Zn metal anodes stabilized by an intrinsically safe, dilute, and hydrous organic electrolyte

Rechargeable Zn batteries hold great promise for large-scale energy storage applications but their reversibility is limited by non-compact and dendritic Zn deposition along with interfacial parasitic reactions in conventional electrolytes. Herein, we report an intrinsically safe, dilute, and hydrous organic electrolyte by coupling hydrated Zn(BF4)2 salt with trimethyl phosphate (TMP) solvent for highly reversible Zn batteries, without the need of concentrated electrolyte strategies. The formulated 1 m Zn(BF4)2/TMP enables spatially compact, dendrite-free, and corrosion-free Zn electrodeposition even at high areal capacity (5 and 10 mAh cm−2) using a pressure-free electrolytic cell. Moreover, the hydrous organic electrolyte with low water activity expands the electrochemical window to 3 V (versus Zn2+/Zn) and in-situ forms a protective ZnF2-Zn3(PO4)2-rich interphase on Zn. The resultant Zn electrode achieves long-term cycling over 4200 h with a superhigh cumulative plating capacity of 10500 mAh cm−2 under 5 mA cm−2 in Zn//Zn cell and exhibits high efficiency of 99.5% over 600 cycles in Zn//Cu cell (1 mA cm−2; 1 mAh cm−2). Moreover, this electrolyte supports the stable operation of a full Zn//V2O5·nH2O battery by significantly suppressing cathode dissolution. This work would enlighten the design of hydrous organic electrolytes for practical Zn batteries.