Coated separator, and preparation method therefor and use thereof

Abstract

The present application provides a coated separator, and a preparation method therefor and the use thereof. The coated separator comprises a substrate and a coating that coats at least one side of the substrate. Raw materials for the preparation of the coating comprise an emulsion-based adhesive, a solvent-based adhesive and inorganic particles. The average particle size of the emulsion-based adhesive is denoted as A, the average particle size of the inorganic particles is denoted as B, the average pore size of the substrate is denoted as C, the D10 particle size of the inorganic particles is denoted as D, and then A, B, C and D satisfy the following relations: C:A:B=(0.4-0.8):1:(2-9); and A+D≥3.5C. In the present application, by means of the addition of the emulsion-based adhesive to the preparation raw materials for the coating, the water resistance of the coated separator can be improved, and the ratio of the particle size of the emulsion-based adhesive to the particle size of the inorganic particles to the pore size of the substrate can be controlled within a specific range, thereby enabling the separator to have a relatively good air permeability.

Description

A coated separator and a preparation method and application thereof TECHNICAL FIELD

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

[0002] In the structure of a lithium ion battery, a separator is one of the key inner components. The performance of the separator determines the interface structure and internal resistance of the battery, and directly affects the capacity, cycle and safety performance of the battery. A separator with excellent performance plays an important role in improving the overall performance of the battery. The main function of the separator is to separate the positive and negative electrodes of the battery to prevent short circuiting of the two electrodes, and the separator also has the function of allowing electrolyte ions to pass through.

[0003] At present, an inorganic coating layer is often coated on the surface of a base film to improve the heat resistance of the separator. However, the inorganic coating layer causes the overall air permeability of the separator to decrease. In order to improve the adhesion of the coated separator to the electrode, a polymer coating layer is often coated on the surface of the coated separator. In the process of coating the polymer coating layer, the coating layer needs to be solidified through water bath. The inorganic coating layer has poor water resistance, and the inorganic coating layer dissolves or falls off in water bath, which causes the overall heat resistance of the separator to decrease.

[0004] Therefore, it is desirable in the art to develop a coated separator with good water resistance and air permeability. SUMMARY

[0005] The present application provides a coated separator and a preparation method and application thereof. The existing high-heat-resistant formula separator has the problem that the heat resistance of the separator is weakened when the separator is exposed to water, and the performance of the separator is attenuated (the coating layer dissolves and falls off) after the water bath of the secondary water-based coating or oily coating on the surface of the separator, which causes the 150℃ heat shrinkage rate of the separator to be greater than 5%. In the present application, an emulsion type adhesive and a solvent type adhesive are compounded in the preparation process of the slurry, and the ratio of the particle size of the emulsion type adhesive, the particle size of the inorganic particles and the pore size of the base material is controlled within a specific range, so that the separator has good air permeability. At the same time, the water resistance of the inorganic coating layer is improved, and the heat resistance of the separator is improved to a certain extent. As a further preferred solution, a crosslinking agent is added to the coating system, and a coating layer with better water resistance and heat resistance is formed on the surface of the separator after low-temperature baking, which can effectively improve the above problems. In addition, the breaking temperature of the crosslinked separator is also improved, which greatly improves the safety performance of the battery.

[0006] In a first aspect, the present application provides a coated separator, which comprises a base material and a coating layer coated on at least one side (for example, one side or two sides) of the base material, and the preparation raw materials of the coating layer comprise an emulsion type adhesive, a solvent type adhesive and inorganic particles.

[0007] The average particle size of the emulsion adhesive is denoted as A, the average particle size of the inorganic particles is denoted as B, the average pore size of the substrate is denoted as C, and the D10 particle size of the inorganic particles is denoted as D. A, B, C, and D satisfy the following relationship: C:A:B = (0.4-0.8):1:(2-9); A+D≥3.5C; wherein 0.4-0.8 can be any one of 0.4, 0.5, 0.6, 0.7, or 0.8, or a range value between any two of them; 2-9 can be any one of 2, 3, 4, 5, 6, 7, 8, or 9, or a range value between any two of them; and A+D can be any one of 3.5C, 4C, 4.5C, 5C, 5.5C, 6C, 6.5C, 7C, 7.5C, or 8C, or a range value between any two of them.

[0008] In the present application, the addition of the emulsion adhesive in the preparation raw material of the coating can improve the water resistance of the coated separator. By controlling the ratio of the particle size of the emulsion adhesive, the particle size of the inorganic particles, and the pore size of the substrate within a certain range, the separator has good air permeability.

[0009] If the average particle size of the emulsion adhesive is too large, it will result in a less dense coating (i.e., the coating cannot cover the entire surface of the substrate), causing the heat resistance to decrease. Meanwhile, if the average particle size of the emulsion adhesive is too large, it will result in poor stability of the emulsion adhesive itself, increased viscosity, and poor workability. If the average particle size of the emulsion adhesive is too small, it will easily penetrate into the pores of the substrate, causing the pores of the substrate to be blocked, affecting the air permeability of the separator, and also affecting the bonding of the inorganic particles (the glue participating in the bonding of the inorganic particles penetrates into the pores).

[0010] Preferably, 3.5C≤A+D≤6C. By controlling A+D to be greater than or equal to 3.5C, the inorganic particles and the emulsion adhesive are less likely to fall into the pores of the substrate. By controlling A+D to be less than or equal to 6C, it is beneficial to control the thickness of the coating, so that the single-sided coating thickness is less than or equal to 1.2μm, and thinning is achieved.

[0011] Preferably, the emulsion adhesive includes any one or a combination of at least two of polyacrylate, polystyrene-acrylate, polymethyl methacrylate, polybutyl methacrylate, polyethyl acrylate, polyvinyl acetate, or ethylene-vinyl acetate.

[0012] Preferably, the solvent-based adhesive contains carboxyl and / or amide groups in its molecular structure.

[0013] Preferably, the solvent-based adhesive includes polyacrylic acid and / or polyacrylamide.

[0014] Preferably, the average particle size (D50) of the inorganic particles is 0.1-1.0 μm, for example, any one of 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm or 1.0 μm or a range value between any two of them.

[0015] It can be understood that the particle size D10 and D50 of the inorganic particles described in the present application can be detected by using a Malvern LS609 laser particle size analyzer, selecting the refractive index of the corresponding material, and obtaining the cumulative particle size distribution of the inorganic particle powder. The particle size D10 is the cumulative 10% particle size from the microparticle side, and the particle size D50 is the cumulative 50% particle size. The particle size of the emulsion type adhesive can be detected by using a Malvern TOPSIZER laser particle size analyzer, selecting the refractive index of the corresponding material, and obtaining the cumulative particle size distribution of the emulsion. The average particle size of the emulsion type adhesive is the cumulative 50% particle size from the microparticle side. Of course, other instruments can also be used for testing, and the present application is not limited thereto.

[0016] Preferably, the inorganic particles include any one of alumina, boehmite, barium titanate, silicon dioxide, magnesium oxide, titanium dioxide or double metal hydroxide or a combination of at least two thereof.

[0017] Preferably, the double metal hydroxide includes any one of magnesium-aluminum double metal hydroxide, lithium-aluminum double metal hydroxide (LiAlLDH), zinc-aluminum double metal hydroxide or nickel-aluminum double metal hydroxide or a combination of at least two thereof.

[0018] Preferably, the inorganic particles are porous inorganic particles, for example, LiAlLDH, which can further improve the air permeability and wettability of the coated separator.

[0019] Preferably, the preparation raw material of the coating further includes a crosslinking agent.

[0020] As a preferred technical solution of the present application, a crosslinking agent is added to the preparation raw material of the coating. The solvent type adhesive and the crosslinking agent can undergo crosslinking reaction under the conventional baking conditions of the coated separator (i.e. the baking temperature of 60-80°C in the following), and the emulsion type adhesive does not participate in the crosslinking reaction. The crosslinked network structure is formed, and the organic crosslinked skeleton formed can improve the heat resistance of the coated separator. After the water bath stage of the oil coating process, the coated separator after the water bath tank does not have obvious powder dropping phenomenon, and the heat shrinkage of the coating at 150°C is ≤5%. At the same time, the breaking temperature of the crosslinked coated separator is also improved to a certain extent, which greatly improves the safety performance of the battery.

[0021] That is, the addition of the crosslinking agent can further improve the water resistance and heat resistance of the coated separator, and the above-mentioned effects can be achieved under the condition of small coating amount.

[0022] Preferably, the crosslinking agent comprises a carboxyl crosslinking agent.

[0023] Preferably, the crosslinking agent has a functionality of 2-4, such as 2, 2.2, 2.4, 2.6, 2.8, 3, 3.2, 3.4, 3.6, 3.8, or 4, etc. A crosslinking agent with a functionality of 2 or above can cause the body structure to crosslink, and the higher the functionality or the more crosslinking agent added, the higher the crosslinking degree; a crosslinking agent with a functionality of more than 4 will not have a too obvious effect on the improvement of the crosslinking degree due to the influence of steric hindrance, and the performance of the separator product will not be obviously improved. At the same time, due to the too high functionality, the activity of the crosslinking agent is too high, which may cause premature crosslinking, so that the molecular chain is less likely to spread on the surface of the inorganic particles, resulting in a decrease in the adhesion effect. Moreover, due to the reason that the molecular chain is curled and the carboxyl group is reacted, the solubility in water is decreased, the viscosity of the slurry is reduced, and the production cost and difficulty are increased.

[0024] Preferably, the crosslinking agent comprises any one or a combination of at least two of a blocked isocyanate crosslinking agent, a carbodiimide crosslinking agent, an aziridine crosslinking agent, or an epoxy silane crosslinking agent. It should be understood that the carbodiimide, aziridine, and epoxy silane here refer to polymers containing corresponding functional groups and can be used as crosslinking agents.

[0025] Preferably, the crosslinking agent comprises an aziridine-modified isocyanate.

[0026] Preferably, the preparation raw material of the coating further comprises any one or a combination of at least two of water, a dispersing agent, or a surfactant.

[0027] Preferably, the water comprises pure water.

[0028] Preferably, the dispersing agent comprises any one or a combination of at least two of ammonium polyacrylate, sodium tripolyphosphate, sodium hexametaphosphate, or sodium pyrophosphate.

[0029] Preferably, the surfactant comprises any one or a combination of at least two of a polyether silane copolymer, a polyether-modified polysiloxane, an alkyl phenol polyoxyethylene ether, a fatty alcohol polyoxyethylene ether, a fatty acid polyoxyethylene ether, a fatty amine polyoxyethylene ether, or a fluorinated alkyl ethoxy alcohol ether.

[0030] Preferably, the preparation raw material of the coating comprises the following components in terms of weight fraction:

[0031] Preferably, the amount of water in the preparation of the coating can be any one of 60 parts, 62 parts, 64 parts, 66 parts, 68 parts, 70 parts, 72 parts, 74 parts, 76 parts, 78 parts, 80 parts, 82 parts, 84 parts, or 85 parts, or a range between any two of the values.

[0032] Preferably, the amount of inorganic particles in the preparation of the coating can be any one of 20 parts, 22 parts, 24 parts, 26 parts, 28 parts, 30 parts, 32 parts, 34 parts, 36 parts, 38 parts, or 40 parts, or a range between any two of the values.

[0033] Preferably, the amount of dispersant in the preparation of the coating can be any one of 0.8 parts, 0.9 parts, 1 part, 1.1 parts, or 1.2 parts, or a range between any two of the values.

[0034] Preferably, the amount of emulsion adhesive in the preparation of the coating can be any one of 0.1 parts, 0.3 parts, 0.5 parts, 0.8 parts, 1 part, 1.2 parts, 1.4 parts, 1.6 parts, 1.8 parts, 2 parts, 2.2 parts, 2.4 parts, 2.6 parts, 2.8 parts, or 3 parts, or a range between any two of the values.

[0035] Preferably, the amount of solvent adhesive in the preparation of the coating can be any one of 0.2 parts, 0.3 parts, 0.4 parts, 0.5 parts, 0.6 parts, 0.7 parts, 0.8 parts, 0.9 parts, 1 part, 1.1 parts, 1.2 parts, 1.3 parts, 1.4 parts, or 1.5 parts, or a range between any two of the values.

[0036] Preferably, the amount of crosslinking agent in the preparation of the coating can be any one of 0.01 parts, 0.02 parts, 0.03 parts, 0.04 parts, 0.05 parts, 0.06 parts, 0.07 parts, 0.08 parts, 0.09 parts, 0.1 parts, 0.11 parts, 0.12 parts, 0.13 parts, 0.14 parts, 0.15 parts, 0.16 parts, 0.17 parts, 0.18 parts, 0.19 parts, or 0.2 parts, or a range between any two of the values.

[0037] Preferably, the amount of surfactant in the preparation of the coating can be any one of 0.05 parts, 0.06 parts, 0.07 parts, 0.08 parts, 0.09 parts, 0.1 parts, 0.2 parts, 0.3 parts, 0.4 parts, 0.5 parts, 0.6 parts, 0.7 parts, 0.8 parts, 0.9 parts, or 1 part, or a range between any two of the values.

[0038] Preferably, the mass ratio of the emulsion adhesive to the solvent adhesive is 3:(0.5-3), 0.5-3 may be, for example, any one of 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.2, 1.4, 1.6, 1.8, 2, 2.2, 2.4, 2.6, 2.8, or 3, or a range value between any two of them.

[0039] Preferably, the mass ratio of the solvent adhesive to the crosslinking agent is 100:(3-12), 3-12 may be, for example, any one of 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12, or a range value between any two of them.

[0040] Preferably, the total coating amount of the coating is 2.4-3.2 g / m 2 , for example, any one of 2.4 g / m 2 , 2.5 g / m 2 , 2.6 g / m 2 , 2.7 g / m 2 , 2.8 g / m 2 , 2.9 g / m 2 , 3 g / m 2 , 3.1 g / m 2 , or 3.2 g / m 2 , or a range value between any two of them.

[0041] Preferably, the single-side thickness of the coating is 0.5-4 μm, for example, any one of 0.5 μm, 0.8 μm, 1 μm, 1.2 μm, 1.4 μm, 1.6 μm, 1.8 μm, 2 μm, 2.2 μm, 2.4 μm, 2.6 μm, 2.8 μm, 3 μm, 3.2 μm, 3.4 μm, 3.6 μm, 3.8 μm, or 4 μm, or a range value between any two of them.

[0042] Preferably, the substrate may be, for example, a PP-based film, a PE-based film, or a PP / PE / PP composite film.

[0043] In a second aspect, the application provides a preparation method of the coated separator according to the first aspect, the preparation method comprising the following steps:

[0044] (1) mixing the preparation raw materials of the coating to obtain a slurry;

[0045] (2) coating the slurry on one side or both sides of the base film and baking to obtain the coated separator.

[0046] Preferably, step (1) specifically comprises the following steps:

[0047] Mix water and dispersant, then add inorganic particles, disperse, and then add emulsion adhesive, solvent adhesive, crosslinking agent, and surfactant, and disperse uniformly to obtain slurry;

[0048] Preferably, the step of adding inorganic particles and dispersing further comprises a step of sanding.

[0049] Preferably, the flow rate of sanding is 800-1200L / h, such as any one of 800L / h, 850L / h, 900L / h, 950L / h, 1000L / h, 1050L / h, 1100L / h, 1150L / h, or 1200L / h, or a range value between any two of them, and the rotation speed of sanding is 700-800rpm, such as any one of 700rpm, 720rpm, 740rpm, 760rpm, 780rpm, or 800rpm, or a range value between any two of them.

[0050] Preferably, the emulsion adhesive, solvent adhesive, crosslinking agent, and surfactant are added in the order of the four raw materials, and the next raw material is added after the previous one is uniformly dispersed (for example, the emulsion adhesive is added, and the solvent adhesive is added after the emulsion adhesive is uniformly dispersed).

[0051] Preferably, the coating method of step (2) comprises using a micro-concave roller for coating.

[0052] Preferably, the baking temperature is 60-80℃, such as any one of 60℃, 62℃, 64℃, 66℃, 68℃, 70℃, 72℃, 74℃, 76℃, 78℃, or 80℃, or a range value between any two of them.

[0053] Preferably, the baking time is 10-30s, such as any one of 10s, 12s, 14s, 16s, 18s, 20s, 22s, 24s, 26s, 28s, or 30s, or a range value between any two of them.

[0054] In a third aspect, the application provides a use of the coated separator as described in the first aspect in a battery.

[0055] Compared with the prior art, the application has at least the following beneficial effects:

[0056] In the application, the addition of the emulsion adhesive in the preparation raw materials of the coating can improve the water resistance of the coated separator, and the ratio of the particle size of the emulsion adhesive, the particle size of the inorganic particles, and the pore size of the substrate is controlled within a certain range, so that the separator has good air permeability. DETAILED DESCRIPTION

[0057] The technical solutions of the present application are further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments are only used to help understand the present application and should not be regarded as specific limitations on the present application.

[0058] Example 1

[0059] The present embodiment provides a coated separator, which comprises a substrate and a coating layer coated on both sides of the substrate, and the raw materials for preparing the coating layer comprise the following components in parts by weight:

[0060] The specific selection and parameters of each raw material are shown in Table 1.

[0061] The preparation method comprises the following steps:

[0062] (1) The raw materials for preparing the coating layer are mixed according to the formula to obtain a slurry;

[0063] (2) The slurry is coated on both sides of the base film by using a micro-concave roller, and baked at 70°C for 20s to obtain the coated separator.

[0064] Examples 2-12

[0065] Examples 2-12 each provide a coated separator, and the substrate material and parameters of the coated separator, the specific selection, parameters and amount (amount in parts) of the raw materials for preparing the coating layer, and the preparation method are shown in Table 1 and Table 2. For the contents not shown in Table 1 and Table 2, they are the same as Example 1.

[0066] Comparative Examples 1-4

[0067] Comparative Examples 1-4 each provide a coated separator, and the substrate material and parameters of the coated separator, the specific selection, parameters and amount (amount in parts) of the raw materials for preparing the coating layer, and the preparation method are shown in Table 3. For the contents not shown in Table 3, they are the same as Example 1.

[0068] Table 1

[0069] Table 2

[0070] Table 3

[0071] The coated separators provided by the examples and comparative examples are tested for performance, and the test method is as follows:

[0072] (1)150℃ shrinkage: the coated separator provided by the examples and comparative examples was cut into 160mm*130mm, a line of 100mm*100mm was drawn on the cut sample, 11 A4 papers were placed above and below, and the sample was placed in a 150℃ oven and tested for 30min at 150℃;

[0073] (2)water resistance: take one A4 paper (210mm*297mm) size test film and weigh it as X, soak it in 500mL of pure water for 10min, take out the coating and dry it, then weigh it as X1, the unit area coating loss G (g / m 2 ) is recorded as G=(X-X1) / 0.06237;

[0074] (3)air permeability increment: using Asahi EG01-55-1MR film air permeability tester to test the time required for 100mL air to pass through the base film and the coated separator provided by the application, the difference between the time required for air to pass through the coated separator and the time required for air to pass through the base film is the air permeability increment.

[0075] The performance test results are shown in Table 4.

[0076] Table 4

[0077] As can be seen from Table 4, the coated separator provided by the examples of the application has good water resistance, heat resistance (150℃ shrinkage, TD: 1%-4.8%, MD: 0.9%-4.7%) and good air permeability (air permeability increment: 8.7-39s / 100mL) under the condition of small coating thickness (thin coating layer) compared with the comparative examples.

[0078] Compared with Example 1, the heat resistance of the coated separator provided by Comparative Example 1 is poor; the air permeability of the coated separator provided by Comparative Example 3 is poor; the heat resistance of the coated separator provided by Comparative Example 4 is significantly poor; compared with Example 3, the air permeability and water resistance of the coated separator provided by Comparative Example 2 is significantly poor.

[0079] The applicant declares that the application is illustrated by the above examples, but the application is not limited to the above examples, i.e. it does not mean that the application must rely on the above examples to be implemented. Those skilled in the art should understand that any improvement of the application, equivalent replacement of each raw material of the product of the application, addition of auxiliary ingredients, selection of specific methods, etc. fall within the protection scope and disclosure scope of the application.

Claims

1. A coated separator comprising a substrate and a coating layer coated on at least one side of the substrate, raw materials for preparing the coating layer comprising an emulsion type adhesive, a solvent type adhesive and inorganic particles; an average particle size of the emulsion type adhesive is denoted as A, an average particle size of the inorganic particles is denoted as B, an average pore size of the substrate is denoted as C, and a D10 particle size of the inorganic particles is denoted as D, A, B, C and D satisfy the following relationship: C: A: B = (0.4-0.8): 1: (2-9); A+D≥3.5C.

2. The coated separator of claim 1, wherein, 3.5C≤A+D≤6C.

3. The coated separator of claim 1 or 2, wherein, The emulsion type adhesive comprises any one or a combination of at least two of polyacrylate, polystyrene-acrylate, polymethyl methacrylate, polybutyl methacrylate, polyethyl acrylate, polyvinyl acetate or ethylene-vinyl acetate.

4. The coated separator of any one of claims 1-3, wherein, The solvent type adhesive contains carboxyl and / or amide groups in the molecular structure thereof; Preferably, the solvent type adhesive comprises polyacrylic acid and / or polyacrylamide.

5. The coated separator of any one of claims 1-4, wherein, The average particle size of the inorganic particles is 0.1-1.0 μm; Preferably, the inorganic particles comprise any one or a combination of at least two of alumina, boehmite, barium titanate, silicon dioxide, magnesium oxide, titanium dioxide or double metal hydroxide; Preferably, the double metal hydroxide comprises any one or a combination of at least two of magnesium-aluminum double metal hydroxide, lithium-aluminum double metal hydroxide, zinc-aluminum double metal hydroxide or nickel-aluminum double metal hydroxide; Preferably, the inorganic particles are porous inorganic particles.

6. The coated separator of any one of claims 1-5, wherein, The raw materials for preparing the coating layer further comprise a crosslinking agent.

7. The coated separator of claim 6, wherein, The crosslinking agent comprises a carboxyl crosslinking agent; Preferably, the functionality of the crosslinking agent is 2-4; Preferably, the crosslinking agent comprises any one or a combination of at least two of blocked isocyanate crosslinking agent, carbodiimide crosslinking agent, aziridine crosslinking agent or epoxy silane crosslinking agent; Preferably, the crosslinking agent comprises aziridine-modified isocyanate.

8. The coated separator of any one of claims 1-7, wherein, The raw materials for preparing the coating layer further comprise any one or a combination of at least two of water, dispersant and surfactant.

9. The coated separator of claim 8, wherein, The water comprises pure water; Preferably, the dispersant comprises any one or a combination of at least two of ammonium polyacrylate, sodium tripolyphosphate, sodium hexametaphosphate and sodium pyrophosphate; Preferably, the surfactant comprises any one or a combination of at least two of polyether silane copolymer, polyether-modified polysiloxane, alkylphenol polyoxyethylene ether, fatty alcohol polyoxyethylene ether, fatty acid polyoxyethylene ether, fatty amine polyoxyethylene ether or fluorinated alkyl ethoxy alcohol ether.

10. The coated separator of any one of claims 1-9, wherein, The raw materials for preparing the coating layer comprise the following components in parts by weight:

11. The coated separator of any one of claims 1-10, wherein, The mass ratio of the emulsion type adhesive to the solvent type adhesive is 3: (0.5-3); Preferably, the mass ratio of the solvent type adhesive to the crosslinking agent is 100: (3-12).

12. The coated separator of any one of claims 1-11, wherein, The total coating amount of the coating is 2.4-3.2 g / m 2 ; Preferably, the single-side thickness of the coating layer is 0.5-4 μm. 13.A method for preparing the coated separator according to any one of claims 1-12, comprising the following steps: (1) mixing raw materials for preparing the coating layer to obtain a slurry; (2) coating the slurry on one side or both sides of the substrate film and baking to obtain the coated separator.

14. The production method according to claim 13, wherein The coating method in step (2) comprises coating by using a micro-concave roller. Preferably, the temperature of the toasting is 60-80°C; Preferably, the time of the toasting is 10-30s.

15. Use of the coated separator according to any one of claims 1-12 in a battery.

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