Enhancing Zn Anode Reversibility via Solvation Structure Reconstruction by a Trimethyl Phosphate Additive

Aqueous zinc-metal batteries are regarded as the most promising energy conversion and storage devices in the near future because of high volume energy density, low cost, and extreme safety. However, the practical industrialization of zinc-metal batteries is still facing the challenges of poor Zn anode reversibility, such as Zn dendrite propagation, interface corrosion, and hydrogen evolution reaction. Here, we report an optimized Zn²⁺ solvation structure composite electrolyte modified by trimethyl phosphate (TMP) additive, which can suppress the rough growth of Zn dendrites, the formation of H₂, the corrosion of zinc, and the formation of passivation layer. Because TMP has a higher Gutmann donor number than H₂O, the higher electron cloud density of O atoms in TMP enhances the strength of hydrogen bonds with H₂O. Resultantly, the coordination environment of Zn²⁺ with H₂O is broken instead of reconstructed Zn²⁺ solvation structure with moderate TMP additive. The electrochemical reversibility of the Zn anode is enhanced in the optimized electrolyte with TMP. Consequently, the cycling stability of Zn plating/stripping is promoted by 15% TMP modified electrolyte with high CE of 99.22% at 1 mA cm^-2, stably cycled for 850 cycles compared with short-term lifespan less than 200 cycles in the blank electrolyte. The Zn||Zn symmetrical cells can sustain dendrite-free for more than 3000 h with overpotentials of 0.1 V. In addition, the Zn||V₂O₅ full cell can contribute an unexceptionable long-term cycling stability for over 1000 cycles even at 1 A g^-1 with the reversible capacity retention of 66 mA h g^-1. This work proposes a facile strategy to regulate the metal-ion solvation structure in aqueous metal batteries.