Preparation And Performance Of ZrO₂/PET Composite Fiber Separator And PET Based Lithium-ion Battery Separator

Due to its high energy density and long cycle life,lithium-ion batteries have been widely used as an efficient energy storage system in the fields of portable electronic equipment and electric vehicles.Current research on lithium-ion batteries is focused on improving their safety and energy density.Among them,as one of the key components in the battery,the battery separator also has a certain influence on the battery performance,and plays a decisive role in the battery-to isolate the positive and negative electrodes to prevent the battery from short circuit,and to provide channels for the interpenetration of lithium ions.How to improve the performance of the battery from the perspective of the separator is also the research focus of this paper.Polyethylene terephthalate(PET)and zirconium oxide(ZrO₂)composite non-woven fiber membranes were prepared respectively in this paper,and the influence of different substrates on the performance of lithium-ion battery membrane and its assembled battery performance was investigated.The effects of different proportions of polydopamine on the performance of PET composite fiber membrane as battery membrane and battery performance were investigated.Of composite fiber membrane surface morphology,mechanical properties,thermal stability,physical properties such as electrolyte wettability and flexibility,and the cell cycle performance and rate performance,such as impedance electrochemical properties were studied,and the composite fiber membrane and commercial application of polyolefin separator performance comparison,summarized its advantages and disadvantages.Through the above investigation,we aim to obtain a lithium-ion battery diaphragm with simple preparation process,high safety and excellent battery performance.The specific research content is divided into the following three parts:(1)Using PET powder and dopamine hydrochloride(HDA)as raw materials,the PET-HDA composite fiber membrane was prepared by electrospinning method,and the PET-PDA composite fiber membrane was obtained by in-situ growth.The thickness of polydopamine(PDA)on the surface of the prepared PET-PDA composite fibers was controlled by changing the proportion of HDA added to the spinning solution.At the same time,the effects of adding different proportions of HDA on the membrane performance and battery performance of PET-PDA composite fiber membrane were studied.The results show that the PET fiber modified by HDA has excellent hydrophilicity,and the contact Angle of the PET-PDA composite fiber separator is 0°(the contact Angle of the PET fiber film is 134.1°).The composite fiber separator with 2.5%,5.0%,10%and 20%HDA was compared respectively.In general,the composite fiber membrane with PET-2.5%PDA had relatively good battery performance.At 200?,the thermal shrinkage rate is 9.75%(PP membrane is 100%),and the ionic conductivity is 0.5350 mS·cm-1(PP membrane is 0.2793 mS·cm-1).The assembled battery also shows good advantages in terms of the cycle performance and rate performance of the battery.(2)Using PET powder and ZrO₂ inorganic staple fiber as raw materials,ZrO₂ inorganic staple fiber was added into PET spinning solution,and the PET@ZrO₂ composite fiber membrane with beaded structure was prepared by electrospinning method.The effects of different proportion of ZrO₂ inorganic short fibers on the thermal stability,tensile strength and the performance of assembled batteries of composite fiber membrane were investigated.The results show that with the increase of the number of ZrO₂ inorganic short fibers added,the bead structure in the PET@ZrO₂ composite fiber membrane increases continuously,and the thermal stability of the composite fiber membrane also increases continuously.The thermal shrinkage rate of PET@2.0ZrO₂ composite fiber membrane at 250? is 1.24%.Compared with the composite fiber membrane with different proportion of ZrO₂ inorganic short fiber,the PET@0.5ZrO₂ composite fiber membrane with the mass ratio of PET powder and ZrO₂ inorganic short fiber of 1:0.5 has the best performance.The absorptivity of electrolyte was up to 282.3%(PP membrane was 111.5%),the tensile strength was 15.01 MPa,and the ionic conductivity was 0.765 mS·cm-1.Compared with commercial PP membrane,PET@2.0ZrO₂ composite fiber membrane has better battery cycle performance and rate performance.(3)Using ZrO₂ inorganic fiber as the substrate and PET solution as the adhesive,ZrO₂-PET composite fiber membrane was prepared by paper making method.The effects of different concentrations of PET solution as an adhesive on the surface structure,tensile strength,thermal stability and battery performance of the composite fiber membrane were investigated.The results showed that with the increase of PET concentration,the strength of composite fiber membrane increased from 0.5 MPa to 5.5 MPa.At the same time,ZrO₂-PET composite fiber membrane has excellent thermal stability,and the thermal shrinkage rate at 300? is 0%(PP membrane is 100%).By comprehensive comparison of composite fiber membrane with different concentrations of PET solution,PTZ5 composite fiber membrane with 5%PET solution has relatively better battery performance.The electrolyte absorption rate is as high as 301.8%.At room temperature,PTZ5 composite fiber diaphragm has good cycling performance and rate performance,maintaining 100%capacity retention rate and coulomb efficiency in the first 100 cycles.After 25 cycles at 60?,the specific discharge capacity of PTZ5 composite fiber membrane is 26 mAh/g higher than that of PP membrane,which is more suitable for high temperature use.