Subnanoscopically and homogeneously dispersed SiO_x/C composite spheres for high-performance lithium ion battery anodes

Silicon suboxide (SiO_x x < 2) possesses high specific capacity as lithium ion battery anode. However, the cyclability and rate performance of SiO_x are still unsatisfactory because of its huge volume change and low conductivity. Here, we report SiO_x/C composite spheres with high cyclability and rate performance, which are synthesized by heating liquid mixture of polydimethylsiloxane and hexane in sealed vessels and subsequent heat treatment. High pressure generated in the sealed vessels at high temperature induces formation of the spherical morphology. The SiO_x/C spheres consist of subnanoscopically and homogeneously dispersed SiO_x and free carbon. Such dispersion structure increases tolerance for volume change and electrical conductivity. The spherical shape benefits uniform distribution of the SiO_x/C spheres in electrodes, ensuring high electrical connectivity and uniform distribution of volume change. Consequently, the SiO_x/C spheres exhibit outstanding cycle stability (96.1% capacity retention after 400 cycles), excellent rate performance (146.2 mAh g⁻¹ at 10 A g⁻¹), and high specific capacity (1667.3 mAh g⁻¹). Particularly, at a high mass loading of 3.0 mg cm⁻² the electrodes possess high areal capacities of 2.6-2.0 mAh cm⁻² during 400 cycles, showing high promise for practical application.