A new strategy to improve the cyclic stability of high voltage lithium nickel manganese oxide cathode by poly(butyl methacrylate-acrylonitrile-styrene) terpolymer as co-binder in lithium ion batteries

High voltage LiNi0.5Mn1.5O4 material is a promising cathode for lithium ion battery, but the unsatisfied cycle stability hinders its further development in higher energy density battery. Amorphous terpolymer poly(butyl methacrylate-acrylonitrile-styrene) (P(BMA-AN-St)), which possesses good affinity with carbonated liquid electrolyte and high adhesion ability, is used together with traditional poly(vinylidene fluoride) (PVDF) binder to improve the cyclic performance of LiNi0.5Mn1.5O4 cathode. The retention ability of discharge capacity is 92% for Li/LiNi0.5Mn1.5O4 coin cell after 300 cycles at 1C rate when the cathode uses the co-binders of PVDF and P(BMA-AN-St) (2:1 in weight), compared with 55% capacity retention for the cathode fabricated with PVDF binder alone. From the physical and electrochemical characterizations of the cycled electrode, it is found that the introduced terpolymer enhances the liquid electrolyte uptake ability of LiNi0.5Mn1.5O4 cathode and the adhesion strength inside the particles by building a better interconnected conductive structure. Furthermore, the improved cycle stability of co-binder based cathode is contributed to the passivating layer formed by the terpolymer on the surface of LiNi0.5Mn1.5O4 particles, which effectively suppresses the decomposition of liquid electrolyte at high voltage and maintains the structural integrity of active material in the repeated intercalation/de-intercalation process.