A solubility-limited, non-protonic polar small molecule co-solvent reveals additive selection in inorganic zinc salts

Abstract

Organic additives, like ester organic molecules, are greatly compatible with aqueous electrolyte with organic zinc salts, thus playing an enhanced role in electrochemical performance. However, due to poor compatibility, some organic molecules have never been attempted in low-cost inorganic zinc salt electrolytes for zinc ion batteries. Herein, for the first time, according to the limited intercalation of an non-protonic polar small molecule trimethyl phosphate (TMP) in ZnSO4 electrolytes, the regularity of additive selection based on inorganic zinc salts is revealed in depth. Generally, by adding a small percentage, TMP can interact with Zn2+ to modify the solvated structure, while getting preferentially adsorbed on the anode surface to reshape the water-rich electric double layer (EDL). Thereby, a stable electrode/molecule/solution hydrophobic interface is formed, effectively promoting desolvation and reduction process of Zn2+. The TMP additive achieve ultra-long lifespan in symmetrical cells with a 24-fold improvement increase for dendrite-free Zn plating/exfoliation (over 2000 h at 1 mA cm−2 and 1 mAh cm−2), enabling Zn//V2O5 full cell to achieve 3500 cycles with high capacity retention (71.4 %). This novel strategy reaffirms the importance of inorganic zinc salts in additive strategies, thus opening up new ways for designing stable and long-lived zinc anodes.