Enhanced high voltage cyclability of LiCoO2 cathode by adopting poly[bis-(ethoxyethoxyethoxy)phosphazene] with flame-retardant property as an electrolyte additive for lithium-ion batteries

Abstract Poly[bis-(ethoxyethoxyethoxy)phosphazene] (EEEP) with electro-oxidable of the P-O bond is prepared by a facile method and utilized as an electrolyte additive to enhance the cycling performance of LiCoO 2 cathodes under high-voltage operations. We found that 5 wt.% EEEP made the blank electrolyte obviously reduce the flammability, as well as the capacity retention of Li/LiCoO 2 half-cell assembling with the EEEP-containing electrolyte is elevated to 89.9% from 51.2% after 100 cycles at a high cutoff voltage of 4.4 V. The enhanced cycling performance of LiCoO 2 cathode in the EEEP-containing electrolyte at a high potential should be ascribed to the formation of stable film on the cathode surface, resulting in suppression of the subsequent decomposition of electrolyte under high voltage working. The characterization from scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) indicates that EEEP can be electrochemically oxidized to form a robust and protective film on LiCoO 2 , and improve the interfacial stability of LiCoO 2 cathode/electrolyte at high potentials.