Reducing crystallinity in solid polymer electrolytes for lithium-metal batteries via statistical copolymerization

The discovery that polyethylene oxide promotes ionic conductivity led to the development of solid polymer electrolytes. However, their conductivity is severely reduced by crystallinity. Here, statistical copolymerization is used to design macromolecular architectures where crystallinity is disrupted by a minimal amount of non-ethylene oxide comonomer units. Using the Flory exclusion model, we demonstrate that polymers containing 18 mol% comonomer and 18 wt% LiTFSI are devoid of crystallinity. A 10 mol% comonomer content is sufficient to reach a conductivity of 0.3 × 10−4 S cm−1 at 25 °C. The Li+ transference number is 0.6, indicating that the comonomer units not only limit the crystallinity but also weaken the strength of the Li+ coordination to the polymer. The resulting solid polymer electrolyte is effective in an all-solid LFP|Li-metal battery operating at 25 °C, demonstrating that statistical copolymerization is an efficient tool for polymer electrolyte design. Polyethylene oxide is a common solid polymer electrolyte for solid-state lithium metal batteries. Here, statistical copolymerization is shown to be an effective approach to reduce its crystallinity, enabling a high ionic conductivity during room temperature battery operation.