Wettability-Gradient Interphase for Reconciling Water Shielding with Zincate Transport in Alkaline Zn-Ni Batteries

Artificial interfacial layers on Zn anodes are a promising route for stabilizing alkaline Zn-Ni batteries, but their practical effectiveness is often limited by a trade-off between suppressing water-induced parasitic reactions and maintaining rapid Zn-containing species transport. Herein, a hydrophobic-hydrophilic gradient composite layer is developed on a Zn substrate through sequential perfluorooctyltrichlorosilane (PFOTS) modification followed by crosslinked polyvinyl alcohol (PVA) coating. This gradient interphase couples a buried hydrophobic PFOTS layer with an outer hydrophilic PVA layer, thereby balancing water shielding, electrolyte affinity, mechanical compliance, and Zn-containing species transport at the Zn/electrolyte interface. As a result, the symmetric cell based on PFOTS/PVA-modified Zn (ZP) delivers stable cycling for 1200 h at 1 mA cm-2 and 1 mAh cm-2. When coupled with a Ni(OH)2-based cathode, the resulting alkaline Zn-Ni full cell exhibits an output voltage of ≈1.77 V, retains 93.2% of its capacity after resting for 48 h, sustains stable operation for more than 1100 h at 1 C, and maintains durable cycling over 1500 cycles at 2 C. This work demonstrates that wettability-gradient interfacial engineering can reconcile water regulation, Zn-containing species transport, and mechanical compliance for durable alkaline Zn anodes.