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.