Influence of Polymer Backbone Fluorination on the Electrochemical Behavior of Single-Ion Conducting Multiblock Copolymer Electrolytes

The presence of fluorine, especially in the electrolyte, frequently has a beneficial effect on the performance of lithium batteries owing to, for instance, the stabilization of the interfaces and interphases with the positive and negative electrodes. However, the presence of fluorine is also associated with reduced recyclability and low biodegradability. Herein, we present a single-ion conducting multiblock copolymer electrolyte comprising a fluorine-free backbone and compare it with the fluorinated analogue reported earlier. Following a comprehensive physicochemical and electrochemical characterization of the copolymer with the fluorine-free backbone, the focus of the comparison with the fluorinated analogue was particularly on the electrochemical stability toward oxidation and reduction as well as the reactions occurring at the interface with the lithium-metal electrode. To deconvolute the impact of the fluorine in the ionic side chain and the copolymer backbone, suitable model compounds were identified and studied experimentally and theoretically. The results show that the absence of fluorine in the backbone has little impact on the basic electrochemical properties, such as the ionic conductivity, but severely affects the electrochemical stability and interfacial stability. The results highlight the need for a very careful design of the whole polymer for each desired application, essentially, just like for liquid electrolytes.