The high-yield synthesis of Li 2 MnSiO 4 /C composites was realized under hot isostatic pressure (HIP) using a stainless steel capsule. We investigated the effect of temperature and pressure on the synthesis of Li 2 MnSiO 4 and found that the synthesis temperature decreased with the increase of HIPing pressure and vice versa. By adjusting the reaction parameters (temperature, pressure, and time), we obtained Li 2 MnSiO 4 /C composites with different size and morphology. Among these various products, Li 2 MnSiO 4 /C films, which are composed of nanoparticles about 10–15 nm diameter, deliver a discharge capacity of 273 mAh g −1 at 0.05 C, and maintain a discharge capacity of 180 mAh g −1 after 50 cycles. When the current is increased to 5 C, the discharge capacity of 86 mAh g −1 can be retained after 20 cycles.