Improving high-rate performance of mesoporous Li2FeSiO4/Fe7SiO10/C nanocomposite cathode with a mixed valence Fe7SiO10 nanocrystal

Abstract

Li₂FeSiO₄ is considered to be one of the most promising cathode materials for lithium-ion batteries due to its theoretical specific capacity as high as 330 mA h g⁻¹, resource abundance, low cost, and environmental benignity. However, Li₂FeSiO₄ possesses a poor conductivity, and co-exists with a small amount of an insulating glassy SiO₂ impurity, leading to severe capacity decay at high rates. Herein, we report a mesoporous Li₂FeSiO₄/Fe₇SiO₁₀ hetero-nanocrystal/C nanocomposite as a cathode material for high power lithium-ion batteries. By controlling the crystallization and composition of the materials, a smaller amount of mixed valence Fe₇SiO₁₀ nanocrystals intergrow with Li₂FeSiO₄ nanocrystals instead of glassy SiO₂, thus minimizing the insulating SiO₂ in the Li₂FeSiO₂ cathode. The conductive hybrid framework consisting of a three-dimensional carbon network and conductive Fe₇SiO₁₀ nanocrystals offers a continuous electron transport network in the material, and sponge-like mesoporosity allows efficient penetration, transport and storage of an electrolyte within a cathode. By intergrowing Li₂FeSiO₄/Fe₇SiO₁₀ hetero-nanocrystals, a remarkably improved high-rate performance is achieved with a reversible discharge capacity of 112 mA h g⁻¹ over 80 cycles at a current rate of 10 C. Our finding represents a new approach towards designing conductive nanostructures of insulating oxides for high-power lithium-ion batteries on a mesoscopic scale.