Cresyl diphenyl phosphate effect on the thermal stabilities and electrochemical performances of electrodes in lithium ion battery

To improve the safety of lithium ion battery, cresyl diphenyl phosphate (CDP) is used as a flame-retardant additive in a LiPF6 based electrolyte. The electrochemical performances of LiCoO2/CDP-electrolyte/Li and Li/CDP-electrolyte/C half cells are evaluated. The thermal behaviors of Li0.5CoO2 and Li0.5CoO2–CDP-electrolyte, and LixC6 and LixC6–CDP-electrolyte are examined using a C80 micro-calorimeter. For the LiCoO2/CDP-electrolyte/Li cells, the onset temperature of single Li0.5CoO2 is put off and the heat generation is decreased greatly except the one corresponding to 5% CDP-containing electrolyte. When Li0.5CoO2 coexists with CDP-electrolyte, the thermal stability is enhanced. CDP improves the thermal stability of lithiated graphite anode effectively and the addition of 5% CDP inhibits the decomposition of solid electrolyte interphase (SEI) films significantly. The electrochemical tests on LiCoO2/CDP-electrolyte/Li and Li/CDP-electrolyte/C cells show that when less than 15% CDP is added to the electrolyte, the electrochemical performances are not worsen too much. Therefore, the addition of 5–15% CDP to the electrolyte almost does not worsen the electrochemical performance of LiCoO2 cathode and graphite anode, and improves theirs thermal stability significantly; thus, it is a possible choice for electrolyte additive.

► CDP as a flame-retardant additive in LiPF6 based electrolyte was explored.
► The onset temperatures are put off and heat generations are decreased greatly, and the thermal stability is enhanced.
► The battery's electrochemical performances keep well when CDP content is less than 15%.