Li~+ Solvation Structure In Propylene Carbonate Electrolytes Determined By Ultrafast Vibrational Spectroscopy

In this paper we have introduced the development history,fundamental,experimental equipment and application of two-dimensional infrared spectroscopy briefly.The technology have been applied to the lithium ion electrolyte solution and the coordination kinetics of Lithium Hexafluorophosphate?LiPF₆?dissolve in Propylene Carbonate?PC?solution has been investigated by using Polarization selective ultrafast vibration spectroscopy.Through the combination of experimental and theoretical research methods,we found that the coordination number of PC molecules which were bonded with lithium-ion decreased from 4 to 2 with the increase of the concentration at room temperature.The solvation structure of the ion with the solvent were predicted by theoretical simulation.In addition,according to the one-dimensional infrared and two-dimensional infrared experimental data,we found that 70±10%of the lithium salts dissociated into Li⁺in 1 mol/kg-LiPF₆/PC solution at room temperature,and the Li⁺non-contact with a PF₆^-anion were bounded with two PC molecules in the solution,forming the structure solvent Shared ion pair?non-contact ion pair?.According to the conductivity data that measured at different concentrations,we found that the conductivity of LiPF₆/PC electrolyte solution increased rapidly with the concentration increasing at the low concentration?<0.5mol/kg?and if the concentration were increasing when the conductivity reaches the highest value,the conductivity will decrease.The change of solvation structure explained the change of conductivity with concentration.