Ion Transport in Ether-Based Polymer Electrolytes

Polymer electrolytes, typically poly(ethylene oxide) (PEO) mixed with a lithium salt, have emerged as promising solid electrolytes for lithium ion batteries. However, polymer electrolytes still exhibit lower conductivities than commercial liquid electrolytes. We report a novel ether-based polymer, poly(diethylene oxide-alt-oxymethylene), (P(2EO-MO)), which was synthesized via cationic ring-opening polymerization of the cyclic acetal monomer, 1,3,6-trioxocane. The polymer electrolytes, which are mixtures of P(2EO-MO) and various concentrations of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt, were characterized by electrochemical methods. P(2EO-MO)/LiTFSI exhibits lower ionic conductivity than PEO/LiTFSI due to increasing glass transition temperatures in the presence of lithium salts. However, the steady-state transference number of P(2EO-MO)/LiTFSI is significantly higher than that of PEO/LiTFSI at most salt concentrations. We investigate the thermodynamic factor and steady-state current of P(2EO-MO)/LiTFSI as a function of salt concentration and compare the results to PEO/LiTFSI. This work suggests that the overall efficacy of ion transport in P(2EO-MO) is greater than that in PEO, and P(2EO-MO) is a favorable electrolyte for lithium ion batteries.