阅读说明：本技术 一种耐高温对位芳纶涂覆锂离子电池隔膜及其制备方法 (High-temperature-resistant para-aramid coated lithium ion battery diaphragm and preparation method thereof ) 是由 徐萌 刘杲珺 白耀宗 周阳 马平川 翟萌萌 韩超 于 2020-12-21 设计创作，主要内容包括：本发明提出一种耐高温对位芳纶涂覆锂离子电池隔膜及其制备方法,所述隔膜包括基膜和涂覆于基膜单侧的对位芳纶涂层,所述对位芳纶涂层经有机溶剂涂布、对位芳纶浆料涂布、饱和蒸汽析出、水洗、干燥后获得,所述对位芳纶浆料使用对位芳纶原液,并在其中均匀分散有无机填料,所述对位芳纶原液是在对位芳纶中引入刚性基团的聚合液。与现有以凝固浴使涂层析出的方式相比,本发明采用饱和蒸汽使涂层析出得到的对位芳纶涂覆锂离子电池隔膜具有更好的微观结构和耐高温特性,同时减少有机溶剂的使用,利于保护环境,成本也相对较低。(The invention provides a high-temperature-resistant para-aramid coated lithium ion battery diaphragm and a preparation method thereof, wherein the diaphragm comprises a base film and a para-aramid coating coated on one side of the base film, the para-aramid coating is obtained by coating an organic solvent, coating para-aramid pulp, precipitating saturated steam, washing and drying, the para-aramid pulp is prepared by using para-aramid stock solution, and inorganic filler is uniformly dispersed in the para-aramid stock solution, and the para-aramid stock solution is a polymerization solution for introducing a rigid group into para-aramid. Compared with the existing mode of separating out the coating by using a coagulating bath, the method disclosed by the invention has the advantages that the para-aramid coated lithium ion battery diaphragm obtained by separating out the coating by using saturated steam has a better microstructure and a better high-temperature resistance characteristic, the use of organic solvents is reduced, the environment is protected, and the cost is relatively low.)

1. The high-temperature-resistant para-aramid coated lithium ion battery separator is characterized by comprising a base film (1) and a para-aramid coating (2) coated on one side of the base film, wherein the thickness of the base film (1) is 5-30 mu m, the porosity is 20-80%, and the air permeability is 50-800s/100 cc; the thickness of the para-aramid coating (2) is 2-6 mu m, the para-aramid coating (2) comprises para-aramid fibers (21) and inorganic fillers (22), the inorganic fillers (22) are uniformly dispersed in the para-aramid fibers (21), the content of the para-aramid fibers (21) accounts for 20-50% of the whole coating, and the average particle size of the inorganic fillers (22) is 10-300 nm.

2. The high-temperature-resistant para-aramid coated lithium ion battery separator as claimed in claim 1, wherein the para-aramid fiber (21) is formed by coating with an organic solvent, coating with para-aramid composite slurry, precipitating with saturated steam, washing with water and drying, wherein the para-aramid composite slurry comprises a para-aramid stock solution with a rigid group introduced into a para-aramid polymer, the weight percentage of the para-aramid polymer in the para-aramid stock solution is 1-4%, and the apparent viscosity of the para-aramid stock solution is 300-20000 cp.

3. The high temperature resistant p-aramid coated lithium ion battery separator as claimed in claim 2, wherein the rigid group is introduced into the p-aramid polymer by introducing a rigid structural unit into the main chain of the p-aramid polymer or by copolycondensating the p-aramid polymer with a monomer containing a rigid group.

4. The high-temperature-resistant para-aramid coated lithium ion battery separator as claimed in claim 1, wherein the base film comprises any one of polyethylene microporous film, polypropylene/polyethylene/polypropylene three-layer composite microporous film, polyvinylidene fluoride-hexafluoropropylene microporous film, polyimide microporous film, polyethylene non-woven fabric, polypropylene non-woven fabric, polyester non-woven fabric, polyimide non-woven fabric, aramid non-woven fabric and spandex non-woven fabric.

5. The high temperature resistant para-aramid coated lithium ion battery separator of claim 1, wherein the inorganic filler comprises at least one of alumina, magnesia, calcium oxide, barium oxide, zinc oxide, silica, titanium dioxide, zirconium dioxide, magnesium hydroxide, aluminum hydroxide.

6. The high temperature resistant para-aramid coated lithium ion battery separator of claim 1, wherein the organic solvent comprises at least one of N-methylpyrrolidone (NMP), N-Dimethylformamide (DMF), N-Dimethylacetamide (DMAC), Tetramethylurea (TMU).

7. A method for preparing a high-temperature-resistant para-aramid coated lithium ion battery diaphragm is characterized by comprising the following steps of:

step 1: dispersing inorganic filler in a certain proportion into a para-aramid raw solution, filtering and degassing to obtain para-aramid composite slurry, wherein the para-aramid raw solution comprises a para-aramid polymer with introduced rigid groups;

step 2: coating an organic solvent on one side of the base film, and coating the para-aramid composite slurry obtained in the step 1 on the other side of the base film to obtain a coating film;

and step 3: the coating film slowly separates out a coating through saturated steam, the para-aramid polymer is separated out in a fiber form, and the organic solvent and the water vapor are mutually dissolved and taken away by hot air for recycling;

and 4, step 4: and (4) the coating film enters a water tank for washing, and then enters a drying oven for drying to obtain the para-aramid coated lithium ion battery diaphragm.

8. The method for preparing the high-temperature-resistant p-aramid coated lithium ion battery separator according to claim 7, wherein the inorganic filler in the step 1 comprises at least one of alumina, magnesia, calcium oxide, barium oxide, zinc oxide, silicon dioxide, titanium dioxide, zirconium dioxide, magnesium hydroxide and aluminum hydroxide, and the dispersion mode comprises any one of a mechanical stirring method, an ultrasonic dispersion method, a high-pressure dispersion method, a medium dispersion method and a high-speed shearing emulsification method.

9. The method for preparing the high-temperature-resistant para-aramid coated lithium ion battery separator according to claim 7, wherein the base film in the step 2 comprises any one of a polyethylene microporous film, a polypropylene/polyethylene/polypropylene three-layer composite microporous film, a polyvinylidene fluoride-hexafluoropropylene microporous film, a polyimide microporous film, a polyethylene non-woven fabric, a polypropylene non-woven fabric, a polyester non-woven fabric, a polyimide non-woven fabric, an aramid non-woven fabric and a spandex non-woven fabric.

10. The method for preparing a high temperature resistant p-aramid coated lithium ion battery separator as claimed in claim 7, wherein the organic solvent in step 2 comprises at least one of N-methylpyrrolidone (NMP), N-Dimethylformamide (DMF), N-Dimethylacetamide (DMAC), Tetramethylurea (TMU).

11. The preparation method of the high-temperature-resistant para-aramid coated lithium ion battery separator as claimed in claim 7, wherein the coating manner in the step 2 comprises any one of gravure coating, slit coating, dip coating, blade coating, bar coating, blade coating and wire bar coating.

12. The preparation method of the high-temperature-resistant p-aramid coated lithium ion battery separator according to claim 7, wherein the temperature of the saturated steam in the step 3 is 40-60 ℃, the humidity is 60-90% RH, and the coating precipitation time is 10-60 s; the wind speed of the hot wind is 50-80m/min, and the temperature is less than or equal to 60 ℃.

13. The preparation method of the high-temperature-resistant p-aramid coated lithium ion battery separator as claimed in claim 7, wherein 8 sections of water tanks in the step 4 are filled with pure water, overflow from the 8 th stage to the front stage, and the washing time is 30-300 s; the drying adopts a steam heating or electric heating mode, the drying temperature is 60-90 ℃, and the drying time is 30-300 s.

Technical Field

The invention belongs to the technical field of lithium ion batteries, and particularly relates to a high-temperature-resistant para-aramid coated lithium ion battery diaphragm and a preparation method thereof.

Background

The energy density of the lithium ion battery reaches 300Wh/Kg in 2020 proposed by China, the ternary NCM of the domestic power lithium battery is at stages 523, 622 and 811 at present, and the energy density does not reach a target value yet. While the NCA21700 energy density currently used by tesla has reached 300Wh/Kg, it is the para-aramid coated membrane supplied by sumitomo chemistry. The aramid fiber raw material has low density, the gram weight of the diaphragm prepared under the condition of the same thickness is low, and the advantage of high energy density expressed in the battery is incomparable with ceramic materials.

The higher the energy density, the lower the decomposition temperature, which means the lower the safety, and the decomposition temperature of the aramid is more than 500 ℃, and from the view point of the heat shrinkage performance of the membrane, the heat shrinkage rate of the meta-aramid membrane is far higher than that of the para-aramid, so that the inhabitants use the para-aramid as the coating material.

The para-aramid is called poly-p-phenylene terephthalamide, the whole molecular main chain is of a benzene ring and amido bond alternating structure, a pi conjugated effect is formed, and the para-aramid is difficult to dissolve in an organic solvent due to strong intermolecular action. To solve this problem, sumitomo chemistry uses a polymerized para-aramid stock solution directly for coating (patent No. PCT/JP 2007/0586132007.04.20), but the para-aramid stock solution is not easy to store, and it is necessary to polymerize first and then immediately put into coating use. Shanghai Enjie adopts concentrated sulfuric acid to dissolve para-aramid (patent number CN107732106A), and is not suitable for industrial production.

At present, when the para-aramid coated diaphragm is prepared, the processes of coating, coagulating bath pre-coagulation, washing and drying are mostly adopted, wherein the coagulating bath is a mixed solution of an organic solvent and water, when the para-aramid is pre-coagulated by the coagulating bath, the conditions are severe, fibers are not separated out in time to form a coating, and the thermal shrinkage rate of the prepared coated diaphragm is high. If the ratio of the organic solvent in the coagulation bath is increased, the coating formation rate can be moderated, the heat shrinkage performance of the separator can be reduced, but the organic solvent is more lost, which causes environmental pollution and increases the cost. Cangzhou Mingzhu (patent No. CN104979515A) steam pre-solidifies aramid fiber slurry-coated diaphragm in an environment with humidity more than 90%, in the method, an emulsifier and a binder are added into an aramid fiber polymer solution in a plurality of times, so that the preparation time of the slurry is increased, in addition, the addition of the binder can cause the air permeability value of a coating film to be increased, and the corona treatment is carried out on a base material before coating, so that the steps are complicated. In the Chinese Union of China (patent No. CN107170942A), the diaphragm coated with the aramid fiber membrane casting solution stays for 5-60s, and then enters a coagulating bath of an organic solvent with a certain concentration or is pre-coagulated in water vapor, the coagulation time is 1-10min, the whole process is long in time, and the industrial production is not facilitated.

Disclosure of Invention

The invention aims to provide a high-temperature-resistant para-aramid coated lithium ion battery diaphragm, which is characterized in that para-aramid stock solution with rigid groups introduced into para-aramid is selected as a coating main body, saturated steam is adopted for precipitation, the microstructure is uniform, the thermal shrinkage performance is good, the preparation process is simple, the environmental pollution is less, the cost is low, and the industrialization is easy to realize.

The technical solution for realizing the purpose of the invention is as follows:

a high-temperature-resistant para-aramid coated lithium ion battery diaphragm comprises a base film and a para-aramid coating coated on one side of the base film, wherein the thickness of the base film is 5-30 mu m, the porosity is 20-80%, and the air permeability is 50-800s/100 cc; the thickness of the para-aramid coating is 2-6 mu m, the para-aramid coating comprises para-aramid fibers and inorganic filler, the inorganic filler is uniformly dispersed in the para-aramid fibers, the content of the para-aramid fibers accounts for 20-50% of the whole coating, and the average grain size of the inorganic filler is 10-300 nm.

Further, the high-temperature-resistant para-aramid coated lithium ion battery diaphragm is formed by coating an organic solvent, coating para-aramid composite slurry, precipitating saturated steam, washing and drying para-aramid fiber, wherein the para-aramid composite slurry comprises para-aramid stock solution with a rigid group introduced into para-aramid polymer, the weight percentage of the para-aramid polymer in the para-aramid stock solution is 1-4%, and the apparent viscosity of the para-aramid stock solution is 300-20000 cp.

Furthermore, the high-temperature-resistant para-aramid coated lithium ion battery diaphragm is characterized in that a rigid group is introduced into the para-aramid polymer in a way that a rigid structural unit is introduced into a main chain of the para-aramid polymer, or the para-aramid polymer and a monomer containing the rigid group are subjected to copolycondensation.

Further, the high-temperature-resistant para-aramid coated lithium ion battery diaphragm comprises a base film which comprises any one of a polyethylene microporous film, a polypropylene/polyethylene/polypropylene three-layer composite microporous film, a polyvinylidene fluoride-hexafluoropropylene microporous film, a polyimide microporous film, a polyethylene non-woven fabric, a polypropylene non-woven fabric, a polyester non-woven fabric, a polyimide non-woven fabric, an aramid non-woven fabric and a spandex non-woven fabric.

Further, the high-temperature-resistant para-aramid coated lithium ion battery separator provided by the invention has the advantages that the inorganic filler comprises at least one of aluminum oxide, magnesium oxide, calcium oxide, barium oxide, zinc oxide, silicon dioxide, titanium dioxide, zirconium dioxide, magnesium hydroxide and aluminum hydroxide.

Further, the high-temperature-resistant para-aramid coated lithium ion battery separator provided by the invention has the advantage that the organic solvent comprises at least one of N-methyl pyrrolidone (NMP), N-Dimethylformamide (DMF), N-Dimethylacetamide (DMAC) and Tetramethylurea (TMU).

A method for preparing a high-temperature-resistant para-aramid coated lithium ion battery diaphragm comprises the following steps:

step 1: dispersing inorganic filler in a certain proportion into a para-aramid raw solution, filtering and degassing to obtain para-aramid composite slurry, wherein the para-aramid raw solution comprises a para-aramid polymer with introduced rigid groups;

step 2: coating an organic solvent on one side of the base film, and coating the para-aramid composite slurry obtained in the step 1 on the other side of the base film to obtain a coating film;

and step 3: the coating film slowly separates out a coating through saturated steam, the para-aramid polymer is separated out in a fiber form, and the organic solvent and the water vapor are mutually dissolved and taken away by hot air for recycling;

and 4, step 4: and (4) the coating film enters a water tank for washing, and then enters a drying oven for drying to obtain the para-aramid coated lithium ion battery diaphragm.

Further, in the preparation method of the high-temperature-resistant para-aramid coated lithium ion battery separator, in the step 1, the inorganic filler comprises at least one of aluminum oxide, magnesium oxide, calcium oxide, barium oxide, zinc oxide, silicon dioxide, titanium dioxide, zirconium dioxide, magnesium hydroxide and aluminum hydroxide, and the dispersion mode of the inorganic filler comprises any one of a mechanical stirring method, an ultrasonic dispersion method, a high-pressure dispersion method, a medium dispersion method and a high-speed shearing emulsification method.

Further, in the preparation method of the high-temperature-resistant para-aramid coated lithium ion battery diaphragm, the base film in the step 2 comprises any one of a polyethylene microporous film, a polypropylene/polyethylene/polypropylene three-layer composite microporous film, a polyvinylidene fluoride-hexafluoropropylene microporous film, a polyimide microporous film, a polyethylene non-woven fabric, a polypropylene non-woven fabric, a polyester non-woven fabric, a polyimide non-woven fabric, an aramid non-woven fabric and a spandex non-woven fabric.

Further, in the preparation method of the high-temperature-resistant p-aramid coated lithium ion battery separator, the organic solvent in the step 2 comprises at least one of N-methylpyrrolidone (NMP), N-Dimethylformamide (DMF), N-Dimethylacetamide (DMAC) and Tetramethylurea (TMU).

Further, according to the preparation method of the high-temperature-resistant para-aramid coated lithium ion battery separator, the coating mode in the step 2 comprises any one of gravure coating, slit coating, dip coating, scraper coating, bar coating, scraper coating and wire bar coating.

Further, according to the preparation method of the high-temperature-resistant para-aramid coated lithium ion battery separator, the temperature of saturated steam in the step 3 is 40-60 ℃, the humidity is 60-90% RH, and the coating precipitation time is 10-60 s; the wind speed of the hot wind is 50-80m/min, and the temperature is less than or equal to 60 ℃.

Further, according to the preparation method of the high-temperature-resistant para-aramid coated lithium ion battery diaphragm, 8 sections of water tanks in the step 4 are filled with pure water, overflow from the 8 th stage to the front stage, and the washing time is 30-300 s; the drying adopts a steam heating or electric heating mode, the drying temperature is 60-90 ℃, and the drying time is 30-300 s.

Compared with the prior art, the invention adopting the technical scheme has the following technical effects:

1. the high-temperature-resistant para-aramid coated lithium ion battery diaphragm disclosed by the invention selects para-aramid stock solution with a rigid group introduced into para-aramid as a coating main body, so that the storage time of the para-aramid stock solution can be prolonged, and convenience is provided for coating.

2. According to the preparation method of the high-temperature-resistant para-aramid coated lithium ion battery diaphragm, before slurry is coated, one side of the base film is coated with the organic solvent, so that the para-aramid stock solution can be prevented from blocking micropores of the base film, the ventilation value is reduced, and the problem of easy generation of bubbles in the coating process can be solved.

3. Compared with the method for pre-solidifying the coating film by using a coagulating bath, the preparation method of the high-temperature-resistant para-aramid coated lithium ion battery diaphragm has the advantages that the microstructure of the diaphragm obtained by adopting saturated steam is uniform, and the thermal shrinkage performance is better. And the use amount of the organic solvent can be reduced, the environment is protected, and the cost is relatively low.

Drawings

FIG. 1 is a flow chart of a preparation method of the high-temperature-resistant para-aramid coated lithium ion battery separator.

Fig. 2 is a schematic structural diagram of the high-temperature-resistant para-aramid coated lithium ion battery separator of the present invention.

FIG. 3 is a surface topography of the high temperature resistant para-aramid coated lithium ion battery separator of the present invention.

Fig. 4 is a surface topography plot of a p-aramid coated lithium ion battery separator prepared using a coagulation bath (comparative example 1).

Fig. 5 is a surface topography of a p-aramid coated lithium ion battery separator prepared using pure water as the solidification medium (comparative example 3).

Reference signs mean: 1. a base film; 2. aramid fiber coating; 21. para-aramid fiber; 22. an inorganic filler.

Detailed Description

Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the same or similar elements or elements having the same or similar function throughout. The embodiments described below with reference to the accompanying drawings are illustrative only for the purpose of explaining the present invention, and are not to be construed as limiting the present invention.

A high-temperature-resistant p-aramid coated lithium ion battery diaphragm is shown in figure 2 and comprises a base film 1 and a p-aramid coating layer 2 coated on one side of the base film. Wherein:

the base film 1 has a thickness of 5 to 30 μm, a porosity of 20 to 80%, and an air permeability of 50 to 800s/100 cc. The base film comprises any one of a polyethylene microporous film, a polypropylene/polyethylene/polypropylene three-layer composite microporous film, a polyvinylidene fluoride-hexafluoropropylene microporous film, a polyimide microporous film, a polyethylene non-woven fabric, a polypropylene non-woven fabric, a polyester non-woven fabric, a polyimide non-woven fabric, an aramid non-woven fabric and a spandex non-woven fabric.

The thickness of the para-aramid coating 2 is 2-6 mu m, the para-aramid coating 2 comprises para-aramid fibers 21 and inorganic filler 22, the content of the para-aramid fibers 21 accounts for 20-50% of the whole coating, the content of para-aramid polymers is too low, the temperature resistance of the diaphragm is reduced, the content is too high, and the air permeability of the diaphragm is reduced. The inorganic filler 22 is uniformly dispersed in the para-aramid fiber 21, and the average particle diameter of the inorganic filler 22 is 10 to 300 nm. The inorganic filler includes at least one of alumina, magnesia, calcium oxide, barium oxide, zinc oxide, silica, titania, zirconia, magnesium hydroxide, and aluminum hydroxide.

The para-aramid fiber 21 is formed by coating an organic solvent, coating para-aramid composite slurry, precipitating saturated steam, washing and drying. Wherein the organic solvent comprises at least one of N-methylpyrrolidone (NMP), N-Dimethylformamide (DMF), N-Dimethylacetamide (DMAC), and Tetramethylurea (TMU). The para-aramid composite size comprises para-aramid stock solution with rigid groups introduced into para-aramid polymer, and the rigid groups are introduced into para-aramid, so that the storage time of the para-aramid stock solution can be prolonged, and convenience is provided for coating of the para-aramid size. The weight percentage of the para-aramid polymer in the para-aramid stock solution is 1-4%, the apparent viscosity of the para-aramid stock solution is 300-20000cp, the viscosity is too low, the strength of the obtained coating is not enough, the viscosity is too high, and the para-aramid stock solution is difficult to form a film. The method for introducing the rigid group into the para-aramid polymer is to introduce a rigid structural unit into a main chain of the para-aramid polymer or to carry out copolycondensation on the para-aramid polymer and a monomer containing the rigid group.

A method for preparing a high-temperature-resistant p-aramid coated lithium ion battery separator is shown in figure 1 and comprises the following steps:

step 1: dispersing inorganic filler with a certain proportion into a para-aramid stock solution, filtering and degassing to obtain para-aramid composite slurry, wherein the para-aramid stock solution comprises a para-aramid polymer with introduced rigid groups. The inorganic filler comprises at least one of alumina, magnesia, calcium oxide, barium oxide, zinc oxide, silicon dioxide, titanium dioxide, zirconium dioxide, magnesium hydroxide and aluminum hydroxide, and the dispersion mode of the inorganic filler comprises any one of a mechanical stirring method, an ultrasonic dispersion method, a high-pressure dispersion method, a medium dispersion method and a high-speed shearing emulsification method.

Step 2: 1) one side of the base film is coated with an organic solvent, and the base film comprises any one of a polyethylene microporous film, a polypropylene/polyethylene/polypropylene three-layer composite microporous film, a polyvinylidene fluoride-hexafluoropropylene microporous film, a polyimide microporous film, a polyethylene non-woven fabric, a polypropylene non-woven fabric, a polyester non-woven fabric, a polyimide non-woven fabric, an aramid non-woven fabric and a spandex non-woven fabric. The organic solvent includes at least one of N-methylpyrrolidone (NMP), N-Dimethylformamide (DMF), N-Dimethylacetamide (DMAC), Tetramethylurea (TMU). The organic solvent is firstly used for coating one side of the base film, so that the micropores of the base film can be occupied in advance, the air permeability of the diaphragm is prevented from being reduced when para-aramid slurry permeates the micropores of the base film, and the phenomena of bubbles and curling in the coating process can be improved.

2) And (3) coating the para-aramid composite slurry obtained in the step (1) on the other side of the base film to obtain a coating film.

The coating method includes any one of gravure coating, slit coating, dip coating, blade coating, bar coating, blade coating, and wire bar coating.

And step 3: the coating film slowly separates out the coating through saturated steam, the para-aramid polymer is separated out in a fiber form, and the organic solvent and the water vapor are mutually soluble and are taken away by hot air for recycling. The temperature of saturated steam is 40-60 ℃, the humidity is 60-90% RH, and the coating precipitation time is 10-60 s; the wind speed of the hot wind is 50-80m/min, and the temperature is less than or equal to 60 ℃. Saturated steam is selected to slowly precipitate the coating, the obtained microstructure is a network structure with fibers arranged in a crossed mode (as shown in figure 3), a coagulation bath precipitation mode is adopted, para-aramid fibers are not completely precipitated yet and undergo phase transfer, the para-aramid fibers are coagulated to obtain a coarse and uneven framework, the sizes of holes are not uniform (as shown in figure 4), and therefore the thermal shrinkage rate is higher than that of a saturated steam precipitation mode. In addition, pure water is used as a coagulating bath (as shown in fig. 5), and the phase transfer is rapid, so that the surface micropores of the coating layer are small, the number of the micropores is small, and the air permeability of the product is high.

And 4, step 4: and (4) the coating film enters a water tank for washing, and then enters a drying oven for drying to obtain the para-aramid coated lithium ion battery diaphragm. The water tanks are 8 sections, all contain pure water and overflow from the 8 th stage forward, and the washing time is 30-300 s; the drying adopts a steam heating or electric heating mode, the drying temperature is 60-90 ℃, and the drying time is 30-300 s.

The present invention is further illustrated by the following specific examples.

Example 1

(1) Dispersing alumina powder in a certain proportion in a para-aramid stock solution with a rigid group, the mass fraction of which is 1.5% and the apparent viscosity of which is 300cp, stirring for 30min by a high-speed dispersion emulsifying machine, and filtering by a 1000-mesh filter screen to obtain uniform para-aramid pulp, wherein the alumina contains two particle sizes of 10nm and 300 nm;

(2) selecting a wet-process synchronous double-drawing polyethylene diaphragm with the thickness of 5 mu m, wherein the porosity is 37 percent, the air permeability is 110s/100cc, firstly coating one side of a base film by using an organic solvent in a gravure coating mode, and then coating the para-aramid pulp on the other side of the base film in the gravure coating mode;

(3) the prepared coating film stays for 30s in a saturated steam atmosphere of 60 ℃ and 60% RH, then enters a pure water tank for washing for 120s, and then enters a 75 ℃ drying oven for drying for 60s to obtain the p-aramid coated lithium ion battery diaphragm.

Example 2

(1) Dispersing alumina powder in a certain proportion in a para-aramid stock solution with a rigid group and a mass fraction of 2% and an apparent viscosity of 20000cp, stirring for 60min by a high-speed dispersion emulsifying machine, and filtering by a 1000-mesh filter screen to obtain uniform para-aramid pulp, wherein the average particle size of the alumina is 100 nm;

(2) selecting a wet-process synchronous double-drawing polyethylene diaphragm with the thickness of 12 mu m, coating one side of a base film by using an organic solvent in a wire rod coating mode, and then coating the para-aramid slurry on the other side of the base film in a scraper coating mode, wherein the porosity is 40%, and the air permeability is 190s/100 cc;

(3) the prepared coating film stays for 10s in a saturated steam atmosphere of 50 ℃ and 70% RH, then enters a pure water tank for washing for 200s, and then enters a 90 ℃ oven for drying for 90s to obtain the p-aramid coated lithium ion battery diaphragm.

Example 3

(1) Dispersing alumina powder in a certain proportion in a para-aramid stock solution with mass fraction of 4% and apparent viscosity of 5000cp and rigid groups, stirring for 2h by a high-speed dispersion emulsifying machine, and filtering by a 1000-mesh filter screen to obtain uniform para-aramid pulp, wherein the average particle size of the alumina is 200 nm;

(2) selecting a wet-process synchronous double-drawing polyethylene diaphragm with the thickness of 9 mu m, coating one side of a base film by using an organic solvent in a gravure coating mode, and then coating the para-aramid slurry on the other side of the base film in a scraper coating mode, wherein the porosity is 38% and the air permeability is 160s/100 cc;

(3) the prepared coating film stays for 60s in a saturated steam atmosphere of 40 ℃ and 90% RH, then enters a pure water tank for washing for 30s, and then enters a 60 ℃ oven for drying for 120s to obtain the p-aramid coated lithium ion battery diaphragm.

Comparative example 1

(1) Dispersing alumina powder in a certain proportion in a para-aramid stock solution with a rigid group, the mass fraction of which is 1.5% and the apparent viscosity of which is 300cp, stirring for 30min by a high-speed dispersion emulsifying machine, and filtering by a 1000-mesh filter screen to obtain uniform para-aramid pulp, wherein the alumina contains two particle sizes of 10nm and 300 nm;

(2) selecting a wet-process synchronous double-drawing polyethylene diaphragm with the thickness of 5 mu m, coating the para-aramid pulp on the other side of the base film in a gravure coating mode, wherein the porosity is 37 percent, and the air permeability is 110s/100 cc;

(3) the prepared coating film stays for 30s in a saturated steam atmosphere of 60 ℃ and 60% RH, then enters a pure water tank for washing for 120s, and then enters a 75 ℃ drying oven for drying for 60s to obtain the p-aramid coated lithium ion battery diaphragm.

Comparative example 2

(1) Dispersing alumina powder in a certain proportion in a para-aramid stock solution with a rigid group and a mass fraction of 2% and an apparent viscosity of 20000cp, stirring for 60min by a high-speed dispersion emulsifying machine, and filtering by a 1000-mesh filter screen to obtain uniform para-aramid pulp, wherein the average particle size of the alumina is 100 nm;

(2) selecting a wet-process synchronous double-drawing polyethylene diaphragm with the thickness of 12 mu m, coating one side of a base film by using an organic solvent in a wire rod coating mode, and then coating the para-aramid slurry on the other side of the base film in a scraper coating mode, wherein the porosity is 40%, and the air permeability is 190s/100 cc;

(3) the prepared coating film is pre-solidified for 20s in a gradient solidification bath with the NMP mass ratio of 70-30-10%, then enters a pure water tank for washing for 200s, and then enters a 90 ℃ drying oven for drying for 90s to obtain the p-aramid coated lithium ion battery diaphragm.

Comparative example 3

(1) Dispersing alumina powder in a certain proportion in a para-aramid stock solution with a rigid group and a mass fraction of 2% and an apparent viscosity of 20000cp, stirring for 60min by a high-speed dispersion emulsifying machine, and filtering by a 1000-mesh filter screen to obtain uniform para-aramid pulp, wherein the average particle size of the alumina is 100 nm;

(2) selecting a wet-process synchronous double-drawing polyethylene diaphragm with the thickness of 12 mu m, coating one side of a base film by using an organic solvent in a wire rod coating mode, and then coating the para-aramid slurry on the other side of the base film in a scraper coating mode, wherein the porosity is 40%, and the air permeability is 190s/100 cc;

(3) the prepared coating film is pre-solidified for 20s in a solidifying bath with the mass ratio of NMP of 90%, then enters a pure water tank for washing for 200s, and then enters a drying oven with the temperature of 90 ℃ for drying for 90s to obtain the p-aramid coated lithium ion battery diaphragm.

Comparative example 4

(1) Dispersing alumina powder in a certain proportion in a para-aramid stock solution with a rigid group and a mass fraction of 2% and an apparent viscosity of 20000cp, stirring for 60min by a high-speed dispersion emulsifying machine, and filtering by a 1000-mesh filter screen to obtain uniform para-aramid pulp, wherein the average particle size of the alumina is 100 nm;

(2) selecting a wet-process synchronous double-drawing polyethylene diaphragm with the thickness of 12 mu m, coating one side of a base film by using an organic solvent in a wire rod coating mode, and then coating the para-aramid slurry on the other side of the base film in a scraper coating mode, wherein the porosity is 40%, and the air permeability is 190s/100 cc;

(3) the prepared coating film is pre-solidified in pure water for 20s, then enters a next-stage pure water tank for washing for 200s, and then enters a 90 ℃ oven for drying for 90sn to obtain the p-aramid coated lithium ion battery diaphragm.

Comparative example 5

(1) Dispersing alumina powder in a certain proportion in a para-aramid stock solution with mass fraction of 4% and apparent viscosity of 5000cp and rigid groups, stirring for 2h by a high-speed dispersion emulsifying machine, and filtering by a 1000-mesh filter screen to obtain uniform para-aramid pulp, wherein the average particle size of the alumina is 200 nm;

(2) selecting a wet-process synchronous double-drawing polyethylene diaphragm with the thickness of 9 mu m, coating one side of a base film by using an organic solvent in a gravure coating mode, and then coating the para-aramid slurry on the other side of the base film in a scraper coating mode, wherein the porosity is 38% and the air permeability is 160s/100 cc;

(3) the prepared coating film is pre-solidified for 20s in a gradient solidification bath with the NMP mass ratio of 70-30-10%, then the coating film enters a pure water tank for washing for 30s, and then the coating film enters a 60 ℃ drying oven for drying for 120s to obtain the p-aramid coated lithium ion battery diaphragm.

The lithium ion battery separators coated with the para-aramid fibers obtained in the examples and the comparative examples of the present invention were subjected to thickness, air permeability and thermal shrinkage tests, respectively, and the test results are shown in table 1.

The thickness was measured according to the method specified in GB/T6672-2001, the air permeability was measured according to the method specified in GB/1038 and the heat shrinkage was measured according to the method specified in GB/T12027-2004.

TABLE 1

In comparison with example 1, comparative example 1 did not coat with an organic solvent before the slurry coating, and as a result, the air permeability of the obtained para-aramid coated separator was decreased. The slurry, base film and preparation method used in comparative examples 2,3 and 4 were the same as in example 2, and the slurry, base film and preparation method used in comparative example 5 were the same as in example 3, except that the coating deposition pattern was different. As can be seen from the data in table 1, the thermal shrinkage of the para-aramid coated membranes obtained by precipitation in the coagulation bath in comparative examples 2,3,4 and 5 was higher than that of examples 2 and 3, while the products obtained by slowly precipitating the coating with saturated steam had better high temperature resistance, and the para-aramid coated membranes obtained by using pure water as the coagulation bath in comparative example 4 had higher air permeation increment. In conclusion, the para-aramid coated lithium ion battery diaphragm and the preparation method provided by the invention can effectively improve the diaphragm performance, reduce the use of organic solvents, reduce the cost and have high industrialization value.

The foregoing is directed to embodiments of the present invention and, more particularly, to a method and apparatus for controlling a power converter in a power converter, including a power converter, a power.