Polycarbonate Copolymer Solid Electrolyte for Stable Cycling of a Li∥LiCoO2 Cell via In Situ Ultraviolet Irradiation

To solve the problems of narrow oxidation decomposition potential and low room temperature ionic conductivity of the traditional poly(ethylene oxide) (PEO)-based solid polymer electrolyte (SPE), a polycarbonate-based SPE is developed by facile in situ ultraviolet-irradiated polymerization for high-energy-density lithium metal batteries (LMBs). Since the weak complexation between carbonate groups and Li+-ions in the vinyl ethylene carbonate (VEC) section provides the ionic transport capability, while the rigid hydroxyethyl methacrylate (HEMA) segment facilitates the mechanical strengths, the prepared P(VEC-HEMA) copolymer-based SPE exhibits a high ionic conductivity of 0.8 × 10–3 S cm–1 at room temperature, an antioxidation potential exceeding 5.0 V, and a high Young's modulus value of 2.3 GPa that can effectively prevent the puncture of lithium dendrites. Notably, the P(VEC-HEMA) copolymer presents a stronger binding energy with TFSI– than that of the PVEC oligomer, ascribed to the hydroxyl group in HEMA section that also gives a fast transport pathway for Li+-ions through hydrogen bonds. Contributed by the advanced functional groups inhered from distinct monomers, the assembled Li∥SPE∥LiCoO2 full cell using P(VEC-HEMA) electrolyte exhibits excellent rate capacity and long cyclic stability, which shows the specific discharge capacity of 138.1 mA h g–1 at 0.1 C rate in the voltage range of 3.0–4.2 V, maintaining 93.5% of initial capacity after 100 cycles. For comparison, the full cell using PVEC electrolyte has a short circuit after 13 cycles. Therefore, the proposed polycarbonate solid electrolyte gives a bright future to revitalize the development of high-energy-density LMBs.