Herein, we report the design of styrene-based poly(ethylene oxide) (PEO) side-chain block copolymers featuring a microphase separation and their application as solid polymer electrolytes in high-voltage lithium-metal batteries. A straightforward synthesis was established, overcoming typical drawbacks of PEO block copolymers prepared by anionic polymerization or ester-based PEO side-chain copolymers. Both the PEO side-chain length and the LiTFSI content were varied, and the underlying relationships were elucidated in view of polymer compositions with high ionic conductivity. Subsequently, a selected composition was subjected to further analyses, including phase-separated morphology, providing not only excellent self-standing films with intrinsic mechanical stability but also the ability to suppress lithium dendrite growth as well as good flexibility, wettability, and good contacts with the electrodes. Furthermore, good thermal and electrochemical stability was demonstrated. To do so, linear sweep and cyclic voltammetry, lithium plating/stripping tests, and galvanostatic overcharging using high-voltage cathodes were conducted, demonstrating stable lithium-metal interfaces and a high oxidative stability of around 4.75 V. Consequently, cycling of Li||NMC622 cells did not exhibit commonly observed rapid cell failure or voltage noise associated with PEO-based electrolytes in Li||NMC622 cells, attributed to the high mechanical stability. A comprehensive view is provided, highlighting that the combination of PEO and high-voltage cathodes is not impossible per se.

Herein, we report on the synthesis of a systematic library of vinyl ether-based poly­(ethylene oxide) (PEO) side-chain copolymers in order to reduce the crystallization of PEO. The influence of different grafted PEO side chain lengths, the grafting density, and the [Li+]:[EO] ratio after mixing with LiTFSI on the glass transition temperature (T g), the crystallinity, and the resulting ionic conductivity was examined. Copolymers bearing longer PEO side chains and higher grafting densities show higher crystallization tendencies while their T g is reduced at the same time. Furthermore, the addition of LiTFSI reduces crystallization but increases T g. Because these effects are directly impacting the ionic conductivity, we demonstrate that the different parameters need to be carefully adjusted in order to balance their influence. In this way, a fundamental view that shows the potential of PEO side-chain copolymers for their applications as polymer electrolytes is provided.

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