Investigating HxCrS2 as an Electrode Material for Reversible Energy Storage via Electrochemical Impedance Spectroscopy

Abstract

Alternatives to lithium-ion (Li-ion) batteries are becoming increasingly important as energy storage requirements increase for applications such as electric vehicles and renewable energy. In particular, electrode materials compatible with the naturally abundant metals sodium (Na) and magnesium (Mg) are desirable. Transition metal dichalcogenides (TMDs) are promising for Na and Mg battery systems since chalcogenides are larger and more polarizable than oxides, which are commonly used with Li-ion batteries, and they can be chemically and mechanically manipulated to improve their electrochemical behavior. HxCrS2 is a novel dichalcogenide-containing material with alternating amorphous and crystalline layers that can be exfoliated into CrxSy nanosheets. This work reports the investigation of bulk HxCrS2 and CrxSy nanosheets as electrode materials using electrochemical impedance spectroscopy (EIS) to probe their diffusion behavior. EIS revealed significantly lower impedances and higher diffusion coefficients for discharged HxCrS2 compared to NaCrS2 and LiCrS2, indicating improved intercalation and faster charging/discharging capability. Galvanostatic cycling with potential limitation data also suggest increased reversibility for HxCrS2 vs. Na compared to NaCrS2 vs. Na and HxCrS2 vs. Li. The investigation of CrxSy nanosheets remains inconclusive, but the results for HxCrS2 indicate electrochemical improvements as a result of chemical manipulation of the stacking order of electrode materials for Na-ion battery systems. Successful improvements to battery materials for Na and Mg-ion storage are important for improving the sustainability and charge density of energy storage technologies.