Nanostructured 0.8Li2FeSiO4/0.4Li2SiO3/C composite cathode material with enhanced electrochemical performance for lithium-ion batteries

Abstract

A strategy is proposed and developed to promote Li⁺ diffusion in polyanion cathode materials such as 0.8Li₂FeSiO₄/0.4Li₂SiO₃/C with the incorporation of Li₂SiO₃ as a lithium ionic conductive matrix. It is shown that the presence of Li₂SiO₃ separates the Li₂FeSiO₄ particles into small domains of a few nanometres and provides a fast Li⁺ diffusion channel, thus effectively enhancing Li⁺ diffusion in the 0.8Li₂FeSiO₄/0.4Li₂SiO₃/C composite. As a result, the composite material shows enhanced electrochemical performance and delivers a capacity as high as 240 mA h g⁻¹ (corresponding to 1.44 electrons exchange per active Li₂FeSiO₄ formula unit) with good cyclic stability at 30 °C. The XRD and FTIR results indicate that the Li₂SiO₃ component exists in an amorphous phase. SEM and TEM analyses show an aggregate structure consisting of primary nanocrystallites (about tens of nanometres in diameter). The primary particles consist of a crystal Li₂FeSiO₄ phase and an amorphous Li₂SiO₃ and C, and a nanocrystalline Li₂FeSiO₄ surrounded by amorphous Li₂SiO₃ and C which are well known as a lithium ion conductor and electron conductor. The smaller nanoparticles of Li₂FeSiO₄ and the presence of lithium ionic and electronic conducting amorphous Li₂SiO₃ and carbon matrix both contributed to the enhanced electrochemical performance of the composite.