In situ nitrogen-doped double-shell SiOx nanospheres: a novel approach for enhancing lithium-ion battery performance

Effectively alleviating the volume change of silicon oxide (SiO_x) anodes and improving their conductivity are crucial for enhancing the structural integrity and cycling stability of lithium-ion batteries (LIBs). In this study, ZIF-67 hollow nanospheres (ZIF-67 HNSs) were synthesized for the first time and used as templates to achieve a hollow structure, nanostructuring, and in situ nitrogen doping in SiO_x anodes, resulting in the successful preparation of N/SiO_x@N/SiO_x@C double-shell layer hollow nanospheres. The material features a robust nitrogen-doped SiO_x double-shell structure, which, combined with oxygen content regulation, effectively alleviates the volume expansion of high-capacity SiO_x anodes. Additionally, in situ nitrogen doping into the SiO_x matrix further optimizes the electronic conductivity and ion diffusivity. Electrochemical impedance spectroscopy and distribution of relaxation time analyses indicate that the anode exhibits excellent charge transfer kinetics and a stable solid electrolyte interfacial layer, which remains stable even after prolonged cycling. In situ Raman spectroscopy further confirms that the double-shell structure effectively preserves the integrity of the electrode. The anode achieves a high specific capacity of 893.1 mAh g⁻¹ after 1000 cycles at 1 A g⁻¹ and demonstrates excellent rate capability (447.4 mAh g⁻¹ at 3 A g⁻¹). This study presents a novel approach for designing SiO_x anodes with in situ nitrogen doping and spatially engineered double-shell structures, offering new insights into the design of high-performance LIB anodes with enhanced cycling stability and capacity retention.