The root cause of the rate performance improvement after metal doping: A case study of LiFePO₄

This study investigates a root cause of the improved rate performance of LiFePO₄ after metal doping to Fesites. This is because the metal doped LiFePO₄/C maintains its initial capacity at higher C-rates than undoped one. Using LiFePO₄/C and doped LiFe_0.97M _0.03PO₄/C (M=Al³⁺, Cr³⁺, 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 LiFePO₄/C 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 LiFePO₄/C after chemical delithiation is attributed to the low binding energy induced by weak Li-O interactions. The improved capacity retention of the doped LiFePO₄/C at high discharge rates is, therefore, achieved by relatively low binding energy between Li and O ions, which leads to fast Li diffusivity.