Slurry, battery diaphragm, preparation method of battery diaphragm and battery

Abstract

The invention discloses slurry, a battery diaphragm, a preparation method of the battery diaphragm and a battery, and belongs to the technical field of batteries. The slurry comprises the following components: ceramic particles, carbon nanofibers, a binder I and a solvent I, the ceramic particles comprise ceramic particles I and ceramic particles II; the particle size of the ceramic particles I is 0.55-1 [mu] m, and the particle size of the ceramic particles II is 0.05-0.45 [mu] m. The battery diaphragm comprises a base membrane and a composite coating, the composite coating is attached to at least one surface of the base film; the composite coating is formed by curing the slurry provided by the invention. The battery diaphragm provided by the invention has good thermal stability and mechanical strength, the passing rate of the lithium ion battery in coping with safety tests such as extrusion, puncture and heavy object impact is greatly improved, and meanwhile, the electrochemical performance of the lithium ion battery is also improved.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to a slurry, a battery separator, a preparation method thereof, and a battery. Background Art

[0002] The separator is an important component of lithium-ion batteries. It is a microporous membrane used to separate the positive and negative electrodes. It is a polymer functional material with a nano-scale microporous structure. In lithium-ion batteries, the separator prevents the positive and negative electrodes from short-circuiting, absorbs electrolyte, and provides ion channels. It determines the battery's interface structure, liquid retention performance, and internal resistance, which in turn affects important characteristics such as capacity, cycle performance, charge and discharge current density, and safety performance.

[0003] At present, commercial lithium-ion battery separators have some disadvantages in application:

[0004] (1) Poor thermal stability at high temperatures: Polyethylene (PE), polypropylene (PP) or composite films (PP / PE / PP) made from polyolefins will shrink, close pores or melt and rupture when they are close to their melting points (PP-160°C, PE-135°C). Although traditional inorganic ceramic coating modification technology can reduce the thermal shrinkage rate of polyolefin diaphragms below their melting points to a certain extent, when faced with higher temperature conditions, the shrinkage of the diaphragm will still cause a short circuit between the positive and negative electrodes. This is especially true when dealing with extreme safety tests such as thermal abuse, overcharging, and external short circuits. The safety of the battery operating at high temperatures cannot be fully guaranteed.

[0005] (2) Low mechanical strength: When lithium-ion batteries are subjected to safety tests such as extrusion, needle puncture, and heavy object impact, the mechanical strength of some diaphragm materials is relatively low. Under the action of external forces, they undergo severe deformation until they are damaged or torn, causing the positive and negative electrodes to contact and cause an internal short circuit, leading to safety problems such as battery fire and explosion.

[0006] In summary, the poor thermal stability and low mechanical strength of the diaphragm have a significant impact on the safety performance of lithium-ion batteries. Therefore, it is urgent to develop a lithium-ion battery diaphragm material with high safety performance to meet the lithium-ion battery's demand for extreme safety performance. Summary of the invention

[0007] The main purpose of the present application is to provide a slurry, a battery separator and a preparation method thereof and a battery, so as to solve the problems of poor thermal stability and low mechanical strength of the battery separator in the prior art.

[0008] In order to achieve the above-mentioned purpose, according to one aspect of the present application, a slurry is provided, the components of which include: ceramic particles, carbon nanofibers, a binder I, a dispersant and a solvent I; wherein the ceramic particles include ceramic particles I and ceramic particles II; the particle size of ceramic particles I is 0.55 to 1 μm, and the particle size of ceramic particles II is 0.05 to 0.45 μm.

[0009] Furthermore, the weight ratio of ceramic particles I to ceramic particles II is (0.25-4):1.

[0010] Furthermore, the particle size ratio of the ceramic particles I to the particle size of the ceramic particles II is (1.2-20):1.

[0011] Furthermore, in parts by weight, the weight of the ceramic particles in the slurry is 20 to 40 parts, the weight of the carbon nanofibers is 1 to 5 parts, the weight of the binder I is 1 to 5 parts, the weight of the dispersant is 0.1 to 5 parts, and the weight of the solvent I is 45 to 70 parts.

[0012] Furthermore, the viscosity of the slurry is 150-300 mPa.s, and the pH of the slurry is 7-9.

[0013] Furthermore, the ceramic particles I are selected from at least one of alumina, boehmite, magnesium hydroxide, silicon carbide, silicon dioxide, silicon nitride, boron carbide, and boron nitride.

[0014] Furthermore, the ceramic particles II are selected from at least one of alumina, boehmite, magnesium hydroxide, silicon carbide, silicon dioxide, silicon nitride, boron carbide and boron nitride.

[0015] Furthermore, the carbon nanofiber has a diameter of 50 nm to 500 nm, a length of 10 to 30 μm, an aspect ratio of 20 to 600, and a purity of 99.000% to 99.999%.

[0016] Furthermore, the binder I is selected from at least one of polyvinylidene fluoride, styrene-butadiene rubber, polyvinyl pyrrolidone, polymethyl methacrylate, polyacrylonitrile, polyacrylic acid and polyvinyl alcohol.

[0017] Furthermore, the dispersant is selected from at least one of carboxymethyl cellulose, ammonium citrate, polyethylene glycol, ammonium polymethacrylate, polyacrylic acid and sodium salt thereof.

[0018] Furthermore, solvent I is water.

[0019] According to a second aspect of the present application, a method for preparing the above-mentioned slurry is provided, the method comprising: mixing the components of the slurry to obtain the slurry.

[0020] Furthermore, the preparation method of the slurry includes the following steps: mixing carbon nanofibers, a dispersant and a solvent to obtain a carbon nanofiber glue; mixing ceramic particles I and ceramic particles II to obtain mixed ceramic particles; mixing the mixed ceramic particles and the carbon nanofiber glue to obtain a mixed solution; mixing the mixed solution and a binder to obtain a slurry.

[0021] Furthermore, the slurry preparation process is carried out in a vacuum environment.

[0022] Furthermore, in the entire slurry preparation process, each mixing step adopts the following process parameters: stirring speed is 10-30 rpm, dispersion speed is 200-800 rpm, and dispersion time is 30-180 min.

[0023] According to the third aspect of the present application, a battery separator is provided, which includes a base film and a composite coating; the composite coating is attached to at least one surface of the base film; wherein the composite coating is formed by curing the above-mentioned slurry or the slurry prepared by the above-mentioned preparation method.

[0024] Further, the composite coating is attached to two opposite surfaces of the base film.

[0025] Furthermore, an organic polymer coating is attached to at least one surface of the composite coating.

[0026] Furthermore, the thickness of the base film is 3 to 16 μm.

[0027] Furthermore, the thickness of the composite coating is 1 to 3 μm.

[0028] Furthermore, the thickness of the organic polymer coating is 0.5-5 μm.

[0029] Furthermore, the base film is selected from a composite film, a polyethylene film or a polypropylene film; wherein the composite film is formed by laminating a polypropylene film, a polyethylene film and a polypropylene film in sequence.

[0030] Furthermore, the slurry of the organic polymer coating layer consists of a binder II and a solvent II.

[0031] Furthermore, the binder II is selected from at least one of polyvinylidene fluoride, styrene-butadiene rubber, polyvinyl pyrrolidone, polymethyl methacrylate, polyacrylonitrile, polyacrylic acid and polyvinyl alcohol.

[0032] Furthermore, the solvent II is selected from at least one of deionized water, ethanol, glycerol, acetone, dimethylacetamide and N-methylpyrrolidone.

[0033] According to the fourth aspect of the present application, a method for preparing the above-mentioned battery separator is provided, the preparation method comprising: coating the slurry on at least one surface of the base film, and forming a battery separator with a composite coating attached to the surface of the base film after drying and curing.

[0034] Furthermore, the drying temperature is 60 to 90° C., and the drying time is 3 to 10 minutes.

[0035] Furthermore, the specific process of coating the slurry on the two surfaces of the base film includes: first coating the slurry on one surface of the base film, and forming a first composite coating of the base film after drying and curing; then coating the slurry on the other opposite surface of the base film, and forming a second composite coating of the base film after drying and curing.

[0036] Furthermore, after coating to form the composite coating, the preparation method further comprises: coating the organic polymer coating slurry on the surface of the first composite coating and / or the second composite coating to form a battery separator with the organic polymer coating attached to the surface of the composite coating.

[0037] Furthermore, the coating method of the composite coating and / or the coating method of the organic polymer coating is selected from at least one of gravure roller coating, spray coating or dip coating.

[0038] Furthermore, the organic polymer coating slurry is coated on the surface of the first composite coating by gravure roller coating, and after drying and curing, the organic polymer coating slurry is coated on the surface of the second composite coating by spraying.

[0039] According to a fifth aspect of the present application, a battery is provided, comprising a positive electrode plate, a separator, a negative electrode plate and an electrolyte; the separator is the above-mentioned battery separator or a battery separator prepared by the above-mentioned preparation method.

[0040] The technical solution of the present application is applied to provide a slurry, a battery separator, a preparation method thereof and a battery. The present application forms a slurry by mixing ceramics of different particle sizes with carbon nanofibers to form a high heat-resistant composite coating, and then applies the polymer slurry to the surface of the composite coating, and finally obtains a lithium-ion battery separator with high temperature resistance and high safety performance. The prepared separator has excellent high temperature resistance, small thermal shrinkage, and the contact area between the double-sided heat-resistant composite coating and the base film is twice that of the single-sided coating. The ceramic layer has greater resistance to the shrinkage of the base film. The addition of carbon nanofibers further improves the heat resistance of the coating and has a stronger ability to inhibit the thermal shrinkage of the base film. Therefore, it can effectively delay the thermal runaway time of the battery and greatly improve the pass rate of the thermal abuse test. At the same time, the carbon nanofibers dispersed between the inorganic ceramic particles can not only enrich the channels for lithium ion shuttle, but also have better liquid absorption and retention capabilities for electrolytes, thereby improving ionic conductivity, and can also significantly improve the puncture resistance and mechanical strength of the diaphragm, making it less likely to deform, break, and tear when resisting external forces, maintaining a stable structure, thereby reducing the probability of short circuits caused by contact between the positive and negative electrodes, and greatly improving the pass rate of lithium-ion batteries in safety tests such as extrusion, puncture, and heavy object impact. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] The drawings constituting part of the present application are used to provide a further understanding of the present application. The exemplary embodiments and descriptions of the present application are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0042] Figure 1 A schematic structural diagram of a battery separator according to an embodiment of the present application is shown.

[0043] Reference numerals:

[0044] 1. Basement membrane;

[0045] 2. Composite coating; 21. Ceramic particles I, 22. Ceramic particles II, 23. Carbon nanofibers;

[0046] 3. Organic polymer coating. DETAILED DESCRIPTION

[0047] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0048] Conventional separators have poor thermal stability and low mechanical strength, which have a serious impact on the safety performance of lithium-ion batteries. Therefore, the present application improves the thermal stability and mechanical strength of the separator by improving the material and structure of the battery separator.

[0049] According to one aspect of the present application, a slurry is provided, the components of which include: ceramic particles, carbon nanofibers, a binder I, a dispersant and a solvent I; wherein the ceramic particles include ceramic particles I and ceramic particles II; the particle size of the ceramic particles I is 0.55 to 1 μm, and the particle size of the ceramic particles II is 0.05 to 0.45 μm.

[0050] The particle size of the above-mentioned ceramic particles I in the present application is any value among 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 1 μm, or a range value between any two of them; the particle size of the ceramic particles II is any value among 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45 μm, or a range value between any two of them; the particle size of the ceramic particles I is, for example, 0.6 to 1 μm; the particle size of the ceramic particles II is, for example, 0.05 to 0.3 μm.

[0051] When selecting ceramic particles, the present application uses two types of ceramic particles with different particle sizes, and limits the particle sizes of the two ceramic particles to the above range; compared with the use of ceramic particles of a single particle size in conventional slurries, the present application gives the coating more microporous channels with different pore sizes by mixing the above two types of ceramic particles with specific particle sizes. The abundant pores are conducive to the rapid migration of lithium ions and have better liquid absorption and retention capabilities for electrolytes; the coating made of the slurry has better heat resistance, porosity, ionic conductivity and electrolyte wettability, which helps to improve the safety performance, rate performance, cycle performance, etc. of the battery.

[0052] Carbon nanofibers are selected in the slurry of the present application. Compared with other inorganic or organic fibers, the carbon nanofibers have the advantages of large aspect ratio, high mechanical strength, excellent heat resistance, good conductivity, etc. They are dispersed in the gaps between the above-mentioned inorganic ceramic particles of different sizes to provide radial shuttle channels for the diffusion of lithium ions, thereby improving the ion conductivity, electrolyte wettability, puncture resistance and mechanical strength; and the porous network structure formed by the carbon nanofibers will not significantly increase the coating thickness, thereby improving the performance of the diaphragm without occupying more volume, which is helpful to improve the energy density of the battery; at the same time, the high mechanical strength and high modulus of the carbon nanofibers significantly improve the puncture strength and deformation resistance of the diaphragm, and can also significantly improve the heat resistance of the battery diaphragm.

[0053] In some embodiments, the weight ratio of ceramic particles I and ceramic particles II is (0.25-4):1; for example, the weight ratio is 0.25:1, 0.5:1, 1:1, 2:1, 3:1, 4:1, etc.; for example, (0.25-3):1.

[0054] By regulating the ratio of large and small ceramic particles, the present application can further provide the composite coating with richer pores with different pore sizes, which is more conducive to the rapid migration of lithium ions and has better liquid absorption and retention capabilities for electrolytes, helping to improve the safety performance, rate performance, cycle performance, etc. of the battery.

[0055] In some embodiments, the particle size ratio of the ceramic particles I to the ceramic particles II is (1.2-20):1; for example, 1.2:1, 1.5:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, 11:1, 12:1, 13:1, 14:1, 15:1, 16:1, 17:1, 18:1, 19:1, 20:1. The present application can give the coating more abundant pores by mixing two ceramic particles of a specific particle size ratio, which is conducive to the rapid migration of lithium ions and improves the conductivity and liquid absorption rate.

[0056] In some embodiments, in parts by weight, the weight of the ceramic particles in the slurry is 20-40 parts, the weight of the carbon nanofibers is 1-5 parts, the weight of the binder I is 1-5 parts, the weight of the dispersant is 0.1-5 parts, and the weight of the solvent I is 45-65 parts; for example, the weight of the ceramic particles is any value among 20, 25, 30, 35, 40, or a range of any two of them; the weight of the carbon nanofibers is any value among 1, 2, 3, 4, 5, or a range of any two of them; the weight of the binder I is any value among 1, 2, 3, 4, 5, or a range of any two of them; the weight of the dispersant is any value among 0.1, 0.5, 1, 2, 3, 4, 5, or a range of any two of them; the weight of the solvent I is any value among 45, 50, 55, 60, 65, 70, or a range of any two of them.

[0057] The present application forms a good synergistic relationship between the multiple components by adjusting the ratio of ceramic particles, carbon nanofibers, binder and solvent in the slurry, making the slurry more dispersible, which is beneficial to improving the thermal stability and mechanical strength of the composite coating.

[0058] In some embodiments, the ceramic particles are selected from at least two of aluminum oxide, boehmite, magnesium hydroxide, silicon carbide, silicon dioxide, silicon nitride, boron carbide, and boron nitride. The types of ceramic particles I and ceramic particles II can be the same or different. For example, ceramsite particles I can select at least one of aluminum oxide, boehmite, magnesium hydroxide, silicon carbide, silicon dioxide, silicon nitride, boron carbide, and boron nitride; for another example, ceramsite particles I are aluminum oxide, magnesium oxide, silicon nitride, and boron nitride. Ceramic particles II can select at least one of aluminum oxide, boehmite, magnesium hydroxide, silicon carbide, silicon dioxide, silicon nitride, boron carbide, and boron nitride; for example, boron carbide, silicon carbide, silicon dioxide, boehmite, etc.

[0059] The above-mentioned ceramic particle types selected in the present application have excellent thermal stability, electrolyte wettability, and electrochemical stability, which improve the high temperature resistance and liquid absorption and retention of the composite coating, thereby improving the safety performance of the diaphragm.

[0060] In some embodiments, the carbon nanofibers have a diameter of 50 nm to 500 nm, a length of 10 to 30 μm, an aspect ratio of 20 to 600, and a purity of 99.000% to 99.999%.

[0061] The carbon nanofibers of the above-mentioned size selected in the present application have the advantages of large aspect ratio, high mechanical strength, excellent heat resistance, etc., which can further improve the ionic conductivity, electrolyte wettability, puncture resistance and mechanical strength of the diaphragm, thereby significantly improving the heat resistance and puncture resistance of the battery diaphragm.

[0062] In some embodiments, the binder I is selected from at least one of polyvinylidene fluoride, styrene-butadiene rubber, polyvinyl pyrrolidone, polymethyl methacrylate, polyacrylonitrile, polyacrylic acid and polyvinyl alcohol; the solvent I is water; the viscosity of the slurry is 150-300 mPa.s, and the pH of the slurry is 7-9.

[0063] The present application adjusts the slurry viscosity and pH value to make the slurry have good fluidity, stability and uniformity, reduce the phenomena of too high or too low slurry viscosity, sedimentation, agglomeration, uneven dispersion, etc., improve the coating quality, uniformity and consistency, make the coating more dense and uniform, and greatly enhance the heat resistance, liquid absorption and retention, and the uniformity of distribution of ceramic particles and carbon nanofibers.

[0064] The present application selects the above-mentioned solvents and multiple binders, and adjusts the above-mentioned slurry viscosity and pH to further improve the membrane's wettability to the electrolyte and its ability to absorb and retain liquid, and significantly improves the adhesion between the membrane and the electrode plates, thereby ensuring that the battery has better cycle performance.

[0065] In some embodiments, the dispersant is selected from at least one of carboxymethyl cellulose, ammonium citrate, polyethylene glycol, ammonium polymethacrylate, polyacrylic acid and sodium salt thereof. The present application can further improve the dispersibility of the slurry by adding a dispersant.

[0066] According to a second aspect of the present application, a method for preparing the above-mentioned slurry is provided, and the method comprises the following steps: mixing the components of the slurry to obtain the slurry.

[0067] In some embodiments, the method for preparing the slurry includes the following steps: mixing carbon nanofibers, a dispersant and a solvent to obtain a carbon nanofiber glue; mixing ceramic particles I and ceramic particles II to obtain mixed ceramic particles; mixing the mixed ceramic particles and the carbon nanofiber glue to obtain a mixed solution; mixing the mixed solution and a binder to obtain a slurry; the slurry preparation process is carried out in a vacuum environment; each mixing step adopts the following parameters: a stirring speed of 10 to 30 rpm, a dispersion speed of 200 to 800 rpm, and a dispersion time of 30 to 180 min.

[0068] The present application adopts a step-by-step mixing method to achieve mixing of all components, which is beneficial to the dispersion and uniformity of the slurry and is beneficial for the coated diaphragm to have better mechanical strength.

[0069] According to the third aspect of the present application, a battery separator is provided, which includes a base film and a composite coating; the composite coating is attached to at least one surface of the base film; wherein the composite coating is formed by curing the above-mentioned slurry or the slurry prepared by the above-mentioned preparation method.

[0070] The present application utilizes the above-mentioned special slurry to be coated on the surface of the base film, thereby forming a highly heat-resistant composite coating on the surface of the base film, so that the diaphragm has a small thermal shrinkage rate, a high liquid absorption and retention capacity, and a strong puncture resistance.

[0071] In some embodiments, the composite coating is attached to two opposing surfaces of the base film.

[0072] In the present application, the above-mentioned slurry is coated on both surfaces of the base film. The area of ​​the double-sided composite coating is twice the area of ​​the single-sided coating. The coating has greater resistance to the base film and has a stronger ability to inhibit the shrinkage of the base film. Therefore, it can effectively delay the thermal runaway time of the battery and greatly improve the pass rate of the thermal abuse test; it can further improve the thermal stability and mechanical properties of the base film such as puncture resistance.

[0073] In some embodiments, an organic polymer coating is attached to at least one surface of the composite coating; for example, the organic polymer coating is coated on the surfaces of two composite coatings respectively to form a structure in which the composite coating and the organic polymer coating are attached to both sides of the base film in sequence; wherein the base film can be selected from polyethylene, polypropylene or polypropylene / polyethylene / polypropylene composite film; the slurry of the organic polymer coating is composed of a binder II and a solvent II; for example, the binder II is selected from at least one of polyvinylidene fluoride, styrene-butadiene rubber, polyvinyl pyrrolidone, polymethyl methacrylate, polyacrylonitrile, polyacrylic acid and polyvinyl alcohol; for example, the solvent II is selected from at least one of deionized water, ethanol, glycerol, acetone, dimethylacetamide and N-methylpyrrolidone.

[0074] Compared with the modified diaphragm with traditional coating, the diaphragm with the composite structure of the present application has a more obvious inhibitory effect on the shrinkage of the base film by the double-sided coating, and there is liquid storage space between the diaphragm and the positive and negative electrode sheets, so it has a stronger ability to absorb and retain liquid and stronger adhesion, which has a significant effect on inhibiting high-temperature cycle expansion and extending the cycle life; the lithium-ion battery assembled with the diaphragm has better safety and greatly increases the probability of the battery passing the extreme safety test.

[0075] In some embodiments, the thickness of the base film is 3 to 16 μm; the thickness of the composite coating is 1 to 3 μm; the thickness of the organic polymer coating is 0.5 to 5 μm; the base film is selected from a composite film, a polyethylene film or a polypropylene film; wherein the composite film is a polypropylene film, a polyethylene film and a polypropylene film laminated in sequence.

[0076] The base film thickness selected in the present application within the above range can meet the technical indicators such as mechanical strength, porosity, ionic conductivity, etc. of the diaphragm materials required by various types of battery products in different application fields, so that the comprehensive characteristics of the diaphragm materials meet the requirements of the battery for product characteristics such as energy density, safety performance, rate performance, and cycle performance; the selected composite coating thickness within the above range can significantly improve the thermal stability and mechanical strength of the diaphragm, and with the change of the composite coating thickness, high energy density and high safety performance can be taken into account; the selected organic polymer coating thickness within the above range can not only improve the adhesion between the diaphragm and the positive and negative electrode sheets, but also enhance the diaphragm's ability to absorb and retain electrolyte, thereby significantly improving the battery's cycle performance and safety performance.

[0077] According to the fourth aspect of the present application, a method for preparing the above-mentioned battery separator is provided, the method comprising: coating the slurry on at least one surface of the base film, and drying and curing to form a battery separator with a composite coating attached to the surface of the base film. For example, the drying temperature is 60 to 90° C., and the drying time is 3 to 10 minutes.

[0078] In some embodiments, the specific process of coating the slurry on the two surfaces of the base film includes: first coating the slurry on one surface of the base film, and forming a first composite coating of the base film after drying and curing; then coating the slurry on the other opposite surface of the base film, and forming a second composite coating of the base film after drying and curing.

[0079] In some embodiments, after coating to form the composite coating, the preparation method further comprises: coating the organic polymer coating slurry on the surface of the first composite coating and / or the second composite coating to form a battery separator with the organic polymer coating attached to the surface of the composite coating.

[0080] In some embodiments, the coating method of the composite coating and / or the coating method of the organic polymer coating is selected from at least one of gravure roller coating, spray coating, or dip coating.

[0081] In some embodiments, the organic polymer coating slurry is coated on the surface of the first composite coating by gravure roller coating, and after drying and curing, the organic polymer coating slurry is coated on the surface of the second composite coating by spraying.

[0082] This application adopts the above two coating methods. On the one hand, the organic polymer coating slurry can be uniformly and densely coated on the surface of the composite coating by gravure roller coating, so that the polymer swells rapidly under the infiltration of the electrolyte to form a gel, and the polymer molecules and the components in the battery pole piece are hydrogen bonded by the van der Waals force to exert strong adhesion; on the other hand, the organic polymer coating slurry is dispersedly coated on the surface of the composite coating by spraying, and is distributed in a sporadic island shape, reducing the coverage ratio of the glue layer, improving the permeability of lithium ions in the pores of the diaphragm, reducing the permeability value of the coating, and avoiding the organic polymer from swelling and blocking the pores on the surface of the diaphragm, thereby improving the charge and discharge performance and rate performance of the battery. The above coating method can not only ensure that the diaphragm and the pole piece have a strong bonding strength, but also improve the permeability and lithium ion permeability of the diaphragm, and finally significantly improve the cycle performance, safety performance and rate performance of the battery.

[0083] The above-mentioned method of coating slurry or organic polymer slurry on the base film of the present application can also be selected according to actual conditions.

[0084] According to a fifth aspect of the present application, a battery is provided, comprising a positive electrode plate, a separator, a negative electrode plate and an electrolyte; the separator is the above-mentioned battery separator or a battery separator prepared by the above-mentioned preparation method.

[0085] The present application is further described in detail below in conjunction with specific embodiments. These embodiments should not be construed as limiting the scope of protection claimed in the present application.

[0086] All raw materials used in the examples of this application are prior art and can be purchased commercially.

[0087] Example 1

[0088] Slurry formula: by weight, 20 parts of ceramic particles, 5 parts of carbon nanofibers, 5 parts of polyvinylidene fluoride binder, 3 parts of carboxymethyl cellulose dispersant, and 67 parts of water; wherein the ceramic particles include alumina (average particle size 0.7 μm) and boehmite (average particle size 0.3 μm), with a weight ratio of 4:1; the carbon nanofibers have an average diameter of 200 nm, a length of 10 μm, and a purity of 99.998%;

[0089] Preparation of slurry: at a temperature of 25±5℃, under vacuum conditions, carbon nanofibers, dispersants and water are mixed and stirred evenly, and a stable and uniform carbon nanofiber glue is obtained after ultrasonic dispersion, and low-speed vacuum stirring is maintained for standby use; two ceramic particles of different sizes are mixed by mechanical mixing to obtain mixed ceramic particles; then the mixed ceramic particles and carbon nanofiber glue are mixed, and after stirring and dispersing evenly, a mixed solution of ceramics and carbon nanofibers is obtained; finally, the mixed solution is mixed with a binder. In the slurry preparation process, the process parameters of each step are: stirring speed is 10-30rpm, dispersion speed is 200-800rpm, and the total time of stirring and dispersing is 150min; the slurry viscosity is controlled to be 170-230mpa.s, and the pH is adjusted to 7-8.

[0090] Diaphragm preparation: The substrate is a wet-process biaxially oriented polyethylene (PE) diaphragm with a thickness of 7 μm.

[0091] The high heat-resistant composite coating prepared by the above-mentioned slurry is coated on both sides of the base film surface by a gravure roller coating process. The preparation process of the composite coating is as follows: the prepared slurry is coated on one surface of the polyethylene base film by gravure roller coating, the oven temperature is controlled to 60°C, and the coating is dried for 10 minutes. After drying and curing, a first high heat-resistant composite coating of the base film is formed with a thickness of 1 μm; the slurry is then coated on the other opposite surface of the base film by gravure roller coating, and the coating is dried at the same temperature for 10 minutes. After drying and curing in the oven, a second high heat-resistant composite coating of the base film is formed with a thickness of 1 μm.

[0092] Then, an organic polymer coating is prepared on the surface of the high heat-resistant composite coating diaphragm. The preparation process of the organic polymer coating is as follows: PVDF is selected as the organic coating material, and water is used as the solvent to prepare a slurry. The slurry is coated on one side of the surface of the high heat-resistant composite coating diaphragm by gravure roller coating, and the other side is coated by spraying. The roller coating surface density is controlled at 0.75-0.85 g / m 2 , thickness is 1.5μm, and the coating density of the spray layer is controlled at 0.65~0.75g / m 2 , with a thickness of 2 to 3 μm, and a total thickness of 3.5 to 4.5 μm on one side of the coating layer. Drying at 75°C for 10 minutes finally yields the lithium-ion battery separator with high safety performance, such as Figure 1 shown.

[0093] Example 2

[0094] The difference between Example 2 and Example 1 is that the slurry formula is different; in parts by weight, the ceramic particles are 35 parts, the carbon nanofibers are 4 parts, the polyvinylidene fluoride binder is 3 parts, the carboxymethyl cellulose dispersant is 3 parts, and the water is 55 parts; wherein the ceramic particles include magnesium hydroxide (average particle size 0.6 μm) and silicon dioxide (average particle size 0.2 μm), and the weight ratio is 1:4; the carbon nanofibers have an average diameter of 200 nm, a length of 10 μm, and a purity of 99.998%. The other conditions are the same as in Example 1.

[0095] Example 3

[0096] The difference between Example 3 and Example 1 is that the slurry formula is different; in parts by weight, the ceramic particles are 40 parts, the carbon nanofibers are 4 parts, the polyvinylidene fluoride binder is 3 parts, the carboxymethyl cellulose dispersant is 3 parts, and the water is 50 parts; wherein the ceramic particles include silicon nitride (average particle size 0.9 μm) and silicon carbide (average particle size 0.05 μm), and the weight ratio is 1:1; the carbon nanofibers have an average diameter of 200 nm, a length of 10 μm, and a purity of 99.998%. The other conditions are the same as in Example 1.

[0097] Example 4

[0098] The difference between Example 4 and Example 1 is that the slurry formula is different; in parts by weight, 30 parts of ceramic particles, 1 part of carbon nanofibers, 4 parts of polyvinyl pyrrolidone binder, 2 parts of carboxymethyl cellulose dispersant, and 63 parts of water; wherein the ceramic particles include boron nitride (average particle size 1 μm) and boron carbide (average particle size 0.1 μm), and the weight ratio is 3:1; the carbon nanofibers have an average diameter of 200 nm, a length of 10 μm, and a purity of 99.998%. The other conditions are the same as in Example 1.

[0099] Comparative Example 1

[0100] The difference between Comparative Example 1 and Example 1 is that in the slurry formula of the composite coating, the inorganic ceramic particles only select one material, boehmite, and boehmite D50 = 300nm, and are not mixed with large-particle ceramic particles to prepare a lithium-ion battery separator. The other conditions are the same as Example 1.

[0101] Comparative Example 2

[0102] The difference between Comparative Example 2 and Example 1 is that aramid fiber is used instead of the carbon nanofiber in Example 1, the purity of the aramid fiber used is 99.995%, and the fiber length is 1-2 μm. Two inorganic ceramic particles with different particle sizes, alumina and boehmite, are selected to prepare a coating slurry with aramid fiber, a binder, a dispersant, and water and coated on both sides of the base film to prepare a lithium ion battery separator, and the other conditions are the same as in Example 1.

[0103] Comparative Example 3

[0104] The difference between Comparative Example 3 and Example 1 is that the slurry formula of the composite coating used is different;

[0105] Slurry formula: ordered mesoporous carbon, polymethyl methacrylate microspheres (particle size 2 μm), boehmite powder (particle size 0.4 μm), nanocellulose, sodium carboxymethyl cellulose powder dispersant, polyacrylate binder and water in a mass ratio of 2:10:100:5:5:7:250. Other conditions are the same as in Example 1.

[0106] The thickness, air permeability, surface density, puncture strength, tensile strength, elongation, 150°C 1H thermal shrinkage, 180°C 1H thermal shrinkage, ionic conductivity, electrolyte contact angle and other performance indicators of the lithium ion battery separators prepared in Examples 1 to 4 and Comparative Examples 1 to 3 were tested respectively.

[0107] The test methods for thickness, air permeability, surface density, puncture strength, tensile strength, elongation, thermal shrinkage and ionic conductivity refer to GB / T 36363-2018.

[0108] Electrolyte contact angle test: Fix the diaphragm flat on the sample table, suck the electrolyte with a syringe, drop a certain volume of electrolyte on the diaphragm surface, and use a contact angle tester to measure the contact angle between the diaphragm surface and the electrolyte.

[0109] The test results of Examples 1 to 4 and Comparative Examples 1 to 3 are shown in Table 1. At least 3 data are tested for each indicator, and the average value is recorded in Table 1.

[0110] Table 1 Performance test results of the diaphragms of Examples 1 to 4 and Comparative Examples 1 to 3

[0111]

[0112]

[0113] The test data in Table 1 show that compared with Comparative Examples 1 to 3, the total thickness of the battery separators prepared in Examples 1 to 4 of the present application is 14.0 to 14.2 μm; the air permeability is 165 to 189 Sec / 100 ml; the surface density is 9.76 to 10.62 g / m 2 ; Puncture strength reaches 532~580gf; Tensile strength MD reaches 3250~3360kgf / cm 2 ;Tensile strength TD reaches 3036~3308kgf / cm 2; Elongation MD reaches 102-108%; elongation TD reaches 113-123%; 150℃1H heat shrinkage MD is 0.9-2.5%; 150℃1H heat shrinkage TD is 0.2-1.8%; 180℃1H heat shrinkage MD is 1.8-4.5%; 180℃1H heat shrinkage TD is 0.5-3.9%; ionic conductivity is 14.88-20.33 10 -4 S / cm; the electrolyte contact angle is 0.9-2.3°. The above test results show that the battery separator prepared by the method of the present application has better thermal stability, ionic conductivity, electrolyte wettability, puncture strength, tensile strength, elongation and other characteristics, indicating that the separator has excellent mechanical properties, high temperature resistance, and small thermal shrinkage.

[0114] As the proportion of ceramic components in the slurry increases, the thermal shrinkage rate of the diaphragm gradually decreases, the ionic conductivity increases, the electrolyte contact angle decreases, the diaphragm has better liquid absorption and retention capabilities, the puncture resistance and mechanical strength of the diaphragm gradually increase, and the puncture resistance and mechanical strength of the diaphragm can be significantly improved, making it less likely to deform, break and tear when resisting external forces, thereby maintaining a stable structure.

[0115] From the data in Table 1, it can be seen that compared with Comparative Example 1, the thickness, tensile strength and elongation of the diaphragm of Example 1 have no significant changes, but the air permeability, surface density, puncture strength, thermal shrinkage, ionic conductivity, electrolyte contact angle and other indicators have been significantly improved. Among them, the puncture strength is increased from 460gf to 532gf, indicating that compared with the small-particle boehmite single coating of Comparative Example 1, the large and small particle mixed coating of Example 1 has higher puncture resistance; the 150℃1H thermal shrinkage and 180℃1H thermal shrinkage of Example 1 are significantly lower than those of Comparative Example 1, indicating that the high temperature resistance of the diaphragm of Example 1 is better; the ionic conductivity is increased from 10.82×10 -4 S / cm increased to 15.16×10 -4 S / cm, which is increased by about 40%, indicating that the diaphragm of Example 1 has better ion permeability, thereby ensuring that the lithium-ion battery has a smaller internal resistance and a faster lithium ion migration rate during the charge and discharge process; the electrolyte contact angle is reduced from 12.8° to 2.3°, indicating that the electrolyte wettability of the diaphragm is significantly improved. From the above results, it can be seen that compared with the ceramic coating of a single particle size, the large and small particle ceramics used in the present invention are mixed, so that the diaphragm has higher heat resistance, and the abundant gaps provide more channels for ion conduction, and the liquid absorption and retention capacity is significantly enhanced, and the diaphragm has higher ionic conductivity and wettability.

[0116] From the data in Table 1, it can be seen that compared with the comparative example 2, the thickness, air permeability and surface density of the separator of Example 1 have no significant changes, and the puncture strength, tensile strength, elongation, thermal shrinkage, ionic conductivity, electrolyte contact angle and other indicators have been significantly improved. Among them, the puncture strength is increased from 503gf to 532gf, indicating that compared with the aramid fiber of the comparative example 2, the carbon nanofiber of Example 1 has higher puncture resistance; the tensile strength is significantly improved from 2800kgf / cm 2 Increased to 3000~3200kgf / cm 2 , increased by about 11%, and the elongation increased from 85% to 102%, an increase of about 20%, indicating that carbon nanofibers have a more obvious improvement effect on mechanical properties such as tensile strength and elongation compared with aramid fibers; the 150℃1H thermal shrinkage rate and 180℃1H thermal shrinkage rate of Example 1 are significantly lower than those of Comparative Example 2, indicating that the high temperature resistance of the diaphragm of Example 1 is better; the ionic conductivity is increased from 12.33×10 -4 S / cm increased to 15.16×10 -4 S / cm, increased by about 23%, indicating that the diaphragm of Example 1 has better ion permeability; the electrolyte contact angle decreased from 8.5° to 2.3°, indicating that the electrolyte wettability of the diaphragm was significantly improved. From the above results, it can be seen that compared with aramid fibers, the carbon nanofibers used in the present invention have better mechanical strength, heat resistance, electrical conductivity, and heat resistance, and dispersed in inorganic ceramsite, which can improve the heat resistance, ionic conductivity, electrolyte wettability, puncture resistance and mechanical strength of the diaphragm.

[0117] It can be seen from the data in Table 1 that compared with Comparative Example 3, the prepared diaphragm in Example 1 has better comprehensive performance, lower air permeability, stronger puncture strength and mechanical properties, lower thermal shrinkage, higher ion conductivity, and smaller electrolyte contact angle. Comparative Example 3 is a slurry prepared by using ceramic powder with uniform particle size and ordinary nanocellulose; the thermal stability, external force resistance and electrical conductivity of the prepared diaphragm are worse; it illustrates that the present application adds ceramic particles and carbon nanofibers with significantly different particle sizes and a reasonable ratio between the components to the base film coating slurry, and multiple factors work together to make the diaphragm have better thermal stability and strong mechanical strength; wherein, the use of ceramic particles of different particle sizes makes the coating have more micropores with different pore sizes, and the abundant pores are conducive to the rapid migration of lithium ions, and have better liquid absorption and retention capabilities for the electrolyte; dispersing carbon nanofibers in the gaps between the above-mentioned inorganic ceramic particles of different particle sizes can provide radial shuttle channels for the diffusion of lithium ions, which can improve ionic conductivity, electrolyte wettability, puncture resistance and mechanical strength; at the same time, the high mechanical strength and high modulus of carbon nanofibers further enhance the puncture strength and deformation resistance of the battery diaphragm, and can also significantly improve the heat resistance of the battery diaphragm.

[0118] In the technical scheme of the present invention, the test results of the performance indexes of the lithium-ion battery separator materials of the above-mentioned embodiments and comparative examples show that: a mixed slurry of large and small ceramic particles and carbon nanofibers uniformly dispersed in the gaps between particles is coated on both sides of a polyolefin base film, and after drying and baking, a high heat-resistant composite coating is made, and then a polymer slurry is coated on both sides of the coating surface, and finally a high-temperature resistant and high-safety lithium-ion battery separator is obtained, which has better high-temperature resistance, puncture resistance, ionic conductivity, mechanical strength and other advantages than traditional coated separators. Therefore, the technical scheme of the present application has a better technical effect.

[0119] It should be noted that the terms "first", "second", etc. in the specification and claims of the present application are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the terms used in this way can be interchangeable where appropriate, so that the embodiments of the present application described herein can be implemented in an order other than those described herein, for example.

[0120] The above description is only an embodiment of the present application and is not intended to limit the present application. For those skilled in the art, the present application may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A slurry, characterized in that: The components of the slurry include: ceramic particles, carbon nanofibers, a binder I, a dispersant and a solvent I; The ceramic particles include ceramic particles I and ceramic particles II; the particle size of the ceramic particles I is 0.55 to 1 μm, and the particle size of the ceramic particles II is 0.05 to 0.45 μm.

2. The slurry according to claim 1, characterized in that The weight ratio of the ceramic particles I to the ceramic particles II is (0.25-4):1; And / or, the ratio of the particle size of the ceramic particles I to the particle size of the ceramic particles II is (1.2-20):1; And / or, in parts by weight, the ceramic particles in the slurry are 20 to 40 parts by weight, the carbon nanofibers are 1 to 5 parts by weight, the binder I is 1 to 5 parts by weight, the dispersant is 0.1 to 5 parts by weight, and the solvent I is 45 to 70 parts by weight; And / or, the viscosity of the slurry is 150-300 mPa.s, and the pH of the slurry is 7-9.

3. The slurry according to claim 1 or 2, characterized in that The ceramic particles I are selected from at least one of alumina, boehmite, magnesium hydroxide, silicon carbide, silicon dioxide, silicon nitride, boron carbide and boron nitride; And / or, the ceramic particles II are selected from at least one of alumina, boehmite, magnesium hydroxide, silicon carbide, silicon dioxide, silicon nitride, boron carbide and boron nitride; And / or, the ceramic particles I and the ceramic particles II are of the same or different types; and / or, the carbon nanofibers have a diameter of 50 nm to 500 nm, a length of 10 to 30 μm, an aspect ratio of 20 to 600, and a purity of 99.000% to 99.999%; And / or, the binder I is selected from at least one of polyvinylidene fluoride, styrene-butadiene rubber, polyvinyl pyrrolidone, polymethyl methacrylate, polyacrylonitrile, polyacrylic acid and polyvinyl alcohol; and / or, the dispersant is selected from at least one of carboxymethyl cellulose, ammonium citrate, polyethylene glycol, ammonium polymethacrylate, polyacrylic acid and sodium salt thereof; And / or, the solvent I is water.

4. A method for preparing the slurry according to any one of claims 1 to 3, characterized in that: The method comprises: mixing the components of the slurry to obtain the slurry; Preferably, the preparation method of the slurry comprises the following steps: mixing the carbon nanofibers, the dispersant and the solvent I to obtain a carbon nanofiber glue; mixing the ceramic particles I and the ceramic particles II to obtain mixed ceramic particles; mixing the mixed ceramic particles and the carbon nanofiber glue to obtain a mixed solution; mixing the mixed solution and the binder I to obtain the slurry; Preferably, the slurry preparation process is carried out in a vacuum environment; Preferably, in the entire slurry preparation process, each mixing process adopts the following parameters: stirring speed is 10-30 rpm, dispersion speed is 200-800 rpm, and dispersion time is 30-180 min.

5. A battery separator, characterized in that: The battery separator includes a base film and a composite coating; the composite coating is attached to at least one surface of the base film; wherein the composite coating is formed by curing the slurry described in any one of claims 1 to 3 or the slurry prepared by the preparation method described in claim 4.

6. The battery separator according to claim 5, characterized in that: The composite coating is attached to two opposite surfaces of the base film; and / or, an organic polymer coating is attached to at least one surface of the composite coating; And / or, the base film has a thickness of 3 to 16 μm; And / or, the thickness of the composite coating is 1 to 3 μm; Preferably, the thickness of the organic polymer coating is 0.5-5 μm.

7. The battery separator according to claim 6, characterized in that: The base film is selected from a composite film, a polyethylene film or a polypropylene film; wherein the composite film is a polypropylene film, a polyethylene film and a polypropylene film laminated in sequence; and / or, the slurry of the organic polymer coating consists of a binder II and a solvent II; Preferably, the binder II is selected from at least one of polyvinylidene fluoride, styrene-butadiene rubber, polyvinyl pyrrolidone, polymethyl methacrylate, polyacrylonitrile, polyacrylic acid and polyvinyl alcohol; Preferably, the solvent II is selected from at least one of deionized water, ethanol, glycerol, acetone, dimethylacetamide and N-methylpyrrolidone.

8. A method for preparing a battery separator according to any one of claims 5 to 7, characterized in that: The preparation method comprises: coating the slurry on at least one surface of a base film, and drying and curing to form the battery separator with a composite coating layer attached to the surface of the base film.

9. The method for preparing a battery separator according to claim 8, characterized in that: The drying temperature is 60 to 90° C., and the drying time is 3 to 10 minutes; And / or, the specific process of coating the slurry on the two surfaces of the base film includes: firstly coating the slurry on one surface of the base film, and forming a first composite coating of the base film after drying and curing; and then coating the slurry on the other opposite surface of the base film, and forming a second composite coating of the base film after drying and curing; And / or, after coating to form the composite coating, the preparation method further comprises: coating an organic polymer coating slurry on the surface of the first composite coating and / or the second composite coating to form the battery separator with the organic polymer coating attached to the surface of the composite coating; Preferably, the coating method of the composite coating and / or the coating method of the organic polymer coating is selected from at least one of gravure roller coating, spray coating or dip coating; Preferably, the organic polymer coating slurry is coated on the surface of the first composite coating by gravure roller coating, and after drying and curing, the organic polymer coating slurry is coated on the surface of the second composite coating by spraying.

10. A battery comprising a positive electrode sheet, a separator, a negative electrode sheet and an electrolyte; characterized in that: The separator is the battery separator according to any one of claims 5 to 7 or the battery separator prepared by the preparation method according to claim 8 or 9.

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