Owing to the inherent properties combining high ionic conductivity and electrochemical stability, the lithium triborates (LBOs) have emerged as a promising solid-state electrolyte for next-generation batteries. Specific fundamental details of the ionic conduction mechanism and related physicochemical properties remain to be understood. In this study, using the first-principles density functional theory calculations, we present a systematic computational investigation on LBOs in the respect of electronic structures, mechanical and thermodynamic properties, Li-ion transport, and interfacial (with Li metal) behaviors. Our results show that LBO is a thermodynamically and mechanically stable insulator with an indirect wide bandgap of 6.4 eV. Notably, LBOs could behave as a fast Li-ion conductor with a low migration energy barrier (15 meV) and are characterized by a zig–zag Li+-diffusion path along the c direction. We found that the interface between Li metal and LBO is both physically and chemically stable with no new phase formed while exhibiting a metallic character due to the charge transfer from a Li metal. Our study highlights the intriguing promise of LBOs as solid-state electrolytes for high-energy cells.