Lithium iron phosphate battery

The lithium iron phosphate (LiFePO₄) battery is a type of rechargeable battery, specifically a lithium ion battery, which uses LiFePO₄ as a cathode material. It is not yet widely in use.

LiFePO₄ cells have higher discharge current and do not explode under extreme conditions, but have lower voltage and energy density than normal Li-ion cells.

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History

LiFePO₄ was developed 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. ^[1][2] A key barrier to commercialization was its intrinsic low electricial conductivity. In 2002, Yet-Ming Chiang and his coworkers at MIT reported that they had successfully doped the cathode with appropriate cations — such as aluminum, niobium, and zirconium.^[1] allowing development to move forward. However, Linda F. Nazar and coworkers later reported that Yet-Ming Chiang's claim that doping was responsible for the improved performance was incorrect. ^[3] The increased performance reported by Yet-Ming Chiang was due to an electronically conductive carbon network formed between grains of lithium iron phosphate - the carbon was mistakenly introduced by organic precursors.

Most lithium batteries (Li-ion) used in 3C (computer, communication, consumer electronics) products are mostly lithium cobalt oxide batteries. Other lithium batteries include lithium-manganese oxide (LiMn₂O₄), lithium-nickel oxide (LiNiO₂), and lithium iron phosphate (LFP). 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 LFP battery is much lower than LiCoO₂ battery, and the market acceptance for large-size batteries is rather low, making the LFP battery hard to massively commercialize. Battery players across the world are currently working to find a way to get the maximum storage performance out of smaller size/weight.^{[citation needed]}

Besides, there are ongoing international patent suits regarding this technology, and mass production with stable and high quality still faces many challenges.^{[citation needed]} These issues make many companies reluctant to produce the LFP batteries.

Specifications

• Cell voltage = Min discharge voltage=2.8V Working voltage=3.0V to 3.3V Max charge voltage=3.6V.
• volumetric Energy Density =?
• Gravimetric Energy Density = ?
• Deep Cycle life = ? (Number of Deep cycles to 66% of capacity)
• 80% Ccycle life = ? (Number of Cycles using 80% of rated capacity)

Safety

LiFePO₄ is an intrinsically safer cathode material than LiCoO₂. 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.

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.^[2]

Usage

Because this type of battery is not widely in production, little performance information is available. LionEV, Pihsiang Energy Technology Co, and ThunderSky. LiFePO₄ batteries (using phosphate material from Phostech Lithium) have already begun shipping in some autos, scooters and electric bicycles^[4]. 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.^[5]. This type of battery is used on the One Laptop per Child project ^[6].

Recent Developments

  LiFePO₄ technology has improved in recent months. The latest advances involve LiFePO₄ cells capable of 100% rated capacity discharges and deep discharge voltages. Lithium cells typically cannot survive discharges that take them below 2.0 volts per cell. These cells would effectively be destroyed. To safeguard against this type of damage, very complex battery management systems had to be employed. On December 14th, 2007, LionEV produced the first LiFePO₄ cells capable of charge and discharge qualities similar to those found in LA cells. With discharge voltages as low as 1.4VDC and cap voltages as high as 3.8VDC the cells lend themselves very well to hybrid LA development. LA batteries experience sag due to their internal resistance to high C draws. LiFePO₄ cells do not experience this sag. Combining the attributes of LA cells, and those of LiFePO₄ cells, would produce a viable alternative to current battery packs. Several experiments sponsored by LionEV show that this technology is a promising avenue to follow. Live testing can be observed at Yahoo's Flikr site under Sag testing.

References

1. ^ ^{a b} "Bigger, Cheaper, Safer Batteries: New material charges up lithium-ion battery work" (html).  sciencenews.org
2. ^ ^{a b} . "Building safer Li ion batteries" (html). houseofbatteries.com
3. ^ http://www.nature.com/nmat/journal/v3/n3/full/nmat1063.html
4. ^ http://fun-ev.ecrater.com/product.php?pid=1490643 Electric Scooter with LiFePO₄ ecrater.com
5. ^ "Next Generation Battery Technology Makes Hybrid and Electric Vehicles a Reality" (html).  lithiumtech.com
6. ^ Laptop With a Mission Widens Its Audience. New York Times. Retrieved on 2007-10-04. LiFePO₄ used in OLPC (no public access!) nytimes.com