Polymer electrolytes (PEs) that consist of polyoxetane with nitrile side chains and lithium bis(trifluoromethanesulfonyl)amide were studied as electrolytes for Li secondary batteries. Our previous study showed that Li+ ion coordination with the polar nitrile groups tethered to the main chain plays a crucial role in enhancing the Li+ ion transport properties in poly(3-(2-cyanoethoxymethyl)-3-ethyloxetane) (PCEO). Herein, we report the effects of the absence of ethyl groups on the main chain of PCEO on Li+ ion coordination, thermal properties, and ionic transport, by employing a structural analog, poly(3-(2-cyanoethoxymethyl)-oxetane). We found that the steric hindrance derived from the ethyl groups in PCEO resulted in more-pronounced Li+ coordination with the nitrile side chains, and thereby more effective Li+ ion transport was achieved. We also demonstrated successful charge/discharge cycling of a Li/LiFePO4 cell using nitrile-functionalized PE.
