阅读说明：本技术 利用聚乙烯接枝共聚物制备高性能锂电池隔膜的工艺 (Process for preparing high-performance lithium battery diaphragm by using polyethylene graft copolymer ) 是由 张德顺 胡伟 何祥燕 吴磊 李汪洋 徐凤锦 张林成 郭浩 贺云 郭志轩 于 2020-12-07 设计创作，主要内容包括：本发明公开了一种利用聚乙烯接枝共聚物制备高性能锂电池隔膜的工艺,涉及锂电池隔膜技术领域,本发明利用烯丙氧基三甲硅烷对线性低密度聚乙烯进行接枝改性,在聚乙烯的分子结构中引入硅氧烷基,制得新型聚乙烯接枝共聚物并将其加工成隔膜,目的是改善聚乙烯隔膜对电解质的亲和性,从而提高锂电池的安全性能；同时保证所制隔膜的力学性能,以适应锂电池组装时的机器缠绕和锂电池的正常运作。(The invention discloses a process for preparing a high-performance lithium battery diaphragm by using a polyethylene graft copolymer, which relates to the technical field of lithium battery diaphragms, and is characterized in that allyloxy trimethyl silane is used for graft modification of linear low-density polyethylene, siloxane groups are introduced into the molecular structure of the polyethylene, so that a novel polyethylene graft copolymer is prepared and processed into a diaphragm, and the purpose is to improve the affinity of the polyethylene diaphragm to electrolyte, thereby improving the safety performance of a lithium battery; and meanwhile, the mechanical property of the prepared diaphragm is ensured so as to adapt to machine winding and normal operation of the lithium battery during lithium battery assembly.)

1. The process for preparing the high-performance lithium battery diaphragm by using the polyethylene graft copolymer is characterized by comprising the following steps of: the method comprises the following steps:

(1) adding allyloxy-trimethoxysilane and an initiator into N, N-dimethylformamide, and heating and stirring to obtain a reactant I; adding linear low-density polyethylene into the dimethylbenzene, heating and stirring to obtain a reactant II; then dropwise adding the reactant I into the reactant II, maintaining the temperature at 80-100 ℃ in the dropwise adding process, carrying out heat preservation reaction after the dropwise adding is finished, cooling, filtering, washing with water, and drying after the reaction is finished to obtain a polyethylene graft copolymer;

(2) mixing the polyethylene graft copolymer and water-soluble inorganic salt, adding the mixture into a double-screw extruder, carrying out melt extrusion, and cooling and forming to obtain a substrate;

(3) preheating a substrate, performing biaxial stretching, soaking the obtained film in water, and drying to form a microporous film;

(4) and (4) carrying out heat setting on the microporous film, cooling and rolling to obtain the lithium battery diaphragm.

2. The process according to claim 1, characterized in that: the initiator is an organic peroxide initiator or an azo initiator.

3. The process according to claim 1, characterized in that: the dosage of the initiator is 0.1-0.5% of the mass of the allyloxy-trimethoxysilane.

4. The process according to claim 1, characterized in that: the dosage of the allyloxy trisilane is 10-50% of the mass of the linear low density polyethylene.

5. The process according to claim 1, characterized in that: the water-soluble inorganic salt is at least one of water-soluble nano hydrochloride, water-soluble nano sulfate and water-soluble nano nitrate.

6. The process according to claim 1, characterized in that: the dosage of the water-soluble inorganic salt is 1-15% of the mass of the polyethylene graft copolymer.

7. The process according to claim 1, characterized in that: the melting temperature of the double-screw extruder is 170-200 ℃.

8. The process according to claim 1, characterized in that: the transverse stretching multiple of the bidirectional stretching is 2-5 times, and the longitudinal stretching multiple is 1.5-3 times.

9. The process according to claim 1, characterized in that: the temperature of the heat setting is 120-150 ℃.

The technical field is as follows:

the invention relates to the technical field of lithium battery diaphragms, in particular to a process for preparing a high-performance lithium battery diaphragm by using a polyethylene graft copolymer.

Background art:

in the construction of lithium batteries, the separator is one of the key internal layer components. The performance of the diaphragm determines the interface structure, internal resistance and the like of the battery, directly influences the capacity, circulation, safety performance and other characteristics of the battery, and the diaphragm with excellent performance plays an important role in improving the comprehensive performance of the battery. The separator has a main function of separating the positive electrode and the negative electrode of the battery to prevent short circuit due to contact between the two electrodes, and also has a function of allowing electrolyte ions to pass therethrough. The separator material is non-conductive, and the physical and chemical properties of the separator have a great influence on the performance of the battery.

At present, polyolefin diaphragm materials are widely applied to lithium batteries and mainly comprise polyethylene diaphragms and polypropylene diaphragms, but the polyethylene diaphragms and the polypropylene diaphragms have poor affinity to electrolytes, so that the problems of short circuit, overcharge, needle punching and the like are caused. Therefore, it is required to develop a lithium battery separator having high affinity for an electrolyte and high safety.

The invention content is as follows:

the technical problem to be solved by the invention is to provide a process for preparing a high-performance lithium battery diaphragm by using a polyethylene graft copolymer, wherein the polyethylene graft copolymer is prepared by grafting modification of allyloxy-trimethoxysilane on polyethylene, and the affinity of the polyethylene diaphragm to an electrolyte is improved, so that the problems of short circuit, overcharge, needle punching and the like are avoided.

The technical problem to be solved by the invention is realized by adopting the following technical scheme:

the process for preparing the high-performance lithium battery diaphragm by using the polyethylene graft copolymer comprises the following steps:

(1) adding allyloxy-trimethoxysilane and an initiator into N, N-dimethylformamide, and heating and stirring to obtain a reactant I; adding linear low-density polyethylene into the dimethylbenzene, heating and stirring to obtain a reactant II; then dropwise adding the reactant I into the reactant II, maintaining the temperature at 80-100 ℃ in the dropwise adding process, carrying out heat preservation reaction after the dropwise adding is finished, cooling, filtering, washing with water, and drying after the reaction is finished to obtain a polyethylene graft copolymer;

(2) mixing the polyethylene graft copolymer and water-soluble inorganic salt, adding the mixture into a double-screw extruder, carrying out melt extrusion, and cooling and forming to obtain a substrate;

(3) preheating a substrate, performing biaxial stretching, soaking the obtained film in water, and drying to form a microporous film;

(4) and (4) carrying out heat setting on the microporous film, cooling and rolling to obtain the lithium battery diaphragm.

The initiator is an organic peroxide initiator or an azo initiator. Under the action of an initiator, allyloxy-trimethoxysilane and polyethylene are subjected to copolymerization reaction, so that allyloxy-trimethoxysilane is grafted to the molecular structure of the polyethylene.

The dosage of the initiator is 0.1-0.5% of the mass of the allyloxy-trimethoxysilane.

The dosage of the allyloxy trisilane is 10-50% of the mass of the linear low density polyethylene.

The water-soluble inorganic salt is at least one of water-soluble nano hydrochloride, water-soluble nano sulfate and water-soluble nano nitrate. The water-soluble nano hydrochloride can be nano sodium chloride, nano potassium chloride or nano ammonium chloride, the water-soluble nano sulfate can be nano sodium sulfate, nano potassium sulfate, nano magnesium sulfate or nano ammonium sulfate, and the water-soluble nano nitrate can be nano sodium nitrate, nano potassium nitrate, nano magnesium nitrate or nano ammonium nitrate.

The dosage of the water-soluble inorganic salt is 1-15% of the mass of the polyethylene graft copolymer.

The melting temperature of the double-screw extruder is 170-200 ℃. Compared with linear low density polyethylene, the prepared polyethylene graft copolymer has the advantages that the melting point is improved, and the characteristics of high strength, good toughness, strong corrosion resistance, good heat resistance and cold resistance and the like of the linear low density polyethylene are reserved.

The transverse stretching multiple of the bidirectional stretching is 2-5 times, and the longitudinal stretching multiple is 1.5-3 times. The ultra-thin separator is manufactured by biaxial stretching and facilitates the formation of micropores on the separator.

The temperature of the heat setting is 120-150 ℃.

According to the invention, the water-soluble inorganic salt is used as the pore-forming agent, and the water is used as the extracting agent, so that the investment cost of the extracting agent is reduced, the use safety and the environmental protection performance of the extracting agent are improved, and the distribution uniformity and the size of formed micropores can be better controlled, thereby ensuring the air permeability of the diaphragm.

The invention eliminates the internal stress generated in the film stretching process through heat setting, so that macromolecules relax to a certain degree, and the effect of fixing the shape of the film is achieved.

The invention has the beneficial effects that: the invention utilizes allyloxy trimethyl silane to graft and modify linear low-density polyethylene, and siloxane groups are introduced into the molecular structure of the polyethylene to prepare a novel polyethylene graft copolymer and process the polyethylene graft copolymer into a diaphragm, so as to improve the affinity of the polyethylene diaphragm to electrolyte and improve the safety performance of a lithium battery; and meanwhile, the mechanical property of the prepared diaphragm is ensured so as to adapt to machine winding and normal operation of the lithium battery during lithium battery assembly.

The specific implementation mode is as follows:

in order to make the technical means, the creation characteristics, the achievement purposes and the effects of the invention easy to understand, the invention is further described with the specific embodiments.

Linear low density polyethylene was purchased from northern european chemical FM 5340.

Example 1

(1) Adding 20g of allyloxytrimethylsilane and 0.1g of azobisisobutyronitrile into 500mL of N, N-dimethylformamide, heating to 45 ℃, and stirring for 15min to obtain a reactant I; adding 80g of linear low-density polyethylene into 500mL of dimethylbenzene, heating to 70 ℃, and stirring for 15min to obtain a reactant II; and then dropwise adding the reactant I into the reactant II, maintaining the temperature at 90 ℃ in the dropwise adding process, preserving the temperature for reacting for 8 hours after the dropwise adding is finished, cooling after the reaction is finished, filtering, washing with water, and drying to obtain the polyethylene graft copolymer. During the post-treatment, the allyloxy-trimethoxysilane is removed by filtration, and infrared detection is carried out on the product, and the unsaturated double bond disappears, so that an infrared characteristic peak of siloxy appears, and the allyloxy-trimethoxysilane is grafted to the polyethylene.

(2) Mixing 1000g of polyethylene graft copolymer and 15g of nano sodium sulfate, adding the mixture into a double-screw extruder, carrying out melt extrusion at 190 ℃, and cooling and forming to obtain the substrate.

(3) Preheating the substrate, performing biaxial stretching, wherein the transverse stretching multiple is 4 times, the longitudinal stretching multiple is 2.5 times, and soaking the obtained film in water for 8 hours and then drying to form the microporous film.

(4) And (3) carrying out heat setting on the microporous film at 135 ℃, cooling and rolling to obtain the lithium battery diaphragm.

Example 2

Example 2 the same procedure as in example 1 was used to prepare a separator, except that the amount of sodium nanosulfate was adjusted.

(1) Adding 20g of allyloxytrimethylsilane and 0.1g of azobisisobutyronitrile into 500mL of N, N-dimethylformamide, heating to 45 ℃, and stirring for 15min to obtain a reactant I; adding 80g of linear low-density polyethylene into 500mL of dimethylbenzene, heating to 70 ℃, and stirring for 15min to obtain a reactant II; and then dropwise adding the reactant I into the reactant II, maintaining the temperature at 90 ℃ in the dropwise adding process, preserving the temperature for reacting for 8 hours after the dropwise adding is finished, cooling after the reaction is finished, filtering, washing with water, and drying to obtain the polyethylene graft copolymer.

(2) Mixing 1000g of polyethylene graft copolymer and 10g of nano sodium sulfate, adding the mixture into a double-screw extruder, carrying out melt extrusion at 190 ℃, and cooling and forming to obtain the substrate.

(3) Preheating the substrate, performing biaxial stretching, wherein the transverse stretching multiple is 4 times, the longitudinal stretching multiple is 2.5 times, and soaking the obtained film in water for 8 hours and then drying to form the microporous film.

(4) And (3) carrying out heat setting on the microporous film at 135 ℃, cooling and rolling to obtain the lithium battery diaphragm.

Example 3

Example 3 the same procedure as in example 1 for preparing a separator was followed, except that the amount of allyloxytrimethylsilane was adjusted.

(1) Adding 25g of allyloxytrimethylsilane and 0.1g of azobisisobutyronitrile into 500mL of N, N-dimethylformamide, heating to 45 ℃, and stirring for 15min to obtain a reactant I; adding 80g of linear low-density polyethylene into 500mL of dimethylbenzene, heating to 70 ℃, and stirring for 15min to obtain a reactant II; and then dropwise adding the reactant I into the reactant II, maintaining the temperature at 90 ℃ in the dropwise adding process, preserving the temperature for reacting for 8 hours after the dropwise adding is finished, cooling after the reaction is finished, filtering, washing with water, and drying to obtain the polyethylene graft copolymer.

(2) Mixing 1000g of polyethylene graft copolymer and 15g of nano sodium sulfate, adding the mixture into a double-screw extruder, carrying out melt extrusion at 190 ℃, and cooling and forming to obtain the substrate.

(3) Preheating the substrate, performing biaxial stretching, wherein the transverse stretching multiple is 4 times, the longitudinal stretching multiple is 2.5 times, and soaking the obtained film in water for 8 hours and then drying to form the microporous film.

(4) And (3) carrying out heat setting on the microporous film at 135 ℃, cooling and rolling to obtain the lithium battery diaphragm.

Comparative example

The comparative example was the same as the procedure for preparing the separator of example 1, except that allyloxytrimethylsilane was not grafted on the polyethylene structure.

(1) Mixing 1000g of linear low-density polyethylene and 15g of nano sodium sulfate, adding the mixture into a double-screw extruder, carrying out melt extrusion at 190 ℃, and cooling and forming to obtain the substrate.

(2) Preheating the substrate, performing biaxial stretching, wherein the transverse stretching multiple is 4 times, the longitudinal stretching multiple is 2.5 times, and soaking the obtained film in water for 8 hours and then drying to form the microporous film.

(3) And (3) carrying out heat setting on the microporous film at 135 ℃, cooling and rolling to obtain the lithium battery diaphragm.

The performance tests were performed on the separators prepared in the above examples and comparative examples, and the test methods and results were as follows:

tensile strength: the standard GB/T1040.3-2006 is adopted;

puncture strength: the standard GB/T21302-2007 is adopted;

liquid absorption rate: mass m₀Soaking the diaphragm in electrolyte (purchased from Shanghai Tongbo materials science and technology Co., Ltd.), taking out after 2h, sucking the electrolyte on the surface of the diaphragm by using filter paper, weighing m₁Calculating the liquid absorption rate K ═ m [ (- ]₁-m₀)/m₀]×100％。

The test was performed in triplicate and the average was taken.

TABLE 1

Item	Tensile strength/MPa	Puncture Strength/N	Imbibition rate/%)
				Example 1	65.8	51.7	332
Example 2	63.7	50.2	311
				Example 3	68.2	53.6	345
Comparative example	57.1	44.5	212

As can be seen from table 1, in the examples, the affinity of the separator for the electrolyte is enhanced and the mechanical strength of the separator is also improved by graft modification of polyethylene.

The foregoing shows and describes the general principles and broad features of the present invention and advantages thereof. It will be understood by those skilled in the art that the present invention is not limited to the embodiments described above, which are described in the specification and illustrated only to illustrate the principle of the present invention, but that various changes and modifications may be made therein without departing from the spirit and scope of the present invention, which fall within the scope of the invention as claimed. The scope of the invention is defined by the appended claims and equivalents thereof.