Surface Treatment And Modification Of Polyolefin Separator For Lithium Ion Battery

Polyolefin microporous membrane is commonly used in lithium ion batteries and its advantages are with good mechanical properties and chemical stability,and has high performance of autism and to strengthen the safety of battery for daily use.But it also has disadvantages,such as low wettability,poor electrolyte retention,low ionic conductivity,which limits the further improvement of the performance of the lithium-ion battery.In order to overcome these shortcomings,it is commonly used in the literature to introduce hydrophilic groups on the surface of the diaphragm to improve the wettability of the membrane by grafting of plasma treatment,grafting of UV light and other radiation.However,the processing equipment prices are relatively high,the process is cumbersome and the cost of raw materials is relatively high,thus are difficult to scale them up.Therefore,we have explored a kind of non-radiation chemical method to preprocess the surface of polypropylene microporous membrane to improve the wettability of polyolefin microporous membrane.Then the method of layer by layer assembly modified with several layers of ionic conducting polymer on the surface of the diaphragm and to improve membrane wettability,imbibition rate and fluid retention rate,and improve the conductivity of the batteries.Followed by the membrane surface modifying graphene oxide?GO?and the ion conductive polymer to improve wettability while preventing the negative electrode of lithium dendrite penetration,increasing the metal lithium as the anode of the battery cycles,which suppressed lithium dendrite growth.Details are as follows:?1?Lithium-ion battery separator?polypropylene microporous membrane?pre-treatment: In order to make the surface of the polypropylene microporous membrane form a polarized chemical group,the infiltration of the electrolyte is improved,and the ion conducting polymer or other functional materials are also easy to be modified at the later stage in the membrane surface.The surface pretreatment of the membrane is a simple chemical oxidation method,which will be used to soak the polypropylene microporous membrane in strong oxidizing solution.By using a chemical oxidation method,a lithium ion battery to improve the wettability of the separator,the oxidizing agent used include nitric acid,hydrogen peroxide,potassium persulfate and potassium permanganate reagents.Based on a variety of experimental conditions of screening,we found that 98%HNO₃,H₂O₂ and K₂S₂O₈ method for pretreatment of membrane is the most effective oxidation conditions.Through the contact angle measurement of the samples to analyze experiment of polyolefin microporous membrane wettability change,and by scanning electron microscopy characterization of diaphragm after pretreatment of morphology,in subsequent chapters also made other characterization of infrared and fluid retention rate.Experimental results show that the microporous membrane by chemical treatment enhances the wettability of the electrolyte,lithium ions through the help,but also conducive to the latter part of the membrane modification.?2?Lithium-ion battery separator?polypropylene microporous membrane?surface modifying ionic conductive polymers: In order to improve the wettability of the separator,aspiration rate and retention capacity of the battery and to improve the ionic conductivity.Through a simple layer by layer assembly method to modify the membrane,the ion conducting polymers?PEO and PAA?are uniformly modified to the surface of the commercially available celgard 2400 porous polymer film pretreated by chemical methods.The modified layer uses the hydrogen bond between PEO and PEO,and PEO is the ionic conducting polymer which promotes the transmission.PAA plays the role of the intermediary layer,and it also forms a hydrogen bond with PEO.Through the contact angle measurement of the samples to analyze experiment of polyolefin microporous membrane wettability change,and through scanning electron microscopy characterization of diaphragm after pretreatment of morphology,infrared,liquid rate and other characterizations.Through the use of Li_1.2Mn_0.54Co_0.13Ni_0.13O₂ and LiFePO₄ as cathode materials assembled into battery,study its electrochemical performance.Experimental results show that the modified PEO and PAA membrane,wettability,liquid uptake and retention capacity has increased significantly,the film morphology characteristic also significantly changed.And the modified layer can improve the electrochemical performance of the battery,and improve the conductivity of the lithium ion.Charge and discharge test,and EIS analysis cycle capacity test results show that the modified layer can not only improve the membrane electrolyte wettability and the formation of SEI film is helpful,and can reduce the charge transfer resistance of the formed SEI film.We have laid a good foundation for our next chapter.?3?Lithium-ion battery separator?polypropylene microporous membrane?surface-modified graphene oxide?GO?: In order to inhibit the growth of lithium dendrites,we have constructed a protective layer on the surface of the membrane modified graphene oxide?GO?and ionic conductive polymer to achieve the effect of inhibiting lithium dendrite.We explore the basis of previous experiments,the graphene oxide?GO?and the ion conductive polymer layer assembly method by modifying the polypropylene microporous membrane.By The samples were analyzed experimental contact angle of the polyolefin microporous membrane wettability changing circumstances,scanning electron microscopy to characterize the membrane morphology after pre-processing,and by doing Li_1.2Mn_0.54Co_0.13Ni_0.13O₂ assembled battery cathode material to test the electrochemical properties.Experimental results show that the modified peroxide graphene?GO?and ion conductive polymer membrane,the wettability improves and membrane morphology characteristics have significantly changed,succeeded in preventing the lithium dendrite growth,and improve the cycle performance of the battery.