What are the main factors causing the decline in the life of lithium iron phosphate batteries?

As these lithium-iron phosphate batteries enter their end-of-life phase, we have to face a thorny problem -- the recycling of used batteries. lithium iron phosphate battery recovery has its own characteristics. Compared with other layered structural materials, lithium iron phosphate has a more stable olivine structure and is therefore very stable. Even if all Li + is removed from the interior of lithium iron phosphate material when charging, Lithium iron phosphate materials can still maintain the FePO4 structure without structural collapse and transformation.

Lithium iron phosphate has good performance, low price, good safety, and has the potential for rapid charging. Therefore, with the rapid development of the domestic electric vehicle industry, the demand for lithium iron phosphate batteries has also rapidly increased. Lithium-iron phosphate batteries are now used in cars with high safety requirements such as electric buses.

Therefore, the decay of lithium iron phosphate batteries during the cycle process is generally not caused by the loss of positive and negative polar active substances. Neelima Paul of the Technical University of Munich, Germany, and his team used neutron diffraction methods for long-term circulation of lithium iron phosphate batteries. (LFP/MCMB) research believes that The main factor that causes the lifetime decline of lithium iron phosphate batteries is the Li consumption caused by the reconstruction and growth of the SEI membrane during the cycle.

Neelima Paul used a neutron diffraction method to analyze a battery stored in the cycle of 1C for 4,750 cycles and at 23 °C for 2 years (20% SoC). It was found that even after the battery was completely discharged (the positive electrode was in the lithium-deposited state, the negative electrode was off Lithium state), but a considerable proportion of FePO4 was observed in the diffraction peak of the positive electrode, and the ratio of LFP:FP was 67:33 in the battery of 4,750 cycles, and the ratio of LFP: FP was 75 in the battery stored for 2 years: 25, and no diffraction peak of LiC6 was observed in the diffraction peak of the negative electrode.

This result shows that a considerable proportion of Li + in lithium iron phosphate batteries "disappeared out of thin air" during the cycle and storage process. It also shows that positive and negative active substances can participate in the charging and discharging reaction during the cycle process. The loss of active substances, Therefore, the main reason for the decline of lithium iron phosphate batteries is the loss of Li during the cycle.

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