Yolk-shell NiSx@C nanosheets as K-ion battery anodes with high rate capability and ultralong cycle life

Potassium ion batteries have attracted increasing attention as alternatives to lithium ion batteries. However, the large ionic radius of potassium results in large volume expansion and rapid capacity fading of anode materials. Herein, we design and synthesize unique yolk-shell NiSx@C nanosheets through a facile etching process and sulfuration treatment to tackle this challenge. In this composite, NiSx nanoparticles are well confined within hollow carbon nanosheets with enough interior void space. As an anode, it can exhibit high capacity (415 mA h g(-1) at 0.1 A g(-1) after 50 cycles) and good rate performance (232 mA h g(-1) at 2 A g(-1)). More impressively, an ultra-long cycling life of up to 8000 cycles was realized at 0.5 A g(-1), outperforming most anodes reported so far. Such superior battery performance is attributed to the unique microstructural properties of the yolk-shell NiSx@C composite, which can enhance the charge transfer kinetics, offer sufficient void room for volume fluctuation, prevent the agglomeration of NiSx, and preserve the structural integrity during cycles.