Non-flammable electrolytes based on trimethyl phosphate solvent for lithium-ion batteries
(1. School of Metallurgical Science and Engineering, Central South University, Changsha 410083, China;
2. Department of Chemistry and Material Science, Hunan Institute of Humanities, Science and Technology, Loudi 417000, China)
2. Department of Chemistry and Material Science, Hunan Institute of Humanities, Science and Technology, Loudi 417000, China)
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