WO2023159790A1

WO2023159790A1 - Lithium ion battery composite separator and preparation method therefor

Info

Publication number: WO2023159790A1
Application number: PCT/CN2022/095798
Authority: WO
Inventors: 王连广; 刘杲珺; 高飞飞; 白麟; 白耀宗; 孙婧; 秦文娟; 汤晓; 李论
Original assignee: 中材锂膜有限公司
Priority date: 2022-02-24
Filing date: 2022-05-28
Publication date: 2023-08-31
Also published as: CN114243217B; CN114243217A

Abstract

The present invention belongs to the field of batteries, and provides a lithium ion battery composite separator and a preparation method therefor. The lithium ion battery composite separator comprises a base membrane and an aramid coating, which is coated on one side or both sides of the base membrane. The liquid absorption rate of the lithium ion battery composite separator is greater than or equal to 1 mm/min. The preparation method provided in the present invention can improve the liquid absorption performance of the prepared battery separator.

Description

Lithium-ion battery composite diaphragm and preparation method thereof

technical field

The invention belongs to the field of batteries, and more specifically relates to a lithium-ion battery composite diaphragm and a preparation method thereof.

Background technique

Lithium-ion batteries generally include a positive electrode, a negative electrode, a separator, and an electrolyte. As one of the inner components of lithium-ion batteries, the performance of the separator determines the interface structure and internal resistance of the battery, which directly affects the capacity, cycle and safety performance of the battery. A separator with excellent performance is of great importance to improve the overall performance of the battery. role. The main function of the diaphragm is to separate the positive and negative electrodes of the battery, prevent the two electrodes from contacting and short circuit, and also have the function of allowing electrolyte ions to pass through.

At present, most of the separator products on the market are coated with a layer of water-based paint with inorganic particles on the surface of the polyethylene substrate to form an inorganic ceramic coated separator. However, the wetting rate of this type of separator to the electrolyte is poor, which limits the battery capacity. Injection efficiency. Compared with the inorganic ceramic coated diaphragm, the existing oil-based PVDF coated diaphragm has a high liquid absorption rate, but PVDF has the problem of swelling in the electrolyte and poor liquid absorption rate. The aramid separator is the best choice because of its good liquid absorption rate, low swelling performance, and high heat resistance. However, the aramid separator on the market still has a limited absorption rate for the electrolyte. It is necessary to further improve the aramid diaphragm.

Contents of the invention

The object of the present invention is to provide a lithium-ion battery composite diaphragm and a preparation method thereof. The battery composite diaphragm of the invention has a relatively high liquid absorption rate.

In a first aspect, the present invention provides a lithium-ion battery composite diaphragm, comprising a base film and an aramid coating coated on one or both sides of the base film; and the liquid absorption rate of the lithium-ion battery composite diaphragm is greater than or equal to 1mm /min.

In a second aspect, the present invention provides a method for preparing the lithium-ion battery composite separator, the method comprising:

(1) In the presence of a Lewis acid and a first organic solvent, the aramid raw material is subjected to a halogenated alkylation reaction with a chlorinated organic compound shown in formula I to obtain a modified aramid;

Cl(CH ₂ ) _n R Formula I

In formula I, n represents an integer from 1 to 5, and R represents a hydroxyl group or an oxirane group;

(2) dispersing the modified aramid fiber and the inorganic filler in a second organic solvent to obtain a modified aramid fiber slurry;

(3) Coating the modified aramid fiber slurry on the base film, followed by pre-solidification, water washing and drying to obtain the battery composite diaphragm.

The lithium ion battery composite diaphragm of the invention has a relatively high liquid absorption rate. In the preparation process, the chlorinated organic compound shown in formula I is first subjected to halogenated alkylation reaction with the aramid raw material to modify the aramid fiber, so that the surface of the aramid fiber has more hydroxyl groups, and the modified aramid fiber is made When the slurry is coated on the base film, it is easier to form a hydrogen bond with the electrolyte due to the introduction of hydroxyl groups, thereby improving the ability of the aramid fiber to combine with the electrolyte, and further improving the liquid absorption rate of the battery composite separator, which is conducive to improving the injection rate during the battery manufacturing process. liquid rate, and the invention also improves the liquid absorption rate of the diaphragm, which is beneficial to improve battery life.

Other features and advantages of the present invention will be described in detail in the detailed description that follows.

Detailed ways

Specific embodiments of the present invention will be described in detail below. It should be understood that the specific embodiments described here are only used to illustrate and explain the present invention, and are not intended to limit the present invention.

The first aspect of the present invention provides that the present invention provides a kind of lithium-ion battery composite diaphragm, comprises base film and the aramid fiber coating that is coated on one or both sides of described base film; The liquid absorption rate of described lithium-ion battery composite diaphragm ≥1mm/min.

In the present invention, the aramid fiber coating includes modified aramid fibers and inorganic fillers. The modified aramid fiber is prepared through the following steps: in the presence of a Lewis acid and a first organic solvent, the aramid fiber raw material and chlorinated organic matter are subjected to haloalkylation reaction. Described chlorinated organic compound is as shown in formula I:

Cl(CH ₂ ) _n R Formula I

In formula I, n represents an integer from 1 to 5, specifically, n is selected from 1, 2, 3, 4 or 5; R represents hydroxyl (OH) or oxirane. The oxirane group refers to a group formed by oxirane losing a hydrogen atom.

Specifically, the chlorinated organic compound can be selected from 2-chloroethanol (n=2, R is a hydroxyl group), 3-chloro-1-propanol (n=3, R is a hydroxyl group), 4-chloro-1-butanol Alcohol (n=4, R is hydroxyl), 5-chloro-1-pentanol (n=5, R is hydroxyl) and 3-chloro-1,2-propylene oxide (n=1, R is ethylene oxide base) at least one. Preferably, the chlorinated organic compound is selected from at least one of 2-chloroethanol, 3-chloro-1-propanol and 3-chloro-1,2-epoxypropane. In this case, the lithium ion The battery composite separator has a higher liquid absorption rate and liquid absorption rate.

In the present invention, the aramid raw material may be selected from meta-aramid or para-aramid, and the weight average molecular weight (M _w ) of the aramid raw material may be 0.5-100,000. Preferably, the aramid raw material is para-aramid, and the weight-average molecular weight of the para-aramid is 60,000-80,000, more preferably 60,000-30,000.

The present invention has no special limitation on the Lewis acid, as long as the Friedel-Crafts alkylation reaction between the aramid raw material and the chlorinated compound can be realized. Generally, the Lewis acid can be selected from AlCl ₃ , BF ₃ , ZnCl ₂ and the like. Preferably, the Lewis acid is AlCl ₃ .

In the present invention, the first organic solvent can form an intermediate complex, and the first organic solvent can be selected from at least one of ethanol, n-propanol, isopropanol and n-butanol.

In the present invention, the mass ratio of the aramid raw material to the chlorinated organic compound may be 1:(1-10), preferably 1:(1-8). The mass ratio of the aramid raw material to the Lewis acid and the first organic solvent may be 1:(0.01-0.1):(4-7). The reaction temperature of the haloalkylation reaction can be 60-90° C., and the reaction time is not less than 3 hours, for example, the reaction time is 3 hours, 4 hours, 5 hours or 6 hours.

According to the present invention, the Friedel-Crafts alkylation reaction between the aramid raw material and the chlorinated organic matter replaces the -H on the benzene ring of the aramid structure, and introduces the hydroxyl group on the alcohol or the epoxy compound from the aramid fiber. Ethyl oxide, and ethyl oxide can be further hydrolyzed to form hydroxyl due to alkaline aqueous solution (such as lithium hydroxide solution) during the washing process.

In the present invention, the inorganic filler can be selected from α-alumina, γ-alumina, boehmite, calcium carbonate, hydrotalcite, montmorillonite, spinel, titanium dioxide, silicon dioxide, zirconia, oxide At least one of magnesium, calcium oxide, beryllium oxide, magnesium hydroxide, calcium hydroxide and silicon carbide. The median particle size (D50) of the inorganic filler may be 5-700 nm, preferably 10-600 nm, more preferably 100-500 nm. In the aramid fiber coating, the content of the inorganic filler may be 40-80% by weight.

In the present invention, the thickness of the aramid fiber coating may be 1-5 μm, preferably 2-4 μm.

In the present invention, the base film can be selected from polyethylene diaphragms, polypropylene diaphragms, polyethylene/polypropylene hybrid diaphragms, polyethylene/polypropylene/polyethylene three-layer diaphragms, polyimide diaphragms and non-woven fabrics. At least one, the porosity of the base film is 30-60%. Preferably, the base film is a polyethylene membrane or a polypropylene membrane.

The thickness of the base film may be 4-16 μm, preferably 8-12 μm.

The liquid absorption rate of the lithium ion battery composite diaphragm of the present invention is ≥ 1 mm/min, preferably ≥ 1.3 mm/min. The liquid absorption rate is measured in an electrolyte composed of ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) (group EC/EMC/DEC volume ratio = 3/1/6) Obtained, specifically test the height h (mm) of the electrolyte solution climbing when t (t=30min), the liquid absorption rate of the electrolyte solution is h/t, and the unit is mm/min.

A second aspect of the present invention provides a method for preparing the lithium-ion battery composite separator, the method comprising:

(1) In the presence of a Lewis acid and a first organic solvent, the aramid fiber raw material is subjected to a halogenated alkylation reaction with a chlorinated organic compound to obtain a modified aramid fiber;

(3) Coating the modified aramid slurry on one or both sides of the base film, followed by pre-solidification, water washing and drying in sequence to form an aramid coating on the surface of the base film.

In the method provided by the present invention, the description of the Lewis acid, the first organic solvent, the aramid raw material, the chlorinated organic matter, the halogenated alkylation reaction and the inorganic filler is as described in the first aspect of the present invention, and will not be repeated here. .

The method of dispersion is not particularly limited in the present invention, as long as the inorganic filler can be uniformly dispersed in the slurry. For example, the dispersion method may be selected from one or more of high-speed disperser dispersion, grinding dispersion and ultrasonic dispersion.

In step (2), the second organic solvent is used to disperse the inorganic filler and the modified aramid fiber, and the second organic solvent can be selected from N-methylpyrrolidone (NMP), dimethyl sulfoxide (DMSO), N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAC), tetramethylurea (TMU).

In step (2), the mass ratio of the modified aramid fiber, the inorganic filler and the second organic solvent may be 1:(1-4):(20-100).

In the present invention, the quality and content of the modified aramid fiber are calculated based on the raw material of the aramid fiber.

In step (3), the coating method can be selected with reference to the prior art, for example, selected from micro gravure roll coating, wire rod coating, doctor blade coating or extrusion coating.

In step (3), through the pre-solidification, the aramid fiber in the coating can be gradually precipitated into a three-dimensional network structure, and the second organic solvent can be dissolved in the coagulation bath to be slowly replaced. In one embodiment, the pre-solidification process includes: passing the coated base film through a coagulation bath with a concentration gradient, wherein the coagulation bath is a mixture of a second organic solvent and water. The coagulation bath process can be provided with more than 2 coagulation tanks, for example, 2 or 3 coagulation tanks, and the content of the third organic solvent in each coagulation tank is gradually decreased. The pre-solidification time may be 30-120s.

In a preferred embodiment, the number of coagulation tanks containing the coagulation bath is two, and the contents of the second organic solvent in the two coagulation tanks are respectively 35-50% by weight and 15-30% by weight

In step (3), the coating film pre-coagulated by the coagulation bath can enter a water tank for the water washing, and the water washing time can be 120-300s. The sink may be a pure water sink or an alkaline aqueous solution sink.

In step (3), the drying can be carried out in an oven, for example, by means of roller contact heating and drying. The drying temperature may be 60-90°C.

In the battery composite separator prepared by the method of the present invention, the modified aramid fiber slurry is prepared by the method of step (1), and the base film is subsequently coated with the slurry, which can further improve the liquid absorption rate of the separator, while ensuring The battery composite separator has a high liquid absorption rate.

The present invention will be further described below in conjunction with examples, but the scope of the present invention is not limited to these examples.

Example 1

Under the protection of nitrogen, add 10g of para-aramid fiber (M _W =10000) into a reaction bottle containing 60g of absolute ethanol, add 0.5g of anhydrous AlCl ₃ , then add 20g of 2-chloroethanol, heat to 81°C, After reacting for 5 hours, 330 g of NMP was added and stirred evenly to obtain a modified aramid fiber dispersion. After cooling to room temperature, mix the modified aramid dispersion with 20g of alumina powder (α-type, D50=200nm) and stir at high speed (rotational speed 1500rpm) for 60min, then grind it with a grinder for 3 times, and then filter with a 300-mesh filter Finally, a uniform modified aramid fiber slurry is obtained.

A synchronous biaxially stretched polyethylene film with a thickness of 9 μm and a porosity of 38% was selected, and the modified aramid fiber slurry was evenly coated on one side of the base film (that is, on one surface) by wire bar coating. A separator coated with the aramid slurry was formed.

Send the diaphragm coated with aramid slurry into the first coagulation tank and the second coagulation tank for two-stage pre-coagulation. The membrane stays in each coagulation tank for 33 seconds. The coagulation baths in the two coagulation tanks are all water and NMP, and the NMP concentration in the first coagulation bath is 40% by weight, and the NMP concentration in the second coagulation bath is 28% by weight.

Subsequently, the pre-solidified coating film was washed in a pure water tank for 200 s, dried in an oven at 70°C, and wound up to obtain a battery composite separator with a thickness of 12 μm, which was designated as A1.

Example 2

Under the protection of nitrogen, 10g of para-aramid fiber (M _W =10000) was added to a reaction bottle filled with 60g of absolute ethanol, 0.5g of anhydrous AlCl ₃ was added, and then 29g of 3-chloro-1-propanol was added, heated to After reacting for 5 hours at 81°C, add 330g of NMP and stir evenly to obtain a modified aramid fiber dispersion. After cooling to room temperature, mix the modified aramid fiber dispersion with 20g of alumina powder (α type, D50=200nm) Stir (rotating speed 1500rpm), stir for 60min, then grind 3 times with a grinder, and then filter with a 300-mesh filter screen to obtain a uniform modified aramid fiber slurry.

Select a synchronous biaxially oriented polyethylene film with a thickness of 9 μm and a porosity of 38%, and use a wire bar coating method to evenly coat the modified aramid fiber slurry on one side of the base film to form a layer coated with aramid fiber. Slurry diaphragm.

Subsequently, the pre-solidified coating film was washed in a pure water tank for 200 s, and dried in an oven at 70°C. Finally, a battery composite separator with a thickness of 12 μm was obtained after winding, and the separator was designated as A2.

Example 3

Under nitrogen protection, 10g of para-aramid (M _W =10000) was added to a reaction bottle filled with 60g of absolute ethanol, 0.5g of anhydrous AlCl ₃ was added, and then 3-chloro-1,2-propylene oxide was added 28.7g, heated to 81°C, reacted for 5h, added 330g NMP, stirred evenly to obtain modified aramid fiber dispersion, after cooling to room temperature, mixed modified aramid fiber dispersion with 20g alumina powder (α type, D50= 200nm) and then stirred (rotating speed 1500rpm), stirred for 60min, then ground 3 times with a grinder, and then filtered with a 300-mesh filter screen to obtain a uniform modified aramid fiber slurry.

Subsequently, the pre-solidified coating film was sent to a water tank for water washing (1 wt% lithium hydroxide aqueous solution) for 100 seconds, and then into a pure water tank for water washing for 100 seconds. Dry in an oven at 70°C. Finally, a battery composite separator with a thickness of 12 μm was obtained after winding, and the separator was designated as A3.

Example 4

Under nitrogen protection, 10g of para-aramid (M _W =10000) was added to a reaction flask filled with 60g of absolute ethanol, 0.5g of anhydrous AlCl ₃ was added, and then 33.7g of 4-chloro-1-butanol was added, Heat to 81°C, react for 5 hours, add 330g NMP, stir evenly to obtain a modified aramid fiber dispersion, after cooling to room temperature, mix the modified aramid fiber dispersion with 20g of alumina powder (α type, D50=200nm) Afterwards, stir at a high speed (1500 rpm) for 60 minutes, then grind 3 times with a grinder, and then filter with a 300-mesh filter screen to obtain a uniform modified aramid fiber slurry.

Subsequently, the pre-solidified coating film was washed in a pure water tank for 200 seconds, and dried in an oven at 70°C. Finally, a battery composite separator with a thickness of 12 μm was obtained after winding, and the separator was designated as A4.

Example 5

Under nitrogen protection, 10g of para-aramid (M _W =10000) was added to a reaction bottle containing 60g of absolute ethanol, 0.5g of anhydrous AlCl ₃ was added, 76.2g of 5-chloro-1-pentanol was added, and heated After reacting for 5 hours at 81°C, add 330g of NMP and stir evenly to obtain a modified aramid dispersion. After cooling to room temperature, mix the modified aramid dispersion with 20g of alumina powder (α-type, D50=200nm) Stir (rotating speed 1500rpm), stir for 60min, then grind 3 times with a grinder, and then filter with a 300-mesh filter screen to obtain a uniform modified aramid fiber slurry.

Subsequently, the pre-solidified coating film was washed in a pure water tank for 200 seconds, and dried in an oven at 70°C. Finally, a battery composite separator with a thickness of 12 μm was obtained after winding, and the separator was designated as A5.

Comparative example 1

The biaxially stretched polyethylene film used in Example 1 was used as a comparative separator, which was denoted as D1.

Comparative example 2

A synchronous biaxially oriented polyethylene film with a thickness of 12 μm and a porosity of 38% was selected as a comparison separator, which was denoted as D2.

Comparative example 3

Mix 20g of alumina powder (α-type, D50=200nm) with 30g of water and stir at high speed (1500rpm) for 60min, then use a grinder to grind 3 times, add 3g of polyacrylic resin suspension and 0.03g of Wetting agent, and then filtered through a 300-mesh filter to obtain a uniformly dispersed alumina slurry.

A synchronous biaxially oriented polyethylene film with a thickness of 9 μm and a porosity of 38% was selected, and the aluminum oxide slurry was uniformly coated on one side of the base film by wire bar coating to form a layer coated with aluminum oxide slurry. diaphragm.

Subsequently, the coated film was dried in an oven at 70°C. Finally, an aluminum oxide-coated separator with a thickness of 12 μm was obtained after winding, which was denoted as D3.

Comparative example 4

Add 10g of para-aramid fiber to 390g of NMP solvent, heat to 81°C and stir for 5h. After stirring evenly, a para-aramid fiber liquid is obtained. After cooling to room temperature, mix the para-aramid fiber liquid with 20g of alumina powder (α-type , D50=200nm) after mixing, continue to stir at a high speed (1500rpm) for 60min, then grind 3 times with a grinder, and then filter through a 300-mesh filter screen to obtain a uniform modified aramid fiber slurry.

Select a synchronous biaxially oriented polyethylene film with a thickness of 9 μm and a porosity of 38%, and use a wire bar coating method to evenly coat the aramid slurry on one side of the base film to form a layer coated with aramid slurry. diaphragm.

Subsequently, the pre-solidified coating film was sent to a water tank for washing for 200 s, and dried in an oven at 70°C. Finally, an aramid coated film with a thickness of 12 μm was obtained after winding, which was denoted as D4.

Example 6

Under the protection of nitrogen, 10g of para-aramid fiber (M _W =10000) was added to a reaction flask filled with 60g of anhydrous n-propanol, 0.5g of anhydrous AlCl ₃ was added, and then 18g of 2-chloroethanol was added, heated to 81 ℃, after reacting for 5 hours, add 330g of DMAC and stir evenly to obtain a modified aramid dispersion. After cooling to room temperature, mix the modified aramid dispersion with 20g of alumina powder (α-type, D50=200nm) and stir at high speed (rotating speed 1800rpm) for 45 minutes, then grind 3 times with a grinder, and then filter with a 300-mesh filter screen to obtain a uniform modified aramid fiber slurry.

The diaphragm coated with aramid slurry is sent to the first coagulation tank and the second coagulation tank for two-stage pre-coagulation. The membrane stays in each coagulation tank for 35 seconds. The coagulation baths in the two coagulation tanks are all water and DMAC, and the DMAC concentration in the first coagulation bath is 38% by weight, and the DMAC concentration in the second coagulation bath is 26% by weight.

Subsequently, the pre-solidified coating film was sent to a water tank for washing for 230 seconds, and dried in an oven at 70°C. Finally, an aramid coated film with a thickness of 12 μm was obtained after winding, which was designated as A6.

Comparative example 5

Under the protection of nitrogen, add 10g of para-aramid fiber (M _W =10000) into 390g of DMAC, heat to 81°C and stir for 5h. After stirring evenly, aramid fiber dispersion is obtained. After cooling to room temperature, the modified aramid fiber dispersion is mixed with After mixing 20g of alumina powder (α-type, D50=200nm), continue high-speed stirring (1800rpm) for 45 minutes, then grind 3 times with a grinder, and then filter with a 300-mesh filter to obtain a uniform modified aramid fiber slurry.

Subsequently, the pre-solidified coating film was sent to a water tank for washing for 230 seconds, and dried in an oven at 70°C. Finally, an aramid coating film with a thickness of 12 μm was obtained after winding, which was recorded as D5.

Comparative example 6

According to the modification method in the patent document CN111969160A embodiment 1, modify the para-aramid fiber (MW=10000), obtain the modified aramid fiber dispersion liquid, after cooling to room temperature, mix the modified aramid fiber dispersion liquid with 20g alumina powder ( α type, D50=200nm) after mixing, high-speed stirring (rotating speed 1500rpm) for 60 minutes, then grinding 3 times with a grinder, and then filtering with a 300-mesh filter to obtain a uniform modified aramid fiber slurry.

Subsequently, the pre-solidified coating film was sent to a water tank for water washing (1 wt% lithium hydroxide aqueous solution) for 100 seconds, and then into a pure water tank for water washing for 100 seconds. Dry in an oven at 70°C. Finally, a battery composite separator with a thickness of 12 μm was obtained after winding, and the separator was marked as D6.

test case

The properties of the separators A1-A6 and D1-D6 prepared in the examples and comparative examples were tested.

1. Test of liquid absorption rate

Cut the diaphragm into a strip-shaped diaphragm sample with a width of 25mm and a length of 150mm, and soak one end of the width of the diaphragm sample into the electrolyte solution with a depth of 10mm (composition: EC/EMC/DEC volume ratio = 3/1/6) , start timing, and test the height h (mm) of the electrolyte solution climbing at t (t=30min), and the liquid absorption rate of the electrolyte solution is h/t, and the unit is mm/min.

2. Test of liquid absorption rate

Cut the diaphragm into a strip-shaped diaphragm sample with a width of 25mm and a length of 150mm, test the mass m ₀ of the initial sample, and completely soak the diaphragm sample into the electrolyte (the composition is: EC/EMC/DEC volume ratio=3/1 /6), place it sealed for 2 hours, take out the diaphragm, wipe the electrolyte on the surface of the diaphragm with filter paper, weigh the mass m ₁ of the diaphragm after soaking in the electrolyte, and calculate the liquid absorption rate of the diaphragm according to the following formula:

Diaphragm liquid absorption = (m ₁ -m ₀ )/m ₀ ×100%

The test results are shown in Table 1.

Table 1

It can be seen from the above that compared with Comparative Examples 1-6, in Examples 1-6, the battery separator coated with the modified aramid coating has a higher liquid absorption rate, and also has a higher liquid absorption rate .

Having described various embodiments of the present invention, the foregoing description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and alterations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments.

Neither the endpoints nor any values of the ranges disclosed herein are limited to such precise ranges or values, and these ranges or values are understood to include values approaching these ranges or values. For numerical ranges, between the endpoints of each range, between the endpoints of each range and individual point values, and between individual point values can be combined with each other to obtain one or more new numerical ranges, these values Ranges should be considered as specifically disclosed herein.

Claims

A lithium-ion battery composite diaphragm, characterized in that the lithium-ion battery composite diaphragm comprises a base film and an aramid coating coated on one or both sides of the base film, and the aramid coating contains modified aramid A fiber and an inorganic filler, wherein the modified aramid fiber is prepared by a method comprising the following steps: in the presence of a Lewis acid and a first organic solvent, the aramid fiber raw material and the chlorinated organic compound represented by formula I are subjected to haloalkylation Chemical reaction, then pre-coagulation, washing and drying;

Cl(CH 2 ) n R Formula I

In formula I, n represents an integer from 1 to 5, R represents a hydroxyl group or an oxirane group,

The aramid raw material is para-aramid;

The water washing is carried out in a water tank, and when the R in the formula I represents a hydroxyl group, the water tank is a pure water tank; when the R in the formula I represents an oxirane group, the process of the water washing is: first in the alkali Rinse in an aqueous solution tank, and then in a pure water tank;

Moreover, the liquid absorption rate of the lithium-ion battery composite diaphragm is ≥ 1mm/min; the liquid absorption rate is an electrolyte composed of ethylene carbonate, ethyl methyl carbonate and diethyl carbonate according to a volume ratio of 3:1:6 Measured in the test, the test time t is the height h of the electrolyte climb when the test time t is 30min, and the liquid absorption rate of the electrolyte is h/t, and the unit is mm/min.
The lithium-ion battery composite separator according to claim 1, characterized in that, the weight average molecular weight of the para-aramid fiber is 60,000-80,000.
The lithium-ion battery composite separator according to claim 1, wherein the chlorinated organic matter is selected from 2-chloroethanol, 3-chloro-1-propanol, 4-chloro-1-butanol, 5-chloro -at least one of 1-pentanol and 3-chloro-1,2-propylene oxide; the mass ratio of the aramid raw material to the chlorinated organic compound is 1:(1-10).
The lithium-ion battery composite diaphragm according to claim 1, wherein the inorganic filler is selected from α-alumina, γ-alumina, boehmite, calcium carbonate, hydrotalcite, montmorillonite, spinel , at least one of titanium dioxide, silicon dioxide, zirconium dioxide, magnesium oxide, calcium oxide, beryllium oxide, magnesium hydroxide, calcium hydroxide and silicon carbide; in the aramid fiber coating, the content of the inorganic filler It is 40 to 80% by weight.
The lithium-ion battery composite diaphragm according to claim 1, wherein the base film is selected from polyethylene diaphragm, polypropylene diaphragm, polyethylene/polypropylene mixed diaphragm, polyethylene/polypropylene/polyethylene three-layer diaphragm 1. At least one of polyimide diaphragm and non-woven fabric, the porosity of the base film is 30-60%.
The lithium-ion battery composite separator according to claim 1, wherein the thickness of the base film is 4-16 μm; the thickness of the aramid coating is 1-5 μm.
A method for preparing a lithium-ion battery composite diaphragm according to any one of claims 1-6, characterized in that the method comprises:

(1) In the presence of a Lewis acid and the first organic solvent, the aramid raw material is subjected to a halogenated alkylation reaction with a chlorinated organic compound to obtain a modified aramid fiber, and the chlorinated organic compound is shown in formula I:

Cl(CH 2 ) n R Formula I

In formula I, n represents an integer from 1 to 5, and R represents a hydroxyl group or an oxirane group;

(2) dispersing the modified aramid fiber and the inorganic filler in a second organic solvent to obtain a modified aramid fiber slurry;

(3) Coating the modified aramid slurry on one or both sides of the base film, followed by pre-solidification, washing and drying, to form an aramid coating on the surface of the base film;

The water washing is carried out in a water tank, and when the R in the formula I represents a hydroxyl group, the water tank is a pure water tank; when the R in the formula I represents an oxirane group, the process of the water washing is: first in the alkali Rinse in an aqueous solution tank, and then in a pure water tank.
The method according to claim 7, wherein, in step (1), the first organic solvent is selected from at least one of ethanol, n-propanol, isopropanol and n-butanol; the Lewis acid is selected from From at least one of AlCl 3 , BF 3 and ZnCl 2 ; the mass ratio of the aramid raw material to the Lewis acid and the first organic solvent is 1: (0.01-0.1): (4-7) ; The reaction temperature of the haloalkylation reaction is 60-90° C., and the reaction time is not less than 3 hours.
The method according to claim 7, characterized in that, in step (2), the second organic solvent is selected from N-methylpyrrolidone, dimethylsulfoxide, N,N-dimethylformamide, N , at least one of N-dimethylacetamide and tetramethylurea;

The mass ratio of the modified aramid fiber, the inorganic filler and the second organic solvent is 1:(1-4):(20-100).
The method according to claim 7, wherein the pre-solidification process comprises: passing the coated base film through a concentration gradient coagulation bath, and the coagulation bath is a mixture of the second organic solvent and water;

The number of coagulation tanks containing the coagulation bath is two, and the contents of the second organic solvent in the two coagulation tanks are 35-50% by weight and 15-30% by weight respectively.