Restraining formation of Fe-Li anti-site defects via in-situ surface construction on single-crystal LiFePO4 cathode for extending fast charging lifespan

Abstract

The widespread utilization of olivine LiFePO4 is impeded by its inadequate electrochemical characteristics, primarily caused by the inherently low diffusion coefficient of Li+ ions. This deficiency is further exacerbated by the presence of Fe-Li anti-site defects, which significantly deteriorate the diffusion coefficient during prolonged cycling periods. Herein, a highly efficient and cost-effective method is employed to fabricate single-crystal LiFePO4 possessing minimal Fe-Li anti-site defects. The Fe-O bond is reinforced by the formation of a uniform and stable carbon layer through the introduction of acetylene. This reinforcement effectively hinders the migration of Fe ions to the 4a site, which is associated with the Li site (known as LiFe defects). The validity of this phenomenon has been confirmed through theoretical calculations. The uniform carbon layer on LiFePO4 surface not only facilitates the migration of Li+ ions without obstruction but also significantly enhances the pseudo-capacitance, leading to remarkable preservation of capacity even at a high discharge rate of 10 C, with a retention rate of 80.86 % after undergoing 1500 cycles. The present study signifies a notable advancement in the acquisition of uniformly carbon-coated single-crystal cathode materials, thereby presenting a novel methodology for augmenting their electrochemical efficacy.