A facile strategy to improve the cycle stability of 4.45 V LiCoO2 cathode in gel electrolyte system via succinonitrile additive under elevated temperature

Abstract

The rapid capacity fading of LiCoO2 cathodes under high temperature limits its further development in high energy density of lithium ion batteries, caused by the unmatched liquid electrolyte that tends to decompose when the working potential exceeds 4.2 V (vs. Li+/Li). Gel polymer membrane blended with PEO (poly(ethylene oxide)) and P(VdF-HFP) (poly(vinylidene fluoride-co-hexafluoropropylene)) is used to enhance the oxidative stability of liquid electrolyte in the polymer matrix. In order to maximize the capacity of LiCoO2 cathode, proper amount of SN (succinonitrile) that helps to construct a stable CEI (cathode electrolyte interface) film is added into the electrolyte. The SN-contained GPE (gel polymer electrolyte) has the highest oxidative decomposition potential of 5.2 V and the lowest interfacial resistance. At 55 °C, the LiCoO2/GPE/Li coin-cell keeps 82% of capacity after 350 cycles in 3.0 V ~ 4.45 V at 1C rate, compared with that of 9% capacity retention using the polyethylene separator saturated with liquid electrolyte. The enhancement in the cyclic stability under elevated temperature attributes to the dual strategies: the GPE guarantees the better oxidative stability by suppressing the further oxidative decomposition of liquid electrolyte, while the high quality CEI film formed by the SN additive protects the structural integrity of LiCoO2 cathode.