Study On The Performance And Mechanism Of Li-ion Battery Electrolyte Containing Sulfur And Nitrile Additives

Electrolyte is one of the key component of Li-ion battery.Using of lithium ion battery electrolyte additive to improve some performance of battery is considered to be an economic and effective way.The electrochemical performance of Li-ion batteries at low temperatures and electrochemical properties at high cut-off potential are also expected to be improved by using lithium ion battery electrolyte additives.The research content of this thesis mainly includes two parts:the first part is about the effects of partial sulfur additives on the low-temperature performance of Li-ion battery and other one is effects of two kinds of nitrile additives on the NCM811 cathode material.This thesis compares the effect of three kinds of additives with different sulfur-containing functional groups which include DTD(ethylene sulfate),1,3-PS(1,3-propane sultone)and ES(ethylene sulfite)on the low temperature performance of commercial artificial graphite anode and high voltage LiCoO2 cathode materials.Results show low temperature performance of the Li-ion battery mainly depends on the graphite anode.The density functional theory(DFT)calculations,scanning voltammetry(CV),scanning electron microscopy(SEM),Fourier transform infrared spectroscopy(FTIR)and galvanostatic charge-discharge measurement measurements clearly demonstrated that all three sulfur-containing additives could participate in formation of films on the surface of electrode and have a greater impact on the low-temperature properties.The cycle results by three electrode battery indicated that under 15?,the battery with 1%DTD has the highest capacity of 111 mAh/g after 50 cycles,and the reference group was only 37 mAh/g.Electrochemical impedance spectroscopy(EIS)and X-ray photoelectron spectroscopy(XPS)indicate the film formed by DTD has a smaller resistance,and the improvement on low-temperature is apparent,in contrast,1,3-PS is not conductive to low-temperature performance and ES has no obvious effect.Three kinds of additives also participate in the film of cathode surface,but the effects on positive electrode is lower compared to anode.This thesis also studied an effect of two kinds of nitrile additives includes suberonitrile(SUN)and succinonitrile(SN)on NCM811 materials and their possible reasons.From DFT theory calculation,LSV testing,floating charge methods,we can prove that SUN and SN can improve the oxidation stability of based electrolyte,but subsequent cycle test showed that only the battery with 1%of SUN can improve the cycle performance of battery.Through the study of the EIS,SEM and XPS,we speculated the effects of 1%SUN due to the parallel adsorption happened in material surface,thus inhibiting the continuous decomposition of the electrolyte and improve the electrochemical performance.