Investigation of a Biomass Hydrogel Electrolyte Naturally Stabilizing Cathodes for Zinc-Ion Batteries

Aqueous zinc-ion batteries (AZIBs) have the potential to be utilized in a grid-scale energy storage system owing to their high energy density and cost-effective properties. However, the dissolution of cathode materials and the irreversible extraction of preintercalated metal ions in the electrode materials restrict the stability of AZIBs. Herein, a cathode-stabilized ZIB strategy is reported based on a natural biomass polymer sodium alginate as the electrolyte coupling with a Na⁺ preintercalated δ-Na_0.65Mn₂O₄·1.31H₂O cathode. The dissociated Na⁺ in alginate after gelation directly stabilizes the cathodes by preventing the collapse of layered structures during charge processes. The as-fabricated ZIBs deliver a high capacity of 305 mA h g^-1 at 0.1 A g^-1, 10% higher than the ZIBs with an aqueous electrolyte. Further, the hybrid polymer electrolyte possessed an excellent Coulombic efficiency above 99% and a capacity retention of 96% within 1000 cycles at 2 A g^-1. A detailed investigation combining ex situ experiments uncovers the charge storage mechanism and the stability of assembled batteries, confirming the reversible diffusions of both Zn²⁺ and preintercalated Na⁺. A flexible device of ZIBs fabricated based on vacuum-assisted resin transfer molding possesses an outstanding performance of 160 mA h g^-1 at 1 A g^-1, which illustrates their potential for wearable electronics in mass production.