Electrochemical Performance of Polymer-Derived in-situ Generated Nano-Silicon/SiNx Composite Anodes for Lithium-Ion Storage

Silicon (Si) anodes are promising alternatives to graphite in lithium-ion batteries (LIBs), but their effective use requires a well-designed matrix to address associated challenges. Polymer-derived ceramic (PDC) processing has been successfully employed to create Si-based compositions for LIB anodes. However, the in-situ nanoengineering of Si nanocrystals using the PDC approach was only recently developed. In this study, we report the first production and characterization of SiNx nanocomposite electrodes with in-situ precipitated Si nanocrystals, obtained through the controlled pyrolysis (950–1250 °C) of a polysilazane precursor. The pyrolysis temperature was key in expanding Si nanocrystal domains and crystallizing silicon nitride (Si3N4) at 1250 °C. The aerogel-derived Si/SiNx nanocomposite (Si/Nx_1200A) anode exhibits superior performance, with the best rate capability (755–507 mAh g−1 at current densities between 18–1860 mA g−1) and stable cycling behaviour (> 400 mAh g−1 after 200 cycles at 372 mA g−1). Interestingly, among the non-aerogel samples, the one obtained at 950 °C, containing the fewest Si nanocrystals, achieves the highest first-cycle capacity of 748 mAh g−1 at 18 mA g−1, but shows more significant capacity fading over cycles. Impedance studies of Si/Nx_1200A confirm good stability and a reduction in charge transfer resistance after repetitive cycling.