Enhancing cathode-electrolyte interface stability in high-voltage lithium metal batteries through phase-separated cyano-containing copolymer-based elastomeric electrolytes

[Display omitted] •Newly designed solid polymer electrolytes (SPEs) with cyano groups for superior cycling performance of full cells at 4.7 V.•Bi-continuous structured SPEs for both the high ionic conductivity, mechanical properties and high-voltage operation.•Elucidating the role of cyano-containing SPEs in stabilizing the cathode/electrode interface. Solid-state polymer electrolytes (SPEs) are a promising alternative to conventional liquid electrolytes in lithium metal batteries (LMBs). However, their low ionic conductivity and poor oxidation stability hinder the operation of LMBs, particularly when paired with high-voltage, Ni-rich cathodes. To address this challenge, our aim is to integrate the cyano group, known for its ability to enhance oxidation stability through its electron-withdrawing property, into the phase-separated SPEs that exhibit superior ionic conductivity and mechanical properties. Specifically, we synthesize cyano-containing SPEs by incorporating cyanoethyl acrylate (CEA) into an elastomeric electrolyte featuring a bicontinuous structure composed of cyano-containing copolymers and plastic crystals. The phase-separated structure of various SPEs is controlled by adjusting the molar ratio of butyl acrylate (BA) and CEA. At the optimal molar ratio of BA to CEA (specifically, 9:1), this tailored electrolyte shows high ionic conductivity (9.8 × 10−4 S cm−1 at 30 °C) and cycling performance at high cut-off voltage of 4.7 V vs. Li/Li+. The cyano-containing bicontinuous SPEs are expected to play a pivotal role in enhancing oxidation stability and developing robust interfaces consisting of transition metal-anchored framework and inorganic-rich components. These interfaces effectively suppress degradation of cathode structure, thereby achieving high-energy solid-state LMBs.