Potential Solid-State Electrolytes with Good Balance between Ionic Conductivity and Electrochemical Stability:...

Exploring new solid-state electrolyte (SSE) materials with good electrochemical stability and high Li-ion conductivity for all-solid-state Li-ion batteries is vital for the development of technologies. Herein, we employ two lithium aluminates, α- and β-Li₅AlO₄ (α- and β-LAO), as the model framework, which have an orthorhombic crystal structure and isolated AlO₄ tetrahedron units connected in lithium atoms, exhibiting large band gaps, low migration barriers (0.30-0.40 eV), fast Li-ion conductivity (LIC, in a magnitude of 10^-4 S/cm), and a good electrochemical stability window (ESW, [0.01-3.20 V] vs Li⁺/Li). We tabulate the expected decomposition products at the interface, while considering cathodes in combination with the LAO electrolyte to discuss their compatibility. We also examine the electrochemical stability, H₂O/CO₂ stability, and Li-ion mobility of Li_4.6Al_0.6Si_0.4O₄ (LASO), Li₅GaO₄ (LGaO), and Li_4.6Ga_0.6Ge_0.4O₄ (LGaGeO) compounds. In general, there is usually a trade-off between the LIC and the ESW; however, LAO features a good balance between an outstanding LIC and a wide ESW, making the compound a promising candidate for next-generation SSE materials.