Stabilizing the LAGP/Li interface and in situ visualizing the interfacial structure evolution for high-performance solid-state lithium metal batteries

Abstract

Direct tracking of the structure and composition evolution at the solid-state electrolyte/electrode interface and properly addressing the interfacial issues are crucial for the performance improvement of solid-state lithium metal batteries (SSLMBs). In this study, we investigate the structure evolution of the interface between Li_1.5Al_0.5Ge_1.5(PO₄)₃ (LAGP) and the lithium anode using in situ transmission electron microscopy (TEM). It is found that the reaction between lithium and pristine LAGP results in a continuous volume expansion and contact loss, even without applying voltage. To stabilize the interface, we construct a multi-layer solid electrolyte where the LAGP is coated with the polymer electrolyte (P-DOL), enabling the interface layer to maintain its pristine morphology throughout the lithiation process. In addition, P-DOL promotes the formation of rich LiF at the interface, inhibiting the electron transport and volume expansion of LAGP, as further confirmed by the cryo-TEM and simulation analysis. The effectiveness and cyclability of the unique multi-layer electrolyte are demonstrated in various cells, even under harsh testing conditions, such as a high rate (10 C), a high active material loading (11.7 mg cm⁻²), a wide voltage range (2.8–4.45 V), and temperatures ranged from −20 to 50 °C. By applying the same interfacial modification method, LLZTO-based (Li_6.4La₃Zr_1.4Ta_0.6O₁₂) electrolytes with both high ionic conductivity and interfacial stability are also prepared. This work provides valuable guidance for investigations of contact reactions and failure mechanisms at solid–solid interfaces, ultimately facilitating the design of high-performance SSLMBs.