In-situ constructed SnO2 gradient buffer layer as a tight and robust interphase toward Li metal anodes in LATP solid state batteries

Li1.3Al0.3Ti1.7(PO4)3 (LATP), of much interest owing to its high ionic conductivity, superior air stability, and low cost, has been regarded as one of the most promising solid-state electrolytes for next-generation solid-state lithium batteries (SSLBs). Unfortunately, the commercialization of SSLBs is still impeded by severe interfacial issues, such as high interfacial impedance and poor chemical stability. Herein, we proposed a simple and convenient in-situ approach to constructing a tight and robust interface between the Li anode and LATP electrolyte via a SnO2 gradient buffer layer. It is firmly attached to the surface of LATP pellets due to the volume expansion of SnO2 when in-situ reacting with Li metal, and thus effectively alleviates the physical contact loosening during cycling, as confirmed by the mitigated impedance rising. Meanwhile, the as-formed SnO2/Sn/LixSn gradient buffer layer with low electronic conductivity successfully protects the LATP electrolyte surface from erosion by the Li metal anode. Additionally, the LixSn alloy formed at the Li surface can effectively regulate uniform lithium deposition and suppress Li dendrite growth. Therefore, this work paves a new way to simultaneously address the chemical instability and poor physical contact of LATP with Li metal in developing low-cost and highly stable SSLBs.