To use all functions of this page, please activate cookies in your browser.
With an accout for my.chemeurope.com you can always see everything at a glance – and you can configure your own website and individual newsletter.
- My watch list
- My saved searches
- My saved topics
- My newsletter
Lithium iron phosphate battery
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.
Additional recommended knowledge
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.  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. 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.  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.
Besides, there are ongoing international patent suits regarding this technology, and mass production with stable and high quality still faces many challenges. These issues make many companies reluctant to produce the LFP batteries.
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.
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. 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 project .
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.
|This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Lithium_iron_phosphate_battery". A list of authors is available in Wikipedia.|