In Situ Pyrolysis Concerted Formation of Si/C Hybrids during Molten Salt Electrolysis of SiO₂@Polydopamine

Aiming to enhanced productivity and improved functionality of electrolytic silicon from electroreduction of solid silica in molten salts, we herein report a one-pot electrochemical preparation of Si/C hybrids via pyrolysis-cum-electrolysis (PCE) of SiO2@polydopamine (SiO2@PDA) in molten NaCl–CaCl2 at 800 °C. The obtained hybrids, denoted Si@C@Si, are composed of outmost silicon thin layers due to electrodeposition, sandwiched N-doped carbon hollow spheres derived from pyrolysis of PDA, and encapsulated silicon nanoparticles stemming from direct electrodeoxidation of SiO2. The PCE protocol shows intriguing merits on accelerated electroreduction of SiO2 and retarded generation of inconvenient SiC. The preparation conditions of Si@C@Si are optimized by varying electrolysis time and applied voltage, with the optimal conditions being identified as PCE at 2.6 V for 2 h. When evaluated as an anode for lithium-ion batteries, the obtained Si@C@Si exhibits a reversible specific capacity of 904 mAh g–1 after 100 galvanostatic charge/discharge cycles at 500 mA g–1. The proposed PCE method is highlighted as an intensified Si extraction method for advanced lithium-ion batteries, promising practical applications.