The Root Cause of the Rate Performance Improvement After Metal Doping: A Case Study of LiFePO4

摘要

This study investigates a root cause of the improved rate performance of LiFePO4 after metal doping to Fe-sites. This is because the metal doped LiFePCVC maintains its initial capacity at higher C-rates than undoped one. Using LiFePCVC and doped LiFe_(0.97)M_(0.03)PCVC (M=Al~(3+), Cr~(3+) Zr~(4+)), which are synthesized by a mechanochemical process followed by one-step heat treatment, the Li content before and after chemical delithiation in the LiFePCVC and the binding energy are compared using atomic absorption spectroscopy (AAS) and X-ray photoelectron spectroscopy (XPS). The results from AAS and XPS indicate that the low Li content of the metal doped LiFePCVC after chemical delithiation is attributed to the low binding energy induced by weak Li-O interactions. The improved capacity retention of the doped LiFePCVC at high discharge rates is, therefore, achieved by relatively low binding energy between Li and O ions, which leads to fast Li diffusivity.