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The lithium iron phosphate (LiFePO4) battery (also designated "LFP") is a type of rechargeable battery, specifically a lithium ion battery, which uses LiFePO4 as a cathode material.
LiFePO4 cells have higher discharge current, very fast charge times (5 minutes), high power density and do not explode under extreme conditions, but have lower voltage and energy density than normal Li-ion cells.
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LiFePO4 was discovered by John Goodenough's research group at the University of Texas in 1997[1] as a cathode material for rechargeable lithium batteries. Because of its low cost, non-toxicity, the high abundance of iron, its excellent thermal stability, safety characteristics, good electrochemical performance, and high specific capacity (170 mA·h/g) it has gained some acceptance. [2][3]
The key barrier to commercialization was its intrinsic low electrical conductivity, however, reducing the particle size and effectively coating the LiFePO4 particles with conductive materials such as carbon as well as the doping[2] approaches developed by Yet-Ming Chiang and his coworkers at MIT with appropriate cations — such as aluminum, niobium, and zirconium overcomes this problem. It has been shown later that most of the conductivity improvement is due to presence of nanoscopic carbon, originated from organic precursors [4]. Products using the carbonized and doped nanophosphate materials developed by Chiang are now in high volume mass production by A123Systems and various other companies and are in use in industrial volumes by major corporations including Black and Decker, DeWalt, General Motors, Daimler, Cessna and BAE Systems among others.
Most lithium batteries (Li-ion) used in consumer electronics products are mostly lithium cobalt oxide batteries. Other lithium batteries include lithium-manganese oxide (LiMn2O4) and lithium-nickel oxide (LiNiO2). The cathodes of lithium batteries are made with the above materials, and the anodes are generally made of carbon.
Being a lithium-ion-derived chemistry, the LiFePO4 chemistry shares many of the advantages and disadvantages of lithium ion chemistry. Stores lots of energy. Key differences are safety and current rating. Cost is claimed to be a major difference, but that cannot be verified until the cells are more widely accepted.
LFP batteries have some drawbacks.
1. The capacity/size ratio of an LFP battery is somewhat lower than that of a LiCoO2 battery. Battery players across the world are currently working to find a way to get the maximum storage performance as well as smaller size/weight.[5]
2. Brand new LFP's have been found to fail prematurely if they are "deep cycled" (discharged below 33% level) too early. A break-in period of 20 charging cycles is currently recommended by some distributors.
3. Rapid charging LFP's will shorten their life-span when compared to traditional trickle charging.
LiFePO4 is an intrinsically safer cathode material than LiCoO2 and manganese spinel. The Fe-P-O bond is stronger than the Co-O bond so that when abused, (short-circuited, overheated, etc.) the oxygen atoms are much harder to remove. This stabilization of the redox energies also helps fast ion migration. Only under extreme heating (generally over 800 °C) does breakdown occur, which prevents the thermal runaway that LiCoO2 is prone to. Watch a video of safety aspects of Lithium Phosphate technology compared to traditional metal-oxide battery technology.
As lithium migrates out of the cathode in a LiCoO2 cell, the CoO2 undergoes non-linear expansion, which affects the structural integrity of the cell. The fully lithiated and unlithiated states of LiFePO4 are structurally similar, which means that LiFePO4 cells are more structurally stable than LiCoO2 cells.
No lithium remains in the cathode of a fully charged LiFePO4 cell — in a LiCoO2 cell, approximately 50% remains in the cathode. LiFePO4 is highly resilient during oxygen loss, which typically results in an exothermic reaction in other lithium cells.[3]
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Lithium Technology Corp. announced in May 2007 the immediate availability of cells large enough for use in hybrid cars, claiming they are "the largest cells of their kind in the world."[6].
This type of battery is used on the One Laptop per Child (OLPC) project [7].
Segway Personal Transporters advanced from a 10 mile range to a 24 mile range with Valence Lithium Phosphate technology.[citation needed]
OLPC batteries are manufactured by BYD Company of Shenzhen, China, the world's largest producer of Li-ion batteries. BYD, also a car manufacturer, plans to use Lithium Iron Phosphate batteries to power its own PHEV, the F3DM and F6DM (Dual Mode), which will be the first plug-in hybrid vehicles on sale in the world. It plans to mass produce the cars in 2009.