Investigation towards scalable processing of silicon/graphite nanocomposite anodes with good cycle stability and specific capacity

Silicon/graphite(Si/Gr)nanocomposites with controlled void spaces and encapsulated by a carbon shell(Si/Gr@void@C)are synthesized by utilizing high-energy ball milling to reduce micron-sized particles to nanoscale,followed by carbonization of polydopamine(PODA)to form a carbon shell,and finally partial etching of the nanostructured Si core by NaOH solution at elevated temperatures.In particular,the effects of ball milling time and NaOH etching temperature on the electrochemical properties of Si/Gr@void@C are investigated.Increasing the ball milling time results in the improved specific capacity of Si-based anodes.Carbon coating further enhances the specific capacity and capacity retention over charge/discharge cycles.The best cycle stability is achieved after partial etching of the Si core inside Si/Gr@void@C particles at either 70 or 80C,leading to little or no capacity decay over 130 cycles.However,it is found that both carbon coating and NaOH etching processes cause some surface oxidation of the nanostructured Si particles derived from high-energy ball milling.The surface oxidation of the nanostructured Si results in decreases in specific capacity and should be minimized in future studies.The mechanistic understanding developed in this study paves the way to further improve the electrochemical performance of Si/Gr@void@C nanocomposites in future.