A new phosphonamidate, bis(N,N-diethyl)(2-methoxyethoxy)methylphosphonamidate (DEMEMPA) has been synthesized as N-P collaborative flame retardant additive in electrolytes for lithium ion batteries (LIBs). It is found that adding 10vol.% of DEMEMPA to 0.9M LiPF6/EC/DMC can significantly inhibit the burning of electrolytes and provide a wide electrochemical window. Further studies indicate that the electrolytes with and without DEMEMPA have similar electrochemical behavior with natural graphite and LiFePO4 electrodes. These support the feasibility of using DEMEMPA as a flame retardant additive for LIBs.