In this paper, we prepared a phosphazenic compound triethoxyphosphazen-N-phosphoryldiethylester (PNP) by a facile method and characterized as a flame-retarding electrolyte additive for lithium ion batteries. The flammability and electrochemical performance of the PNP-containing electrolyte were investigated. The self-extinguishing time (SET) value of 10% PNP in the electrolyte is 40% decreased compared to base electrolyte, implying strong inhabitation to the flammability. The electrochemical performances of MCMB/Li, LiFePO4/Li and LiMn2O4/Li half-cells in 10% PNP electrolyte exhibit considerable capacity, coulombic efficiency and cycling stability compared to the base electrolyte. Therefore, PNP as flame-retarding additive is a promising candidate combining efficient flame retardancy and good electrochemical performance for safer lithium ion batteries.