Battery separator, secondary battery and electrical device

Abstract

A battery separator, a secondary battery and an electrical device. The battery separator comprises a separator substrate and a coating provided on at least one surface of the separator substrate; the coating comprises an inorganic heat-resistant layer containing inorganic particles and polymer particles; the inorganic heat-resistant layer is provided with a first surface and a second surface which are oppositely arranged, and the first surface of the inorganic heat-resistant layer is in contact with the separator substrate; at least some of the polymer particles are embedded in the inorganic heat-resistant layer, and form protrusion structures on the second surface of the inorganic heat-resistant layer, the distribution density of the protrusion structures being 500-3700 protrusions per mm2.

Description

Battery separator, secondary battery, and electric device

[0001] Cross-reference to related applications

[0002] This application claims priority to Chinese Invention Patent Application No. CN202411364384.5, filed on September 27, 2024, the entire contents of which are incorporated herein by reference. TECHNICAL FIELD

[0003] The present application belongs to the technical field of batteries, and specifically relates to a battery separator, a secondary battery, and an electric device. BACKGROUND

[0004] New energy batteries dominated by lithium batteries are mainly composed of five parts: positive electrode material, negative electrode material, separator, electrolyte, and packaging material. The separator between the positive electrode material and the negative electrode material has the functions of preventing direct contact between the positive and negative electrodes, preventing short circuit of the battery, and transmitting ions, and is a key component that affects the cycle performance and safety performance of the battery. Currently, the commercialized battery separator is mainly a polyolefin separator based on polyethylene and polypropylene. Although this type of separator has good insulation, mechanical strength, and electrochemical stability, its thermal stability is poor. To improve the thermal stability of the polyolefin separator, an inorganic heat-resistant layer is formed on the surface of the polyolefin separator by coating an inorganic material such as ceramic. The commonly used coated separator is coated twice or three times, for example, a pure ceramic coating is first coated on the surface of the polyolefin separator by micro-gravure coating, and then an adhesive layer is coated on the surface of the pure ceramic coating by spraying, spotting, dipping, or rolling, to finally form a coated separator. However, the production cost of this coated separator is high, and it has great risks to the battery consistency, long-term reliability, and safety performance. SUMMARY

[0005] The present application provides a battery separator, a secondary battery, and an electric device.

[0006] To achieve the above-mentioned purpose, the technical solution adopted by the present application is as follows:

[0007] In a first aspect, the present application provides a battery separator, comprising a separator substrate and a coating layer provided on at least one side of the separator substrate; the coating layer comprises an inorganic heat-resistant layer containing inorganic particles and polymer particles.

[0008] The inorganic heat-resistant layer has a first surface and a second surface arranged oppositely, and the first surface of the inorganic heat-resistant layer is in contact with the separator substrate; at least part of the polymer particles are embedded in the inorganic heat-resistant layer, and a protruding structure is formed on the second surface of the inorganic heat-resistant layer; the distribution density of the protruding structure is 500-3700 pieces / mm 2 .

[0009] In some embodiments, the mass percentage of the polymer particles in the coating layer is 2% to 23%.

[0010] In some embodiments, the glass transition temperature of the polymer particles is 10°C to 100°C.

[0011] In some embodiments, the polymer particles include at least one of butyl methacrylate-acrylonitrile-styrene copolymer, butyl methacrylate-acrylamide-styrene copolymer, butyl methacrylate-acrylic acid-styrene copolymer, butyl methacrylate-ethylene oxide-styrene copolymer, butyl methacrylate-hexafluoropropylene-styrene copolymer, butyl methacrylate-acetate-styrene copolymer, and vinylidene fluoride-hexafluoropropylene-acrylate copolymer.

[0012] In some embodiments, the particle size Dv50 of the inorganic particles is 0.1 to 1.5 μm; and / or, the particle size Dv50 of the polymer particles is 2 to 9 μm.

[0013] In some embodiments, the inorganic heat-resistant layer further includes a first adhesive and a second adhesive;

[0014] The first adhesive includes at least one of polyacrylate, polyacrylic acid, polyacrylamide, and silica-phosphorus sol;

[0015] The second adhesive includes at least one of polyacrylate, sodium carboxymethyl cellulose, polyacrylic acid, polyacrylonitrile, polyacrylic acid copolymer, and silica-phosphorus sol.

[0016] In some embodiments, the mass percentage of the first adhesive in the coating layer is 1% to 10%; and / or, the mass percentage of the second adhesive in the coating layer is 0.01% to 2%.

[0017] In some embodiments, at least one of conditions (1) to (5) is satisfied:

[0018] (1) The average height of the protruding structure is 2.8 to 30 μm;

[0019] (2) There is a gap between the inorganic particles, and at least part of the polymer particles are embedded in the gap;

[0020] (3) The polymer particles are solid particles;

[0021] (4) The inorganic particles include at least one of alumina, boehmite, silica, magnesium hydroxide, and barium sulfate;

[0022] (5) The air permeability of the battery separator is 160 to 400 s / 100cc.

[0023] In some embodiments, the separator substrate comprises at least one of a polyolefin separator, a PET non-woven fabric, and a polyimide porous membrane.

[0024] In some embodiments, the inorganic particles comprise boehmite and barium sulfate.

[0025] In some embodiments, the mass ratio of the boehmite to the barium sulfate is 1:(0.1-0.5).

[0026] In a second aspect, the present application provides a secondary battery comprising a positive electrode sheet, a negative electrode sheet, and the battery separator described above.

[0027] In a third aspect, the present application provides an electric device comprising the secondary battery described above, wherein the secondary battery serves as a power supply for the electric device.

[0028] Compared with the prior art, the present application has the following beneficial effects:

[0029] The battery separator of the present application is provided with an inorganic heat-resistant layer on the surface of the separator substrate to enhance the thermal stability, and the inorganic heat-resistant layer is embedded with polymer particles to form a protruding structure, and the distribution density of the protruding structure is regulated to enhance the hot-press bonding performance of the battery separator and the electrode sheet, and to improve the wettability of the electrolyte, thereby significantly improving the cycle performance and safety performance of the battery. BRIEF DESCRIPTION OF DRAWINGS

[0030] FIG. 1 is a structural schematic diagram of the battery separator obtained in Example 1;

[0031] FIG. 2 is a structural schematic diagram of the battery separator obtained in Example 18;

[0032] FIG. 3 is a surface SEM image of the coating side of the battery separator obtained in Example 2;

[0033] FIG. 4 is a cross-sectional SEM image of the battery separator obtained in Example 2 before hot-pressing;

[0034] FIG. 5 is a cross-sectional SEM image of the battery separator obtained in Example 2 after hot-pressing. DETAILED DESCRIPTION

[0035] In order to better illustrate the purpose, technical scheme and advantages of the present application, the present application will be further described below in conjunction with specific examples and comparative examples, which are intended to provide a detailed understanding of the content of the present application, rather than limiting the present application. All other examples obtained by those of ordinary skill in the art without making creative efforts fall within the protection scope of the present application. The experimental reagents and instruments involved in the implementation of the present application are all common ordinary reagents and instruments unless otherwise specified.

[0036] According to a first aspect of the present application, a battery separator is provided, comprising a separator substrate and a coating layer provided on at least one side of the separator substrate; the coating layer comprises an inorganic heat-resistant layer containing inorganic particles and polymer particles;

[0037] The inorganic heat-resistant layer has oppositely arranged first and second surfaces, and the first surface of the inorganic heat-resistant layer is in contact with the separator substrate; at least part of the polymer particles are embedded in the inorganic heat-resistant layer, and form a protruding structure on the second surface of the inorganic heat-resistant layer; the distribution density of the protruding structure is 500-3700 / mm 2 .

[0038] The battery separator of the present application provides an inorganic heat-resistant layer on the surface of the separator substrate to enhance thermal stability, embeds polymer particles in the inorganic heat-resistant layer to form a protruding structure, controls the hot-press bonding performance of the battery separator by regulating the distribution density of the protruding structure, and forms a certain space between the battery separator and the electrode plate to accommodate electrolyte, thereby improving the wettability of the electrolyte and enhancing the cycle performance of the battery.

[0039] Optionally, the distribution density of the protruding structure can be one of or a range value of any two of 500 / mm 2 , 1000 / mm 2 , 1500 / mm 2 , 2000 / mm 2 , 2500 / mm 2 , 3000 / mm 2 , 3200 / mm 2 , 3700 / mm 2 .

[0040] Optionally, the separator substrate in the above battery separator can be selected from at least one of polyolefin separators (such as polyethylene separators, polypropylene separators), PET non-woven fabrics, and polyimide porous membranes.

[0041] In some embodiments, the inorganic heat-resistant layer comprises inorganic particles, and the particle size Dv50 ratio of the inorganic particles to the polymer particles is (0.1-1.5):(2-9). Optionally, the particle size Dv50 ratio of the inorganic particles to the polymer particles can be one of or a range value of any two of 0.1:9, 0.3:8, 0.5:7, 0.7:6, 0.9:5, 1.1:4, 1.3:3, 1.5:2.

[0042] By regulating the ratio of the particle size Dv50 of the inorganic particles and the polymer particles, the heat resistance and the bonding performance of the battery separator can be balanced. When the ratio of the particle size Dv50 of the inorganic particles and the polymer particles is within the above range, the battery separator can have good heat resistance, excellent bonding performance, and further improved cycle performance of the battery.

[0043] In some embodiments, the mass percentage of the polymer particles in the coating layer is 2% to 20%. Optionally, the mass percentage of the polymer particles in the coating layer can be one of 2%, 3%, 5%, 7%, 9%, 11%, 13%, 15%, 17%, 19%, 20%, or a range value of any two thereof.

[0044] The mass percentage of the polymer particles in the coating layer affects the heat resistance, direct current resistance (DCR), and hot-press bonding performance of the battery separator. When the mass percentage of the polymer particles in the coating layer is within the above range, the battery separator can not only maintain high heat resistance, low direct current resistance, and good kinetic performance, but also better enhance the hot-press bonding between the battery separator and the electrode sheet, and improve the processing and manufacturing performance of the battery separator.

[0045] In some embodiments, the glass transition temperature of the polymer particles is 10°C to 100°C. Optionally, the glass transition temperature of the polymer particles can be one of 10°C, 20°C, 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, 100°C, or a range value of any two thereof.

[0046] The glass transition temperature of the polymer particles mainly affects the hot-press bonding performance of the battery separator. When the glass transition temperature is 10°C to 100°C, the battery separator can have better hot-press bonding performance. The glass transition temperature (Tg) of the polymer particles can be measured by differential scanning calorimetry (DSC), and can refer to the standard GB / T19466.

[0047] In some embodiments, the polymer particles include at least one of butyl methacrylate-acrylonitrile-styrene copolymer, butyl methacrylate-acrylamide-styrene copolymer, butyl methacrylate-acrylic acid-styrene copolymer, butyl methacrylate-ethylene oxide-styrene copolymer, butyl methacrylate-hexafluoropropylene-styrene copolymer, butyl methacrylate-acetate-styrene copolymer, and vinylidene fluoride-hexafluoropropylene-acrylate copolymer. When the polymer particles are selected from the above polymers, the battery separator can not only have better hot-press bonding performance, but also be beneficial to improving the electrochemical performance of the assembled battery.

[0048] In some embodiments, the particle size Dv50 of the inorganic particles is 0.1-1.5 μm; and / or, the particle size Dv50 of the polymer particles is 2-9 μm. Optionally, the particle size Dv50 of the inorganic particles can be one of 0.1 μm, 0.2 μm, 0.4 μm, 0.6 μm, 0.8 μm, 1.0 μm, 1.2 μm, 1.4 μm, 1.5 μm or a range value between any two of them; and / or, the particle size Dv50 of the polymer particles can be one of 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm or a range value between any two of them.

[0049] The combination of the inorganic particles and the polymer particles with the above-mentioned particle size Dv50 can make the battery separator have better heat resistance, heat-press bonding performance and kinetic performance, while effectively reducing the risk of powder dropping and tab misplacement. The particle size Dv50 of the inorganic particles or the polymer particles can be measured by Malvern 3000 laser particle size analyzer.

[0050] In some embodiments, the inorganic heat-resistant layer further comprises a first adhesive and a second adhesive.

[0051] The first adhesive comprises at least one of polyacrylate, polyacrylic acid, polyacrylamide and silica-phosphorus sol.

[0052] The second adhesive comprises at least one of polyacrylate, sodium carboxymethyl cellulose, polyacrylic acid, polyacrylonitrile, polyacrylic acid copolymer and silica-phosphorus sol.

[0053] The first adhesive mainly plays a bonding role in the coating to ensure that a stable solidified interface is formed between the inorganic particles and between the inorganic particles and the surface of the separator substrate, thereby improving the heat resistance of the battery separator. The mass percentage of the first adhesive in the coating can be 1%-10%, preferably 2%-6%, and specifically can be one of 1%, 2%, 3%, 4%, 5%, 7%, 8%, 9%, 10% or a range value between any two of them.

[0054] The second adhesive mainly plays a dispersing and bonding role in the coating. The mass percentage of the second adhesive in the coating can be 0.01%-2%, preferably 0.5%-1.5%, and specifically can be one of 0.01%, 0.1%, 0.2%, 0.3%, 0.4%, 0.6%, 0.8%, 1%, 1.2%, 1.4%, 1.6%, 1.8%, 2% or a range value between any two of them.

[0055] When the mass ratio of the first adhesive in the coating is 1% to 10%, or the mass ratio of the second adhesive in the coating is 0.01% to 2%, the heat resistance, uniformity and electrolyte infiltration performance of the battery separator can be improved.

[0056] In some embodiments, the average height of the protruding structure is 2.8 to 30 μm. In some embodiments, the average height of the protruding structure is 2.8 to 12 μm. When the average height of the protruding structure is 2.8 to 30 μm, the battery separator can maintain good adhesion between the battery separator and the pole piece while having better kinetic performance.

[0057] In some embodiments, gaps exist between the inorganic particles in the inorganic heat-resistant layer, and at least part of the polymer particles are embedded in the gaps.

[0058] In some embodiments, the polymer particles are solid particles. When the polymer particles are embedded in the gaps between the inorganic particles, more infiltration channels can be provided for the electrolyte of the battery during the cycle process, and more buffer space can be provided for the expansion of the pole piece during the cycle process, thereby improving the long-term performance of the battery.

[0059] In some embodiments, the inorganic particles include at least one of alumina (Al2O3), boehmite (γ-AlOOH), silicon dioxide, magnesium hydroxide, and barium sulfate. In some embodiments, the inorganic particles are a mixture of boehmite and barium sulfate; the combination of boehmite and barium sulfate as inorganic particles can ensure that the surface density of the battery separator is reduced while better heat resistance is considered, and further, to optimize the heat resistance of the battery separator, the mass ratio of boehmite and barium sulfate in the inorganic particles is 1:(0.1 to 0.5).

[0060] In some embodiments, the air permeability of the battery separator is 160 to 400 s / 100cc. Alternatively, the air permeability of the battery separator can be specifically one of 160 s / 100cc, 200 s / 100cc, 250 s / 100cc, 300 s / 100cc, 350 s / 100cc, 400 s / 100cc, or a range value of any two thereof. Research has found that the battery separator with the above air permeability range can have lower impedance and better kinetic performance.

[0061] The air permeability of the above battery separator can be measured by the following test method: taking an area >10 mm 2 The separator sample is placed in the air permeability tester Gurley device, and the time required for 100 cc of gas to pass through is counted.

[0062] In a second aspect, the application provides a secondary battery, comprising a positive electrode sheet, a negative electrode sheet, and the battery separator described above; the average gap between the battery separator and the positive electrode sheet and the negative electrode sheet is 0-30 μm; in some embodiments, the average gap between the battery separator and the positive electrode sheet and the negative electrode sheet can be 2.7-28.2 μm; in some embodiments, the average gap between the battery separator and the positive electrode sheet and the negative electrode sheet can be 0-9 μm. By adjusting the average gap between the separator and the electrode sheet to be within the range of 0-30 μm, more infiltration channels can be provided for the electrolyte, and a buffer gap can be provided for the expansion of the electrode sheet during the cycle process, thereby better improving the long-term performance of the battery.

[0063] In some embodiments, the secondary battery comprises at least one of a wound soft-pack battery, a wound aluminum shell battery, a wound cylindrical battery, a stacked soft-pack battery, a stacked aluminum shell battery, etc. The electrode sheet in the secondary battery comprises a positive electrode sheet and a negative electrode sheet, the positive electrode active material in the positive electrode sheet can comprise at least one of a nickel-cobalt-manganese ternary material, a lithium iron phosphate material, a lithium iron manganese phosphate material; the negative electrode active material in the negative electrode sheet comprises at least one of a carbon-based material, a silicon-based material, a tin-based material.

[0064] In a third aspect, the application provides an electric device comprising the secondary battery described above, which serves as the power supply of the electric device.

[0065] In order to clearly understand the technical solutions of the application, the application will be further described in detail below with reference to specific embodiments, which should not be construed as limiting the scope of the application.

[0066] Embodiment 1

[0067] The embodiment provides a battery separator (as shown in FIG. 1), and a preparation method thereof comprises the following steps:

[0068] S1, mix inorganic particles (α-Al2O3, particle size Dv50 is 0.5 μm), a first adhesive (polyacrylate), a second adhesive (sodium hydroxymethyl cellulose), and polymer particles (butyl methacrylate-acrylonitrile-styrene copolymer, particle size Dv50 is 5.1 μm) according to a mass ratio of 90.0:4.9:1.0:4.0, and then stir and mix uniformly after adding a wetting agent substance, to obtain a coating slurry;

[0069] S2, use a micro-gravure process to coat the coating slurry in S1 on one side of a separator substrate (a PE separator with a thickness of 7 μm), the coating thickness is 2 μm, then dry at 60°C, and then roll up and cut for standby use.

[0070] Embodiment 2

[0071] This example provides a battery separator, which differs from Example 1 in that the mass ratio of the inorganic particles, the first binder, the second binder, and the polymer particles in Step S1 is 87.7:5.1:1.1:6.0.

[0072] Example 3

[0073] This example provides a battery separator, which differs from Example 1 in that the mass ratio of the inorganic particles, the first binder, the second binder, and the polymer particles in Step S1 is 85.5:3.1:1.1:8.1.

[0074] Example 4

[0075] This example provides a battery separator, which differs from Example 1 in that the mass ratio of the inorganic particles, the first binder, the second binder, and the polymer particles in Step S1 is 80.9:5.1:1.2:12.1.

[0076] Example 5

[0077] This example provides a battery separator, which differs from Example 1 in that the mass ratio of the inorganic particles, the first binder, the second binder, and the polymer particles in Step S1 is 76.4:6.2:1.3:16.1.

[0078] Example 6

[0079] This example provides a battery separator, which differs from Example 1 in that the mass ratio of the inorganic particles, the first binder, the second binder, and the polymer particles in Step S1 is 71.8:6.6:1.4:20.2.

[0080] Example 7

[0081] This example provides a battery separator, which differs from Example 1 in that the mass ratio of the inorganic particles, the first binder, the second binder, and the polymer particles in Step S1 is 69.5:6.8:1.4:22.2.

[0082] Example 8

[0083] This example provides a battery separator, which differs from Example 1 in that the mass ratio of the inorganic particles, the first binder, the second binder, and the polymer particles in Step S1 is 92.3:4.7:1.0:2.0.

[0084] Example 9

[0085] This example provides a battery separator, which differs from Example 1 in that the mass ratio of the inorganic particles, the first binder, the second binder, and the polymer particles in Step S1 is 83.99:10:0.01:6.

[0086] Example 10

[0087] This example provides a battery separator, which differs from Example 1 in that the mass ratio of the inorganic particles, the first binder, the second binder, and the polymer particles in Step S1 is 91:1:2:6.

[0088] Example 11

[0089] This example provides a battery separator, which differs from Example 2 in that the particle size Dv50 of the inorganic particles in Step S1 is 0.1 pm and the particle size Dv50 of the polymer particles is 9 pm.

[0090] Example 12

[0091] This example provides a battery separator, which differs from Example 2 in that the particle size Dv50 of the inorganic particles in Step S1 is 1.5 pm and the particle size Dv50 of the polymer particles is 2 pm.

[0092] Example 13

[0093] This example provides a battery separator, which differs from Example 2 in that the material of the polymer particles in Step S1 is butyl methacrylate-acrylamide-styrene copolymer.

[0094] Example 14

[0095] This example provides a battery separator, which differs from Example 2 in that the material of the polymer particles in Step S1 is butyl methacrylate-acrylic acid-styrene copolymer.

[0096] Example 15

[0097] This example provides a battery separator, which differs from Example 2 in that the material of the polymer particles in Step S1 is butyl methacrylate-ethylene oxide-styrene copolymer.

[0098] Example 16

[0099] This example provides a battery separator, which differs from Example 2 in that the material of the polymer particles in Step S1 is butyl methacrylate-hexafluoro-propylene-styrene copolymer.

[0100] Example 17

[0101] This example provides a battery separator, which differs from Example 2 in that the material of the polymer particles in Step S1 is vinylidene fluoride-hexafluoro-propylene-acrylate copolymer.

[0102] Example 18

[0103] The present embodiment provides a battery separator, which differs from Example 2 in that the coating slurry in S1 is coated on both sides of the separator substrate in step S2, and a structural diagram of the obtained battery separator is shown in Figure 2.

[0104] Example 19

[0105] The present embodiment provides a battery separator, which differs from Example 2 in that the inorganic particles in step S1 are boehmite and barium sulfate with a mass ratio of 1:0.3, the first binder is polyacrylamide, and the second binder is polyacrylic acid.

[0106] Comparative Example 1

[0107] The present comparative example provides a battery separator, which differs from Example 2 in that the mass ratio of the inorganic particles, the first binder, the second binder, and the polymer particles in step S1 is 92.4:5.4:1.2:1.

[0108] Comparative Example 2

[0109] The present comparative example provides a battery separator, which differs from Example 1 in that the mass ratio of the inorganic particles, the first binder, the second binder, and the polymer particles in step S1 is 60:6.8:1.4:31.8.

[0110] Table 1: Each component in the coating of the battery separator in each example and comparative example

[0111] Performance test

[0112] 1. The battery separators in each example and comparative example were tested for performance, and the test results are shown in Table 2, with the specific test methods as follows:

[0113] 1) Test method for the thickness of the battery separator: Take 2-3 m of the battery separator and place it under the probe of the Mahr thickness tester to test, and record the thickness data displayed by the equipment.

[0114] 2) Test method for the air permeability of the battery separator: Take an area >10 mm 2 The battery separator sample was placed in the air permeability tester Gurley equipment, and the time required for 100 cc of gas to pass through was counted.

[0115] 3) Test method for the distribution density of the protruding structure: Place the battery separator sample on the scanning electron microscope SEM sample stage, randomly select 10 positions, take pictures at a magnification of 500 times at each position, and count the number of protruding structures in the field of view (170x227 μm 2The number of the protruding structures of the battery separator is counted, and then the average number of the protruding structures is calculated, that is, the distribution density of the protruding structures in the battery separator is obtained.

[0116] 4) Test method of average height of protruding structures: using a Malvern thickness tester, the battery separator is placed flat on the test table after being stacked in 5 layers, the thickness H1 of the battery separator, the thickness H2 of the separator substrate and the thickness H3 of the inorganic heat-resistant layer are tested, and the average height H0 of the protruding structures is H1-H2-H3.

[0117] Table 2 Performance of battery separators in each example and comparative example

[0118] 2. The battery separators in each example and comparative example are stacked in order with the positive electrode sheet and the negative electrode sheet, with the battery separator being in the middle of the positive and negative electrode sheets, and are wound to form an inner core, and are heat-pressed to shape (temperature 95℃, pressure 3MPa, time 30s), and after tab welding, a bare battery cell is obtained, and the bare battery cell is placed in an outer packaging aluminum plastic film, and is placed in an oven at 85±10℃ for 24h, and electrolyte is injected into the dried battery, and after standing, formation and capacity distribution, the preparation of the lithium ion soft package battery is completed;

[0119] The preparation of the above positive electrode sheet includes the following steps:

[0120] Lithium iron phosphate, polyvinylidene fluoride (PVDF), carbon black and polyvinylpyrrolidone dry powder are mixed in a weight ratio of 97.55:1.8:0.5:0.15, then added into N-methyl pyrrolidone (NMP) and stirred thoroughly, forming a positive electrode slurry with a solid content of 65% and a viscosity of 6000-9000mPa·s, then the positive electrode slurry is coated on a carbon-coated aluminum foil, dried, rolled, and cut to obtain a positive electrode sheet.

[0121] The preparation of the above negative electrode sheet includes the following steps:

[0122] Graphite, carbon black, sodium carboxymethyl cellulose, polyacrylonitrile and styrene acrylate dry powder are mixed in a weight ratio of 97:0.3:0.6:1.0:1.1, then added into deionized water and stirred thoroughly, forming a negative electrode slurry with a solid content of 48.5% and a viscosity of 2000-8000mPa·s, then the negative electrode slurry is coated on a copper foil, dried, rolled, and cut to obtain a negative electrode sheet.

[0123] The above electrolyte is a 1mol / L lithium hexafluorophosphate solution, wherein the solvent is composed of DMC:EMC:EC in a volume ratio of 5:2:3, and contains 5% of fluoroethylene carbonate (FEC).

[0124] The above lithium ion soft package battery is subjected to performance testing, and the test results are shown in Table 3, and the specific test methods are as follows:

[0125] 1) Average gap between the coating of the battery separator film and the electrode sheet in the inner core (R angle average gap of the roll core): Average gap = [total thickness of the roll core - (total thickness of the positive electrode sheet + total thickness of the negative electrode sheet + total thickness of the separator)] / (number of winding layers - 1).

[0126] 2) Battery DCR test method: adjust the battery to 50% SOC state in a 25°C constant temperature box, then test the direct current impedance value corresponding to the battery when discharged at 5C direct current for 10s.

[0127] 3) Battery cycle performance test method: cycle the lithium ion soft package battery at 1C / 1C in the 0-100% SOC range under a 25°C constant temperature box to a capacity retention rate of 2500 cycles, record the capacity retention rate of the battery at this time, and the voltage interval is 2.5V-3.65V. Capacity retention rate (%) = discharge specific capacity of the 2500th cycle / discharge specific capacity of the first cycle * 100%.

[0128] Table 3 Performance of lithium ion soft package batteries corresponding to the battery separator in each example and comparative example

[0129] According to the data in Table 3, the battery DCR of the lithium ion soft package batteries in Examples 1-19 is all ≤0.70 mΩ, and the capacity retention rate after 2500 cycles is all above 75%, indicating that the battery separator of the application has a low direct current impedance value, which can give the battery excellent long-term cycle performance. According to Comparative Example 2, if the distribution density of the protruding structures is greater than 3700 / mm 2 , the battery DCR will increase, and the cycle performance will decrease, which may be due to the decrease of the inorganic particle proportion in the separator when the distribution density is too large, causing the decrease of the stability of the battery separator.

[0130] In addition, the surface of the battery separator in Example 2 and the cross section before and after hot pressing were observed, and the results are shown in Figures 3-5, wherein Figure 3 is a surface graph of the battery separator, Figure 4 is a cross section graph of the battery separator before hot pressing, and Figure 5 is a cross section graph of the battery separator after hot pressing. According to Figures 3 and 4, it can be seen that the protruding structures in the battery separator are composed of polymer particles of different sizes embedded in the inorganic heat-resistant layer in the form of spheres or sphere-like shapes; at the same time, according to Figure 5, it can be found that the protruding structures in the battery separator and the active material layer in the electrode sheet are bonded under the action of hot pressing, and a certain electrolyte containing space is formed between the battery separator and the electrode sheet.

[0131] Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the present application and not to limit the scope of protection of the present application. Although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application can be modified or equivalently replaced without departing from the essence and scope of the technical solutions of the present application.

Claims

1.A battery separator comprising a separator base and a coating layer provided on at least one side of the separator base; the coating layer comprising an inorganic heat-resistant layer containing inorganic particles and polymer particles. The inorganic heat-resistant layer has a first surface and a second surface arranged oppositely, and the first surface of the inorganic heat-resistant layer is in contact with the diaphragm base; at least part of the polymer particles are embedded in the inorganic heat-resistant layer, and form a convex structure on the second surface of the inorganic heat-resistant layer; the distribution density of the convex structure is 500-3700 / mm 2 . 2.The battery separator according to claim 1, wherein the polymer particles account for 2% to 23% in mass in the coating layer. 3.The battery separator according to claim 1, wherein the polymer particles have a glass transition temperature of 10℃ to 100℃. 4.The battery separator according to claim 1, wherein the polymer particles comprise at least one of butyl methacrylate-acrylonitrile-styrene copolymer, butyl methacrylate-acrylamide-styrene copolymer, butyl methacrylate-acrylic acid-styrene copolymer, butyl methacrylate-ethylene oxide-styrene copolymer, butyl methacrylate-hexafluoropropylene-styrene copolymer, butyl methacrylate-acetate-styrene copolymer, and vinylidene fluoride-hexafluoropropylene-acrylate copolymer. 5.The battery separator according to claim 1, wherein the inorganic particles have a particle size Dv50 of 0.1 to 1.5μm; and / or, the polymer particles have a particle size Dv50 of 2 to 9μm. 6.The battery separator according to claim 1, wherein the inorganic heat-resistant layer further comprises a first binder and a second binder; the first binder comprises at least one of polyacrylate, polyacrylic acid, polyacrylamide, and silica sol; and the second binder comprises at least one of polyacrylate, sodium carboxymethyl cellulose, polyacrylic acid, polyacrylonitrile, polyacrylic acid copolymer, and silica sol. 7.The battery separator according to claim 6, wherein the first binder accounts for 1% to 10% in mass in the coating layer; and / or, the second binder accounts for 0.01% to 2% in mass in the coating layer. 8.The battery separator according to claim 1, wherein the battery separator satisfies at least one of conditions (1) to (5): (1) the average height of the protruding structure is 2.8 to 30μm; (2) there are gaps between the inorganic particles, and at least part of the polymer particles are embedded in the gaps; (3) the polymer particles are solid particles; (4) the inorganic particles comprise at least one of alumina, boehmite, silica, magnesium hydroxide, and barium sulfate; and (5) the battery separator has a gas permeability of 160 to 400s / 100cc. 9.The battery separator according to claim 1, wherein the separator base comprises at least one of polyolefin separator, PET non-woven fabric, and polyimide porous membrane. 10.The battery separator according to claim 1, wherein the inorganic particles comprise boehmite and barium sulfate. 11.The battery separator according to claim 10, wherein the mass ratio of the boehmite to the barium sulfate is 1:(0.1 to 0.5). 12.A secondary battery comprising a positive electrode sheet, a negative electrode sheet, and the battery separator according to any one of claims 1 to 11. 13.An electric device comprising the secondary battery according to claim 12 as a power supply for the electric device. ​ ​ ​ ​ ​ ​ ​ ​

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