Coating slurry and preparation method thereof, diaphragm and preparation method thereof, and battery

Abstract

The invention provides coating slurry and a preparation method thereof, a diaphragm and a preparation method thereof and a battery, the diaphragm comprises a base material and a coating layer arranged on at least one surface of the base material, and the coating layer comprises agglomerated particles formed by a first polymer and a second polymer; at least a portion of the second polymer is distributed inside the agglomerated particles. According to the present invention, the separator has good adhesion performance, such that the battery has good cycle performance.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-ion batteries, and in particular relates to a coating slurry and a preparation method thereof, a diaphragm and a preparation method thereof, and a battery. Background Art

[0002] To improve separator performance, such as adhesion, liquid absorption and retention, and wettability, an adhesive coating is typically applied to the base film or ceramic coating. During lithium battery processing, heat and pressure are required to bond the separator to the positive and negative electrodes. However, currently available adhesive coatings on the market exhibit suboptimal adhesion even after hot pressing.

[0003] Therefore, developing a diaphragm with high bonding strength is an urgent problem to be solved in this field. Summary of the Invention

[0004] In view of the shortcomings of the prior art, the present invention aims to provide a coating slurry and a preparation method thereof, a diaphragm and a preparation method thereof, and a battery. The provided diaphragm has better bonding performance than the diaphragms of the prior art.

[0005] To achieve this object, the present invention adopts the following technical solutions:

[0006] In a first aspect, the present invention provides a diaphragm comprising a substrate and a coating layer disposed on at least one surface of the substrate, wherein the coating layer comprises agglomerated particles formed by a first polymer and a second polymer; at least a portion of the second polymer is distributed inside the agglomerated particles.

[0007] In the present invention, the membrane coating layer includes agglomerated particles formed by a first polymer and a second polymer, and at least a portion of the second polymer is distributed inside the agglomerated particles. When the agglomerated particles have similar sizes, the distribution of the first polymer and the second polymer in the agglomerated particles is more reasonable, so that the effective bonding area of the coating layer is larger and the bonding performance is more uniform. Therefore, the membrane in the present invention has a better bonding effect than the prior art.

[0008] Generally, to improve the interfacial stability between the battery pole piece and the separator, the separator and the positive and negative electrodes of the battery are usually bonded using high-temperature hot pressing (e.g., 60-90°C). The higher the temperature, the better the bonding effect. However, when the separator and the positive and negative electrodes are bonded by heating, on the one hand, since neither the battery pole piece nor the separator has good thermal conductivity, the temperature from the outermost to the innermost part of the battery is uneven, resulting in low bonding strength. On the other hand, if heating equipment is added or the hot pressing time is extended, costs are increased and production efficiency is reduced. In addition, the heating method of hot pressing requires a high temperature, which poses a safety hazard.

[0009] Furthermore, the present invention preferably has a glass transition temperature (Tg) of the first polymer ≤ -32°C, for example, it can be any value among -70°C, -68°C, -65°C, -62°C, -60°C, -58°C, -55°C, -52°C, -50°C, -48°C, -46°C, -44°C, -42°C, -40°C, -38°C, -36°C, -34°C, -32°C, etc., or a range value between any two values, more preferably -60 to -32°C.

[0010] Preferably, the first polymer satisfies at least one of the following:

[0011] a) the melting point (T) of the first polymer is ≤ 145°C, for example, it can be any value among 110°C, 112°C, 114°C, 116°C, 118°C, 120°C, 122°C, 124°C, 126°C, 128°C, 130°C, 132°C, 134°C, 136°C, 138°C, 140°C, 142°C, 144°C, 145°C, etc., or a range between any two values.

[0012] b) the softening point of the first polymer is 60-100°C, for example, it can be any value of 60°C, 62°C, 65°C, 68°C, 70°C, 72°C, 75°C, 78°C, 80°C, 82°C, 85°C, 88°C, 90°C, 92°C, 95°C, 98°C, 100°C, etc., or a range value between any two values.

[0013] In the present invention, the Tg, T and softening point of the first polymer are within a specific range, which is more conducive to obtaining agglomerated particles with the second polymer distributed inside, thereby improving the bonding effect of the diaphragm at a lower temperature; wherein, if the Tg of the first polymer is too low, there is no significant improvement in the bonding performance and air permeability, but it will lead to an increase in the synthesis cost of the material and a decrease in production efficiency.

[0014] Preferably, the first polymer comprises a fluoropolymer.

[0015] In the present invention, the fluorine-containing polymer includes at least one of polyvinylidene fluoride homopolymer, polyvinylidene fluoride-hexafluoropropylene copolymer, polytetrafluoroethylene or fluorinated ethylene-propylene copolymer.

[0016] In the present invention, the D50 particle size of the first polymer is 100 to 500 nm, for example, it can be any value among 100 nm, 150 nm, 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, 450 nm, 500 nm, etc., or a range between any two values.

[0017] Preferably, the glass transition temperature of the second polymer is ≤10°C, for example, it can be any value among -45°C, -44°C, -42°C, -40°C, -38°C, -36°C, -34°C, -32°C, -30°C, -28°C, -26°C, -24°C, -22°C, -20°C, -18°C, -16°C, -14°C, -12°C, -10°C, -8°C, -6°C, -4°C, -2°C, 0°C, 2°C, 4°C, 6°C, 8°C, 10°C, etc., or a range value between any two values, more preferably -30 to 10°C.

[0018] In the present invention, the Tg of the second polymer is too low, which does not significantly improve the bonding performance and air permeability, but will increase the synthesis cost and reduce the production efficiency.

[0019] In the present invention, by forming a structure in which at least part of the second polymer is distributed inside the agglomerated particles, and at the same time selecting the first polymer and the second polymer that meet specific parameters, the diaphragm does not need to be heated to a high temperature, and can be well bonded to the positive and negative electrodes under pressurization conditions at a relatively low temperature (about 25°C), with high adhesion; and the pressure conduction is completed instantly, and the time is short, which effectively improves production efficiency, reduces costs, and improves production safety; in addition, under the condition of no heating and only pressurization, the battery has better bonding consistency from the inside to the outside, improves the interface stability between the battery electrode and the diaphragm, and thus ensures the consistency of battery performance, thereby improving the battery's impedance, liquid absorption and retention, and circulation performance.

[0020] Preferably, the D50 particle size of the second polymer is 200-500 nm, for example, it can be any value among 200 nm, 220 nm, 250 nm, 280 nm, 300 nm, 320 nm, 350 nm, 380 nm, 400 nm, 420 nm, 450 nm, 480 nm, 500 nm, etc., or a range value between any two values.

[0021] Preferably, the second polymer comprises an acrylic polymer.

[0022] In the present invention, the acrylic polymer is a homopolymer and / or copolymer of an acrylic monomer; the present invention does not impose excessive restrictions on its type, as long as its glass transition temperature is within the aforementioned range. Exemplarily, the acrylic monomer includes but is not limited to alkyl (meth)acrylates (the number of carbon atoms of the alkyl group is ≥1, for example, it can be 1, 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, etc.), and at least one H in the alkyl group can be substituted by a hydroxyl group; exemplarily, the alkyl (meth)acrylates include but are not limited to methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, hexyl (meth)acrylate, lauryl (meth)acrylate, hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, etc.

[0023] Preferably, the mass ratio of the first polymer to the second polymer is (9-40):1; wherein the specific value in (9-40) can be, for example, any value of 9, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30, 32, 34, 36, 38, 40, etc., or a range value between any two values.

[0024] Preferably, the area of the coating layer in the diaphragm accounts for 10 to 30% of the area of the substrate, for example, it can be any value among 10%, 12%, 14%, 16%, 18%, 20%, 22%, 24%, 26%, 28%, 30%, etc., or a range value between any two values; more preferably, it is 20 to 25%.

[0025] Preferably, the surface density of the coating layer in the diaphragm is 0.3 to 1.2 g / m 2 , for example, it can be 0.3g / m 2 , 0.4g / m 2 , 0.5g / m 2 , 0.6g / m 2 , 0.7g / m 2 , 0.8g / m 2 , 0.9g / m 2 , 1g / m 2 , 1.1g / m 2 , 1.2g / m 2 Any value or range between any two values; more preferably 0.5 to 0.8 g / m 2 .

[0026] It can be understood that controlling the area ratio and surface density of the membrane coating layer of the present invention within a certain range is beneficial to taking into account better air permeability and adhesion, while reducing production costs and improving production efficiency.

[0027] In a second aspect, the present invention provides a coating slurry comprising agglomerated particles formed by a first polymer and a second polymer and a solvent; the absolute value of the light intensity change rate of the coating slurry after standing at 25° C. for 24 hours is ≤1.8%.

[0028] In the present invention, the absolute value of the light intensity change rate of the coating slurry when it is left at 25°C for 24 hours is ≤1.8%, for example, it can be any value among 0.1%, 0.2%, 0.4%, 0.6%, 0.8%, 1%, 1.2%, 1.4%, 1.5%, 1.6%, 1.8%, etc., or a range value between any two values; preferably, the absolute value of the light intensity change rate of the coating slurry when it is left at 25°C for 24 hours is ≤1.5%.

[0029] In the present invention, the absolute value of the light intensity change rate of the coating slurry after standing at 25°C for 24 hours is ≤1.8%, indicating that the second polymer is at least partially distributed inside the agglomerated particles; when the absolute value of the light intensity change rate of the coating slurry after standing at 25°C for 24 hours is ≤1.5%, it indicates that the second polymer has entered the interior of the agglomerated particles more, causing the absolute value of the light intensity change rate of the entire slurry to decrease; the light intensity change value is obtained by testing using a multiple light scattering instrument (FORMULACTION, France, AGS model).

[0030] Preferably, the first polymer satisfies at least one of the following:

[0031] a) the glass transition temperature of the first polymer is ≤-32°C, for example, it can be any value among -70°C, -68°C, -65°C, -62°C, -60°C, -58°C, -55°C, -52°C, -50°C, -48°C, -46°C, -44°C, -42°C, -40°C, -38°C, -36°C, -34°C, -32°C, etc., or a range between any two values.

[0032] b) the melting point of the first polymer is ≤145°C, for example, it can be any value among 110°C, 112°C, 114°C, 116°C, 118°C, 120°C, 122°C, 124°C, 126°C, 128°C, 130°C, 132°C, 134°C, 136°C, 138°C, 140°C, 142°C, 144°C, 145°C, etc., or a range between any two values.

[0033] c) the softening point of the first polymer is 60-100°C, for example, it can be any value among 60°C, 62°C, 65°C, 68°C, 70°C, 72°C, 75°C, 78°C, 80°C, 82°C, 85°C, 88°C, 90°C, 92°C, 95°C, 98°C, 100°C, etc., or a range value between any two values.

[0034] d) The first polymer comprises a fluorine-containing polymer.

[0035] In the present invention, the D50 particle size of the first polymer is 100 to 500 nm, for example, it can be any value among 100 nm, 150 nm, 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, 450 nm, 500 nm, etc., or a range between any two values.

[0036] Preferably, the second polymer satisfies at least one of the following:

[0037] a) the glass transition temperature of the second polymer is ≤10°C, for example, it can be any value among -45°C, -44°C, -42°C, -40°C, -38°C, -36°C, -34°C, -32°C, -30°C, -28°C, -26°C, -24°C, -22°C, -20°C, -18°C, -16°C, -14°C, -12°C, -10°C, -8°C, -6°C, -4°C, -2°C, 0°C, 2°C, 4°C, 6°C, 8°C, 10°C, etc., or a range between any two values.

[0038] b) The second polymer comprises an acrylic polymer.

[0039] In the present invention, the D50 particle size of the second polymer is 200 to 500 nm, for example, it can be any value among 200 nm, 220 nm, 250 nm, 280 nm, 300 nm, 320 nm, 350 nm, 380 nm, 400 nm, 420 nm, 450 nm, 480 nm, 500 nm, etc., or a range value between any two values.

[0040] Preferably, the mass ratio of the first polymer to the second polymer is (9-40):1, wherein the specific value in (9-40) can be, for example, any value of 9, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30, 32, 34, 36, 38, 40, etc., or a range value between any two values.

[0041] Preferably, the solvent includes at least one of water, acetone, ethanol, and N-methylpyrrolidone.

[0042] Preferably, the coating slurry further comprises 0-10% of an auxiliary agent, for example, it can be any value among 0%, 2%, 4%, 6%, 8%, 10%, etc., or a range value between any two values.

[0043] In the present invention, the auxiliary agent may be added as needed, including but not limited to a wetting and dispersing agent.

[0044] Preferably, the solid content of the coating slurry is 5 to 30%, for example, it can be any value among 5%, 6%, 8%, 10%, 12%, 14%, 16%, 18%, 20%, 22%, 24%, 26%, 28%, 30%, etc., or a range value between any two values.

[0045] In the present invention, the D50 particle size of the coating slurry is 6 to 12 μm, for example, it can be any value among 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm, 9.5 μm, 10 μm, 10.5 μm, 11 μm, 11.5 μm, 12 μm, etc., or a range value between any two values, more preferably 8 to 10 μm.

[0046] In the present invention, the particle size mentioned can be tested using an OMEC TOPSIZER PLUS particle size analyzer.

[0047] In a third aspect, the present invention provides a method for preparing the coating slurry according to the second aspect, the preparation method comprising the following steps:

[0048] The first polymer, the second polymer and the solvent are mixed and ground to obtain the coating slurry.

[0049] Preferably, the mixed material also includes an additive; the mixing speed is 1500-2500 rpm, for example, it can be any value of 1500 rpm, 1600 rpm, 1700 rpm, 1800 rpm, 1900 rpm, 2000 rpm, 2100 rpm, 2200 rpm, 2300 rpm, 2400 rpm, 2500 rpm, etc., or a range value between any two values.

[0050] Preferably, the grinding method includes sand milling, and the sand milling includes a first sand milling and a second sand milling performed sequentially; the rotation speed of the first sand milling is greater than the rotation speed of the second sand milling; and the flow rate of the first sand milling is greater than the flow rate of the second sand milling. It is understood that the rotation speed of the first sand milling can be, for example, 400 to 800 rpm, with a flow rate of 1000 to 1800 L / min, and the rotation speed of the second sand milling can be 100 to 600 rpm, with a flow rate of 500 to 1400 L / min, but the rotation speed of the first sand milling is greater than the rotation speed of the second sand milling; the flow rate of the first sand milling is greater than the flow rate of the second sand milling, so that the structure of the polymer agglomerated particles in the final slurry is controlled, which is manifested as a better light intensity change rate.

[0051] Preferably, the rotation speed of the first sand mill is 500-700 rpm, for example, it can be any value among 500 rpm, 520 rpm, 550 rpm, 580 rpm, 600 rpm, 620 rpm, 650 rpm, 680 rpm, 700 rpm, etc., or a range value between any two values; the flow rate is 1200-1600 L / min, for example, it can be any value among 1200 L / min, 1220 L / min, 1250 L / min, 1280 L / min, 1300 L / min, 1320 L / min, 1350 L / min, 1380 L / min, 1400 L / min, 1420 L / min, 1450 L / min, 1480 L / min, 1500 L / min, 1520 L / min, 1550 L / min, 1580 L / min, 1600 L / min, etc., or a range value between any two values.

[0052] Preferably, the rotation speed of the second sand mill is 250-500 rpm, for example, it can be any value of 250 rpm, 260 rpm, 280 rpm, 300 rpm, 320 rpm, 340 rpm, 360 rpm, 380 rpm, 400 rpm, 420 rpm, 440 rpm, 460 rpm, 480 rpm, etc., or a range between any two values; the flow rate is 800-1200 L / min, for example, it can be 800 L / min, Any value among 820L / min, 850L / min, 880L / min, 900L / min, 920L / min, 950L / min, 980L / min, 1000L / min, 1020L / min, 1050L / min, 1080L / min, 1100L / min, 1120L / min, 1150L / min, 1180L / min, 1200L / min, etc., or the range value between any two values.

[0053] When a first polymer (such as polyvinylidene fluoride) is mixed with a second polymer (such as an acrylic polymer) to prepare a slurry, the first polymer usually agglomerates itself to form a state of agglomerated particles. At this time, the second polymer usually coats the surface of the agglomerated particles and does not enter the interior of the agglomerated particles, resulting in insufficient bonding performance of the obtained material. The present invention adopts a specific sanding process, that is, the agglomerated particles formed by the first polymer are first opened and dispersed under high-speed and high-flow conditions; then, under low-speed and low-flow conditions, the dispersed first polymer is bonded together by the second polymer to complete the coated secondary agglomeration, and agglomerated particles with the second polymer distributed inside are obtained, thereby improving the bonding effect of the diaphragm under pressurized conditions, and can achieve bonding at a lower temperature without the need for hot pressing. Of course, in other possible schemes, other technical means can also be used to control the structure of the agglomerated particles so that the second polymer at least partially enters the interior of the agglomerated particles.

[0054] In a third aspect, the present invention provides a method for preparing a diaphragm, the method comprising the following steps:

[0055] S1: Provide substrate;

[0056] S2: preparing the coating slurry as described in the second aspect and applying it to at least one surface of the substrate;

[0057] S3: drying the coating slurry at a temperature of 50-80° C. to obtain the diaphragm.

[0058] Preferably, the coating speed in step S2 is 100-200 m / min, for example, any value among 100 m / min, 110 m / min, 120 m / min, 130 m / min, 140 m / min, 150 m / min, 160 m / min, 170 m / min, 180 m / min, 190 m / min, 200 m / min, etc., or a range between any two values. It is understood that the coating includes but is not limited to conventional technical means in the art such as roller coating, spray coating, and spot coating.

[0059] It should be noted that the “surface” refers to the two surfaces with the largest area and arranged opposite to each other in a film or layer.

[0060] In a fourth aspect, the present invention provides a battery comprising at least one of the following:

[0061] (1) The diaphragm according to the first aspect;

[0062] (2) The diaphragm prepared by the preparation method described in the third aspect;

[0063] (3) A coating layer made from the coating slurry described in the second aspect.

[0064] The numerical ranges described in the present invention not only include the point values listed above, but also any point values between the above numerical ranges that are not listed. Due to space limitations and for the sake of brevity, the specific point values included in the described ranges are not exhaustively listed in the present invention.

[0065] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0066] The separator provided by the present invention, the coating layer includes agglomerated particles formed by a first polymer and a second polymer, and at least part of the second polymer is distributed inside the agglomerated particles, which can improve the bonding effect of the coating layer; further, in a preferred embodiment, the separator provided by the present invention does not need to be heated to a high temperature, and can be well bonded to the positive and negative electrode sheets only under pressure, with high adhesive force, low production cost, high efficiency and good safety. Specific Embodiments

[0067] The technical solution of the present invention will be further described below through specific embodiments. Those skilled in the art should understand that the described embodiments are only to help understand the present invention and should not be regarded as specific limitations to the present invention.

[0068] The main materials used in the present invention are all developed specifically in cooperation with specific manufacturers. Polyvinylidene fluoride: Customized development by Arkema France. Acrylate polymer: Customized development by Guangzhou Rongdong Chemical Co., Ltd.

[0069] Substrate: Shenzhen Xingyuan Materials Technology Co., Ltd., SA212C, 12μm polypropylene-based film.

[0070] Among them, the test method for the light intensity change rate of the coating slurry is as follows:

[0071] Take 20 ml of the coating slurries of Examples 1 to 15 and Comparative Example 1 respectively, place them in a multiple light scattering instrument (AGS model, manufactured by FORMULACTION France), and measure the average value L0 (parallel test 3 times) of the initial light intensity value (i.e., 0 h) in the middle of the sample bottle and the average value L1 of the light intensity value when placed for 24 h (parallel test 3 times) at room temperature (25°C). The light intensity change rate (L%) of the coating slurry described in the present invention is calculated by the following formula: L% = {(丨L1 - L0丨) / L0} × 100%.

[0072] Example 1

[0073] This example provides a separator, including a substrate and a coating layer provided on one surface of the substrate; the area of the coating layer accounts for 20% of the area of the base film; the surface density of the coating layer is 0.6 g / m 2; The coating layer includes agglomerated particles formed by polyvinylidene fluoride and acrylic polymer; the acrylic polymer is distributed inside and on the surface of the agglomerated particles; the polyvinylidene fluoride has a Tg of -45°C, a T of 140°C, a softening point of 80°C, and a D50 particle size of 200nm; the acrylic polymer has a Tg of -10°C, and a D50 particle size of 350nm; the mass ratio of polyvinylidene fluoride to acrylic polymer is 28:1.

[0074] This embodiment provides a method for preparing a diaphragm, comprising the following steps:

[0075] (1) According to the formula, polyvinylidene fluoride, acrylic polymer, wetting dispersant and deionized water are uniformly mixed at a rotation speed of 1800 rpm; then, the mixture is sand-milled at a rotation speed of 600 rpm and a flow rate of 1400 L / min for 20 min, and then sand-milled at a rotation speed of 400 rpm and a flow rate of 1000 L / min for 20 min to obtain a coating slurry; the mass percentage of the wetting dispersant in the coating slurry is 0.1%; the solid content of the coating slurry is 20%, the D50 particle size is 9.2 μm, and the absolute value of the light intensity change rate after standing at 25°C for 24 hours is 0.73%.

[0076] (2) The coating slurry obtained in step (1) is sprayed onto one surface of the substrate at a speed of 150 m / min, with a coating weight of 0.6 g / m 2 , the coating layer coverage is 20% (by area); and then drying is carried out at 60° C. to obtain the diaphragm.

[0077] Example 2

[0078] This embodiment provides a diaphragm, comprising a substrate and a coating layer disposed on one surface of the substrate; the area of the coating layer accounts for 15% of the area of the base film; the surface density of the coating layer is 0.4 g / m 2 ; The coating layer includes agglomerated particles formed by polyvinylidene fluoride and acrylic polymer; the acrylic polymer is distributed inside and on the surface of the agglomerated particles; the Tg of the polyvinylidene fluoride is -54°C, T is 130°C, the softening point is 60°C, and the D50 particle size is 300nm; the Tg of the acrylic polymer is 5°C, and the D50 particle size is 450nm; the mass ratio of the polyvinylidene fluoride to the acrylic polymer is 10:1.

[0079] This embodiment provides a method for preparing a diaphragm, comprising the following steps:

[0080] (1) According to the formula, polyvinylidene fluoride, acrylic polymer, wetting dispersant and deionized water are uniformly mixed at a rotation speed of 1500 rpm; then, the mixture is sand-milled at a rotation speed of 500 rpm and a flow rate of 1200 L / min for 20 min, and then sand-milled at a rotation speed of 300 rpm and a flow rate of 800 L / min for 20 min to obtain a coating slurry; the mass percentage of the wetting dispersant in the coating slurry is 0.1%; the solid content of the coating slurry is 20%, the D50 particle size is 10 μm, and the absolute value of the light intensity change rate after standing at 25°C for 24 hours is 0.52%.

[0081] (2) The coating slurry obtained in step (1) is applied to one surface of the substrate at a speed of 100 m / min, with a coating weight of 0.4 g / m 2 , the coating layer coverage is 15% (by area); and then drying is carried out at 60° C. to obtain the diaphragm.

[0082] Example 3

[0083] This embodiment provides a diaphragm, comprising a substrate and a coating layer disposed on one surface of the substrate; the area of the coating layer accounts for 25% of the area of the base film; the surface density of the coating layer is 1 g / m 2 ; The coating layer includes agglomerated particles formed by polyvinylidene fluoride and acrylic polymer; the acrylic polymer is distributed inside and on the surface of the agglomerated particles; the polyvinylidene fluoride has a Tg of -38°C, a T of 148°C, a softening point of 96°C, and a D50 particle size of 400nm; the acrylic polymer has a Tg of -28°C, and a D50 particle size of 220nm; the mass ratio of polyvinylidene fluoride to acrylic polymer is 36:1.

[0084] This embodiment provides a method for preparing a diaphragm, comprising the following steps:

[0085] (1) According to the formula, polyvinylidene fluoride, acrylic polymer, wetting dispersant and deionized water are uniformly mixed at a rotation speed of 1800 rpm; then, the mixture is sand-milled at a rotation speed of 700 rpm and a flow rate of 1600 L / min for 20 min, and then sand-milled at a rotation speed of 500 rpm and a flow rate of 1200 L / min for 20 min to obtain a coating slurry; the mass percentage of the wetting dispersant in the coating slurry is 0.1%; the solid content of the coating slurry is 20%, the D50 particle size is 7 μm, and the absolute value of the light intensity change rate after standing at 25°C for 24 hours is 0.81%.

[0086] (2) The coating slurry obtained in step (1) is applied to one surface of the substrate at a speed of 200 m / min, with a coating weight of 1 g / m2 , the coating layer coverage is 25% (based on area); and then drying is carried out at 60° C. to obtain the diaphragm.

[0087] Example 4

[0088] This embodiment provides a diaphragm, which differs from Example 1 only in that the polyvinylidene fluoride has a Tg of -25°C, a T of 160°C, and a softening point of 110°C, and the other components, amounts, and preparation methods are the same as those in Example 1; wherein the obtained coating slurry has a D50 particle size of 9.5 μm, and the absolute value of the light intensity change rate after standing at 25°C for 24 hours is 0.88%.

[0089] Example 5

[0090] This embodiment provides a diaphragm, which differs from Example 1 only in that the polyvinylidene fluoride has a Tg of -65°C, a T of 110°C, and a softening point of 40°C, and the other components, amounts, and preparation methods are the same as those in Example 1; wherein the D50 particle size of the obtained coating slurry is 9.3 μm, and the absolute value of the light intensity change rate after standing at 25°C for 24 hours is 0.75%.

[0091] Example 6

[0092] This embodiment provides a diaphragm, which differs from Example 1 only in that the Tg of the acrylic polymer is -40°C, and the other components, amounts, and preparation methods are the same as those in Example 1; wherein the obtained coating slurry has a D50 particle size of 9.1 μm, and the absolute value of the light intensity change rate after standing at 25°C for 24 hours is 0.72%.

[0093] Example 7

[0094] This embodiment provides a diaphragm, which differs from Example 1 only in that the Tg of the acrylic polymer is 20°C, and the other components, amounts, and preparation methods are the same as those in Example 1; wherein the obtained coating slurry has a D50 particle size of 9 μm, and the absolute value of the light intensity change rate after standing at 25°C for 24 hours is 0.76%.

[0095] Example 8

[0096] This embodiment provides a diaphragm, which differs from Example 1 only in that the D50 particle size of the acrylic polymer is 100 nm, and the other components, amounts, and preparation methods are the same as those in Example 1; wherein the D50 particle size of the obtained coating slurry is 8.9 μm, and the absolute value of the light intensity change rate after standing at 25° C. for 24 hours is 0.79%.

[0097] Example 9

[0098] This embodiment provides a diaphragm, which differs from Example 1 only in that the D50 particle size of the acrylic polymer is 600 nm, and the other components, amounts, and preparation methods are the same as those in Example 1; wherein the D50 particle size of the obtained coating slurry is 9.8 μm, and the absolute value of the light intensity change rate after standing at 25°C for 24 hours is 1.05%.

[0099] Example 10

[0100] This embodiment provides a diaphragm, which differs from Example 1 only in that the total mass of the polyvinylidene fluoride and the acrylic polymer remains unchanged, with a mass ratio of 5:1, and the other components, amounts, and preparation methods are the same as those in Example 1; wherein the D50 particle size of the obtained coating slurry is 9.2 μm, and the absolute value of the light intensity change rate after standing at 25° C. for 24 hours is 0.48%.

[0101] Example 11

[0102] This embodiment provides a diaphragm, which differs from Example 1 only in that the total mass of the polyvinylidene fluoride and the acrylic polymer remains unchanged, with a mass ratio of 45:1, and the other components, amounts, and preparation methods are the same as those in Example 1; wherein the D50 particle size of the obtained coating slurry is 9.3 μm, and the absolute value of the light intensity change rate after standing at 25° C. for 24 hours is 1.02%.

[0103] Example 12

[0104] This embodiment provides a diaphragm, which differs from the embodiment 1 only in that the area of the coating layer accounts for 5% of the area of the substrate, and the surface density of the coating layer is 0.2 g / m 2 , the other components, amounts and preparation methods are the same as those in Example 1; wherein, the D50 particle size of the obtained coating slurry is 8.5 μm, and the absolute value of the light intensity change rate after standing at 25° C. for 24 hours is 0.77%.

[0105] Example 13

[0106] This embodiment provides a diaphragm, which differs from the embodiment 1 only in that the area of the coating layer accounts for 40% of the area of the substrate, and the surface density of the coating layer is 1.4 g / m 2 , the other components, amounts and preparation methods are the same as those in Example 1; wherein, the D50 particle size of the obtained coating slurry is 9.4 μm, and the absolute value of the light intensity change rate after standing at 25° C. for 24 hours is 0.75%.

[0107] Example 14

[0108] This embodiment provides a diaphragm, which differs from Example 1 only in that the first sanding speed in the preparation method is 400 rpm and the flow rate is 1000 L / min, the second sanding speed is 100 rpm and the flow rate is 500 L / min, and the other components, amounts and preparation methods are the same as those in Example 1; wherein the D50 particle size of the obtained coating slurry is 9.6 μm, and the absolute value of the light intensity change rate after standing at 25°C for 24 hours is 1.53%.

[0109] Example 15

[0110] This embodiment provides a diaphragm, which differs from Example 1 only in that the first sanding speed in the preparation method is 800 rpm and the flow rate is 1800 L / min, the second sanding speed is 600 rpm and the flow rate is 1400 L / min, and the other components, amounts and preparation methods are the same as those in Example 1; wherein the D50 particle size of the obtained coating slurry is 9.3 μm, and the absolute value of the light intensity change rate after standing at 25°C for 24 hours is 1.51%.

[0111] Comparative Example 1

[0112] This comparative example provides a diaphragm, which differs from Example 1 only in that the acrylic polymer in the agglomerated particles is coated on the outside of the polyvinylidene fluoride and does not enter the interior of the agglomerated particles; in the preparation method, step (1) does not require sanding and can be directly mixed evenly, and the other components, amounts, and preparation method are the same as those in Example 1; wherein the D50 particle size of the obtained coating slurry is 9 μm, and the absolute value of the light intensity change rate after standing at 25°C for 24 hours is 1.92%.

[0113] Performance Testing

[0114] Adhesion

[0115] The diaphragms provided in Examples 1 to 15 and Comparative Example 1 were cut into 60 mm × 25 mm samples and laminated with negative electrode sheets of the same size (purchased from Guangdong Candlelight New Energy Technology Co., Ltd.). The samples were pressed for 40 s at room temperature of 25°C and 1000 kg, and stretched at 180° and 200 mm / min using a stretching machine (EM6.202 from Shenzhen Tesmel Instruments Co., Ltd.) to test the adhesion between the diaphragm and the negative electrode sheet.

[0116] Increased breathability

[0117] Air permeability was tested on the separators provided in Examples 1-15 and Comparative Example 1, along the TD direction, with the substrate before coating separated by 10 cm. The air permeability at five locations was measured and the average was calculated. The difference between the separator air permeability and the substrate air permeability before coating was recorded as the air permeability increment. Air permeability testing can be conducted in accordance with GB / T36363-2018.

[0118] The specific test results are shown in Table 1.

[0119] Table 1

[0120] Adhesion strength (N / m) Breathability increase(s) Example 1 1.53 13 Example 2 1.66 12 Example 3 1.58 16 Example 4 1.02 14 Example 5 1.56 12 Example 6 1.58 13 Example 7 0.97 12 Example 8 0.88 16 Example 9 0.8 15 Example 10 1.81 21 Example 11 0.83 13 Example 12 0.65 8 Example 13 2.35 25 Example 14 1.01 13 Example 15 1.07 15 Comparative Example 1 0.6 18

[0121] As can be seen from Table 1, the diaphragm provided by the present invention has a coating layer comprising agglomerated particles formed by a first polymer and a second polymer, and at least a portion of the second polymer is distributed inside the agglomerated particles, which can achieve adhesion to the positive and negative electrode sheets at a lower temperature with high bonding strength; the bonding strength of the diaphragm is ≥0.65 N / m, and the air permeability increment is ≤25s.

[0122] The specific embodiments described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above are only specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A diaphragm comprising a substrate and a coating layer disposed on at least one surface of the substrate, characterized in that: The coating layer includes agglomerated particles formed by a first polymer and a second polymer; at least a portion of the second polymer is distributed inside the agglomerated particles.

2. The diaphragm according to claim 1, characterized in that The glass transition temperature of the first polymer is ≤-32°C; Preferably, the first polymer satisfies at least one of the following: a) the melting point of the first polymer is ≤145°C; b) the softening point of the first polymer is 60 to 100° C.; Preferably, the first polymer comprises a fluoropolymer.

3. The diaphragm according to claim 1 or 2, characterized in that The glass transition temperature of the second polymer is ≤10°C; Preferably, the second polymer comprises an acrylic polymer.

4. The diaphragm according to any one of claims 1 to 3, characterized in that The mass ratio of the first polymer to the second polymer is (9-40):1; Preferably, the area of the coating layer in the diaphragm accounts for 10 to 30% of the area of the substrate; Preferably, the surface density of the coating layer in the diaphragm is 0.3 to 1.2 g / m 2 .

5. A coating slurry, characterized in that: The coating slurry includes agglomerated particles formed by a first polymer and a second polymer and a solvent; The absolute value of the light intensity change rate of the coating slurry after being left at 25° C. for 24 hours is ≤1.8%.

6. The coating slurry according to claim 5, characterized in that The first polymer satisfies at least one of the following: a) The glass transition temperature of the first polymer is ≤-32°C b) the melting point of the first polymer is ≤ 145°C; c) the softening point of the first polymer is 60 to 100° C.; d) the first polymer comprises a fluoropolymer; Preferably, the second polymer satisfies at least one of the following: a) the glass transition temperature of the second polymer is ≤10°C; b) the second polymer comprises an acrylic polymer; Preferably, the mass ratio of the first polymer to the second polymer is (9-40):1; Preferably, the solvent comprises at least one of water, acetone, ethanol, and N-methylpyrrolidone; Preferably, the coating slurry further comprises 0-10% of an auxiliary agent; Preferably, the solid content of the coating slurry is 5-30%.

7. A method for preparing the coating slurry according to claim 5 or 6, characterized in that: The preparation method comprises the following steps: The first polymer, the second polymer and the solvent are mixed and ground to obtain the coating slurry.

8. The preparation method according to claim 7, characterized in that The mixed materials also include additives; the mixing speed is 1500-2500 rpm; Preferably, the grinding method includes sanding, and the sanding includes a first sanding and a second sanding performed sequentially; the rotation speed of the first sanding is greater than the rotation speed of the second sanding; the flow rate of the first sanding is greater than the flow rate of the second sanding; Preferably, the rotation speed of the first sand mill is 500-700 rpm and the flow rate is 1200-1600 L / min; Preferably, the rotation speed of the second sand mill is 250-500 rpm, and the flow rate is 800-1200 L / min.

9. A method for preparing a diaphragm, characterized in that: The preparation method comprises the following steps: S1: Provide substrate; S2: preparing the coating slurry according to claim 5 or 6 and applying it to at least one surface of the substrate; S3: drying the coating slurry at a temperature of 50 to 80° C. to obtain the diaphragm; Preferably, the coating speed in step S2 is 100-200 m / min.

10. A battery, characterized in that: The battery includes at least one of the following: (1) The diaphragm according to any one of claims 1 to 4; (2) The diaphragm prepared by the preparation method according to claim 9; (3) A coating layer made from the coating slurry according to claim 5 or 6.