Study On Performane Of Derivatives Of Glycerol Carbonate Applied As Eletrolyte Additives

Electrolyte is one of important factors to determine the quality and cost of the battery.However,LiPF6 has very high reaction activity with electrolyte solvent.The solvent can induce and accelerate the decomposition of LiPF6:LiPF6?LiF+PF5,The produced PF5 not only reacts with the solvent,but also catalyzes polymerization of solvent and damages the formed SEI film,which enhances the impedance of battery and reduces battery's performance.The research of electrolyte additives has become a hot field in developing lithium ion batteries.Some carbonyl compounds can decrease the reaction activity of PF5 by weak binding effect of-C=O and PF5.In full consideration of the advantages and disadvantages of common linear carbonate(dimethyl carbonate,diethyl carbonate and methyl ethyl carbonate,etc.)and ring carbonate(ethylene carbonate and propylene carbonate),and the present situation of widely used linear,circular carbonate as mixed solvent,we designed some compounds had both the linear and circular carbonate group.Carbonic acid bis-(2-oxo-[1,3]dioxolan-4-ylmethyl)ester,oxalic acid bis-(2-oxo-[1,3]dioxolan-4-ylmethyl)ester,benzene-1,2,4,5-tetracarboxylic acid tetrakis-(2-oxo-[1,3]dioxolan-4-ylmethyl)ester were synthesized in this paper.The thermal stability of the compounds was analyzed by TG-FTIR.And the effect of the compounds on electrochemical performance of lithium ion battery was studied by using the electrochemical methods such as constant current charge discharge,impedance(EIS),cyclic voltammetry(CV)and scanning electron microscopy(SEM).The results were listed as follows:(1)Carbonic acid bis-(2-oxo-[1.3]dioxolan-4-ylmethyl)ester:TG-FTIR showed that the compound decomposed at 210?;The electrochemical tests indicated that the compound had little effect on the stability of the battery,but the initial capacity of the battery and the efficiency of the first cycle had been significantly increased,and the increase of the resistance of the battery reduced,especially when the compound adding mass ratio was 1%and 2%.(2)Oxalic acid bis-(2-oxo-[1,3]dioxolan-4-ylmethyl)ester:TG-IR showed that the compound decomposed at 275 ?;The electrochemical tests indicated that the initial capacity and the first efficiency of the battery were decreased.And CV curves showed that compound formed a passive film prior to electrolyte solvent degradation;and the compound improved the cycle stability of the battery,and the increase of the resistance of the battery reduced,especially for 0.5%oxalic acid in the electrolyte.(3)Benzene-1,2,4,5-tetracarboxylic acid tetrakis-(2-oxo-[1,3]dioxolan-4-ylmethyl)ester:TG-FTIR showed that the compound decomposed significantly at 400?;The electrochemical tests indicated that the improvement of the cycle stability is not obvious,but the efficiency of the battery was significantly improved,especially when the addition of mass ratio of 0.7%and 1.0%,the increase of the resistance of the battery was reduced;The compound formed SEI film on the MCMB electrode prior to electrolyte solvent degradation.