SiOx Encapsulated into Nitrogen-Enriched Lignin Porous Carbon for Fast Lithium Storage

The low-cost and high-capacity SiOx is widely recognized as an ideal anode material for lithium storage; however, the challenges of low conductivity and significant volume expansion still need to be addressed. In this work, we incorporated SiOx into a lignin-derived carbon material with an elevated nitrogen content through a step-by-step carbonization strategy. Initially, the electrostatic assembly facilitated the formation of a complex comprising modified lignin and SiO2, which was subsequently subjected to carbonization and etching steps. Finally, due to zinc species inhibiting nitrogen decomposition, the cocarbonization of the lignin porous carbon/SiOx complex, zinc oxalate, and melamine enabled the construction of a nitrogen-enriched carbon/SiOx composite. The resulting carbon/SiOx composite exhibited a moderate specific surface area, abundant mesoporous channels, and an exceptionally high nitrogen doping content of 17.91 at. %. These characteristics effectively enhanced the storage and transportation of lithium ions while mitigating the volume expansion. As anodes in half batteries, the reversible specific capacity of the optimized carbon/SiOx reached 894 mAh/g during stable cycles, which was attributed to the enhanced ion diffusion rate and storage kinetics resulting from the high nitrogen content as well as the improved structural stability due to the encapsulated structure. Furthermore, the assembled lithium-ion capacitor demonstrated an energy density of 82 Wh/kg and maintained a capacity retention rate of 93.1% after undergoing 15,000 cycles. This work presents a novel concept for the synthesis of nitrogen-rich carbon matrixes but also offers insights into the structural optimization of silicon-based negative electrodes using green biomass.