Single-phase synthesis, average, electronic, and local structure and cathode properties of pyroxene type LiFeSi2O6

Abstract

Single-phase LiFeSi2O6 with pyroxene structure was firstly synthesized via a hydrothermal route under specific conditions with optimal water amount. Using both synchrotron X-ray and neutron diffraction techniques, crystal structure refinement with the C2/c space group resulted in well converged anisotropic displacement parameters. The electron density distributions were calculated by the maximum-entropy method (MEM) and showed the difference in the Si-O bond before and after charging. A carbon composite with LiFeSi2O6 exhibited strongly enhanced electrochemical properties as the cathode for Li-ion batteries due to the improved electronic conductivity. The X-ray absorption near edge structure (XANES) spectra revealed the redox of iron was not involved in the charge and discharge processes, while other mechanisms for charge and discharge were predicted to be related to Si or O. The local structure was refined by pair distribution function (PDF) analysis of the synchrotron X-ray and neutron total scatterings, which indicated Li-ion diffusion as a one-dimensional path.