A diaphragm coating composition, composite diaphragm, secondary battery and electrical device

Abstract

The present invention relates to a diaphragm coating composition, a composite diaphragm, a secondary battery and an electrical device, and belongs to the field of battery technology. The diaphragm coating composition of the present invention comprises polyvinylidene fluoride and its copolymer derivatives, a ceramic material and a water-soluble high molecular polymer, and satisfies 3%≤C / (A+B)≤15%; wherein A is the weight fraction of the polyvinylidene fluoride and its copolymer derivatives, B is the weight fraction of the ceramic material, and C is the weight fraction of the water-soluble high molecular polymer; the weight average molecular weight of the polyvinylidene fluoride and its copolymer derivatives is ≤1 million g / mol. The porous coating formed by the diaphragm coating composition not only has a uniform macroporous structure to accelerate lithium ion transmission, but also has good bonding performance with the pole piece.

Description

Technical Field

[0001] The invention belongs to the technical field of batteries, and in particular relates to a diaphragm coating composition, a composite diaphragm, a secondary battery and an electrical device. Background Art

[0002] At present, commercialized diaphragms are mainly polyolefin diaphragms such as polyethylene single-layer film, polypropylene single-layer film or PP / PE / PP three-layer film diaphragm, but polyolefin diaphragms have poor thermal stability, pose safety hazards, and have poor wettability to electrolytes, resulting in poor battery cycle performance. In order to improve safety and electrochemical performance, polyolefin diaphragms are usually modified by coating technology. For example, inorganic ceramic coating, water-based PVDF coating, oily PVDF coating, oily aramid coating, etc. The role or effect of different coating materials is also different. The main role of inorganic ceramic or aramid coating materials is to improve the high-temperature heat shrinkage performance of the diaphragm to improve safety performance, while the main role of PVDF coating is to increase the hardness of the battery cell during hot pressing and maintain the consistency of the thickness of the battery cell. However, although the conventional PVDF porous coating has good adhesion properties, its pore size is small, which is not conducive to the rapid transmission of lithium ions. Summary of the invention

[0003] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a diaphragm coating composition, a composite diaphragm, a secondary battery and an electrical device.

[0004] To achieve the above object, the technical solution adopted by the present invention is:

[0005] In a first aspect, the present invention provides a membrane coating composition, comprising polyvinylidene fluoride and its copolymer derivatives, ceramic materials and water-soluble high molecular polymers, and satisfying 3%≤C / (A+B)≤15%;

[0006] Wherein, A is the weight percentage of the polyvinylidene fluoride and its copolymer derivatives, B is the weight percentage of the ceramic material, and C is the weight percentage of the water-soluble high molecular polymer;

[0007] The weight average molecular weight of the polyvinylidene fluoride and its copolymer derivatives is ≤1 million g / mol.

[0008] As an embodiment of the present invention, the following components are included in parts by weight: 70 to 100 parts of polyvinylidene fluoride and its copolymer derivatives, 0 to 30 parts of ceramic materials, and 3 to 15 parts of water-soluble high molecular polymers.

[0009] As an embodiment of the present invention, the weight average molecular weight of the polyvinylidene fluoride and its copolymer derivatives is 200,000 to 1,000,000 g / mol.

[0010] As an embodiment of the present invention, the water-soluble high molecular polymer includes at least one of polyethylene glycol, polyvinyl alcohol, polyacrylamide and polyvinyl pyrrolidone.

[0011] As an embodiment of the present invention, the ceramic material includes at least one of aluminum oxide, magnesium oxide, calcium oxide, barium oxide, zinc oxide, silicon dioxide, titanium dioxide, zirconium dioxide, magnesium hydroxide, aluminum hydroxide, boehmite, and ceramic fiber.

[0012] As an embodiment of the present invention, the polyvinylidene fluoride copolymer derivative includes at least one of vinylidene fluoride-chlorotrifluoroethylene copolymer, vinylidene fluoride-trifluoroethylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-perfluoromethyl vinyl ether copolymer, vinylidene fluoride-propylene fluoride copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, vinylidene fluoride-hexafluoropropylene copolymer, and vinylidene fluoride-tetrafluoroethylene copolymer.

[0013] As an embodiment of the present invention, the polyvinylidene fluoride copolymer derivative is PVDF-HFP, and the mass content ratio of HFP to PVDF in the PVDF-HFP is 1% to 8.7%.

[0014] In a second aspect, the present invention provides a composite diaphragm, comprising a base membrane and a porous coating disposed on at least one surface of the base membrane, wherein the porous coating is made of a coating slurry comprising the above-mentioned diaphragm coating composition.

[0015] In a third aspect, the present invention provides a secondary battery comprising the above-mentioned composite separator.

[0016] In a fourth aspect, the present invention provides an electrical device, comprising the above-mentioned secondary battery, wherein the secondary battery serves as a power supply for the electrical device.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] The present invention combines polyvinylidene fluoride and its copolymer derivatives with a specific weight-average molecular weight with a ceramic material and a water-soluble high molecular polymer in a specific mass ratio to form a diaphragm coating composition. After the composition is mixed with a solvent, the water-soluble high molecular polymer is dissolved and evenly dispersed in the polyvinylidene fluoride and its copolymer derivatives to form a coating slurry; the coating slurry is coated on the surface of the base film and subjected to a coagulation bath to complete phase transformation, and the water-soluble high molecular polymer is dissolved to form a uniform macroporous structure, while also enabling the formed porous coating to have good bonding properties with the electrode. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a SEM image of the surface of the composite diaphragm in Example 1 (magnification is 5000 times);

[0020] Figure 2 This is the SEM image of the surface of the composite diaphragm in Comparative Example 1 (magnification is 5000 times). DETAILED DESCRIPTION

[0021] In order to better illustrate the purpose, technical solutions and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments and comparative examples, the purpose of which is to understand the content of the present invention in detail, rather than to limit the present invention. All other embodiments obtained by those of ordinary skill in the art without making creative work premise belong to the protection scope of the present invention. The experimental reagents and instruments involved in the implementation of the present invention, unless otherwise specified, are all commonly used common reagents and instruments.

[0022] According to a first aspect of the present invention, there is provided a membrane coating composition, comprising polyvinylidene fluoride and its copolymer derivatives, a ceramic material and a water-soluble high molecular polymer, and satisfying 3%≤C / (A+B)≤15%;

[0023] Wherein, A is the weight percentage of the polyvinylidene fluoride and its copolymer derivatives, B is the weight percentage of the ceramic material, and C is the weight percentage of the water-soluble high molecular polymer;

[0024] The weight average molecular weight of the polyvinylidene fluoride and its copolymer derivatives is ≤1 million g / mol.

[0025] The present invention combines polyvinylidene fluoride and its copolymer derivatives with a specific weight-average molecular weight with a ceramic material and a water-soluble high molecular polymer in a specific mass ratio to form a diaphragm coating composition. After the composition is mixed with a solvent, the water-soluble high molecular polymer is dissolved and evenly dispersed in the polyvinylidene fluoride and its copolymer derivatives to form a coating slurry; when the coating slurry is coated on the surface of the base film and undergoes a coagulation bath to complete phase transformation, the water-soluble high molecular polymer is dissolved to form a uniform macroporous structure, and at the same time, the formed porous coating can have good bonding properties with the electrode.

[0026] Moreover, the study found that when the weight-average molecular weight of polyvinylidene fluoride and its copolymer derivatives is greater than 1 million g / mol, the molecular chains of polyvinylidene fluoride and its copolymer derivatives will be entangled with each other, making it difficult for water-soluble polymers to be evenly dispersed in polyvinylidene fluoride and its copolymer derivatives, which is not conducive to the formation of a macroporous structure in the coating and also reduces the uniformity of the pores.

[0027] Optionally, the weight average molecular weight of the polyvinylidene fluoride and its copolymer derivatives can be any one of 1,000,000 g / mol, 800,000 g / mol, 700,000 g / mol, 600,000 g / mol, 500,000 g / mol, 400,000 g / mol, 300,000 g / mol, and 200,000 g / mol, or any two of them. The weight average molecular weight of polyvinylidene fluoride and its copolymer derivatives can be measured by gel permeation chromatography (GPC).

[0028] Optionally, the polyvinylidene fluoride copolymer derivative can be copolymerized by vinylidene fluoride monomer and other comonomers, and the other comonomers can be one or more selected from hexafluoropropylene, tetrafluoroethylene, trifluoroethylene, trichloroethylene, acrylic acid, methacrylic acid, methacrylate and vinyl acetate.

[0029] Optionally, C / (A+B) can be any one of or any two of 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 10%, 11%, 12%, 13%, 14%, 15%.

[0030] As an embodiment of the present invention, the following components are included in parts by weight: 70 to 100 parts of polyvinylidene fluoride and its copolymer derivatives, 0 to 30 parts of ceramic materials, and 3 to 15 parts of water-soluble high molecular polymers.

[0031] Optionally, the weight proportion of polyvinylidene fluoride and its copolymer derivatives in the above-mentioned diaphragm coating composition can be 70 parts, 75 parts, 80 parts, 85 parts, 90 parts, 95 parts, and 100 parts; the weight proportion of ceramic material can be 5 parts, 10 parts, 15 parts, 20 parts, 25 parts, and 30 parts; the weight proportion of water-soluble high molecular polymer can be 3 parts, 4 parts, 5 parts, 6 parts, 7 parts, 8 parts, 9 parts, 10 parts, 11 parts, 12 parts, 13 parts, 14 parts, and 15 parts.

[0032] As an embodiment of the present invention, the weight average molecular weight of the polyvinylidene fluoride and its copolymer derivatives is 200,000 to 1,000,000 g / mol.

[0033] As an embodiment of the present invention, the water-soluble high molecular polymer includes at least one of polyethylene glycol (PEG), polyvinyl alcohol (PVA), polyacrylamide (PAM), and polyvinyl pyrrolidone (PVP).

[0034] As an embodiment of the present invention, the ceramic material includes at least one of aluminum oxide, magnesium oxide, calcium oxide, barium oxide, zinc oxide, silicon dioxide, titanium dioxide, zirconium dioxide, magnesium hydroxide, aluminum hydroxide, boehmite, and ceramic fiber.

[0035] As an embodiment of the present invention, the polyvinylidene fluoride copolymer derivative includes at least one of vinylidene fluoride-chlorotrifluoroethylene copolymer, vinylidene fluoride-trifluoroethylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-perfluoromethyl vinyl ether copolymer, vinylidene fluoride-propylene fluoride copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, vinylidene fluoride-hexafluoropropylene copolymer, and vinylidene fluoride-tetrafluoroethylene copolymer.

[0036] As an embodiment of the present invention, the polyvinylidene fluoride copolymer derivative is PVDF-HFP (vinylidene fluoride-hexafluoropropylene copolymer), and the mass content ratio of HFP to PVDF in the PVDF-HFP is 1% to 8.7%.

[0037] As an embodiment of the present invention, the components of the separator coating composition further include an organic solvent, and the organic solvent includes at least one of acetone, dimethylacetamide, N,N-dimethylformamide, and N-methylpyrrolidone.

[0038] In a second aspect, the present invention provides a composite diaphragm, comprising a base membrane and a porous coating disposed on at least one surface of the base membrane, wherein the porous coating is made of a coating slurry comprising the above-mentioned diaphragm coating composition.

[0039] Optionally, the base film is any one of a polyolefin film, a PET film, and a PI film; specifically, the polyolefin film may be a PE film, a PP film, a PE / PP composite film, and the like.

[0040] The preparation method of the composite diaphragm includes the following steps: coating a coating slurry (including polyvinylidene fluoride and its copolymer derivatives, ceramic materials, water-soluble polymers, and organic solvents) on the surface of a base film, and then completing a phase conversion through a coagulation liquid (composed of an organic solvent and water, wherein the mass fraction of the organic solvent is 15% to 50%), and then washing and drying with water to obtain a composite diaphragm with a porous coating.

[0041] In a third aspect, the present invention provides a secondary battery comprising the above-mentioned composite separator.

[0042] In a fourth aspect, the present invention provides an electrical device, comprising the above-mentioned secondary battery, wherein the secondary battery serves as a power supply for the electrical device.

[0043] In order to clearly understand the technical solution of the present invention, the present invention is further described in detail below in conjunction with specific embodiments. These embodiments should not be construed as limiting the scope of protection claimed by the present invention.

[0044] PVDF-1, weight average molecular weight 600,000 g / mol, brand 21216, manufacturer Solvay, USA;

[0045] PVDF-2, weight average molecular weight of 800,000 g / mol, brand 6020, manufacturer Solvay, USA;

[0046] PVDF-3, weight average molecular weight is 1.2 million g / mol, brand 5130, manufacturer Solvay, USA;

[0047] PVA, brand 17-88, manufacturer Anhui Wanwei Group Co., Ltd.;

[0048] PEG, brand name PEG-4000, manufacturer: Jiangsu Haian Petrochemical.

[0049] Example 1

[0050] This embodiment provides a membrane coating composition, including the following components in parts by weight: 90 parts of PVDF-1 (weight average molecular weight of 600,000 g / mol), 10 parts of ceramic material (alumina), and 10 parts of water-soluble high molecular polymer (PVA), that is, C / (A+B)=10%.

[0051] This embodiment provides a composite diaphragm, which is prepared by the following preparation method:

[0052] S1, uniformly dispersing the ceramic material in an organic solvent (NMP) to obtain a dispersion;

[0053] S2, dispersing and dissolving PVDF in the dispersion in S1 to obtain a first slurry;

[0054] S3, mixing PVA and an organic solvent (NMP) in a mass ratio of 5:95 to obtain a second slurry;

[0055] S4, adding the first slurry in S2 to the second slurry in S3 and mixing them evenly to obtain a diaphragm coating slurry;

[0056] S5. Coat the membrane coating slurry in S4 on one side of the polyolefin base film (PE membrane), pass through a coagulation tank (the coagulation liquid in the coagulation tank consists of NMP and water, wherein the mass content of NMP is 15% to 50%), wash with pure water, and dry at 35 to 60°C to obtain a composite membrane with a porous coating.

[0057] Example 2

[0058] This embodiment provides a membrane coating composition, including the following components in parts by weight: 90 parts of PVDF-1 (weight average molecular weight of 600,000 g / mol), 10 parts of ceramic material (alumina), and 5 parts of water-soluble high molecular polymer (PVA), that is, C / (A+B)=5%.

[0059] This embodiment provides a composite membrane, and its preparation method is the same as that of embodiment 1.

[0060] Example 3

[0061] This embodiment provides a membrane coating composition, including the following components in parts by weight: 70 parts of PVDF-1 (weight average molecular weight of 600,000 g / mol), 30 parts of ceramic material (alumina), and 15 parts of water-soluble high molecular polymer (PVA), that is, C / (A+B)=15%.

[0062] This embodiment provides a composite membrane, and its preparation method is the same as that of embodiment 1.

[0063] Example 4

[0064] This embodiment provides a membrane coating composition, including the following components in parts by weight: 100 parts of PVDF-1 (weight average molecular weight of 600,000 g / mol), 0 parts of ceramic material, and 3 parts of water-soluble high molecular polymer (PVA), that is, C / (A+B)=3%.

[0065] This embodiment provides a composite membrane, and its preparation method is the same as that of embodiment 1.

[0066] Example 5

[0067] This embodiment provides a membrane coating composition, including the following components in parts by weight: 90 parts of PVDF-2 (weight average molecular weight of 800,000 g / mol), 10 parts of ceramic material (alumina), and 10 parts of water-soluble high molecular polymer (PVA), that is, C / (A+B)=10%.

[0068] This embodiment provides a composite membrane, and its preparation method is the same as that of embodiment 1.

[0069] Example 6

[0070] This embodiment provides a membrane coating composition, including the following components in parts by weight: 90 parts of PVDF-1 (weight average molecular weight of 600,000 g / mol), 10 parts of ceramic material (boehmite), and 10 parts of water-soluble high molecular polymer (PEG), that is, C / (A+B)=10%.

[0071] This embodiment provides a composite membrane, and its preparation method is the same as that of embodiment 1.

[0072] Comparative Example 1

[0073] This comparative example provides a membrane coating composition, including the following components in parts by weight: 90 parts of PVDF-1 (weight average molecular weight of 600,000 g / mol), 10 parts of ceramic material (alumina), and 1 part of water-soluble high molecular polymer (PVA), that is, C / (A+B)=1%.

[0074] This comparative example provides a composite diaphragm, and its preparation method is the same as that of Example 1.

[0075] Comparative Example 2

[0076] This comparative example provides a membrane coating composition, including the following components in parts by weight: 90 parts of PVDF-1 (weight average molecular weight of 600,000 g / mol), 10 parts of ceramic material (alumina), and 17 parts of water-soluble high molecular polymer (PVA), that is, C / (A+B)=17%.

[0077] This comparative example provides a composite diaphragm, and its preparation method is the same as that of Example 1.

[0078] Comparative Example 3

[0079] This comparative example provides a membrane coating composition, including the following components in parts by weight: 90 parts of PVDF-3 (weight average molecular weight is 1.2 million g / mol), 10 parts of ceramic material (alumina), and 10 parts of water-soluble high molecular polymer (PVA), that is, C / (A+B)=10%.

[0080] This comparative example provides a composite diaphragm, and its preparation method is the same as that of Example 1.

[0081] Table 1 Weight parts of each component of the diaphragm coating composition in Examples 1 to 6 and Comparative Examples 1 to 3

[0082] Components PVDF-1 PVDF-2 PVDF-3 Alumina boehmite PVA PEG C / (A+B) Example 1 90 / / 10 / 10 / 10％ Example 2 90 / / 10 / 5 / 5％ Example 3 70 / / 30 / 15 / 15％ Example 4 100 / / / / 3 / 3％ Example 5 / 90 / 10 / 10 / 10％ Example 6 90 / / / 10 / 10 10％ Comparative Example 1 90 / / 10 / 1 / 1％ Comparative Example 2 90 / / 10 / 17 / 17％ Comparative Example 3 / / 90 10 / 10 / 10％

[0083] Performance Testing

[0084] 1) Bonding strength: The porous coating side of the composite membrane in each embodiment and comparative example is hot-pressed with the positive electrode sheet (the current collector is aluminum foil, and the positive electrode active layer is composed of LiCoO2, a conductive agent (conductive carbon black) and a binder (polyvinylidene fluoride) in a mass ratio of 96:2:2) at 1 MPa and 95°C for 3 min, and then a 180° peeling tensile test is performed on the composite membrane and the positive electrode sheet using a universal tensile testing machine. The tensile speed is 100 mm / min. The force detected when the positive electrode sheet is peeled off is the bonding strength between the composite membrane and the positive electrode sheet.

[0085] 2) Air permeability: Under standard atmospheric pressure, the air permeability of the porous coating in the composite membrane was tested using a Wang Yan-type air permeability meter for 5 seconds; the air permeability of the porous coating = the air permeability of the composite membrane - the air permeability of the PE membrane.

[0086] Table 2 Performance of the composite membranes of various embodiments and comparative examples

[0087]

[0088] According to the data in Table 2, Figure 1 and Figure 2 It can be seen that the bonding strength between the composite diaphragm and the positive electrode plate in Examples 1 to 6 is ≥11N / m, and the air permeability of the porous coating in the composite diaphragm is ≤11s / 100mL, indicating that the diaphragm coating composition of the present invention can effectively improve the porosity of the diaphragm coating, and the formed porous coating not only has a uniform macroporous structure to accelerate lithium ion transmission, but also has good bonding properties with the electrode plate.

[0089] At the same time, according to Comparative Examples 1 and 2, it can be found that when C / (A+B) is too small, the pores of the porous coating in the composite diaphragm are small. Although it can maintain a high bonding strength between the composite diaphragm and the positive electrode, it also causes a significant decrease in the air permeability of the porous coating; and when C / (A+B) is too large, although it is conducive to improving the air permeability of the porous coating, it will also significantly reduce the bonding strength between the composite diaphragm and the positive electrode. In addition, according to Comparative Example 3, when the weight-average molecular weight of PVDF is too large, the effect of improving the bonding strength is limited, and the air permeability of the porous coating cannot be effectively improved.

[0090] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the essence and scope of the technical solution of the present invention.

Claims

1. A membrane coating composition, characterized in that Including polyvinylidene fluoride and its copolymer derivatives, ceramic materials and water-soluble high molecular polymers, and satisfying 3%≤C / (A+B)≤15%; Wherein, A is the weight percentage of the polyvinylidene fluoride and its copolymer derivatives, B is the weight percentage of the ceramic material, and C is the weight percentage of the water-soluble high molecular polymer; The weight average molecular weight of the polyvinylidene fluoride and its copolymer derivatives is ≤1 million g / mol.

2. The diaphragm coating composition according to claim 1, characterized in that The invention comprises the following components by weight: 70 to 100 parts of polyvinylidene fluoride and its copolymer derivatives, 0 to 30 parts of ceramic materials and 3 to 15 parts of water-soluble high molecular polymers.

3. The diaphragm coating composition according to claim 1, characterized in that The weight average molecular weight of the polyvinylidene fluoride and its copolymer derivatives is 200,000 to 1,000,000 g / mol. 4 . The membrane coating composition according to claim 1 , wherein the water-soluble high molecular polymer comprises at least one of polyethylene glycol, polyvinyl alcohol, polyacrylamide and polyvinyl pyrrolidone.

5. The diaphragm coating composition according to claim 1, characterized in that The ceramic material includes at least one of aluminum oxide, magnesium oxide, calcium oxide, barium oxide, zinc oxide, silicon dioxide, titanium dioxide, zirconium dioxide, magnesium hydroxide, aluminum hydroxide, boehmite, and ceramic fiber.

6. The diaphragm coating composition according to claim 1, characterized in that The polyvinylidene fluoride copolymer derivative includes at least one of vinylidene fluoride-chlorotrifluoroethylene copolymer, vinylidene fluoride-trifluoroethylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-perfluoromethyl vinyl ether copolymer, vinylidene fluoride-propylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, vinylidene fluoride-hexafluoropropylene copolymer, and vinylidene fluoride-tetrafluoroethylene copolymer.

7. The diaphragm coating composition according to claim 6, characterized in that The polyvinylidene fluoride copolymer derivative is PVDF-HFP, and the mass content ratio of HFP to PVDF in the PVDF-HFP is 1% to 8.7%.

8. A composite diaphragm, characterized in that: The invention comprises a base film and a porous coating layer provided on at least one surface of the base film, wherein the porous coating layer is made of a coating slurry comprising the diaphragm coating composition according to any one of claims 1 to 7.

9. A secondary battery, characterized in that: Comprising the composite diaphragm as described in claim 8.

10. An electrical device, characterized in that: The secondary battery according to claim 9 is included, and the secondary battery is used as a power supply for the electrical device.

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