Intermediate Phase-Assisted Li-Intercalation/Extraction Behavior for LiFePO4 Cathode Materials

Understanding the basic mechanism of Li-insertion/extraction in LiFePO4 batteries will be greatly beneficial to enhance their high-power capability or low-temperature performance, which is vitally important for the electric vehicle industry. Here, we present a viewpoint on the Li-insertion/extraction mechanism for our hierarchical LiFePO4/C samples. Instead of a traditional direct FePO4/LiFePO4 reaction, Fe2PO5 and (LiPO3)(4)center dot 2H(2)O phases emerge, assisted by electrolytes as intermediate phases, which make the Li-ion (de)intercalation process most likely a nucleation-limited reaction. During this process, the rate of enablement of the phase transition is the lowest, and once a phase has initiated at the moment of nucleation, the subsequent phase transformation is much faster. The Fe2PO5 phase, which contains both Fe2+ and Fe3+ ions, would result in the delocalization of electrons and enable electrons to conduct from nanocrystalline grains to conductive carbon-coated films nearby, accelerating electron conduction near the lithium site. This work provides a possibility for improving the high rate or low-temperature performance of LiFePO4 batteries by appropriate electrolyte additives that increase supersaturation of the (LiPO3)(4)center dot 2H(2)O or Fe2PO5 intermediate phase based on the understanding of intermediate phase-assisted Liintercalation/extraction behavior.

Automated summary

Understanding the mechanism of Li-insertion/extraction in LiFePO4 batteries is crucial for improving their high-power capability or low-temperature performance. This study reveals the existence of Fe2PO5 and (LiPO3)·2H2O phases as intermediate phases, which assist the Li-ion (de)intercalation process. The Fe2PO5 phase with Fe2+ and Fe3+ ions enables electron conduction near the lithium site, leading to enhanced battery performance. This work suggests that electrolyte additives can increase the supersaturation of intermediate phases and potentially improve the rate or low-temperature performance of LiFePO4 batteries.