How Water Accelerates Bivalent Ion Diffusion at the Electrolyte/Electrode Interface.

The effect of H2 O in electrolytes and in electrode lattices on the thermodynamics and kinetics of reversible multivalent-ion intercalation chemistry based on a model platform of layered VOPO4 has been investigated. The presence of H2 O at the electrolyte/electrode interface plays a key role in assisting Zn2+ diffusion from electrolyte to the surface, while H2 O in the lattice structure alters the working potential. More importantly, a dynamic equilibrium between bulk electrode and electrolyte is eventually reached for H2 O transport during the charge/discharge cycles, with the water activity serving as the key parameter determining the direction of water movement and the cycling stability.