Improvement in LiFePO4-Li battery performance via poly(perfluoroalkylsulfonyl)imide (PFSI) based ionene composite binder

Lithiated poly(perfluoroalkylsulfonyl)imide (PFSILi) ionene is synthesized and blended with poly(vinylidene) difluoride (PVDF) to serve as binder for the electrode of a lithium ion battery. The incorporation of the PFSILi ionene adds ionic conducting channels inside the electrodes and prevents electrolyte depletion during rapid charging-discharging. The small composition change results in an increase in the battery performance, including a better reversibility, lower polarization or internal resistance and an improved discharge capacity, as well as a higher energy density at high rates or elevated temperatures. At the rate of 2 C and 60 degrees C, the discharge plateau potential for the cell with the ionene based binder is 0.29 V higher than that for the cell with a PVDF only cathode binder. At a 4 C rate, the discharge capacity and energy density of a LiFePO4-Li half-cell with the ionic binder are 50% and 66%, respectively, higher than those of the cell using the nonionic PVDF binder at room temperature. Thus, the ionene polymer offers a new route, rather than just altering the active materials, to overcome the limitations of capacity and power density for rechargeable lithium batteries.