Multilevel Gradient‐Ordered Silicon Anode with Unprecedented Sodium Storage

Abstract

While cost‐effective sodium‐ion batteries (SIBs) with crystalline silicon anodes promise high theoretical capacities, they perform poorly because silicon stores sodium ineffectively (capacity <40 mAh g−1). To address this issue, herein an atomic‐order structural‐design tactic is adopted for obtaining unique multilevel gradient‐ordered silicon (MGO‐Si) by simple electrochemical reconstruction. In situ‐formed short‐range‐, medium‐range‐, and long‐range‐ordered structures construct a stable MGO‐Si, which contributes to favorable Na–Si interaction and fast ion diffusion channels. These characteristics afford a high reversible capacity (352.7 mAh g−1 at 50 mA g−1) and stable cycling performance (95.2% capacity retention after 4000 cycles), exhibiting record values among those reported for pure silicon electrodes. Sodium storage of MGO‐Si involves an adsorption–intercalation mechanism, and a stepwise construction strategy of gradient‐ordered structure further improves the specific capacity (339.5 mAh g−1 at 100 mA g−1). Reconstructed Si/C composites show a high reversible capacity of 449.5 mAh g−1, significantly better than most carbonaceous anodes. The universality of this design principle is demonstrated for other inert or low‐capacity materials (micro‐Si, SiO2, SiC, graphite, and TiO2), boosting their capacities by 1.5–6 times that of pristine materials, thereby providing new solutions to facilitate sodium storage capability for better‐performing battery designs.