Sulphonated poly (ether ether ketone) (SPEEK) was synthesized and used as ionic conducting binder for LiFePO₄ cathodes. In order to further increase its ionic conductivity, SPEEK was lithiated by adding various amounts of LiClO₄ (Li-SPEEK). SPEEK, Li-SPEEK and conventional polyvinylidene fluoride (PVDF) binders were applied to fabricate LiFePO₄ cathodes for comparison. The LiFePO₄ cathodes using Li-SPEEK with optimized amount of lithiation exhibited higher discharge capacity of 108 mAh/g under high discharge rate (10 C), compared with the LiFePO₄ cathode with PVDF binder (80 mAh/g). It can be attributed to the lower charge transfer resistance resulted from the use of Li-SPEEK binder, which contained Li⁺ ions and exhibited ionic conductivity. The electrochemical impedance spectra showed more than 50 % of reduction in charge transfer resistance for Li-SPEEK compared with PVDF used samples. In addition, the LiFePO₄ cathodes using Li-SPEEK and conventional binders exhibited comparable cycling stability in 100 cycles with capacity retention higher than 93%. It indicates that Li-SPEEK is a good candidate as an alternative binder for high rate applications.