Preparation Of Zeolite Imidazolide Framework (ZIFs)-based Materials And Its Application As A Lithium Ion Battery Separator

With the development of new energy vehicles,the performance of lithium-ion batteries has received great attention.As one of the three important components of lithium-ion batteries,separators have become the focus of research in recent years.Among them,improving the safety of batteries is the top priority in the development of lithium-ion batteries.For now,the type of commercial separator is usually polyolefins.This type of diaphragm is widely used in the production of lithium ion batteries because of its good toughness and relatively stable electrochemical performance.First of all,from the perspective of battery safety,polyolefin-based separators have poor high-temperature performance.When the battery temperature increases,the separator is easily pierced and deformed,resulting in a smaller contact area between the separator and the positive and negative electrodes.Causes the positive and negative electrodes to contact and cause the battery to short circuit.Second,the ordinary polyolefin-based separator has poor lyophilic ability.When it is in contact with the electrolyte,due to the disadvantages of poor wettability and the like,the charge-discharge rate of the battery at a high rate is limited,and the electrochemical performance of the battery is affected.Therefore,finding the separator with good thermal stability and excellent electrochemical performance has become the focus of research.Zeolite imidazolate framework material（ZIFs）is a special framework material with a large porosity,so it can be used as a lithium ion battery separator.In addition,ZIFs have good thermal stability and can maintain structural stability at higher temperatures,preventing short circuits in batteries.In this paper,ZIFs were used as the substrate to fabricate lithium ion battery separators,and the electrochemical performance of ZIFs based separators was further studied.The main research contents are as follows:（1）An electrode support membrane was prepared by directly coating a zirconium imidazolate skeleton structure ZIF-4 slurry on the electrode material Li[Ni_1/3Co_1/3Mn_1/3]O₂,and the porosity and the liquid absorption rate of the membrane were obtained.As well as invasive properties such as test characterization.The results show that compared with the traditional polypropylene（PP）separator materials,the porosity and the liquid-absorption rate of the ZIF-4 separator are obviously better than those of the PP separator,and the ZIF-4 separator has good infiltration performance to the electrolyte.Liquid retention properties.Through the ionic conductivity test,it can be found that the ionic conductivity of the ZIF-4separator is higher.The battery using ZIF-4 separator at the same time has good electrochemical performance.Under the discharge rate of 1 C(150 mAh g^-1),the discharge capacity is obviously higher than that of the battery using PP separator.The high-temperature performance test results show that the ZIF-4 separator has better thermal stability than the PP separator and no deformation occurs at high temperatures,which is of great significance for improving the safety of the battery.（2）Prepare zeolite membrane imidazole ester framework structure ZIF-8 by hydrothermal method,and apply it directly on the surface of NCM cathode material,and measure its porosity,liquid absorption rate and liquid retention rate.Through testing,it was found that the physical properties of the ZIF-8 separator are excellent.And the conductivity of the ZIF-8 diaphragm is significantly higher than the PP diaphragm.Through its electrochemical performance tests,it is found that the ZIF-8separator has good cycle stability and high specific discharge capacity,which is of great significance for improving the overall battery capacity.The battery consisting of the ZIF-8 diaphragm was exposed to a high temperature of 55°C.The ZIF-8diaphragm exhibited excellent electrochemical performance.Therefore,the ZIF-8separator exhibits good thermal stability,which provides an important guarantee for improving the safety performance of the battery.（3）Based on the above two studies,ZIF-8 with excellent physical and electrochemical properties was combined with a conventional PP separator to achieve surface modification of the PP separator.The results show that the modified separator has excellent electrochemical performance compared with the unmodified separator,and its wetting ability with the electrolyte is also greatly improved,and effectively increases the absorption of the electrolyte and ensure Liquid capacity improves battery capacity and cycle stability.The test found that after 200 cycles,the battery stability and discharge specific capacity of the modified PP separator were significantly better than those of unmodified PP separator.