LAUSR

This study presents a new material, “HxCrS2” (denotes approximate composition) formed by proton‐exchange of NaCrS2 which has a measured capacity of 728 mAh g−1 with significant improvements to capacity retention, sustaining over 700 mAh g−1 during cycling experiments. This is the highest reported capacity for a transition metal sulfide electrode and outperforms the most promising proposed sodium anodes to date. HxCrS2 exhibits a biphasic structure featuring alternating crystalline and amorphous lamella on the scale of a few nanometers. This unique structural motif enables reversible access to Cr redox in the material resulting in higher capacities than seen in the parent structure which features only S redox. Pretreatment by proton‐exchange offers a route to materials such as HxCrS2 which provide fast diffusion and high capacities for sodium‐ion batteries.