Using CoS cathode materials with 3D hierarchical porosity and an ionic liquid (IL) as an electrolyte additive for high capacity rechargeable magnesium batteries

Abstract

Developing high capacity, rechargeable magnesium batteries is highly desired to meet increasing energy demands while targeting viable replacements for lithium batteries. In the present work, cobalt sulfide (CoS) spheres with three-dimensional (3-D) hierachical porosity, CoS_HE, were prepared in a mixed solvent comprising equal volumes of water and ethylene glycol using a solvothermal method. The resultant CoS_HE offers large pore volumes (0.227 cm³ g⁻¹) and appreciable specific surface areas (SSAs, 27 m² g⁻¹) as well as flexible structures that provide efficient Mg²⁺ transport channels and accommodate the volume expansion that occurs during the discharge–charge process. Moreover, our data reveal that the introduction of an IL into the electrolyte consisting of 2-(tert-butyl)-4-methylphenolate magnesium chloride (TBMPOMgCl) and aluminium chloride at a molar ratio of 2 : 1 not only significantly activates the discharge/charge process, but also enhances the specific capacity, perhaps by altering the thermodynamic and kinetics of the reaction between CoS and Mg. As a result, a high capacity (up to 370 mA h g⁻¹), good cycling stability (around 340 mA h g⁻¹ after 88 cycles) and considerable rate performance (around 300 mA h g⁻¹ at 50 mA g⁻¹) were achieved cooperatively by using the CoS_HE cathode and the IL electrolyte additive.