Atomic Layer Deposited Lithium Silicates as Solid-State Electrolytes for All-Solid-State Batteries

Development of solid-state electrolyte (SSE) thin films is a key toward the fabrication of all-solid-state batteries (ASSBs). However, it is challenging for conventional deposition techniques to deposit uniform and conformal SSE thin films in a well-controlled fashion. In this study, atomic layer deposition (ALD) was used to fabricate lithium silicate thin films as a potential SSE for ASSBs. Lithium silicates thin films were deposited by combining ALD Li₂O and SiO₂ subcycles using lithium tert-butoxide, tetraethylorthosilane, and H₂O as precursors. Uniform and self-limiting growth was achieved at temperatures between 225 and 300 °C. X-ray absorption spectroscopy analysis disclosed that the as-deposited lithium silicates were composed of SiO₄ tetrahedron structure and lithium oxide as the network modifier. X-ray photoelectron spectroscopy confirmed the chemical states of Li in the thin films were the same with that in standard lithium silicate. With one to one subcycle of Li₂O and SiO₂ the thin films had a composition close to Li₄SiO₄ whereas one more subcycle of Li₂O delivered a higher lithium content. The lithium silicate thin film prepared at 250 °C exhibited an ionic conductivity of 1.45× 10^–6 S cm^–1 at 373 K. The high ionic conductivity of lithium silicate was due to the higher lithium concentration and lower activation energy.