Gel polymer electrolytes: definitions, classification, rheology, and interfacial properties

Lithium-based batteries have revolutionized the electrochemical energy storage field, where liquid electrolytes are most used. Despite having high energy density and ionic conductivity, unwanted Li dendrite formation, leakage, and safety issues are ongoing challenges. In addition, the continuous lithiation/delithiation during charging/discharging processes affects both electrodes and electrolytes in terms of crack formation in the electrode, solid electrolyte interphase (SEI), cyclic compression/elongation of the electrolyte, and detachment of the interface especially in the solid electrolyte, which all can be addressed by using appropriate gel polymer electrolytes (GPEs). Therefore, this perspective starts with the definition of gels from a rheological perspective, categorizing GPEs, and finally discussing rheological considerations in electrolyte design and interfacial phenomena at electrode-electrolyte junctions.