HE Kaiyuan, CHEN Qiqiang, HUANG Jingyao, CHENG Yuanyuan
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With the accelerated transformation of the global energy structure, the development of energy storage technologies that are highly safe, low-cost and sustainable has become an urgent need. Sodium-ion batteries are regarded as important candidates for the next-generation energy storage system due to their advantages such as abundant sodium resources, low cost and wide temperature range adaptability. However, they still face bottlenecks such as low volumetric energy density, insufficient cycle life and sodium dendrite growth. Thin-film solid electrolytes, by replacing liquid electrolytes, can significantly enhance battery safety, inhibit dendrite growth and increase energy density, thus becoming a key path to solve the above problems. This paper systematically reviews the latest research progress of thin-film solid electrolytes in sodium-ion solid-state batteries. Starting from the ion transport mechanism, it comparatively analyzes the differences between solid electrolytes and traditional liquid systems. The characteristics of sodium ions, interface compatibility and key challenges in material design are deeply discussed. The performance optimization strategies of oxides, sulfides, halides and organic-inorganic composite electrolytes are classified and reviewed. The research results show that NASICON-type oxide electrolytes can significantly increase the ionic conductivity, up to 5.27 mS/cm, through element doping. Sulfide electrolytes, such as Na3PS4, exhibit high room-temperature ionic conductivity of 32 mS/cm, and organic-inorganic composites have the advantages of both flexibility and low cost. However, the practical application of thin-film solid electrolytes is still limited by challenges such as low ion migration rate, high interface impedance and complex preparation process. In the future, it is necessary to promote the commercial application of thin-film solid electrolytes in sodium-ion batteries through element doping, interface engineering, the development of new materials, such as metal-glass type and carbon-based materials, and the optimization of large-scale preparation processes, providing important support for achieving efficient, safe and sustainable energy storage technologies.