Method for preparing high temperature resistant composite separator by lithium ion battery

Abstract

The invention discloses a method for preparing a high temperature resistant composite separator by a lithium ion battery, and belongs to the field of lithium ion battery separators. The method comprises the following steps: active groups are introduced into the surface of a polyolefin microporous film and a micropore through the surface pretreatment of a substrate film, silica sol is prepared by a sol-gel method, and a silica coating is introduced, and is bonded with the substrate film by a chemical bond. The method is simple in preparation process, low in requirement on equipment, and easy to realize the industrialization; the prepared composite separator has the advantages of high mechanical strength, good air permeability, good high temperature resistance, high ionic conductivity, and good adhesion property of silica coating and polyolefin microporous film, and the silica coating is not easy to fall off, so that the safety performance and the comprehensive property of the separator are improved.

Description

technical field [0001] The invention belongs to the field of lithium-ion battery diaphragm materials, and in particular relates to a preparation method of a high-temperature-resistant composite diaphragm for lithium-ion batteries. Background technique [0002] Lithium-ion batteries are considered to be one of the most promising forms of new energy power due to their excellent electrical properties such as high energy density, long cycle life, and high voltage, and have become a research hotspot for second-generation batteries today. At present, it has been widely used in the fields of small electronic products such as mobile phones, portable computers, cameras, and video cameras, and has gradually expanded to the fields of electric vehicles, electric bicycles, and large power supplies. Therefore, it has higher safety performance and electrochemical performance of lithium batteries. requirements. [0003] In the structure of lithium batteries, although the separator does not...

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Problems solved by technology

Although these technologies are simple and convenient, the adhesion between the base film and the coating of the composite film has not been well resolved, thus affecting the safety performance of the diaphragm, and the heat resistance of the film is not much improved.

[0010] JP2004014127A discloses a technology of forming an inorganic oxide porous film on an organic film by a sol-gel method. Even if the internal organic film melts at high temperature, the inorganic layer can still prevent a large-area short circuit inside the battery and improve the safety performance of the separator. However, it is difficult to control the distribution of porosity on the inorganic membrane, and it is also difficult to control the adhesion between the inorganic membrane and the separator substrate, so it is necessary to improve

[0011] CN 101710614 B, US 20110171523 A and CN 102064301 A report adding inorganic particles or heat-resistant resins during the extrusion and stretching of polyolefin diaphragms to improve the heat resistance of the film. These methods have higher requirements for equipment, so The cost is increased. Due to the existence of inorganic particles, the basic properties of the membrane, such as air permeability, porosity, pore size, and thickness, cannot be well controlled within a certain range, so it cannot be effectively applied and cannot meet the needs of high-end lithium batteries. needs

[0012] Due to the special closed-cell properties of polyolefin microporous membranes, current commercial low-power lithium-ion batteries mainly use PE, PP or PP and PE multilayer composite separators. However, it is difficult for them to ensure the integrity at high temperatures. In the case of high discharge current, excessive discharge current or thermal inertia during the heating process of the electrolyte, even if the current is blocked, the battery temperature may continue to rise, making the diaphragm easily damaged, resulting in a large area of ​​short circuit, and even causing the battery to explode. The safety performance is low, and it cannot meet the higher safety and electrochemical performance requirements of high-energy lithium-ion batteries

[0013] In view of the suitable closing temperature of polyolefin microporous membrane and the wide application of commercial PE and PP separators, people try to modify it to improve its safety performance, but because polyolefin is a non-polar material, its surface is not active. At present, the more commonly used modification method is simple coating coating, which relies on physical force to bond the coating and the surface of the film, so the adhesion is not strong, and the coating is easy to fall off

In order to improve the adhesion between the substrate film and the coating, people try to introduce chemically bonded -NH on the surface of the film. 2 , -OH, -COOH and other polar groups, so that the surface of the film is converted from non-polar to polar, thereby improving the adhesion between the inorganic layer and the substrate film, such as chemical oxidation, plasma polymerization, electron beam radiation , ozone treatment, ultraviolet radiation and other methods, the group grafting rate of the chemical oxidation method is too low, and other technologies themselves are too complicated, have high requirements for equipment, and the cost is relatively high, so they cannot be industrialized well. application

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