阅读说明：本技术 一种耐热动力锂电池隔膜的制备方法及其制备方法 (Preparation method and preparation method of heat-resistant power lithium battery diaphragm ) 是由 胡伟 何祥燕 杨建军 李汪洋 吴磊 张德顺 张建安 陈曼 刘久逸 吴明元 吴庆云 于 2020-12-31 设计创作，主要内容包括：本发明属于属于高分子材料领域,尤其是一种耐热动力锂电池隔膜的制备方法及其制备方法,制备方法简单、原料来源广泛,本发明采用以聚烯烃为主要原料,采用聚1-丁烯改善隔膜的耐热性能,经熔融挤出基膜、热处理、多层复合、拉伸成孔、分层、分切等工艺生产出锂电池隔膜,产品具有孔隙分布均匀,收缩比小,穿刺强度高等特点,可广泛应用于新能源汽车动力锂离子电池,储能锂离子电池及数码锂离子电池等。(The invention belongs to the field of high polymer materials, and particularly relates to a preparation method and a preparation method of a heat-resistant power lithium battery diaphragm, wherein the preparation method is simple and wide in raw material source.)

1. The preparation method of the heat-resistant power lithium battery diaphragm is characterized in that the cleanliness of a production workshop from the outer package to the inner package process after the outer package is removed and the raw and auxiliary materials enter a clean area is ten thousand, and the preparation method comprises the following steps:

(1) drying raw materials of polypropylene, polyethylene and poly-1-butylene, extruding, casting and co-extruding the raw materials into a film by a double-screw extruder, and controlling the thickness of each layer to prepare a three-layer casting composite film consisting of a PP layer, a PB-1 layer and a PE layer; (2) annealing the prepared three-casting film at a high temperature of 100-115 ℃ to form regular platelets; (3) stacking the annealed 35-40 three layers of casting films in a laminating manner, and stretching and forming holes together, wherein the stretching ratio is 1.5-3.0 times; (4) and (3) stacking and layering the stretched and formed holes, and stripping a three-layer casting composite film consisting of a PP layer, a PE layer and a PB-1 layer, namely the heat-resistant power lithium battery diaphragm.

2. The method for preparing a heat-resistant power lithium battery separator as claimed in claim 1, wherein the poly-1-butene is a poly-1-butene having an isotacticity of 80-86% and a melt index of 0.4-1.0 g/10 min.

3. The method of claim 1, wherein the PE layer is a second fused closed pore layer with a fusing temperature of 130 ℃ to 150 ℃, and the PB-1 layer is a first fused closed pore layer with a fusing temperature of 125 ℃ to 145 ℃.

4. The method for preparing a heat-resistant power lithium battery diaphragm according to claim 1, wherein the raw material of the PE layer is high-density polyethylene with a melt index of 0.04-0.055 g/10 min.

5. The method for preparing a heat-resistant lithium battery separator as claimed in claim 1, wherein the lithium battery separator has a thickness of 20 to 30 μm; the thickness of the PP layer is 4-10 micrometers, and the thickness of the PE layer is 4-10 micrometers; the thickness of the PB-1 layer is 4-10 micrometers, and the porosity of the PB-1 layer is 50% -70%.

6. The method for preparing a heat-resistant power lithium battery separator as claimed in claim 1, wherein the temperature of the forced air drying in the step (1) is 60-80 ℃ and the drying time is 2-5 hours.

7. The method for preparing a heat-resistant power lithium battery separator as claimed in claim 1, wherein the twin-screw extruder in step (1) comprises six zones, wherein the temperature and the screw rotation speed of each zone of poly-1-butene are respectively as follows: the temperature of the first area is 125-130 ℃, the temperature of the second area is 125-130 ℃, the temperature of the third area is 130-135 ℃, the temperature of the fourth area is 140-155 ℃, the temperature of the fifth area is 145-160 ℃, the temperature of the sixth area is 145-160 ℃, and the temperature of the machine head is 145-150 ℃; the rotating speed of the screw is 150 to 200 r/min.

Technical Field

The invention belongs to the technical field of high polymer materials, and particularly relates to a preparation method and a preparation method of a heat-resistant power lithium battery diaphragm.

Background

The diaphragm is a key part of the lithium ion battery, plays the electronic conductance of negative and positive electrodes in the battery, allows electrolyte ions to freely pass through so as to realize the important function of ion conduction, and is an important determinant factor of battery capacity, cycle capacity and safety performance. The requirements of the power battery on high-power output performance and safety provide great challenges for the lithium battery, and during high-power discharge, the local temperature of the battery reaches about 100 ℃ to cause the decomposition of a negative Solid Electrolyte Interface (SEI) protective film and release heat, so that the battery is further heated to cause the decomposition of organic electrolyte and other substances and the melting of a diaphragm (Melt-down), and direct reaction and even explosion of a positive electrode and a negative electrode are caused. A puncture or impact experienced by the battery during use may also cause the battery voltage to drop momentarily. The sharp increase in current generates a large amount of heat, which causes the temperature to rapidly rise, thereby subjecting the battery separator to a high temperature state. In addition, the overcharge of the battery causes the deposition of lithium metal on the surface of the negative electrode to form lithium dendrites, and the penetration of the separator is also caused, which is aggravated by the operation of the power battery under dynamic conditions. The lithium ion battery diaphragm has the functions of separating the positive electrode and the negative electrode of the battery, preventing the positive electrode and the negative electrode from contacting to cause short circuit, allowing ions to pass through but not allowing electrons to pass through, and thus completing the rapid transmission of lithium ions between the positive electrode and the negative electrode in the charging and discharging process. At present, the preparation method of the lithium ion battery diaphragm mainly comprises dry-method unidirectional stretching, dry-method bidirectional stretching and wet-method processes, and the product mainly comprises a single-layer Polyethylene (PE) diaphragm, a single-layer polypropylene (PP) diaphragm, a double-layer PP/PE diaphragm and a double-layer PPPP diaphragm. The diaphragm material used for the automobile power lithium battery mainly comprises a three-layer PP/PE/PP composite diaphragm and a double-layer PP/PE diaphragm. Compared with the lithium battery for communication, the power lithium battery has the requirements of larger capacity, higher voltage, longer cycle life, higher safety performance, uniform performance of long-time stable output and capability of providing instant accelerated high-rate discharge performance for automobiles. Therefore, power lithium batteries put higher demands on the separator: the diaphragm has more uniform and consistent pore size distribution, higher mechanical strength, better heat resistance and better closed pore performance. PE and PP are difficult to melt, have large difference of crystallization temperature and have huge structural difference. The performance of a lithium battery diaphragm produced conventionally is difficult to meet the requirement of a power lithium battery, and for the defects of the performance of the current power lithium battery diaphragm, research institutions and production enterprises at home and abroad are actively dedicated to research and development and production of a high-performance power lithium battery diaphragm, but the current power lithium battery diaphragm cannot well meet the current use requirement, and technical personnel in the field need to develop a preparation method of a heat-resistant power lithium battery diaphragm urgently to meet the current performance requirement and market requirement.

Disclosure of Invention

In view of the above problems, the present invention is directed to a method for preparing a heat-resistant power lithium battery separator.

The invention is realized by the following technical scheme:

the preparation method of the heat-resistant power lithium battery diaphragm comprises the following steps of removing external packages from raw and auxiliary materials, entering a clean area, and keeping the cleanliness of ten thousand grades in a production workshop of an internal packaging process:

(1) drying raw materials of polypropylene, polyethylene and poly-1-butylene, extruding, casting and co-extruding the raw materials into a film by a double-screw extruder, and controlling the thickness of each layer to prepare a three-layer casting composite film consisting of a PP layer, a PB-1 layer and a PE layer; (2) annealing the prepared three-casting film at a high temperature of 100-115 ℃ to form regular platelets; (3) stacking the annealed 35-40 three layers of casting films in a laminating manner, and stretching and forming holes together, wherein the stretching ratio is 1.5-3.0 times; (4) and (3) stacking and layering the stretched and formed holes, and stripping a three-layer casting composite film consisting of a PP layer, a PE layer and a PB-1 layer, namely the heat-resistant power lithium battery diaphragm.

Further, the polyethylene is high-density polyethylene with a melt index of 0.04-0.055 g/10 min; the poly-1-butene has an isotacticity of 80-86% and a melt index of 0.4-1.0 g/10 min.

Furthermore, the PE layer is a second melting closed pore layer, the fusing temperature of the PE layer is 130-150 ℃, and the PB-1 layer is a first melting closed pore layer, and the fusing temperature of the PB-1 layer is 125-145 ℃.

Furthermore, the raw material of the PE layer is high-density polyethylene with a melt index of 0.04-0.055 g/10min, and the porosity of the PE layer is 38% -50%.

Further, the porosity of the PP layer is 38% -50%.

Further, the thickness of the lithium battery diaphragm is 20-30 microns; the thickness of the PP layer is 4-10 micrometers, and the thickness of the PE layer is 4-10 micrometers; the thickness of the PB-1 layer is 4-10 micrometers, and the porosity of the PB-1 layer is 50% -70%.

Further, the temperature of the forced air drying in the step (1) is 60-80 ℃, and the drying time is 2-5 hours.

Further, the twin-screw extruder described in step (1) comprises six zones, wherein the temperature and the screw rotation speed of each zone of the poly-1-butene are respectively as follows: the temperature of the first area is 125-130 ℃, the temperature of the second area is 125-130 ℃, the temperature of the third area is 130-135 ℃, the temperature of the fourth area is 140-155 ℃, the temperature of the fifth area is 145-160 ℃, the temperature of the sixth area is 145-160 ℃, and the temperature of the machine head is 145-150 ℃; the rotating speed of the screw is 150 to 200 r/min.

The invention has the beneficial effects that:

the heat-resistant power lithium battery diaphragm disclosed by the invention has high cost performance, wherein the PP/PE/PB-1 and three-layer co-extruded diaphragms have the characteristics of high puncture strength, low short circuit rate, high conductivity, good liquid retention property and the like, and have the characteristics of capability of realizing ultrathin production, high toughness, falling resistance, high safety, strong heat shrinkage and the like, the PB-1 can be uniformly stretched like a polyester film without necking polyethylene and polypropylene which are used in the past when being stretched, the processing and forming are facilitated, the heat-resistant power lithium battery diaphragm has the advantages of a dry-method diaphragm and a wet-method diaphragm, has more advantages compared with wet-method coating, can improve the impact resistance, the environmental stress cracking resistance and the creep property of the diaphragm, the difference between the PE melting point and the PP melting point of the three-layer co-extruded PB-1/PE/PP diaphragm is larger, when the internal temperature of a lithium battery exceeds 120 ℃, the PE layer starts to be closed, until the film is broken at about 160 ℃, the difference between the hot closed-hole temperature and the hot melting temperature is high, namely, a heat-resistant coating is added on the HDPE film, so that the thermal shutdown function and the double closed-hole safety are really realized, and the safety performance is better. The melting point of PB-1 and PP is utilized to relieve the safety problem caused by the shrinkage of the diaphragm after the temperature of the battery core rises, and the middle layer PE mainly plays a role in closing hole protection.

Compared with the prior art, the invention has the following advantages:

the heat-resistant power lithium battery diaphragm disclosed by the invention has high cost performance, the lithium battery diaphragm is produced by using polyolefin as a main raw material through processes of melt extrusion of a base film, heat treatment, multilayer compounding, stretching and pore forming, layering, slitting and the like, the product has the characteristics of uniform pore distribution, small shrinkage ratio, high puncture strength and the like, has innovativeness in aspects of diaphragm crystallization speed, crystal form control and the like, and can be widely applied to new energy automobile power lithium ion batteries, energy storage lithium ion batteries, digital lithium ion batteries and the like.

Detailed Description

The invention is illustrated by the following specific examples, which are not intended to be limiting.

Example 1

The preparation method of the heat-resistant power lithium battery diaphragm comprises the following steps of removing external packages from raw and auxiliary materials, entering a clean area, and keeping the cleanliness of ten thousand grades in a production workshop of an internal packaging process:

(1) drying raw materials of polypropylene, polyethylene and poly-1-butylene, extruding, casting and co-extruding the raw materials into a film by a double-screw extruder, and controlling the thickness of each layer to prepare a three-layer casting composite film consisting of a PP layer, a PB-1 layer and a PE layer; (2) annealing the prepared three-casting film at the high temperature of 100 ℃ to form regular platelets; (3) stacking the annealed 35 three-layer casting films in a laminating manner, and stretching and forming holes together, wherein the stretching ratio is 3.0 times; (4) and (3) stacking and layering the stretched and formed holes, and stripping a three-layer casting composite film consisting of a PP layer, a PE layer and a PB-1 layer, namely the heat-resistant power lithium battery diaphragm. The polyethylene is high-density polyethylene with the melt index of 0.04g/10 min; the poly-1-butene has the isotacticity of 86 percent and the melt index of 0.4g/10 min. Further, the PE layer is a second fused closed pore layer, the fusing temperature of the PE layer is 150 ℃, the PB-1 layer is a first fused closed pore layer, the fusing temperature of the PB-1 layer is 145 ℃, the porosity of the PE layer is 38%, the porosity of the PP layer is 38%, and the thickness of the lithium battery diaphragm is 30 micrometers; wherein the thickness of the PP layer is 10 microns, and the thickness of the PE layer is 10 microns; the thickness of the PB-1 layer is 10 microns, the porosity of the PB-1 layer is 70%, the temperature of the forced air drying in the step (1) is 80 ℃, and the drying time is 5 hours. Further, the twin-screw extruder described in step (1) comprises six zones, wherein the temperature and the screw rotation speed of each zone of the poly-1-butene are respectively as follows: the temperature of a first area is 125 ℃, the temperature of a second area is 125 ℃, the temperature of a third area is 130 ℃, the temperature of a fourth area is 140 ℃, the temperature of a fifth area is 145 ℃, the temperature of a sixth area is 145 ℃, and the temperature of a machine head is 150 ℃; the screw rotating speed is 200r/min, the poly-1-butene is Mitsui PB0110M, the polypropylene is extended medium coal elm functionalized FA-030Y, and the polyethylene is Korean Lotte HDPE 7000F.

Example 2

The preparation method of the heat-resistant power lithium battery diaphragm comprises the following steps of removing external packages from raw and auxiliary materials, entering a clean area, and keeping the cleanliness of ten thousand grades in a production workshop of an internal packaging process:

(1) drying raw materials of polypropylene, polyethylene and poly-1-butylene, extruding, casting and co-extruding the raw materials into a film by a double-screw extruder, and controlling the thickness of each layer to prepare a three-layer casting composite film consisting of a PP layer, a PB-1 layer and a PE layer; (2) annealing the prepared three-casting film at the high temperature of 115 ℃ to form regular platelets; (3) stacking the annealed 40 three-layer casting films in a laminating way, and stretching and forming holes together, wherein the stretching ratio is 1.5 times; (4) layering the laminated layers after stretching and pore forming, and stripping a three-layer casting composite film consisting of a PP layer, a PE layer and a PB-1 layer, namely the heat-resistant power lithium battery diaphragm, wherein the polyethylene is high-density polyethylene with a melt index of 0.04-0.055 g/10 min; the poly-1-butene is poly-1-butene with isotacticity of 86% and melt index of 1.0g/10min, the PE layer is a second fused closed pore layer, the fusing temperature of the PE layer is 150 ℃, the PB-1 layer is a first fused closed pore layer, the fusing temperature of the PB-1 layer is 125 ℃, the raw material of the PE layer is high-density polyethylene with melt index of 0.04g/10min, the porosity of the PE layer is 50%, the porosity of the PP layer is 38%, and the thickness of the lithium battery diaphragm is 20 micrometers; wherein the thickness of the PP layer is 10 microns, and the thickness of the PE layer is 4 microns; the thickness of the PB-1 layer is 6 microns, the porosity of the PB-1 layer is 50%, the temperature of the forced air drying in the step (1) is 60 ℃, the drying time is 2 hours, and the twin-screw extruder in the step (1) comprises six zones, wherein the temperature and the screw rotating speed of each zone of the poly-1-butene are respectively as follows: the temperature of a first area is 125-130 ℃, the temperature of a second area is 130 ℃, the temperature of a third area is 135 ℃, the temperature of a fourth area is 155 ℃, the temperature of a fifth area is 160 ℃, the temperature of a sixth area is 160 ℃, and the temperature of a machine head is 150 ℃; the rotating speed of the screw is 200r/min, the poly-1-butene is Mitsui M1600SAA, the polypropylene is extended medium coal elm functionalized FA-030Y, and the polyethylene is Korean Lotte HDPE 7000F.

Comparative example 1

This comparative example 1 compares with example 1 in that the poly-1-butene used in step (1) is replaced by the polypropylene used, except that the process steps are otherwise the same.

Comparative example 2

In comparison with example 2, in this comparative example 2, the polyethylene in step (1) was omitted and the original three-layer composite membrane was changed to two layers, except that the other steps were the same.

Comparative example 3

This comparative example 3 compares with example 2 in that the polypropylene used in step (1) is replaced by the poly-1-butene used, except that the process steps are otherwise the same.

The physical property test results of the heat-resistant power lithium battery separator materials of examples 1-2 and comparative examples 1-3 and the control group are shown in table 1:

table 1 test results of physical and chemical properties of heat-resistant power lithium battery separators of examples and comparative examples 1 to 3 and a control group

Note: the detection was performed with reference to the following criteria: GB/T36363-2018 polyolefin diaphragm for lithium ion batteries; determination of tensile Properties of GB/T1040.3-2006 part 3: test conditions for films and sheets; standard environment GB/T6672-: test methods.

In conclusion, the heat-resistant power lithium battery diaphragm prepared by the method has high porosity, good affinity to electrolyte, low thermal shrinkage and higher melting temperature, has thermal dimensional stability and high temperature resistance superior to those of a stretched film, is easy to control the pore diameter, thickness and uniformity, and can meet the requirements of different customers by changing the process and production materials.