Polymer-based composite solid-state electrolyte in li-ion batteries: Advancement, challenges & electrochemical characterization

Solid-state batteries are widely regarded as a promising next-generation energy storage technology capable of addressing the safety concerns and energy-density limitations of conventional liquid electrolyte lithium-ion batteries. This review provides a comprehensive overview of solid-state lithium batteries, beginning with their fundamental operating mechanism and progressing through electrolyte materials, fabrication approaches, and electrochemical evaluation methods. Emphasis is placed on solid-state electrolytes including inorganic, polymer, and composite systems with detailed discussion of their ionic conductivity, electrochemical stability window, mechanical properties, and interfacial compatibility with lithium metal. Strategies for enhancing ionic conductivity, expanding voltage stability, suppressing dendrite formation, and reducing interfacial resistance are critically analyzed with quantitative comparisons from recent studies. The review also outlines half-cell and full-cell testing methodologies to evaluate intrinsic electrolyte behavior and overall battery performance. Major electrochemical characterization techniques, including electrochemical impedance spectroscopy, DC polarization, cyclic voltammetry, and galvanostatic charge–discharge analysis, are explained to clarify how key performance parameters are determined. A comparative assessment of different battery systems and a global benchmark of solid-state electrolyte performance are provided to help researchers contextualize their experimental results. Finally, current challenges and future research directions are discussed to support continued progress in solid-state energy storage technologies.