Ca2+ Pre-Intercalated Bilayered Vanadium Oxide for High-Performance Aqueous Mg-Ion Batteries

CaVOnH achieves a first discharge capacity of 273 mAh g−1 with capacity retention of 91% at 50 mA g−1 in 0.8 m Mg(TFSI)2-85%PEG-15%H2O (polyethylene glycol, PEG), but limited rate capability due to the low ionic conductivity of electrolyte.

Dimethyl sulfoxide (DMSO) is used as a co-solvent to tune the physical-chemical properties of aqueous Mg-ion electrolyte (AME), resulting in the reorganization of Mg2+ solvation and hydrogen bond network. The AME containing DMSO shows improved ionic conductivity, low viscosity, and high Mg2+ diffusion coefficient and allows CaVOnH and V2O5 to achieve a much-improved rate capability and capacity. Moreover, the reaction mechanism and reversibility of CaVOnH are elucidated by combining in operando and ex situ techniques.