⭐LFP contains neither nickel nor cobalt, both of which are in limited supply and expensive. (for ternary)
⭐ LFP chemistry has a longer cycle life than other Li-ion methods
LiFePO4 batteries have a slower rate of capacity loss (also known as longer calendar life) compared to lithium-ion battery chemistries such as cobalt (LiCoO) or manganese spinel (LiMn2O4) lithium-ion polymer batteries (LiPo batteries) or Lithium Ion Battery. After one year, the energy density of LiCoO2 cells is generally about the same as that of aLiFePO.
⭐ Compared with other lithium-ion chemical plants, an important advantage is thermal stability and chemical stability. The P-O bond in the lithium iron phosphate crystal is stable and difficult to decompose, and it will not be like cobalt acid even at high temperature or overcharge. Lithium-like structure collapses and generates heat or forms strong oxidizing substances. The decomposition temperature of lithium iron phosphate is about 600 ° C, so it has good safety.
Focus: Low cost, minimum battery price of $80/kWh ($12.5Wh/$)
Disadvantages: ternary battery life is high, charging efficiency is high, low temperature performance is worse than ternary lithium
Research on the fault direction of lithium iron phosphate battery
1. Impurities in the active electrode material lead to battery failure.
During the synthesis of LiFePO4, a small amount of impurities, such as Fe2O3 and Fe, will appear. These impurities will be reduced on the negative electrode surface and may penetrate the separator and cause an internal short circuit. When LiFePO4 is exposed to air for a long time, moisture can deteriorate the battery. During the early stages of aging, amorphous iron phosphate forms on the surface of the material. Its local composition and structure are similar to that of LiFePO4(OH); with the insertion of OH, LiFePO4 is continuously consumed, showing a volume increase; later, it slowly recrystallizes to form LiFePO4(OH). The Li3PO4 impurity in LiFePO4 is electrochemically inert. The higher the impurity content of the graphite anode, the greater the irreversible capacity loss.
2. The battery fails due to the formation method
The irreversible loss of active lithium ions is first reflected in the lithium ions consumed during the formation of the solid-electrolyte interfacial film. The study found that increasing the formation temperature resulted in irreversible loss of lithium ions. When the formation temperature increases, the proportion of inorganic components in the SEI film will increase. The gas released during the transition from the organic part ROCO2Li to the inorganic component Li2CO3 will cause more defects in the SEI film. A large amount of lithium ions dissolved by these defects will intercalate into the negative graphite electrode.
(1) During the formation process, the composition and thickness of the SEI film formed by low-current charging are uniform but time-consuming; high-current charging will lead to more side reactions, resulting in increased irreversible lithium ion loss and negative electrode interface impedance. , but saves time. Time; now, the formation mode of small current constant current - high current constant current and constant voltage is used more frequently, so the advantages of both can be considered.
Battery failure due to moisture in the production environment
In practical production, batteries inevitably come into contact with air, because the positive and negative materials are mostly micro or nano-sized particles, and the solvent molecules in the electrolyte have large negatively charged carbonyl groups and variable carbon-carbon double bonds. All of these easily absorb moisture from the air.
(2) The water molecule reacts with the lithium salt (especially LiPF6) in the electrolyte, the lithium salt decomposes and consumes the electrolyte (decomposes to form PF5), and produces the acidic species HF. Both PF5 and HF will destroy the SEI film, and HF will also promote the corrosion of the LiFePO4 active material. Water molecules also exfoliate the lithium-inserted graphite anode, forming lithium hydroxide at the bottom of the SEI film. In addition, the dissolved O2 in the electrolyte also accelerates the aging of LiFePO4 batteries.
In the production process, in addition to the production process that affects the battery performance, the main factors that cause the failure of LiFePO4 power batteries include raw materials (including water) and impurities in the formation process, so the purity of the material, environmental humidity control, formation method, etc. factors are critical.