Lithium iron phosphate battery

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.

History

LiFePO₄ was identified as a cathode material for rechargeable lithium batteries by John Goodenough's research group at the University of Texas in 1997. 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.

The key barrier to commercialization was its intrinsic low electricial conductivity, however, reducing the particle size and effectively coating the LiFePO₄ particles with conductive materials such as carbon as well as the doping 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 . 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. The variant C-LiFePO4 is being studied for electric car use and is being used in R/C models.

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.

Advantages and disadvantages

Being a lithium-ion-derived chemistry, the LiFePO₄ chemistry shares many of the advantages and disadvantages of lithium ion chemistry. 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. 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.

Specifications

• LiFePO4

• Cell voltage = Min discharge voltage = 2.8V Working voltage = 3.0V to 3.3V Max charge voltage = 3.6V.
• Volumetric Energy Density = 657 kJ/L
• Gravimetric Energy Density = 324 kJ/kg
• Deep Cycle life = ? (Number of Deep cycles to 66% of capacity)
• 80% Cycle life = 2000 (Number of Cycles using 80% of rated capacity)

• C-LiFePO4 Variant of LiFePO4
• Cathode Composition (weight)
• 90% C-LiFePO4, grade Phos-Dev-12
• 5% Carbon EBN-10-10 (Superior Graphite)
• 5% PVDF
• Cell Configuration
• Carbon-Coated Aluminium current collector 15
• 1.54 cm2 cathode
• Electrolyte: EC-DMC 1-1 LiClO4 1M
• Anode: Metallic Lithium
• Experimental conditions:
• Room temperature
• Voltage limits: 2.5 – 4.2V
• Charge: C/4 up to 4.2V, then potentiostatic at 4.2V until I <C/24

Safety

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.

Usage

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," and that a Toyota Prius powered by their batteries obtained 125+ MPG.. This type of battery is used on the One Laptop per Child (OLPC) project .

Segway Personal Transporters advanced from a 10 mile range to a 24 mile range with Valence Lithium Phosphate technology. Valence Technology leads the industry in lithium phosphate design, development and application of advanced, intelligent packs.

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.