Robust and fast-ion conducting channels empowering biomass Si anode toward high energy lithium ion batteries

The silicon (Si) based materials with robust structural adaptability and abundant Li⁺ transportation pathway have attracted great attentions due to their enviable high capacity and long lifespan. However, the severe structural collapse and intrinsic low conductivity hinder its practical applications. In this work, the mild magnesiothermic reduction (MMR) is exploited for the scalable fabrication of spongy-like porous silicon (NC/SP-Si) using rice husk derived Mg₂Si and SiO₂ as the reductant and reactant, respectively. Benefiting from the buffering effect of MMR, the structural collapse is effectively avoided and spherical-lamellar symbiotic Si sponge is successfully constructed, resulting in fast-ion Li⁺ conducting channels and robust high mechanical flexibility. Importantly, ultrathin nitrogen doped carbon layers derived from chitosan further boost the intrinsic low conductivity of Si and prevent the undesirable interface side reactions. When utilized as anodes for lithium ion batteries, the NC/SP-Si delivers a high capacity of 1282 mAh g⁻¹ after 100 cycles at 0.1 A g⁻¹. Even at 1 A g⁻¹, the electrode delivers a capacity of 710.6 mAh g⁻¹ after 1000 cycles. The ex-situ characterizations demonstrate that the ingenious spongy Si and heteroatom doped carbon layers can effectively enhance the accommodation to volume expansion, provide multilevel fast Li⁺ conducting channels, and accelerate the formation of LiF-rich solid electrolyte interface films. Encouragingly, the assembled NCM811‖NC/SP-Si full cell shows excellent electrochemical performance after 400 cycles with a high energy density of 555.8 Wh kg⁻¹. This work reveals the significance of constructing robust multilevel Li⁺ conducting channels and regulating stable LiF-rich SEI in improving the performance of Si, which provides a new perspective for boosting the large-scale application of biomass derived Si based anodes.