TiS2 as a high performance potassium ion battery cathode in ether-based electrolyte

Potassium ion batteries are potential energy storage devices owing to their low cost and good K+ diffusion kinetics due to the small Stoke's radius. Here, we report a layered TiS2 cathode material, demonstrating outstanding potassium storage cycling and rate performances in ether-based electrolyte, with a capacity of 80 mAh g(-1) at 20 C and 63 mAh g(-1) after 600 cycles (1.5-3.0 V, corresponding to 4.8 A g(-1)). The phase transitions during K ion intercalation at the atomic level are explored via High Resolution Transmission Electron Microscopy (HRTEM) and ex-situ X-ray diffraction (XRD) combined with Rietveld refinements. It undergoes a second-stage structure to be K0.11TiS2 and then first-stage K0.56TiS2. The K cations intercalate into trigonal prismatic sites with a sliding of Ti-S plane by 120 degree-rotation, rendering a root 3 x root 3 commensurate superstructure along the [001] zone. The K stage intercalation is in favor of a Daumas-Herold model rather than Rudorff model. This study demonstrates that the layer structure materials are promising candidates for high performances K-ion batteries and highlights the importance of improving electrochemical performances with electrolyte modification.