Rational construction of densely packed Si/MXene composite microspheres enables favorable sodium storage

The fast and reversible sodiation/desodiation of anode materials remains an indelible yet fascinating target. Herein, a class of the densely packed Si/MXene composite microspheres is constructed and prepared, taking advantages of the synergistic effects of the activated Si nanoparticles and conductive flower-like MXene microspheres with ample ion-diffusion pathways. Consequently, the intrinsic MXene nanosheets with intelligently regulated interlayer spacing can accommodate the volume change induced strain during cycling, and the strong interaction between the Si and MXene matrix greatly contributes to the robust structural stability. As expected, the Si/MXene composite architecture exhibits boosted sodium storage performance, in terms of an inspiring reversible capacity of 751 mAh·g⁻¹ at 0.1 A·g⁻¹, remarkable long-term cycling stability of 376 mAh·g⁻¹ at 0.1 A·g⁻¹ over 500 cycles, and outstanding rate capability (after one consecutive current density changing from 0.1 to 2.0 A·g⁻¹, a large capacity of 275 mAh·g⁻¹ is regained after suddenly returning the initial current density back to 0.1 A·g⁻¹ and in the subsequent 200 cycles this composite architecture anode still delivers a capacity of 332 mAh·g⁻¹). The kinetics analysis indicates superior pseudocapacitive property, high electronic conductivity, and favorable sodium-ion adsorption and diffusion capability, confirming fast sodium storage performance. Impressively, ex-situ X-ray diffraction and selected area electron diffraction characterizations corroborate the formation of NaSi₆ as the main sodiation products during the reversible evolutions of cycled proceeding with sodium-ion insertion. This work sheds light on the elaborate design of silicon-based nanostructured anodes towards advanced high-performance sodium-ion batteries.