Preparation And Properties Of Ultra-high Molecular Weight Polyethylene Resins For Lithium Battery Diaphragm

With the continuous changes in the global energy structure,non-renewable energy sources are gradually being exploited and exhausted.Now we need to seek a renewable and green new energy source to meet our daily needs.As the focus of the new energy industry,lithium batteries have the advantages of good durability,high-energy density,high-specific capacity and high-safety performance,and have gradually attracted widespread attention.As an important part of its internal structure,the lithium battery separator affects the permeability,porosity,safety and other properties of the lithium battery.The separator is usually an insulating porous polymer film that prevents direct contact between the positive electrode and the negative electrode,but allows lithium ions to be exchanged between the two electrodes.UHMWPE is the material of choice for the manufacture of diaphragms because of its excellent chemical inertness,wear resistance and extremely high mechanical strength.There are three main catalysts for preparing UHMWPE,which is Ziegler-Natta catalyst,metallocene catalyst and non-metallocene catalyst.Since Ziegler-Natta catalyst has the advantages of high catalytic activity,uniform product particle size,and low preparation cost,it has attracted extensive attention in the academic circles since its introduction,and has quickly occupied a dominant position in the catalysts of the polyolefin industry.This paper mainly studies a Ziegler-Natta catalyst for the synthesis of UHMWPE lithium battery separators.The main research contents are as follows:（1）The performance of Ziegler-Natta catalysts was investigated in terms of internal electron donor,aging reaction temperature,aging and titanium wash.The catalysts were characterized by element content,particle size and particle size distribution,scanning electron microscopy（SEM）,energy dispersive X-ray spectroscopy（EDS）.The experimental results show that the addition of TEOS is beneficial to increase the catalytic efficiency of Ti active centers,increasing the reaction temperature and increasing the aging process is beneficial to optimizing particle morphology.We obtained Gz-1#catalyst with uniform element distribution,good particle shape,concentrated particle size distribution and good mechanical strength,which has good comprehensive performance and can maintain the long-term stable operation of the production unit.（2）We synthesized UHMWPE numbered S₁～S₅,which were catalyzed with Gz-1#～Gz-5#catalysts as the main catalyst and triethylaluminum（TEA）as the cocatalyst,respectively.The molecular weight,particle size and distribution,morphology,melt index,bulk density,density and crystallization properties of UHMWPE were analyzed by Ubbelohde viscometer,laser particle size distribution analyzer,SEM,melt flow rate analyzer,bulk density meter,density balance and differential scanning calorimeter,respectively.The results show that:S₁ has the best comprehensive performance and is the most suitable for lithium battery separator.（3）The molecular weight,mesh number and mesh number distribution,morphology,melt index,bulk density,crystallization properties and swelling properties of S₁ and the reference UHMWPE powder were compared and analyzed.The results showed that:S₁product has the highest molecular weight and bulk density,more concentrated mesh number distribution,less fine powder content,rougher particle surface,uniform particle size,and good swelling effect.Suitable for making lithium battery separators.（4）Using the wet-process lithium battery diaphragm experimental device,the S₁ resin was made into diaphragm 1#through engineering processes such as plasticization,extrusion,biaxial stretching,washing and drying,and the self-made 1#was prepared with the reference UHMWPE resin.The performance comparison of lithium battery separators was carried out.The results show that the 1#separator is in good plasticized state,with uniform thickness,and the puncture strength,porosity and other indicators are comparable to the lithium battery separator prepared by the comparative UHMWPE resin,which meets the needs of lithium battery separator production.