The Synthesis And Characterization Of Organic Electrolyte Additives In Lithium-ion Secondary Battery

As high-energy green batteries,lithium-ion batteries have outstanding advantages like high voltage,high energy density,long cycle-life,low self-discharge and environment-friendly,but they still have some issues like durability,operating temperature and safety to improve.The additives for electrolyte could increase performance of batteries remarkably with small quantity.Addition of a small amount of functional additives in the electrolyte is considered to be one of the most economical and effective way to improve the performance of lithium-ion batteries.Therefore,research and development of new additives has become an important research direction in lithium-ion batteries.In this paper,three kinds of glycerol carbonate derivatives:bis(2,3-cyclic glycerol carbonate)succinate,bis(2,3-cyclic glycerol carbonate)terephthalate and tris(2,3-cyclic glycerol carbonate)trimesoate were designed and synthesized.And their chemical structures were characterized by 1H NMR and FT-IR.Additionally,their thermal stability and the pyrolysis process were carefully investigated by TG-FTIR technology,and the theoretical calculation data of compounds’ bond dissociation energy(BDE)were carried out to verify the results of TG-FTIR.Finally,these compounds as additives were added to the 1 M LiPF6/EC+DMC(v/v,1:1)electrolyte for studying their effects on the electrochemical performance of lithium-ion batteries by using a variety of electrochemical tests,respectively.TG-FTIR results showed that the initial pyrolysis temperature of bis(2,3-cyclic glycerol carbonate)succinate,bis(2,3-cyclic glycerol carbonate)terephthalate and tris(2,3-cyclic glycerol carbonate)trimesoate was 262℃,284℃,251℃,respectively.Three compounds had good thermal stability and could meet the practical requirements of lithium-ion batteries.In thermal pyrolysis process,the C-C,C-O bonds of five-membered ring structure fractured preferentially,and then the C-O bonds nearby five-membered ring cracked,for tris(2,3-cyclic glycerol carbonate)trimesoate,the C-C bonds connected to benzene ring would continue to break.The BDE data also confirmed the above thermal cracking process.Based on the solubility of three compounds in the basis electrolyte,the concentration of these compounds was 0.5,0.7 and 1.0 wt.%,respectively.The electrochemical results showed that when the concentration of bis(2,3-cyclic glycerol carbonate)succinate was 0.7 wt.%,the cycle performance and the rate performance of the batteries had been significantly improved,impedance of the batteries decreased after 20 cycles,SEI film had suitable thickness and became more compact,but the batteries’ electrochemical stability window did not changed better;When the concentration of tris(2,3-cyclic glycerol carbonate)trimesoate was 0.7 wt.%,the rate performance of the batteries was slightly improved,but it did not make other performance better.In other cases,the electrochemical results were not predictable.