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

Understanding the basic mechanism of Li-insertion/extraction in LiFePO 4 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 LiFePO 4 /C samples. Instead of a traditional direct FePO 4 /LiFePO 4 reaction, Fe 2 PO 5 and (LiPO 3 ) 4 ·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 Fe 2 PO 5 phase, which contains both Fe 2+ and Fe 3+ 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 LiFePO 4 batteries by appropriate electrolyte additives that increase supersaturation of the (LiPO 3 ) 4 ·2H 2 O or Fe 2 PO 5 intermediate phase based on the understanding of intermediate phase-assisted Li-intercalation/extraction behavior.