Double-Layer Solid Composite Electrolytes Enabling Improved Room-Temperature Cycling Performance for High-Voltage Lithium Metal Batteries

[Image: see text] The development of solid-state electrolytes (SSEs) for high energy density lithium metal batteries (LMBs) usually needs to take into account of the interfacial compatibility against lithium metal and the electrolyte stability suitable for a high-potential cathode. In this study, through a facile two-step coating process, novel double-layer solid composite electrolytes (SCEs) with Janus characteristics are customized for the high-voltage LMBs with improved room-temperature cycling performance. Among which, high-voltage resistant poly(vinylidene fluoride) (PVDF) is adopted here for the construction of an electrolyte layer facing the cathode, while the other layer against the lithium anode is composed of the polymer matrix of poly(ethylene oxide) (PEO) blended with PVDF to obtain a lithium metal-friendly interface. With the further incorporation of Laponite clay, the PVDF/(PEO+PVDF)-L SCEs not only exhibit improved mechanical properties, but also achieve a highly increased ionic conductivity (5.2 × 10(–4) S cm(–1)) and lithium ion migration number (0.471) at room temperature. The assembled NCM523|PVDF/(PEO+PVDF)-L SCEs|Li cells thus are able to deliver the initial discharge capacity of 153.9 mAh g(–1) with 80.8% capacity retention after 200 cycles at 0.3 C. Such easily manufactured double-layer SCEs capable of operating steadily at room temperature provide a competitive electrolyte option for high-voltage solid-state LMBs.