Investigation of Ion Transport and Stability in Solid-State Electrolytes for High-Performance All-Solid-State Batteries

All-solid-state batteries (ASSBs) offer opportunities to achieve high energy density, long life, and excellent safety, making them promising for electric vehicles. However, ASSBs still face several key challenges: (1) sluggish lithium-ion transport in solid-state electrolytes (SSEs) and interfaces between SSEs and electrodes; (2) electrochemical stability between SSEs and electrodes; (3) limited cycling stability. To address these challenges, the approach focuses on three key approaches: (1) developing new electrolytes to enhance ionic conductivity and stability; (2) creating artificial electrodeelectrolyte interfaces to enhance cathode kinetic behavior; (3) advanced characterization and theoretical calculations to help understand the ion transport and mechanisms of stability. In this thesis, SSEs based on thiosilicate and borohydride were developed, and utilized composite cathode, to enhance ion transport and electrochemical stability. First, amorphous 5Li2S-3SiS2 SSE was synthesized, which has a unique dimer structure that lowers lithium diffusion energy barriers and boosts conductivity to 1.2 mS/cm. Next, this SSE was enhanced by adding closo-type complex hydride Li2B9H9-Li2B12H12, improving conductivity to 2 mS/cm and reducing lithium dendrite growth. Hydroborate electrolytes, LiBH4-LiI-LixMOy (M=P, C) were also explored. Due to the B-O electrostatic effect, these SSEs exhibit high ionic conductivity. Additionally, these materials demonstrate good chemical stability with chalcogen (Se, S, Li₂S) cathodes and Li metal anodes. Finally, a universal surface chemistry was discovered for designing the dynamic surface of high-loading Li₂S cathode. Advanced characterization techniques, including synchrotron, NMR, and theoretical calculations, have been employed to study the local structure of the amorphous SSEs, as well as interface transportation and chemical stability.