Slurry stability and interfacial degradation in borate-water-based quasi-solid electrolytes for lithium-ion batteries

Aqueous quasi-solid electrolytes have attracted increasing attention as safe and environmentally benign alternatives for lithium-ion batteries. Here, we systematically investigate the slurry properties, interfacial structure, and electrochemical behavior of a borate–water-based three-dimensional slime-interface quasi-solid electrolyte (3D-SLISE), composed of an amorphous Li 2 B 4 O 7 matrix, lithium salts, carboxymethyl cellulose, and water. Owing to its slime-like aqueous network, 3D-SLISE exhibits three-dimensional ionic conduction and adaptive interfacial adhesion, enabling fully atmospheric fabrication and eliminating the need for dry-room processing. Systematic analyses reveal that slurry stability is governed by crystallization-induced aggregation and polymer adsorption, while electrochemical degradation is dominated by reductive decomposition accompanied by hydrogen evolution at the anode interface. The effects of electrolyte composition and surface modification of anode materials on suppressing parasitic reactions are quantitatively evaluated. Furthermore, the water-soluble borate matrix enables redispersion of electrode composites, offering a practical route for direct recovery of active materials. These results clarify the key physicochemical factors governing processability and electrochemical stability in aqueous quasi-solid electrolytes and provide practical guidelines for developing scalable and reliable quasi-solid-state lithium-ion batteries. • Slurry stability and interfacial structure of borate–water electrolytes are clarified. • 3D-SLISE enables ambient fabrication without electrolyte injection. • Hydrogen evolution governs degradation in aqueous quasi-solid electrolytes. • Anode interface engineering improves long-term cycling stability. • Water-soluble matrices enable direct cathode recycling.