Silicon suboxide (SiOx, x < 2) possesses high specific capacity as lithium ion battery anode. However, the cyclability and rate performance of SiOx are still unsatisfactory because of its huge volume change and low conductivity. Here, we report SiOx/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 SiOx/C spheres consist of subnanoscopically and homogeneously dispersed SiOx and free carbon. Such dispersion structure increases tolerance for volume change and electrical conductivity. The spherical shape benefits uniform distribution of the SiOx/C spheres in electrodes, ensuring high electrical connectivity and uniform distribution of volume change. Consequently, the SiOx/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.