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Lithium-Iron Phosphate Rechargeable Batteries (Glossary) |
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| Lithium-iron phosphate rechargeable batteries are a variant of the lithium-ion rechargeable batteries, which were developed in 1997 at the University of Texas and which use lithium-iron phosphate (LiFePO4, 'LFP') as the cathode material instead of lithium-cobalt oxide (LiCoO2). Lithium-iron phosphate has various advantages and disadvantages as a cathode material compared to conventional lithium-ion rechargeable batteries and alternative technologies such as lithium-ion/manganese high-current cells, and these are decisive in determining future market opportunities and application areas. The decisive advantages of LFP batteries are their favourable price as well as their intrinsic safety and lower environmental impact. The disadvantages are their poor electrical conductivity and slow lithium diffusion; these cause the performance problems of LFP cells that need to be overcome. Raw Material Situation LiFePO4 is the basic chemical material that makes up the yellow to grass green mineral tavorite. However, the LFP powder used for rechargeable batteries is manufactured synthetically (solid substance reactions at high temperatures exclusively). Iron phosphate can be manufactured considerably cheaper than the cobalt oxide used for lithium-ion batteries. However, a much more serious consideration is that cobalt can be supplied only by very few countries, which makes the raw material more susceptible to price fluctuations due to raw material speculations. This is less likely for iron phosphate, since the raw materials for this substance are readily available all over the world. Intrinsic Safety and Environmental Impact Thanks to the strong chemical binding of its oxygen content, LFP does not tend to be susceptible to fire or explosion ('thermal runaway'). LFP cells hence already have a high intrinsic safety because of their very design and construction. This positive characteristic is further enhanced by the high structural stability of LFP cathodes as well as the fact that LFP is non-poisonous and has a low environmental impact. Poor Conductivity The main obstacle in the development of LFP cells were the poor electrical conductivity of LiFePO4 as well as the low diffusion speed of lithium in LFP. Initial practical measurable results were far below the specifications that appeared to be possible, for example the theoretically achievable capacity of 170 Ah/kg. However, by coating them with carbon, adding foreign metal atoms and creating nano structures with optimised sizes, the performance data of LFP cells gradually improved. Performance Data and Application Areas Today LFP cells produce impressive characteristic data and can often already compete with lithium-ion or lithium-ion/manganese cells. Operating voltage: 3 to 3.3 volts Temperature operating range: -45 to 70°C Cyclic stability: up to over 5,000 cycles The favourable price, high intrinsic safety, high number of cycles and great temperature operating range make this technology ideal for use in hybrid electric vehicles – a sector where great demand is expected. © Marc Stenzel |
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Keywords: accumulator accumulators secondary cell cells rechargeable battery batteries Lithium Iron Phosphate LFP |
