Lithium battery separator and method of making the same

Abstract

The application discloses a lithium battery diaphragm and a preparation method thereof. The lithium battery diaphragm comprises a base film and a coating layer on the base film, wherein the coating layer comprises a dispersing agent, TiC x , and a wetting agent, wherein TiC x is a non-stoichiometric compound, TiC x is prepared from TiC and Ti, and x is 0.25-0.5. In the non-stoichiometric compound TiC x of the application, a large number of C vacancies exist, and the kinetic diameter of the vacancies is larger than the kinetic diameter of Li + , so that the C vacancies can provide a channel for the migration of Li + in the coating process. The lithium battery diaphragm greatly improves the ionic conductivity of the diaphragm, reduces the internal resistance of the battery, guarantees the thickness, improves the heat resistance of the diaphragm, and improves the safety of the battery.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of battery separator, and particularly relates to a lithium battery separator and a preparation method thereof. BACKGROUND

[0002] With the rapid development of modern industrial society, the reserves of non-renewable energy represented by coal, oil and natural gas are decreasing, leading to new energy crisis caused by fossil energy depletion. At the same time, the large-scale use of fossil fuels not only destroys the ecological environment of the earth, but also aggravates the greenhouse effect and leads to global warming. Therefore, the development of new renewable clean energy has become the primary task in the development process of all countries in the world. Renewable energy represented by wind energy, solar energy and tidal energy is expected to replace traditional fossil energy and provide "power" for social development. However, due to the great influence of external factors such as geographical environment, these clean energy cannot meet the demand for energy storage system in daily production and life. In recent years, with the rapid development of electric vehicles and portable electronic equipment market, the demand for high energy density, high power density and environment-friendly energy storage conversion devices is increasing. Among many energy storage systems, electrochemical energy storage devices are highly concerned as a high-efficiency and economical energy storage method. Lithium ion secondary battery occupies the dominant position in the energy storage system market due to its high energy density, long cycle life, wide working temperature range, no memory effect and other advantages. At present, lithium ion battery has been widely used in 3C electronic products, hybrid electric vehicles / fully electric vehicles, unmanned aerial vehicles, smart grids and other fields, which has greatly changed people's way of production and life.

[0003] The separator is an important component of lithium ion battery, which can avoid the direct contact of positive and negative electrodes and promote the shuttling of lithium ions between positive and negative electrodes. The traditional commercial polyolefin separator has the advantages of low production cost, uniform pore structure and excellent mechanical strength, and has always occupied the dominant position in the lithium battery separator market. However, the commercial polyolefin separator also has many problems that cannot be ignored: (1) poor wettability with electrolyte, which hinders the transmission and diffusion of lithium ions in the separator, thereby affecting the performance of the battery; (2) poor high-temperature thermal stability, the separator will shrink seriously when heated, which will cause internal short circuit of the battery and lead to safety accidents such as thermal runaway; (3) when applied in lithium-sulfur battery, the separator cannot inhibit the shuttling effect of polysulfides due to its large pore size and single structure. Although the separator does not directly participate in the electrochemical reaction, its properties determine the electrochemical performance and safety performance of lithium ion battery. The separator should have high porosity and electrolyte absorption rate so that lithium ions can transfer quickly. In addition, it should also have excellent thermal stability, and the separator should maintain its structural integrity when the lithium dendrite penetrates, so as to prevent internal short circuit. Therefore, a high-performance material is needed, which can ensure the mechanical strength and electronic insulation of the separator while having good ion permeability and high-temperature thermal stability. SUMMARY

[0004] In view of the deficiencies of the prior art, the present application aims to provide a lithium battery separator.

[0005] Another object of the present application is to provide a preparation method of the lithium battery separator.

[0006] The object of the present application is achieved by the following technical solutions.

[0007] A lithium battery separator comprises a base film and a coating layer on the base film, wherein the coating layer comprises a dispersant, TiC x , and a wetting agent, and the ratio of the dispersant, TiC x , and the wetting agent is (0.1-0.5):(15-20):(0.03-0.1) by mass fraction, wherein TiC x is a non-stoichiometric compound, TiC x , x=0.25-0.5.

[0008] In the above technical solution, the dispersant is a mixture of one or both of polyacrylic acid and polyvinyl ether.

[0009] In the above technical solution, the wetting agent is a mixture of one or both of polyoxyethylene alkyl phenol ether, sodium dodecyl benzene sulfonate, and sodium dodecyl sulfate.

[0010] In the above technical solution, the method for preparing TiC x comprises mixing a powder and a powder dispersion control agent, ball milling until uniform, sealing, and mechanical alloying to obtain TiC x , wherein the powder is titanium carbide (TiC) powder and titanium (Ti) powder, and the ratio of the titanium carbide powder to the titanium powder is 1:(1-3) by mole fraction.

[0011] In the method for preparing TiC x , the powder dispersion control agent is ethanol, and the powder dispersion control agent is used to inhibit the agglomeration of the powder during ball milling.

[0012] In the method for preparing TiC x , the ratio of the powder to the powder dispersion control agent is (30-70):1 by mass fraction.

[0013] In the method for preparing TiC x , the method specifically comprises mixing titanium carbide (TiC) powder and titanium (Ti) powder, placing the mixture into a hard alloy ball, adding a powder dispersion control agent dropwise, mixing uniformly, sealing, and mechanical alloying at a rotation speed of 400-600 r / min under an inert gas or nitrogen atmosphere at room temperature for 50-80 h to obtain TiC x .

[0014] In the above technical solution, the mechanical alloying is carried out at room temperature for 50-80 hours at a rotating speed of 400-600 r / min, wherein, the machine is stopped every 2 hours for 30 minutes (heat dissipation), and the material is stirred every 30 hours.

[0015] In the above technical solution, the ratio of the hard alloy ball and the powder is (15-25):1 by mass fraction.

[0016] In the above technical solution, the diameters of the hard alloy balls are 8 mm, 5 mm and 2 mm, and the ratio of the hard alloy balls with diameters of 8 mm, 5 mm and 2 mm is 6:3:1 by mass fraction.

[0017] The preparation method of the lithium battery separator comprises the following steps: coating a slurry on a base film, drying, obtaining a coating layer on the base film, and obtaining a lithium battery separator.

[0018] In the above technical solution, the coating speed is 10-20 m / min.

[0019] In the above technical solution, the material of the base film is polyethylene or polypropylene.

[0020] In the above technical solution, the thickness of the coating layer is 1-5 μm.

[0021] A slurry comprises: a dispersing agent, water, TiC x , a pore-forming agent, a thickening agent, a glue adhesive and a wetting agent, and the ratio of the dispersing agent, water, TiC x , the pore-forming agent, the thickening agent, the glue adhesive and the wetting agent is (0.1-0.5):(23-30):(15-20):(1.5-2.5):(2-5):(1.3-3):(0.03-0.1) by mass fraction.

[0022] In the above technical solution, the thickening agent is one or a mixture of two of carboxymethyl cellulose and sodium carboxymethyl cellulose.

[0023] In the above technical solution, the glue adhesive is one or a mixture of several of acrylate, epoxy resin, phenolic resin and polyurethane.

[0024] The method for preparing the above slurry comprises the following steps: mixing the dispersing agent, water, TiC x , the pore-forming agent, the thickening agent, the glue adhesive and the wetting agent uniformly to obtain the slurry.

[0025] In the above technical solution, the pore-forming agent is one of ammonium bicarbonate and isopropyl alcohol.

[0026] In the above technical solution, the method for preparing the slurry comprises the following steps:

[0027] Step 1, mix dispersant, water and TiC x to uniformity to obtain a first material;

[0028] In step 1, mix dispersant, water and TiC x to uniformity to obtain a first material.

[0029] Step 2, mix the first material and pore-forming agent to uniformity to obtain a second material, mix the second material and thickening agent to uniformity to obtain a third material, mix the third material, adhesive and wetting agent to uniformity to obtain the slurry.

[0030] In step 2, mix the first material and pore-forming agent to uniformity to obtain a second material.

[0031] In step 2, mix the second material and thickening agent to uniformity to obtain a third material.

[0032] In step 2, mix the third material, adhesive and wetting agent to uniformity to obtain the slurry.

[0033] Compared with the prior art, the present application has the following advantages:

[0034] 1. The non-stoichiometric compound TiC x in the present application has a large number of C vacancies, and the kinetic diameter of the vacancies is larger than that of Li + , so that the C vacancies can provide a channel for the migration of Li + during coating, greatly improving the ionic conductivity of the separator without affecting other properties of the separator, reducing the internal resistance of the battery, ensuring the thickness while improving the heat resistance of the separator, and improving the safety of the battery;

[0035] 2. TiC x has excellent mechanical properties, can be used as a rigid ceramic support skeleton, and can improve the heat shrinkage performance, high temperature stability and insulation performance of the polyolefin separator, and ensure that the battery is not punctured;

[0036] 3. The TiC x prepared in the present application has high purity, low content of magnetic substances and stable performance. BRIEF DESCRIPTION OF DRAWINGS

[0037] Figure 1 is the XRD pattern of TiC x ;

[0038] Figure 2SEM image of TiC x SEM image of TiC DETAILED DESCRIPTION

[0039] The technical solutions of the present application are further illustrated below in combination with specific examples.

[0040] The base film in the following examples is a polyethylene film.

[0041] The embossing roll speed ratio in the following examples is 140%.

[0042] Ion conductivity: temperature: room temperature 25±5℃; relative humidity: 40-50%.

[0043] Liquid absorption and liquid retention rate: the separator is cut into 50mm*50mm samples, and for the separator with a width less than 50mm, the full-width separator with a length of 50mm is taken, and the edge length is accurate to 1mm. The cut sample is weighed and recorded as m1 (accurate to 0.01mg). The weighed separator is soaked in electrolyte, soaked at room temperature for (30±1) min, and the free electrolyte on the surface of the separator is wiped off until no granular electrolyte can be seen with the naked eye, weighed, and recorded as m2 (accurate to 0.01mg). Then, it is left for one hour, weighed, and recorded as m3 (accurate to 0.01mg). Each sample is tested for at least 3 sets of data. The liquid absorption and liquid retention rates of the separator are calculated according to the following formula:

[0044] Liquid absorption rate EU (%) = (m2-m1) / m1*100%

[0045] Liquid retention rate EU1 (%) = (m3-m1) / m1*100%

[0046] In the formula:

[0047] m1 is in milligrams (mg);

[0048] m2 is in milligrams (mg);

[0049] m3 is in milligrams (mg).

[0050] The average value of three sets of data is calculated, and the result is rounded to two decimal places. The separator is one of the lithium battery separators of Examples 4-6 and Comparative Examples 3-6.

[0051] Examples 1-3

[0052] A method for preparing a slurry, comprising the following steps:

[0053] Step 1, dispersant, water and non-stoichiometric compound (TiC x) mixing, stirring A min at room temperature at a self-rotation speed of 2000 r / min and a revolution speed of 40 r / min to make TiC x dispersed evenly in water, sand-milling for 5 min to be uniform to obtain a first substance (TiC x dispersion), the dispersant being polyacrylic acid;

[0054] Step 2, mixing the first substance and a pore-forming agent, stirring for 10 min to be uniform to obtain a second substance, mixing the second substance and a thickening agent, stirring for 10 min to be uniform to obtain a third substance, mixing the third substance, an adhesive and a wetting agent, stirring for 10 min to be uniform to obtain a slurry, the ratio of the dispersant, water, TiC x , the pore-forming agent, the thickening agent, the adhesive and the wetting agent being B, the pore-forming agent being isopropyl alcohol, the thickening agent being carboxymethyl cellulose, the adhesive being acrylate and the wetting agent being polyoxyethylene alkyl phenol ether.

[0055] The method for preparing TiC x is as follows: loading the powder (titanium carbide (TiC) powder and titanium (Ti) powder) into a ball mill tank (hard alloy tank), putting hard alloy balls, adding dropwise a powder dispersion control agent, mixing uniformly (hand mixing for 10 min), sealing, placing the ball mill tank on a planetary ball mill, mechanical alloying for 60 h at a rotation speed of 400 r / min under a nitrogen atmosphere at room temperature (stopping every 2 h for 30 min (heat dissipation), and stirring once when mechanical alloying for 30 h), to obtain TiC x , the ratio of the titanium carbide powder and the titanium powder being C, the value of “x” being D, wherein the powder dispersion control agent is ethanol (used to inhibit the agglomeration of the powder in the ball milling process). The ratio of the powder and the powder dispersion control agent is 50:1 by mass fraction, the ratio of the hard alloy balls and the powder is 20:1 by mass fraction, the hard alloy balls are balls with diameters of 8 mm, 5 mm and 2 mm, respectively, the ratio of the hard alloy balls with diameters of 8 mm, 5 mm and 2 mm is 6:3:1 by mass fraction. The values of A, B, C and D are shown in Table 1.

[0056] Table 1

[0057] Examples A (min) B C D Example 1 30 0.2：25.2：17.5：1.95：3.5：1.6：0.05 2：3 0.4 Example 2 25 0.3：25.74：16：2.5：3：2：0.04 2：3 0.4 Example 3 30 0.2：25.2：17.5：1.95：3.5：1.6：0.05 1：3 0.25

[0058] Comparative Example 1

[0059] A method for preparing a slurry is basically the same as that of Example 1, except that “TiC x ” is replaced by “alumina powder”.

[0060] Comparative Example 2

[0061] A method for preparing slurry is basically the same as that of Example 2, except that: x ” is replaced by “alumina powder”.

[0062] Examples 4 to 6 and Comparative Examples 3 to 4

[0063] A method for preparing a lithium battery separator comprises: placing a base film on a coating machine loaded with slurry (the coating machine has an unwinding tension of 32N and a winding tension of 4N), coating the slurry on one side of the base film at a coating speed of Xm / min, drawing the base film into a drying apparatus via a traction roller and drying it at 65°C for 2 minutes, thereby obtaining a coating with a thickness of Yμm on the base film to obtain a lithium battery separator. The slurry is one of the slurries prepared in Examples 1-3 and Comparative Examples 1-2. The base film has a specification of Z1, and the anilox roller has a specification of Z2.

[0064] X, Y, Z1 and Z2 are shown in Table 2.

[0065] Table 2

[0066]

[0067] Comparative Example 5

[0068] A method for preparing a lithium battery separator is substantially the same as that of Comparative Example 3, differing only in the base film and anilox roller used. In Comparative Example 5, the base film has dimensions of 1000 mm x 7 μm, and the anilox roller has dimensions of 1150 mm x 100 mm x 2 μm (the coating thickness of the lithium battery separator in Comparative Example 5 is 2 μm).

[0069] Comparative Example 6

[0070] A wrinkled MXene-modified separator for a lithium-ion battery is disclosed, which is Example 1 of the invention patent with publication number CN 114927830 A.

[0071] The test data of the lithium battery separators of Examples 4 to 6, Comparative Examples 3 to 5, and the wrinkled MXene modified separator for lithium ion batteries of Comparative Example 6 are shown in Table 3.

[0072] Table 3

[0073]

[0074] Figure 1 TiC x XRD pattern of Figure 1 It can be seen that in addition to a small amount of tungsten carbide (from the ball mill and cemented carbide balls), there are no other phases in the XRD pattern. xThe high purity and low content of magnetic substances indicate that the Ti in the raw material reacts completely with the C element in TiC, or that the C atoms diffuse into the Ti lattice during the ball milling process, causing the crystal structure of Ti, which is a hexagonal structure at low temperature, to change and finally exist in the form of a face-centered cubic structure of TiC. The two phases are synthesized into a single stable phase. And the prepared TiC is obtained by calculation. x The lattice constant is The lattice constant of TiC is TiC x The lattice constant of TiC is smaller than that of TiC because the above reaction occurs. Ti atoms enter the TiC lattice during the ball milling process, resulting in lattice distortion. A large number of C vacancies cause TiC x The lattice constant becomes smaller.

[0075] Figure 2 TiC x SEM picture of Figure 2 It can be seen that TiC x The particles are spherical, with a size of about 0.1-0.2μm, and the particle size distribution is relatively uniform, which is beneficial to TiC x Dispersion and coating in slurry. x It achieves overall densification through its own accumulation, serving as both a ceramic skeleton reinforcement phase of the diaphragm and an ion conducting phase, which helps to improve the comprehensive performance of the diaphragm.

[0076] Comparative Example 7

[0077] A high-strength and tough layered structure TiC x / Ti-based composite material, which is Example 1 of the invention patent with publication number CN 118082355 A.

[0078] The material prepared by the invention patent with publication number CN 118082355 A contains metal impurities and has too high electronic conductivity. It will leak electricity when used to prepare lithium battery separators and cannot be used in actual production.

[0079] The above is an exemplary description of the present invention. It should be noted that, without departing from the core of the present invention, any simple deformation, modification or other equivalent replacement that can be made by other skilled in the art without expending creative labor falls within the scope of protection of the present invention.

Claims

1. A lithium battery separator, characterized by, Comprising: Base film and coating on the base film, the coating comprising: dispersant, TiC x and wetting agent, the ratio of dispersant, TiC x and wetting agent is (0.1-0.5):(15-20):(0.03-0.1) by mass fraction, wherein TiC x is a non-stoichiometric compound, x=0.25-0.5; the method for preparing TiC x is mixing the powder and the powder dispersing control agent, ball milling to uniform, sealing, mechanical alloying to obtain TiC x , the powder being titanium carbide powder and titanium powder, the ratio of titanium carbide powder and titanium powder being 1:(1-3) by mole fraction.

2. The lithium battery separator of claim 1, wherein, The powder dispersing control agent is ethanol, and the powder dispersing control agent is used to inhibit the caking of the powder in the ball milling process.

3. The lithium battery separator of claim 2, wherein, The ratio of the powder and the powder dispersing control agent is (30-70):1 by mass fraction.

4. The lithium battery separator of claim 3, wherein, Titanium carbide powder and titanium powder are mixed, put into a hard alloy ball, drop the powder dispersing control agent, mix uniformly, seal, mechanical alloying at room temperature, inert gas or nitrogen atmosphere for 50-80h, to obtain TiC x .

5. The method of producing a separator for lithium batteries according to any one of claims 1 to 4, characterized in that, Comprising: coating the slurry on the base film, drying, obtaining a coating layer on the base film, and obtaining the lithium battery separator.

6. A slurry for a lithium battery separator, characterized by, Comprising: dispersant, water, TiC x , pore forming agent, thickening agent, adhesive and wetting agent, the ratio of dispersant, water, TiC x , pore forming agent, thickening agent, adhesive and wetting agent is (0.1-0.5) :(23-30) :(15-20) :(1.5-2.5) :(2-5) :(1.3-3) :(0.03-0.1) by mass fraction; the method for preparing TiC x is: mixing the powder and the powder dispersing control agent, ball milling to be uniform, sealing, mechanical alloying, to obtain TiC x , the powder is titanium carbide powder and titanium powder, the ratio of titanium carbide powder and titanium powder is 1 :(1-3) by mole fraction.

7. Process for the preparation of the slurry according to claim 6, characterized in that, Comprising: The dispersant, water, TiC x , pore-forming agent, thickening agent, adhesive and wetting agent are mixed to be uniform to obtain a slurry.

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