All-solid-state lithium metal batteries (ASSLMBs) that incorporate solid electrolyte (SE) and lithium metal anode suggest considerable potential in addressing the security concerns and energy density limitation of conventional lithium-ion batteries (LIBs). However, the practical application of ASSLMBs is always restricted by the interfacial instability of lithium metal anode/electrolyte and inevitable lithium dendrites propagation in SE. Herein, a solvate ionic liquid is adopted to modify the interface stability of lithium metal anode/electrolyte and inhibit the growth of lithium dendrites via an in-situ formation of a robust solid electrolyte interphase (SEI) on the surface of lithium metal anode. Consequently, the ASSLMBs assembled with Li₆PS₅Cl (LPSCl) electrolyte, lithium metal anode that protected by robust SEI layer, and LiNbO₃@NCM622 cathode exhibit high initial capacity of 126.5 mAh·g⁻¹ and improved cycling stability with a capacity retention of 80.3% over 60 cycles at 0.1 C. This work helps to provide a facile route for the design of robust SEI in the application of ASSLMBs.

Lithium metal batteries based on solid electrolytes are considered as promising candidates with high energy density and safety. However, the weak solid-solid contact between electrolyte and electrode can easily lead to interface instability and lithium ions discontinuous migration, which seriously reduces the electrochemical performance of the battery. Herein, we construct a soft gel interfacial layer to improve the stability of the solid-solid interface between electrolyte and electrode by means of polyester-based monomers and imidazole-based ionic liquids. Based on this, garnet-type Li_6.4La₃Zr_1.4Ta_0.6O₁₂ (LLZTO) particles as inorganic ceramic filler were introduced in the layer to obtain composite electrolytes with high ionic conductivity (up to 1.1 × 10⁻³ S/cm at 25 ℃). As a result, the assembled lithium symmetric battery of Li|THCE-15%LLZTO|Li suggests excellent cycling stability with 700 h at 0.1 mA/cm² at 50 ℃, and the lithium metal batteries of LFP|THCE-15%LLZTO|Li delivers high initial discharge capacity of 128.2 mA ·h/g with capacity retain of 75.48% after 150 cycles at 2 C. This work paves a new route to build safe and stable lithium metal batteries with synergistic introduction of composite electrolytes between electrolyte and electrode using soft gel interfacial layer and inorganic filler.