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 °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.