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

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.