Quantum Calculation And Electrochemical Properties Of Sulfone-based High-voltage Electrolytes For Li-ion Battery

Research on the development of lithium-ion battery in recent years has focused on both electrode materials and electrolytes in many aspects to improve its performance, such as battery output voltage and power density, etc., in order to expand the application of lithium-ion battery for high-power electrical equipments. Several cathode materials, such as LiNi0.5Mn1.5O4, their discharge voltage can get around 5 V, and the traditional carbonate electrlytes fail to meet the demand of 5 V charging and discharging platform, thus to explore a new type of electrolyte solvent to meet the demand of high voltage system has drawn much attention in recent years. Using the theoretical quantum chemistry calculation when doing research on lithium-ion battery electrolytes has also attacted many researchers’ attention.In this paper, we used three different methods to go on quantum chemistry calculation about several sulfone solvents, preliminarily explored and chose several sulfones, and combined with electrochemical performance test, made analysis on the structure effect of sulfone molecules to further build up a method of combining theoretical calculation as well as the experiments. Considering the chemical and physical properties of sulfone solvents, we chose TMS as the subject solvent of this study, for the reason that it possesses more excellent performance and stability, at the same time, DMS and DES were chosen to be cosolvents of TMS in order to reduce the viscosity of electrolytes. By comparing three kinds of lithium salts dissolved in the sulfone solvents, it is shown that three kinds of lithium salts, LiBOB, LiTFSI and LiPF6, were added into TMS-DMS(1:1) and TMS-DES(1:1), all presented an electrochemical window of 5.4 V or above, and their electrolyte conductivity at room temperature could reach above 3 mS/cm, among which, Li BOB-TMS/DMS was proved to be the most stable electrolyte. We also tested the relationship between lithium salt concentration and the ionic conductivity of the electrolytes, the results showed to perform the best ionic conductivity of the electrolytes, lithium salt concentration of LiBOB is 0.8 M, LiTFSI and LiPF6’s is 1 M. And finally FTIR was tested, which could offers explanation about the change on molecular functional groups to further study the influence of three kinds of lithium salts in solvent systems, the result has shown that the molecular of LiTFSI and LiPF6 for solvent systems had bigger influence on the solvents’ vibration, whereas Li BOB could relatively keep the original solvent system vibration band, to some extent, this could also give some explanations on the fact that lithium salts lay effect on the main functional sufone groups and sulfonic acid ester group, thus make influence the ionic conductivity and electrochemical stability of solvent system. Sulfone-based solvents with high electrochemical stability are expected to become a new generation of high voltage organic electrolytic liquid system, so in the future research we could further explore the matching attribute with high voltage cathode materials based on the research of this paper.