A fluoride gradient, Zn-salt-rich hydrophobic interphase formed by a zincophilic, hydrophobic, anion-philic polymer “skin” for an anode-free solid Zn battery†

Manipulating ion solvation sheath behaviour is of great significance for alleviating dendritic growth, hydrogen production, and metal corrosion in order to achieve the long-term stability of zinc ion batteries. Herein, we rationally design a Zn²⁺·OC group-derived contact ion pair (CIP)/aggregate (AGG)-rich electrolyte with zincophilic and hydrophobic features through in situ polymerization of 3-methacryloxypropyl trimethoxysilane monomers. Due to its unique design, this electrolyte “skin” enables the generation of a fluoride gradient, Zn-salt-rich hydrophobic solid electrolyte interface (SEI) layer through increasing the ratio of ZnF₂/ZnO in the SEI layer. Moreover, the amount of ZnF₂ in the inner SEI is higher than that in the outer SEI. Due to the higher dendrite-suppressing and desolvation ability of ZnF₂ than that of ZnO, the SEI exhibits excellent capability to suppress the growth of Zn dendrites and restrain H₂O-related side reactions. Owing to its unprecedented average modulus (71.25 GPa), the SEI effectively inhibits the external stress originating from dendritic growth, the undesirable volume expansion of Zn and the long-lasting anode/electrolyte side reactions. Consequently, at a high depth of discharge of 34.2%, the symmetric cell shows long-term stability for over 1000 h, and the anode-free battery shows a high capacity retention of 99.2% after 110 cycles.