Unlocking High Capacity and Fast Na⁺ Diffusion of H_xCrS₂ by Proton-Exchange Pretreatment

This study presents a new material, “H_xCrS₂” (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. H_xCrS₂ 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 H_xCrS₂ which provide fast diffusion and high capacities for sodium-ion batteries.