Initially commercialized in power tool applications, Lithium-ion iron phosphate cells are being used today in numerous applications where high cycle life, quick charge, or rapid discharge specifications must be met. Lithium-ion iron phosphate (LiFePO4) cells utilize an iron phosphate cathode material. The chemistry has seen a substantial amount of market interest in the past 5 years. Many vendors now ship cells based on the technology.
The iron phosphate cathode chemical characteristics exhibit excellent thermal and chemical stability. The inherent stability of the chemistry yields a number of very positive attributes in cells constructed with the chemistry. Compared to other Lithium-ion chemistries, the phosphates are seen as being safer.
At the core of the iron phosphate cathode, the FeP-oxygen bond is, in electrochemical terms, much stronger than the bond created by a cobalt-oxygen material. The strength of this bond is interesting in situations where the bond is broken (extreme heat). Cobalt oxide cathodes release oxygen gas inside the cell when put under thermal stress (caused by external sources or potentially due to heating generated inside the cell during use). When this oxygen combines with the flammable electrolyte in the separator layer, the key elements for fire are available. As the heat increases, gases inside the cell can become dangerous and potentially cause the cell to “vent.” The iron phosphate bond holds the oxygen much more securely and thus is far less susceptible to the oxygen gas building up than oxide-based cathodes.
As the Lithium-ion industry has advanced, many variations of the original iron phosphate cathode have been explored. The use of nano-particles has also been utilized to dramatically increase the surface area of the cathode. In other iron phosphate variations, chemical compounds have been used to coat the surfaces of larger iron phosphate particles or chemically “doped” into the structure with good results. These advancements build on the underlying technology and produce a number of differences in the chemistry’s attributes.
1.Low internal impedance – Provides high output currents with little internal heating
2. Chemistry can support charge rates over 1C with some cells rated at up to 4C charge
3. Low self-discharge
4. Long cycle life
5. High degree of safety
Energy density – A compounded effect of lower nominal voltage and chemical energy density give the chemistry a 40% to 60% lower energy density versus cobalt oxide cells which means that more cells are required which increases volume, weight and cost.
Today, iron phosphate has had success and shows promise in many high-power and/or fast charge applications where power density is more important than energy density. Cordless power tools, hybrid electric vehicles, off grid power back-up and some military applications are all suited to this chemistry.
MERITSUN can provide battery solutions usign Lithium ion - Iron Phosphate chemistry where fast charge, high discharge or long cycle life are a requirement. Please contact us to discuss your requirements.
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