Liquid crystal reinforced ultra-high molecular weight polyethylene lithium battery diaphragm and preparation method thereof

文档序号：737805 发布日期：2021-04-20 浏览：30次中文

阅读说明：本技术 一种液晶增强超高分子量聚乙烯锂电池隔膜及其制备方法 (Liquid crystal reinforced ultra-high molecular weight polyethylene lithium battery diaphragm and preparation method thereof ) 是由巢雷李正林翁星星陈朝晖贡晶晶于 2020-12-08 设计创作，主要内容包括：本发明涉及一种液晶增强超高分子量聚乙烯锂电池隔膜及其制备方法,包括如下重量百分比的组分：超高分子量聚乙烯45～75wt％,超高分子量聚乙烯接枝料5～15wt％；液晶高分子20～40wt％。使用超高分子量聚乙烯作为隔膜的基体材料,液晶高分子作为骨架材料,超高分子量聚乙烯接枝物作为相容剂,通过共混挤出工艺将具有高度取向的液晶高分子均匀分散在隔膜中,经过纵向和横向高倍率拉伸,液晶高分子在纵横方向交错形成高度取向的网状结构,由于液晶高分子具有高强度、高耐热、高阻燃的特性,能够综合提升隔膜的性能,从而达到提升锂电池安全系数的目的。(The invention relates to a liquid crystal reinforced ultra-high molecular weight polyethylene lithium battery diaphragm and a preparation method thereof, wherein the diaphragm comprises the following components in percentage by weight: 45-75 wt% of ultrahigh molecular weight polyethylene and 5-15 wt% of ultrahigh molecular weight polyethylene graft material; 20-40 wt% of liquid crystal polymer. The ultra-high molecular weight polyethylene is used as a base material of the diaphragm, the liquid crystal polymer is used as a framework material, the ultra-high molecular weight polyethylene graft is used as a compatilizer, the highly oriented liquid crystal polymer is uniformly dispersed in the diaphragm through a blending extrusion process, and the liquid crystal polymer is stretched in a longitudinal direction and a transverse direction at high multiplying power, so that the liquid crystal polymer is staggered in the longitudinal direction and the transverse direction to form a highly oriented net-shaped structure.)

1. The liquid crystal reinforced ultra-high molecular weight polyethylene lithium battery diaphragm is characterized by comprising the following components in percentage by weight: 45-75 wt% of ultrahigh molecular weight polyethylene, 5-15 wt% of ultrahigh molecular weight polyethylene graft material and 20-40 wt% of liquid crystal polymer.

2. The ultra-high molecular weight polyethylene lithium battery separator of claim 1, wherein the average molecular weight of the ultra-high molecular weight polyethylene is greater than 200 ten thousand; the ultrahigh molecular weight polyethylene grafting material contains Glycidyl Methacrylate (GMA) functional groups on molecular chains, and the content of the functional groups is 1-4 mol%; the melting point of the liquid crystal polymer is 185-205 ℃, and the structure of the liquid crystal polymer is as follows:

3. the preparation method of the liquid crystal reinforced ultra-high molecular weight polyethylene lithium battery diaphragm as claimed in any one of claims 1 to 2, characterized by comprising the following steps:

(1) preparing a liquid crystal polymer solution: weighing liquid crystal polymers according to weight percentage, dissolving the liquid crystal polymers in methanesulfonic acid, and mixing to form a uniform liquid crystal polymer organic solution;

(2) preparing an ultrahigh molecular weight polyethylene grafting material: dissolving glycidyl methacrylate and dicumyl peroxide in toluene to form an initiating solution; putting ultra-high molecular weight polyethylene powder into a stirrer, adding the initiating solution, introducing nitrogen for protection, and performing solid-phase grafting reaction to obtain an ultra-high molecular weight polyethylene grafting material;

(3) preparing a liquid crystal reinforced ultra-high molecular weight polyethylene diaphragm: weighing ultrahigh molecular weight polyethylene according to the weight percentage, putting the ultrahigh molecular weight polyethylene grafting material prepared in the step (2) into a mixer, pouring the liquid crystal polymer organic solvent prepared in the step (1), blending, dispersing and drying to obtain a mixture;

putting the mixture into an extruder, adding white oil from an oil filling port of the extruder, performing melt extrusion, and performing tape casting on a melt to a cooling roller through a die orifice of the extruder to obtain a tape casting membrane;

and sequentially carrying out longitudinal stretching, transverse stretching, extraction, heat setting and rolling on the casting membrane to obtain the liquid crystal reinforced ultra-high molecular weight polyethylene membrane.

4. The method for preparing the liquid crystal reinforced ultra-high molecular weight polyethylene lithium battery diaphragm as claimed in claim 3, wherein the mixing speed in the step (1) is 200rpm to 500rpm, the mixing time is 5h to 10h, and the mixing temperature is 40 ℃ to 50 ℃; the dosage of the methanesulfonic acid is 1-2 times of the dosage of the liquid crystal polymer.

5. The method for preparing the liquid crystal reinforced ultra-high molecular weight polyethylene lithium battery diaphragm as claimed in claim 3, wherein the raw materials used in the ultra-high molecular weight polyethylene graft material in the step (2) comprise the following raw materials in percentage by mass: 3-5 wt% of glycidyl methacrylate, 0.1-0.3 wt% of dicumyl peroxide and 94.7-96.7 wt% of ultrahigh molecular weight polyethylene; the dosage ratio of the glycidyl methacrylate to the toluene in the initiation solution is (3-5) g, (50-500) mL; the solid phase grafting reaction condition is that the reaction is carried out for 3 to 6 hours at the stirring speed of 50 to 100rpm and the reaction temperature of 80 to 100 ℃.

6. The preparation method of the liquid crystal reinforced ultra-high molecular weight polyethylene lithium battery diaphragm as claimed in claim 3, wherein the blending and dispersing speed of the mixture in the step (3) is 50rpm to 200rpm, and the blending and dispersing temperature is 60 ℃ to 80 ℃;

the addition amount of the white oil is 2-3 times of the weight of the mixture;

the melt extrusion temperature is 150-230 ℃, the screw rotating speed of the extruder is 80-120 rpm, and the extrusion amount is 200-600 kg/h;

the temperature of the cooling roller is 20-40 ℃;

the longitudinal stretching temperature is 80-120 ℃, and the stretching ratio is 2-8 times;

the transverse stretching temperature is 100-130 ℃, and the stretching magnification is 2-12 times;

the extraction adopts a dichloromethane solvent, the extraction temperature is 5-20 ℃, and the flow of dichloromethane is 1-8 m during the extraction³/h；

The heat setting temperature is 120-160 ℃.

Technical Field

The invention relates to the technical field of lithium battery diaphragms, in particular to a liquid crystal reinforced ultra-high molecular weight polyethylene lithium battery diaphragm and a preparation method thereof.

Background

Lithium ion batteries, as a new generation of energy storage technology, have been widely studied and applied, but almost only work in room temperature environments. High or low temperatures cause the performance of the lithium battery to be degraded, and the life and capacity to be compromised. Especially, under high temperature conditions, a large amount of heat may be generated inside the battery to float, thereby causing safety accidents such as explosion.

For a power lithium battery pack, the optimal use temperature is generally 30-60 ℃, and the performance and safety of the battery beyond the range are affected. In the test that the lithium battery is subjected to high temperature, the test has an extreme temperature test of 200 ℃, 500 ℃ and even 800 ℃. Lithium batteries may discharge instantaneously at this temperature to generate a large amount of current, resulting in spontaneous combustion or explosion. Therefore, the explosion-proof valve is generally arranged in the design of the lithium battery, and when high temperature or electrode short circuit occurs, the explosion-proof valve can be automatically destroyed to release the pressure in the battery and prevent the battery from exploding.

As lithium ion batteries are more and more widely applied to the production and life of people, the safety of the lithium ion batteries becomes the primary concern.

Disclosure of Invention

In order to solve the technical problem of safety of the lithium ion battery, a liquid crystal reinforced ultra-high molecular weight polyethylene lithium battery diaphragm and a preparation method thereof are provided. The invention solves the safety problem of the lithium battery from the angle of the lithium battery diaphragm, uses the ultra-high molecular weight polyethylene as a base material, uses the liquid crystal polymer as a framework material and uses the ultra-high molecular weight polyethylene graft as a compatilizer, uniformly disperses the highly oriented liquid crystal polymer in the diaphragm through a blending extrusion process, and the highly oriented liquid crystal polymer is staggered in the longitudinal direction and the transverse direction to form a net-shaped structure through high-rate stretching in the longitudinal direction and the transverse direction.

In order to achieve the purpose, the invention is realized by the following technical scheme:

the liquid crystal reinforced ultra-high molecular weight polyethylene lithium battery diaphragm is characterized by comprising the following components in percentage by weight: 45-75 wt% of ultrahigh molecular weight polyethylene, 5-15 wt% of ultrahigh molecular weight polyethylene graft material and 20-40 wt% of liquid crystal polymer.

Further, the average molecular weight of the ultra-high molecular weight polyethylene is more than 200 ten thousand; the ultrahigh molecular weight polyethylene grafting material contains Glycidyl Methacrylate (GMA) functional groups on molecular chains, and the content of the functional groups is 1-4 mol%; the melting point of the liquid crystal polymer is 185-205 ℃, and the structure of the liquid crystal polymer is as follows:

the preparation method of the liquid crystal reinforced ultra-high molecular weight polyethylene lithium battery diaphragm comprises the following steps:

Further, the mixing speed in the step (1) is 200-500 rpm, the mixing time is 5-10 h, and the mixing temperature is 40-50 ℃; the dosage of the methanesulfonic acid is 1-2 times of the dosage of the liquid crystal polymer.

Further, the raw materials used in the ultrahigh molecular weight polyethylene graft material in the step (2) are as follows by mass percent: 3 wt% of glycidyl methacrylate, 0.1-0.3 wt% of dicumyl peroxide and 94.7-96.7 wt% of ultrahigh molecular weight polyethylene; the dosage ratio of the glycidyl methacrylate to the toluene in the initiation solution is (3-5) g, (50-500) mL; the solid phase grafting reaction condition is that the reaction is carried out for 3 to 6 hours at the stirring speed of 50 to 100rpm and the reaction temperature of 80 to 100 ℃.

Further, the blending and dispersing speed of the mixture in the step (3) is 50-200 rpm, and the blending and dispersing temperature is 60-80 ℃;

the addition amount of the white oil is 2-3 times of the weight of the mixture;

the melt extrusion temperature is 150-230 ℃, the screw rotating speed of the extruder is 80-120 rpm, and the extrusion amount is 200-600 kg/h;

the temperature of the cooling roller is 20-40 ℃;

the longitudinal stretching temperature is 80-120 ℃, and the stretching ratio is 2-8 times;

the transverse stretching temperature is 100-130 ℃, and the stretching magnification is 2-12 times;

the extraction adopts a dichloromethane solvent, the extraction temperature is 5-20 ℃, and the flow of dichloromethane is 1-8 m during the extraction³/h；

The heat setting temperature is 120-160 ℃.

The beneficial technical effects are as follows:

the invention selects ultra-high molecular weight polyethylene as a diaphragm matrix material, liquid crystal polymer as a supporting framework material, ultra-high molecular weight polyethylene graft material as a compatilizer, white oil as a pore-forming agent, the white oil is blended and extruded by a double-screw extruder, the liquid crystal polymer is uniformly dispersed in the matrix material, the liquid crystal material forms a highly oriented crossed net structure after longitudinal stretching and transverse stretching, the white oil is dissolved out after extraction by dichloromethane to form a microporous structure, and finally the liquid crystal reinforced ultra-high molecular weight polyethylene lithium battery diaphragm is prepared through heat setting and winding.

The liquid crystal polymer adopted by the invention is semi-aromatic polyarylate with a side chain containing phosphorus and a flexible aliphatic group, the flexible aliphatic group and the aromatic group in the main chain structure of the liquid crystal polymer enable the liquid crystal polymer to have good processability and simultaneously have high temperature resistance and easy orientation crystallization performance, and the side chain containing phosphorus group enables the liquid crystal polymer to have high flame retardance. In the processing process, the liquid crystal polymer forms a highly oriented network structure in the diaphragm substrate after longitudinal stretching and transverse stretching, so that the framework support is provided for the diaphragm substrate, and the strength, heat resistance and flame retardance of the diaphragm are improved. When the lithium battery pack is subjected to high temperature, the high strength and high heat resistance of the liquid crystal reinforced ultra-high molecular weight lithium battery diaphragm can avoid the contact of a positive electrode and a negative electrode, and prevent collapse from causing short circuit; when the lithium battery is on fire, the diaphragm component in the lithium battery has the flame-retardant characteristic, so that the spread of fire can be delayed. The liquid crystal polymer reinforced ultra-high molecular weight lithium battery diaphragm provided by the invention has the advantages that the safety of the lithium battery in an extreme use environment is improved from the aspects of improving the mechanical strength, thermal stability and flame retardance of the diaphragm, and the occurrence of malignant accidents can be effectively reduced.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. The following description of at least one exemplary embodiment is merely illustrative in nature and is in no way intended to limit the invention, its application, or uses. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Unless specifically stated otherwise, the numerical values set forth in these examples do not limit the scope of the invention. Techniques, methods known to those of ordinary skill in the relevant art may not be discussed in detail, but are intended to be part of the specification where appropriate. In all examples shown and discussed herein, any particular value should be construed as merely illustrative, and not limiting. Thus, other examples of the exemplary embodiments may have different values.

The experimental methods of the following examples, which are not specified under specific conditions, are generally determined according to national standards; if no corresponding national standard exists, the method is carried out according to the universal international standard or the standard requirement proposed by related enterprises. Unless otherwise indicated, all parts are parts by weight and all percentages are percentages by weight.

The adopted ultra-high molecular weight polyethylene is VH095 produced by Dahan oiling; the ultrahigh molecular weight polyethylene graft is prepared by solid phase grafting reaction; the liquid crystal polymer is prepared by the following method: Cheng-Shou, Z, C.Li, and W.Yu-Zhong, A phosphor-containing thermoplastic liquid crystalline copolymer with low-level mesophase temperature and high-level catalyst reaction [ J ]. Journal of Polymer Science Part A (Polymer Chemistry),2008.46(17): p.5752-9.

Example 1

A liquid crystal reinforced ultra-high molecular weight polyethylene lithium battery diaphragm is prepared by weighing the following components in percentage by weight: 75 wt% of ultrahigh molecular weight polyethylene, 5 wt% of ultrahigh molecular weight polyethylene graft material and 20 wt% of liquid crystal polymer;

wherein the average molecular weight of the ultra-high molecular weight polyethylene is more than 200 ten thousand;

wherein the ultrahigh molecular weight polyethylene grafting material contains Glycidyl Methacrylate (GMA) functional groups on molecular chains, and the specific preparation method comprises the following step (2);

wherein the melting point of the liquid crystal polymer is 185-205 ℃, and the structure of the liquid crystal polymer is as follows:

wherein Y, Z, 1-Y-Z indicates the overall composition rather than chain length, and the content of Y, Z is related to the number of moles of the added raw materials.

The liquid crystal reinforced ultra-high molecular weight polyethylene lithium battery diaphragm is prepared according to the following steps:

(1) preparing a liquid crystal polymer solution: dissolving the weighed liquid crystal polymer in methanesulfonic acid, wherein the dosage of the methanesulfonic acid is 1.5 times of the dosage of the liquid crystal polymer, stirring in a dispersion machine at the speed of 200rpm, and mixing for 6 hours at 50 ℃ to form a uniform liquid crystal polymer organic solution;

(2) preparing an ultrahigh molecular weight polyethylene grafting material: weighing 4 wt% of Glycidyl Methacrylate (GMA) and 0.2 wt% of dicumyl peroxide (DCP) and dissolving in toluene to prepare an initiating solution, wherein GMA in the initiating solution is 4 g/300 mL; weighing 95.8 wt% of ultra-high molecular weight polyethylene powder, putting the powder into a stirrer, adding the initiating solution, introducing nitrogen for protection, and carrying out solid-phase grafting reaction for 6 hours at the stirring speed of 80rpm and the reaction temperature of 100 ℃ to obtain an ultra-high molecular weight polyethylene graft material;

(3) preparing a liquid crystal reinforced ultra-high molecular weight polyethylene diaphragm: weighing 75 wt% of ultra-high molecular weight polyethylene, pouring the liquid crystal polymer organic solution prepared in the step (1), blending and dispersing at 80 ℃ at a speed of 100rpm, and drying to obtain a mixture;

putting the obtained mixture into an extruder, adding white oil which is 2.5 times of the weight of the mixture from an oil filling port of the extruder, carrying out melt extrusion at the temperature of 220 ℃, the rotating speed of a screw rod of the extruder being 100rpm, and the extrusion capacity being 350kg/h, and carrying out tape casting on a melt through a die orifice of the extruder to a cooling roller at the temperature of 30 ℃ to obtain a tape casting membrane;

longitudinally stretching the cast film at 120 deg.C by 8 times, transversely stretching at 130 deg.C by 12 times, and washing the stretched film in dichloromethane extraction tank to obtain microporesThe structure is that the extraction temperature of dichloromethane is 10 ℃, and the flow rate is 8m³H; and then coiling after heat setting at 140 ℃ to finally prepare the liquid crystal reinforced ultra-high molecular weight polyethylene lithium battery diaphragm.

Example 2

A liquid crystal reinforced ultra-high molecular weight polyethylene lithium battery diaphragm is prepared by weighing the following components in percentage by weight: 70 wt% of ultrahigh molecular weight polyethylene and 10 wt% of ultrahigh molecular weight polyethylene grafting material; 20 wt% of liquid crystal polymer.