In situ XAS study of the local structure of the nano-Li2FeSiO4/C cathode

Abstract

Despite the challenges in achieving its full theoretical capacity of reversible extraction of two Li ions, the Li2FeSiO4 (LFS) cathode shows a remarkable cycling stability once its low electronic conductivity is addressed. By studying the local structure around the iron during electrochemical cycling using in situ x-ray absorption spectroscopy (XAS), it is possible to gain insight into the factors which determine the electrochemical properties of this material. In order to practically perform in situ XAS studies, the charge/discharge of LFS was maximized using two approaches: (a) reducing the particle size of LFS samples from micro-scale to nano-scale in order to reduce the diffusion path for intercalating ions; and (b) applying a conductive coating to each nanoparticle to facilitate electron transfer. A family of LFS materials was synthesized and characterized using x-ray diffraction, and scanning electron microscopy with energy dispersive analysis for structural and morphological analysis, as well as cyclic voltammetry and cycling tests for electrochemical performance diagnosis. This material was then characterized by in situ XAS. The results provide insight into the stable electrochemical performance of LFS and suggest new synthetic routes to reaching the theoretical capacity.