Compatibility of Molybdenum Disulfide and Magnesium Fluorinated Alkoxyaluminate Electrolytes in Rechargeable Mg Batteries

Abstract

Molybdenum disulfide (MoS₂)-based cathodes have exhibited good electrochemical reactions in all phenyl complex (APC) electrolytes. However, APC electrolytes are highly corrosive and susceptible to oxidation. Alternatively, magnesium fluorinated alkoxyaluminate electrolyte (Mg[Al(HFIP)₄]₂) is a pioneering chloride-free electrolyte with remarkable electrochemical activity in rechargeable Mg batteries (RMBs). This study aims to investigate the compatibility of various MoS₂ nanomaterials with Mg[Al(HFIP)₄]₂ in RMBs. Seven MoS₂ nanomaterials were synthesized under different hydro/solvothermal conditions and evaluated as cathode materials in RMBs. The results revealed that the electrochemical activity of the as-synthesized MoS₂ in RMBs significantly varied and MoS₂ with high content of 1T-phase (M5) exhibited the best specific capacity of ca. 35 mAh g⁻¹. Heteroatom doping, graphene oxide (GO) incorporation, and dual-salt electrolytes were employed to enhance the electrochemical performance of M5. The electrochemical tests showed that all doped-MoS₂ and GO-MoS₂ delivered poor specific capacities (<20 mAh g⁻¹), properly due to the disorder of the cathode material and the entrapment of Mg²⁺ ions. In contrast, dual-salt electrolytes (0.3 M Mg[Al(HFIP)₄]₂/0.3 M LiCl) improved the initial specific capacity by 242 %. This is attributed to the preferential intercalation of Li⁺ ions that reduces the diffusion energy barrier and facilitates the intercalation of Mg⁺² ions.