Unlocking record capacity and rate capability of HxCrS2 by proton-exchange pretreatment

Unsustainable mining and limited availability of lithium-ion battery materials have created a driving need to develop alternatives such as sodium hosts.[1–4] The development of suitable anode materials remains a major challenge facing sodium-ion battery development. Efforts into studying the charge storage of sodium in transition metal sulfides have gained traction due to improved kinetics compared with oxides.[5] Van der Waals CrS2 has been predicted to be a good intercalation host for Na but has not been isolated as a bulk phase. Rather, [CrS2 ]− layers exist in delafossite-related materials such as NaCrS2 , which has only a moderate reversible capacity of about 100 mAh/g.[6] Here we present a new material, “HxCrS2” (denotes approximate composition) formed by proton-exchange of NaCrS2 which has a measured capacity of 728 mAh/g with significant improvements to capacity retention, sustaining over 700 mAh/g during cycling experiments. This is the highest reported capacity for a sulfide electrode and is higher than the capacity of antimony (576 mAh/g) which has been the most promising anode to date, pairing high capacity with high rates.[7] Pretreatment by proton-exchange offers a route to materials such as HxCrS2 which provide fast diffusion and high capacities for sodium-ion batteries.