Advances and challenges in inorganic lithium solid electrolytes

Lithium-ion battery (LIB) is the most widely used secondary battery and has been extensively studied in the past few decades due to its many advantages compared to other secondary batteries, such as higher energy density and better cycling performance. Considering the potential risks of environmental pollution and fire hazard induced by leakage or overheating of conventional electrolytes composed of flammable organic solvent-dissolving Li salts, non-flammable solid electrolytes (SEs), especially ceramic electrolytes with different structural types have been developed to improve the safety performance of LIBs. As the properties of SEs significantly depend on the microstructure, this review systemically summarized the recent progress in inorganic solid electrolytes based on the classification of microstructure and presented the relevant discussion in detail, including the microstructures, the mechanisms of Li ionic migration and performance optimization. Additionally, several challenges for realizing industrial application of SEs, such as lower ionic conductivities compared to liquid electrolytes and unsatisfactory stability in ambient atmosphere were mentioned. To effectively boost the development of SEs, more advanced transmission electron microscopy and atom probe tomography should be considered to deeply investigate the relationship between microstructure and properties in the future.