(603b) Design of High Transference Number Battery Electrolytes

High transference number electrolytes, those in which the electrochemically active lithium cation diffuses faster than its electrochemically inert counterion, have the potential to improve battery performance by limiting concentration polarization. High cation transference electrolytes are typically polymers with anions fixed to their backbone (ionomers), thereby only allowing cation diffusion over large length scales. In their dry state, such polymer electrolytes generally have substantially lower ion conductivity, particularly at room temperature, than liquid electrolytes, negating the advantages that polymers provide in terms of safety or Li⁺ transference. Therefore, our research has focused on identifying routes to improve ion conductivity of ionomers through small molecule plasticization or improve Li⁺ transference numbers of liquid electrolytes by using ionomers as the salt. Here, we have designed a series of poly(ethylene oxide) (PEO) based ionomers containing lithium sulfonate to explore these concepts. Our initial results on improving transference numbers of liquid electrolytes using these polymers as salts will be presented. By tuning the molecular weight of the polymer, solvent donor number, and concentration of polymer in solution, we begin to understand the relationship between electrolyte characteristics and performance. Preliminary results show that in the case of poorly dissociated ions, the ion and counterion move together, with a transference number of close to 0.5. However, in the case where ions are well dissociated, very high cation transference numbers (0.94) can be achieved.