Preparation Of Cationic Polysulfone Binders And Their Lithium-sulfur Battery Performances

Lithium-sulfur(Li-S)batteries have broad development prospects in the field of energy storage due to their high theoretical specific capacity,high theoretical energy density,abundant raw material storage,and environmental friendliness,which have attracted wide attention.As the one of the key components in the Li-S battery positive electrode,the binder should tightly bond the active material,conductive carbon and current collector.At the same time,the binder should have a large number of sulfur-fixing sites.However,the development of the binder mainly meet the problem of poor sulfur fixation effect at present.In this thesis,a polysulfone polymer binder containing different cations was designed and synthesized.The cationic polymeric binder effectively adsorbs polysulfides generated during discharge through electrostatic interaction between cations and polysulfides,preventing polysulfides from entering ethers.The electrolyte improves the sulfur fixation effect of the Li-S battery,thereby increasing the capacity retention rate.The paper investigated the effect of cationic structure on the sulfur-fixing effect of binders and electrochemical properties.The main contents are as follows:(1)Preparation and electrochemical properties of different cationic functionalized polysulfone binders.First,polysulfone was modified to obtain chloromethylated polysulfone with different degrees of chloromethylation,and then 1-methylimidazole,triethylamine,N-methylmorpholine was used as the ionizing agent to obtain three different kinds of quaternized polysulfone binders.The effects of ionic functional groups on the adsorption of polysulfides were investigated by adsorption experiments,X-ray photoelectron spectroscopy and electrochemical methods,which was correlated with the degree of ionization of cationic polysulfone binders in ether electrolytes.It was found that the 1-methylimidazolium polysulfone binder has the best performance among the three positively charged binders.The capacity retention of the cationic polymeric binder having the optimal ionic functional group was 76% after 100 cycles at 0.2C,and 84% after 120 cycles at 0.5C,showing good electrochemical performance.(2)Preparation and electrochemical performance of double quaternied polysulfone binder.As the concentration of the cationic functional group increases,the polarity of the cationic polymeric binder increases,and the swelling in the ether electrolyte increases,so the polyelectrolyte binder can not ensure the structural stability of the electrode,while promoting the transport of lithium ions.In view of this,the cationic polymeric binder with double ion was prepared on the basis of the same concentration in the cationic polymeric binder.That is,triethylenediamine was used as the ionizing agent to realize quaternary ammonium of chloromethylated polysulfone to obtain a dicationic polymer binder.After 100 cycles at 0.2C,the capacity retention rates of single ion and double ion binder were 43% and 74%,respectively,and the capacity retention rate increased significantly by 31% with increasing ion concentration,after 200 cycles at 0.5C,the capacity retention rates were 46% and 68%,respectively;With the increase in ion concentration,the capacity retention rate is significantly improved.This indicates that the large amount of sulfur-fixing sites provided by the double-ion structure gives the binder an excellent sulfur-fixing effect.