Inorganic Oxide-Based "Hydrophobic-Hydrophilic-Hydrophobic" Separators Systems for Long-Life Zinc-Ion Batteries

Hydrogen reduction reaction (HER) and corrosion limit the long-life cycle of zinc-ion batteries. However, hydrophilic separators are unable to prevent direct contact between water and electrodes, and hydrophobic separators have difficulty in transporting electrolytes. In this work, an inorganic oxide-based "hydrophobic-hydrophilic-hydrophobic" self-assembled separator system is proposed. The hydrophobic layer consists of a porous structure, which can isolate a large amount of free water to avoid HER and corrosion reactions, and can transport electrolyte by binding water. The middle hydrophilic layer acts as a storage layer consisting of the GF separator, storing large amounts of electrolyte for proper circulation. By using this structure separator, Zn||Zn symmetric cell achieve 2200 h stable cycle life at 5 mA cm^-2 and 1mAh cm^-2 and still shows a long life of 1800 h at 10 mA cm^-2 and 1mAh cm^-2. The assembled Zn||VO₂ full cell displays high specific capacity and excellent long-term durability of 60.4% capacity retention after 1000 cycles at 2C. The assembled Zn||VO₂ pouch full cell displays high specific capacity of 172.5mAh g^-1 after 40 cycles at 0.5C. Changing the inorganic oxide materials, the hydrophobic-hydrophilic-hydrophobic structure of the separators still has excellent performance. This work provides a new idea for the engineering of water-based battery separators.