Template-free hydrothermal synthesis of Li2FeSiO4 hollow spheres as cathode materials for lithium-ion batteries

Abstract

Li₂FeSiO₄ hollow spheres were successfully synthesized for the first time via a template-free hydrothermal approach, with the hydrothermal process monitored in detail. It was found that the growth mechanism of the Li₂FeSiO₄ hollow sphere could be attributed to the Ostwald ripening theory. Structural characterizations by XRD, FTIR and TEM measurements revealed that the Li₂FeSiO₄ hollow spheres had a hollow micro-/nanostructure, where micro-/nanosized void spaces provided more access of the electrolyte to the electrode surface, thereby facilitating charge transfer across the electrode/electrolyte interface. Moreover, the thin wall of the hollow spheres reduced the path lengths for lithium ion diffusion. To further improve the electronic conductivity, the Li₂FeSiO₄ hollow spheres were coated by a carbon layer, and the electrochemical performance of the Li₂FeSiO₄/C electrode materials obtained with different morphologies were investigated in detail. As a result, nanosized Li₂FeSiO₄ hollow spheres that were hydrothermally synthesized for three days showed the best performance, with a high specific capacity of 152 mA h g⁻¹ at 0.05 C in the voltage window of 1.5–4.8 V at room temperature.