Comparison of lithium-polymer cell performance with unity and nonunity transference numbers

This work compares the performance of lithium batteries with polymer electrolytes with unity (“ionomer”) and nonunity (“polymer electrolyte”) transference numbers. The study is performed with respect to a particular cell chemistry, Li metal∣polymer∣LiV₆O₁₃-composite electrode, which is currently a top candidate for use in electric vehicles. Cell performance was modeled to determine the best possible performance of cells containing four different electrolytes: “ideal” polymer membrane and ionomer with properties defined by USABC goals, and the presently best available polymer electrolyte and ionomer. Positive electrode thickness, porosity, and current density were varied to find the cell geometry with the highest combined energy density and peak power performance for cells with each electrolyte, and concentration and potential profiles are examined to determine the limitations of the electrolytes. The results show that at 40°C, the “ideal” polymer electrolyte can provide 104 W h/kg and 99 W_p/kg, the “ideal” ionomer can provide 94 W h/kg and 58 W_p/kg, and the currently available electrolytes can provide about one-fifth of these values.