The use of methyl, methoxy ethyl and triflouro ethyl phosphates in lithium-ion battery electrolytes

1 M LiPF6 salt containing electrolytes were prepared using methyl (TMP), methoxy ethyl (TMEP) and triflouro ethyl (TFEP) phosphates as solvent, solvent component and additives to be used in Lithium-ion batteries. Using these eelctrolytes, coincell batteries with lithium as anode and LiFePO4 as cathode were assembled. Cyclic voltammetry experiments, impedance measurements and charge-discharge-efficiency measurements at different C rates were performed. Although the contribution of phosphates as solvent and solvent component to the battery performance was not enough, they improved the battery performance as additives. At the end of 100 cycles, the reference solution underwent a 20% performance loss and dropped to a value of 121 mAhg-1 discharge capacity while a much lower performance drop (7-140 mAhg-1 discharge capacity) was found by adding 1% TFEP as additive onto the reference solution. When the additive ratio is increased to 2%, a discharge capacity of 145 mAhg-1 is measured with a performance drop of 4%. When TMEP was added as additive in 1% and 2% ratios, the values were 134 mAhg-1 with 10% performance drop and 125 mAhg-1 with 6% performance drop respectively. TMP was added 1% as additive, 130 mAhg-1 discharge capacity with a 13% performance drop was measured. According to these results, the best performance value was obtained with an electrolyte solution containing 2% TFEP as an additive.