Binder slurry and preparation method thereof, coating diaphragm and preparation method thereof

Abstract

The invention provides binder slurry and a preparation method thereof, and a coating diaphragm and a preparation method thereof, and relates to the technical field of battery diaphragms. The binder slurry comprises a binder, a mixed solvent, a polymeric dispersant, EB curable resin and a defoaming agent. A unique binder slurry is prepared, a specially designed plate roller is coated on the surface of the diaphragm in a regular point coating or line coating manner, EB curing is carried out after drying, curing resin and active monomers in a coating are subjected to a cross-linking curing reaction, binder particles are firmly attached to the surface of the diaphragm, and the coating is good in adhesive force. The size, shape and number of coating spots / lines are controllable through the design of the plate roller, the coating coverage rate and the coating gram weight can be freely adjusted, the coating spots / lines have the regular and ordered characteristics, the thickness uniformity, the ventilation uniformity, the hot-pressing bonding force and the uniformity of the coating are remarkably improved, and the coating quality is improved. The problems that the spraying thickness of a traditional rotating disc type spraying device is not uniform, the bonding force fluctuates, and holes are blocked are solved.

Description

Technical Field

[0001] The present invention relates to the technical field of battery separators, and particularly relates to an adhesive slurry, a preparation method thereof, a coated separator, and a preparation method thereof. Background Art

[0002] Lithium-ion batteries have been recognized by the application market and developed rapidly due to their high energy density, long cycle life, low self-discharge, good safety performance, and fast charge and discharge rate. Conventional wet-process PE separators and dry-process PP separators have been mass-produced and marketed, and are currently the most mature and cost-effective separator products for lithium-ion batteries. However, as the market's requirements for the performance of lithium-ion batteries, such as capacity, energy density, cycle life, and fast charge and discharge, are getting higher and higher, both pure PE or PP separators have certain performance limitations and can no longer meet the application requirements.

[0003] Currently, in the fields of power and energy storage, the application proportion of high-capacity square large aluminum shell and large soft-pack batteries is very high. For these two types of lithium batteries in mid- to high-end application scenarios, the separator is required to have an adhesive function. Generally, a polyvinylidene fluoride (PVDF) or acrylic coating is applied on one or both sides of the separator to endow the separator with an adhesive functional layer.

[0004] When applying a PVDF or acrylic material coating on the surface of the separator, spraying is generally used. Spraying generally uses a rotary disk spraying device. After the slurry passes through a flow meter and is pumped into the center of a high-speed rotating disk, extremely fine atomized substances are ejected under the action of centrifugal force and land on the surface of the separator to complete the coating process. It can be seen that this method is spot coating, and the coating is random. The size, shape, and quantity of the coating points are uncertain, which can be considered an uncontrollable coating method. The microscopic non-uniform combination forms a relatively uniform macroscopic coating surface. Such a sprayed separator product inevitably has problems such as uneven thickness, fluctuating adhesion force, and blocked pores in battery applications, which are pain points in the application and urgently need to be solved. Summary of the Invention

[0005] In view of this, the purpose of the present invention is to provide an adhesive slurry, a preparation method thereof, a coated separator, and a preparation method thereof. The coated separator prepared by the present invention has uniform thickness and air permeability, stable adhesion force when applied to lithium-ion batteries, and good consistency in battery electrical performance.

[0006] In order to achieve the above-mentioned invention purpose, the present invention provides the following technical solutions:

[0007] The present invention provides an adhesive slurry, which includes an adhesive, a mixed solvent, a polymer dispersant, an EB-curable resin, and an antifoaming agent; the adhesive is one or more of polyvinylidene fluoride, modified polyvinylidene fluoride, polymethyl methacrylate, and its derivatives; the adhesive exists in the form of an aggregate with a multi-porous and loose structure;

[0008] The mass ratio of the binder to the mixed solvent is 1:4 to 24;

[0009] The mixed solvent includes an inactive monomer and an active monomer; the active monomer contains an unsaturated double bond; the inactive monomer is water and / or alcohol;

[0010] The mass of the polymer dispersant is 0.5 to 15% of the mass of the binder;

[0011] The mass of the EB-curable resin is 1 to 10% of the mass of the binder;

[0012] The mass of the defoamer is 0.01 to 1.0% of the total mass of the binder slurry.

[0013] Preferably, the mass content of the active monomer in the mixed solvent is 5 to 20%.

[0014] Preferably, the polymer dispersant includes one or more of ammonium polyacrylate, sodium polyacrylate, and block-type polymer dispersants.

[0015] Preferably, the EB-curable resin includes unsaturated resin, prepolymer, or oligomer.

[0016] The present invention provides a method for preparing the binder slurry described in the above solution, including the following steps:

[0017] Mix the binder powder, the mixed solvent, and the polymer dispersant, and disperse under the conditions of self-rotation and revolution. The binder powder forms aggregates to obtain a dispersion;

[0018] Mix the dispersion, the EB-curable resin, and the defoamer to obtain the binder slurry.

[0019] Preferably, the rotation speed of the self-rotation is 800 to 1500 rpm; the rotation speed of the revolution is 20 to 50 rpm.

[0020] The present invention provides a method for preparing a coated separator, including the following steps: Place the binder slurry in an anilox roll and roll-coat it on the surface of the battery separator. After drying the formed wet coating, perform EB curing to obtain the coated separator; The surface of the anilox roll is provided with engraved holes and / or engraved lines;

[0021] The binder slurry is the binder slurry described in the above solution or the binder slurry prepared by the preparation method described in the above solution.

[0022] Preferably, the sizes of the engraved holes and engraved lines are 1.2 to 1.8 times the target sizes of the roll-coated spots and lines.

[0023] The present invention provides a coated separator prepared by the preparation method described in the above solution, which includes a battery separator and an adhesive coating applied on the surface of the battery separator; the adhesive coating is distributed in dots and / or lines; the thickness deviation of the adhesive coating is ±0.5 μm.

[0024] Preferably, the thickness of the adhesive coating is 1-5 μm, the coating coverage rate is 5-50%, and the grammage is 0.2-0.8 g / m 2 .

[0025] The present invention provides an adhesive slurry, which includes an adhesive, a mixed solvent, a polymer dispersant, an EB-curable resin, and an antifoaming agent; the adhesive is one or more of polyvinylidene fluoride, modified polyvinylidene fluoride, polymethyl methacrylate, and its derivatives; the adhesive exists in the form of aggregates with a porous and loose structure; the mass ratio of the adhesive to the mixed solvent is 1:4-24; the mixed solvent includes water, alcohol, and an active monomer; the active monomer contains an unsaturated double bond; the mass of the polymer dispersant is 0.5-15% of the mass of the adhesive; the mass of the EB-curable resin is 1-10% of the mass of the adhesive; the mass of the antifoaming agent is 0.01-1.0% of the total mass of the adhesive slurry.

[0026] In the adhesive slurry provided by the present invention, the adhesive exists in the form of aggregates, showing a porous and loose structure, which can form a network structure to maintain the stability of the adhesive particles and ensure the uniformity and consistency of the adhesive coating spots / line patterns; by using an EB-curable resin and an active monomer, after EB curing, a cross-linking curing reaction occurs, firmly attaching the adhesive particles to the surface of the separator. The coating has good adhesion and excellent chemical resistance, can play a better pole piece bonding function, and helps to improve the interface, cycle performance, and electrical performance of lithium / sodium batteries.

[0027] The present invention provides a preparation method of a coated separator. By using a gravure roll with engraved holes and / or engraved lines for roll coating, the size, shape, and quantity of the coating spots / line patterns are controllable, the coating coverage rate and coating grammage can be adjusted, and a regular coating structure is formed. The coating spots / line patterns have regular and orderly characteristics, realizing the uniformity of coating at the microscopic level, and ensuring high consistency of the product in battery applications (stable and uniform adhesion, uniform thickness, uniform air permeability, and good consistency of battery electrical performance).

[0028] The results of the examples show that the thickness deviation of the coated separator prepared by the present invention is ±0.5 μm, the air permeability deviation is ±10 s / 100 ml. When the coated separator is applied to a battery, the hot press adhesion force ≥ 3 N / m, and the deviation is ±1 N / m. Description of the Drawings

[0029] Figure 1 It is a schematic structural diagram of a gravure roll with engraved holes.

[0030] Figure 2 Schematic diagram of the roller coating effect of a plate roller with engraved holes;

[0031] Figure 3 SEM image of the binder slurry in Example 1. Detailed implementation manners

[0032] The present invention provides a binder slurry, which includes a binder, a mixed solvent, a polymer dispersant, an EB-curable resin, and an antifoaming agent; the binder is one or more of polyvinylidene fluoride, modified polyvinylidene fluoride, polymethyl methacrylate, and its derivatives; the binder exists in the form of aggregates with a multi-porous and loose structure;

[0033] The mass ratio of the binder to the mixed solvent is 1:4 to 24;

[0034] The mixed solvent includes an inactive monomer and an active monomer; the active monomer contains an unsaturated double bond; the inactive monomer is water and / or alcohol;

[0035] The mass of the polymer dispersant is 0.5 to 15% of the mass of the binder;

[0036] The mass of the EB-curable resin is 1 to 10% of the mass of the binder;

[0037] The mass of the antifoaming agent is 0.01 to 1.0% of the total mass of the binder slurry.

[0038] The binder slurry provided by the present invention comprises a binder. In the present invention, the binder is one or more of polyvinylidene fluoride, modified polyvinylidene fluoride, polymethyl methacrylate and its derivatives; in the present invention, the derivative of the modified polyvinylidene fluoride may be a polyvinylidene fluoride - hexafluoropropylene copolymer, and the derivative of the polymethyl acrylate may be a styrene - isooctyl acrylate - methyl methacrylate terpolymer; in the present invention, the binder is a commercially available product well - known in the art. The binder exists in the form of aggregates with a multi - porous and loose structure; specifically, it is formed by the aggregation of countless small particles, having a multi - porous and loose structure, and the dispersant is dispersed inside and outside the aggregates, forming a network structure to maintain the stability of the spherical particles. In the present invention, the aggregates may be spherical, ellipsoidal, disc - shaped or spheroid - like with angular surfaces, and the present invention does not make special limitations on this. In the present invention, the particle size of the aggregates is preferably 1 - 20 μm, and the median particle size is preferably 3 - 8 μm. In specific embodiments, the median particle size of the aggregates may be 3 μm, 4 μm, 5 μm, 6 μm, 7 μm or 8 μm. The binder exists in the form of aggregates with a multi - porous and loose structure, which can increase the porosity of the coating, facilitate the passage of lithium ions, reduce the internal resistance of the battery and improve the consistency of the battery capacity. The present invention selects one or more of PVDF, modified polyvinylidene fluoride, PMMA and its derivatives as the binder and applies it to lithium / sodium batteries. After the battery hot - pressing process, PVDF, modified PVDF and PMMA and their derivatives can play a binding role, firmly binding the separator and the electrode sheet together, thereby improving the battery interface, the battery cycle life and the electrical performance.

[0039] The binder slurry provided by the present invention comprises a mixed solvent; the mixed solvent comprises an inactive monomer and an active monomer; the active monomer contains an unsaturated double bond. In the present invention, the active monomer is preferably one or more of styrene, vinylbenzene, butadiene, acrylonitrile, acrylamide and acrylic acid - type active monomers; the acrylic acid - type active monomers are preferably one or more of acrylic acid, methacrylic acid, methyl methacrylate, ethyl methacrylate, ethyl acrylate, butyl acrylate, dimethylaminoethyl acrylate, dimethylaminohexyl acrylate, glycidyl methacrylate and hydroxyethyl acrylate. In the present invention, the mass content of the active monomer in the mixed solvent is preferably 5 - 20%, and in specific embodiments, it may be 5%, 10%, 15% or 20%.

[0040] In the present invention, the inactive monomer is water and / or alcohol, more preferably water and alcohol; the alcohol is preferably one or more of methanol, ethanol, isopropanol and butanol. In the present invention, when the inactive monomer is water and alcohol, the present invention has no special requirements for the ratio between the two, and any ratio is acceptable.

[0041] The present invention uses a mixed solvent. Among them, the role of the active monomer is to undergo a cross-linking reaction after EB curing to improve the adhesion of the binder particles to the surface of the battery separator; the role of water and / or alcohol is, firstly, to serve as a dispersion medium during the dispersion stage of the binder; secondly, it can serve as a pore-forming agent. After the slurry is coated on the surface of the separator and dried, pores can be left after the water and alcohol volatilize, increasing the porosity of the coating and improving the air permeability of the coating.

[0042] In the present invention, the mass ratio of the binder to the mixed solvent is preferably 1:4 to 24, and in specific embodiments, it can be 1:4, 1:7, 1:10, 1:15, 1:20 or 1:24.

[0043] The binder slurry provided by the present invention includes a polymer dispersant; the polymer dispersant preferably includes one or more of ammonium polyacrylate, sodium polyacrylate and block copolymer polymer dispersants, and more preferably a block copolymer polymer dispersant. In the present invention, the block copolymer polymer dispersant preferably includes one or more of ammonium polyacrylate, sodium polyacrylate, acrylic acid-acrylate copolymer and acrylonitrile-acrylate copolymer. The present invention uses a polymer dispersant to uniformly disperse the binder.

[0044] In the present invention, the mass of the polymer dispersant (referring to the solid of the polymer dispersant) is 0.5 to 15% of the mass of the binder, and in specific embodiments, it can be 0.5%, 2%, 5%, 8%, 10%, 12% or 15%.

[0045] The binder slurry provided by the present invention includes an EB-curable resin (i.e., an electronically curable resin); the EB-curable resin preferably includes an unsaturated resin, a prepolymer or an oligomer; specifically, the EB-curable resin can be a combination of one or several of epoxy acrylate resin, unsaturated polyester, acrylic polyester, acrylic resin, polyurethane acrylate, and acrylated polyurethane. In the present invention, the mass of the EB-curable resin is 1 to 10% of the mass of the binder, and in specific embodiments, it can be 1%, 3%, 5%, 7%, 8% or 10%. In the present invention, the EB-curable resin will cross-link after EB curing to improve the adhesion of the binder to the surface of the battery separator.

[0046] The binder slurry provided by the present invention includes an antifoaming agent; the antifoaming agent is preferably a silicone antifoaming agent, a polyether-type antifoaming agent or a polyether-modified silicone-type antifoaming agent. In a specific embodiment, the silicone antifoaming agent can be Dow Corning AFE-1410, the polyether-type antifoaming agent can be Dow DF104, and the polyether-modified silicone-type antifoaming agent can be DF-410. In the present invention, the mass of the antifoaming agent is preferably 0.01-1.0% of the total mass of the binder slurry, and in specific embodiments, it can be 0.01%, 0.1%, 0.3%, 0.5%, 0.7%, 0.8% or 1.0%. In the present invention, the role of the antifoaming agent is to reduce the surface tension of the slurry and prevent foam formation.

[0047] The present invention provides a method for preparing the binder slurry described in the above solution, including the following steps:

[0048] Mix the binder powder, the mixed solvent and the polymer dispersant, and disperse under the conditions of self-rotation and revolution. The binder powder forms aggregates to obtain a dispersion;

[0049] Mix the dispersion, the EB-curable resin and the antifoaming agent to obtain the binder slurry.

[0050] In the present invention, unless otherwise specified, the raw materials used are all well-known commercially available products in the art.

[0051] The present invention mixes the binder powder, the mixed solvent and the polymer dispersant, and disperses under the conditions of self-rotation and revolution. The binder powder forms aggregates to obtain a dispersion.

[0052] In the present invention, when the binder is PVDF and / or modified PVDF, the particle size of the binder powder is preferably 100-300 nm. When the binder is PMMA and its derivatives, the particle size of the binder powder is preferably 300-600 nm. In the present invention, the mixing of the binder powder, the mixed solvent and the polymer dispersant preferably includes: first, perform intermediate mixing of the binder powder and the mixed solvent, and then add the polymer dispersant to the obtained mixed system. The present invention has no special requirements for the process of the intermediate mixing, and it is only necessary to mix the binder powder and the mixed solvent evenly. In a specific embodiment, uniform mixing is achieved by mechanical stirring.

[0053] In the present invention, the polymer dispersant is preferably used in the form of a polymer dispersant solution, and the solid content of the polymer dispersant solution is preferably 10-40%. In specific embodiments, it can be 10%, 20%, 30% or 40%. In the present invention, the commercially purchased polymer dispersant is generally in the form of a polymer dispersant solution, or a solid polymer dispersant can also be purchased and a polymer dispersant solution is prepared with water or a water-alcohol mixture.

[0054] In the present invention, the rotation speed of the self-rotation is preferably 800 - 1500 rpm, and in specific embodiments, it can be 800 rpm, 1000 rpm, 1200 rpm or 1500 rpm; the revolution speed is preferably 20 - 50 rpm, and in specific embodiments, it can be 20 rpm, 30 rpm, 40 rpm or 50 rpm; the time of the self-rotation and revolution (i.e., the dispersion time) is preferably 0.5 - 2 h, and in specific embodiments, it can be 0.5 h, 1 h, 1.5 h or 2 h. The present invention uses a combination of high-speed self-rotation and low-speed revolution for dispersion, promoting the formation of an aggregate with a porous and loose structure of the binder powder.

[0055] After the self-rotation and revolution are completed, the present invention preferably cools and stands at room temperature to obtain a dispersion liquid.

[0056] After obtaining the dispersion liquid, the present invention mixes the dispersion liquid, the EB-curable resin and the defoaming agent to obtain the binder slurry.

[0057] The present invention has no special requirements for the mixing process, and it is only necessary to mix each component evenly. In the embodiment, specifically, it is stirred at a rotation speed of 800 - 1000 rpm for 0.5 - 2 h.

[0058] The present invention provides a method for preparing a coated separator, comprising the following steps: placing the above-mentioned binder slurry in a plate roll and performing roll coating on the surface of the battery separator, drying the formed wet coating and then performing EB curing to obtain the coated separator; the surface of the plate roll is provided with engraved holes and / or engraved lines.

[0059] In the present invention, the engraved holes are preferably discontinuous points; the engraved holes can be circular, elliptical or square, and the present invention has no special requirements for this; the engraved lines can be square or strip-shaped, and the present invention is not specifically limited. In the present invention, the plate roll preferably includes a sealing structure, and the binder slurry can only relieve pressure through the holes and / or lines. The binder slurry and the dried compressed air respectively enter the cavity of the plate roll through sealed pipelines (as shown in Figure 1 ), and the roll coating process can realize the transfer matching of the slurry with the production speed by adjusting the internal pressure of the plate roll and the slurry supply amount, ensuring the uniform transfer of the coated slurry; the outer surface of the plate roll and the separator complete the transfer through physical contact (the effect after transfer is as shown in Figure 2 ).

[0060] In the present invention, the sizes of the engraved holes and engraved lines are preferably 1.2 to 1.8 times the target sizes of the roll-coated spots and line patterns. For example, when it is desired to coat spots with a diameter of 1 mm, the size of the engraved holes should be designed to be 1.2 to 1.8 mm. Due to the transfer ratio, the actual coated size is smaller than the designed size. On the other hand, designing the sizes of the engraved holes and engraved lines to be 1.2 to 1.8 times the target sizes of the roll-coated spots and line patterns can prevent the engraving roll from being blocked.

[0061] The present invention does not make any special limitation on the arrangement of the engraved holes and / or engraved lines in the engraving roll, and can be set according to actual needs.

[0062] In the present invention, roll coating is carried out by using an engraving roll provided with engraved holes and / or engraved lines. The size, shape and quantity of the coated spots / lines can be controlled, the coating coverage rate and coating grammage can be adjusted, a regular coating structure is formed, and the coated spots / lines have regular and orderly characteristics, realizing the uniformity of coating microscopically. The coating process can achieve the transfer matching of the slurry with the production speed by adjusting the internal pressure of the engraving roll and the slurry supply amount. Therefore, the coating thickness can be regulated by controlling the feeding flow rate. In addition, the coating thickness can also be regulated by controlling the solid content of the binder slurry.

[0063] In the present invention, the battery separator preferably comprises a wet-process PE separator or a dry-process PP separator.

[0064] In the present invention, the drying is preferably carried out by infrared drying and hot air drying simultaneously. In the present invention, the power of the infrared drying is preferably 100 to 150 W, and can be 100 W, 120 W, 130 W or 150 W in specific embodiments; the distance between the infrared tube and the film surface is preferably 120 to 140 mm, and can be 120 mm, 130 mm or 140 mm in specific embodiments. In the present invention, the temperature of the hot air used for hot air drying is preferably 50 to 60 °C, and can be 50 °C, 55 °C or 60 °C in specific embodiments. The infrared drying transfers heat to the coating and the separator by means of thermal radiation, and has high drying efficiency; the hot air can discharge the evaporated solvents (alcohols and water), reduce the solvent vapor pressure, and improve the drying efficiency. The present invention does not make any special limitation on the drying time, and the coating can be completely dried.

[0065] After the drying is completed, the present invention preferably cools to 20 to 50 °C, and then EB curing is carried out.

[0066] In the present invention, the electron energy of the EB curing is preferably 80 - 300 keV, and in specific embodiments, it can be 80 keV, 100 keV, 150 keV, 200 keV, 250 keV or 300 keV; the time of the EB curing is preferably 0.01 - 0.1 s, and in specific embodiments, it can be 0.01 s, 0.05 s or 0.1 s. In the present invention, the EB curing is preferably carried out under the conditions of nitrogen gas passing and positive pressure. During the EB curing process of the present invention, the EB curable resin and the reactive monomer can undergo a cross-linking curing reaction, firmly attaching the PVDF / PMMA particles to the surface of the separator, with good coating adhesion and good chemical resistance.

[0067] The present invention provides a coated separator prepared by the preparation method described in the above solution, including a battery separator and an adhesive coating coated on the surface of the battery separator; the adhesive coating is distributed in dots and / or lines; the thickness deviation of the adhesive coating is ±0.5 μm.

[0068] In the present invention, the air permeability deviation of the coated separator is preferably ±10 s / 100 ml; when the coated separator is applied to a battery, the hot pressing adhesion force is preferably ≥3 N / m, and the deviation is ±1 N / m.

[0069] In the present invention, the thickness of the adhesive coating is preferably 1 - 5 μm, and in specific embodiments, it can be 1 μm, 2 μm, 3 μm, 4 μm or 5 μm; the coating coverage rate is preferably 5 - 50%, and in specific embodiments, it can be 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45% or 50%; the grammage is preferably 0.2 - 0.8 g / m 2 and in specific embodiments, it can be 0.2 g / m 2 、0.3 g / m 2 、0.4 g / m 2 、0.5 g / m 2 、0.6 g / m 2 、0.7 g / m 2 or 0.8 g / m 2 。In the present invention, when the adhesive coating is distributed in dots, the spot size is preferably 0.1 - 1.0 mm; when the adhesive coating is distributed in lines, the line width is preferably 0.1 - 1.0 mm.

[0070] The following will combine examples to detail the adhesive slurry provided by the present invention, its preparation method, the coated separator and its preparation method, but they cannot be understood as limiting the protection scope of the present invention.

[0071] Example 1

[0072] ① Preparation of the dispersion: 10 parts of polyvinylidene fluoride - hexafluoropropylene copolymer powder (particle size 100 - 300 nm, grade LBG, manufacturer ARKEMA) were added to a mixed solvent composed of 20 parts of ethanol, 60 parts of water, and 12 parts of acrylic acid, and mechanically stirred at 800 rpm for 0.5 h; then 2.5 parts of an acrylate - acrylate copolymer solution dispersant with a solid content of 20% was added, and dispersion was carried out for 1 h under the condition of a combination of high - speed self - rotation and low - speed revolution, with high - speed self - rotation at 1000 rpm and low - speed revolution at 30 rpm, followed by cooling and standing to obtain the dispersion.

[0073] ② Preparation of the slurry: 0.8 part of acrylic curing resin and 0.2 part of Dow Corning AFE - 1410 defoamer were added to the above - mentioned dispersion, and mechanically stirred at 800 rpm for 1.0 h, followed by cooling and standing to obtain a binder slurry with a solid content of 24%. Figure 3 Figure 5 is the scanning electron micrograph of the binder slurry for Example 1, and it can be seen that the binder exists in the form of aggregates with a porous and loose structure.

[0074] ③ Coating of the slurry: The above - mentioned binder slurry was coated on one side of the separator in a regular dot - coating manner through a specially designed plate roller at a coating speed of 100 m / min, and then entered an oven for infrared and hot - air drying. The hot - air temperature was selected as 55 °C, the power of the infrared heat source was selected as 130 W, the distance between the infrared tube and the membrane surface was 130 mm, and at this time the membrane surface temperature reached about 75 °C to remove water and ethanol solvents; after drying and cooling to 30 °C, it entered an EB curing device, the EB energy was selected as 100 keV, and the curing time was 0.05 s. The curing resin and active monomers in the coating underwent a cross - linking curing reaction to obtain a coated separator.

[0075] The separator is a uniaxially stretched PP material (dry - process PP separator) with a thickness of 12 μm, a porosity of 40%, the thickness of the coating is 3 ± 0.3 μm, the air - permeability deviation is ±8 s / 100 ml, the spot diameter is 0.2 - 0.5 mm, the coating coverage rate is 15%, and when the coated separator is applied to a battery, the hot - pressing adhesion force is 4.6 N / m, with a deviation of ±0.5 N / m.

[0076] Example 2

[0077] ① Preparation of the dispersion: 25 parts of PMMA powder (particle size 300 - 600 nm) were added to a mixed solvent composed of 50 parts of isopropanol, 150 parts of water, and 50 parts of acrylonitrile, and mechanically stirred at 600 rpm for 1.0 h; then 37.5 parts of an acrylonitrile - acrylate copolymer solution dispersant with a solid content of 10% was added, and dispersion was carried out for 1.5 h under the condition of a combination of high - speed self - rotation and low - speed revolution, with high - speed self - rotation at 1500 rpm and low - speed revolution at 50 rpm, followed by cooling and standing to obtain the dispersion.

[0078] ② Preparation of the slurry: Add 2.5 parts of polyurethane acrylate and 3.2 parts of polyether-modified silicone type DF104 defoamer to the above-mentioned dispersion liquid, and mechanically stir at 1000 rpm for 1.2 h to obtain a binder slurry with a solid content of about 36%.

[0079] ③ Coating of the slurry: Coat the above-mentioned binder slurry on one side of the separator in a regular dot coating manner through a specially designed plate roller. The coating speed is 100 m / min, and then it enters the oven for infrared and hot air drying. The hot air temperature is selected as 60 °C, and the infrared heat source power is selected as 150 W (the infrared tube is 140 mm away from the film surface). At this time, the film surface temperature reaches about 80 °C to remove water and isopropyl alcohol solvents. After drying and cooling to 50 °C, it enters the EB curing device. The EB energy is selected as 300 keV, and the curing time is 0.1 s. The cured resin and active monomer in the coating undergo a cross-linking curing reaction to obtain a coated separator.

[0080] The separator is a unidirectionally stretched PP material (dry-process PP separator), with a thickness of 16 μm, a porosity of 35%, a coating thickness of 4 ± 0.5 μm, an air permeability deviation of ±10 s / 100 ml, a spot diameter of 0.6 - 0.8 mm, a coating coverage rate of 50%, and when the coated separator is applied to the battery, the hot pressing adhesion force is 6.0 N / m, with a deviation of ±0.5 N / m.

[0081] Example 3

[0082] ① Preparation of the dispersion liquid: Add 50 parts of PVDF powder (particle size 100 - 300 nm) to a mixed solvent composed of 560 parts of butanol, 580 parts of water, and 60 parts of acrylamide, and mechanically stir at a mechanical speed of 500 rpm for 0.5 h; then add 1.25 parts of an ammonium polyacrylate solution dispersant with a solid content of 40%, and disperse for 0.8 h under the condition of a combination of high-speed self-rotation and low-speed revolution. The high-speed self-rotation speed is 800 rpm, and the low-speed revolution speed is 20 rpm. Cool and let stand to obtain the dispersion liquid.

[0083] ② Preparation of the slurry: Add 0.5 parts of acrylic polyester and 0.125 parts of polyether-modified silicone type DF-410 defoamer to the above-mentioned dispersion liquid, and mechanically stir at a mechanical speed of 800 rpm for 0.5 h. Cool and let stand to obtain a binder slurry with a solid content of 9%.

[0084] ③ Coating of the slurry: The above-mentioned binder slurry is coated on one side of the separator in a regular line coating manner through a specially designed plate roller at a coating speed of 100 m / min, and then enters the oven for drying by infrared and hot air. The hot air temperature is selected as 50 °C, and the infrared heat source power is selected as 100 W (the distance between the infrared tube and the membrane surface is 120 mm). At this time, the membrane surface temperature reaches about 70 °C to remove water and butanol solvents; after drying and cooling to 20 °C, it enters the EB curing device. The EB energy is selected as 80 keV, and the curing time is 0.01 s. The cured resin and active monomer in the coating undergo a cross-linking curing reaction, thereby obtaining a coated separator.

[0085] The separator is a unidirectionally stretched PP material (dry-process PP separator), with a thickness of 14 μm, a porosity of 45%, a coating thickness of 2 ± 0.2 μm, an air permeability deviation of ±6 s / 100 ml, a line width of 0.8 - 1.0 mm, a coating coverage rate of 5%, and when the coated separator is applied to a battery, the hot pressing adhesion force is 3.2 N / m, with a deviation of ±1 N / m.

[0086] Comparative Example 1

[0087] The difference between Comparative Example 1 and Example 1 is that: in step ①, water is used instead of the active monomer to prepare the dispersion liquid, and the other components and preparation methods are the same as those in Example 1.

[0088] Comparative Example 2

[0089] The difference between Comparative Example 2 and Example 1 is that: in step ①, the block copolymer dispersant is not added when preparing the dispersion liquid, and the other components and preparation methods are the same as those in Example 1.

[0090] Comparative Example 3

[0091] The difference between Comparative Example 3 and Example 1 is that: in step ②, the cured resin is not added, and the other components and preparation methods are the same as those in Example 1.

[0092] Comparative Example 4

[0093] The difference between Comparative Example 4 and Example 1 is that: in step ③, the coating is carried out by the ordinary rotary spraying method, and the other components and preparation methods are the same as those in Example 1.

[0094] Comparative Example 5

[0095] The difference between Comparative Example 5 and Example 1 is that: in step ③, the EB curing process is omitted, and the other components and preparation methods are the same as those in Example 1.

[0096] Comparative Example 6

[0097] Using the dry-process PP substrate of Example 1 without any coating processing, the substrate thickness is 12 μ, and the porosity is 40%.

[0098] Performance Test

[0099] The six groups of lithium battery diaphragms in the above 3 examples and 6 comparative examples were made into square aluminum shell lithium iron phosphate batteries with a rated capacity of 280 Ah, a positive electrode of LiFePO4, and a negative electrode of graphite; electrolyte: EC / EMC (ethylene carbonate / ethyl methyl carbonate) = 3 / 7 (v / v), 1 M LiPF6, 2% VC (vinylene carbonate);

[0100] Measure the thickness, air permeability value and deviation, spot diameter, coating coverage rate, hot pressing adhesion force and deviation and other properties of the lithium-ion battery diaphragms in Examples 1 to 3 and the diaphragms in Comparative Examples 1 to 6. After making the diaphragms into batteries, measure the battery resistance, short-circuit rate, interface bonding and fitting effect, and capacity consistency of the batteries; among them, the air permeability value is measured by a Wang Yan type air permeability tester along the TD (transverse) direction at a certain interval, and then calculate the air permeability deviation = maximum air permeability value - minimum value; the test method for hot pressing adhesion force: use a hot press and a tensile machine to hot press the coated surface of the diaphragm with the positive electrode sheet (hot pressing process: temperature 100 °C, pressure 2 MPa, hot pressing time 60 s), and then test the 180° peel strength with a tensile speed of 100 mm / min. The test results are shown in Table 1.

[0101] Table 1 Test results of various properties of diaphragms and batteries prepared in examples and comparative examples

[0102]

[0103] As can be seen from Table 1, Example 1 manufactures a coated diaphragm with the best comprehensive physical and chemical properties through an optimal formula combination and process: moderate coating thickness, small thickness deviation, small air permeability value deviation, spot diameter, moderate coating coverage rate, high hot pressing adhesion force and small deviation; the battery prepared from the functional coating dry-process PP diaphragm manufactured in Example 1 has the best comprehensive battery performance: small battery internal resistance, low short-circuit rate, good interface bonding and fitting effect, and good capacity consistency.

[0104] In Example 2, as the coating thickness increases to 4 μm, the thickness deviation becomes larger, the air permeability value increases, there is slight pore blockage, the air permeability value deviation becomes larger, the spot diameter and coating coverage rate are moderately above the upper limit, the hot pressing adhesion force is good and the deviation is small. The internal resistance and short-circuit rate of the battery manufactured from the diaphragm in Example 2 increase slightly, the interface bonding and fitting effect is good but the capacity consistency becomes slightly worse, and it is not preferred;

[0105] In Example 3, as the coating thickness is thinned to 2 μm, the thickness deviation becomes smaller, the air permeability value increment becomes smaller, and the air permeability value deviation also becomes smaller, but the coating coverage rate is on the small side, resulting in a decrease in the hot pressing adhesion force and a larger deviation. The internal resistance and short-circuit rate of the battery manufactured from the diaphragm in Example 3 basically remain unchanged, the battery interface bonding and fitting effect is good but the capacity consistency becomes worse, and it is not preferred;

[0106] Compared with Example 1, Comparative Example 1 lacks the reactive monomer. The reactive monomer could have undergone a crosslinking curing reaction with the curing resin in the coating. Without it, the adhesion of the adhesive coating is insufficient, resulting in a significant decrease in the hot pressing adhesion force and a significant increase in deviation. The interfacial bonding and fitting effect of the battery manufactured with the separator of Comparative Example 1 is average, and the capacity consistency becomes poor.

[0107] Compared with Example 1, Comparative Example 2 lacks the polymer dispersant, leading to poor dispersion of Material P, a significant increase in the deviation of the coating thickness, clogging of pores, an increase in the air permeability value, a wider range of spot diameters, a significant decrease in the hot pressing adhesion force and a significant increase in deviation. The short - circuit rate of the battery manufactured with the separator of Comparative Example 2 increases, the short - circuit rate rises, the interfacial bonding and fitting effect of the battery is average, and the capacity consistency becomes poor.

[0108] Compared with Example 1, Comparative Example 3 omits the curing resin, so that the binder cannot effectively adhere to the surface of the separator, resulting in insufficient coating adhesion, a significant decrease in the hot pressing adhesion force and a significant increase in deviation. The interfacial bonding and fitting effect of the battery manufactured with the separator of Comparative Example 3 is poor, and the capacity consistency becomes poor.

[0109] Compared with Example 1, in Comparative Example 4, the coating is applied by the ordinary rotary spraying method in Step ③. This method is a scattered - point coating, and the coating has randomness. The size, shape, and quantity of the coating points are uncertain, which can be considered an uncontrollable coating method. In application, there are problems such as uneven thickness, fluctuating adhesion force, and clogging of pores. The deviation of the coating thickness becomes larger, the air permeability value increases, there is slight pore clogging, the hot pressing adhesion force also decreases, and the deviation becomes larger. The interfacial bonding and fitting effect of the battery manufactured with the separator of Comparative Example 4 is good, but the capacity consistency is not good.

[0110] Compared with Example 1, Comparative Example 5 omits the EB curing process in Step ③. Without this process, the reactive monomer cannot undergo a crosslinking curing reaction with the curing resin in the coating, the adhesion of the functional coating becomes poor, resulting in a significant decrease in the hot pressing adhesion force and a significant increase in deviation. The interfacial bonding and fitting effect of the battery manufactured with the separator of Comparative Example 5 is poor, and the capacity consistency is poor.

[0111] Comparative Example 6 directly uses a 12 - μm dry - process PP separator as the substrate without any processing. The hot pressing adhesion force is almost 0. The interfacial bonding and fitting effect of the battery manufactured with the PP separator is non - existent, the interfacial effect is poor, and the capacity consistency is poor.

[0112] From the test results of each separator prepared in the above examples and comparative examples, it can be seen that the binder coating has a very significant impact on the performance of the PP separator. The binder coating is mainly composed of PVDF / PMMA, and also includes a network structure formed by a polymer dispersant, a curing resin, and an active monomer curing and crosslinking, as well as an antifoaming agent. Through the unique formula and process combination of the present invention, a unique binder slurry is prepared and coated on the surface of the separator in a regular dot coating or line coating manner by a specially designed plate roller, and then enters the oven for infrared and hot air drying to remove the solvent. After drying and cooling, it enters the EB curing device, where the curing resin and the active monomer in the coating undergo a crosslinking curing reaction, firmly attaching the PVDF / PMMA particles to the surface of the separator. The coating has good adhesion and excellent chemical resistance. This process can achieve controllability of the size, shape, and quantity of the coating spots / line patterns through the combined process of the plate roller texture, the feeding flow rate, and the air pressure, and can freely adjust the coating coverage rate and the coating grammage. The coating spots / line patterns have regular and orderly characteristics. Significantly improve the thickness uniformity, air permeability uniformity, hot pressing adhesion force and uniformity of the coating, and solve the problems of uneven thickness, fluctuating adhesion force, and blocked holes in the spraying of the traditional rotary spraying device. Using the coated separator of the present invention effectively improves the battery resistance, short-circuit rate, interface bonding and fitting effect, and capacity consistency of the battery.

[0113] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A binder slurry, characterized in that: It comprises a binder, a mixed solvent, a polymer dispersant, an EB-curable resin and a defoamer; the binder is one or more of polyvinylidene fluoride, modified polyvinylidene fluoride, polymethyl methacrylate and its derivatives; the binder exists in the form of agglomerates with a porous loose structure; The mass ratio of the binder to the mixed solvent is 1:4-24; The mixed solvent comprises an inactive monomer and an active monomer; the active monomer contains an unsaturated double bond; the inactive monomer is water and / or alcohol; The mass of the polymer dispersant is 0.5 to 15% of the mass of the binder; The mass of the EB-curable resin is 1 to 10% of the mass of the binder; The mass of the defoamer is 0.01-1.0% of the total mass of the binder slurry.

2. The binder slurry according to claim 1, characterized in that The mass content of active monomers in the mixed solvent is 5-20%.

3. The binder slurry according to claim 1, characterized in that: The polymer dispersant includes one or more of ammonium polyacrylate, sodium polyacrylate and block polymer dispersants.

4. The binder slurry according to claim 1, characterized in that The EB-curable resin includes an unsaturated resin, a prepolymer or an oligomer.

5. The method for preparing the binder slurry according to any one of claims 1 to 4, comprising the following steps: The binder powder, the mixed solvent and the polymer dispersant are mixed and dispersed under the conditions of rotation and revolution, so that the binder powder forms agglomerates to obtain a dispersion; The dispersion, EB-curable resin and defoamer are mixed to obtain the binder slurry.

6. The preparation method according to claim 5, characterized in that: The rotation speed is 800-1500 rpm; the revolution speed is 20-50 rpm.

7. A method for preparing a coated diaphragm, characterized in that: The following steps are involved: The binder slurry is placed in a plate roller and roller-coated on the surface of the battery separator, and the formed wet coating is dried and then EB cured to obtain the coated separator; the surface of the plate roller is provided with engraved holes and / or engraved lines; The binder slurry is the binder slurry described in any one of claims 1 to 4 or the binder slurry prepared by the preparation method described in any one of claims 5 to 6.

8. The preparation method according to claim 7, characterized in that: The size of the engraved holes and engraved lines is 1.2 to 1.8 times the target size of the roller coating spots and lines.

9. The coated diaphragm prepared by the preparation method according to any one of claims 7 to 8 comprises a battery diaphragm and an adhesive coating coated on the surface of the battery diaphragm; the adhesive coating is distributed in points and / or lines; the thickness deviation of the adhesive coating is ±0.5 μm.

10. The coated diaphragm according to claim 9, characterized in that The thickness of the adhesive coating is 1-5 μm, the coating coverage is 5-50%, and the gram weight is 0.2-0.8 g / m 2 .

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