Tailored Cellulose Gel Electrolytes with Dual Pores, Aligned Channels, and Dendrite Mitigation for Improved K/Zn Dual-Ion Battery

Gel electrolytes, with their excellent flexibility and reduced risk of leakage, hold significant promise for use in aqueous K/Zn dual-ion batteries. However, their performance is often hampered by the gel’s internally discontinuous interpenetrating polymer network, which impedes fast and uniform ion transport, leading to suboptimal battery efficiency and dendrite formation. To address this issue, a cellulose gel electrolyte featuring a hierarchical porous structure was developed by using a salt-assisted ice templating method. During its fabrication, K2CO3 served as an effective pore-forming agent, while gelatin (GE) and polymerized allyl cellulose ether (PACE) acted as the polymer bases. The resultant polymer film (DFK) displayed a high porosity of 73.4% after undergoing directional freeze-drying. This structure not only facilitates uninterrupted ion transport, reducing the distance ions must travel, but also increases the specific surface area and introduces additional paths with low tortuosity, courtesy of the pore formation via K2CO3. This enhances the ion diffusion and electrochemical kinetics. Additionally, the polymer matrix’s rich polar functional groups (−OH, −COOH, −NH2) attract water molecules, further aiding ion transfer. As a result, DFK achieves an impressive electrolyte absorption rate of 1777% and a superior ion conductivity of 23.6 mS cm–1. Its dual-pore setup also efficiently redistributes Zn2+ ion flow and encourages even Zn2+ deposition. These features extended the life span of Zn//Zn symmetric cells to 1000 h at 1 mA cm–2 and enabled the zinc hexacyanoferrate (ZnHCF)//Zn battery to deliver a high reversible specific capacity of 0.068 mAh cm–2 (68.0 mAh g–1) at 1 mA cm–2, with a capacity retention of 85.3% after 1000 cycles. It further showcased an energy density of 134.5 Wh kg–1 and a power density of 5.2 kW kg–1. Moreover, when tested in a ZnHCF//Zn pouch cell under deformation, it exhibited considerable potential for flexible and wearable devices. The strategy of incorporating a hierarchical porous structure within gel electrolytes offers a promising avenue for the advancement and development of high-performance K/Zn dual-ion batteries.