Preparation Of Zirconia Coaxial Coated Polyimide Nanofiber Membrane And Its Application As Separator For Lithium Ion Battery

Lithium-ion batteries have been widely used in various fields of daily life due to their many outstanding advantages.In recent years,with the increasing demand for energy and the continuous optimization of energy structure,the proportion of lithium-ion batteries in the field of new energy has increased year by year,people have put forward higher requirements for the safety of high-capacity high-energy lithium-ion batteries.Conventional polyolefin separators are difficult to meet the requirements of high temperature safety and high rate charge and discharge due to their poor temperature resistance and electrolyte wettability.Therefore,the development of a new type of lithium ion battery separator with high temperature resistance and high wettability has become an increasingly popular topic.The polyimide nanofiber membrane prepared by the electrospinning method not only has the inherent temperature resistance and chemical stability of polyimide,but also has a high specific surface area and a high liquid retention rate of the nanofiber membrane.This makes it a great prospect in the field of lithium ion battery separators.The "inorganic ceramics" modification which coatsthe surface of the polyimide nanofibers with a layer of inorganic ceramic particles,can not only achieve the regulation of the pore structure of the fiber membrane and the improvement of the mechanical properties,but also make it possible to cover the hydrophobic groups on the surface and further improve the wettability and temperature resistance of the fiber membrane,which has been the focus of attention in recent years.In this paper,two methods of surface inorganic nanoparticle loading,in situ adsorption alkaline hydrolysis and in situ complexation deposition were proposed to prepare polyimide nanofiber membranes coated with zirconium dioxide.In situ adsorption alkaline hydrolysis method is characterized by strong adsorption of strong polar groups on the surface of PI nanofiber membrane.First,a layer of zirconium oxychloride solution is adsorbed on the surface of nanofiber by impregnation method.Then put zirconium oxychloride in an alkaline gas atmosphere to make it fully hydrolyzed Finally,a high temperature heat treatment is performed to remove excess solvent and other impurities to obtain a polyimide-coated nanofiber membrane coated with zirconium dioxide.The in situ complexation deposition method is based on the mechanism that the preliminary hydrolysis product of zirconium oxychloride under the action of H2O2 can complex with the carboxyl group on the surface of the PI nanofiber after the alkali decompression,so that the hydrolyzed product is complexed on the surface of the fiber.First,the hydrolyzed product is complex-grown on the surface of the fiber to form a complex layer of zirconium.The imide ring is then reclosed by high temp erature heat treatment while the zirconium complex layer is converted to zirconium dioxide.Finally a polyimide composite nanofiber membrane coated with zirconium dioxide was obtained.In this paper,the in-situ adsorption alkaline hydrolysis method and in situ complexation deposition method successfully achieved the coaxial coating of zirconium dioxide on the surface of polyimide nanofibers.Then the microstructure,thermal decomposition temperature,mechanical properties,thermal stability,electrolyte affinity,porosity and liquid absorption rate of the composite nanofiber membrane were evaluated by various characterization methods and its application as a separator for lithium ion batteries was studied.The results show that the loading of zirconium dioxide greatly improves the pore structure and mechanical strength of the fiber membrane,and further improves the temperature resistance,dimensional stability and wettability of the nanofiber membrane.When the composite nanofiber membrane is used as a lithium ion battery separator,it exhibits higher ionic conductivity,discharge specific capacity,and cycle performance than the Celgard separator.It can be used as a new type of high performance separator to meet the needs of high-capacity,high-energy lithium-ion batteries.