East China Institute of Technology develops new ultra-thin boehmite coated diaphragm to enhance the safety of lithium-ion batteries
Recently, Chongwen Yang and others from Huazhong University of Science and Technology have developed a Boehmite (AlOOH) coated membrane that can significantly reduce the thickness of the coating by 1.15um while maintaining thermal stability. Mainly because the PE reaches 140 ° C after melting, AlOOH and PE merge to form a stable interface structure, thus preventing the PE membrane from continuing to shrink.
Safety has always been the focus of lithium-ion batteries. With the increasing energy density of lithium-ion batteries, non-active materials such as diaphragms are also continuously thinning, which makes the safety risk of lithium-ion batteries continue to rise. The fiery Samsung Note 7 mobile phone explosion is believed to be due to the pursuit of high energy density, which leads to thinning of the diaphragm, which makes the battery safer and the battery will explode under certain circumstances. In order to improve the safety of lithium-ion batteries, especially in the special case of short circuit and needling, a new type of coated diaphragm has been developed. In the event of a short circuit or internal short circuit, the inside of the battery is overheated and coated. The layer treated membrane can effectively prevent high temperature shrinkage, thereby avoiding direct contact between the positive and negative electrodes, causing more serious thermal runaway and avoiding serious safety problems such as fire and explosion of the battery.
Conventional coated membranes generally use Al2O3 or MgO particles as raw materials, and the coating thickness is generally 2-3um. Recently, Chongwen Yang et al. from Huazhong University of Science and Technology developed a Boehmite (AlOOH) coated separator, according to Chongwen. Yang said that the diaphragm can greatly reduce the thickness of the coating by 1.15um under the premise of ensuring the thermal stability. This is mainly because the PE and the PE are melted and the AlOOH and PE merge to form a stable interface structure. In order to prevent the PE diaphragm from continuing to shrink, the research results have been published in the latest issue of the Journal of PowerSource.
In the experiment, Chongwen Yang dissolved AlOOH particles (35%) with an average diameter of 350 nm and polyvinyl alcohol PVA (1%) in deionized water, and then applied a layer on the front and back sides of the 16 μm PE separator by roller coating equipment. The above slurry (1.15 um) was then dried at 60 ° C for 24 h, and the thickness of the coating layer was controlled by controlling the speed of the roll coating. Chongwen Yang tested the shrinkage and wettability of the modified and unmodified membranes, as well as the ionic conductivity, to compare the performance of the two membranes.
In the other performance tests performed on the separator, the results are shown in the following table. From the results, the modified diaphragm has only a slight decrease in the needle strength and tensile strength, but in terms of gas permeability compared to the original PE separator. There is a 20% drop, which will have a certain effect on ion migration, but fortunately this disadvantage is offset by the good wettability of the AlOOH modified membrane. The wetting angle of the original PE membrane is 42.5 degrees, while AlOOH The wetting angle of the modified separator was 0 degree, indicating that the modified separator has excellent electrolyte wettability.
Ionic conductivity is also an important indicator affecting the ion permeability of the diaphragm. The ion conductivity test is to make the diaphragm into a button cell, then test it by AC impedance, and then calculate it by the following formula, where d and S are diaphragms respectively. The thickness and area, Rb is the equivalent resistance. The test results show that the ionic conductivity of the AlOOH modified separator is 6.56'10-3S/cm, while the ionic conductivity of the original PE separator is only 3.48'10-3S/cm.
Chongwen Yang also made LTO half-cells using the above diaphragms to test the rate performance and cycle performance of the modified diaphragm. The test results are shown in the figure below. From the results of the rate test, at higher rates (1C and 2C), the AlOOH modified membrane has better performance. The cycle test also showed that the AlOOH coating treatment can improve the cycle performance of the battery. After circulating 100 times at 1 C rate, the capacity retention rate of the AlOOH modified separator battery was 96.3%, while the capacity retention rate of the original PE separator battery was 94.6%.
Studies have shown that the modified separator can also significantly improve the overcharge performance of the battery. The following figure is an experiment of overcharging to 10V at 3C rate using an AlOOH modified separator and an ordinary PE separator LFP battery. In Figure a, the original is used. After the battery of PE separator is overcharged for 15 minutes, the battery leaks and a large amount of white smoke is emitted. The surface temperature of the battery reaches 104.8 °C, while the battery with AlOOH modified diaphragm does not leak or smoke during the overcharging process, and the surface temperature of the battery reaches 103.4 ° C.
In general, the AlOOH coating can significantly improve the thermal stability of the separator at a lower coating thickness, improve the safety of the lithium ion battery, improve the rate performance and cycle performance of the battery, and at the same time be thinner. The coating thickness helps to increase the volumetric energy density and weight energy density of the lithium ion battery.
Safety has always been the focus of lithium-ion batteries. With the increasing energy density of lithium-ion batteries, non-active materials such as diaphragms are also continuously thinning, which makes the safety risk of lithium-ion batteries continue to rise. The fiery Samsung Note 7 mobile phone explosion is believed to be due to the pursuit of high energy density, which leads to thinning of the diaphragm, which makes the battery safer and the battery will explode under certain circumstances. In order to improve the safety of lithium-ion batteries, especially in the special case of short circuit and needling, a new type of coated diaphragm has been developed. In the event of a short circuit or internal short circuit, the inside of the battery is overheated and coated. The layer treated membrane can effectively prevent high temperature shrinkage, thereby avoiding direct contact between the positive and negative electrodes, causing more serious thermal runaway and avoiding serious safety problems such as fire and explosion of the battery.
Conventional coated membranes generally use Al2O3 or MgO particles as raw materials, and the coating thickness is generally 2-3um. Recently, Chongwen Yang et al. from Huazhong University of Science and Technology developed a Boehmite (AlOOH) coated separator, according to Chongwen. Yang said that the diaphragm can greatly reduce the thickness of the coating by 1.15um under the premise of ensuring the thermal stability. This is mainly because the PE and the PE are melted and the AlOOH and PE merge to form a stable interface structure. In order to prevent the PE diaphragm from continuing to shrink, the research results have been published in the latest issue of the Journal of PowerSource.
In the experiment, Chongwen Yang dissolved AlOOH particles (35%) with an average diameter of 350 nm and polyvinyl alcohol PVA (1%) in deionized water, and then applied a layer on the front and back sides of the 16 μm PE separator by roller coating equipment. The above slurry (1.15 um) was then dried at 60 ° C for 24 h, and the thickness of the coating layer was controlled by controlling the speed of the roll coating. Chongwen Yang tested the shrinkage and wettability of the modified and unmodified membranes, as well as the ionic conductivity, to compare the performance of the two membranes.
In the other performance tests performed on the separator, the results are shown in the following table. From the results, the modified diaphragm has only a slight decrease in the needle strength and tensile strength, but in terms of gas permeability compared to the original PE separator. There is a 20% drop, which will have a certain effect on ion migration, but fortunately this disadvantage is offset by the good wettability of the AlOOH modified membrane. The wetting angle of the original PE membrane is 42.5 degrees, while AlOOH The wetting angle of the modified separator was 0 degree, indicating that the modified separator has excellent electrolyte wettability.
Ionic conductivity is also an important indicator affecting the ion permeability of the diaphragm. The ion conductivity test is to make the diaphragm into a button cell, then test it by AC impedance, and then calculate it by the following formula, where d and S are diaphragms respectively. The thickness and area, Rb is the equivalent resistance. The test results show that the ionic conductivity of the AlOOH modified separator is 6.56'10-3S/cm, while the ionic conductivity of the original PE separator is only 3.48'10-3S/cm.
Chongwen Yang also made LTO half-cells using the above diaphragms to test the rate performance and cycle performance of the modified diaphragm. The test results are shown in the figure below. From the results of the rate test, at higher rates (1C and 2C), the AlOOH modified membrane has better performance. The cycle test also showed that the AlOOH coating treatment can improve the cycle performance of the battery. After circulating 100 times at 1 C rate, the capacity retention rate of the AlOOH modified separator battery was 96.3%, while the capacity retention rate of the original PE separator battery was 94.6%.
Studies have shown that the modified separator can also significantly improve the overcharge performance of the battery. The following figure is an experiment of overcharging to 10V at 3C rate using an AlOOH modified separator and an ordinary PE separator LFP battery. In Figure a, the original is used. After the battery of PE separator is overcharged for 15 minutes, the battery leaks and a large amount of white smoke is emitted. The surface temperature of the battery reaches 104.8 °C, while the battery with AlOOH modified diaphragm does not leak or smoke during the overcharging process, and the surface temperature of the battery reaches 103.4 ° C.
In general, the AlOOH coating can significantly improve the thermal stability of the separator at a lower coating thickness, improve the safety of the lithium ion battery, improve the rate performance and cycle performance of the battery, and at the same time be thinner. The coating thickness helps to increase the volumetric energy density and weight energy density of the lithium ion battery.
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