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.