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Lithium-Ion

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Lithium-Ion

Not to be confused with lithium battery or lithium polymer battery.
"Lithium-ion" redirects here. For the metal element, see Lithium.
Lithium-ion battery
Specific energy

100–265 W·h/kg[1][2]

(0.36–0.95 MJ/kg)
Energy density

250–730 W·h/L[2]

(0.90–2.23 MJ/L)
Specific power ~250-~340 W/kg[1]
Charge/discharge efficiency 80–90%[3]
Energy/consumer-price 2.5 W·h/US$
Self-discharge rate 8% at 21 °C
15% at 40 °C
31% at 60 °C
(per month)[4]
Cycle durability

400–1200 cycles

[5]
Nominal cell voltage NMC 3.6 / 3.7 V, LiFePO4 3.2 V

A lithium-ion battery (sometimes Li-ion battery or LIB) is a member of a family of rechargeable battery types in which lithium ions move from the anode to the cathode during discharge and back when charging. Li-ion batteries use an intercalated lithium compound as the electrode material, compared to the metallic lithium used in non-rechargeable lithium battery.

Lithium-ion batteries are common in consumer electronics. They are one of the most popular types of rechargeable battery for portable electronics, with one of the best energy densities, no memory effect (note, however, that new studies have shown signs of memory effect in lithium-ion batteries[6]), and only a slow loss of charge when not in use. Beyond consumer electronics, LIBs are also growing in popularity for military, electric vehicle and aerospace applications.[7] For example, Lithium-ion batteries are becoming a common replacement for the lead acid batteries that have been used historically for golf carts and utility vehicles. Instead of heavy lead plates and acid electrolyte, the trend is to use a lightweight lithium/carbon anode and lithium iron phosphate cathode. Lithium-ion batteries can provide the same voltage as lead-acid batteries, so no modification to the vehicle's drive system is required.[8]

Chemistry, performance, cost and safety characteristics vary across LIB types. Handheld electronics mostly use LIBs based on lithium cobalt oxide (Template:Chem/link), which offers high energy density, but presents safety risks, especially when damaged. Lithium iron phosphate (LFP), lithium manganese oxide (LMO) and lithium nickel manganese cobalt oxide (NMC) offer lower energy density, but longer lives and inherent safety. Such batteries are widely used for electric tools, medical equipment and other roles. NMC in particular is a leading contender for automotive applications. Lithium nickel cobalt aluminum oxide (NCA) and lithium titanate (LTO) are specialty designs aimed at particular niche roles.

Lithium-ion batteries can be dangerous under some conditions and can pose a safety hazard since they contain, unlike other rechargeable batteries, a flammable electrolyte and are also kept pressurized. This makes the standards of these batteries high, and it consists of many safety features. There have been many reported accidents as well as recalls done by some companies.

History


Lithium batteries were first proposed by M. S. Whittingham, now at Binghamton University, while working for Exxon in the 1970s.[9] Whittingham used titanium(IV) sulfide and lithium metal as the electrodes.

Reversible intercalation in graphite[10][11] and intercalation into cathodic oxides[12][13] was discovered in the 1970s by J. O. Besenhard at TU Munich. Besenhard proposed its application in lithium cells.[14][15] Electrolyte decomposition and solvent co-intercalation into graphite were severe early drawbacks for battery life.

Primary lithium batteries with metallic lithium anodes pose safety issues. As a result, lithium-ion batteries were developed in which both electrodes are made of a material containing lithium ions.

At Oxford University, England, in 1979, John Goodenough and Koichi Mizushima demonstrated a rechargeable cell with voltage in the 4 V range using lithium cobalt oxide (Template:Chem/link) as the positive electrode and lithium metal as the negative electrode.[16] This innovation provided the cathode material that made LIBs possible. Template:Chem/link is a stable positive electrode material which acts as a donor of lithium ions, which means that it can be used with a negative electrode material other than lithium metal. By enabling the use of stable and easy-to-handle negative electrode materials, Template:Chem/link opened a whole new range of possibilities for novel rechargeable battery systems.

In 1977, Samar Basu demonstrated electrochemical intercalation of lithium in graphite at the University of Pennsylvania.[17][18] This led to the development of a workable lithium intercalated graphite electrode at Bell Labs (Template:Chem/link)[19] to provide an alternative to the lithium metal electrode battery.

In 1980, Rachid Yazami demonstrated the reversible electrochemical intercalation of lithium in graphite.[20][21] The organic electrolytes available at the time would decompose during charging with a graphite anode, slowing the development of a rechargeable lithium/graphite battery. Yazami used a solid electrolyte to demonstrate that lithium could be reversibly intercalated in graphite through an electrochemical mechanism. The graphite electrode discovered by Yazami is currently the most commonly used electrode in commercial lithium ion batteries.

In 1983, Michael M. Thackeray, Goodenough, and coworkers identified manganese spinel as a cathode material.[22] Spinel showed great promise, given its low-cost, good electronic and lithium ion conductivity, and three-dimensional structure, which gives it good structural stability. Although pure manganese spinel fades with cycling, this can be overcome with chemical modification of the material.[23] As of 2013 manganese spinel was used in commercial cells.[24]

In 1985, Akira Yoshino assembled a prototype cell using carbonaceous material into which lithium ions could be inserted as one electrode, and lithium cobalt oxide (Template:Chem/link), which is stable in air, as the other.[25] By using materials without metallic lithium, safety was dramatically improved. Template:Chem/link) enabled industrial-scale production and represents the birth of the current lithium-ion battery.

In June 2012 John Goodenough, Rachid Yazami and Akira Yoshino received the 2012 IEEE Medal for Environmental and Safety Technologies for developing the lithium ion battery.

Modern batteries

In 1989, Goodenough and Arumugam Manthiram of the University of Texas at Austin showed that cathodes containing polyanions, e.g., sulfates, produce higher voltages than oxides due to the induction effect of the polyanion.[26]

In 1991, Sony and Asahi Kasei released the first commercial lithium-ion battery.

In 1996, Goodenough, Akshaya Padhi and coworkers proposed lithium iron phosphate (Template:Chem/link) and other phospho-olivines (lithium metal phosphates with the same structure as mineral olivine) as cathode materials.[27]

In 2002, Yet-Ming Chiang and his group at MIT showed a substantial improvement in the performance of lithium batteries by boosting the material's conductivity by doping it with aluminium, niobium and zirconium. The exact mechanism causing the increase became the subject of widespread debate.[28]

In 2004, Chiang again increased performance by utilizing iron phosphate particles of less than 100 nanometers in diameter. This decreased particle density almost one hundredfold, increased the cathode's surface area and improved capacity and performance. Commercialization led to a rapid growth in the market for higher capacity LIBs, as well as a patent infringement battle between Chiang and Goodenough.[28]

As of 2011, lithium-ion batteries accounted for 66% of all portable secondary (i.e., rechargeable) battery sales in Japan.[29]

Construction

The three primary functional components of a lithium-ion battery are the anode, cathode and electrolyte. Generally, the anode of a conventional lithium-ion cell is made from carbon. The cathode is a metal oxide, and the electrolyte is a lithium salt in an organic solvent.[30] The electrochemical roles of the electrodes reverse between anode and cathode, depending on the direction of current flow through the cell.

The most commercially popular anode is graphite. The cathode is generally one of three materials: a layered oxide (such as lithium cobalt oxide), a polyanion (such as lithium iron phosphate) or a spinel (such as lithium manganese oxide).[31]

The electrolyte is typically a mixture of organic carbonates such as ethylene carbonate or diethyl carbonate containing complexes of lithium ions.[32] These non-aqueous electrolytes generally use non-coordinating anion salts such as lithium hexafluorophosphate (Template:Chem/link), lithium hexafluoroarsenate monohydrate (Template:Chem/link), lithium perchlorate (Template:Chem/link), lithium tetrafluoroborate (Template:Chem/link) and lithium triflate (Template:Chem/link).

Depending on materials choices, the voltage, energy density, life and safety of a lithium-ion battery can change dramatically. Recently, novel architectures using nanotechnology have been employed to improve performance.

Pure lithium is highly reactive. It reacts vigorously with water to form lithium hydroxide and hydrogen gas. Thus, a non-aqueous electrolyte is typically used, and a sealed container rigidly excludes moisture from the battery pack.

Lithium ion batteries are more expensive than NiCd batteries but operate over a wider temperature range with higher energy densities. They require a protective circuit to limit peak voltage.

For notebooks or laptops, lithium-ion cells are supplied as part of a battery pack with temperature sensors, voltage converter/regulator circuit, voltage tap, battery charge state monitor and the main connector. These components monitor the state of charge and current in and out of each cell, capacities of each individual cell (drastic change can lead to reverse polarities which is dangerous),[33] temperature of each cell and minimize the risk of short circuits.[34]

Formats


Li-ion cells are available in various form factors, which can generally be divided into four groups:[35][full citation needed]

  • Small cylindrical (solid body without terminals, such as laptop batteries)
  • Large cylindrical (solid body with large threaded terminals)
  • Pouch (soft, flat body, such as those used in cell phones)
  • Prismatic (semi-hard plastic case with large threaded terminals, such as vehicles' traction packs)

The absence of a case gives pouch cells the highest energy density; however, pouch cells (and prismatic cells) require an external means of containment to prevent expansion when their state-of-charge (SOC) level is high.[36]

Electrochemistry

The three participants in the electrochemical reactions in a lithium-ion battery are the anode, cathode and electrolyte.

Both electrodes allow lithium ions to migrate towards and away from them. During insertion (or intercalation) ions move into the electrode. During the reverse process, extraction (or deintercalation), ions move back out. When a lithium-based cell is discharging, the positive ion is extracted from the negative electrode (usually graphite) and inserted into the positive electrode (lithium containing compound). When the cell is charging, the reverse occurs.

Useful work is extracted when electrons flow through a closed external circuit. The following equations show one example of the chemistry, in units of moles, making it possible to use coefficient n.

The positive electrode half-reaction is:[37]

\mathrm{LiCoO_2} \leftrightarrows \mathrm{Li}_{1-n}\mathrm{CoO_2} + n\mathrm{Li^+} + n\mathrm{e^-}

The negative electrode half-reaction is:

n\mathrm{Li^+} + n\mathrm{e^-} + \mathrm{C} \leftrightarrows \mathrm{Li_nC}

The overall reaction has its limits. Overdischarge supersaturates lithium cobalt oxide, leading to the production of lithium oxide,[38] possibly by the following irreversible reaction:

\mathrm{Li^+} + \mathrm{e^-} + \mathrm{LiCoO_2} \rightarrow \mathrm{Li_2O} + \mathrm{CoO}

Overcharge up to 5.2 volts leads to the synthesis of cobalt(IV) oxide, as evidenced by x-ray diffraction:[39]

\mathrm{LiCoO_2} \rightarrow \mathrm{Li^+} + \mathrm{CoO_2} +\mathrm{e^-}

In a lithium-ion battery the lithium ions are transported to and from the cathode or anode by oxidizing the transition metal, cobalt (Co), in Template:Chem/link from Template:Chem/link to Template:Chem/link during charge, and reduced from Template:Chem/link to Template:Chem/link during discharge.

The cell's energy is equal to the voltage times the charge. Each gram of lithium represents Faraday'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 kg. This is a bit more than the heat of combustion of gasoline, but does not consider the other materials that go into a lithium battery and that make lithium batteries many times heavier per unit of energy.

Electrolytes

The cell voltages given in the Electrochemistry section are larger than the potential at which aqueous solutions will electrolyze. Given lithium metal's high reactivity to water, nonaqueous or aprotic solutions are used.

Liquid electrolytes in lithium-ion batteries consist of lithium salts, such as , or in an organic solvent, such as ethylene carbonate, dimethyl carbonate, and diethyl carbonate. A liquid electrolyte acts as a carrier between the cathode and the anode when current flows through an external circuit. Typical conductivities of liquid electrolyte at room temperature (20 °C (68 °F)) are in the range of 10 mS/cm (1 S/m), increasing by approximately 30–40% at 40 °C (104 °F) and decreasing slightly at 0 °C (32 °F)[40]

Organic solvents easily decompose on anodes during charge. However, when appropriate organic solvents are used as the electrolyte, the solvent decomposes on initial charging and forms a solid layer called the solid electrolyte interphase (SEI),[41] which is electrically insulating yet provides significant ionic conductivity. The interphase prevents decomposition of the electrolyte after the second charge. For example, ethylene carbonate is decomposed at a relatively high voltage, 0.7 V vs. lithium, and forms a dense and stable interface.[42]

Composite electrolytes based on POE (poly(oxyethylene)) developed by Syzdek et al., provide a relatively stable interface[43][44] 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.[45]

Charge and discharge

During discharge, lithium ions Template:Chem/link carry the current from the negative to the positive electrode, through the non-aqueous electrolyte and separator diaphragm.[46]

During charging, an external electrical power source (the charging circuit) applies an over-voltage (a higher voltage but of the same polarity) than that produced by the battery, forcing the current to pass in the reverse direction. The lithium ions then migrate from the positive to the negative electrode, where they become embedded in the porous electrode material in a process known as intercalation.

Charging procedure

The charging procedures for single Li-ion cells, and complete Li-ion batteries, are slightly different.

  • A single Li-ion cell is charged in two stages:[33]
  1. CC
  2. CV
  • A Li-ion battery (a set of Li-ion cells in series) is charged in three stages:
  1. CC
  2. Balance (not required once a battery is balanced)
  3. CV

CC: Apply charging current to the battery, until the voltage limit per cell is reached.

Balance: Reduce the charging current (or cycle the charging on and off to reduce the average current) while the state of charge of individual cells is brought to the same level by a balancing circuit, until the battery is balanced. Some fast chargers skip this stage. Some chargers accomplish the balance by charging each cell independently.

CV: Apply a voltage equal to the maximum cell voltage times the number of cells in series to the battery, as the current gradually declines asymptotically 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 below 4.05 V/cell.

Lithium-ion is charged at approximately 4.2 ± 0.05 V/cell except for "military long life" that uses 3.92 V to extend battery life. Most protection circuits cut off if voltage greater than 4.3 V or temperature greater than 90 °C is reached. Below 2.50 V/cell the battery protection circuit may render the battery unchargeable with regular charging equipment. Most battery circuits stop at 2.7–3.0 V/cell.

Failure to follow current and voltage limitations can result in an explosion.[47]

Production

Industry produced about 660 million cylindrical lithium-ion cells in 2012; the 18650 format is by far the most popular for cylindrical cells. If Tesla meets its goal of shipping 40,000 Model S units in 2014 and if the 85-kWh battery proves as popular overseas as it has in the U.S., by next year the Model S alone will soak up almost 40 percent of global cylindrical battery production.[48] Production is gradually shifting to higher capacity 3000+ mAhr cells. Flat polymer cell demand is expected to exceed 700 million per year in 2013.[49]

Specifications

  • Specific energy density: 150 to 250 W·h/kg (540 to 900 kJ/kg)[1]
  • Volumetric energy density: 250 to 620 W·h/l (900 to 1900 J/cm³)[2]
  • Specific power density: 300 to 1500 W/kg (@ 20 seconds and 285 W·h/l)[1]

Because lithium-ion batteries can have a variety of cathode and anode materials, the energy density and voltage vary accordingly.

They have a high open circuit voltage in comparison to aqueous batteries (such as lead acid, nickel-metal hydride and nickel-cadmium).[50] The internal resistance of widely used Template:Chem/link batteries is higher than that of nickel-metal hydride, nickel-cadmium, and Template:Chem/link and lithium-polymer cells.[51] Internal resistance increases with both cycling and age.[50][52] Rising internal resistance causes the voltage at the terminals to drop under load, which reduces the maximum current draw. Eventually increasing resistance means that the battery can no longer operate for an adequate period.

Batteries with a lithium iron phosphate cathode and graphite anode 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 cathodes with graphite anodes have a 3.7 V nominal voltage with a 4.2 V max charge. 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. Some lithium-ion varieties can reach 90% in as little as 10 minutes.[53]

Materials used in construction

The increasing demand for batteries has led vendors and academics to focus on improving the energy density, operating temperature, safety, durability, charging time, output power, and cost of LIB solutions.

Cathode

Cathode
Technology Researchers Target application Date Benefit
Manganese spinel (LMO) Lucky Goldstar Chemical,[54] NEC, Samsung,[24] Hitachi,[55] Nissan/AESC,[56] EnerDel[57] Hybrid electric vehicle, cell phone, laptop 1996 durability, cost
Lithium iron phosphate University of Texas/Hydro-Québec,[58]/Phostech Lithium Inc., Valence Technology, A123Systems/MIT[59][60] Segway Personal Transporter, power tools, aviation products, automotive hybrid systems, PHEV conversions 1996 moderate density (2 A·h outputs 70 amperes) operating temperature >60 °C (140 °F)
Lithium nickel manganese cobalt (NMC) Imara Corporation, Nissan Motor,[61][62] Microvast Inc. 2008 density, output, safety
Lithium Managnese Oxide/NMC Sony, Sanyo[63] power, safety (although limited durability)
Lithium iron fluorophosphate University of Waterloo[64] 2007 durability, cost (replace Li with Na or Na/Li)
5% Vanadium-doped lithium iron phosphate olivine Binghamton University[65] 2008 output
Lithium purpurin Arava Leela Mohana Reddy Rice University[66] 2012 Organic material, low production cost
90 milliamp hours per gram after 50 charge/discharge cycles
Lithium manganese dioxide on porous tin University of Illinois at Urbana-Champaign[67] automotive, electronics 2013 energy density, power, fast charge using microstructured porous tin
Air IBM, Polyplus[68] Automotive 2012 Energy density: up to 10,000 mA·h per gram of cathode material. Rechargeable.
Air University of Dayton Research Institute[69][70] automotive 2009 density, safety
Water Polyplus Corporation[71][72] Marine 2012 Energy density: 1300 w·h/kg Non-rechargeable. Solid lithium anode. Solid electrolyte. Reduced self-discharge.

Anode

Anode
Technology Density Durability Researchers Target application Date Benefit
Lithium-titanate battery (LT) 9,000 Altairnano, Microvast Inc. automotive (Phoenix Motorcars), electrical grid (PJM Interconnection Regional Transmission Organization control area,[73] United States Department of Defense[74]), bus (Proterra) 2008 output, charging time, durability (, safety, operating temperature (−50–70 °C (−58–158 °F)[75]
Lithium vanadium oxide 745W·h/l Samsung/Subaru.[76] automotive 2007 density[77]
Cobalt-oxide nanowires from genetically modified virus MIT 2006 density, thickness[78]
Three-dimensional (3D) porous particles composed of curved 2D nanolayers specific energy >2000 mA·h/g Georgia Institute of Technology high energy batteries for electronics and electrical vehicles 2011 high efficiency, rapid low-cost synthesis[79]
Iron-phosphate nanowires from genetically modified virus MIT 2009 density, thickness, self-assembly[80][81][82]
Silicon/titanium dioxide composite nanowires from genetically modified tobacco virus 2000mA·h/g 150 University of Maryland explosive detection sensors, biomimetic structures, water-repellent surfaces, micro/nanoscale heat pipes 2010 density, low charge time[83]
Silicon whisker on carbon nanofiber composite 800-1000mA·h/g Junqing Ma, Physical sciences, Inc. portable electronics, electrical vehicles, electrical grid 2009 high capacity, good cycle life, fast rate, low charge time[84]
Silicon nanowires on stainless steel 4,200 mA·h/g Stanford University wireless sensors networks, 2007 circumvents swelling[85][86] (shift from anode- to cathode-limited), durability issue remains (wire cracking)
Silicon oxide-coated double-walled silicon nanotubes 6,000 Yi Cui/Stanford University[87][88] Automotive and electronics 2012
Metal hydrides 1480 mA·h/g Laboratoire de Réactivité et de Chimie des Solides, General Motors 2008 [89]
Silicon nanotubes (or silicon nanospheres) confined within rigid carbon outer shells 2400 mA·h/g Georgia Institute of Technology, MSE, NanoTech Yushin's group[90] stable high energy batteries for cell phones, laptops, netbooks, radios, sensors and electrical vehicles 2010 ultra-high Coulombic Efficiency and outstanding SEI stability[91]
Silicon nanopowder in a conductive polymer binder 1400 mA·h/g Lawrence Berkeley National Laboratory [92] Automotive and Electronics 2011 Compatible with commercial Si, good cycling characteristics
Silicon oxycarbide-coated carbon nanotubes ~225 mA·h/g at 1.6A/g; ~750 mA·h/g at 50 mA/g G Singh/Kansas State University[93] Automotive 2013 ~99.6 % average coulombic efficiency); Anode active weight (1.0 mg/cm2), Thickness (~125 micrometers)
Electro-plated tin Washington State University[88] Consumer electronics 2012 Reduced cost. 3x capacity vs conventional Li-ion
Solid-state plated copper antimonide nanowire 750 Prieto battery[88] Consumer electronics 2012 Reduced charging time from reduced cathode/anode gap. Increased energy density.
Boron-doped silicon nanoparticles 1,400 mA·h/g at a current rate of 1 A/g, 1,000 mA·h/g at 2 A/g 200 University of Southern California Chongwu Zhou[94]>[95] Various 2012 Ten minute charging time. Scalable construction.
Hard carbon Energ2[96] Consumer electronics 2013 greater storage capacity
Silicon/conducting polymer hydrogel 2,500 mA·h/g to 1,100 mA·h/g at charge/discharge rate from 0.3 to 3.0 A g-1. Volumetric capacity: ~1,080 mA·h/cm 5,000 Stanford University[97][98] Various 2013 10x energy density of carbon without destruction caused by 400% anode expansion under charge
Nanomatrix structure Volumetric: 580 W·h/l Amprius[99]` Smartphones, providing 1850 mA·h capacity 2013 Uses silicon and other electrochemicals. Energy density
Carbon-encased silicon nanoparticles 2800 mA·h/g at C/10 1000 at 74% capacity Stanford[100] Various 2013 Commercially available Si nanoparticles sealed inside conformal, self-supporting carbon shells, with rationally designed void space between particles and shell. The space allows Si particles to expand without breaking the outer carbon shell, stabilizing the SEI on the shell surface. Coulombic efficiency of 99.84%.
Lithium/titanium/oxide Ener1/Delphi,[57] 2006 durability, safety (limited density)
Université Paul Sabatier/Université Picardie Jules Verne[101][102] 2006 density
Nanophosphate 2,000 A123 Systems[103]

[104][105]

Automotive 2012 Operation at high and low ambient temperature
Nickel/Tin on porous nickel Power density: 7.4 mW cm−2 μm−1 University of Illinois at Urbana-Champaign[106][107] Automotive, electronics 2013 energy density and power using microstructured metal as the substrate for thin film Nickel/Tin. These are assembled as three-dimensional bicontinuous interdigitated microelectrodes.

Electrolyte

Electrolyte
Technology Durability Researchers Target application Date Benefit
Lithium imide 750-800 at 80% Leyden[88] Consumer electronics 2012 Reduced thermal expansion.

Separator

Separator
Technology Durability Researchers Target application Date Benefit
Ceramic Automotive, grid stabilization 2008 Heat resistance up to 700 °C (1,292 °F)[108]

Uses

Li-ion batteries provide lightweight, high energy density power sources for a variety of devices. To power larger devices, such as electric cars, connecting many small batteries in a parallel circuit is more effective[109] and more efficient than connecting a single large battery. Such devices include:

Though not suitable for AAA, AA, C or D form factors due to voltage per cell being more than 2 volts (i.e. 3.7 volts), some devices such as AA/14500 torches are designed to use either voltage range. Most devices designed for a voltage that is a multiple of 1.5 can run safely on a voltage that is 30% higher.

Self-discharge

Li+ batteries have a self-discharge rate of approximately 5–10% per month, compared to over 30% per month in common nickel metal hydride batteries, approximately 1.25% per month for low self-discharge NiMH batteries and 10% per month in nickel-cadmium batteries.[110]

Battery life

Rechargeable batteries degrade with use, the capacity decreasing until it is unusably small. Li+ batteries last longer[111] if not deeply discharged (depleted) before recharging. The smaller the depth of discharge, the longer the battery will last.[112]

Batteries may last longer if not stored fully discharged. As the battery self-discharges over time, its voltage gradually reduces. When depleted below the low-voltage threshold of the protection circuit (2.4 to 2.9 V/cell, depending on chemistry) it will be disabled and cannot be further discharged until recharged.[111] It is recommended to store batteries at 40% charge level.[111]

The rate of degradation of lithium-ion batteries is strongly temperature-dependent; they degrade much faster if stored or used at higher temperatures. The carbon anode of the cell also generates heat. High charge levels and elevated temperatures (whether from charging or ambient air) hasten capacity loss.[50] A test on a commonly-used Template:Chem/link cell showed that over one year a fully charged cell kept at 25 °C (77 °F) permanently lost 20% of total capacity; the loss was lower when stored at lower charge levels and lower temperatures. Poor ventilation may increase temperatures, further shortening battery life. Loss rates vary by temperature: 6% loss at 0 °C (32 °F), 20% at 25 °C (77 °F), and 35% at 40 °C (104 °F). When stored at 40%–60% charge level, the capacity loss is reduced to 2%, 4%, and 15%, respectively. In contrast, the calendar life of cells is not affected by high charge states.[113] They may be stored in a refrigerator.[114][115]

Charging forms deposits inside the electrolyte that inhibit ion transport. The increase in internal resistance reduces the cell's ability to deliver current. This problem is more pronounced in high-current applications. Older batteries also do not charge as much as new ones (charging time required decreases).

Conditioning

The need to "condition" NiCd and NiMH batteries has incorrectly leaked into folklore surrounding Li-ion batteries. The recommendation for the older technologies is to leave the device plugged in for seven or eight hours, even if fully charged.[116] This may be a confusion of battery software calibration instructions with the "conditioning" instructions for NiCd and NiMH batteries.[117] The software of a typical smart phone, for example, learns how to accurately gauge the battery's life by watching it discharge and leaving it on the charger produces a series of "micro discharges" that the software can watch and learn from.

Multicell devices

Li-ion batteries require a battery management system to prevent operation outside each cell's safe operating area (over-charge, under-charge, safe temperature range) and to balance cells to eliminate state of charge mismatches, thereby significantly improving battery efficiency and increasing overall capacity. As the number of cells and load currents increase, the potential for mismatch increases. The two kinds of mismatch are state-of-charge (SOC) and capacity/energy ("C/E"). Though SOC is more common, each problem limits pack charge capacity (mA·h) to that of the weakest cell.

Safety

If overheated or overcharged, Li-ion batteries may suffer thermal runaway and cell rupture.[118] In extreme cases this can lead to combustion. Deep discharge may short-circuit the cell, in which case recharging would be unsafe. To reduce these risks, lithium-ion battery packs contain fail-safe circuitry that shuts down the battery when its voltage is outside the safe range of 3–4.2 V per cell.[37][110] When stored for long periods the small current draw of the protection circuitry may drain the battery below its shut down voltage; normal chargers are then ineffective. Many types of lithium-ion cell cannot be charged safely below 0 °C.[119]

Other safety features are required in each cell:[37]

  • Shut-down separator (for overheating)
  • Tear-away tab (for internal pressure)
  • Vent (pressure relief)
  • Thermal interrupt (overcurrent/overcharging)

These devices occupy useful space inside the cells, add additional points of failure and irreversibly disable the cell when activated. They are required because the anode produces heat during use, while the cathode may produce oxygen. These devices and improved electrode designs reduce/eliminate the risk of fire or explosion. Further, these features increase costs compared to nickel metal hydride batteries, which require only a hydrogen/oxygen recombination device (preventing damage due to mild overcharging) and a back-up pressure valve.[120] Contaminants inside the cells can defeat these safety devices.

Short-circuiting a battery will cause the cell to overheat and possibly to catch fire. Adjacent cells may then overheat and fail, possibly causing the entire battery to ignite or rupture. In the event of a fire, the device may emit dense irritating smoke.[121] The fire energy content (electrical + chemical) of cobalt-oxide cells is about 100 to 150 kJ per A·h, most of it chemical. Extinguishing this fire is dangerous as lithium burns violently when it comes in contact with water or moisture in the air; a suitable waterless fire extinguisher is recommended.[33][122]

Replacing the lithium cobalt oxide cathode material in lithium-ion batteries with a lithium metal phosphate such as lithium iron phosphate improves cycle counts, shelf life and safety, but lowers capacity. Currently, these 'safer' lithium-ion batteries are mainly used in electric cars and other large-capacity battery applications, where safety is critical.[123]

Lithium-ion batteries, unlike other rechargeable batteries, have a flammable electrolyte kept in pressure; because of this Li-ion batteries have a strict quality control in manufacturing.[124] Faulty chargers can also affect the safety of the battery because they can destroy the battery's protection circuit. While charging at temperatures below 0 °C, the anode of the cells gets plated with pure lithium, which can compromise the safety of the whole pack. Battery packs which are not branded by a reputable manufacturer may not be built to the same safety standard as branded ones.

In some applications the consequences of fire are particularly serious. Large lithium-ion batteries started to be used to power systems on aircraft in the 2010s; as of July 2013 there had been at least three cases of fires on the Boeing 787 passenger aircraft, introduced in 2011, which did not cause crashes but had the potential to do so.[125]

Environmental concerns and recycling

Since Li-ion batteries contain no toxic metals (unlike other types of batteries which may contain lead or cadmium)[37] they are generally categorized as non-hazardous waste. Li-ion battery elements including iron, copper, nickel and cobalt are considered safe for incinerators and landfills. These metals can be recycled, but mining generally remains cheaper than recycling.[126] At present, not much is invested into recycling Li-ion batteries due to costs, complexities and low yield. The most expensive metal involved in the construction of the cell is cobalt. Lithium iron phosphate is cheaper but has other drawbacks. Lithium is less expensive than other metals used. The manufacturing processes of nickel and cobalt for the cathode and also the solvent, present potential environmental and health hazards.[127][128]

Recalls

In October 2004, Kyocera Wireless recalled approximately 1 million mobile phone batteries to identify counterfeits.[129]

In December 2006, Dell recalled approximately 22,000 laptop batteries.[130] Approximately 10 million Sony batteries used in Dell, Sony, Apple, Lenovo, Panasonic, Toshiba, Hitachi, Fujitsu and Sharp laptops were recalled in 2006. 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.[131]

In March 2007, Lenovo recalled approximately 205,000 batteries at risk of explosion. In August 2007, Nokia recalled over 46 million batteries at risk of overheating and exploding.[132] One such incident occurred in the Philippines involving a Nokia N91, which used the BL-5C battery.[133]

Transport restrictions

IATA estimates that over a billion lithium cells are flown each year.[122] In January 2008, the United States Department of Transportation ruled that passengers on commercial aircraft could carry lithium batteries in their checked baggage if the batteries were installed in a device. Types of batteries covered by this rule are those containing small amounts of lithium, including Li-ion, lithium polymer, and lithium cobalt oxide chemistries. Lithium-ion batteries containing more than 25 grams (0.88 oz) equivalent lithium content (ELC) are forbidden in US air travel.[134]

Additionally, a limited number of replacement batteries may be transported in carry-on luggage. Such batteries must be sealed in their original protective packaging or in individual containers or plastic bags.[134][135]

Some postal administrations restrict air shipping (including EMS) of lithium and lithium-ion batteries, either separately or installed in equipment. Such restrictions apply in Hong Kong,[136] Australia and Japan.[137]

On 16 May 2012, United States Postal Service (USPS) banned shipping anything containing a lithium battery to an overseas address due to fires from transport of batteries.[138] Because of this restriction, it became difficult to send anything containing lithium batteries to military personnel overseas, as the USPS was the only method of shipment to these addresses. The ban was lifted on 15 November 2012.[139]

The Boeing 787 Dreamliner contains lithium cobalt oxide[140] batteries which are more reactive than newer types of batteries such as Template:Chem/link.[141]

Substandard examples

As with other concentrated energy sources, it may be hazardous to bypass the accepted safety practices. Batteries included in devices or sold separately as retail in developed countries generally conform to standard safety control, but low priced examples available in international trade may not be subject to the same precautions. It may be advisable to avoid importing lithium based batteries offered for unusually low prices, with extravagant claims or with aggressive brand names.

Research

Researchers are working to improve the power density, safety, recharge cycle, cost and other characteristics of these batteries.

Solid-state designs[142] have the potential to deliver three times the energy density of typical 2011 lithium-ion batteries at less than half the cost per kilowatt-hour. This approach eliminates binders, separators and liquid electrolytes. By eliminating these, "you can get around 95% of the theoretical energy density of the active materials."[143]

Earlier trials of this technology encountered cost barriers, because the semiconductor industry's vacuum deposition technology cost 20–30 times too much. The new process deposits semiconductor-quality films from a solution. The nanostructured films grow directly on a substrate and then in layers on top of each other. The process allows the firm to "spray-paint a cathode, then a separator/electrolyte, then the anode. It can be cut and stacked in various form factors."[143]

Sandia has studied ways to improve safety and robustness of lithium ion batteries by using electrolytes such as hydrofluoro ether and separators such as high-melting temperature polymers and ceramics, made via fiber spinning, casting and vapor deposition.[144]

Tin electrodes

Washington State University researchers developed a tin anode technology that they predicted would triple the energy capacity of lithium ion batteries. The technology involves using standard electroplating process to create tin nanoneedles that do not shortciruit when the tin expands by one third during charging.[145][146]

Microporous tin has been used as a substrate for anode and cathodes that exhibit high energy density, power and fast recharge. The substrate self-assembles. Small spheres are packed onto a surface, forming a lattice. The area between the spheres is coated with the substrate material (nickel). The spheres are dissolved/melted and the resulting surface is electro-polished to enlarge the pores. Finally the substrate is coated with a thin film of the active material (Ni/Sn for anode, Template:Chem/link for cathode.)[67][106]

Extrusion

PARC’s Hardware Systems Laboratory designed a cathode that contains more lithium by using one dense material optimised for storage and a second, porous one to enable speedy charge transfer. Wide storage regions alternate with narrow conductive regions. The storage region is 100 µm across, compared with ten for the conductor.[147]

The two materials are mixed with an organic material to form pastes and fed into an additive manufacturing device that extrudes the pastes adjacent to each other on a metal foil. Drying the substrate removes most of the organic material, leaving a solid cathode. In tests against otherwise identical batteries with monolithic cathodes, the new battery could store twenty percent more energy.[147]

The researchers envision extruding entire batteries using five pastes—two each for the cathode and the anode, plus a separator.[147]

See also


References

Bibliography

External links

  • DMOZ
  • U.S. Environmental Protection Agency, April 2013.

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