High-stability double-layer polymer–inorganic composite electrolyte fabricated through ultraviolet curing process for solid-state lithium metal batteries

Electrolyte interface resistance and low ionic conductivity are essential issues for commercializing solid-state lithium metal batteries (SSLMBs). This work details the fabrication of a double-layer solid composite electrolyte (DLSCE) for SSLMBs. The composite comprises poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF–HFP) and poly(methyl methacrylate) (PMMA) combined with 10 wt.% of Li_6.4La₃Zr_1.4Ta_0.6O₁₂ (LLZTO), synthesized through an ultraviolet curing process. The ionic conductivity of the DLSCE (2.6 × 10⁻⁴ S·cm⁻¹) at room temperature is the high lithium-ion transference number (0.57), and the tensile strength is 17.8 MPa. When this DLSCE was assembled, the resulted LFP/DLSCE/Li battery exhibited excellent rate performance, with the discharge specific capacities of 162.4, 146.9, 93.6, and 64.0 mA·h·g⁻¹ at 0.1, 0.2, 0.5, and 1 C, respectively. Furthermore, the DLSCE demonstrates remarkable stability with lithium metal batteries, facilitating the stable operation of a Li/Li symmetric battery for over 200 h at both 0.1 and 0.2 mA·cm⁻². Notably, the formation of lithium dendrites is also effectively inhibited during cycling. This work provides a novel design strategy and preparation method for solid composite electrolytes.