Secondary battery, battery module, battery pack and device

Abstract

The present application relates to a secondary battery, a battery module, a battery pack and a device for use in the field of electrochemistry. The secondary battery comprises the positive pole piece, the negative pole piece and the isolating membrane, and the isolating membrane is simple in preparation process and excellent in heat resistance. In addition, the secondary battery and the device of the present application have good safety and good cycle performance.

Description

Technical Field

[0001] The present application relates to a secondary battery used in the electrochemical field, and its related battery module, battery pack and device. Background Art

[0002] Secondary batteries are widely used in various consumer electronic products and electric vehicles due to their outstanding features such as light weight, no pollution, and no memory effect.

[0003] With the continuous development of the new energy industry, customers have put forward higher requirements for the use of secondary batteries. For example, the energy density of secondary batteries is designed to be higher and higher. However, the improvement of battery energy density is often not conducive to balancing kinetic performance, electrochemical performance or safety performance.

[0004] Therefore, how to make the battery have both cycle performance and safety performance is a key challenge in the field of battery design. Summary of the invention

[0005] The purpose of the present application is to provide a secondary battery, aiming to make the secondary battery have better cycle performance and safety performance.

[0006] In order to achieve the above-mentioned object, the first aspect of the present application provides an isolation film, which includes: a substrate and a coating disposed on at least one surface of the substrate. The coating includes inorganic particles and organic particles. The organic particles include first organic particles, which are embedded in the inorganic particles and form protrusions on the surface of the coating. The first organic particles are secondary particles, and the number average particle size of the first organic particles is ≥13 μm. The area coverage of the first organic particles on the surface of the coating is ≤10%.

[0007] Compared with the prior art, the present application at least has the following beneficial effects: The isolation membrane of the present application includes inorganic particles and the first organic particles in the same coating, and the first organic particles are specially designed. With the mutual cooperation of the two, the battery can have good cycle performance and safety performance while maintaining a higher energy density.

[0008] In any embodiment of the present application, the area coverage of the first organic particles on the coating surface is 0.5%-8%; optionally 0.8%-5%. When the area coverage of the first organic particles is within the given range, the cycle performance and safety performance of the battery can be further improved.

[0009] In any embodiment of the present application, the number average particle size of the first organic particles is 15 μm - 25 μm. When the number average particle size of the first organic particles is within the given range, the cycle performance and safety performance of the battery can be further improved.

[0010] In any embodiment of the present application, the first organic particles include homopolymers or copolymers of fluorine-containing olefinic monomer units, homopolymers or copolymers of olefinic monomer units, homopolymers or copolymers of unsaturated nitrile monomer units, homopolymers or copolymers of alkylene oxide monomer units, and one or more modified compounds of the above homopolymers or copolymers.

[0011] In any embodiment of the present application, the first organic particles include polytetrafluoroethylene, polychlorotrifluoroethylene, polyvinyl fluoride, polyvinylidene fluoride, polyethylene, polypropylene, polyacrylonitrile, polyethylene oxide, copolymers of different fluorine-containing olefin monomer units, copolymers of fluorine-containing olefin monomer units and vinyl monomer units, copolymers of fluorine-containing olefin monomer units and acrylic monomer units, copolymers of fluorine-containing olefin monomer units and acrylic ester monomer units, and one or more of the modified compounds of the above homopolymers or copolymers.

[0012] In any embodiment of the present application, the first organic particles include one or more of vinylidene fluoride-trifluoroethylene copolymer, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-trifluoroethylene-hexafluoropropylene copolymer, vinylidene fluoride-hexafluoropropylene-acrylic acid copolymer, vinylidene fluoride-hexafluoropropylene-acrylate copolymer, and modified compounds of the above copolymers.

[0013] In any embodiment of the present application, the mass percentage of the first organic particles in the coating is ≥12%. Optionally, the mass percentage of the first organic particles in the coating is 15%-25%.

[0014] In any embodiment of the present application, the mass percentage of the inorganic particles in the coating is ≤80%. Optionally, the mass percentage of the inorganic particles in the coating is 65%-75%.

[0015] In any embodiment of the present application, the coating further comprises a second type of organic particles, the second type of organic particles are embedded in the inorganic particles and form protrusions on the surface of the coating, and the second type of organic particles are primary particles.

[0016] In any embodiment of the present application, the number average particle size of the second organic particles is 2 μm-8 μm; optionally, the number average particle size of the second organic particles is 2.5 μm-6 μm.

[0017] In any embodiment of the present application, the mass percentage of the second organic particles in the coating is less than the mass percentage of the first organic particles in the coating.

[0018] In any embodiment of the present application, the mass percentage of the second organic particles in the coating is ≤8%; optionally, the mass percentage of the second organic particles in the coating is 2%-6%.

[0019] In any embodiment of the present application, the sum of the area coverage of the first organic particles and the second organic particles on the coating surface is ≤15%; optionally, the sum of the area coverage of the first organic particles and the second organic particles on the coating surface is 1%-8%.

[0020] In any embodiment of the present application, the ratio of the area coverage of the first organic particles to the second organic particles on the coating surface is 1:1-20:1; optionally 2:1-10:1.

[0021] In any embodiment of the present application, the second organic particles include homopolymers or copolymers of acrylate monomer units, homopolymers or copolymers of acrylic acid monomer units, homopolymers or copolymers of styrene monomer units, polyurethane compounds, rubber compounds, and one or more modified compounds of the above homopolymers or copolymers.

[0022] In any embodiment of the present application, the second organic particles include copolymers of acrylic acid ester monomer units and styrene monomer units, copolymers of acrylic acid monomer units and styrene monomer units, copolymers of acrylic acid monomer units-acrylic acid ester monomer units-styrene monomer units, copolymers of styrene monomer units-unsaturated nitrile monomer units, copolymers of styrene monomer units-olefin monomer units-unsaturated nitrile monomer units, and one or more of the modified compounds of the above copolymers.

[0023] In any embodiment of the present application, the second organic particles include butyl acrylate-styrene copolymer, butyl methacrylate-isooctyl methacrylate copolymer, isooctyl methacrylate-styrene copolymer, methacrylate-methacrylic acid-styrene copolymer, methyl acrylate-isooctyl methacrylate-styrene copolymer, butyl acrylate-isooctyl methacrylate-styrene copolymer, butyl acrylate-isooctyl methacrylate-styrene copolymer, butyl methacrylate-isooctyl methacrylate-styrene copolymer, butyl methacrylate-isooctyl methacrylate-styrene copolymer, butyl methacrylate-isooctyl methacrylate-styrene copolymer, styrene-acrylonitrile copolymer, styrene-butadiene-acrylonitrile copolymer, methyl acrylate-styrene-acrylonitrile copolymer, isooctyl methacrylate-styrene-acrylonitrile copolymer, styrene-vinyl acetate copolymer, styrene-vinyl acetate-pyrrolidone copolymer, and one or more of the modified compounds of the above copolymers.

[0024] In any embodiment of the present application, the inorganic particles include one or more of boehmite (γ-AlOOH), aluminum oxide (Al2O3), barium sulfate (BaSO4), magnesium oxide (MgO), magnesium hydroxide (Mg(OH)2), silicon dioxide (SiO2), tin dioxide (SnO2), titanium oxide (TiO2), calcium oxide (CaO), zinc oxide (ZnO), zirconium oxide (ZrO2), yttrium oxide (Y2O3), nickel oxide (NiO), cerium oxide (CeO2), zirconium titanate (SrTiO3), barium titanate (BaTiO3), and magnesium fluoride (MgF2).

[0025] In any embodiment of the present application, the air permeability of the isolation membrane is 100s / 100mL-300s / 100mL. Optionally, the air permeability of the isolation membrane is 150s / 100mL-250s / 100mL.

[0026] In any embodiment of the present application, the transverse tensile strength (MD) of the separator is 1500 kgf / cm 2 -3000kgf / cm 2 Optionally, the transverse tensile strength of the isolation film is 1800kgf / cm 2 -2500kgf / cm 2 .

[0027] In any embodiment of the present application, the longitudinal tensile strength (TD) of the separator is 1000 kgf / cm 2 -2500kgf / cm 2 Optionally, the longitudinal tensile strength of the isolation film is 1400kgf / cm 2 -2000kgf / cm 2 .

[0028] In any embodiment of the present application, the transverse elongation at break of the isolation film is 50%-200%; optionally, the transverse elongation at break of the isolation film is 100%-150%.

[0029] In any embodiment of the present application, the longitudinal elongation at break of the isolation film is 50%-200%; optionally, the longitudinal elongation at break of the isolation film is 100%-150%.

[0030] In any embodiment of the present application, the inorganic particles and the organic particles form a non-uniform pore structure in the coating.

[0031] In any embodiment of the present application, the distance between any two adjacent inorganic particles is recorded as L1, and the distance between any adjacent inorganic particle and one organic particle is recorded as L2, then L1<L2.

[0032] In a second aspect, the present application provides a method for preparing an isolation membrane, the method comprising at least the following steps: (1) Providing substrate; (2) providing a coating slurry, wherein the coating slurry comprises component materials and a solvent, wherein the component materials comprise inorganic particles and organic particles, and wherein the organic particles comprise first organic particles; (3) applying the coating slurry described in step (2) on at least one side of the substrate described in step (1) to form a coating and drying the coating to obtain the isolation film; Wherein, the isolation film includes: a substrate; and a coating formed on at least one surface of the substrate; the coating includes inorganic particles and organic particles, and the organic particles include first organic particles; the first organic particles are embedded in the inorganic particles and form protrusions on the surface of the inorganic particle layer; the first organic particles are secondary particles, the number average particle size of the first organic particles is ≥13μm, and the area coverage of the first organic particles on the coating surface is ≤10%.

[0033] In any embodiment of the present application, in the step (2), the coating slurry further comprises a second type of organic particles, and the second type of organic particles are primary particles.

[0034] In any embodiment of the present application, in the step (2), the second organic particles account for less than 8% of the total dry weight of the component materials, and can be optionally 2%-6%.

[0035] In any embodiment of the present application, in the step (2), the added mass of the first organic particles accounts for more than 12% of the total dry weight of the component materials; it can be optionally 12%-30%.

[0036] In any embodiment of the present application, in the step (2), the solid content of the coating slurry is 28%-45%, optionally 30%-38%, based on the weight of the coating slurry.

[0037] In any embodiment of the present application, the coating is performed using a coater, and the coater includes a gravure roller, and the line number of the gravure roller is 100LPI-300LPI, and can be optionally 125LPI-190LPI.

[0038] In any embodiment of the present application, in the step (3), the coating speed is 30 m / min-90 m / min, and can be optionally 50 m / min-70 m / min.

[0039] In any embodiment of the present application, in the step (3), the coating line speed ratio is 0.8-2.5, and can be optionally 0.8-1.5.

[0040] In any embodiment of the present application, in the step (3), the drying temperature is 40°C-70°C, and can be optionally 50°C-60°C.

[0041] In any embodiment of the present application, in the step (3), the drying time is 10s-120s, and can be optionally 20s-80s.

[0042] A third aspect of the present application provides a secondary battery, which includes the isolation membrane of the first aspect of the present application or includes the isolation membrane prepared according to the method of the second aspect of the present application.

[0043] A fourth aspect of the present application provides a battery module, which includes the secondary battery of the third aspect of the present application.

[0044] A fifth aspect of the present application provides a battery pack, which includes the battery module of the fourth aspect of the present application.

[0045] A sixth aspect of the present application provides a device comprising at least one of the secondary battery of the third aspect of the present application, the battery module of the fourth aspect of the present application, or the battery pack of the fifth aspect of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] In order to more clearly illustrate the technical solution of the present application, the following is a brief introduction to the drawings used in the present application. Obviously, the drawings described below are only some embodiments of the present application, and for ordinary technicians in this field, other drawings can be obtained based on the drawings without creative work.

[0047] Figure 1-1 It is a schematic diagram of the coating structure of one embodiment of the isolation membrane of the present application.

[0048] Figure 1-2 It is a schematic diagram of the coating structure of another embodiment of the isolation membrane of the present application.

[0049] Figure 2 This is a scanning electron microscope (SEM) image of an embodiment of the isolation film of the present application.

[0050] Figure 3 This is an ion polishing cross-sectional morphology (CP) image of an embodiment of the isolation membrane of the present application.

[0051] Figure 4-1 It is a schematic structural diagram of an embodiment of the isolation membrane of the present application.

[0052] Figure 4-2It is a schematic structural diagram of another embodiment of the isolation membrane of the present application.

[0053] Figure 5 is a schematic diagram of one embodiment of a secondary battery.

[0054] Figure 6 yes Figure 5 Exploded diagram of .

[0055] Figure 7 is a schematic diagram of one embodiment of a battery module.

[0056] Figure 8 is a schematic diagram of one embodiment of a battery pack.

[0057] Fig. 9 yes Figure 8 Exploded diagram of .

[0058] Fig.10 is a schematic diagram of one embodiment of a device in which a secondary battery is used as a power source. DETAILED DESCRIPTION

[0059] The present application is further described below in conjunction with specific implementations. It should be understood that these specific implementations are only used to illustrate the present application and are not used to limit the scope of the present application.

[0060] For simplicity, only some numerical ranges are specifically disclosed herein. However, any lower limit can be combined with any upper limit to form an unspecified range; and any lower limit can be combined with other lower limits to form an unspecified range, and any upper limit can be combined with any other upper limit to form an unspecified range. In addition, each separately disclosed point or single value can itself be combined as a lower limit or upper limit with any other point or single value or with other lower limits or upper limits to form an unspecified range.

[0061] In the description of this article, it should be noted that, unless otherwise specified, "above" and "below" are inclusive of the number itself, and "several" in "one or several" means two or more.

[0062] In the description herein, unless otherwise specified, the term "or" is inclusive. That is, the phrase "A or (or) B" means "A, B, or both A and B". More specifically, any of the following conditions satisfies the condition "A or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0063] Unless otherwise specified, the terms used in this application have the commonly known meanings generally understood by those skilled in the art. Unless otherwise specified, the numerical values ​​of the parameters mentioned in this application can be measured using various measurement methods commonly used in the art (for example, they can be tested according to the methods given in the examples of this application).

[0064] Unless otherwise stated, all the operating methods in this application are carried out at room temperature and atmospheric pressure.

[0065] Secondary battery A secondary battery is a battery that can be recharged to activate the active materials after being discharged and continue to be used.

[0066] Generally, a secondary battery includes a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte. During the battery charging and discharging process, active ions are embedded and released back and forth between the positive electrode sheet and the negative electrode sheet. The separator is arranged between the positive electrode sheet and the negative electrode sheet to play a role of isolation. The electrolyte plays a role of conducting ions between the positive electrode sheet and the negative electrode sheet.

[0067] [Isolation film] The isolation film provided by the present application includes: a substrate and a coating disposed on at least one surface of the substrate. The coating includes inorganic particles and organic particles. The organic particles include first organic particles, which are embedded in the inorganic particles and form protrusions on the surface of the coating. The first organic particles are secondary particles, and the number average particle size of the first organic particles is ≥13μm. The area coverage of the first organic particles on the surface of the coating is ≤10%.

[0068] It should be noted that the number average particle size of the organic particles refers to the arithmetic mean of the particle sizes of the organic particles counted by the number of organic particles in the isolation film coating. The particle size of the organic particles refers to the distance between the two farthest points on the organic particles.

[0069] The area coverage of organic particles on the coating surface refers to the ratio of the area of ​​organic particles to the total area of ​​the coating.

[0070] Without being bound by any theory, the isolation membrane of the present application contains inorganic particles and specific first organic particles in the same coating layer. Compared with the isolation membrane having two coating layers of inorganic particles and organic particles, the overall thickness of the isolation membrane is greatly reduced, thereby improving the energy density of the battery; and the organic particles and the inorganic particles form a special coating structure, which can form a sufficient and unevenly distributed pore structure between the inorganic particles and the organic particles, ensuring the smooth flow of ion transmission channels, so that the battery has good cycle performance; at the same time, the area coverage of the first organic particles on the coating surface is within a specific range. When the battery is in a normal working environment (for example, below 45°C), the first organic particles in the coating can be effectively prevented from swelling in the electrolyte to form a dense film, ensuring that the isolation membrane has appropriate pores to facilitate ion transmission, thereby further improving the cycle performance of the battery; in particular, when the battery is in a high temperature working environment (for example, above 100°C), the first organic particles with a specific area coverage will form an appropriate film structure at high temperature, quickly reduce ion diffusion channels, and delay the time of heat spread, thereby effectively improving the safety performance of the battery.

[0071] The applicant has found through in-depth research that when the isolation membrane of the present application satisfies the above-mentioned design conditions and optionally satisfies one or more of the following conditions, the performance of the secondary battery can be further improved.

[0072] In some embodiments, the area coverage of the first organic particles on the coating surface is 0.5%-10%, optionally 0.5%-8%; for example, the area coverage of the first organic particles on the coating surface can be 0.5-7%, 0.5%-5%, 0.5%-3%, 0.8%-10%, 0.8%-8%, 0.8%-6%, 0.8%-5%, 0.8%-2.5%, 1%-8%, 1%-6%, 1%-3%, 1.5%-10%, 1.5%-5.5%, 1.5%-3.5%, 1.5%-2.5%, 1.8%-5.5%, 1.8%-3.5%, 2%-10%, 4%-8%. When the area coverage of the first organic particles on the coating surface is within the given range, the cycle performance and safety performance of the battery can be further improved.

[0073] In some embodiments, the number average particle size of the first organic particles may be 15 μm - 25 μm. When the number average particle size of the first organic particles is within the given range, sufficient gaps can be formed between the organic particles, and even if the organic particles swell in the electrolyte, sufficient ion transmission channels can be formed, thereby further improving the cycle performance of the battery.

[0074] The number average particle size of the organic particles refers to the arithmetic mean value of the particle sizes of the organic particles counted according to the number of organic particles in the isolation film coating.

[0075] In some embodiments, the first organic particles include homopolymers or copolymers of fluorine-containing olefinic monomer units, homopolymers or copolymers of olefinic monomer units, homopolymers or copolymers of unsaturated nitrile monomer units, homopolymers or copolymers of alkylene oxide monomer units, and one or more of the modified compounds of the above homopolymers or copolymers.

[0076] In some embodiments, the fluorine-containing olefinic monomer unit may be selected from one or more of difluoroethylene, vinylidene fluoride, trifluoroethylene, chlorotrifluoroethylene, tetrafluoroethylene, and hexafluoropropylene.

[0077] In some embodiments, the olefin-based monomer unit may be selected from one or more of ethylene, propylene, butadiene, isoprene, and the like.

[0078] In some embodiments, the unsaturated nitrile monomer unit may be selected from one or more of acrylonitrile, methacrylonitrile, and the like.

[0079] In some embodiments, the alkylene oxide monomer unit can be selected from one or more of ethylene oxide, propylene oxide, and the like.

[0080] In some embodiments, the first organic particles include polytetrafluoroethylene, polychlorotrifluoroethylene, polyvinyl fluoride, polyvinylidene fluoride, polyethylene, polypropylene, polyacrylonitrile, polyethylene oxide, copolymers of different fluorine-containing olefin monomer units, copolymers of fluorine-containing olefin monomer units and vinyl monomer units, copolymers of fluorine-containing olefin monomer units and acrylic monomer units, copolymers of fluorine-containing olefin monomer units and acrylic ester monomer units, and one or more of the modified compounds of the above homopolymers or copolymers.

[0081] In some embodiments, the first organic particles include one or more of vinylidene fluoride-trifluoroethylene copolymer, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-trifluoroethylene-hexafluoropropylene copolymer, vinylidene fluoride-hexafluoropropylene-acrylic acid copolymer, vinylidene fluoride-hexafluoropropylene-acrylate copolymer, and modified compounds of the above copolymers.

[0082] In some embodiments, the number average molecular weight of the first organic particles is 300,000-800,000, for example, 400,000-650,000.

[0083] In some embodiments, the inorganic particles may include one or more of boehmite (γ-AlOOH), aluminum oxide (Al2O3), barium sulfate (BaSO4), magnesium oxide (MgO), magnesium hydroxide (Mg(OH)2), silicon dioxide (SiO2), tin dioxide (SnO2), titanium oxide (TiO2), calcium oxide (CaO), zinc oxide (ZnO), zirconium oxide (ZrO2), yttrium oxide (Y2O3), nickel oxide (NiO), cerium oxide (CeO2), zirconium titanate (SrTiO3), barium titanate (BaTiO3), and magnesium fluoride (MgF2); for example, the inorganic particles may include one or more of boehmite (γ-AlOOH) and aluminum oxide (Al2O3).

[0084] In some embodiments, the volume average particle size Dv of the inorganic particles is 50 ≤2.5μm; for example, the volume average particle size of the inorganic particles can be 0.5μm-2.5μm, 1.5μm-2.5μm, 0.3μm-0.7μm, etc. When the volume average particle size of the inorganic particles is controlled within the given range, the isolation membrane can be ensured to further improve the volume energy density of the battery under the premise of good cycle performance and safety performance.

[0085] In some embodiments, the mass percentage of the first organic particles in the coating is ≥12%; for example, the mass percentage of the first organic particles in the coating is 12%-30%, 15%-25%.

[0086] In some embodiments, the mass percentage of the inorganic particles in the coating is ≤80%; for example, the mass percentage of the inorganic particles in the coating is 65%-75%.

[0087] By selecting the appropriate content of the first organic particles and inorganic particles, the two can play a better synergistic role, ensuring that the isolation membrane has an appropriate pore structure while ensuring safety performance, while achieving the lightweight of the isolation membrane, thereby further improving the energy density of the battery.

[0088] In some embodiments, the coating further comprises a second organic particle, the second organic particle is embedded in the inorganic particle and forms a protrusion on the surface of the coating, and the second organic particle is a primary particle. When the coating further comprises a second organic particle, the safety performance of the battery can be further improved.

[0089] It should be noted that the morphology of organic particles (primary particles and secondary particles) has a well-known meaning in the art. Primary particles refer to particles that have not formed an agglomerated state. Secondary particles refer to particles that are agglomerated by two or more primary particles.

[0090] In some embodiments, the number average particle size of the second organic particles is 2μm-8μm; for example, the number average particle size of the second organic particles can be 2.5μm-8μm, 2.5μm-6μm, 3.0μm-5.5μm. The inventors have found that when the number average particle size of the second organic particles is within the given range, the cycle performance and safety performance of the battery can be further improved. After a lot of research, the inventors found that if the number average particle size of the second organic particles is too small (for example, less than 2μm), it is easy to swell in the electrolyte to form a film structure, which will block the transmission channel of the separator when the battery is working normally, thereby affecting the cycle performance of the battery; if the number average particle size of the second organic particles is too large (for example, greater than 8μm), it may cause the isolation membrane and the electrode plate to be too firmly bonded after the hot pressing process of the battery preparation, resulting in poor infiltration of the electrolyte, thereby affecting the cycle performance of the battery.

[0091] In some embodiments, the second organic particles include homopolymers or copolymers of acrylate monomer units, homopolymers or copolymers of acrylic acid monomer units, homopolymers or copolymers of styrene monomer units, polyurethane compounds, rubber compounds, and one or more modified compounds of the above homopolymers or copolymers.

[0092] In some embodiments, the second organic particles include copolymers of acrylic acid ester monomer units and styrene monomer units, copolymers of acrylic acid monomer units and styrene monomer units, copolymers of acrylic acid monomer units-acrylic acid ester monomer units-styrene monomer units, copolymers of styrene monomer units-unsaturated nitrile monomer units, copolymers of styrene monomer units-olefin monomer units-unsaturated nitrile monomer units, and one or more of the modified compounds of the above copolymers.

[0093] In some embodiments, the acrylic acid ester monomer unit can be selected from one or more of methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, methyl methacrylate, butyl methacrylate, isooctyl methacrylate, and the like.

[0094] In some embodiments, the acrylic monomer unit may be selected from one or more of acrylic acid, methacrylic acid, and the like.

[0095] In some embodiments, the styrene monomer unit may be selected from one or more of styrene, methyl styrene, and the like.

[0096] In some embodiments, the unsaturated nitrile monomer unit may be selected from one or more of acrylonitrile, methacrylonitrile, and the like.

[0097] In some embodiments, the second organic particles include butyl acrylate-styrene copolymer, butyl methacrylate-isooctyl methacrylate copolymer, isooctyl methacrylate-styrene copolymer, methacrylate-methacrylic acid-styrene copolymer, methyl acrylate-isooctyl methacrylate-styrene copolymer, butyl acrylate-isooctyl methacrylate-styrene copolymer, butyl acrylate-isooctyl methacrylate-styrene copolymer, butyl methacrylate-isooctyl methacrylate-styrene copolymer, butyl methacrylate-isooctyl methacrylate-styrene copolymer, butyl methacrylate-isooctyl methacrylate-styrene copolymer, styrene-acrylonitrile copolymer, styrene-butadiene-acrylonitrile copolymer, methyl acrylate-styrene-acrylonitrile copolymer, isooctyl methacrylate-styrene-acrylonitrile copolymer, styrene-vinyl acetate copolymer, styrene-vinyl acetate-pyrrolidone copolymer, and one or more of the modified compounds of the above copolymers.

[0098] In the present application, the modified compound of each homopolymer or copolymer refers to a modified compound obtained by copolymerizing a monomer unit in each homopolymer or copolymer with a monomer unit containing a specific functional group. For example, a fluorine-containing olefin monomer unit can be copolymerized with a compound containing a carboxyl functional group to obtain a modified compound thereof.

[0099] In some embodiments, the number average molecular weight of the second organic particles is 10,000-100,000, such as 20,000-80,000.

[0100] In some embodiments, the mass percentage of the second organic particles in the coating layer is less than the mass percentage of the first organic particles in the coating layer.

[0101] In some embodiments, the mass percentage of the second organic particles in the coating is ≤8%; for example, it may be 2%-8%, 2%-6%, or 3%-6.5%. In some embodiments, the sum of the area coverage of the first organic particles and the second organic particles on the coating surface is ≤20%, optionally ≤15%; optionally, the sum of the area coverage of the first organic particles and the second organic particles on the coating surface is 1%-20%, 1%-16%, 1%-13%, 1%-8%, 2%-15%, 2%-10%, 2.5%-12%, 3%-18%, 3.5%-9%, 4.5%-15%, 4.5%-8%. When the sum of the area coverage of the first organic particles and the second organic particles on the coating surface is within the above range, the cycle performance and safety performance of the battery can be further improved.

[0102] In some embodiments, the ratio of the area coverage of the first organic particles and the second organic particles on the coating surface is 1: 1-20: 1; optionally 2: 1-10: 1, 3: 1-5: 1. When the ratio is within the above range, the content of the first organic particles and the second organic particles can be optimally matched, thereby further improving the energy density and cycle performance of the battery. If the content of the first organic particles is too much, the energy density of the battery may be affected; if the content of the second organic particles is too much, the cycle performance of the battery may be affected.

[0103] According to some embodiments, the coating may further include other organic compounds, for example, a polymer for improving heat resistance (referred to as "heat-resistant glue"), a dispersant, a wetting agent, other types of binders, etc. The above-mentioned other organic compounds are all non-granular substances in the coating. The present application has no particular restrictions on the types of the above-mentioned other organic compounds, and any known material with good improved performance can be selected.

[0104] In the present application, there is no particular restriction on the material of the substrate, and any known substrate with good chemical stability and mechanical stability can be selected, such as one or more of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The substrate can be a single-layer film or a multi-layer composite film. When the substrate is a multi-layer composite film, the materials of each layer can be the same or different.

[0105] In some embodiments, the thickness of the substrate is ≤10 μm; for example, the thickness of the substrate may be 5 μm-10 μm, 5 μm-9 μm, or 7 μm-9 μm. When the thickness of the substrate is controlled within the given range, the energy density of the battery can be further improved while ensuring the battery rate performance and safety performance.

[0106] In some embodiments, the coating weight per unit area on one side of the isolation film is ≤3.0 g / m 2 For example, the coating weight per unit area on one side of the separator may be 1.5 g / m 2 -3.0 g / m 2 , 1.5 g / m 2 -2.5 g / m 2 , 1.8 g / m 2 -2.3 g / m 2 Etc. By controlling the coating weight on one side of the separator per unit area within a given range, the energy density of the battery can be further improved while ensuring the battery cycle performance and safety performance.

[0107] In some embodiments, the air permeability of the isolation membrane may be 100 s / 100 mL-300 s / 100 mL; for example, the air permeability of the isolation membrane may be 150 s / 100 mL-250 s / 100 mL, 170 s / 100 mL-220 s / 100 mL.

[0108] In some embodiments, the longitudinal tensile strength (TD) of the separator may be 1000 kgf / cm 2 -2500kgf / cm 2 For example, the longitudinal tensile strength of the isolation film may be 1400 kgf / cm 2 -2000 kgf / cm 2 .

[0109] In some embodiments, the longitudinal elongation at break of the isolation film may be 50%-200%; for example, the longitudinal elongation at break of the isolation film may be 100%-150%.

[0110] In some embodiments, the transverse tensile strength (MD) of the separator may be 1500 kgf / cm 2 -3000kgf / cm 2 For example, the transverse tensile strength of the isolation film can be 1800 kgf / cm 2 -2500 kgf / cm 2 .

[0111] In some embodiments, optionally, the transverse elongation at break of the isolation film may be 50%-200%; for example, the transverse elongation at break of the isolation film may be 100%-150%.

[0112] In some embodiments, the inorganic particles and the organic particles form a non-uniform pore structure in the coating.

[0113] In some embodiments, the distance between any two adjacent inorganic particles is recorded as L1, and the distance between any adjacent inorganic particle and one organic particle is recorded as L2, and L1<L2.

[0114] Related parameter test methods According to some embodiments, the area coverage of organic particles on the coating surface can be tested using equipment and methods known in the art. As an example, the area coverage of the first type of organic particles on the coating surface can be tested as follows: a test sample of a certain size (e.g., length × width = 50 mm × 100 mm) is randomly selected on the isolation film, and the area of ​​the test sample is calculated and recorded as S; a scanning electron microscope (e.g., ZEISS Sigma 300) is used, for example, with reference to JY / T010-1996, to randomly select a test area in the test sample, and obtain a SEM image of the test area at a certain magnification (e.g., 1000 times).

[0115] The morphology and particle size of the organic particles were tested according to the above method. When the organic particles were in the morphology of secondary particles and the particle size was greater than or equal to 12 μm, the coverage area was calculated by fitting the organic particles into a standard circle (it should be noted that the standard circle refers to the diameter of the organic particle as the smallest circular diameter of all shapes that includes the organic particles, and then the area of ​​the circle is calculated by fitting as the area of ​​the organic particle). The total area of ​​the organic particles in the test sample with secondary particle morphology and a particle size greater than or equal to 12 μm was counted and recorded as S1. The area coverage of the first type of organic particles on the coating surface = S1 / S × 100%.

[0116] A plurality of test areas (for example, 10) are randomly selected from the test sample, the area coverage S1 of the first type of organic particles on the coating surface in each test area is counted, and the value of S1 / S×100% is calculated, and the average value calculated in each test area is taken as the final test result.

[0117] The area coverage of the second organic particles is also tested using the above method. According to some embodiments, the particle size and number average particle size of the organic particles can be tested using equipment and methods known in the art. For example, a scanning electron microscope (such as ZEISS Sigma 300) is used, for example, with reference to JY / T010-1996, to obtain a SEM image of the isolation film. As an example, the test can be performed in the following manner: a test sample with a length × width = 50 mm × 100 mm is randomly selected on the isolation film, and multiple test areas (such as 5) are randomly selected in the test sample, and the particle size of each organic particle in each test area is read at a certain magnification (such as 500 times when measuring the first organic particle and 1000 times when measuring the second organic particle), that is, the distance between the two farthest points on the organic particle is taken as the particle size of the organic particle, which is the particle size of the organic particles described in the present application. The number and particle size values ​​of the organic particles in each test area are counted, and the arithmetic mean of the particle size of the organic particles in each test area is taken, which is the number average particle size of the organic particles in the test sample. In order to ensure the accuracy of the test results, multiple test samples (for example, 10) may be taken to perform the above test, and the average value of each test sample may be taken as the final test result.

[0118] According to some embodiments, the morphology of the organic particles can be tested using equipment and methods known in the art. For example, a scanning electron microscope (such as ZEISS Sigma 300) can be used for testing. As an example, the following steps can be followed: first, the isolation film is cut into a test sample of a certain size (for example, 6mm×6mm), and the test sample is clamped with two conductive and thermally conductive thin sheets (such as copper foil), and the test sample and the thin sheet are glued and fixed with glue (such as double-sided tape), and a flat iron block of a certain mass (such as about 400g) is used to press for a certain time (such as 1h) to make the gap between the test sample and the copper foil as small as possible, and then the edges are trimmed with scissors, and glued to the sample stage with conductive glue, and the sample is slightly protruding from the edge of the sample stage. Then put the sample stage into the sample holder and lock it, turn on the power of the argon ion cross-section polisher (such as IB-19500CP) and evacuate it (such as 10 Pa -4Pa), set the argon gas flow (such as 0.15MPa) and voltage (such as 8KV) and polishing time (such as 2 hours), adjust the sample stage to the rocking mode and start polishing. After polishing, use a scanning electron microscope (such as ZEISS Sigma300) to obtain the ion polishing cross-sectional morphology (CP) image of the test sample.

[0119] According to some embodiments, the material type of the organic particles can be tested using equipment and methods known in the art. For example, the infrared spectrum of the material can be tested to determine the characteristic peaks contained therein, thereby determining the material type. Specifically, the organic particles can be subjected to infrared spectrum analysis using instruments and methods known in the art, such as an infrared spectrometer, such as an IS10 Fourier transform infrared spectrometer from Nicolet, USA, and tested in accordance with the general rules for infrared spectrum analysis methods of GB / T6040-2002.

[0120] According to some embodiments, the volume average particle size Dv of the inorganic particles is 50 The meaning is well known in the art and can be measured using instruments and methods known in the art. For example, it can be measured using a laser particle size analyzer (such as Master Size 3000) with reference to GB / T 19077-2016 particle size distribution laser diffraction method.

[0121] According to some embodiments, the air permeability, transverse tensile strength (MD), longitudinal tensile strength (TD), transverse elongation at break, and longitudinal elongation at break of the isolation membrane all have meanings known in the art and can be measured using methods known in the art. For example, they can all be tested with reference to standard GB / T 36363-2018.

[0122] According to some embodiments, the distance between any two adjacent inorganic particles refers to: in the SEM image of the isolation film, any two adjacent inorganic particles are selected in the coating (when the inorganic particles are irregular in shape, the particles can be treated as circumscribed circles), and the distance between the centers of the two inorganic particles is tested as the distance between the two inorganic particles, and is recorded as L1.

[0123] According to some embodiments, the distance between any adjacent inorganic particle and organic particle refers to: in the SEM image of the isolation film, any adjacent inorganic particle and organic particle are selected in the coating (when the inorganic particle or organic particle is irregular in shape, the particle can be circumscribed), and the distance between the centers of the inorganic particle and the organic particle is tested as the distance between the inorganic particle and the organic particle, which is recorded as L2. The above-mentioned organic particles can be the first organic particles or the second organic particles.

[0124] The above spacing can be measured using instruments known in the art. For example, it can be measured using a scanning electron microscope. As an example, the spacing L2 between any adjacent inorganic particle and organic particle can be tested as follows: the isolation film is made into a test sample with a length × width = 50 mm × 100 mm; the isolation film is tested using a scanning electron microscope (such as ZEISS Sigma 300). The test can refer to JY / T010-1996. Randomly select an area in the test sample for scanning test, and obtain a SEM image of the isolation film at a certain magnification (for example, 3000 times). In the SEM image, select any adjacent inorganic particle and organic particle (when the inorganic particle or organic particle is an irregular body, the particle can be circumscribed), and measure the distance between the center of the inorganic particle (or its circumscribed circle) and the center of the organic particle (or its circumscribed circle), which is the spacing between the adjacent inorganic particles and organic particles described in this application, recorded as L2. In order to ensure the accuracy of the test results, multiple groups of adjacent particles (for example, 10 groups) can be selected from the test sample to repeat the above test, and the average value of the test results of each group can be taken as the final result.

[0125] Similarly, the distance L1 between any two adjacent inorganic particles can also be tested according to the above method.

[0126] The present application also provides a method for preparing the above-mentioned isolation film, which at least comprises the following steps: (1) Providing substrate; (2) providing a coating slurry, wherein the coating slurry comprises component materials and a solvent, wherein the component materials comprise inorganic particles and organic particles, and wherein the organic particles comprise first organic particles; (3) applying the coating slurry described in step (2) on at least one side of the substrate described in step (1) to form a coating and drying the coating to obtain the isolation film; Wherein, the isolation film includes: a substrate; and a coating formed on at least one surface of the substrate; the coating includes inorganic particles and organic particles, and the organic particles include first organic particles; the first organic particles are embedded in the inorganic particles and form protrusions on the surface of the inorganic particle layer; the first organic particles are secondary particles, the number average particle size of the first organic particles is ≥13 μm, and the area coverage of the first organic particles on the coating surface is ≤10%.

[0127] The nature or components of the coating have the same definitions as described above in relation to the barrier film.

[0128] The coating layer may be provided on only one surface of the substrate, or may be provided on both surfaces of the substrate.

[0129] like Figure 4-1As shown, the isolation film includes a substrate (A) and a coating (B), wherein the coating (B) is disposed on only one surface of the substrate (A).

[0130] like Figure 4-2 As shown, the isolation film includes a substrate (A) and a coating (B), wherein the coating (B) is disposed on both surfaces of the substrate (A).

[0131] The present application embodiment has no particular restrictions on the material of the substrate, and any known substrate with good chemical stability and mechanical stability can be selected, such as one or more of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The substrate can be a single-layer film or a multi-layer composite film. When the substrate is a multi-layer composite film, the materials of each layer can be the same or different.

[0132] In some embodiments, in step (2), the solvent may be water, such as deionized water.

[0133] In some embodiments, in step (2), the component material may further include the aforementioned second organic particles. The parameters of the second organic particles can be referred to the aforementioned content and will not be described in detail here.

[0134] In some embodiments, in step (2), the component materials may also include other organic compounds, for example, polymers for improving heat resistance, dispersants, wetting agents, other types of binders, etc. The above-mentioned other organic compounds are all non-granular substances in the coating. The present application has no particular restrictions on the types of the above-mentioned other organic compounds, and any known material with good improved performance can be selected.

[0135] In some embodiments, in step (2), component materials are added to a solvent and stirred evenly to obtain a coating slurry.

[0136] In some embodiments, in step (2), the added mass of the first organic particles is greater than 12% of the total dry weight of the component materials; for example, 12%-30%, 15%-30%, 15%-25%, 15%-20%, 16%-22%.

[0137] In some embodiments, in step (2), the added mass of the second organic particles is less than 8% of the total dry weight of the component materials, for example, 2%-10%, 2%-6%, 3%-7%, 3%-5%.

[0138] It should be noted that when the component material is solid, the dry weight of the component material is the added mass of the component material. When the component material is a suspension, emulsion or solution, the dry weight of the component material is the product of the added mass of the component material and the solid content of the component material. The total dry weight of the component material is the sum of the dry weights of the component materials.

[0139] In some embodiments, in step (2), the solid content of the coating slurry can be controlled at 28%-45%, for example, 30%-38%, based on the weight of the coating slurry. When the solid content of the coating slurry is within the above range, the film surface problems of the coating can be effectively reduced and the probability of uneven coating can be reduced, thereby further improving the cycle performance and safety performance of the battery.

[0140] In some embodiments, in step (3), the coating is performed using a coating machine.

[0141] In the embodiments of the present application, there is no special restriction on the model of the coater, and a commercially available coater can be used.

[0142] In some embodiments, in step (3), the coating may be performed by transfer coating, spin spray coating, dip coating or the like; for example, the coating may be performed by transfer coating.

[0143] In some embodiments, the coater includes a gravure roll; the gravure roll is used to transfer the coating slurry to the substrate.

[0144] In some embodiments, the line number of the gravure roller may be 100 LPI-300 LPI, for example, 125 LPI-190 LPI (LPI is lines per inch). When the line number of the gravure roller is within the above range, it helps to control the amount of the first organic particles and the second organic particles, thereby further improving the cycle performance and safety performance of the isolation film.

[0145] In some embodiments, in step (3), the coating speed can be controlled within the range of 30 m / min-90 m / min, such as 50 m / min-70 m / min. When the coating speed is within the above range, it is helpful to adjust the average height of the protrusions so that the ratio of the average height of the protrusions to the thickness of the inorganic particle layer is controlled within the given range; at the same time, it can also effectively reduce the film surface problems of the coating and reduce the probability of uneven coating, thereby further improving the cycle performance and safety performance of the battery.

[0146] In some embodiments, in step (3), the coating line speed ratio can be controlled at 0.8-2.5, for example, 0.8-1.5, 1.0-1.5.

[0147] In some embodiments, in step (3), the drying temperature may be 40°C-70°C, for example, 50°C-60°C.

[0148] In some embodiments, in step (3), the drying time may be 10s-120s, for example, 20s-80s, 20s-40s.

[0149] By controlling the above process parameters within the given range, the performance of the isolation membrane of the present application can be further improved. Those skilled in the art can selectively adjust one or more of the above process parameters according to actual production conditions.

[0150] In order to further improve the performance of the secondary battery, the inorganic particles and the organic particles may optionally satisfy one or more of the aforementioned parameter conditions, which will not be described in detail here.

[0151] The above-mentioned substrate, first organic particles and second organic particles can all be obtained commercially.

[0152] The isolation membrane preparation method of the present application obtains the coating by one-time coating, which greatly simplifies the production process of the isolation membrane; at the same time, the isolation membrane prepared by the above method is used in the battery, which can effectively improve the cycle performance and safety performance of the battery.

[0153] [Positive electrode] In a secondary battery, the positive electrode plate generally includes a positive electrode current collector and a positive electrode film layer disposed on the positive electrode current collector, wherein the positive electrode film layer includes a positive electrode active material.

[0154] The positive electrode current collector may be a conventional metal foil or a composite current collector (a metal material may be disposed on a polymer substrate to form a composite current collector). As an example, the positive electrode current collector may be an aluminum foil.

[0155] The specific type of the positive electrode active material is not limited, and any active material known in the art that can be used for the positive electrode of a secondary battery can be used, and those skilled in the art can select it according to actual needs.

[0156] As an example, the positive electrode active material may include, but is not limited to, one or more of lithium transition metal oxides, lithium-containing phosphates with an olivine structure and their respective modified compounds. Examples of lithium transition metal oxides may include, but are not limited to, one or more of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide and their modified compounds. Examples of lithium-containing phosphates with an olivine structure may include, but are not limited to, one or more of lithium iron phosphate, a composite material of lithium iron phosphate and carbon, lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, a composite material of lithium iron manganese phosphate and carbon and their modified compounds. These materials can all be obtained commercially.

[0157] In some embodiments, the modified compounds of the above materials may be doping-modified and / or surface-coated modified materials.

[0158] The positive electrode film layer may also include a binder, a conductive agent and other optional additives.

[0159] As an example, the conductive agent may be one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, Super P (SP), graphene, and carbon nanofibers.

[0160] As an example, the binder may be one or more of styrene-butadiene rubber (SBR), water-based acrylic resin, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene-vinyl acetate copolymer (EVA), polyacrylic acid (PAA), carboxymethyl cellulose (CMC), polyvinyl alcohol (PVA) and polyvinyl butyral (PVB).

[0161] [Negative electrode] In a secondary battery, the negative electrode plate generally includes a negative electrode current collector and a negative electrode film layer disposed on the negative electrode current collector, wherein the negative electrode film layer includes a negative electrode active material.

[0162] The negative electrode current collector may be a conventional metal foil or a composite current collector (for example, a metal material may be disposed on a polymer substrate to form a composite current collector). As an example, the negative electrode current collector may be a copper foil.

[0163] The specific type of the negative electrode active material is not limited, and active materials known in the art that can be used for the negative electrode of a secondary battery can be used, and those skilled in the art can choose according to actual needs. As an example, the negative electrode active material may include, but is not limited to, one or more of artificial graphite, natural graphite, hard carbon, soft carbon, silicon-based materials and tin-based materials. The silicon-based material can be selected from one or more of elemental silicon, silicon oxide compounds (such as silicon monoxide), silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material can be selected from one or more of elemental tin, tin oxide compounds, and tin alloys. These materials can all be obtained through commercial channels.

[0164] In some embodiments, in order to further improve the energy density of the battery, the negative electrode active material may include a silicon-based material.

[0165] The negative electrode film layer may also optionally include a binder, a conductive agent and other optional additives.

[0166] As an example, the conductive agent may be one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

[0167] As an example, the binder may be one or more of styrene-butadiene rubber (SBR), water-based acrylic resin, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene-vinyl acetate copolymer (EVA), polyvinyl alcohol (PVA) and polyvinyl butyral (PVB).

[0168] As an example, other optional auxiliary agents may be thickeners and dispersants (such as sodium carboxymethyl cellulose CMC-Na), PTC thermistor materials, etc.

[0169] [Electrolyte] The present application embodiment has no special restrictions on the selection of the electrolyte, and the electrolyte is used to conduct ions between the positive electrode plate and the negative electrode plate. The electrolyte may include an electrolyte salt and a solvent.

[0170] As an example, the electrolyte salt may be selected from one or more of LiPF6 (lithium hexafluorophosphate), LiBF4 (lithium tetrafluoroborate), LiClO4 (lithium perchlorate), LiAsF6 (lithium hexafluoroarsenate), LiFSI (lithium bis(fluorosulfonyl)imide), LiTFSI (lithium bis(trifluoromethanesulfonyl)imide), LiTFS (lithium trifluoromethanesulfonate), LiDFOB (lithium difluorooxalatoborate), LiBOB (lithium dioxalatoborate), LiPO2F2 (lithium difluorophosphate), LiDFOP (lithium difluorooxalatophosphate) and LiTFOP (lithium tetrafluorooxalatophosphate).

[0171] As an example, the solvent can be selected from one or more of ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), ethyl methyl sulfone (EMS) and diethyl sulfone (ESE).

[0172] In some embodiments, the electrolyte further includes additives, such as additives that may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high temperature performance, and additives that improve battery low temperature performance.

[0173] In some embodiments, the secondary battery of the present application may be a lithium ion secondary battery.

[0174] The embodiment of the present application has no particular limitation on the shape of the secondary battery, which may be cylindrical, square or any other shape. Figure 5 The secondary battery 5 is a square structure as an example.

[0175] In some embodiments, the secondary battery may include an outer package for packaging a positive electrode sheet, a negative electrode sheet, and an electrolyte.

[0176] In some embodiments, reference Figure 6 The outer package may include a shell 51 and a cover plate 53. The shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity.

[0177] The positive electrode sheet, the negative electrode sheet and the separator can be wound or laminated to form an electrode assembly 52. ​​The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the secondary battery 5 can be one or more, which can be adjusted according to needs.

[0178] In some embodiments, the outer packaging of the secondary battery may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the secondary battery may also be a soft package, such as a bag-type soft package. The material of the soft package may be plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), polybutylene succinate (PBS), etc.

[0179] In some embodiments, secondary batteries may be assembled into a battery module. The battery module may contain multiple secondary batteries, and the specific number may be adjusted according to the application and capacity of the battery module.

[0180] Figure 7 4 is an example of a battery module. Figure 7 In the battery module 4, the plurality of secondary batteries 5 may be arranged in sequence along the length direction of the battery module 4. Of course, they may also be arranged in any other manner. Further, the plurality of secondary batteries 5 may be fixed by fasteners.

[0181] Optionally, the battery module 4 may further include a housing having a receiving space, and the plurality of secondary batteries 5 are received in the receiving space.

[0182] In some embodiments, the battery modules described above may also be assembled into a battery pack, and the number of battery modules contained in the battery pack may be adjusted according to the application and capacity of the battery pack.

[0183] Figure 8 and Fig. 9 1 is a battery pack 1 as an example. Figure 8 and Fig. 9 The battery pack 1 may include a battery box and a plurality of battery modules 4 disposed in the battery box. The battery box includes an upper box body 2 and a lower box body 3. The upper box body 2 can cover the lower box body 3 and form a closed space for accommodating the battery modules 4. The plurality of battery modules 4 can be arranged in the battery box in any manner.

[0184] [Device] The present application also provides a device, which includes at least one of the secondary battery, battery module, or battery pack described in the present application. The secondary battery, battery module, or battery pack can be used as a power source for the device, or as an energy storage unit for the device. The device can be, but is not limited to, a mobile device (such as a mobile phone, a laptop computer, etc.), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship and a satellite, an energy storage system, etc.

[0185] The device can select a secondary battery, a battery module or a battery pack according to its usage requirements.

[0186] Fig.10 The device is used as an example. The device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. In order to meet the device's requirements for high power and high energy density of secondary batteries, a battery pack or a battery module can be used.

[0187] Another example of a device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is usually required to be thin and light, and a secondary battery may be used as a power source.

[0188] The beneficial effects of the present application are further illustrated below in conjunction with embodiments.

[0189] Example In order to make the technical problems, technical solutions and beneficial effects solved by the present application clearer, the present application will be further described in detail below in conjunction with the embodiments and drawings. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all of the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is by no means intended to limit the present application and its applications. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field without creative work are within the scope of protection of the present application.

[0190] 1. Preparation of isolation membrane The raw materials used in this application can be obtained commercially: For example: the substrate can be purchased from Shanghai Enjie New Materials Co., Ltd.

[0191] Inorganic particles can be purchased from Yishitong Materials Technology Co., Ltd.

[0192] The first organic particle can be purchased from Arkema (Changshu) Chemical Co., Ltd.

[0193] The second type of organic particles can be purchased from Sichuan Yindi Le Technology Co., Ltd.

[0194] Heat-resistant glue can be purchased from Sichuan Yindile Technology Co., Ltd.

[0195] Wetting agents are available commercially from The Dow Chemical Company.

[0196] The dispersant can be purchased from Changshu Weiyi Technology Co., Ltd.

[0197] Isolation film 1: (1) Providing a PE substrate, for example, the thickness of the substrate is 7 μm and the porosity is 40%; (2) Preparation of coating slurry: Inorganic particles of aluminum oxide (Al2O3), the first organic particles of vinylidene fluoride-hexafluoropropylene copolymer (number average molecular weight of 550,000), heat-resistant adhesive acrylic acid-acrylonitrile copolymer, dispersant sodium carboxymethyl cellulose (CMC-Na) and wetting agent silicone modified polyether are mixed in solvent deionized water at a mass ratio of 60:30:8:1.5:0.5 (dry weight ratio) to obtain a coating slurry with a solid content of 36% based on the weight of the coating slurry. The volume average particle size Dv50 of the inorganic particles of aluminum oxide (Al2O3) is 1 μm, the first organic particles are secondary particles, and the number average particle size of the first organic particles is 15 μm; (3) The coating slurry prepared in step (2) is coated on the two surfaces of the PE substrate by roller coating, and a separator 1 is obtained by drying and slitting. The line number of the gravure roller of the coating machine is 190 LPI, the coating speed is 60 m / min, and the coating line speed ratio is 1.2; the single-side coating weight per unit area on the separator is 2.3 g / m 2 In the isolation film 1, the first organic particles are embedded in the inorganic particle layer and form protrusions on the surface of the inorganic particle layer, and the area coverage of the first organic particles on the coating surface is 10%.

[0198] The preparation methods of isolation films 2-19 and comparative isolation films 1-3 are similar to that of isolation film 1, except that the number average particle size, type and mass ratio of the first organic particles are adjusted, as shown in Table 1 for details.

[0199] The preparation method of isolation film 20-33 is similar to that of isolation film 1, except that a second type of organic particles is added to the coating, and the number average particle size and type thereof are adjusted, as shown in Table 2 for details.

[0200] 2. Preparation of batteries Example 1 1. Preparation of positive electrode sheet The positive electrode active material LiNi0.5Co0.2Mn0.3O2 (NCM523), the conductive agent carbon black (Super P), and the binder polyvinylidene fluoride (PVDF) are mixed uniformly in a proper amount of solvent N-methylpyrrolidone (NMP) at a mass ratio of 96.2: 2.7: 1.1 to obtain a positive electrode slurry, and the positive electrode slurry is coated on the positive electrode current collector aluminum foil, and the positive electrode sheet is obtained through drying, cold pressing, striping, cutting and other processes. Optionally, the surface density of a single side of the positive electrode sheet is 0.207 mg / mm 2 The compaction density of the positive electrode is 3.5g / cm 3 .

[0201] 2. Preparation of negative electrode sheet The negative electrode active material artificial graphite, conductive agent carbon black (Super P), binder styrene butadiene rubber (SBR) and sodium carboxymethyl cellulose (CMC-Na) are mixed evenly in a proper amount of solvent deionized water at a mass ratio of 96.4: 0.7: 1.8: 1.1 to obtain a negative electrode slurry, and the negative electrode slurry is coated on the negative electrode current collector copper foil, and the negative electrode sheet is obtained through drying, cold pressing, striping, cutting and other processes. Optionally, the surface density of a single side of the negative electrode sheet is 0.126 mg / mm 2 The compaction density of the negative electrode is 1.7g / cm 3 .

[0202] 3. Isolation film The isolation film adopts the isolation film 1 prepared above.

[0203] 4. Preparation of electrolyte Ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are mixed at a mass ratio of 30:70 to obtain an organic solvent, and fully dried electrolyte salt LiPF6 is dissolved in the mixed solvent, wherein the concentration of the electrolyte salt is 1.0 mol / L, and the mixture is evenly mixed to obtain an electrolyte solution.

[0204] 5. Preparation of secondary batteries The positive electrode sheet, the separator, and the negative electrode sheet are stacked in order, so that the separator is placed between the positive and negative electrode sheets to play an isolating role, and then they are wound to obtain an electrode assembly; the electrode assembly is placed in an outer package, and the prepared electrolyte is injected into the dried secondary battery. After vacuum packaging, standing, formation, shaping and other processes, a secondary battery is obtained.

[0205] The preparation methods of the secondary batteries of Examples 2-33 and Comparative Examples 1-3 are similar to the preparation methods of the secondary battery of Example 1, except that different isolation membranes are used. For details, see Tables 1 and 2.

[0206] 3. Battery performance test 1. 45℃ Cycle Performance At 45°C, the secondary batteries prepared in the examples and comparative examples were charged at a constant current of 1 C to a charge cut-off voltage of 4.2V, then charged at a constant voltage to a current of ≤0.05C, left to stand for 30 minutes, and then discharged at a constant current of 0.33 C to a discharge cut-off voltage of 2.8V, left to stand for 30 minutes, and the battery capacity C0 at this time was recorded. The battery was charged and discharged 1500 times in this way, and the battery capacity after 1500 cycles was recorded as C1.

[0207] Battery cycle capacity retention rate at 45°C = C1 / C0×100% 2. Heat spread performance At 25°C, the secondary batteries prepared in the embodiments and comparative examples were charged at a constant current of 1 C to a charging cut-off voltage of 4.2V, then charged at a constant voltage to a current ≤0.05C, and allowed to stand for 10 min; then a metal heating plate was placed close to the surface of the battery, the battery was clamped with a clamp at a position of the battery that did not contact the heating plate, and a 3mm thermal insulation pad was added between the clamp and the battery, and the battery was heated at a constant temperature of 200°C until thermal runaway occurred in the battery; the time when thermal runaway occurred in the battery was recorded.

[0208] 3. Crack SOH performance test At 25°C, the secondary batteries prepared in the embodiments and comparative examples were charged at a constant current of 0.5C to a charge cut-off voltage of 4.25 V, then charged at a constant voltage to a current ≤ 0.05C, left standing for 30 min, and then discharged at a constant current of 0.33C to a discharge cut-off voltage of 2.8V, left standing for 30 min, and the battery capacity C0 at this time was recorded.

[0209] The battery is subjected to a cyclic charge and discharge test according to this method. When the battery capacity decays by 1% on the basis of C0, the battery is subjected to an X-ray CT test (X-ray computed tomography). When a break is observed at the corner of the positive or negative electrode of the battery, the battery capacity C1 at this time is recorded.

[0210] Crack SOH=C1 / C0×100% Tables 1 and 2 show the measured battery performance of each embodiment and comparative example.

[0211]

[0212]

[0213]

[0214]

[0215] As can be seen from Table 1, the secondary batteries containing the isolation membrane of the present application have achieved excellent cycle capacity retention, heat spread and Crack SOH improvement values; for example, the cycle capacity retention rate of the obtained secondary battery after 1500 cycles can be as high as 91.7%, and the heat spread performance of the secondary battery can be as high as 559 seconds, and the Crack SOH value can be greater than 70%. In the case of using the first organic particle alone, Comparative Examples 1 and 2 using a particle size of less than 13 μm are not as good as the secondary battery containing the isolation membrane of the present application in terms of cycle retention and heat spread time of the secondary battery. At the same time, even if the first organic particle in the number average particle size range of the present invention is used, if its mass proportion in the isolation membrane is too large, the cycle performance and safety performance of the obtained secondary battery will be reduced, see Comparative Example 3.

[0216] It can be seen from Table 2 that by further adding the second organic particles of a specific amount, type and number average particle size range, the obtained isolation film still meets the requirements of the safety performance and cycle performance of the secondary battery.

[0217] The inventors also conducted experiments using other amounts and materials of inorganic particles, first organic particles and second organic particles within the scope of the present application, other substrates, other coating process parameters and other process conditions, and obtained similar effects of improving the cycle performance and safety performance of the battery as in Examples 1-32.

[0218] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any technician familiar with the technical field can easily think of various equivalent modifications or replacements within the technical scope disclosed in the present application, and these modifications or replacements should be included in the protection scope of the present application. Therefore, the protection scope of the present application shall be based on the protection scope of the claims.

Claims

1. A secondary battery comprising a positive electrode sheet, a separator and a negative electrode sheet; The isolation film comprises: Base material; and a coating disposed on at least one surface of the substrate; The coating layer comprises inorganic particles and organic particles, wherein the organic particles comprise first organic particles, wherein the first organic particles are embedded in the inorganic particles and form protrusions on the surface of the coating layer; The first organic particles are secondary particles, the number average particle size of the first organic particles is ≥13 μm, and the area coverage of the first organic particles on the coating surface is ≤10%; The coating further comprises second organic particles, the second organic particles are embedded in the inorganic particles and form protrusions on the surface of the coating, the second organic particles are primary particles, and the number average particle size of the second organic particles is 2 μm-8 μm; The negative electrode plate includes a negative electrode current collector and a negative electrode film layer arranged on the negative electrode current collector, the negative electrode film layer includes a negative electrode active material, and the negative electrode active material includes one or more of artificial graphite, natural graphite, hard carbon, soft carbon, silicon-based materials and tin-based materials.

2. The secondary battery according to claim 1, wherein The area coverage of the first organic particles on the coating surface is 0.5%-8%, and can be optionally 0.8%-5%.

3. The secondary battery according to any one of claims 1 to 2, wherein: The number average particle size of the first organic particles is 15 μm-25 μm.

4. The secondary battery according to any one of claims 1 to 3, wherein: The first organic particles include homopolymers or copolymers of fluorine-containing olefin monomer units, homopolymers or copolymers of olefin monomer units, homopolymers or copolymers of unsaturated nitrile monomer units, homopolymers or copolymers of alkylene oxide monomer units, and one or more of the modified compounds of the above homopolymers or copolymers; Optionally, the first organic particles include polytetrafluoroethylene, polychlorotrifluoroethylene, polyvinyl fluoride, polyvinylidene fluoride, polyethylene, polypropylene, polyacrylonitrile, polyethylene oxide, copolymers of different fluorine-containing olefinic monomer units, copolymers of fluorine-containing olefinic monomer units and olefinic monomer units, copolymers of fluorine-containing olefinic monomer units and acrylic monomer units, copolymers of fluorine-containing olefinic monomer units and acrylic ester monomer units, and one or more modified compounds of the above homopolymers or copolymers.

5. The secondary battery according to any one of claims 1 to 4, wherein: The first organic particles include one or more of vinylidene fluoride-trifluoroethylene copolymer, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-trifluoroethylene-hexafluoropropylene copolymer, vinylidene fluoride-hexafluoropropylene-acrylic acid copolymer, vinylidene fluoride-hexafluoropropylene-acrylate copolymer, and modified compounds of the above copolymers.

6. The secondary battery according to any one of claims 1 to 5, wherein: The isolation film satisfies at least one of the following (1)-(2): (1) The mass percentage of the first organic particles in the coating is ≥12%. Optionally, the mass percentage of the first organic particles in the coating is 15%-25%; (2) The mass percentage of the inorganic particles in the coating is ≤80%. Optionally, the mass percentage of the inorganic particles in the coating is 65%-75%.

7. The secondary battery according to any one of claims 1 to 6, wherein: The number average particle size of the second organic particles is 2.5 μm-6 μm.

8. The secondary battery according to any one of claims 1 to 7, wherein: The mass percentage of the second organic particles in the coating is less than the mass percentage of the first organic particles in the coating; Optionally, the mass percentage of the second organic particles in the coating is ≤8%; Optionally, the mass percentage of the second organic particles in the coating is 2%-6%.

9. The secondary battery according to any one of claims 1 to 8, wherein: The second organic particles include one or more of homopolymers or copolymers of acrylate monomer units, homopolymers or copolymers of acrylic acid monomer units, homopolymers or copolymers of styrene monomer units, polyurethane compounds, rubber compounds, and modified compounds of the above homopolymers or copolymers; Optionally, the second organic particles include copolymers of acrylic acid ester monomer units and styrene monomer units, copolymers of acrylic acid monomer units and styrene monomer units, copolymers of acrylic acid monomer units-acrylic acid ester monomer units-styrene monomer units, copolymers of styrene monomer units and unsaturated nitrile monomer units, copolymers of styrene monomer units-olefin monomer units-unsaturated nitrile monomer units, and one or more of the modified compounds of the above copolymers.

10. The isolation film according to any one of claims 1 to 9, wherein: The second organic particles include butyl acrylate-styrene copolymer, butyl methacrylate-isooctyl methacrylate copolymer, isooctyl methacrylate-styrene copolymer, methacrylate-methacrylic acid-styrene copolymer, methyl acrylate-isooctyl methacrylate-styrene copolymer, butyl methacrylate-isooctyl methacrylate-styrene copolymer, styrene-acrylonitrile copolymer, styrene-butadiene-acrylonitrile copolymer, methyl acrylate-styrene-acrylonitrile copolymer, isooctyl methacrylate-styrene-acrylonitrile copolymer, styrene-vinyl acetate copolymer, styrene-vinyl acetate-pyrrolidone copolymer, and one or more of the modified compounds of the above copolymers.

11. The secondary battery according to any one of claims 1 to 10, wherein: The sum of the area coverage of the first organic particles and the second organic particles on the coating surface is ≤15%; optionally, the sum of the area coverage of the first organic particles and the second organic particles on the coating surface is 1%-8%.

12. The secondary battery according to any one of claims 1 to 11, wherein: The ratio of the area coverage of the first organic particles to the second organic particles on the coating surface is 1:1-20:1, and can be optionally 2:1-10:

1.

13. The secondary battery according to any one of claims 1 to 12, wherein: The inorganic particles include one or more of boehmite (γ-AlOOH), aluminum oxide (Al2O3), barium sulfate (BaSO4), magnesium oxide (MgO), magnesium hydroxide (Mg(OH)2), silicon dioxide (SiO2), tin dioxide (SnO2), titanium oxide (TiO2), calcium oxide (CaO), zinc oxide (ZnO), zirconium oxide (ZrO2), yttrium oxide (Y2O3), nickel oxide (NiO), cerium oxide (CeO2), zirconium titanate (SrTiO3), barium titanate (BaTiO3), and magnesium fluoride (MgF2).

14. The secondary battery according to any one of claims 1 to 13, wherein: The isolation film satisfies one or more of the following (1)-(5): (1) The air permeability of the isolation membrane is 100s / 100mL-300s / 100mL, and optionally, the air permeability of the isolation membrane is 150s / 100mL-250s / 100mL; (2) The transverse tensile strength (MD) of the separator is 1500 kgf / cm 2 -3000kgf / cm 2 Optionally, the transverse tensile strength of the isolation film is 1800kgf / cm 2 -2500kgf / cm 2 ; (3) The longitudinal tensile strength (TD) of the separator is 1000 kgf / cm 2 -2500kgf / cm 2 Optionally, the longitudinal tensile strength of the isolation film is 1400kgf / cm 2 -2000kgf / cm 2 ; (4) The transverse elongation at break of the isolation film is 50%-200%; optionally, the transverse elongation at break of the isolation film is 100%-150%; (5) The longitudinal elongation at break of the isolation film is 50%-200%; Optionally, the longitudinal elongation at break of the isolation film is 100%-150%.

15. The secondary battery according to any one of claims 1 to 14, wherein: The inorganic particles and the organic particles form a non-uniform pore structure in the coating layer.

16. The secondary battery according to any one of claims 1 to 15, wherein: The distance between any two adjacent inorganic particles is recorded as L1, and the distance between any adjacent inorganic particle and one organic particle is recorded as L2, then L1<L2.

17. The secondary battery according to any one of claims 1 to 16, wherein: The positive electrode plate includes a positive electrode current collector and a positive electrode film layer arranged on the positive electrode current collector, the positive electrode film layer includes a positive electrode active material, and the positive electrode active material includes one or more of lithium transition metal oxides, olivine-structured lithium-containing phosphates and their respective modified compounds.

18. The secondary battery according to any one of claims 1 to 17, wherein: The secondary battery includes an electrolyte solution, wherein the electrolyte solution includes an electrolyte salt; The electrolyte salt includes one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium difluorophosphate, lithium difluorobis(oxalatophosphate) and lithium tetrafluorooxalatophosphate.

19. A battery module comprising the secondary battery according to any one of claims 1 to 18. 20 . A battery pack comprising at least one of the secondary battery according to any one of 1 to 18 and the battery module according to claim 19 .

21. A device comprising at least one of the secondary battery of any one of claims 1 to 18, the battery module of claim 19, or the battery pack of claim 20.

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