Design,Preparation And Characterization Of High Safety Composite Separator For Lithium-ion Battery

Lithium-ion batteries(LIBs)are widely used in portable electronic devices due to their high energy-density and excellent cycle life.Furthermore,LIBs are also regarded as the most competitive power source for large-scale battery applications,such as in electric vehicle(EV)and energy storage systems(ESSs),provided that their safety and cost can be substantially improved.In LIBs,a separator plays the crucial role of preventing contact of the cathode and anode electrodes,while at the same time permitting ion transport inside the cell.Currently,the separators used in LIBs are mainly based on microporous polyolefin membranes,which exhibit high thermal shrinkage at elevated temperatures,leading to a safety hazard.To overcome the problems,functional separators with rational stereocomplex structure are designed and prepared by composite modification.Combine the function of ceramic-coating and heat resistant polymer via synergistic effect,the composite modified separators display excellent thermal stability.Specifically,the dissertation mainly includes the following contents:(1)By a simple dip-coating process,polydopamine(PDA)formed an overall-covered self-supporting film,both on the ceramic layer and on the pristine polyolefin separator,which made the ceramic layer and polyolefin separator appear as a single aspect and furthermore,this layer amended the film-forming properties of the separator.Combining the function of the ceramic and PDA,the developed PDA-ceramic composite modified separator displays substantially enhanced thermal and mechanical stability,with no visual thermal shrink and can maintain its mechanical strength up to 230 ℃ when the polyethylene separator acts as the pristine separator.(2)Inspired by the polymerization mechanism of the dopamine and the structure of the PDA,take the low cost of binary composite monomer-catechol(CA)and polyethylene imine(PEI),instead of expensive dopamine,to copolymerize to modify the ceramic-coated separator,the cost of which is less than tenth of that of dopamine.The results indicate that the composite monomer copolymer has similar properties to polydopamine and can also form a stereocomplex structure via the in-situ autoxidation polymerization and can achieve a performance comparable to that of dopamine.The composite monomer copolymer(CP)-ceramic composite modified separator not only have not any shrinkage at a temperature up to 200 ℃,but also display an excellent shutdown feature.The industrial-class safety test show that the battery with the CP-ceramic composite modified separator has excellent safety performance.