A composite separator, a method for preparing the same, a battery containing the same, and a manufacturing method

Abstract

The present application belongs to the technical field of battery materials, and provides a composite diaphragm, a preparation method thereof, a battery containing the same and a manufacturing method. The composite diaphragm comprises a base film and an oily coating layer arranged on one side surface of the base film; the oily coating layer comprises porous inorganic fillers, polymer materials and adhesive materials; the peeling strength F1 between the oily coating layer and the base film and the pore size L of the porous inorganic fillers satisfy the relationship 170×10 ‑9 N≤L×F1≤230×10 ‑9 N. Through the correlation of F1 and L, the oily coating layer can obtain the special effect of strong bonding force and low peeling strength from the base film, and then the oily coating layer is fully transferred to the surface of the positive electrode sheet through the hot pressing process in the assembly and manufacturing process of the battery, which is equivalent to transferring a layer of high heat-resistant film on the surface of the positive electrode sheet, so that it can insulate the positive and negative electrodes at high temperature without affecting the electrochemical performance of the positive electrode sheet.

Description

Technical Field

[0001] This invention belongs to the field of battery materials, and relates to a composite separator, its preparation method, a battery containing the separator, and its manufacturing method. Background Technology

[0002] The rapid development and widespread application of lithium-ion battery technology have made it an indispensable part of modern life. From electric vehicles to large-scale energy storage power stations and 3C electronic products, lithium batteries occupy an important position in many fields due to their superior performance. However, as battery cells continue to develop towards larger capacities and higher rate capabilities, concerns and attention regarding issues such as battery thermal runaway, combustion, and explosion are also increasing, which undoubtedly places increasingly stringent requirements on battery safety.

[0003] The separator, as a key component inside a lithium-ion battery, plays a crucial role. It not only needs to effectively isolate the positive and negative electrodes to prevent short circuits at room temperature, but also needs to remain stable at high temperatures to avoid thermal runaway caused by temperature increases. Therefore, developing separators with high safety characteristics has become an important research direction for improving the overall performance and safety of lithium-ion batteries.

[0004] To achieve these goals, researchers have proposed a scheme to optimize and improve the separator by coating it with heat-resistant materials, such as aramid and polyimide, to form a heat-resistant coating. These heat-resistant materials are generally formed using an oil-based slurry obtained by dissolving them in an organic solvent. However, to ensure the adhesion of the heat-resistant layer and the rigidity of the battery cell, a water-based slurry containing adhesive materials is further applied. This method of preparing the oil-based and water-based coatings separately often involves multiple winding and unwinding of the separator, making the process cumbersome and difficult to control processing costs.

[0005] To address this, CN106058126A discloses a functional coated separator and a battery containing the separator. The coated separator comprises a polyolefin substrate and a coating applied to the surface of the polyolefin substrate. The coating preparation slurry includes aqueous polyvinylidene fluoride, inorganic nano-ceramic particles, and hydroxymethyl cellulose adhesive. This prior art uses an aqueous polyvinylidene fluoride binder combined with highly heat-resistant inorganic nano-ceramic particles to prepare a functional coated separator. This results in a separator that not only possesses the performance of conventional oil-based P(VDF-HFP) coated separators but also exhibits superior adhesion and heat resistance, effectively suppressing separator shrinkage and coating detachment at high temperatures. However, for methods that directly form the coating on the base membrane, while optimizing the coating's composition and materials can further enhance its heat resistance or adhesion properties, the base membrane itself often lacks sufficient heat resistance. Under extremely high temperatures and other harsh environments, the overall separator may still shrink or rupture, leading to contact between the positive and negative electrodes and posing a risk of battery thermal runaway.

[0006] To address this issue, another solution is to directly coat the positive electrode surface with a layer of heat-resistant ceramic material. For example, CN112397716A discloses an oil-based ceramic slurry, its preparation method, a positive electrode sheet coated with this slurry, and a lithium-ion battery. This prior art solves the problems of large swelling and easy detachment of water-based ceramic coatings, and easy phase separation, easy detachment, and excessive hardness of oil-based ceramic coatings by using a combination of a first binder, a second binder, ceramic powder, and an organic solvent. By using the oil-based ceramic slurry of this invention to prepare edge-coated positive electrode sheets, the problem of short circuit between positive and negative electrodes can be solved. However, while directly coating the positive electrode sheet to form a ceramic layer can continue to provide insulation even when the separator shrinks and cracks, this method has the drawback of severely sacrificing the battery's energy density and increasing manufacturing costs.

[0007] In view of the above, existing improvement measures cannot completely eliminate all potential safety hazards. Therefore, research and development of high-safety separators still need to be continued in depth to ensure the safety protection performance of lithium-ion batteries while balancing the relationship between battery performance such as energy density and cost-effectiveness, so as to provide the market with more comprehensive product options. Summary of the Invention

[0008] In view of the problems existing in the prior art, the purpose of the present invention is to provide a composite separator, a method for preparing the same, a battery containing the same, and a manufacturing method thereof. The composite separator includes a base membrane and an oily coating disposed on one side surface of the base membrane. The oily coating includes a porous inorganic filler, a polymer material, and an adhesive material. The peel strength F1 between the oily coating and the base membrane satisfies the relationship 170 × 10⁻¹⁰ with respect to the pore size L of the porous inorganic filler. -9N≤L×F1≤230×10 -9 N. Through the correlation between F1 and L, the oily coating can achieve a special effect of strong adhesion but low peel strength from the base film. This allows the oily coating to be fully transferred to the surface of the positive electrode sheet during the battery assembly and manufacturing process through a hot pressing process. This is equivalent to transferring a high heat-resistant film onto the surface of the positive electrode sheet, enabling it to isolate the positive and negative electrodes at high temperatures without affecting the electrochemical performance of the positive electrode sheet.

[0009] To achieve this objective, the present invention adopts the following technical solution:

[0010] In a first aspect, the present invention provides a composite separator, the composite separator comprising a base membrane and an oily coating disposed on one side surface of the base membrane; the oily coating comprising a porous inorganic filler, a polymer material, and an adhesive material; the pore size (diameter) of the porous inorganic filler is denoted as L, and the peel strength between the oily coating and the base membrane is denoted as F1, then 170 × 10 -9 N≤L×F1≤230×10 -9 N.

[0011] The oily coating of this invention includes a porous inorganic filler. "Porous" refers to the presence of pores on the surface and inside the inorganic filler. This porous structure reduces the contact area between the oily coating and the base film, thereby reducing the peel strength between them. Therefore, when using the composite separator of this invention to prepare a battery, for example, during the hot-pressing process of preparing a prismatic battery, the oily coating can be transferred from the base film to the surface of the positive electrode sheet. This is equivalent to setting a high-heat-resistant film on the surface of the positive electrode sheet, retaining the characteristics of this working method. It avoids the isolation failure caused by the shrinkage and rupture of the overall separator due to changes in the base film under extreme conditions such as high temperatures, further effectively preventing thermal runaway, combustion, and explosion problems, and significantly improving battery safety.

[0012] It should be noted that in the oily coating, the larger the pore size of the porous inorganic filler, the smaller the contact area between the porous inorganic filler and the base film, and the lower the peel strength (adhesion). Therefore, when L×F1≤170×10 -9 When the pore size is too small, the effect of the inorganic filler and polymer material forming a homogeneous mixture deteriorates; while when L×F1≥230×10 -9 When the pore size (N) is too large, the inorganic filler is prone to floating in oily slurries, which deteriorates the heat resistance and coating transfer effect of the oily coating. It should also be noted that the unit of pore size (L) in porous inorganic fillers is nm, while the unit of peel strength (F1) is N / m. Therefore, a unit conversion is needed when calculating L×F1 to ensure the calculated result is in N.

[0013] The following are preferred technical solutions of the present invention, but are not intended to limit the technical solutions provided by the present invention. The technical objectives and beneficial effects of the present invention can be better achieved and realized through the following technical solutions.

[0014] As a preferred embodiment of the present invention, the peel strength F1 between the oily coating and the base film is 3 N / m to 10 N / m.

[0015] Preferably, the pore size L of the porous inorganic filler is 20 nm to 55 nm.

[0016] Preferably, the particle size of the porous inorganic filler is 100 nm to 600 nm.

[0017] Preferably, the porous inorganic filler includes at least one of porous alumina, porous boehmite, porous barium sulfate, porous aluminum sulfate, porous titanium dioxide, porous aluminum nitride, porous magnesium nitride, porous magnesium hydroxide, porous molybdenum disulfide, or porous barium titanate.

[0018] Preferably, the morphology of the porous inorganic filler includes at least one of granular, flake, or rod-shaped forms.

[0019] As a preferred embodiment of the present invention, the polymer material includes at least one of meta-aramid, para-aramid, polyamide, or polyimide.

[0020] As a preferred embodiment of the present invention, the adhesive material includes polyacrylonitrile and polyvinylidene fluoride.

[0021] Preferably, the adhesive material is grafted with oxygen-containing groups.

[0022] Preferably, the adhesive material comprises polyacrylonitrile and polyvinylidene fluoride modified with sodium dodecyl sulfate.

[0023] It should be noted that the polyacrylonitrile and polyvinylidene fluoride modified with sodium dodecyl sulfate refer to a mixture of polyacrylonitrile and polyvinylidene fluoride that has been modified with sodium dodecyl sulfate and grafted with oxygen-containing groups. The specific modification process includes: preparing a tert-butanol solution of sodium dodecyl sulfate with a mass concentration of 3 ± 0.2%; stirring the polyacrylonitrile and polyvinylidene fluoride in the above solution at room temperature for 0.2 to 0.8 hours, preferably 0.5 hours; followed by washing with water and drying to obtain sodium dodecyl sulfate-modified polyacrylonitrile and polyvinylidene fluoride.

[0024] As a preferred technical solution of the present invention, the thickness of the oily coating is denoted as H1, where H1 is 1μm to 5μm.

[0025] Preferably, the air permeability of the oily coating is 10s / 100cc to 70s / 100cc.

[0026] It should be noted that the air permeability refers to the area through which 100 mL of air passes under a pressure of 1.21 kPa, which is 6.45 cm². 2 The time required for the diaphragm to be in place.

[0027] Preferably, the adhesion force between the oily coating and the oily coating of another composite diaphragm (or diaphragm to diaphragm) is denoted as F2, where F2 is 13 N / m to 50 N / m.

[0028] It should be noted that the adhesion between the diaphragm and the adhesion between the oil coating and the positive electrode sheet are directly proportional. Therefore, the higher the value of F2, the stronger the adhesion between the oil coating and the positive electrode sheet.

[0029] As a preferred embodiment of the present invention, the oily coating comprises, by weight, 20 to 25 parts of the porous inorganic filler, 80 to 100 parts of polymer material, and 50 to 100 parts of adhesive material.

[0030] Preferably, the base film is made of at least one of polyethylene (PE), polypropylene (PP), polyimide (PI), or aramid.

[0031] Preferably, the thickness of the base film is 3μm to 20μm.

[0032] Preferably, the base film has a pore size of 15nm to 120nm, a porosity of 25% to 65%, and an air permeability of 50s / 100cc to 500s / 100cc.

[0033] As a preferred embodiment of the present invention, the oily coating further includes an ionic conductive material.

[0034] Preferably, the ionic conductivity material includes at least one of lithium aluminum germanium phosphate, lithium lanthanum titanium oxide, or lithium thiophosphate.

[0035] Preferably, the particle size of the ionic conductive material is 600 nm to 1100 nm.

[0036] Preferably, the ionic conductivity of the ionic conductive material is 1×10⁻⁶. -4 S / cm~1×10 -2 S / cm.

[0037] Preferably, the oily coating comprises 0.8 to 1.2 parts by weight of the ionic conductive material.

[0038] As a preferred embodiment of the present invention, the composite membrane further includes an aqueous coating disposed on the surface of the base membrane on the side away from the oily coating.

[0039] As a preferred technical solution of the present invention, the water-based coating includes inorganic particles, adhesive material, binder, dispersant and wetting agent.

[0040] As a preferred embodiment of the present invention, the inorganic particles include at least one of zirconium oxide, zirconium nitride, zirconium titanate, zirconium silicide, or zirconium boride.

[0041] Preferably, the morphology of the inorganic particles includes at least one of granular, flake-like, or rod-like shapes.

[0042] Preferably, the particle size of the inorganic particles is 100nm to 1200nm.

[0043] As a preferred technical solution of the present invention, the adhesive layer material includes polyolefin materials and / or hydrogenated nitrile butadiene rubber (HNBR).

[0044] Preferably, the polyolefin material includes at least one of polyethylene microspheres, polypropylene microspheres, or polybutene microspheres.

[0045] Preferably, the glass transition temperature of the adhesive layer material is -20℃ to 70℃.

[0046] Preferably, the particle size D of the adhesive layer material is... 10 For particles ≥1.3μm, 2.8μm ≤ particle size D 50 ≤7.1μm, particle size D 90 ≤11.2μm, particle size D 99 ≤13μm.

[0047] As a preferred embodiment of the present invention, the adhesive includes at least one of acrylic materials, acrylate materials, or acrylamide materials.

[0048] Preferably, the acrylic material includes sodium acrylate or polyacrylic acid derivatives, etc.; the acrylate material includes methyl methacrylate, butyl acrylate or 2-ethylhexyl acrylate, etc.; and the acrylamide material includes polyacrylamide, etc.

[0049] Preferably, the glass transition temperature of the adhesive is 50°C to 270°C.

[0050] As a preferred technical solution of the present invention, the thickness of the water-based coating is denoted as H2, where H2 is 1μm to 3μm.

[0051] Preferably, the particle size D of the adhesive layer material is... 50 The relationship between the thickness H2 of the water-based coating and the thickness H2 is: 0.8 ≤ D 50 / H2≤4.2.

[0052] As a preferred embodiment of the present invention, the wetting agent includes at least one of polyether materials, siloxane materials, and enol materials.

[0053] Preferably, the polyether material is polyethylene glycol or polyoxyethylene ether, etc.; the siloxane material includes polydimethylsiloxane, etc.; and the enol material includes nonylphenol polyoxyethylene ether, fatty alcohol polyoxyethylene ether, or alkenyl succinate sulfonate, etc.

[0054] As a preferred embodiment of the present invention, the dispersant includes at least one of n-butanol, tert-butanol, or ethanol.

[0055] Preferably, by weight, the water-based coating comprises 78 to 92 parts of inorganic particles, 3 to 16 parts of adhesive material, 2.7 to 6 parts of binder, 0.25 to 1 part of wetting agent and 0.1 to 0.5 parts of dispersant.

[0056] Secondly, the present invention provides a method for preparing the composite separator described in the first aspect, the method comprising:

[0057] An oil-based coating slurry is prepared and applied to one side of the base membrane to form an oil-based coating, thereby obtaining the composite diaphragm.

[0058] As described above, this invention, through research, has discovered that when the inorganic filler in the oily coating is in a porous state, the size of its pores can affect the peel strength between the oily coating and the base film. Based on this, a new method for preparing and operating the separator is proposed. That is, the oily coating is still directly formed on the base film by coating method to obtain the separator. This method retains the advantages of simplicity, convenience, ease of preparation, and ease of storage, transportation, and assembly, while avoiding the adverse effects of directly forming a coating on the positive electrode sheet on the battery's energy density and electrochemical performance. At the same time, the oily coating can be fully transferred to the surface of the positive electrode sheet during the assembly and manufacturing process of batteries and other devices through a hot pressing process. This is equivalent to transferring a high heat-resistant film onto the surface of the positive electrode sheet, thus retaining the advantages and characteristics of this method. It effectively avoids the problem of overall separator shrinkage and rupture caused by changes in the base film under extreme conditions such as high temperature, and further effectively avoids the occurrence of thermal runaway, combustion, and explosion problems, greatly improving battery safety. Therefore, the composite separator obtained by the above preparation method is a high-safety separator.

[0059] As a preferred embodiment of the present invention, the oily coating slurry includes an organic solvent, which includes at least one of N,N-dimethylacetamide (DMAc), N-methylpyrrolidone (NMP), N,N-dimethylformamide (DMF) or dimethyl sulfoxide (DMSO).

[0060] As a preferred embodiment of the present invention, the oily coating slurry further includes a co-solvent for promoting the dissolution of the polymer material, wherein the co-solvent includes at least one of calcium chloride (CaCl2), lithium chloride (LiCl), or potassium chloride (KCl).

[0061] Preferably, the mass of the co-solvent accounts for 3.5% to 6% of the total mass of the oily coating slurry.

[0062] As a preferred embodiment of the present invention, the solid content of the oily coating slurry is 2% to 8%, and the viscosity is 30 cps to 60 cps.

[0063] As a preferred technical solution of the present invention, the oil coating process includes, in sequence, unwinding the base film, coating with the oil coating slurry, over-solidification molding, washing, and drying.

[0064] As a preferred technical solution of the present invention, the preparation method further includes preparing an aqueous coating slurry, and after forming the oily coating, without winding it up, directly applying an aqueous coating to the surface of the base film on the other side away from the oily coating to form an aqueous coating, thereby obtaining the composite diaphragm.

[0065] Preferably, the aqueous coating slurry includes an aqueous solvent, which includes water.

[0066] Preferably, the solid content of the water-based coating slurry is 27% to 33%, and the viscosity is 10 cps to 80 cps.

[0067] Preferably, the surface density of the adhesive material in the water-based coating is 0.08 g / m³. 2 ~0.56g / m 2 .

[0068] Thirdly, the present invention provides a method for manufacturing a battery, the method comprising:

[0069] Provide a composite separator as described in the first aspect or a composite separator obtained by the preparation method described in the second aspect, and provide a positive electrode, a negative electrode, and an electrolyte; assemble the positive electrode, the negative electrode, and the composite separator into a shape, wherein the oily coating of the composite separator faces and contacts the positive electrode to obtain an electrode assembly;

[0070] The electrode assembly is first hot-pressed to transfer the oily coating on the composite separator to the positive electrode sheet, and then encapsulated, baked and injected with electrolyte in sequence to obtain the battery.

[0071] As a preferred technical solution of the present invention, the assembly process includes a stacking process or a winding process.

[0072] As a preferred technical solution of the present invention, the hot pressing temperature is 60℃~90℃, the surface pressure is 0.5MPa~3MPa, and the time is 25s~240s.

[0073] As a preferred technical solution of the present invention, the baking temperature is 95℃~105℃ and the time is 8h~12h, and the baking causes the oily coating to be transferred from the diaphragm to the positive electrode sheet.

[0074] As a preferred technical solution of the present invention, the manufacturing method further includes post-processing of the obtained battery, the post-processing including pre-charging, formation and capacity testing in sequence.

[0075] As a preferred embodiment of the present invention, the battery includes a prismatic battery.

[0076] As a preferred technical solution of the present invention, the positive electrode sheet includes at least one of lithium cobalt oxide, lithium manganese oxide, ternary materials, lithium iron phosphate, lithium manganese iron phosphate or lithium-rich manganese-based materials, preferably including at least lithium iron phosphate.

[0077] Fourthly, the present invention provides a battery obtained according to the manufacturing method described in the third aspect.

[0078] Compared with existing technical solutions, the present invention has at least the following beneficial effects:

[0079] (1) The inorganic filler used in the oily coating of the composite separator of the present invention has a porous structure. By limiting the specific pore size, the contact area between the porous inorganic filler and the base film is reduced, thereby reducing the peel strength between the oily coating and the base film. During the battery assembly and manufacturing process, the oily coating can be transferred to the positive electrode by hot pressing, and the transfer rate is >99.0%, which basically achieves complete transfer. This is consistent with the isolation effect of forming an oily coating directly on the positive electrode. It avoids the problem of isolation failure caused by the shrinkage and rupture of the overall separator due to changes in the base film under extreme conditions such as high temperature. It further effectively avoids the occurrence of thermal runaway, combustion and explosion problems, greatly improves the safety of the battery, and avoids the impact on the electrochemical performance such as capacity and energy density of the positive electrode.

[0080] (2) In this invention, the adhesive material in the oily coating is modified to make it grafted with oxygen-containing groups to have self-crosslinking properties. Through the baking heat treatment in the subsequent battery assembly manufacturing process, it can undergo crosslinking reaction with the oxygen-containing groups on the surface of the positive electrode, further improving the adhesion. This makes the hardness of the battery cell further improved after baking, which is beneficial to maintain the coverage of the oily coating on the positive electrode after liquid injection, making it basically equivalent to the transfer rate after hot pressing, thus ensuring the integrity and stability of the oily coating.

[0081] (3) In this invention, an aqueous coating is provided on the side of the composite diaphragm away from the oily coating. The negative electrode is bonded to the adhesive material in the aqueous coating, which is beneficial for the two to adhere. The particle size of the adhesive material and the thickness of the aqueous coating are controlled, increasing the wetting space, which is beneficial for electrolyte storage and also helps to achieve the effect of no lithium plating at the interface after the battery cell is fully charged.

[0082] (4) In this invention, the preparation method of the diaphragm is a scheme that completes oil and water coating in one go, i.e. oil and water continuous coating, which can avoid the complex process of multiple winding and unwinding, facilitate large-scale continuous production, and help reduce costs. Detailed Implementation

[0083] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0084] In one specific embodiment, the present invention provides a composite separator, the composite separator comprising a base membrane and an oily coating disposed on one side surface of the base membrane; the oily coating comprising a porous inorganic filler, a polymer material, and an adhesive material; the pore size of the porous inorganic filler is denoted as L, and the peel strength between the oily coating and the base membrane is denoted as F1, then 170 × 10 -9 N≤L×F1≤230×10 -9 N, for example, L×F1 can be 170×10 -9 N, 175×10 - 9 N, 180×10 -9 N, 185×10 -9 N, 190×10 -9 N, 195×10 -9 N, 200×10 -9 N, 205×10 -9 N, 210×10 -9 N, 215×10 -9 N, 220×10 -9 N, 225×10 -9 N or 230×10 -9 N, etc.

[0085] In one embodiment, the peel strength F1 between the oily coating and the base film is 3N / m to 10N / m, such as 3N / m, 3.5N / m, 4N / m, 4.5N / m, 5N / m, 5.5N / m, 6N / m, 6.5N / m, 7N / m, 7.5N / m, 8N / m, 8.5N / m, 9N / m, 9.5N / m, or 10N / m.

[0086] In one embodiment, the pore size L of the porous inorganic filler is 20nm to 55nm, such as 20nm, 23nm, 25nm, 28nm, 30nm, 32nm, 35nm, 38nm, 40nm, 42nm, 45nm, 48nm, 50nm, 52nm or 55nm, etc.

[0087] It should be noted that the pore size L of the porous inorganic filler refers to the range from the minimum pore size to the maximum pore size. The two extreme values ​​of this range can be reasonably adjusted between 20 nm and 55 nm to meet the 170 × 10⁻⁶ pore size requirement. -9 N≤L×F1≤230×10 -9 N.

[0088] In one embodiment, the particle size of the porous inorganic filler is 100nm to 600nm, such as 100nm, 130nm, 150nm, 180nm, 200nm, 250nm, 280nm, 300nm, 320nm, 350nm, 380nm, 400nm, 420nm, 450nm, 480nm, 500nm, 520nm, 550nm, 580nm, or 600nm.

[0089] In this invention, when the pore size of the porous inorganic filler is determined, the particle size of the porous inorganic filler also has a certain influence on the peel strength between the oily coating and the base film. Preferably, smaller particle size particles are used, which can further reduce the peel strength between the oily coating and the base film.

[0090] In one embodiment, the porous inorganic filler includes at least one of porous alumina, porous boehmite, porous barium sulfate, porous aluminum sulfate, porous titanium dioxide, porous aluminum nitride, porous magnesium nitride, porous magnesium hydroxide, porous molybdenum disulfide, or porous barium titanate. Typical combinations include combinations of porous alumina and porous boehmite, combinations of porous barium sulfate and porous aluminum sulfate, combinations of porous alumina and porous titanium dioxide, combinations of porous alumina and porous aluminum nitride, combinations of porous aluminum nitride and porous magnesium nitride, combinations of porous magnesium nitride and porous magnesium hydroxide, or combinations of porous molybdenum disulfide and porous barium titanate.

[0091] In one embodiment, the morphology of the porous inorganic filler includes at least one of granular, flake, or rod-shaped forms. Typical combinations include combinations of granular and flake-shaped forms, combinations of granular and rod-shaped forms, or combinations of flake and rod-shaped forms.

[0092] In one embodiment, the polymer material includes at least one of meta-aramid, para-aramid, polyamide, or polyimide. Typical examples of combinations include combinations of meta-aramid and para-aramid, meta-aramid and polyamide, meta-aramid and polyimide, or polyamide and polyimide.

[0093] In one embodiment, the adhesive material includes polyacrylonitrile and polyvinylidene fluoride.

[0094] In one embodiment, the adhesive material is grafted with oxygen-containing groups.

[0095] In one embodiment, the adhesive material comprises polyacrylonitrile and polyvinylidene fluoride modified with sodium dodecyl sulfate.

[0096] Typically, battery assembly involves electrolyte injection, where electrolyte is injected into the cell. This process can reduce the adhesion of the oily coating transferred via hot pressing, potentially causing it to peel off from the positive electrode. To address this, the present invention preferably uses an adhesive material grafted with oxygen-containing groups in the oily coating. This adhesive material possesses self-crosslinking properties, allowing for activation of the crosslinking reaction with the oxygen-containing groups on the positive electrode surface during battery assembly processes, such as baking, under suitable heat treatment conditions. This further strengthens the bond between the oily coating and the positive electrode, improving the adhesion between them and the cell's hardness after baking. This effectively ensures that the oily coating remains fully and stably covering the positive electrode after electrolyte injection, maintaining a coverage rate comparable to that after hot pressing, thus achieving good separation between the positive and negative electrodes.

[0097] It is understood that grafting refers to modification performed on the main chain. For example, the oxygen-containing groups include hydroxyl, carboxyl, and sulfonic acid groups. The grafting method may be to graft-modify polymer monomers and then polymerize them to form a polymer material.

[0098] It should be noted that this invention does not limit the positive electrode sheet to needing to be modified or optimized in order to function in conjunction with the grafted modified adhesive material. Since the positive electrode active material is usually an oxide-containing material, such as ternary materials and lithium iron phosphate, the positive electrode active material itself can undergo a cross-linking reaction with the grafted adhesive material containing oxygen groups. Therefore, the positive electrode active material and positive electrode sheet used in the prior art can be applied to this invention. Of course, the grafted adhesive material containing oxygen groups can also be used to replace the conventional binder in the positive electrode sheet as appropriate.

[0099] In one embodiment, the oxygen-containing group includes hydroxyl, carboxyl, or sulfonic acid groups, etc.

[0100] In one embodiment, the grafting method may be to graft and modify the polymer monomers, and then polymerize them to form a polymer material.

[0101] In one embodiment, the thickness of the oily coating is denoted as H1, where H1 is 1 μm to 5 μm, for example, 1 μm, 1.3 μm, 1.5 μm, 1.8 μm, 2 μm, 2.2 μm, 2.5 μm, 2.8 μm, 3 μm, 3.2 μm, 3.5 μm, 3.8 μm, 4 μm, 4.3 μm, 4.5 μm, 4.8 μm, or 5 μm.

[0102] In one embodiment, the air permeability of the oily coating is 10s / 100cc to 70s / 100cc, such as 10s / 100cc, 15s / 100cc, 20s / 100cc, 25s / 100cc, 30s / 100cc, 35s / 100cc, 40s / 100cc, 45s / 100cc, 50s / 100cc, 55s / 100cc, 60s / 100cc, 65s / 100cc, or 70s / 100cc.

[0103] In one embodiment, the adhesion force between the oily coating and the oily coating of another composite diaphragm is denoted as F2, where F2 is 13 N / m to 50 N / m, for example, 13 N / m, 15 N / m, 18 N / m, 20 N / m, 23 N / m, 25 N / m, 28 N / m, 30 N / m, 32 N / m, 35 N / m, 38 N / m, 40 N / m, 42 N / m, 45 N / m, 48 N / m, or 50 N / m.

[0104] In one embodiment, the oily coating comprises, by weight, 20 to 25 parts of the porous inorganic filler, such as 20, 20.3, 20.5, 20.8, 21, 21.2, 21.5, 21.8, 22, 22.3, 22.5, 22.8, 23, 23.2, 23.5, 23.8, 24, 24.2, 24.5, 24.8, or 25 parts; and 80 to 100 parts of polymer material, such as 80, 81.3, 82.5, 83.8, 84.5, 85.8, 86.3, 87.5, 88.8 parts, etc. 89.3 parts, 90.8 parts, 91.5 parts, 92.3 parts, 93.8 parts, 94.5 parts, 95.3 parts, 96.8 parts, 97.5 parts, 98.3 parts, 99.3 parts, or 100 parts, etc.; and 50 to 100 parts of adhesive material, such as 50.8 parts, 52.5 parts, 53.3 parts, 55.8 parts, 58.5 parts, 60.3 parts, 62.8 parts, 63.5 parts, 65.3 parts, 68.8 parts, 70.5 parts, 72.3 parts, 75.8 parts, 78.5 parts, 80.3 parts, 82.8 parts, 85.5 parts, 88.3 parts, 90.8 parts, 93.5 parts, 95.3 parts, 98 parts, or 100 parts, etc.

[0105] In one embodiment, the base film includes at least one of polyethylene (PE), polypropylene (PP), polyimide (PI), or aramid, for example typical combinations include combinations of PE and PP, PE and PI, PI and aramid, PE and aramid, PI and PP, or PE and PP, etc.

[0106] In one embodiment, the thickness of the base film is 3μm to 20μm, such as 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, 16μm, 17μm, 18μm, 19μm or 20μm.

[0107] In one embodiment, the pore size of the base film is 15nm to 120nm, such as 15nm, 25nm, 30nm, 35nm, 40nm, 45nm, 50nm, 55nm, 60nm, 65nm, 70nm, 75nm, 80nm, 85nm, 90nm, 95nm, 100nm, 105nm, 110nm, 115nm, or 120nm; the porosity is 25% to 65%, and the air permeability is 50s / 100cc to 500s / 100cc.

[0108] It should be noted that the pore size of the base film refers to the range from the minimum pore size to the maximum pore size, and is not the average pore size or a certain pore size limit value.

[0109] In one embodiment, the oily coating further includes an ionicly conductive material.

[0110] In one embodiment, the ionic conductivity material includes at least one of lithium aluminum germanium phosphate, lithium lanthanum titanium oxide, or lithium thiophosphate. Typical combinations include combinations of lithium lanthanum titanium oxide and lithium aluminum germanium phosphate, combinations of lithium lanthanum titanium oxide and lithium thiophosphate, or combinations of lithium thiophosphate and lithium aluminum germanium phosphate.

[0111] In one embodiment, the particle size of the ionic conductive material is 600nm to 1100nm, such as 600nm, 650nm, 700nm, 750nm, 800nm, 850nm, 900nm, 950nm, 1000nm, 1050nm, or 1100nm.

[0112] In one embodiment, the ionic conductivity of the ionic conductive material is 1×10⁻⁶. -4 S / cm~1×10 -2 S / cm, for example 1×10 -2 S / cm, 9×10 -3 S / cm, 7×10 -3 S / cm, 5×10 -3 S / cm, 3×10 -3 S / cm, 1×10 -3 S / cm, 9×10 -4 S / cm, 8×10 -4 S / cm, 6×10 -4 S / cm, 4×10 -4 S / cm, 2×10 -4 S / cm or 1×10 -4 S / cm, etc.

[0113] In one embodiment, the oily coating comprises, by weight, 0.8 to 1.2 parts of the ionic conductive material, such as 0.8 parts, 0.83 parts, 0.85 parts, 0.88 parts, 0.9 parts, 0.92 parts, 0.95 parts, 0.98 parts, 1 part, 1.02 parts, 1.06 parts, 1.09 parts, 1.1 parts, 1.13 parts, 1.15 parts, 1.18 parts, or 1.2 parts.

[0114] In one embodiment, the composite membrane further includes an aqueous coating disposed on the surface of the base membrane on the side opposite to the oily coating.

[0115] In this invention, the oily coating of the composite separator faces the positive electrode, while the other side of the base film is preferably provided with an aqueous coating to bond with the negative electrode, thereby optimizing the interface with the negative electrode, increasing the wetting space, and improving the lithium plating problem at the cell interface.

[0116] In one embodiment, the aqueous coating comprises inorganic particles, an adhesive material, a binder, a dispersant, and a wetting agent.

[0117] In one embodiment, the inorganic particles include at least one of zirconium oxide, zirconium nitride, zirconium titanate, zirconium silicide, or zirconium boride. Typical combinations include combinations of zirconium oxide and zirconium nitride, zirconium oxide and zirconium titanate, zirconium oxide and zirconium silicide, zirconium oxide and zirconium boride, zirconium nitride and zirconium titanate, zirconium nitride and zirconium silicide, zirconium nitride and zirconium boride, zirconium titanate and zirconium silicide, zirconium titanate and zirconium boride, or zirconium silicide and zirconium boride, etc.

[0118] In one embodiment, the morphology of the inorganic particles includes at least one of granular, flake, or rod-shaped forms. Typical combinations include combinations of granular and flake-shaped, granular and rod-shaped, or flake and rod-shaped forms.

[0119] In one embodiment, the particle size of the inorganic particles is 100nm to 1200nm, such as 100nm, 200nm, 300nm, 400nm, 500nm, 600nm, 700nm, 800nm, 900nm, 1000nm, 1100nm or 1200nm.

[0120] It should be noted that, except for specifically specified particle size values, the particle size values ​​of the porous inorganic filler, the ion-conducting material, and the inorganic particles in this invention are all range values ​​represented by the minimum size of the actual particles (including primary particles or agglomerated secondary particles) to the maximum size of the actual particles, and are not the values ​​of the average particle size or other particle size limits.

[0121] In one embodiment, the adhesive layer material includes polyolefin materials and / or hydrogenated nitrile rubber.

[0122] In one embodiment, the polyolefin material includes at least one of polyethylene microspheres, polypropylene microspheres, or polybutene microspheres.

[0123] In one embodiment, the glass transition temperature (Tg) of the adhesive layer material is -20℃ to 70℃, for example -20℃, -19℃, -18℃, -16℃, -15℃, -13℃, 10℃, -8℃, -5℃, 0℃, 5℃, 10℃, 15℃, 20℃, 25℃, 30℃, 35℃, 40℃, 45℃, 50℃, 55℃, 60℃, 65℃, or 70℃.

[0124] In one embodiment, the particle size D of the adhesive layer material 10 For particle sizes ≥1.3μm, such as 1.3μm, 1.5μm, 1.8μm, 2μm, 2.2μm, 2.5μm, or 2.76μm, etc.; for particle sizes ≤2.8μm, the particle size D is ≥1.3μm. 50 ≤7.1μm, such as 2.8μm, 3.3μm, 3.5μm, 3.8μm, 4μm, 4.2μm, 4.5μm, 4.8μm, 5μm, 5.2μm, 5.5μm, 5.8μm, 6μm, 6.2μm, 6.5μm, 6.8μm or 7.1μm, etc.; particle size D 90 ≤11.2μm, such as 7.3μm, 7.8μm, 8μm, 8.5μm, 8.8μm, 9μm, 9.2μm, 9.5μm, 9.8μm, 10μm, 10.2μm, 10.5μm, 10.8μm, 11μm or 11.2μm, etc.; particle size D 99 ≤13μm, such as 11.5μm, 11.8μm, 12μm, 12.2μm, 12.5μm, 12.8μm or 13μm, etc.

[0125] In one embodiment, the adhesive comprises at least one of acrylic materials, acrylate materials, and acrylamide materials. Typical examples of combinations include combinations of acrylic materials and acrylate materials, combinations of polyacrylic materials and acrylamide materials, or combinations of acrylamide materials and acrylate materials.

[0126] In one embodiment, the glass transition temperature (Tg) of the adhesive is 50°C to 270°C, for example, 50°C, 60°C, 80°C, 90°C, 100°C, 120°C, 140°C, 160°C, 180°C, 200°C, 220°C, 230°C, 250°C, or 270°C.

[0127] In one embodiment, the thickness of the aqueous coating is denoted as H2, where H2 is 1μm to 3μm, such as 1μm, 1.3μm, 1.5μm, 1.8μm, 2μm, 2.2μm, 2.5μm, 2.8μm, or 3μm.

[0128] In one embodiment, the particle size D of the adhesive layer material 50The relationship between the thickness H2 of the water-based coating and the thickness H2 is: 0.8 ≤ D 50 / H2≤4.2, for example, D 50 / H2 can be 0.8, 1, 1.2, 1.5, 1.8, 2, 2.2, 2.5, 2.8, 3, 3.2, 3.5, 3.8, 4 or 4.2, etc.

[0129] In this invention, in order to ensure the wetting space provided by the water-based coating, D 50 H2 and D must satisfy the above relationship. 50 / H2 < 0.8, larger (greater than inorganic materials) adhesive particles protrude low from the water-based coating, failing to achieve the effects of bonding and gap-forming to increase the wetting space; while if D 50 When H2 > 4.2, the larger particles of adhesive material are exposed too high above the water-based coating and are prone to falling off, failing to provide a stable bonding effect and resulting in severe powder shedding from the diaphragm.

[0130] In one embodiment, the wetting agent includes at least one of polyether materials, siloxane materials, and enol materials. Typical examples of combinations include combinations of polyether materials and siloxane materials, combinations of polyether materials and enol materials, or combinations of enol materials and siloxane materials.

[0131] In one embodiment, the dispersant includes at least one of n-butanol, tert-butanol, or ethanol, for example typical combinations include combinations of n-butanol and tert-butanol, combinations of n-butanol and ethanol, or combinations of ethanol and tert-butanol.

[0132] In one embodiment, the aqueous coating comprises, by weight, 78 to 92 parts of inorganic particles, 3 to 16 parts of adhesive material, 2.7 to 6 parts of binder, 0.25 to 1 part of wetting agent, and 0.1 to 0.5 parts of dispersant.

[0133] In some specific embodiments, the present invention provides a method for preparing the composite diaphragm described in the first aspect, the method comprising: preparing an oily coating slurry, applying an oily coating to one side surface of a base membrane to form an oily coating, thereby obtaining the composite diaphragm.

[0134] In one embodiment, the oily coating slurry includes an organic solvent, which includes at least one of N,N-dimethylacetamide (DMAc), N-methylpyrrolidone (NMP), N,N-dimethylformamide (DMF), or dimethyl sulfoxide (DMSO). Typical combinations include combinations of N,N-dimethylacetamide and N-methylpyrrolidone, N,N-dimethylacetamide and N,N-dimethylformamide, N,N-dimethylacetamide and dimethyl sulfoxide, or N,N-dimethylformamide and dimethyl sulfoxide.

[0135] In one embodiment, the oily coating slurry further includes a co-solvent for promoting the dissolution of the polymer material. The co-solvent includes at least one of calcium chloride (CaCl2), lithium chloride (LiCl), or potassium chloride (KCl). Typical examples of combinations include combinations of calcium chloride and lithium chloride, calcium chloride and potassium chloride, or potassium chloride and lithium chloride.

[0136] Understandably, the solvents in oil-based coating slurries should have high solubility in both polymer and adhesive materials. Furthermore, co-solvents can be added to promote the dissolution of polymer materials.

[0137] In one embodiment, the mass of the co-solvent accounts for 3.5% to 6% of the total mass of the oily coating slurry, for example, 3.5%, 3.8%, 4%, 4.2%, 4.5%, 4.8%, 5%, 5.3%, 5.5%, 5.8%, or 6%.

[0138] In one embodiment, the solid content of the oily coating slurry is 2% to 8%, such as 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, or 8%, and the viscosity is 30 cps to 60 cps, such as 30 cps, 33 cps, 35 cps, 38 cps, 40 cps, 43 cps, 45 cps, 48 ​​cps, 50 cps, 52 cps, 55 cps, 58 cps, or 60 cps.

[0139] In one embodiment, the oil coating process sequentially includes unwinding the base film, coating with the oil coating slurry, over-solidification, washing, and drying.

[0140] It should be noted that in this invention, when the oil coating process involves a washing process, the washing will remove the co-solvent, and its residual amount in the oil coating is negligible.

[0141] In one embodiment, the preparation method further includes preparing an aqueous coating slurry, and after forming the oily coating, without winding it up, directly applying an aqueous coating to the surface of the base film on the side away from the oily coating to form an aqueous coating, thereby obtaining the composite diaphragm.

[0142] The diaphragm preparation method of this invention is a one-time oil-based and water-based coating process, i.e., continuous oil-water coating. The process includes unwinding, applying an oil-based coating slurry, solidification bath molding, washing, drying, followed by water-based coating, and finally winding after the water-based coating dries. Traditional processes, on the other hand, require unwinding, applying an oil-based coating slurry, solidification bath molding, washing, drying, winding, unwinding, water-based coating, drying, and winding again. As can be seen from the comparison above, the solution of this invention avoids the complex process of multiple unwinding and winding cycles, facilitating large-scale continuous production and reducing costs. However, it should be emphasized that the preparation method should first perform oil-based coating to form an oil-based coating before performing water-based coating. If the water-based coating is formed first, the oil-based coating processes, such as solidification and washing, will affect the already formed water-based coating, even causing it to disperse or break.

[0143] It is also worth noting that in the specific implementation of oil-based coating and water-based coating, drying is required after wet coating in order to obtain a dry coating. In this field, the drying time is generally short and will not affect the adhesion of the obtained oil-based coating or its peel strength from the base film.

[0144] In one embodiment, the aqueous coating slurry includes an aqueous solvent, which includes water.

[0145] In one embodiment, the solid content of the aqueous coating slurry is 27% to 33%, such as 27%, 28%, 29%, 30%, 31%, 32%, or 33%, and the viscosity is 10 cps to 80 cps, such as 10 cps, 15 cps, 20 cps, 25 cps, 30 cps, 35 cps, 40 cps, 45 cps, 50 cps, 55 cps, 60 cps, 65 cps, 70 cps, 75 cps, or 80 cps.

[0146] In one embodiment, the areal density of the adhesive material in the water-based coating is 0.08 g / m². 2 ~0.56g / m 2 For example, 0.08g / m 2 0.1g / m 2 0.13g / m 2 0.15g / m 2 0.18g / m 2 0.2g / m 20.23g / m 2 0.26g / m 2 0.3g / m 2 0.35g / m 2 0.4g / m 2 0.43g / m 2 0.48g / m 2 0.5g / m 2 0.53g / m 2 or 0.56g / m 2+ wait.

[0147] In some specific implementations, the present invention provides a method for manufacturing a battery, the method comprising: providing a composite separator as described in the above embodiments, and providing a positive electrode, a negative electrode, and an electrolyte; assembling the positive electrode, the negative electrode, and the composite separator into a form, wherein the oily coating of the composite separator faces and contacts the positive electrode to obtain an electrode assembly; subjecting the electrode assembly to hot pressing to transfer the oily coating on the composite separator to the positive electrode, and then sequentially encapsulating, baking, and injecting electrolyte to obtain the battery.

[0148] In one embodiment, the assembly process includes a lamination process or a winding process.

[0149] In one embodiment, the lamination process includes Z-shaped lamination or thermal bonding (flying lamination) process.

[0150] In one embodiment, the hot pressing temperature is 60℃ to 90℃, for example, 60℃, 65℃, 70℃, 75℃, 80℃, 85℃, or 90℃; the surface pressure is 0.5MPa to 3MPa, for example, 0.5MPa, 0.8MPa, 1MPa, 1.2MPa, 1.5MPa, 1.8MPa, 2MPa, 2.3MPa, 2.5MPa, 2.8MPa, or 3MPa; and the time is 25s to 240s, for example, 25s, 50s, 75s, 100s, 120s, 140s, 160s, 180s, 200s, 220s, or 240s.

[0151] It should be noted that in this invention, the parameters of the hot pressing process should, on the one hand, meet the requirements for the assembly and forming of the electrode assembly, and on the other hand, meet the requirements for the transfer of the oily coating from the base film to the positive electrode sheet. Theoretically, the larger the hot pressing parameters, the more beneficial it is to the transfer of the oily coating. However, excessively large parameters may cause damage to the electrode assembly and easily lead to adverse effects such as the shedding of the negative electrode. Therefore, the hot pressing parameters should be reasonably adjusted according to the peel strength between the oily coating and the base film.

[0152] In one embodiment, the baking temperature is 95℃ to 105℃, such as 95℃, 96℃, 97℃, 98℃, 99℃, 100℃, 101℃, 102℃, 103℃, 104℃, or 105℃; the baking time is 8h to 12h, such as 8h, 8.3h, 8.5h, 8.8h, 9h, 9.2h, 9.5h, 9.8h, 10h, 10.2h, 10.5h, 10.8h, 11h, 11.2h, 11.5h, 11.8h, or 12h, and the baking causes the oily coating to transfer from the diaphragm to the positive electrode sheet.

[0153] As described above, in this invention, the oily coating has been transferred from the base film to the positive electrode sheet in processes prior to baking, such as hot pressing. Therefore, in actual operation, the self-crosslinking activation temperature of the adhesive material grafted with oxygen-containing groups in the oily coating should be controlled and selected based on the cell baking temperature, preferably at 95°C to 100°C, so that the oily coating and the surface oxygen-containing groups of the positive electrode sheet undergo a crosslinking reaction, thereby achieving the effect and purpose of improving adhesion and maintaining the coverage and stability of the transferred oily coating.

[0154] In one embodiment, based on the cell baking temperature, the self-crosslinking activation temperature of the adhesive material grafted with oxygen-containing groups in the oily coating is controlled and selected, preferably at 95°C to 100°C, so that the oily coating and the surface oxygen-containing groups of the positive electrode sheet undergo a crosslinking reaction.

[0155] In one embodiment, the manufacturing method further includes post-processing the resulting battery, the post-processing including pre-charging, formation, and capacity testing in sequence.

[0156] In one embodiment, the battery comprises a prismatic battery.

[0157] It is worth noting that, typically, prismatic batteries require a hot-pressing process compared to cylindrical and pouch batteries. However, for other types of batteries, appropriate hot-pressing and heat-treatment processes can be added during the battery assembly and manufacturing process, provided that the spirit of this invention is understood, to achieve the transfer of the oily coating or to further achieve the cross-linking and riveting effect between the oily coating and the positive electrode sheet, so that the oily coating can stably cover the surface of the positive electrode sheet and play an insulating role.

[0158] In one embodiment, the positive electrode active material of the positive electrode sheet includes at least one of lithium cobalt oxide, lithium manganese oxide, ternary materials, lithium iron phosphate, lithium manganese iron phosphate, or lithium-rich manganese-based materials, preferably including at least lithium iron phosphate.

[0159] As mentioned above, it is worth noting that this invention does not specifically limit the choice of materials for the positive electrode, negative electrode, and electrolyte in the battery. Positive electrode active materials, negative electrode active materials, binders, conductive agents, slurry solvents, lithium salts, electrolyte solvents, and electrolyte additives used in the art are all applicable to this invention.

[0160] In some specific embodiments, the present invention provides a battery obtained according to the manufacturing method described in the above embodiments.

[0161] Example 1

[0162] This embodiment provides a composite separator, the composite separator comprising:

[0163] The base film is made of aramid fiber, with a thickness of 12 μm, a pore size of 56 nm, a porosity of 35%, and an air permeability of 350 s / 100 cc.

[0164] An oily coating is disposed on one side surface of the base film; by weight, the oily coating comprises 23 parts of porous inorganic filler, 90 parts of polymer material, 70 parts of adhesive material, and 1 part of ionic conductive material; the porous inorganic filler is porous titanium dioxide, with a granular morphology, a particle size of 400 nm, and a pore size L of 33 nm; the adhesive material comprises polyacrylonitrile and polyvinylidene fluoride grafted with oxygen-containing groups using sodium dodecyl sulfate; the polymer material comprises polyimide; the ionic conductive material comprises lithium lanthanum titanium oxide, with a particle size of 850 nm and an ionic conductivity of 5 × 10⁻⁶. -3 S / cm; the peel strength F1 between the oily coating and the base film is 6 N / m, then L×F1=198×10 -9 N; the thickness H1 of the oily coating is 3 μm, and the air permeability is 44 s / 100cc; the adhesion F2 between the oily coating and the oily coating of another composite diaphragm is 33.2 N / m;

[0165] An aqueous coating is disposed on the surface of the base film on the side opposite to the oily coating. By weight, the aqueous coating comprises 86 parts of inorganic particles, 9 parts of adhesive material, 4 parts of binder, 0.68 parts of dispersant, and 0.32 parts of wetting agent. The inorganic particles are granular zirconium nitride with a particle size of 600 nm. The adhesive material is polyethylene microspheres with a glass transition temperature of 35°C and a particle size of D. 10 =1.5μm, D 50 =5.4μm, D 90 =9μm, D 99=12.8μm; the adhesive is methyl methacrylate with a glass transition temperature of 105℃; the wetting agent includes polyethylene glycol; the dispersant includes n-butanol; the thickness H2 of the water-based coating is 2.4μm, then the particle size D of the adhesive material is... 50 There is a D between the thickness H2 of the water-based coating and the thickness D. 50 / H2=2.25.

[0166] This embodiment also provides a method for preparing the composite separator, the method comprising:

[0167] S1. Preparation of oil-based coating slurry: Weigh and mix porous inorganic filler, polymer material, adhesive material, ionic conductivity material, solvent and co-solvent to obtain oil-based coating slurry; the solvent is N,N-dimethylformamide, and the co-solvent is calcium chloride; the mass of the co-solvent is controlled to be 4% of the total mass of the oil-based coating slurry, the solid content of the oil-based coating slurry is 5%, and the viscosity is 45 cps;

[0168] S2. Oil coating: The base film is unwound, and the oil coating slurry is applied to one side of the base film. Then, after solidification, washing and drying, an oil coating is formed.

[0169] S3. Preparation of water-based coating slurry: Weigh inorganic particles, adhesive material, binder, dispersant, wetting agent and solvent water and mix them to obtain water-based coating slurry;

[0170] S4. Water-based coating: Without winding the diaphragm, the water-based coating slurry is directly coated on the other side of the base film forming the oil-based coating, controlling the surface density of the adhesive material in the water-based coating to be 0.32 g / m². 2 After drying, an aqueous coating is formed, resulting in a composite diaphragm.

[0171] Example 2

[0172] This embodiment provides a composite membrane in which the pore size L of the porous inorganic filler is adjusted from 33 nm to 20 nm, thereby adjusting the peel strength F1 between the oily coating and the base film from 6 N / m to 8.5 N / m. Therefore, the value of L × F1 changes from 198 × 10⁻⁶. -9 N becomes 170×10 -9 N, except for the above, the other conditions are exactly the same as in Example 1.

[0173] Example 3

[0174] This embodiment provides a composite membrane in which the pore size L of the porous inorganic filler is adjusted from 33 nm to 50 nm, thereby adjusting the peel strength F1 between the oily coating and the base film from 6 N / m to 4.6 N / m. Therefore, the value of L × F1 changes from 198 × 10⁻⁶. -9 N becomes 230 × 10 -9 N, except for the above, the other conditions are exactly the same as in Example 1.

[0175] Example 4

[0176] This embodiment provides a composite membrane in which the adhesive material is replaced by conventional unmodified polyacrylonitrile and polyvinylidene fluoride instead of oxygen-containing grafted modified polyacrylonitrile and polyvinylidene fluoride. Except for the above, the other conditions are exactly the same as in Example 1.

[0177] Example 5

[0178] This embodiment provides a composite membrane in which the adhesive material is replaced by oxygen-grafted polyacrylonitrile and polyvinylidene fluoride with oxygen-grafted polyacrylonitrile, and the oxygen-grafted polyvinylidene fluoride is not used. Except for the above, the other conditions are exactly the same as in Example 1.

[0179] Example 6

[0180] This embodiment provides a composite membrane in which the adhesive material is replaced by polyvinylidene fluoride grafted with oxygen-containing groups instead of polyvinylidene fluoride grafted with oxygen-containing groups, and polyvinylidene fluoride grafted with oxygen-containing groups is not used. Except for the above, the other conditions are exactly the same as in Example 1.

[0181] Example 7

[0182] This embodiment provides a composite membrane that adjusts the particle size of the adhesive material in the aqueous coating, such that the particle size D of the adhesive material is adjusted. 50 Relationship D with the thickness H2 of the water-based coating 50 / H2=0.5, except for the above, the other conditions are exactly the same as in Example 1.

[0183] Example 8

[0184] This embodiment provides a composite membrane that adjusts the particle size of the adhesive material in the aqueous coating, such that the particle size D of the adhesive material is adjusted. 50 Relationship D with the thickness H2 of the water-based coating 50 / H2=0.8, except for the above, the other conditions are exactly the same as in Example 1.

[0185] Example 9

[0186] This embodiment provides a composite membrane that adjusts the particle size of the adhesive material in the aqueous coating, such that the particle size D of the adhesive material is adjusted. 50 Relationship D with the thickness H2 of the water-based coating 50 / H2 = 4.2, except for the above, the other conditions are exactly the same as in Example 1.

[0187] Example 10

[0188] This embodiment provides a composite membrane that adjusts the particle size of the adhesive material in the aqueous coating, such that the particle size D of the adhesive material is adjusted. 50 Relationship D with the thickness H2 of the water-based coating 50 / H2 = 4.5, except for the above, the other conditions are exactly the same as in Example 1.

[0189] Example 11

[0190] This embodiment provides a composite diaphragm, which is provided with the oil-based coating but not with the water-based coating. Except for the above, the other conditions are exactly the same as those in Embodiment 1.

[0191] Comparative Example 1

[0192] This comparative example provides a composite membrane in which the porous inorganic filler is replaced with a common inorganic filler that does not have a porous structure and has a pore size L of 0. Except for the above, the other conditions are exactly the same as those in Example 1.

[0193] Comparative Example 2

[0194] This comparative example provides a composite membrane in which the pore size L of the porous inorganic filler is adjusted from 33 nm to 12 nm, thereby increasing the peel strength F1 between the oily coating and the base film from 6 N / m to 12.5 N / m. The value of L × F1 then increases from 198 × 10⁻⁶. -9 N becomes 150 × 10 -9 N, except for the above, the other conditions are exactly the same as in Example 1.

[0195] Comparative Example 3

[0196] This comparative example provides a composite membrane in which the pore size L of the porous inorganic filler is adjusted from 33 nm to 100 nm, thereby adjusting the peel strength F1 between the oily coating and the base film from 6 N / m to 2.5 N / m. The value of L × F1 then changes from 198 × 10⁻⁶. -9 N becomes 250×10 -9 N, except for the above, the other conditions are exactly the same as in Example 1.

[0197] The adhesion force F2 between the oily coating and the oily coating of another composite diaphragm in Examples 2 to 11 and Comparative Examples 1 to 3 changed accordingly, as detailed in the characterization and testing results.

[0198] Application Example 1

[0199] This application example provides a battery, which contains a composite separator provided in any one of Examples 1 to 16 or Comparative Examples 1 to 3, and the method for manufacturing the battery includes:

[0200] The system provides a positive electrode, a negative electrode, and an electrolyte. The positive electrode is prepared by using lithium iron phosphate, a conductive agent, a binder, etc., to form a positive electrode slurry. The positive electrode slurry is coated onto carbon-coated aluminum foil and then treated to obtain the positive electrode. The mass percentage of lithium iron phosphate, the positive electrode active material, in the positive electrode active layer is 96.9%. The negative electrode is prepared by using artificial graphite, a conductive agent, a binder, a thickener, etc., to form a negative electrode slurry. The negative electrode slurry is coated onto copper foil and then treated to obtain the negative electrode. The mass percentage of artificial graphite, the negative electrode active material, in the negative electrode active layer is 96.4%. The electrolyte is an electrolyte solution composed of lithium salt, solvent, and additives. Specifically, the electrolyte solution includes 1.2M LiPF6, EC (ethylene carbonate), DMC (dimethyl carbonate), and EMC (ethyl methyl carbonate) in a volume ratio of 1:1:1, 2wt% VC (ethylene carbonate), and 1wt% FEC (fluoroethylene carbonate).

[0201] The positive electrode, negative electrode, and composite separator are assembled into an electrode assembly using a winding process, with the oil-based coating facing the positive electrode and the water-based coating facing the negative electrode. The resulting electrode assembly is hot-pressed for 100 seconds at 78°C and 2 MPa surface pressure. It is then packaged in a square shell, and the packaged cell is baked in an oven at 100°C for 10 hours. Electrolyte is then injected (liquid injection), and the cell is allowed to stand at high temperature for 24 hours. After standing, pre-charging, formation, and capacity testing are performed sequentially to obtain the battery.

[0202] Application Example 2

[0203] This application example provides a battery containing the composite separator provided in Example 1. In the manufacturing method of the battery, the positive electrode active material in the positive electrode sheet is changed from lithium iron phosphate to ternary material NCM523. Except for the above, the other conditions are exactly the same as in Application Example 1.

[0204] Application Comparative Example 1

[0205] This application provides a battery that uses the positive electrode, negative electrode, and electrolyte from Application Example 1, and uses a separator containing only the aqueous coating. The manufacturing method of the battery includes: coating the positive active layer of the positive electrode with an oily ceramic slurry, the oily ceramic slurry being composed of a porous inorganic filler, a binder, and a solvent, the porous inorganic filler and the solvent being the same as in Example 1, and the binder being polyacrylonitrile and polyvinylidene fluoride without oxygen-containing graft modification; then drying to form a ceramic surface coating; and then assembling the positive electrode with the ceramic surface coating, the separator containing the aqueous coating, and the negative electrode into a battery according to the scheme of Application Example 1.

[0206] Application Comparative Example 2

[0207] This application provides a battery that uses the positive electrode, negative electrode, and electrolyte from Application Example 2, and uses a separator containing only the aqueous coating. The manufacturing method of the battery includes: coating the positive active layer of the positive electrode with an oily ceramic slurry, the oily ceramic slurry being composed of a porous inorganic filler, a binder, and a solvent, the porous inorganic filler and the solvent being the same as in Example 1, and the binder being polyacrylonitrile and polyvinylidene fluoride without oxygen-containing graft modification; then drying to form a ceramic surface coating; and then assembling the positive electrode with the ceramic surface coating, the separator containing the aqueous coating, and the negative electrode into a battery according to the scheme of Application Example 2.

[0208] Characterization and testing:

[0209] I. The composite membranes obtained in the examples and comparative examples were subjected to the following tests: 150°C heat shrinkage test, membrane rupture temperature test, adhesion force F2 between the fresh membrane and the two oily coatings of the membrane, and peel strength F1 between the oily coating and the base membrane.

[0210] II. In the application examples and comparative examples, after the electrode assemblies undergo hot pressing, a portion of the electrode assemblies are subjected to a Hipot short-circuit test at 180°C. Another portion of the electrode assemblies from the same batch are disassembled, and the transfer rate (coverage) of the oily coating on the positive electrode is measured. After the cell is filled with electrolyte and allowed to stand at high temperature for 24 hours, the electrode assemblies are disassembled, and the coverage of the oily coating on the positive electrode is measured. The interface of the cell after capacity testing is disassembled, and any abnormalities are observed.

[0211] III. The batteries obtained in the corresponding use cases and application comparisons were subjected to hot box testing, nail penetration testing, and thermal spread testing at 25℃ (normal temperature) and 60℃ (high temperature).

[0212] The results are recorded in Tables 1 and 2.

[0213] Table 1

[0214]

[0215]

[0216] Table 2

[0217]

[0218] From Table 1 and Table 2, we can see that:

[0219] In Application Example 1 and Comparative Example 1, comparing Example 1 with Examples 2 and 3 and Comparative Examples 1-3 reveals that when 170×10 -9 N≤L×F1≤230×10 -9 At N, the coating transfer rate is good after hot pressing and liquid injection, the short-circuit rate test at 180℃ is satisfied, and the safety test is passed. When the inorganic filler is solid (without porous structure), or L×F1 < 170×10 -9 N, the effect of inorganic filler and heat-resistant polymer forming a homogeneous mixture deteriorates, and the coating peel strength increases, while the coating transfer effect worsens, affecting the short-circuit test and safety test results. When L×F1>230×10 -9 In the presence of inorganic fillers, the membrane adhesion weakens due to the floating of the filler in the oily slurry, affecting the coating transfer effect and consequently impacting battery safety. Similarly, comparing Application Example 2 with Comparative Application Example 2 shows that the positive electrode does not differentiate between lithium iron phosphate and ternary cathodes; both cathode systems can achieve the desired effect under this scheme. However, compared to the scheme of directly coating the ternary cathode, the cell safety deteriorates, and this design reduces energy density and affects cycle performance.

[0220] In Application Example 1 and Comparative Application Example 1, comparing Example 1 with Examples 4-6 revealed that when using conventional unmodified polyacrylonitrile and polyvinylidene fluoride, the coating coverage after liquid injection decreased from 99.2% after hot pressing to 90.3%, a significant decrease in coverage, resulting in poorer cell safety performance. However, when using oxygen-containing grafted modified polyacrylonitrile and polyvinylidene fluoride, the coating transfer effect after liquid injection decreased slightly, but did not affect the battery safety test performance.

[0221] In Application Example 1 and Comparative Application Example 1, comparing Example 1 with Examples 7 to 10 reveals that 0.8 ≤ D 50 When / H2≤4.2, it can prevent lithium plating at the interface, and the cell safety test can be passed; when D 50 When / H2 < 0.8, large adhesive particles are not exposed from the ceramic coating and cannot create gaps, leading to lithium plating at the interface and affecting cell safety; when D 50When H2 > 4.2, the large adhesive particles are large in size, exposing more of the ceramic coating. This can damage the integrity of the ceramic coating, increase thermal shrinkage, and worsen the safety of the battery cell. Furthermore, the adhesive layer is prone to powdering during the manufacturing process, and the accumulated dust particles become larger. These particles can be introduced into the battery cell and puncture the separator, further causing safety issues.

[0222] In Application Example 1 and Application Comparative Example 1, comparing Example 1 with Example 11 revealed that without an aqueous coating, the separator lacks one adhesive layer, resulting in poorer overall adhesion. This leads to a weakening of the electrode assembly's hardness after liquid injection, affecting the coverage of the oil-based coating on the positive electrode after liquid injection. Furthermore, the absence of a liquid storage space results in lithium plating at the interface. The lack of a ceramic heat-resistant coating also increases the thermal shrinkage of the separator. Overall, the cell's safety performance deteriorates.

[0223] From the above, we can see that:

[0224] 1) The oil-water continuous coating separator proposed in this invention exhibits a thermal shrinkage of less than 5% at 150°C. The oil-based coating has high adhesion and low peel strength between the coating and the base film, facilitating the transfer of the oil-based coating to the positive electrode after hot pressing. Furthermore, after baking, the adhesive material in the oil-based coating undergoes cross-linking due to modification, further enhancing adhesion. Therefore, after hot pressing and liquid injection, the coating coverage on the positive electrode is >99%, essentially completely transferred to the positive electrode and maintaining its integrity and stability. Even at higher temperatures, even if the separator shrinks, the oil-based coating, having been transferred to the positive electrode, still effectively isolates the positive and negative electrodes, thus passing the 180°C short-circuit test. In contrast, in Comparative Example 1, the separator has relatively poor heat resistance and high peel strength from the coating, resulting in relatively poor coating transfer and failure to pass both the 180°C short-circuit test and the safety test.

[0225] 2) The adhesive material in the aqueous coating of the negative electrode and the separator is used for bonding, which facilitates the adhesion between the two and provides space for electrolyte storage. No lithium plating occurs at the interface after the cell is fully charged. The hot box can withstand 240℃, and both the needle penetration and heat spread tests are passed. However, in Example 16, due to the absence of one aqueous coating layer, the separator's thermal shrinkage is worse, the coating conversion rate decreases significantly after electrolyte injection, short-circuit occurs during the high-temperature hitt test, and the cell safety test fails. Furthermore, lithium plating is present at the negative electrode interface after full charge, severely affecting electrical performance.

[0226] In summary, the oil-based and water-based continuous coating separator proposed in this invention effectively reduces the number of processing steps and lowers processing costs from a process perspective. From a separator performance perspective, this separator exhibits excellent heat resistance. The oil-based coating has good separator adhesion and weak peel strength with the base film, enabling the coating to be transferred to the positive electrode after hot pressing and electrolyte injection, with a coverage rate >99%. After cell baking, the oil-based coating further bonds to the positive electrode, improving adhesion and ensuring that the oil-based coating fully covers the electrode even when immersed in electrolyte. Furthermore, the water-based coating bonds to the negative electrode, optimizing the interface with the negative electrode, increasing the wetting space, and improving the lithium plating problem at the cell interface. At high temperatures, although the separator shrinks, the coating remains isolated from the positive and negative electrodes, greatly reducing the risk of short circuits caused by separator shrinkage. Batteries containing and using the composite separator described in this invention can pass hot box, needle penetration, and thermal runaway tests.

[0227] The present invention has been illustrated with the above embodiments to illustrate its detailed structural features. However, the present invention is not limited to the above detailed structural features, that is, it does not mean that the present invention must rely on the above detailed structural features to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions for the components used in the present invention, additions of auxiliary components, and selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

[0228] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

[0229] It should be noted that the above implementation methods are not limited to the listed numerical values ​​and typical combinations. Numerical values ​​or combinations not listed within the above numerical range can still be selected and applied to this invention.

[0230] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable way without contradiction. In order to avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.

[0231] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.

Claims

1. A composite diaphragm, characterized in that, The system includes a base film and an oily coating disposed on one side surface of the base film. The oily coating comprises a porous inorganic filler, a polymer material, and an adhesive material. The pore size of the porous inorganic filler is denoted as L (in nm), and the peel strength between the oily coating and the base film is denoted as F1 (in N / m). Therefore, 170 × 10⁻⁶ is a specific value. -9 N≤L×F1≤230×10 -9 N; The pore size L of the porous inorganic filler is 20nm~55nm; The adhesive materials include polyacrylonitrile modified with sodium dodecyl sulfate and polyvinylidene fluoride.

2. The composite diaphragm according to claim 1, characterized in that, The peel strength F1 between the oily coating and the base film is 3 N / m to 10 N / m.

3. The composite diaphragm according to claim 1, characterized in that, The particle size of the porous inorganic filler is 100nm~600nm.

4. The composite diaphragm according to claim 1, characterized in that, The thickness of the oily coating is denoted as H1, where H1 is 1μm to 5μm.

5. The composite diaphragm according to claim 1, characterized in that, The air permeability of the oil-based coating is 10s / 100cc to 70s / 100cc.

6. The composite diaphragm according to claim 1, characterized in that, By weight, the oily coating comprises 20 to 25 parts of the porous inorganic filler, 80 to 100 parts of polymer material, and 50 to 100 parts of adhesive material.

7. The composite diaphragm according to claim 1, characterized in that, The oily coating also includes an ionic conductive material.

8. The composite diaphragm according to claim 7, characterized in that, The particle size of the ionic conductive material is 600 nm to 1100 nm.

9. The composite diaphragm according to claim 7, characterized in that, The ionic conductivity of the ionic conductive material is 1×10⁻⁶. -4 S / cm ~ 1×10 -2 S / cm.

10. The composite diaphragm according to claim 7, characterized in that, The oily coating comprises 0.8 to 1.2 parts of the ionic conductive material by weight.

11. The composite diaphragm according to claim 1, characterized in that, The composite membrane further includes an aqueous coating disposed on the surface of the base membrane on the side away from the oily coating.

12. The composite diaphragm according to claim 11, characterized in that, The water-based coating comprises inorganic particles, adhesive materials, binders, dispersants, and wetting agents.

13. The composite diaphragm according to claim 12, characterized in that, The inorganic particles have a particle size of 100nm~1200nm.

14. The composite diaphragm according to claim 12, characterized in that, The adhesive layer material includes polyolefin materials and / or hydrogenated nitrile rubber.

15. The composite diaphragm according to claim 14, characterized in that, The polyolefin material includes at least one of polyethylene microspheres, polypropylene microspheres, or polybutene microspheres.

16. The composite diaphragm according to claim 12, characterized in that, The glass transition temperature of the adhesive layer material is -20℃ to 70℃.

17. The composite diaphragm according to claim 12, characterized in that, The particle size D of the adhesive layer material 10 For particles ≥1.3μm, 2.8μm ≤ particle size D 50 ≤7.1μm, particle size D 90 ≤11.2μm, particle size D 99 ≤13μm.

18. The composite diaphragm according to claim 11, characterized in that, The thickness of the water-based coating is denoted as H2, where H2 is 1μm to 3μm.

19. The composite diaphragm according to claim 12, characterized in that, The particle size D of the adhesive layer material 50 The relationship between the thickness H2 of the water-based coating and the thickness H2 is: 0.8 ≤ D 50 / H2≤4.

2.

20. The composite diaphragm according to claim 11, characterized in that, By weight, the water-based coating comprises 78 to 92 parts of inorganic particles, 3 to 16 parts of adhesive material, 2.7 to 6 parts of binder, 0.25 to 1 part of wetting agent and 0.1 to 0.5 parts of dispersant.

21. A method for preparing the composite diaphragm according to any one of claims 1-20, characterized in that, The preparation method includes: An oil-based coating slurry is prepared and applied to one side of the base membrane to form an oil-based coating, thereby obtaining the composite diaphragm.

22. The method for preparing the composite diaphragm according to claim 21, characterized in that, The oily coating slurry includes an organic solvent, which includes at least one of N,N-dimethylacetamide, N-methylpyrrolidone, N,N-dimethylformamide, or dimethyl sulfoxide.

23. The method for preparing the composite diaphragm according to claim 21, characterized in that, The oily coating slurry also includes a co-solvent, which includes at least one of calcium chloride, lithium chloride, or potassium chloride.

24. The method for preparing the composite diaphragm according to claim 23, characterized in that, The mass of the co-solvent accounts for 3.5% to 6% of the total mass of the oily coating slurry.

25. The method for preparing the composite diaphragm according to claim 21, characterized in that, The oily coating slurry has a solid content of 2% to 8% and a viscosity of 30 cps to 60 cps.

26. The method for preparing the composite diaphragm according to claim 21, characterized in that, The oil-based coating process includes, in sequence: unwinding the base film, coating with the oil-based coating slurry, over-solidification, washing, and drying.

27. The method for preparing the composite diaphragm according to claim 21, characterized in that, The preparation method further includes: preparing an aqueous coating slurry, and after forming the oily coating, without winding it up, directly applying an aqueous coating to the surface of the base film away from the oily coating to form an aqueous coating, thereby obtaining the composite diaphragm.

28. The method for preparing the composite diaphragm according to claim 27, characterized in that, The aqueous coating slurry includes an aqueous solvent, which includes water.

29. The method for preparing the composite diaphragm according to claim 27, characterized in that, The solid content of the water-based coating slurry is 27%~33%, and the viscosity is 10cps~80cps.

30. The method for preparing the composite diaphragm according to claim 27, characterized in that, The surface density of the adhesive material in the water-based coating is 0.08 g / m³. 2 ~0.56g / m 2 .

31. A method for manufacturing a battery, characterized in that, The manufacturing method includes: Provide a composite separator according to any one of claims 1-20 or a composite separator obtained by the preparation method according to any one of claims 21-30, and provide a positive electrode, a negative electrode and an electrolyte; assemble the positive electrode, the negative electrode and the composite separator into a shape, wherein the oily coating of the composite separator faces and contacts the positive electrode to obtain an electrode assembly; The electrode assembly is first hot-pressed to transfer the oily coating on the composite separator to the positive electrode sheet, and then encapsulated, baked and injected with electrolyte in sequence to obtain the battery.

32. The method for manufacturing a battery according to claim 31, characterized in that, The assembly process includes a lamination process or a winding process.

33. The method for manufacturing a battery according to claim 31, characterized in that, The hot pressing temperature is 60℃~90℃, the surface pressure is 0.5MPa~3MPa, and the time is 25s~240s.

34. The method for manufacturing a battery according to claim 31, characterized in that, The baking temperature is 95℃~105℃, and the time is 8h~12h.

35. The method for manufacturing a battery according to claim 31, characterized in that, The manufacturing method further includes post-processing of the resulting battery, which includes pre-charging, formation, and capacity testing in sequence.

36. The method for manufacturing a battery according to claim 31, characterized in that, The battery includes a prismatic battery.

37. The method for manufacturing a battery according to claim 31, characterized in that, The positive electrode active material of the positive electrode sheet includes at least one of lithium cobalt oxide, lithium manganese oxide, ternary materials, lithium iron phosphate, lithium manganese iron phosphate, or lithium-rich manganese-based materials.

38. The method for manufacturing a battery according to claim 31, characterized in that, The positive electrode active material of the positive electrode sheet includes at least lithium iron phosphate.

39. A battery, characterized in that, The battery is obtained by the manufacturing method according to any one of claims 31-38.

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