Multilevel Gradient-Ordered Silicon Anode with Unprecedented Sodium Storage

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.