Non-flammable electrolytes based on trimethyl phosphate solvent for lithium-ion batteries

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 1.3V （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 1mol/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 254.8mA·h/g for Li/graphite and 144.1mA·h/g for Li/LiCoO2. The （graphite/）（LiCoO2） prismatic lithium-ion cell delivers a discharge capacity of 131mA·h/g at first cycle. With an addition of 4%VC to this non-flammable electrolyte, a discharge capacity of 134mA·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.