriate channels, but are thrown away with other waste. The way they are treated by recycling companies can damage them and cause fires, which in turn can lead to large-scale conflagrations. Twelve such fires were recorded in Swiss recycling facilities in 2023.[230]
If overheated or overcharged, Li-ion batteries may sufferthermal runaway and cell rupture.[231][232] During thermal runaway, internal degradation andoxidization processes can keep cell temperatures above 500 °C, with the possibility of igniting secondary combustibles, as well as leading to leakage, explosion or fire in extreme cases.[233] To reduce these risks, many lithium-ion cells (and battery packs) contain fail-safe circuitry that disconnects the battery when its voltage is outside the safe range of 3–4.2 V per cell,[234][74] or when overcharged or discharged. Lithium battery packs, whether constructed by a vendor or the end-user, without effective battery management circuits are susceptible to these issues. Poorly designed or implemented battery management circuits also may cause problems; it is difficult to be certain that any particular battery management circuitry is properly implemented.
Lithium-ion cells are susceptible to stress by voltage ranges outside of safe ones between 2.5 and 3.65/4.1/4.2 or 4.35 V (depending on the components of the cell). Exceeding this voltage range results in premature aging and in safety risks due to the reactive components in the cells.[235] When stored for long periods the small current draw of the protection circuitry may drain the battery below its shutoff voltage; normal chargers may then be useless since thebattery management system (BMS) may retain a record of this battery (or charger) "failure".[236] Many types of lithium-ion cells cannot be charged safely below 0 °C,[237] as this can result in plating of lithium on the anode of the cell, which may cause complications such as internal short-circuit paths.[238]
Other safety features are required[by whom?] in each cell:[234]
These features are required because the negative electrode produces heat during use, while the positive electrode may produce oxygen. However, these additional devices occupy space inside the cells, add points of failure, and may irreversibly disable the cell when activated. Further, these features increase costs compared tonickel metal hydride batteries, which require only a hydrogen/oxygen recombination device and a back-up pressure valve.[74] Contaminants inside the cells can defeat these safety devices. Also, these features can not be applied to all kinds of cells, e.g., prismatic high-current cells cannot be equipped with a vent or thermal interrupt. High-current cells must not produce excessive heat or oxygen, lest there be a failure, possibly violent. Instead, they must be equipped with internal thermal fuses which act before the anode and cathode reach their thermal limits.[239]
Replacing thelithium cobalt oxide positive electrode material in lithium-ion batteries with a lithium metal phosphate such as lithium iron phosphate (LFP) improves cycle counts, shelf life and safety, but lowers capacity. As of 2006, these safer lithium-ion batteries were mainly used inelectric cars and other large-capacity battery applications, where safety is critical.[240] In 2016, an LFP-based energy storage system was chosen to be installed inPaiyun Lodge onMt.Jade (Yushan) (the highest lodge inTaiwan). As of June 2024, the system was still operating safely.[241]
In 2006, approximately 10 million Sony batteries used in laptops were recalled, including those in laptops fromDell,Sony,Apple,Lenovo,Panasonic,Toshiba,Hitachi,Fujitsu andSharp. The batteries were found to be susceptible to internal contamination by metal particles during manufacture. Under some circumstances, these particles could pierce the separator, causing a dangerous short circuit.[242]
IATA estimates that over a billionlithium metal and lithium-ion cells are flown each year.[243] Some kinds of lithium batteries may be prohibited aboard aircraft because of the fire hazard.[244][245] Some postal administrations restrict air shipping (includingEMS) of lithium and lithium-ion batteries, either separately or installed in equipment.
In 2023, most commercial Li-ion batteries employedalkylcarbonate solvent(s) to assure the formationsolid electrolyte interface on the negative electrode. Since such solvents are readily flammable, there has been active research to replace them with non-flammable solvents or to addfire suppressants. Another source of hazard ishexafluorophosphate anion, which is needed to passivate the negative current collector made ofaluminium. Hexafluorophosphate reacts with water and releases volatile and toxichydrogen fluoride. Efforts to replace hexafluorophosphate have been less successful.
Li-ion battery production is heavily concentrated, with 60% coming fromChina in 2024.[246]
In the 1990s, the United States was the World's largest miner of lithium minerals, contributing to 1/3 of the total production. By 2010Chile replaced the USA the leading miner, thanks to the development of lithium brines inSalar de Atacama. By 2024,Australia and China joined Chile as the top 3 miners.
Extraction of lithium,nickel, andcobalt, manufacture of solvents, and mining byproducts present significant environmental and health hazards.[248][249][250] Lithium extraction can be fatal to aquatic life due to water pollution.[251] It is known to cause surface water contamination, drinking water contamination, respiratory problems, ecosystem degradation and landscape damage.[248] It also leads to unsustainable water consumption in arid regions (1.9 million liters per ton of lithium).[248] Massive byproduct generation of lithium extraction also presents unsolved problems, such as large amounts of magnesium and lime waste.[252]
Lithium mining takes place in North and South America, Asia, South Africa, Australia, and China.[253]
Cobalt for Li-ion batteries is largely mined in the Congo (see alsoMining industry of the Democratic Republic of the Congo). Open-pitcobalt mining has led todeforestation and habitat destruction in the Democratic Republic of Congo.[254]
Open-pitnickel mining has led to environmental degradation and pollution in developing countries such as thePhilippines andIndonesia.[255][256] In 2024, nickel mining and processing was one of the main causes ofdeforestation in Indonesia.[257][258]
Manufacturing a kg of Li-ion battery takes about 67megajoule (MJ) of energy.[259][260] Theglobal warming potential of lithium-ion batteries manufacturing strongly depends on the energy source used in mining and manufacturing operations, and is difficult to estimate, but one 2019 study estimated 73 kg CO2e/kWh.[261] Effective recycling can reduce the carbon footprint of the production significantly.[262]
The recycling of lithium-ion batteries is a growing but underdeveloped industry. Despite their value, global recycling rates remain low; the International Energy Agency estimated in 2024 that only 5% of used electric vehicle batteries were recycled worldwide.[263] Li-ion battery elements including iron, copper, nickel, and cobalt can be recycled, but mining new materials often remains cheaper and easier than collecting, transporting, and processing spent batteries.[264] However, since 2018, recycling processes have improved significantly, and recovering lithium, manganese, aluminum, and graphite is now possible at industrial scales.[265]
Accumulation of battery waste presents technical challenges and health hazards.[266] Since the environmental impact of electric cars is heavily affected by the production of lithium-ion batteries, the development of efficient ways to repurpose waste is crucial.[267] Recycling is a multi-step process, starting with the storage of batteries before disposal, followed by manual testing, disassembling, and finally the chemical separation of battery components. Re-use of the battery is preferred over complete recycling as there is lessembodied energy in the process. As these batteries are a lot more reactive than classical vehicle waste like tire rubber, there are significant risks to stockpiling used batteries.[268]
Thepyrometallurgical method uses a high-temperature furnace to reduce the components of the metal oxides in the battery to an alloy of Co, Cu, Fe, and Ni. This is the most common and commercially established method of recycling and can be combined with other similar batteries to increase smelting efficiency and improvethermodynamics. The metalcurrent collectors aid the smelting process, allowing whole cells or modules to be melted at once.[269] The product of this method is a collection of metallic alloy,slag, and gas. At high temperatures, the polymers used to hold the battery cells together burn off and the metal alloy can be separated through a hydrometallurgical process into its separate components. The slag can be further refined or used in thecement industry. The process is relatively risk-free and theexothermic reaction from polymer combustion reduces the required input energy. However, in the process, the plastics,electrolytes, and lithium salts will be lost.[270]
This method involves the use ofaqueous solutions to remove the desired metals from the cathode. The most common reagent issulfuric acid.[271] Factors that affect the leaching rate include the concentration of the acid, time, temperature, solid-to-liquid-ratio, andreducing agent.[272] It is experimentally proven that H2O2 acts as a reducing agent to speed up the rate ofleaching through the reaction:[273]
Once leached, the metals can be extracted throughprecipitation reactions controlled by changing the pH level of the solution. Cobalt, the most expensive metal, can then be recovered in the form of sulfate, oxalate, hydroxide, or carbonate. More recently,[when?] recycling methods experiment with the direct reproduction of the cathode from the leached metals. In these procedures, concentrations of the various leached metals are premeasured to match the target cathode and then the cathodes are directly synthesized.[274]
The main issues with this method, however, are the large volume ofsolvent required and the high cost of neutralization. Although it is easy to shred up the battery, mixing the cathode and anode at the beginning complicates the process, so they will also need to be separated. Unfortunately, the current design of batteries makes the process extremely complex and it is difficult to separate the metals in a closed-loop battery system. Shredding and dissolving may occur at different locations.[275]
Direct recycling is the removal of the cathode or anode from the electrode, reconditioned, and then reused in a new battery. Mixed metal-oxides can be added to the new electrode with very little change to the crystal morphology. The process generally involves the addition of new lithium to replenish the loss of lithium in the cathode due to degradation from cycling. Cathode strips are obtained from the dismantled batteries, then soaked inNMP, and undergo sonication to remove excess deposits. It is treated hydrothermally with a solution containing LiOH/Li2SO4 before annealing.[276]
This method is extremely cost-effective for noncobalt-based batteries as the raw materials do not make up the bulk of the cost. Direct recycling avoids the time-consuming and expensive purification steps, which is great for low-cost cathodes such as LiMn2O4 and LiFePO4. For these cheaper cathodes, most of the cost, embedded energy, andcarbon footprint is associated with the manufacturing rather than the raw material.[277] It is experimentally shown that direct recycling can reproduce similar properties to pristine graphite.
The drawback of the method lies in the condition of the retired battery. In the case where the battery is relatively healthy, direct recycling can cheaply restore its properties. However, for batteries where the state of charge is low, direct recycling may not be worth the investment. The process must also be tailored to the specific cathode composition, and therefore the process must be configured to one type of battery at a time.[278] Lastly, in a time with rapidly developing battery technology, the design of a battery today may no longer be desirable a decade from now, rendering direct recycling ineffective.
Physical materials separation recovered materials by mechanical crushing and exploiting physical properties of different components such as particle size, density, ferromagnetism and hydrophobicity. Copper, aluminum and steel casing can be recovered by sorting. The remaining materials, called "black mass", which is composed of nickel, cobalt, lithium and manganese, need a secondary treatment to recover.[279]
For the biological metals reclamation or bio-leaching, the process uses microorganisms to digest metal oxides selectively. Then, recyclers can reduce these oxides to produce metal nanoparticles. Although bio-leaching has been used successfully in the mining industry, this process is still nascent to the recycling industry and plenty of opportunities exists for further investigation.[279]
Electrolyte recycling consists of two phases. The collection phase extracts the electrolyte from the spent Li-ion battery. This can be achieved through mechanical processes,distillation, freezing,solvent extraction, andsupercritical fluid extraction. Due to the volatility, flammability, and sensitivity of the electrolyte, the collection process poses a greater difficulty than the collection process for other components of a Li-ion battery. The next phase consists of separation/electrolyte regeneration. Separation consists of isolating the individual components of the electrolyte. This approach is often used for the direct recovery of the Li salts from the organic solvents. In contrast, regeneration of the electrolyte aims to preserve the electrolyte composition by removing impurities which can be achieved through filtration methods.[280][281]
The recycling of the electrolytes, which consists 10–15 wt.% of the Li-ion battery, provides both an economic and environmental benefits. These benefits include the recovery of the valuable Li-based salts and the prevention of hazardous compounds, such as volatile organic compounds (VOCs) and carcinogens, being released into the environment.
Compared to electrode recycling, less focus is placed on recycling the electrolyte of Li-ion batteries which can be attributed to lower economic benefits and greater process challenges. Such challenges can include the difficulty associated with recycling different electrolyte compositions,[282] removing side products accumulated from electrolyte decomposition during its runtime,[283] and removal of electrolyte adsorbed onto the electrodes.[284] Due to these challenges, current pyrometallurgical methods of Li-ion battery recycling forgo electrolyte recovery, releasing hazardous gases upon heating. However, due to high energy consumption and environmental impact, future recycling methods are being directed away from this approach.[285]
Extraction of raw materials for lithium-ion batteries may present dangers to local people, especially land-based indigenous populations.[286]
Cobalt sourced from the Democratic Republic of the Congo is often mined by workers using hand tools with few safety precautions, resulting in frequent injuries and deaths.[287] Pollution from these mines has exposed people to toxic chemicals that health officials believe to cause birth defects and breathing difficulties.[288] Human rights activists have alleged, andinvestigative journalism reported confirmation,[289][290] thatchild labor is used in these mines.[291]
A study of relationships between lithium extraction companies and indigenous peoples in Argentina indicated that the state may not have protected indigenous peoples' right tofree prior and informed consent, and that extraction companies generally controlled community access to information and set the terms for discussion of the projects and benefit sharing.[292]
Development of theThacker Pass lithium mine in Nevada, USA has met with protests and lawsuits from several indigenous tribes who have said they were not provided free prior and informed consent and that the project threatens cultural and sacred sites.[293] Links between resource extraction andmissing and murdered indigenous women have also prompted local communities to express concerns that the project will create risks to indigenous women.[294] Protestors have been occupying the site of the proposed mine since January, 2021.[295][296]
Researchers are actively working to improve the power density, safety, cycle durability (battery life), recharge time, cost, flexibility, and other characteristics, as well as research methods and uses, of these batteries.[297]Solid-state batteries are being researched as a breakthrough in technological barriers. Currently,solid-state batteries are expected to be the most promising next-generation battery, and various companies are working to popularize them.
Research areas for lithium-ion batteries include extending lifetime, increasing energy density, improving safety, reducing cost, and increasing charging speed,[298][299] among others. Research has been under way in the area of non-flammable electrolytes as a pathway to increased safety based on the flammability and volatility of the organic solvents used in the typical electrolyte. Strategies includeaqueous lithium-ion batteries, ceramic solid electrolytes, polymer electrolytes, ionic liquids, and heavily fluorinated systems.[300][301][302][303]
One of the ways to improve batteries is to combine the various cathode materials. This allows researchers to improve on the qualities of a material, while limiting the negatives. One possibility is coating lithium nickel manganese oxide with lithium iron phosphate through resonant acoustic mixing. The resulting material benefits from an increase electrochemical performance and improved capacity retention.[304] Similar work was done with iron (III) phosphate.[305] As it is now accepted that not only transition metals, but also anions in cathodes participate in redox activity necessary for Lithium insertion and removal, the design of cathode materials with diverse transition metal cations increasingly consider also oxygen redox reactions in lithium-ion battery cathodes and how these may enhance capacity beyond transition metal limitations, with computational studies using density functional theory helping to optimize materials while minimizing structural degradation. Advances in anionic redox understanding have led to stabilization strategies like surface fluorination, improving cycling stability and safety.[306]
A new class of polymer-based electrolytes that are nonflammable even at high temperatures is being developed to improve lithium-ion battery safety.
Lithium extraction is extremely water intensive and is taking place in some of the driest places on Earth, threatening fragile ecosystems and Indigenous livelihoods.
Commercial lithium ion cells are now optimized for either high energy density or high power density. There is a trade-off in cell design between power and energy requirements.
global lithium-ion battery production from about 20GWh (~6.5bn€) in 2010
Charge at C/2 (12.5 A) to 32 V battery voltage or 4.05 V on any cell.
Creative Commons Attribution license
Temperatures below freezing at 32°F during charging can lead to metallic lithium plating on the anode (lithium metal buildup), increasing the risk of short circuits and increased internal heat of the battery.
H₂O₂ was used as a reducing agent to enhance the leaching efficiency of cobalt and lithium.
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