Loosening the Solvation Cage in Polysaccharide Polymer Electrolyte for Sustainable Lithium Metal Batteries

Biomass with naturally ion-conducting segments (e.g., hydroxyl) holds promise for sustainable batteries. Several expeditions are proposed to successfully enhance the ion conduction in biomass polymer mainly by intermolecular structure regulation. Presently, the recognition and research of biomass polymer electrolytes are still limited, requiring continuous explorations to promote the application of such promising electrolytes. Herein, a molecularly asymmetric electrolyte is produced, comprising polysaccharides of starch and chitosan. The strong Li⁺-O (hydroxyl) interactions are replaced by weak Li⁺-oxygen (O) of ester carbonyl, and the steric hindrance group -NH₃ ⁺ promotes the immobilization of anion and stabilization of the interface. Such intermolecular chemical modulations of biomass are achieved by a one-pot esterification and protonation of polysaccharides. A loosely-solvating cage structure with the participation of O of ester carbonyl, glycerol, and anion, allowing the rapid conduction (1.82 × 10^-4 S cm^-1 at 30 °C) and a high migration number (0.49) of Li⁺. Moreover, Li symmetric cells (2500 h) and Li₄TiO₅ | Li cells (400 cycles) employing the SCA electrolyte show superior cycling stability. The polysaccharide BPEs and solvation regulation strategy open up a promising avenue for constructing sustainable batteries.