Multilevel Gradient-Ordered Silicon Anode with Unprecedented Sodium Storage.

While cost-effective sodium-ion batteries 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 we adopted an atomic-order structural-design tactic 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, which is expected to be an innovative alternative as anodes in SIBs. Sodium storage involves an adsorption-intercalation mechanism, and a stepwise construction strategy of gradient-ordered structure further improved 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, SiO 2 , SiC, graphite, and TiO 2 ), boosting their capacities by 1.5-6 times that of pristine materials, thereby providing new solution to facilitate sodium storage capability for better-performing battery designs. This article is protected by copyright. All rights reserved.