| In recent years,with fast development of lithium ion batteries(LIBs)' technology,it has became to a major chose of storing energy products used in 3C equipment(communication,computer,comsumer),new energy vehicle,etc.As an essential part of LIBs,the separator plays crucial role in its performance.Currently,the commercially available LIBs' separator materials are polyolefins,including polyethylene(PE),polypropylene(PP)and PP/PE/PP three-layer membranes,which have excellent mechanical properties and good electrochemical stability and safety characteristics of thermal shut-down temperature.However,its inherent defects such as poor thermal dimensional stability and insufficient wetting for liqud eletrolyte limit the improvement of LIBs performance,mainly in safty and electrochemical performance.In view of the above problems,this study intends to use PE separators as an example to prepare a series of modified PE separators for high-security LIBs by starting from inorganic coating,organic coating and adhesive improvement.The main results are as follows:(1)Aluminide ceramic coating polyethylene(ACP)separators was prepared by dip coating process in which aluminum oxide(Al2O3)and boehmite(AlOOH)were used as ceramic coating materials,water was used as the solvent,BYK(Beck Chemical Co.,Ltd.)additives were used as the aqueous assistant.As a result,the ACP separators exhibit better thermal stability,lyophilicity,and mechanical strength than PE separators.In addition,coMPared with the PE coated Al2O3(PE-Al2O3)separator,the PE coated AlOOH(PE-AlOOH)separators exhibits more excellent interface stability(peel strength of 0.3 KN/m)and the electrolyte liquid up-take performance(up-take rate 187%),which is mainly due to the presence of hydroxyl(-OH)in the AlOOH crystal structure.(2)An eco-friendly PVDF coating PE(PE-PVDF)separator was prepared by dip coating process in which PVDF was used as coating materials,water was used as the solvent,BYK products were used as the aqueous assistant.Compared with PE separators(51.2%,111.3°±0.12°,0.55 mS/cm),PE-PVDF membranes exhibit more excellent lyophilicity(3.28°±0.21°)and ionic conductivity(1.53 mS/cm),In turn,it plays a significant role in improving the electrochemical performance of LIBs.(3)In order to solve the problem of insufficient high temperature performance of the binder used in coating modified slurry,bisphenol A dianhydride(BPADA)and diaminodiphenyl sulfone(DDS)are used as the main raw materials to synthesize thermoplastic polyimide(PI)binder with sulfone group and flexible group.The synthesized new high temperature resistant PI binder was applied in Al2O3 coated modified PE separator,and then its influence on the performance of coated modified PE separator was studied.The results show that the heat resistance of the Al2O3 coating PE separator with PI adhesive(PI@PE)is significantly improved compared to the bare PE film.And,compared with the traditional PVDF adhesive(170?,30 min,Shrinkage 74%),the thermal performance of the PI@PE separator(170?,shrinkage 38%)also has a significant advantage,which is conducive to maintaining the rate capacity and cycling performance of LIBs under high temperature conditions.In addition,the further study about the effect of the amount of PI binder on the performance of Al2O3 coating PE separator was carried out.As a result,as the amount of PI binder increases,the more weak wettability to liquid elelctrolyte,more uniformly distributed for Al2O3 coating layer and more stable size in high temperature was represented by composite separators.The composite separator shows good long-term cycling stability at 3.9wt%PI binder.After 140 cycles at 1C,the discharge capacity retention rate of 3.9wt%PI composite separator is 91.8%.Based on the above performance,when considering the effect of the amount of PI binder on composite separators comprehensensive performance,the amount of 3.9wt%is best. |
PDF Full Text Request