Are Fe-Li Antisite Defects Necessarily Detrimental to the Diffusion of Li + in LiFePO4/C?

Abstract

The one-dimensional Li+ diffusion channel is the key factor restricting the rate performance and low-temperature performance of the LFP/C composites. By artificially creating a certain content of antisite defects, the Li+ in the LFP material can be diffused two-dimensionally. The LFP/C composites synthesized by the carbothermic reduction method at 700 °C have 3.77% Fe-Li antisite defects, showing higher rate performance, cycle performance, and discharge-specific capacity. The CV, EIS, and GITT tests show that the Li+ diffusion coefficient of LFP is the highest when the content of Fe-Li antisite defects is 3.77%. DFT calculation shows that the single pair of Fe-Li antisite defects is conducive to the two-dimensional diffusion of Li+, while the continuous two pairs of antisite defects greatly inhibit the diffusion of Li+ along the original [010] crystal direction.