Interface Concentrated-Confinement Suppressing Cathode Dissolution in Water-in-Salt Electrolyte

Mass dissolution is one main problems for cathodes in aqueous electrolytes due to the strong polarity of water molecules. In principle, mass dissolution is a thermodynamically favorable process as determined by the Gibbs free energy. However, in real situations, dissolution kinetics, which include viscosity, dissolving mass mobility, and interface properties, are also a critical factor influencing the dissolution rate. Both thermodynamic and kinetic dissolving factors can be regulated by the ratio of salt to solvent in the electrolyte. In this study, concentration-controlled cathode dissolution is investigated in a susceptible Na3V2(PO4)(3)cathode whose time-, cycle-, and state-of-charge-dependent dissolubility are evaluated by multiple electrochemical and chemical methods. It is verified that the super-highly concentrated water-in-salt electrolyte has a high viscosity, low vanadium ion diffusion, low polarity of solvated water, and scarce solute-water dissolving surfaces. These factors significantly lower the thermodynamic-controlled solubility and the dissolving kinetics via time and physical space local mass interfacial confinement, thereby inducing a new mechanism of interface concentrated-confinement which improves the cycling stability in real aqueous rechargeable sodium-ion batteries.