“Water-in-Swelling-Clay” Electrolytes Stabilizing Prussian Blue Analogue Cathodes for Long-Cycle-Life, High-Voltage Aqueous Zinc-Ion Batteries

Prussian blue analogues (PBAs) have been used as cathode materials for aqueous zinc-ion batteries (AZIBs) because of their high working voltage, open channels, and straightforward synthesis. However, the practical deployment of PBAs is severely constrained by the oxygen evolution reaction and water-induced framework degradation. Here, we present a quasi-solid-state "water-in-swelling-clay" electrolyte based on bentonite (BT) clay to confine water within its layered structure, suppressing water activity and broadening the practical electrochemical stability window. When coupled with PBA cathodes, the BT electrolyte suppresses oxygen evolution and mitigates cathode structural distortion, enabling long-cycle life and high-voltage operation. Electrochemical characterizations confirm the effectiveness of the BT electrolyte, enabling high-performance AZIB cycling for over 800 cycles at 0.2 A g-1 with a high operating voltage exceeding 1.9 V. This simple, low-cost, and scalable electrolyte design directly addresses the water-driven failure modes of PBAs and offers a practical route toward durable, high-energy AZIBs.