Diaphragm coating, diaphragm, lithium battery, diaphragm and diaphragm coating preparation method

Abstract

The invention relates to the technical field of lithium battery diaphragms, in particular to a diaphragm coating, a diaphragm, a lithium battery and a preparation method of the diaphragm and the diaphragm coating. Wherein the diaphragm is coated with silicate and a binding agent, the silicate accounts for 10-90 parts by weight, and the binding agent accounts for 10-50 parts by weight. The silicate powder is firmly attached to the surface of the base film under the action of the binder, and powder falling and creases do not occur when the base film is shaken and folded. By adding silicate, the ionic conductivity of the diaphragm can be improved, the electrochemical performance of the battery is improved, meanwhile, the overall thermal stability and safety of the diaphragm are greatly improved, and generally, the diaphragm has relatively high safety and electrochemical performance.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium battery separators, and particularly to a separator coating, a separator, a lithium battery, and a preparation method of the separator and the separator coating. Background Art

[0002] Lithium batteries play a dominant role in energy storage applications of various scales, such as portable electronic devices, electric vehicles, and large-scale energy storage. However, the inherent safety hazards of lithium batteries pose a serious threat to human health and life. Research shows that battery fire accidents are caused by battery thermal runaway, and the thermal shrinkage of the separator and the decomposition of the electrolyte are the main causes of thermal runaway. The main function of the separator is to conduct lithium ions but not electrons, preventing the direct contact between the positive and negative electrodes of the battery and causing battery short circuit. Currently, commercial separators are mainly composed of single or multi-layer combinations of polyethylene (PE) and polypropylene (PP). The thermal reaction temperatures of commercial separators are 130°C and 160°C respectively. When the internal temperature of the battery rises under certain special conditions and approaches the reaction temperature, the separator melts and begins to shrink due to heat, resulting in the direct contact between the positive and negative electrodes and causing short circuit, ultimately leading to battery ignition. Therefore, most current research focuses on improving the thermal stability of the battery, but ignores the electrochemical properties of lithium batteries, and the ionic conductivity of the separator is insufficient.

[0003] Therefore, those skilled in the art are committed to developing a separator coating, a separator, a lithium battery, and a preparation method of the separator and the separator coating with high thermal stability and electrochemical performance. Summary of the Invention

[0004] In view of the above-mentioned defects of the prior art, the technical problem to be solved by the present invention is to provide a separator coating, a separator, a lithium battery, and a preparation method of the separator and the separator coating with high thermal stability and electrochemical performance.

[0005] To achieve the above object, the present invention provides a separator coating, comprising silicate and binder, wherein the weight parts of the silicate are 70 to 90 parts, and the binder is 10 to 30 parts. By using the two raw materials of the present invention, the mechanical properties and thermal stability of the functional coating can be enhanced, and at the same time, the ionic conduction path can be affected, thereby improving the electrochemical performance.

[0006] Preferably, the silicate is one or more of aluminum silicate, magnesium aluminum silicate, and sodium aluminum silicate.

[0007] Preferably, it further comprises an additive, and the weight parts of the additive are 3 to 20 parts. The addition of the additive can improve the wettability and leveling property of the slurry, and contribute to better dispersion and uniform adhesion of the inorganic powder on the surface of the base film. Generally, one or more of defoamers, wetting and dispersing agents, leveling agents, and polymerization inhibitors can be selected. The main function of the additive is to improve the processing properties of the slurry, such as leveling property, wettability, etc.

[0008] The present invention also provides a method for preparing the diaphragm coating as described above, comprising the following steps:

[0009] 1) Stir the silicate, binder, and solvent evenly to form a diaphragm coating slurry;

[0010] 2) Dry to complete the volatilization of the solvent in the diaphragm coating slurry.

[0011] The present invention also provides a diaphragm, comprising a base film, and the outer surface of the base film is coated with the diaphragm coating as described above.

[0012] The present invention also provides a method for preparing the diaphragm as described above, characterized by comprising the following steps:

[0013] S1 Stir the silicate, binder, and solvent evenly to form a diaphragm coating slurry;

[0014] S2 Coat the diaphragm coating slurry on the surface of the base film;

[0015] S3 Dry at 60 - 100 °C until all the solvent has evaporated.

[0016] Preferably, the solvent is one or more of deionized water, methanol, ethanol, N-methyl-2-pyrrolidone (NMP), dichloromethane, acetone, n-butanol, acetonitrile, ethyl acetate, N,N-dimethylformamide (DMF).

[0017] Preferably, in step S3, dry in a vacuum environment for more than 10 hours.

[0018] The present invention also provides a lithium battery comprising the diaphragm coating as described above.

[0019] The beneficial effects of the present invention are as follows: The silicate powder of the present invention firmly adheres to the surface of the base film under the action of the binder, and there is no powder falling off or creases appearing during shaking or folding. The addition of silicate can improve the ionic conductivity of the diaphragm, enhance the electrochemical performance of the battery, and at the same time greatly improve the overall thermal stability and safety of the diaphragm. Generally speaking, the present invention has high safety and electrochemical performance. Description of the Drawings

[0020] Figure 1 It is a comparative morphology diagram of the diaphragm of Example 1 and the comparative example of the present invention at different temperatures.

[0021] Figure 2 It is a comparative diagram of the test results of the diaphragm prepared in Example 1 and a commercially available ordinary PE diaphragm in a blue battery system. Detailed Embodiments

[0022] The present invention will be further described below in conjunction with the drawings and embodiments.

[0023] The present invention provides three embodiments for preparing a membrane coating slurry, which is further coated on a substrate film to achieve the preparation of the membrane in the present invention. The raw materials used in the three embodiments are as follows:

[0024]

[0025] In the present invention, other binders may also be used, such as polyacrylic acid (PAA), etc. The auxiliary agent is mainly used to improve the performance of the solution, and may be added or not added as required.

[0026] In the above embodiments, aluminum silicate is 2Al 2 O 3 ·2SiO 2 ·2H 2 O is McLean, D919802, magnesium aluminum silicate is McLean, M875683, sodium aluminum silicate is McLean, S832352. Carboxymethyl cellulose (CMC) is Aladdin, C104978

[0027] The binder polyvinylidene fluoride (PVDF) is Aladdin, P432380, the polyvinyl alcohol (PVA) is Aladdin, P139546, the carboxymethyl cellulose (CMC) is Aladdin, C104978, and in other embodiments, polyacrylic acid may also be used.

[0028] Among the additives, the defoamer is Airex986 from Digo, the leveling agent is Deqian 432, and the dispersant is DISPERBYK-168 from BYK. Of course, other commercially available models can also be used.

[0029] In the base film, the single-layer PP film uses Celgard2400, and the three-layer PE film and the three-layer PP film use Celgard2325.

[0030] The solvent is added according to the viscosity of the slurry, and generally the slurry viscosity is between 200-500 mPa·s.

[0031] In the above examples, the raw materials not specially described are all conventional commercially available products.

[0032] The preparation methods of Examples 1 to 3 are as follows:

[0033] S1: Mix the silicate, binder and solvent according to the amounts in Table 1 and stir evenly to form a diaphragm coating slurry. This process requires the powder to be completely dissolved;

[0034] S2: coating the membrane coating slurry on the surface of the base membrane. In this step, the coating is performed by scraping or spraying;

[0035] S3 is dried at 60 - 100 °C until all the solvent has evaporated. In this step, the sample prepared in the example is dried in a vacuum oven until all the solvent has evaporated.

[0036] To ensure the integrity of the coating, after the above S1 to S3 are completed, re - coating can be carried out at the uncoated areas, that is, repeat steps S2 and S3.

[0037] After the preparation of the diaphragms in Examples 1 to 3 is completed, and taking a commercially available pure PP base film as a comparative example, a high - temperature heating test is carried out, and the time when obvious shrinkage occurs is recorded. The specific results are shown in Table 2.

[0038] Table 2 Test result table of Examples 1 to 3 and the comparative example.

[0039] Project Apparent shrinkage temperature Example 1 240℃ Example 2 220℃ Example 3 250℃ Comparative example 160℃

[0040] The above results show that compared with the commercial diaphragms in the prior art, the present invention can endow the diaphragm with higher thermal stability and safety.

[0041] Taking Example 1 as an example again, the diaphragm made in Example 1 and the comparative - example diaphragm are heated, and their morphological characteristics are photographed and compared at different temperatures. The results are as follows Figure 1 shown. It can be seen that the comparative - example diaphragm shows obvious shrinkage at 160 °C, but the diaphragm of Example 1 still has a complete circular shape at 240 °C, indicating that the diaphragm of the present invention can still effectively isolate the positive and negative electrodes of the battery in a high - temperature environment, preventing the battery from short - circuiting and catching fire.

[0042] At the same time, in order to verify the electrochemical performance of the present invention, an electrochemical performance verification test is carried out on the diaphragm prepared in Example 1 and a commercially available ordinary PE diaphragm.

[0043] Battery assembly experimental steps:

[0044] 1. Preparation of the positive electrode plate: Lithium iron phosphate (LiFePO 4 ) is stirred and mixed with conductive carbon black (SuperP) and binder (such as PVDF, etc.) in a mass ratio of 8:1:1, and then NMP is added to prepare a slurry. The obtained slurry is blade - coated on aluminum foil, and then the electrode is dried in a vacuum oven at 120 °C for 12 hours to prepare the positive electrode plate. After cooling to room temperature, it is transferred to a glove box (H 2 O, O 2 less than 0.01 ppm) for the next step.

[0045] 2. Assembly of the battery: In the glove box, a lithium metal sheet is used as the negative electrode, the diaphragm prepared in Example 1, and the positive electrode plate prepared in step 1 are sequentially aligned and placed in a CR2032 battery case. Dissolve 1.0 M LiPF 6As the electrolyte, a mixed solvent of ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate (EC / DMC / EMC 1:1:1) was dropped onto the surface of the separator, and finally the battery was assembled.

[0046] In the comparative experiment, the experimental procedure was the same as the above steps, except that the separator was replaced with a commercially available ordinary PE separator.

[0047] Testing process:

[0048] The button batteries assembled in Example 1 and the comparative example were subjected to constant current charge and discharge tests, which are commonly used to study the electrochemical performance of electrode materials. Its basic principle is to charge and discharge the electrode to be tested under a constant current condition, record the change law of its potential with time, and the actual discharge capacity and cycle performance of the battery can be obtained. This experiment was tested using a BlueTEC (LAND CT2001A) system. After the test, the data obtained from the test was plotted into a data graph through Origin software, as Figure 2 shown.

[0049] Through Figure 2 It can be seen that the battery assembled with the PE* separator, that is, the separator of the present invention, still maintains good capacity performance during long cycling. At the same time, as the number of cycling increases, the battery of the present invention has less capacity decay compared to the pure PE separator. Therefore, the battery prepared by the present invention has good electrochemical performance.

[0050] The preferred specific embodiments of the present invention have been described in detail above. It should be understood that those of ordinary skill in the art can make many modifications and variations based on the concept of the present invention without creative work. Therefore, all technical solutions that can be obtained by those skilled in the art in the technical field of the present invention based on the concept of the present invention through logical analysis, reasoning or limited experiments on the basis of the prior art should be within the protection scope determined by the claims.

Claims

1. A diaphragm coating, characterized in that: The invention comprises silicate and a binder, wherein the silicate is 70 to 90 parts by weight and the binder is 10 to 30 parts by weight.

2. The diaphragm coating according to claim 1, characterized in that: The silicate is one or more of aluminum silicate, magnesium aluminum silicate, and sodium aluminum silicate.

3. The diaphragm coating according to claim 1, characterized in that: The invention also comprises an auxiliary agent, wherein the weight portion of the auxiliary agent is 3 to 20 parts.

4. A method for preparing a diaphragm coating according to claim 1, 2 or 3, comprising the following steps: 1) Stir the silicate, binder and solvent evenly to form a diaphragm coating slurry; 2) Drying to completely evaporate the solvent in the membrane coating slurry.

5. A diaphragm, characterized in that: It comprises a base film, the outer surface of which is coated with the diaphragm coating as claimed in claim 1, 2 or 3.

6. A method for preparing the diaphragm according to claim 5, characterized in that: The steps include: S1. Stir the silicate, binder and solvent evenly to form a diaphragm coating slurry; S2: coating the diaphragm coating slurry on the surface of the base film; S3 is dried at 60-100°C until all the solvent evaporates.

7. The method for preparing a diaphragm according to claim 6, characterized in that: The solvent is one or more of deionized water, methanol, ethanol, N-methyl-2-pyrrolidone (NMP), dichloromethane, acetone, n-butanol, acetonitrile, ethyl acetate, and N,N-dimethylformamide (DMF).

8. The method for preparing a diaphragm according to claim 6, characterized in that: In the step S3, drying is performed in a vacuum environment for more than 10 hours.

9. A lithium battery comprising the separator coating as claimed in claim 1, 2 or 3.

Images