Inhibiting VOPO ⋅x H O Decomposition and Dissolution in Rechargeable Aqueous Zinc Batteries to Promote Voltage and Capacity Stabilities.

VOPO ⋅x H O has been proposed as a cathode for rechargeable aqueous zinc batteries. However, it undergoes significant voltage decay in conventional Zn(OTf) electrolyte. Investigations show the decomposition of VOPO ⋅x H O into VO in the electrolyte and voltage drops after losing the inductive effect from polyanions.PO was thus added to shift the decomposition equilibrium. A high concentration of cheap, highly soluble ZnCl salt in the electrolyte further prevents VOPO ⋅x H O dissolution. The cathode shows stable capacity and voltage retentions in 13 m ZnCl /0.8 m H PO aqueous electrolyte, in direct contrast to that in Zn(OTf) where the decomposition product VO provides most electrochemical activity over cycling. Sequential H and Zn intercalations into the structure are revealed, delivering a high capacity (170 mAh g ). This work shows the potential issue with polyanion cathodes in zinc batteries and proposes an effective solution using fundamental chemical principles.