Preparation And Performance Of High Safety Lithium Ion Battery Separator

Compared with traditional electrochemical energy storage devices,lithium-ion batteries have a series of excellent performances such as high specific capacity,long cycle life,and rapid charge and discharge,and have attracted much attention in the field of electrochemical energy storage devices,and have been widely used in civil electronic equipment,new energy electric vehicles,aerospace technology,national defense technology and other important fields.However,the increasing demand for the energy density of lithium-ion batteries has led to more and more potential safety hazards.Separator is one of the important components of lithium-ion batteries,but also its safety and stability of the primary guarantee,the current commercial lithium-ion battery mainly uses polyethylene（PE）separator,polypropylene（PP）separator,or the above base film of ceramic coated separator,such traditional separator has poor thermal stability and other shortcomings.Therefore,in order to solve the above problems,the following two research works are carried out in this paper:（1）With polyimide（PI）as the core material and polyvinylidene fluoride（PVDF）as the shell material,the coaxial nanofiber composite separator was prepared.Taking Celgard 2400 commercial diaphragm as a reference,PI/PVDF diaphragm has smaller heat shrinkage at 200°C,and has excellent flame retardant properties,and has excellent electrolyte wettability and liquid retention due to its higher porosity,thereby reducing the interfacial impedance and improving the lithium-ion conductivity.The initial discharge specific capacity of the high-voltage LiCoO2/Li battery shows excellent high rate performance.The accelerated calorimeter（ARC）test showed that the thermal runaway starting temperature of the battery was 190°C,indicating that the PI/PVDF separator had excellent safety performance.（2）The commercial 7μm thickness PE separator was used as the base film,and the AL₂O₃ coating was carried out by atomic layer deposition technology（ALD）to obtain the ALD-PE separator.The physical properties of the diaphragm are characterized,and the results show that the diaphragm has higher mechanical strength than the PE diaphragm,the tensile strength is high to 105MPa,and it has good electrolyte affinity,the lowest contact angle is 6.7°,and the heat shrinkage performance is much better than that of the traditional PE diaphragm.The thermal runaway test shows that compared with the traditional PE separator,the ALD-PE separator with 75 times plating has excellent performance to suppress thermal runaway.