SnS2 Nanosheets Anchored on Nitrogen and Sulfur Co-Doped MXene Sheets for High-Performance Potassium-Ion Batteries

Potassium-ion batteries (KIBs) are emerging as the prospective alternatives to lithium-ion batteries in energy storage systems owing to the sufficient resources and relatively low cost of K-related materials. However, serious volume expansion and low specific capacity are found in most materials systems resulting from the large intrinsic radius of K+. Herein, SnS2 nanosheets anchored on nitrogen and sulfur co-doped MXene (SnS2 NSs/MXene) are creatively designed as advanced anode materials for KIBs. SnS2 NSs/MXene with a unique hierarchical structure can not only provide fast transmission channels for K+ but also avoid the accumulation of K+ and volume expansion. These novel features make SnS2 NSs/MXene electrodes exhibit a superior reversible specific capacity of 342.4 mA h g–1 under 50 mA g–1. Also, they maintain 206.1 mA h g–1 at an even higher current density of 0.5 A g–1 over 800 cycles almost without capacity decay. Moreover, the multistep alloying reaction mechanism of SnS2 NSs/MXene composites and K+ is revealed by the ex situ X-ray diffraction measurement. In addition, the density functional theory calculations confirm the existence of Ti–S bonds between SnS2 nanosheets and MXene, which significantly enhance the structural stability and cycling electrochemical performance of SnS2 NSs/MXene composites.