The Preparation And Related Performance Study Of Graphene Composite Separator

With the popularization of portable electronic devices and the development of electric vehicles,the performance requirements of lithium-ion batteries are increasing.As an important part of the lithium-ion battery,the separator not only isolated positive and negative extremely,but also determines the internal resistance of the battery and has effects on the energy density,rate performance,cycle performance and safety performance of the battery.Therefore,there are important significance on the research of the separator's performance for lithium-ion batteries and Lithium-sulfur batteries.On the other hand,there are few study on this compared to electrode material.In this paper,we develop the study of grapheme and the preparation that is the composite conductive functional separator combined with the commercial separator has excellent lithium ion permeability and unilateral(graphene layer)conductivity which is considered on the perspective of improving the diffusion of ions and electrons.Finally,we can get the new type separator which have excellent lithium ion permeability and unilateral(graphene layer)conductivity.Firstly,the graphene/PVDF composite separator was prepared and its performance was studied.We use graphene/PVDF functional layer coating on the commercial separator and the flexible graphene layer formed into three-dimensional conductive network which can increase the contact area of the separator and electrolyte and also can enhance solubility with the electrolyte due to the polarity of the PVDF.The combination of graphene and polyethylene not only improved the invasion of the separator and electrolyte and the diffusion of ions and electrons,but also enhanced the thermal stability.The graphene/PVDF composite separator was applied in the lithium-ion batteries which use LiFePO4 as positive,the capacity was about 120mAh/g at 2C which was three times compared to PP separator.The capacity can remain above80mAh/g at 5C.This indicated that the rate performance of Lithium-ion batteries can be improved by increase the diffusion of ions and electrons.This method is simple,easy tooperate and easy to be industrialized.Secondly,we prepared the porous composite separator coated by graphene/ PVDF using the method of water bath treatment.We can control the pore structure of the coating through this method.The porous coating layers can form into three dimensional conductive gel network after imbibition which can better absorbing and preserving the liquid and easy to transport the ions and electrons compared with dense separator.The porous composite separator coated by graphene/PVDF applied in the lithium-ion batteries which use LiFePO4 as positive,the capacity was about 110mAh/g at 5C and the capacity was close to 100% after 600 cycles.The using of the porous graphene/PVDF composite separator in lithium-ion batteries not only can absorb and barrier the sulfur ion,but also can improve the rate performance and cycling stability through the rapid transmission of lithium ion and electron.This study provides a new method for the preparation of long life,fast charge and high power lithium-ion batteries and Lithium-sulfur batteries.