Abstract: The properties of trimethyl phosphate(TMP)-based nonflammable electrolytes with LiPF6 as solute were investigated using graphite anode and LiCoO₂ cathode. The effect of TMP on non-flammability of electrolytes was also evaluated. It is found that the TMP reduction decomposition on graphite electrode at the potential of 1.3V (vs Li/Li⁺) is suppressed with ethylene carbonate(EC), dimethyl carbonate(DMC) and ethylmethyl carbonate(EMC) cosolvents and vinylene carbonate(VC) additives. The results show that the non-flammable electrolyte of 1mol/L LiPF6 61%(EC1.5-DMC1.0-EMC1.0)-39% TMP has good electrochemical properties. The discharge capacities of half-cells after 20 cycles are 254.8mA•h/g for Li/graphite and 144.1mA•h/g for Li/LiCoO₂. The graphite/LiCoO₂ prismatic lithium-ion cell delivers a discharge capacity of 131mA•h/g at first cycle. With an addition of 4%VC to this non-flammable electrolyte, a discharge capacity of 134mA•h/g at first cycle and a capacity ratio of 84.3% after 50 cycles are obtained for prismatic lithium-ion batteries. Furthermore, a nail penetration test demonstrates that the safety of prismatic lithium-ion batteries is dramatically improved by using TMP-containing non-flammable electrolytes.

Key words:  graphite; LiCoO₂; nonflammable electrolyte; trimethyl phosphate; lithium-ion battery