Bifunctional poly(1,3-dioxolane)-graphitic C₃N₄ composite interlayers enable stable and compatible anode interfaces in solid lithium batteries

Polyacrylonitrile (PAN)-based composite solid electrolytes (CSEs) hold great promise in the practical deployment of solid lithium batteries (SLBs) owing to their high voltage stability but suffer from poor stability against Li-metal. Herein, a poly(1,3-dioxolane) (PDOL)-graphitic C₃N₄ (g-C₃N₄, i.e. CN) composite interlayer with high ionic conductivity and electrochemical stability was in-situ introduced into the anode interface. The flexible PDOL enables an intimate interfacial contact and the added g-C₃N₄ microspheres decrease the crystallinity of PDOL via breaking its segment arrangement. Moreover, the three-dimensional (3D) CN provides porous skeletons to load monomers and initiators and promotes the contact between them, thus accelerating the conversion of DOL. Consequently, the PDOL-CN layer with an ionic conductivity of 2.96 × 10^-4 S cm^-1 and an ionic transference number of 0.69 at 30 °C tends to suppress the side reaction between PAN and Li-metal and enables stable cycling of Li symmetric cells for 400 h at 0.3 mA cm^-2. Moreover, the existing CN in the interlayer favors the formation of a Li₃N-enriched solid electrolyte interface (SEI) with fast Li⁺ transfer kinetics and guarantees uniform Li deposition. Therefore, the PDOL-CN layers simultaneously improve the compatibility and chemical stability at the anode interface and contribute to a stable cycling of LiNi_0.6Co_0.2Mn_0.2O₂ (NCM622)||Li full cells with a capacity retention of 88.2 % after 270 cycles at 0.2 C and 30 °C.