Recent advances in inorganic solid electrolytes for lithium-ion batteries

Solid electrolytes are key components in the development of next-generation all-solid-state lithium batteries owing to their potential to enhance energy density, operational safety, and electrochemical stability. Among the various performance metrics, ionic conductivity and activation energy are critical parameters that govern lithium-ion transport and overall battery performance. This review provides a comprehensive analysis of the structure–property relationships, ionic conduction mechanisms, and recent developments in four major classes of inorganic solid electrolytes: NASICON, garnet, perovskite, and sulfide systems. NASICON-type electrolytes, including LiTi2(PO4)3 and LiGe2(PO4)3, exhibit moderate ionic conductivity, which can be substantially improved through aliovalent substitution, particularly Al3+ doping in Li1+XAlXTi2−X(PO4)3, resulting in enhanced charge-carrier concentration and optimized Li+ migration pathways. Garnet-type electrolytes, especially Li7La3Zr2O12 (LLZO), demonstrate excellent electrochemical stability and high ionic conductivity when stabilized in the cubic phase, with dopants such as Al, Ga, Nb, and W promoting phase stabilization and lowering activation barriers for Li+ diffusion. Perovskite-based electrolytes achieve moderate-to-high ionic conductivities through compositional tuning and defect engineering; however, their electrochemical performance remains strongly influenced by crystal structure and dopant chemistry. Sulfide electrolytes exhibit the highest ionic conductivities among the investigated systems, with Li7P3S11 attaining conductivities approaching 10−2 S cm−1 and low activation energies (~ 0.12 to 0.18 eV), facilitating rapid lithium-ion transport. Furthermore, the advantages, limitations, and interfacial challenges associated with each electrolyte family are critically evaluated. Overall, this review highlights compositional engineering, defect regulation, and phase stabilization as effective strategies for enhancing ionic transport, providing insights into the design and development of high-performance solid electrolytes for advanced all-solid-state lithium battery technologies.