Study On Performance Of Cyclic Sulfite Derivatives As Electrolyte Additives

Lithium-ion batterieshave gradually occupied the chemical energy market due to its excellent performance.Now,its application also gradually expands to electric vehicles,smart gridand other fields.However,the energy density,safety and cost of common lithium-ion batteries still cannot meet the requirement of continuously improved battery performance,which makes people to find new superior lithium-ion batteries.Meanwhile,the electrolyte additive is one of the the most cost-effective way to improve battery performance.Cyclic sulfite compounds is a kind of important electrolyte additive of lithium-ion batteries.In this thesis,considering literature and research interest of our team,we combined cyclic glycerol sulfite with cyclic glycerol carbonate and designed a series of cyclic glycerol sulfite derivatives:tris((2-oxido-1,3,2-dioxathiolan-4-yl)methyl)benzene-1,3,5-tricarboxylate(TMBT1),tetrakis((2-oxido-1,3,2-dioxathiolan-4-yl)methyl)benzene-1,2,4,5-tetracarboxylate(TMBT2),bis((2-oxido-1,3,2-dioxathiolan-4-yl)methyl)carbonate(BMC)and bis((2-oxido-1,3,2-dioxathiolan-4-yl)methyl)succinate(BMS).1,2-cyclic sulfite glycerol,the intermediate,was firstly synthesized,then,the above four derivatives were successfully synthesized,respectively.The synthetic condition of 1,2-cyclic sulfite glycerol was systemically optimized.The chemical structures of four derivatives were characterized by 1H NMR and FTIR.Additionally,their thermal stability and the pyrolysis process were investigated by TG-FTIR technology.Finally,these compounds were added to 1 M LiPF6-EC/DMC(1:1,v/v)or LiPF6-EC/DMC/DEC(2:1:1,v/v/v)electrolyte as additives to study their effects on the electrochemical performance of lithium-ion batteries by a variety of electrochemical tests such as cyclic charge-discharge test,electrochemical impedance spectroscopy test,cyclic voltammetry test and so on.Meanwhile,the surface morphology of cathode before and after the cell cycle was observed using scanning electron microscope.The results were listed as follows:1H NMR and FTIR result indicated that the intermediate 1,2-cyclic sulfite glycerol and its four derivatives with high purity were successfully synthesized.The optimium synthetic condition:the reactant ratio of glycerol and sulfoxide chloride was 1.2:1(mole ratio),the reaction time 16 h.The yield was 89.8%.TG-FTIR results showed that the initial pyrolysis temperature of TMBT1,TMBT2,BMC and BMS was 259℃,247℃,226℃ and 220℃,respectively.These compounds had good thermal stability to meet the practical requirements of lithium-ion batteries.The electrochemical results showed that addition of 0.5 wt.%and 0.7 wt.%TMBT1 to electrolyte could certainly improve the cycle stability of lithium-ion batteries;1.0 wt.%ofTMBT1 could enhance the rate performance of the batteries greatly.The impedance value of lithium-ion batteries with 0.5 wt.%and 1.0 wt.%TMBT1 was smaller than the batteries without additives after 100 cycles;The cyclic voltammetry tests showed that TMBT2 can be reduced prioritly in the first cycle,and a densy layer of SEI film was formed in the surface of cathode materials when 1.0 wt.%TMBT2 was added to the electrolyte;When the concentration of BMC was 0.7 wt.%,the rate performance of the batteries was slightly improved,but it did notmake other performances better;Adding BMS did not improve the electrochemical performance of the battery.