We introduce a one-step process that consists of thermal disproportionation and impurity doping to enhance the reversible capacity and electrical conductivity of silicon monoxide (SiO)-based negative electrode materials in Li-ion batteries. Transmission electron microscope (TEM) results reveal that thermally treated SiO at 900 °C (H–SiO) consists of uniformly dispersed nano-crystalline Si (nc-Si) in an amorphous silicon oxide (SiOx) matrix. Compared to that of prinstine SiO, the electrochemical performance of H–SiO shows improved specific capacity, due mainly to the increased reversible capacity by nc-Si and to the reduced volume expansion by thermally disproportionated SiOx matrix. Further electrochemical improvements can be obtained by boron-doping on SiO (HB–SiO) using solution dopant during thermal disproportionation. HB–SiO electrode without carbon coating exhibits significantly enhanced specific capacity superior to that of undoped H–SiO electrode, having 947 mAh g−1 at 0.5C rate and excellent capacity retention of 93.3% over 100 cycles. Electrochemical impedance spectroscopy (EIS) measurement reveals that the internal resistance of the HB–SiO electrode is significantly reduced by boron doping.