Bio-derived physicochemical solid-state buffer separators for stabilizing zinc metal anodes in aqueous batteries

Aqueous zinc-metal batteries (AZMBs) offer inherent safety and cost advantages. However, the zinc (Zn) anode remains plagued by the hydrogen evolution reaction (HER), interfacial pH changes, and non-uniform deposition. Herein, we propose a biomass-derived hierarchical "Physicochemical solid-state buffer" separator strategy that leverages the intrinsic synergistic effect among cellulose, hemicellulose, and lignin in natural wood to simultaneously modulate the dynamic interfacial pH and Zn²⁺ flux, thereby addressing the challenges. Specifically, oriented cellulose microchannels physically facilitate ordered Zn²⁺ transport and desolvation, while hemicellulose enriched with carboxyl groups (-COOH) provides a sustained solid-state buffering capacity through a reversible proton exchange mechanism. Concurrently, the lignin component restricts free water activity, and the -COOH groups in hemicellulose promote the in situ formation of a dense, stable composite solid electrolyte interphase (SEI), thereby creating a multifunctional interfacial platform characterized by ion homogenization, pH stabilization, and interfacial self-passivation. Experimental results demonstrate that Zn||Zn symmetric batteries employing the poplar wood (PopW) separator achieve stable cycling for over 1720 h at 1 mA cm^-2, 1 mAh cm^-2. Furthermore, Zn||Cu batteries exhibit an average coulombic efficiency (CE) of 99.8% over 4000 cycles, which is higher than that of commercial glass fiber (GF) separators. This work establishes a sustainable paradigm for high-performance energy storage via biomolecular regulation.