Non-flammable, dilute, and hydrous organic electrolytes for reversible Zn batteries.

Rechargeable Zn batteries hold great practicability for cost-effective sustainable energy storage but suffer from irreversibility of the Zn anode in aqueous electrolytes due to parasitic H 2 evolution, corrosion, and dendrite growth. Herein, we report a non-flammable, dilute, and hydrous organic electrolyte by dissolving low-cost hydrated Zn(ClO 4 ) 2 ·6H 2 O in trimethyl phosphate (TMP), which homogenizes plating/stripping and enables in situ formation of a Zn 3 (PO 4 ) 2 -ZnCl 2 -rich interphase to stabilize the Zn anode. A dilute 0.5 m Zn(ClO 4 ) 2 ·6H 2 O/TMP electrolyte featuring a H 2 O-poor Zn 2+ -solvation sheath and low water activity enables significantly enhanced Zn reversibility and a wider electrochemical window than the concentrated counterpart. In this formulated electrolyte, the Zn anode exhibits a high efficiency of 99.5% over 500 cycles, long-term cycling for 1200 h (5 mA h cm -2 at 5 mA cm -2 ) and stable operation at 50 °C. The results would guide the design of hydrous organic electrolytes for practical rechargeable batteries employing metallic electrode materials.