Preparation And Lithium-ion Battery Separator Application Performance Of Submicron Boehmite

In recent years,the synthesis of inorganic materials with different particle sizes and the structure-activity relationship of inorganic materials have been one of the hotspots in the field of materials and chemistry.Boehmite is an important new chemical material,which is widely used in catalysts and supports,flame retardants and lithium-ion battery separator coatings due to its abundant surface hydroxyl groups.Especially in the field of lithium-ion battery separator,boehmite has gradually replaced alumina as the mainstream coating material for lithium-ion battery separator due to its advantages of low hardness,low specific gravity,high coating flatness,and low production cost.The purpose of this paper is to investigate the synthesis of boehmite with different particle sizes and its size effect on the application of lithium-ion battery separator.The strategy is to prepare submicron boehmite by hydrothermal method using industrial aluminum hydroxide as raw material.The effect of hydrothermal synthesis conditions and raw materials on the particle size of boehmite are systematically investigated,and the reaction mechanism for preparing different particle sizes of boehmite by adding seeds and activating raw materials are further explored.Moreover,the effect of different particle sizes of boehmite on the performance of the modified separators are investigated,and the physical and electrochemical properties of the separators are tested.The main research content is as follows:（1）Study on the effect of hydrothermal synthesis conditions on the particle size of boehmite.Boehmite was prepared by hydrothermal method using industrial aluminum hydroxide as raw material.The effects of different conditions,including hydrothermal temperature,hydrothermal time,stirring speed,seed content and solid-liquid ratio on the microstructure and particle size of the product boehmite were investigated.The results showed that the hydrothermal temperature and hydrothermal time have an effect on the hydrothermal reaction conversion rate,but have no obvious effect on the morphology and size of the product.The size of the product did not change significantly under static and different stirring speeds.The different particle sizes of boehmite could be obtained by adding appropriate amount of seeds,and the primary particle size of boehmite could be adjusted in the range of 300～2000 nm.Under the condition of high solid-liquid ratio（1:4～1:3）,the addition of seeds could still achieve the regulation of boehmite particle size.（2）Study on the effect of raw material particle size and activity on the particle size of boehmite.Boehmite was prepared by hydrothermal method using activated industrial aluminum hydroxide as raw material.The effects of raw material particle size and activation conditions on the particle size of boehmite were investigated,and the size control mechanism was discussed.The results showed that the size distribution of raw materials could affect the size distribution of boehmite,and the average particle size of boehmite could be effectively reduced by grinding aluminum hydroxide raw materials.Moreover,after the heating activation of aluminum hydroxide（160～220°C）,the particle size of the hydrothermal products could be adjusted in the range of 300～2000 nm.The mechanism was inferred from the structural analysis that a small amount of boehmite was generated during the heating activation of aluminum hydroxide.These boehmite acted as seeds during the hydrothermal conversion of aluminum hydroxide to boehmite.With the increased of activation temperature and activation time,the amount of boehmite seeds increased,the particle size of the hydrothermal products of aluminum hydroxide decreased,and the hydrothermal reaction rate was accelerated.（3）Preparation and performance study of polyethylene separators coated with different particle sizes of boehmite.The water-based slurry of boehmite was coated on one side of PE separator by doctor-blade coating method.The effect of different particle sizes of boehmite on the performance of the modified separator were investigated.The results showed that the modified separators BM-X/PE exhibited better thermal stability,higher electrolyte uptake and ionic conductivity compared with PE separator.The performance of the modified separator was the best when the particle size of coated boehmite is 0.5μm.The battery assembled with BM-0.5/PE separator was cycled for 1000 cycles at 1 C,the discharge capacity decreased from 132.8 m Ah g^-1to 95.6 m Ah g^-1with the capacity retention rate of 72.0%,while the capacity retention rate of PE separator was only 52.4%.