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

Abstract

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.

Graphical abstract

摘要

钠离子电池负极材料的快速和可逆的钠脱嵌仍然是一个令人着迷的目标。利用Si纳米粒子与具有丰富离子扩散路径的导电花状MXene微球的协同作用, 构建并制备了一类致密堆积的Si/MXene复合微球。因此, 具有智能调节层间距特性的MXene纳米片能够适应循环过程中体积变化引起的应变, Si和MXene基体之间的强相互作用有助于结构的稳定。Si/MXene复合结构提高了钠离子的存储性能, 在0.1 A·g⁻¹电流密度下可逆比容量为751 mAh·g⁻¹, 经500次循环后比容量可达376 mAh·g⁻¹。在一个连续电流密度变化从0.1到2.0 A·g⁻¹, Si/MXene复合微球的比容量高达275 mAh·g⁻¹, 返回初始电流密度0.1 A·g⁻¹, 随后经200次循环后, 这种复合负极材料的比容量仍可达332 mAh·g⁻¹。电化学动力学分析表明: 该材料具有良好的赝电容性、高的电子电导率和良好的钠离子吸附和扩散能力, 从而证明了 Si/MXene复合微球具有快速储钠的性能。在钠离子脱嵌循环的可逆演化过程中, 非原位X射线衍射和选定区域电子衍射结果证实了 NaSi₆是主要钠化产物。