Nokia Li-ion battery for powering a mobile phone
|Specific energy||(0.36–0.95 MJ/kg)|
|Energy density||(0.90–2.23 MJ/L)|
|Specific power||~250-~340 W/kg|
|Self-discharge rate||8% at 21 °C
15% at 40 °C
31% at 60 °C
|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 negative electrode to the positive electrode 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 the 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 ), 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. For example, Lithium-ion batteries are becoming a common replacement for the lead acid batteries that have been used historically for golf carts or utility vehicles. Instead of using heavy lead plates and acid electrolyte, the trend is to use a light weight Lithium/Carbon anode and Lithium Iron Phosphate cathode. Lithium-ion batteries can provide the same voltage as lead acid batteries and therefore no modifications of the cart's electrical drive system are required.
Research is yielding a stream of improvements to traditional LIB technology, focusing on energy density, durability, cost, and intrinsic safety.
Chemistry, performance, cost, and safety characteristics vary across LIB types. Handheld electronics mostly use LIBs based on lithium cobalt oxide (LiCoO2), which offers high energy density, but have well-known safety concerns, 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. These chemistries are being 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.
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.
The three primary functional components of a lithium-ion battery are the negative electrode, positive electrode, and the electrolyte. The negative electrode of a conventional lithium-ion cell is made from carbon. The positive electrode is a metal oxide, and the electrolyte is a lithium salt in an organic solvent. The electrochemical roles of the electrodes change between anode and cathode, depending on the direction of current flow through the cell.
The most commercially popular negative electrode material is graphite. The positive electrode 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).
The electrolyte is typically a mixture of organic carbonates such as ethylene carbonate or diethyl carbonate containing complexes of lithium ions. These non-aqueous electrolytes generally use non-coordinating anion salts such as lithium hexafluorophosphate (LiPF6), lithium hexafluoroarsenate monohydrate (LiAsF6), lithium perchlorate (LiClO4), lithium tetrafluoroborate (LiBF4), and lithium triflate (LiCF3SO3).
Depending on materials choices, the voltage, capacity, 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 very 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 water from the battery pack.
Lithium ion batteries are more expensive than NiCd batteries but operate over a wider temperature range with higher energy densities, while being smaller and lighter. They are fragile and so need a protective circuit to limit peak voltages.
The lack of 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.
Lithium batteries were first proposed by M. S. Whittingham, now at Binghamton University, while working for Exxon in the 1970s. Whittingham used titanium(IV) sulfide and lithium metal as the electrodes.
The reversible intercalation in graphite and intercalation into cathodic oxides was also discovered in the 1970s by J. O. Besenhard at TU Munich. Besenhard also proposed the application as high energy density lithium cells. Electrolyte decomposition and solvent co-intercalation into graphite were severe drawbacks for long battery cycle life.
Primary lithium batteries in which the negative electrode is made from metallic lithium 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 high cell voltage in the 4 V range using lithium cobalt oxide (LiCoO2) as the positive electrode and lithium metal as the negative electrode.[clarification needed] This innovation provided the positive electrode material which made LIBs possible. LiCoO2 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, LiCoO2 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. This led to the development of a workable lithium intercalated graphite electrode at Bell Labs (LiC6) to provide an alternative to the lithium metal electrode battery.
In 1980, Rachid Yazami also demonstrated the reversible electrochemical intercalation of lithium in graphite. The organic electrolytes available at the time would decompose during charging if used with a graphite negative electrode, preventing the early development of a rechargeable battery which employed the lithium/graphite system. 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. 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. Manganese spinel is currently used in commercial cells.
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 (LiCoO2), which is stable in air, as the other. By using materials without metallic lithium, safety was dramatically improved over batteries which used lithium metal. The use of lithium cobalt oxide (LiCoO2) enabled industrial-scale production to be achieved easily.
This was the birth of the current lithium-ion battery.
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 inductive effect of the polyanion.
In 1996, Goodenough, Akshaya Padhi and coworkers identified lithium iron phosphate (LiFePO4) and other phospho-olivines (lithium metal phosphates with the same structure as mineral olivine) as cathode materials.
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.
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.
As of 2011, lithium-ion batteries account for 66% of all portable secondary (i.e., rechargeable) battery sales in Japan.
Li-ion batteries provide light weight, high energy density power sources for a variety of devices, where nickel-cadmium or nickel-metal hydride batteries would be too heavy or large. Such devices include:
The three participants in the electrochemical reactions in a lithium-ion battery are the positive and negative electrodes and the electrolyte.
Both electrodes are materials into which, and from which, lithium ions can migrate. During insertion (or intercalation) lithium ions move into the electrode. During the reverse process, extraction (or deintercalation), lithium ions move back out. When a lithium-based cell is discharging, the positive lithium 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 can only be extracted if 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 the coefficient .
The negative electrode half-reaction is:
In a lithium-ion battery the lithium ions are transported to and from the cathode or anode, with the transition metal, cobalt (Co), in being oxidized from Co3+ to Co4+ during charging, and reduced from Co4+ to Co3+ during discharge.
The energy provided by the cell is equal to the voltage times the charge. Each gram of lithium represents Faraday's constant/6.941 or 13 901 coulombs. For a voltage of 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 take into account all the other materials that go into a lithium battery and which make lithium batteries many times heavier per unit of energy.
The cell voltages given in the Electrochemistry section are larger than the potential at which aqueous solutions can electrolyze, in addition lithium is highly reactive to water, therefore, nonaqueous or aprotic solutions are used.
Liquid electrolytes in lithium-ion batteries consist of lithium salts, such as LiPF6, LiBF4 or LiClO4 in an organic solvent, such as ethylene carbonate, dimethyl carbonate, and diethyl carbonate. A liquid electrolyte conducts lithium ions, acting as a carrier between the cathode and the anode when a battery passes an electric current 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 by a slightly smaller amount at 0 °C (32 °F)
Unfortunately, organic solvents easily decompose on anodes during charging. 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), which is electrically insulating yet provides sufficient 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.
A good solution for the interface instability is the application of a new class of composite electrolytes based on POE (poly(oxyethylene)) developed by Syzdek et al. 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.
Concerning the flammability and volatility of the organic solvents present in the electrolyte, another option, how to improve the overall safety of the battery, is in using room temperature ionic liquids (RTILs) as the main component of the electrolyte.
||This article contains a pro and con list. (November 2012)|
Note that both advantages and disadvantages depend on the materials and design that make up the battery. This summary reflects older designs that use carbon anode, metal oxide cathodes, and lithium salt in an organic solvent for the electrolyte.
If overheated or overcharged, Li-ion batteries may suffer thermal runaway and cell rupture. 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. When stored for long periods the small current draw of the protection circuitry itself 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.
Other safety features are required in each cell:
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.
These safety issues present a problem for large scale application of such cells in Electric Vehicles; A dramatic decrease in the failure rate is necessary.
Because lithium-ion batteries can have a variety of cathode and anode materials, the energy density and voltage vary accordingly.
Lithium-ion 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 cathode 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.
The charging procedures for single Li-ion cells, and complete Li-ion batteries, are slightly different.
Stage 1: CC: Apply charging current to the battery, until the voltage limit per cell is reached.
Stage 2: 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 balanced by a balancing circuit, until the battery is balanced. Some fast chargers skip stage 2.
Stage 3: 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 with approximate 4.2 ± 0.05 V/cell except for military long life that uses 3.92 V to extend battery life. Most protection circuits cuts off if either >4.3 V or 90 °C is reached. Also if threshold of below 2.50 V/cell is reached the battery protection circuit may render it 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 explosion.
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||Manganese spinel (LMO)||Lucky Goldstar Chemical, NEC, Samsung, Hitachi, Nissan/AESC||Hybrid electric vehicle, cell phone, laptop||1996||durability, cost|
|Lithium iron phosphate||University of Texas/Hydro-Québec,/Phostech Lithium Inc., Valence Technology, A123Systems/MIT||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, Microvast Inc.||2008||density, output, safety|
|LMO/NMC||Sony, Sanyo||power, safety (although limited durability)|
|Lithium iron fluorophosphate||University of Waterloo||2007||durability, cost (replace Li with Na or Na/Li)|
|Lithium air||University of Dayton Research Institute||automotive||2009||density, safety|
|5% Vanadium-doped Lithium iron phosphate olivine||Binghamton University||2008||output|
|Lithium purpurin||Arava Leela Mohana Reddy Rice University||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||automotive, electronics||2013||energy density, power, fast charge using microstructured porous tin|
|Anode||Lithium-titanate battery (LT)||Altairnano, Microvast Inc.||automotive (Phoenix Motorcars), electrical grid (PJM Interconnection Regional Transmission Organization control area, United States Department of Defense), bus (Proterra)||2008||output, charging time, durability (20 years, 9,000 cycles), safety, operating temperature (-50–70 °C (-58–158 °F)[dead link]|
|Lithium vanadium oxide||Samsung/Subaru.||automotive||2007||density (745Wh/l)|
|Cobalt-oxide nanowires from genetically modified virus||MIT||2006||density, thickness|
|Three-dimensional (3D) porous particles composed of curved 2D nanolayers||Georgia Institute of Technology||high energy batteries for electronics and electrical vehicles||2011||specific capacity > 2000 mA·h/g, high efficiency, rapid low-cost synthesis|
|Iron-phosphate nanowires from genetically modified virus||MIT||2009||density, thickness|
|Silicon/titanium dioxide composite nanowires from genetically modified tobacco virus||University of Maryland||explosive detection sensors, biomimetic structures, water-repellent surfaces, micro/nanoscale heat pipes||2010||density, low charge time|
|Silicon whisker on carbon nanofiber composite||Junqing Ma, Physical sciences, Inc.||portable electronics, electrical vehicles, electrical grid||2009||high capacity, good cycle life, fast rate, low charge time|
|nanosized wires on stainless steel||Stanford University||wireless sensors networks,||2007||density (shift from anode- to cathode-limited), durability issue remains (wire cracking)|
|Metal hydrides||Laboratoire de Réactivité et de Chimie des Solides, General Motors||2008||density (1480 mA·h/g)|
|Silicon nanotubes (or silicon nanospheres) confined within rigid carbon outer shells||Georgia Institute of Technology, MSE, NanoTech Yushin's group||stable high energy batteries for cell phones, laptops, netbooks, radios, sensors and electrical vehicles||2010||specific capacity 2400 mA·h/g, ultra-high Coulombic Efficiency and outstanding SEI stability|
|Silicon nanopowder in a conductive polymer binder||Lawrence Berkeley National Laboratory ||Automotive and Electronics||2011||Compatible with commercial Si, high capacity anodes (1400 mA·h/g) with good cycling characteristics|
|Silicon oxide-coated double-walled silicon nanotubes||Yi Cui/Stanford University||Automotive and electronics||2012||Durability (6,000 charge cycles)|
|Water||Polyplus Corporation||Marine||2012||Energy density: 1500 watt-hours/kg. Non-rechargeable.|
|Air||IBM, Polyplus||Automotive||2012||Energy density: up to 10,000 mA·h per gram of cathode material. Rechargeable.|
|Electro-plated tin||Washington State University||Consumer electronics||2012||Reduced cost. 3x capacity vs conventional Li-ion|
|Solid-state plated copper antimonide nanowire||Prieto battery||Consumer electronics||2012||Reduced charging time from reduced cathode/anode gap. Increased energy density. 750 charging cycles.|
|Boron-doped silicon nanospheres||University of Southern California Chongwu Zhou||Various||2012||Reduced charging time. Increased density.|
|Hard carbon||Energ2||Consumer electronics||2013||30% greater storage capacity than graphite|
|Electrode||LT/LMO||Ener1/Delphi,||2006||durability, safety (limited density)|
|Nanostructure||Université Paul Sabatier/Université Picardie Jules Verne||2006||density|
|Nanophosphate||A123 Systems||Automotive||2012||Operation at high and low ambient temperature|
|Nickel/Tin on porous nickel||University of Illinois at Urbana-Champaign||Automative, electronics||2013||energy density and power using microstructured metal as the substrate for thin film Nickel/Tin.|
|Electrolyte||Lithium imide||Leyden||Consumer electronics||2012||750 and 800 charging cycles with greater than 80% of original capacity. Reduced thermal expansion.|
Batteries may last longer if not stored fully discharged. As the battery will self-discharge over time, its voltage will gradually reduce, and when it is 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 discharged any further until recharged.[clarification needed] It is frequently recommended to store batteries at 40% charge level.
There is a belief that Li+ batteries need to be "conditioned" before first use. One is told to plug the battery/device into a charger and leave it there for seven or eight hours, even if fully charged. But this may simply be a confusion of the battery software calibration instructions with the "conditioning" instructions for NiCd and NiMH batteries. 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.
Lithium ion batteries do not need the "conditioning" of being fully discharged and charged the way NiCd and NiMH batteries do.
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, significantly improving battery efficiency and increasing overall capacity. As the number of cells and load currents increase, the potential for mismatch increases. There are two kinds of mismatch in the pack: state-of-charge (SOC) and capacity/energy ("C/E") mismatch. Though SOC is more common, each problem limits pack current capacity (mA·h) to that of the weakest cell.
Lithium-ion batteries can rupture, ignite, or explode when exposed to high temperature. 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. The fire energy content (electrical + chemical) of cobalt-oxide cells is about 100 to 150 kJ per A·h, most of it chemical. Authorities and handlers lack knowledge on how to treat Li-Ion battery fire.
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 issues are critical.
Lithium-ion batteries normally contain safety devices to protect the cells from disturbance. However, contaminants inside the cells can defeat these safety devices.[clarification needed]
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. One such incident occurred in the Philippines involving a Nokia N91, which uses the BL-5C battery.
In December 2006, Dell recalled approximately 22,000 laptop batteries from the US market. Approximately 10 million Sony batteries used in Dell, Sony, Apple, Lenovo/IBM, 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 short-circuit.
IATA estimates that over a billion lithium cells are flown each year. 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 air travel. This restriction is due to the possibility of batteries short-circuiting and causing a fire.
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.
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, Australia and Japan.
On 16 May 2012, United States Postal Service (USPS) banned shipping anything containing a lithium battery to an overseas address due to fires resulting from transport of batteries. 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.
Researchers are working to improve the power density, safety, recharge cycle, cost and other characteristics of these batteries.
Solid-state designs 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."
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 sequentially 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."
Washington State University researchers expect to bring to market before June 2013 a tin anode technology that will triple the energy capacity of lithium ion batteries. The technology involves using standard electroplating process to create tin nanoneedles.
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, LiMnO2 for cathode.)
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 the speedy transfer of charge. Wide storage regions alternate with narrow conductive regions. The storage region is 100 microns across, compared with ten for the conductor.
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.
The researchers envision extruding entire batteries using five pastes—two each for the cathode and the anode, plus a separator.
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