Biodegradable starch-based hydrogel as a multifunctional SEI for ultra-stable and flexible zinc-ion batteries†

Constructing an artificial solid electrolyte interface (SEI) layer is an effective strategy to suppress dendrite growth and corrosion in aqueous zinc batteries (AZBs). However, 2D material-based SEI coatings are generally non-biodegradable, posing environmental risks due to their persistence in soil. This research introduces a starch/polyacrylamide (STA/PAAm) hydrogel membrane developed as a self-healing SEI layer for AZBs. The incorporation of biomass-derived starch endows the STA/PAAm hydrogel with excellent soil biodegradability, achieving complete degradation within 21 days. Meanwhile, its dual-network structure, reinforced by reversible Al³⁺ crosslinking, offers robust mechanical resilience, self-healing ability, and high ionic conductivity—presenting a sustainable alternative to conventional SEI materials. Theoretical calculations reveal that the hydrogel modulates Zn²⁺ solvation, forming a stable [Zn(H₂O)₄(STA)(AAm)]²⁺ configuration, which suppresses hydrogen evolution and promotes uniform Zn²⁺ deposition along the (002) plane. The STA/PAAm-coated Zn anode exhibits an extended lifespan of over 3000 h at 2 mA cm⁻², significantly surpassing that of bare Zn (531 h). Paired with an AlVO-NMP cathode, the pouch-type full cell retains 87.2% capacity after 2000 cycles at 5 A g⁻¹ and demonstrates remarkable flexibility, powering LEDs under bending and folding conditions. This work bridges high-performance energy storage with environmental sustainability, offering a green paradigm for flexible batteries.