Hybrid and Solid-state Material Integration for Next-generation Battery Technologies: A Comprehensive Review

The growing demand for safer and more sustainable rechargeable batteries has made the drawbacks of conventional liquid electrolytes increasingly clear, particularly their tendency to leak, their flammability and their unstable electrode electrolyte interfaces. Hybrid and composite gel polymer electrolytes (GPEs) have emerged as promising alternatives because they combine the flexibility of polymers with the ionic conductivity and stability provided by liquid and solid components. Nonetheless, the majority of research continues to focus on individual hybrid GPE systems independently and highlights performance improvements without providing comprehensive comparisons, resulting in a limited comprehension of how particular material selections and interfacial engineering methods influence ion movement, interfacial stability, and overall cell performance. This review addresses that gap by systematically compiling and critically analyzing recent work on hybrid and composite GPEs for lithium-ion and sodium-ion batteries. It discusses different polymer matrices, fillers, ionic liquids, plasticizers and crosslinking approaches in terms of their effects on ionic conductivity, electrochemical stability, mechanical properties and electrode compatibility. Based on the reported results, key structure property performance relationships are highlighted and translated into practical design guidelines for next-generation hybrid GPEs. Remaining challenges such as limited room-temperature conductivity, interfacial resistance, dendrite growth and scalable processing are outlined, and future research directions are suggested for the development of robust, high-safety gel polymer electrolyte systems for advanced energy storage.