Research On The Structure And Property Of Polyimide/Cellulose Lithium Battery Separator Paper

With the rapid development of science and technology,battery applications have become more widespread,and high-end performance battery development and manufacturing has gradually attracted people's attention.Lithium-ion batteries are successfully used in portable electronic devices such as mobile phones,computers,and cameras because of their high energy density,stable cycle characteristics,low discharge rate,and high operating voltage.They are also expected to be used in electric vehicles and energy storage systems.A lithium ion battery is composed of a positive electrode,a negative electrode,an electrolyte,and a separator.The performance of the battery separator is a key indicator for evaluating the quality of the battery.The separator is between the positive electrode and the negative electrode to prevent internal short circuit caused by direct contact between the two electrodes,and at the same time,the lithium ion is freely transferred during charging and discharging of the battery.In this thesis,the structure and properties of polyimide/cellulose battery separator paper are studied.Polyimide fiber is used as the matrix material,supplemented by oxidized bacterial cellulose,which is based on traditional papermaking method and combined with vacuum.The adsorption process produces battery separator paper with excellent thermal stability,electrolyte wetting properties and mechanical properties.The main research contents include:?1?The polyimide fiber is treated by physical beating method,and a reasonable degree of beating is explored to obtain a fiber form suitable for preparing a battery separator paper substrate.The fiber morphology of different levels of beating was observed by a microscope.The polyimide fibers having different degrees of beating treatment were subjected to wet papermaking to form a paper-based material having a basis weight of 25 g/m²,and the degree of reasonable beating as a separator substrate was characterized by air permeability and tensile strength.Bacterial cellulose was prepared by TEMPO oxidation.In the process of oxidizing bacterial cellulose,the degree of oxidation was adjusted by changing the amount of sodium hypochlorite.The observation of the atomic force microscope and the calculation of the carboxyl content,and the detection of the permeability and mechanical strength to explore the pores suitable for filling the pores of the polyimide substrate.Reasonable amount.The results show that as the beating time increases,the fiber is sheared and becomes shorter and shorter.The unbleached polyimide fiber has a tensile strength of 37 N·m·g^-1,and the tensile strength drops to 19.4 N·m·g^-1 after 1 h of beating.As the beating time increases to 5 h,the tensile strength of the polyimide paper was reduced to 8.2 N·m·g^-1.The unbeaten polyimide-based paper has a gas permeability of 582 mm/s at 200 Pa and a gas permeability of 220 mm/s when beaten to 5 hours.The degree of oxidation of bacterial cellulose increases as the amount of Oxidizer-H increases,and the fibers become finer and finer.When the bacterial cellulose treated with Oxidizer-H was added in an amount of 1 mmol·g^-1,the tensile strength was 16.56 N·m·g^-1,which was 120.8%higher than that of the polyimide-based paper without added bacterial cellulose.The polyimide-based paper to which no bacterial cellulose was added had a gas permeability of 257 mm/s at200 Pa,and the addition of Oxidizer-H to 1 mmol·g^-1 of treated bacterial cellulose reduced the air permeability by 12.5 mm/s.?2?The battery separator paper substrate was prepared by using polyimide fiber with beating for 5h.After drying,the bacterial cellulose was treated by vacuum adsorption on the surface of sodium hypochlorite.The polyimide/cellulose battery was prepared.Diaphragm paper.Exploring the effect of different amounts of bacterial cellulose on the performance of the composite membrane.The optimal addition formula was selected,and the structure and electrochemical performance of the separator were further explored by scanning electron microscopy,micro-CT,thermal gravimetric analysis,heat shrinkage,AC impedance performance,and battery performance test.The results show that the properties of polyimide/cellulose composite battery separators are significantly improved in terms of heat shrinkage,liquid absorption rate and ionic conductivity.The composite separator has a heat shrinkage rate of<1%at 200°C,a tensile strength of 16.56 N·m·g^-1,a porosity of 67.69%,a liquid absorption rate of 255%,and an ionic conductivity of1.62 mS/cm.The polyimide/cellulose composite battery separator has excellent stable cycle performance and good rate performance compared to the commercial Celgard 2340separator.The polyimide/cellulose composite battery separator exhibits excellent safety characteristics,indicating that the composite separator can be used as a candidate for high-end lithium ion batteries.