Hybrid bio-synthetic polymer gel electrolytes: Synergistic design and advanced applications for zinc-ion batteries

Abstract

Zinc-ion batteries (ZIBs) hold great promise for large-scale energy storage and wearable electronics owing to their high safety, raw material abundance, and environmental friendliness. However, conventional liquid electrolytes suffer from water decomposition, evaporation, and leakage, while zinc dendrites, anode corrosion, and hydrogen/oxygen evolution reactions further compromise battery stability. Polymer gel electrolytes mitigate these issues by forming hydrogen bonds with free water, yet gels based on a single biopolymer gel (BPG) or a single synthetic polymer gel (SPG) electrolytes show clear performance trade-offs, where BPGs offer biocompatibility and good interfacial regulation but lack mechanical strength and high ionic conductivity, whereas SPGs provide strong mechanical properties but poor biocompatibility and weak electrode modulation. This review examines emerging hybrid bio-synthetic gel (HB-SG) electrolytes that combine the strengths of both polymer systems, covering their design principles, four main structural types, key synergistic mechanisms, and fabrication methods. Their performance in ion transport, mechanical resilience, self-healing, temperature tolerance, and resistance to parasitic reactions is discussed alongside practical applications across flexible, extreme-environment, and harsh-condition ZIBs. Current challenges, unclear synergistic mechanisms, limited room-temperature ionic conductivity, storage instability, and industrial scalability barriers are identified, along with future directions including multiscale structural design, theoretical simulation, green manufacturing, intelligent functionalization, and biomedical applications.