Gradient fluoride, Zn-salt-rich hydrophobic interphase enabled by Zn-philic, H2O-phobic, anion-philic polymer 'skin' for anode-free solid Zn battery

Manipulating ion solvation sheath behaviour is of great significance for alleviating dendritic growth, hydrogen production, and metal corrosion, thus achieving long-term stability of zinc ion batteries. Herein, we rationally design a Zn2+·O=C group-derived contact ion pair (CIP)/aggregate (AGG)-rich electrolyte with Zn-philic and H2O-phobic features through in situ polymerization of 3-methacryloxypropyl trimethoxysilane monomers. Being attributed with this unique electrolyte design, this "skin" enables the generation of gradient fluoride, Zn-salt-rich hydrophobic solid electrolyte interface (SEI) layer through increasing the ratios of ZnF2/ZnO in SEI layer. Moreover, the amounts of ZnF2 in inner SEI are higher than those in outer SEI. Considering the higher dendrite-suppressing and desolvation ability of ZnF2 instead of ZnO, the SEI exhibits excellent capability in suppressing the growth of Zn dendrite and restraining 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 high depth of discharge of 34.2%, the symmetric cell maintains long-term stability for over 1000 h, and anode-free battery delivers superior performance with a high-capacity retention of 99.2% after 110 cycles.