Biomass Solid-State Electrolyte with Abundant Ion and Water Channels for Flexible Zinc–Air Batteries

Flexible zinc–air batteries are the leading candidates as the next-generation power source for flexible/wearable electronics. However, constructing safe and high-performance solid-state electrolytes (SSEs) with intrinsic hydroxide ion (OH⁻) conduction remains a fundamental challenge. Herein, by adopting the natural and robust cellulose nanofibers (CNFs) as building blocks, the biomass SSEs with penetrating ion and water channels are constructed by knitting the OH⁻-conductive CNFs and water-retentive CNFs together via an energy-efficient tape casting. Benefiting from the abundant ion and water channels with interconnected hydrated OH⁻ wires for fast OH⁻ conduction under a nanoconfined environment, the biomass SSEs reveal the high water-uptake, impressive OH⁻ conductivity of 175 mS cm⁻¹ and mechanical robustness simultaneously, which overcomes the commonly existed dilemma between ion conductivity and mechanical property. Remarkably, the flexible zinc–air batteries assemble with biomass SSEs deliver an exceptional cycle lifespan of 310 h and power density of 126 mW cm⁻². The design methodology for water and ion channels opens a new avenue to design high-performance SSEs for batteries.