A preparation method of high and low temperature bonding slurry and lithium battery separator and lithium battery

Abstract

The present invention relates to the field of lithium battery technology, and proposes a method for preparing a high-low temperature adhesive slurry and a lithium battery separator, as well as a lithium battery. A high-low temperature adhesive slurry comprises the following components in parts by mass: 10-15 parts of an adhesive material, 5-15 parts of a thickener, 2-15 parts of a binder, 0-0.5 parts of a dispersant, and 50-80 parts of water. The adhesive material is a low-temperature adhesive material coated with a high-temperature adhesive material, and the raw materials of the adhesive material include a low-temperature adhesive material and a high-temperature adhesive material in a mass ratio of 1:9 to 9:1. The above technical solution solves the problem in the related art that aqueous adhesive materials for lithium batteries have poor adhesion to the electrode, and need to soften in a high-temperature environment to have good adhesion.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium batteries, and in particular to a method for preparing a high- and low-temperature bonding slurry and a lithium battery separator, and a lithium battery. Background Art

[0002] As the demand for battery energy density becomes higher and higher, the amount of emerging materials such as high nickel and silicon carbon is increasing. While these materials provide high capacity, they also have significant cyclic expansion and contraction during the charging and discharging process, causing the electrode group system composed of electrode-diaphragm-electrode to twist and deform during creeping and even form gaps. In the mildest case, it affects the shape of the battery and causes the battery pack to swell. In the worst case, it causes lithium deposition on the surface of the negative electrode, and the battery will have safety hazards such as internal short circuit, self-discharge, spontaneous combustion, and explosion.

[0003] In order to solve the above problems, the commonly used method is to modify the surface of the diaphragm to make it adhesive, so that an adhesive layer is formed between the electrode-diaphragm-electrode system and the interface is solidified; commonly used adhesive materials include polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP copolymer), polymethyl methacrylate (PMMA), polyacrylonitrile (PAN), etc.; the process routes used are oil-based (the polymer is dissolved in an organic solvent, the solution is coated, and the surface of the polyolefin base film is modified) and water-based (the polymer is dispersed in water to form a suspension of the polymer, the suspension is coated, and the surface of the polyolefin base film is modified).

[0004] The oil-based route has better bonding effect between the diaphragm and the electrode, but the cost of solvent and environmental control is high; the most commonly used in the water-based route is PVDF-HFP copolymer, which uses water as the dispersion system, does not generate waste gas or waste liquid, has low cost, and good environmental affinity, but has weak bonding strength with the electrode and needs to be softened in a high temperature environment to have better bonding. Summary of the Invention

[0005] The present invention provides a method for preparing a high-low temperature adhesive slurry and a lithium battery separator, and a lithium battery, which solves the problem in the related art that the aqueous adhesive material used in lithium batteries has poor adhesion to the electrode and needs to be softened in a high temperature environment to have good adhesion.

[0006] The technical solutions of the present invention are as follows:

[0007] A high-low temperature bonding slurry comprises the following components in parts by mass: 10-15 parts of bonding material, 5-15 parts of thickener, 2-15 parts of binder, 0-0.5 parts of dispersant, and 50-80 parts of water. The bonding material is a low-temperature bonding material coated with a high-temperature bonding material, and the raw materials of the bonding material include the low-temperature bonding material and the high-temperature bonding material in a mass ratio of 1:9-9:1.

[0008] As a further technical solution, the thickener includes one or both of sodium carboxymethyl cellulose and polyacrylamide.

[0009] As a further technical solution, the adhesive includes one or both of polyvinyl alcohol and acrylic acid.

[0010] As a further technical solution, the dispersant includes one or more of a quaternary ammonium salt dispersant, an acrylate polymer dispersant, and a polyester polymer dispersant.

[0011] As a further technical solution, the mass of the low-temperature adhesive material is ≤ the mass of the high-temperature adhesive material.

[0012] The present invention limits the mass of the low-temperature adhesive material to less than or equal to the mass of the high-temperature adhesive material, thereby further improving the high- and low-temperature bonding strength between the adhesive slurry and the electrode.

[0013] As a further technical solution, the mass ratio of the low-temperature adhesive material to the high-temperature adhesive material is 1:2~4.

[0014] The present invention limits the mass ratio of the low-temperature adhesive material to the high-temperature adhesive material to 1:2-4, which further improves the high and low temperature bonding strength between the adhesive slurry and the electrode.

[0015] As a further technical solution, the low-temperature adhesive material is a polyacrylate polymer, and the high-temperature adhesive material is a fluorine-containing polymer.

[0016] As a further technical solution, the polyacrylate polymer is polymethyl methacrylate, and the fluorine-containing polymer can be any polymer containing fluorine atoms, for example, it can be one or more of polytetrafluoroethylene, polyvinylidene fluoride, and polyvinylidene fluoride-hexafluoropropylene copolymer, preferably polyvinylidene fluoride-hexafluoropropylene copolymer.

[0017] As a further technical solution, the preparation method of the adhesive material includes the following steps: mixing the low-temperature adhesive material and the high-temperature adhesive material uniformly, melt-extruding, and granulating to obtain the adhesive material.

[0018] As a further technical solution, the bonding material is an ethylene-vinyl alcohol copolymer modified bonding material.

[0019] After the adhesive material of the present invention is modified by the ethylene-vinyl alcohol copolymer, the high and low temperature bonding strength between the adhesive slurry and the pole piece is further improved.

[0020] As a further technical solution, the raw materials of the ethylene-vinyl alcohol copolymer modified adhesive material include ethylene-vinyl alcohol copolymer and adhesive material in a mass ratio of 1 to 5:15.

[0021] As a further technical solution, the raw materials of the ethylene-vinyl alcohol copolymer modified adhesive material include ethylene-vinyl alcohol copolymer and adhesive material in a mass ratio of 1:5.

[0022] The present invention limits the raw materials of the ethylene-vinyl alcohol copolymer modified adhesive material to include the ethylene-vinyl alcohol copolymer and the adhesive material in a mass ratio of 1:5, further improving the high and low temperature bonding strength between the adhesive slurry and the electrode.

[0023] As a further technical solution, the preparation method of the ethylene-vinyl alcohol copolymer modified adhesive material includes the following steps: dissolving the ethylene-vinyl alcohol copolymer in a solvent, adding the adhesive material, mixing evenly, and drying to obtain the ethylene-vinyl alcohol copolymer modified adhesive material.

[0024] As a further technical solution, the solvent may be any solvent that dissolves ethylene-vinyl alcohol copolymer, preferably a mixed solvent of water and n-propanol.

[0025] The present invention also proposes a method for preparing a lithium battery separator, comprising the following steps: coating the high and low temperature adhesive slurry on the surface of a polyolefin base film, and drying the slurry to obtain a lithium battery separator.

[0026] As a further technical solution, the coating includes one of full coating, spot coating, intermittent coating, and stripe coating.

[0027] As a further technical solution, the full coating is performed by gravure coating;

[0028] As a further technical solution, the point coating is made into random dots by spraying or into a matrix of evenly distributed dots by using a point coating device.

[0029] The present invention also provides a lithium battery, the raw materials of which include the lithium battery separator.

[0030] The working principle and beneficial effects of the present invention are:

[0031] The present invention provides a high- and low-temperature bonding slurry with good bonding strength to the electrode, comprising a bonding material, a thickener, a binder, a dispersant and water, wherein the bonding material is a low-temperature bonding material coated with a high-temperature bonding material. The bonding material not only has room-temperature bonding properties, but also has strong high-temperature bonding properties. Its bonding temperature range covers most scenarios of lithium batteries from cell preparation to subsequent use, so that the diaphragm and the electrode have sufficient bonding properties, which can ensure the stable performance of the battery cell throughout its life cycle. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0033] Figure 1This is a 15.00K magnified SEM image of a lithium battery separator coated with a spot coating prepared with the high and low temperature adhesive slurry obtained in Example 1 of the present invention;

[0034] Figure 2 This is a 100-fold magnified SEM image of a lithium battery separator coated with a spot coating prepared with the high and low temperature adhesive slurry obtained in Example 1 of the present invention;

[0035] Figure 3 This is a 15.00K magnified SEM image of a lithium battery separator coated with a dot-coated adhesive coating prepared with the high and low temperature adhesive slurry obtained in Comparative Example 1 of the present invention. DETAILED DESCRIPTION

[0036] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0037] The parameters of the raw materials in the following examples and comparative examples are as follows:

[0038] Polymethyl methacrylate is PMMA CM-211;

[0039] The brand of polyvinylidene fluoride-hexafluoropropylene copolymer is Sigma, with an average Mw of 400,000 and an average Mn of 130,000;

[0040] Ethylene-vinyl alcohol copolymer was purchased from Shanghai Zhenzhun Biotechnology Co., Ltd., product number: 55207345;

[0041] Polyvinyl alcohol is PVA 2488;

[0042] The polyacrylamide is a cationic polyacrylamide with a weight average molecular weight of 18 million.

[0043] Example 1

[0044] S1, after uniformly mixing 13.5 parts of polymethyl methacrylate and 1.5 parts of polyvinylidene fluoride-hexafluoropropylene copolymer, melt-extrude and granulate to obtain an adhesive material;

[0045] S2, 69.9 parts of water and 0.1 parts of octadecyldimethylbenzyl ammonium chloride quaternary ammonium salt were mixed and stirred for 10 minutes, 15 parts of adhesive material were added and the stirring was continued for 90 minutes, 5 parts of sodium carboxymethyl cellulose were added and the stirring was continued for 10 minutes, and finally 10 parts of polyvinyl alcohol were added and stirred for 30 minutes to obtain a high and low temperature adhesive slurry (SEM image as shown in FIG. Figure 1 shown).

[0046] Example 2

[0047] S1, after uniformly mixing 13.5 parts of polymethyl methacrylate and 1.5 parts of polyvinylidene fluoride-hexafluoropropylene copolymer, melt-extrude and granulate to obtain an adhesive material;

[0048] S2. Mix 50 parts of water and 0.5 parts of EFKA-4560 high molecular weight polyacrylate dispersant and stir for 5 minutes, then add 10 parts of adhesive material and continue stirring for 10 minutes, add 10 parts of polyacrylamide and continue stirring for 5 minutes, and finally add 2 parts of acrylic acid and stir for 5 minutes to obtain a high and low temperature adhesive slurry.

[0049] Example 3

[0050] S1, after uniformly mixing 13.5 parts of polymethyl methacrylate and 1.5 parts of polyvinylidene fluoride-hexafluoropropylene copolymer, melt-extrude and granulate to obtain an adhesive material;

[0051] S2. Stir 80 parts of water and 13 parts of adhesive material for 120 minutes, add 15 parts of polyacrylamide and continue stirring for 20 minutes, and finally add 15 parts of acrylic acid and stir for 30 minutes to obtain a high and low temperature adhesive slurry.

[0052] Example 4

[0053] The only difference from Example 1 is: S1, 7.5 parts of polymethyl methacrylate and 7.5 parts of polyvinylidene fluoride-hexafluoropropylene copolymer are mixed uniformly, melt-extruded, and granulated to obtain an adhesive material.

[0054] Example 5

[0055] The only difference from Example 1 is: S1, 5 parts of polymethyl methacrylate and 10 parts of polyvinylidene fluoride-hexafluoropropylene copolymer are mixed evenly, melt-extruded, and granulated to obtain an adhesive material.

[0056] Example 6

[0057] The only difference from Example 1 is: S1, 3 parts of polymethyl methacrylate and 12 parts of polyvinylidene fluoride-hexafluoropropylene copolymer are mixed evenly, melt-extruded, and granulated to obtain an adhesive material.

[0058] Example 7

[0059] The only difference from Example 1 is: S1, 1.5 parts of polymethyl methacrylate and 13.5 parts of polyvinylidene fluoride-hexafluoropropylene copolymer are mixed uniformly, melt-extruded, and granulated to obtain an adhesive material.

[0060] Example 8

[0061] S1, after uniformly mixing 3 parts of polymethyl methacrylate and 12 parts of polyvinylidene fluoride-hexafluoropropylene copolymer, melt-extrude and granulate to obtain an adhesive material;

[0062] S2. Dissolve 1 g of ethylene-vinyl alcohol copolymer in 100 mL of a mixed solvent of water and n-propanol in a volume ratio of 1:1, add 15 g of adhesive material, stir at 500 rpm for 20 min, and mix thoroughly. Then, filter and dry to obtain an ethylene-vinyl alcohol copolymer modified adhesive material.

[0063] S3. Mix 69.9 parts of water and 0.1 parts of octadecyldimethylbenzyl ammonium chloride quaternary ammonium salt and stir for 10 minutes, then add 15 parts of ethylene-vinyl alcohol copolymer modified adhesive material and continue stirring for 90 minutes, add 5 parts of sodium carboxymethyl cellulose and continue stirring for 10 minutes, and finally add 10 parts of polyvinyl alcohol and stir for 30 minutes to obtain a high and low temperature adhesive slurry.

[0064] Example 9

[0065] The only difference from Example 8 is that 3 g of ethylene-vinyl alcohol copolymer is used.

[0066] Example 10

[0067] The only difference from Example 8 is: 5 g of ethylene-vinyl alcohol copolymer.

[0068] Comparative Example 1

[0069] 69.9 parts of water and 0.1 parts of octadecyldimethylbenzyl ammonium chloride quaternary ammonium salt were mixed and stirred for 10 minutes, and then 13.5 parts of polymethyl methacrylate and 1.5 parts of polyvinylidene fluoride-hexafluoropropylene copolymer were added and stirred for 90 minutes, and then 5 parts of sodium carboxymethyl cellulose were added and stirred for 10 minutes, and finally 10 parts of polyvinyl alcohol were added and stirred for 30 minutes to obtain a high and low temperature adhesive slurry (SEM image as shown in FIG. Figure 2 shown).

[0070] Preparation of lithium battery separator:

[0071] (1) The high and low temperature adhesive slurry obtained in Example 1 was spot-coated on the surface of a polyolefin base film at a speed of 130 m / min. The thickness of the polyolefin base film was 5 μm. The surface moisture of the coating was dried in an 80°C oven to obtain a spot-coated adhesive coating lithium battery separator with a coating thickness of 3.5 μm and a coverage of 15%. The SEM image is as follows: Figures 1 and 2 shown.

[0072] (2) The high and low temperature adhesive slurry obtained in Example 1 was roller-coated on the surface of a polyolefin base film at a speed of 100 m / min. The thickness of the polyolefin base film was 5 μm. The surface moisture of the coating was dried in an oven at 80°C to obtain a lithium battery separator with a fully roller-coated adhesive coating. The coating thickness was 1.5 μm.

[0073] (3) The high and low temperature adhesive slurry obtained in Example 1 was sprayed on the surface of a polyolefin base film at a speed of 130 m / min. The thickness of the polyolefin base film was 5 μm. The surface moisture of the coating was dried in an 80°C oven to obtain a sprayed adhesive coating lithium battery separator with a coating thickness of 3.5 μm and a coverage of 28%.

[0074] (4) The high and low temperature adhesive slurry obtained in Comparative Example 1 was spot-coated on the surface of a polyolefin base film at a speed of 130 m / min. The thickness of the polyolefin base film was 5 μm. The surface moisture of the coating was dried in an 80°C oven to obtain a spot-coated adhesive coating lithium battery separator with a coating thickness of 3.5 μm and a coverage of 15%. The SEM image is as follows: Figure 3 shown.

[0075] Performance testing:

[0076] The high and low temperature adhesive slurries obtained in Examples 1 to 10 and Comparative Example 1 were subjected to an adhesion test. The test method was as follows: referring to the method for preparing a lithium battery separator (1), the high and low temperature adhesive slurries obtained in Examples 1 to 10 and Comparative Example 1 were respectively prepared into spot-coated adhesive coating lithium battery separators and spot-coated adhesive coating pole pieces. Then, 100 mm × 30 mm samples were cut, and one side of the separator coating and one side of the pole piece coating were aligned. The samples were placed under a hot press and hot pressed at 80°C and 0.3 MPa pressure for 1 s. After that, an electronic tensile tester was used to measure the adhesion between the separator coating and the pole piece coating. The results are shown in Table 1.

[0077] Table 1 Adhesion between diaphragm coating and electrode coating

[0078]

[0079] As can be seen from Table 1, the bonding slurry provided by the present invention has an adhesion strength of more than 1.2 N / m at 30°C, more than 2.1 N / m at 50°C, more than 2.7 N / m at 70°C, and more than 3.3 N / m at 90°C, and has good high and low temperature adhesion with the electrode.

[0080] Compared with Comparative Example 1, in Example 1, low-temperature adhesive material is added to cover the high-temperature adhesive material, and the bonding strength of the obtained adhesive slurry at 30°C, 50°C, 70°C and 90°C is better than that of Comparative Example 1, indicating that low-temperature adhesive material covering high-temperature adhesive material as an adhesive material can improve the high and low temperature bonding strength between the adhesive slurry and the electrode.

[0081] The bonding strength of the bonding pastes obtained in Examples 4 to 7 at 30°C, 50°C, 70°C and 90°C is better than that of Example 1, indicating that the quality of the low-temperature bonding material is less than or equal to the quality of the high-temperature bonding material, further improving the high and low temperature bonding strength between the bonding paste and the electrode.

[0082] The bonding strength of the bonding slurries obtained in Examples 5-6 at 30°C, 50°C, 70°C and 90°C is better than that of Example 4 and Example 7, indicating that the mass ratio of low-temperature bonding material to high-temperature bonding material is 1:2-4, which further improves the high and low temperature bonding strength of the bonding slurry and the electrode.

[0083] The bonding strength of the bonding pastes obtained in Examples 8 to 10 at 30°C, 50°C, 70°C and 90°C is better than that of Example 6, indicating that the high and low temperature bonding strength of the bonding paste to the electrode is further improved after the bonding material is modified by the ethylene-vinyl alcohol copolymer.

[0084] The bonding strength of the bonding slurry obtained in Example 9 at 30°C, 50°C, 70°C and 90°C is better than that of Example 8 and Example 10, indicating that the mass ratio of ethylene-vinyl alcohol copolymer to the bonding material is 1:5, which further improves the high and low temperature bonding strength between the bonding slurry and the electrode.

[0085] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A high and low temperature bonding slurry, characterized in that: The invention comprises the following components in parts by mass: 10-15 parts of ethylene-vinyl alcohol copolymer modified adhesive material, 5-15 parts of thickener, 2-15 parts of binder, 0-0.5 parts of dispersant, and 50-80 parts of water. The raw materials of the ethylene-vinyl alcohol copolymer modified adhesive material include ethylene-vinyl alcohol copolymer and adhesive material in a mass ratio of 1 to 5:15; The adhesive material is a low-temperature adhesive material coated with a high-temperature adhesive material, and the raw materials of the adhesive material include the low-temperature adhesive material and the high-temperature adhesive material in a mass ratio of 1:2-4; The low-temperature adhesive material is a polyacrylate polymer, and the high-temperature adhesive material is a fluorine-containing polymer; The preparation method of the adhesive material comprises the following steps: uniformly mixing a low-temperature adhesive material and a high-temperature adhesive material, melt-extruding, and granulating to obtain the adhesive material; The preparation method of the ethylene-vinyl alcohol copolymer modified adhesive material comprises the following steps: dissolving the ethylene-vinyl alcohol copolymer in a solvent, adding an adhesive material, mixing evenly, and drying to obtain the ethylene-vinyl alcohol copolymer modified adhesive material.

2. A method for preparing a lithium battery separator, characterized in that: The method comprises the following steps: coating the high and low temperature bonding slurry according to claim 1 on the surface of a polyolefin base film, and drying the slurry to obtain a lithium battery separator.

3. A lithium battery, characterized in that: The raw materials include the lithium battery separator according to claim 2.

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