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, the secondary battery comprising: a separator comprising a substrate and a coating layer formed on at least one surface of the substrate; the coating comprises inorganic particles and organic particles, the organic particles comprise a first kind of organic particles and a second kind of organic particles, the first kind of organic particles and the second kind of organic particles are embedded in the inorganic particles and form bulges on the surface of the coating, and the number average particle size of the first kind of organic particles is 8-27 microns; the number-average particle size of the second organic particles is 2-10 [mu] m, and at least a part of the second organic particles comprise a core structure and a shell structure.

Description

Technical Field

[0001] The present application belongs to the technical field of secondary batteries, and specifically relates to a secondary battery, a battery module, a battery pack and a device. Background Art

[0002] Secondary batteries are widely used in various consumer electronic products and electric vehicles due to their outstanding characteristics of 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 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] In view of the technical problems existing in the background technology, the present application provides a secondary battery, which has both good 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 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 and second organic particles, and the first organic particles and the second organic particles are embedded in the inorganic particles and form protrusions on the surface of the coating. The number average particle size of the first organic particles is ≥8μm. The number average particle size of the second organic particles is ≥2μm, and at least a part of the second organic particles includes a core structure and a shell structure.

[0007] Compared with the prior art, the present application at least includes the following beneficial effects: the isolation membrane of the present application contains inorganic particles, the first organic particles and the second organic particles in the same coating, and the particle size and structure of the first organic particles and the second organic particles are specially designed. Under the combined effect of the above conditions, the isolation membrane can be effectively guaranteed to have a moderate and uneven pore structure while enhancing the bonding force between the isolation membrane and the electrode plate. At the same time, when the secondary battery is working at high temperature, the first and second organic particles can form a large-area adhesive film structure to reduce or block the transmission channel of the isolation ions, delay the heat spread of the battery, and thus effectively improve the battery's cycle performance and safety performance at high temperatures.

[0008] In any embodiment of the present application, the number average particle size of the first organic particles is ≥12 μm; for example, the number average particle size of the first organic particles can be 15 μm-25 μm. When the number average particle size of the first organic particles is within the given range, the cycle performance of the battery can be further improved.

[0009] In any embodiment of the present application, the number average particle size of the second organic particles is 3 μm-8 μm; for example, the number average particle size of the second organic particles is 3 μm-6 μm. 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.

[0010] In any embodiment of the present application, the ratio of the number average particle size of the first organic particles to the number average particle size of the second organic particles is ≥ 2; for example, the ratio of the number average particle size of the first organic particles to the number average particle size of the second organic particles is 2.5-4. When the ratio of the number average particle size of the first organic particles to 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.

[0011] In any embodiment of the present application, the first organic particles are secondary particles. When the first organic particles are secondary particles, the safety performance of the battery can be further improved.

[0012] In any embodiment of the present application, the second organic particles are primary particles. When the second organic particles are primary particles, the cycle performance and safety performance of the battery can be further improved.

[0013] In any embodiment of the present application, the first organic particles may 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.

[0014] In any embodiment of the present application, the first organic particles may 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 of the modified compounds of the above homopolymers or copolymers.

[0015] In any embodiment of the present application, the first organic particles may 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.

[0016] In any embodiment of the present application, the core structure and the shell structure in the second organic particles can be independently selected from 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.

[0017] In any embodiment of the present application, the core structure and the shell structure in the second organic particles can be independently selected from the copolymer of acrylic acid ester monomer unit and styrene monomer unit, the copolymer of acrylic acid monomer unit and styrene monomer unit, the copolymer of acrylic acid monomer unit-acrylic acid ester monomer unit-styrene monomer unit, the copolymer of styrene monomer unit and unsaturated nitrile monomer unit, the copolymer of styrene monomer unit-olefin monomer unit-unsaturated nitrile monomer unit, and one or more of the modified compounds of the above copolymers.

[0018] In any embodiment of the present application, the core structure and the shell structure in the second organic particles can be independently selected from 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 materials.

[0019] In any embodiment of the present application, the core structure and the shell structure of the second organic particle may both include one or more of a copolymer of an acrylic acid ester monomer unit and a styrene monomer unit and modified compounds thereof.

[0020] By optimizing the materials of the core structure and shell structure in the second organic particle, the cycle performance of the battery can be further improved.

[0021] In any embodiment of the present application, the glass transition temperature of the shell structure may be higher than the glass transition temperature of the core structure. When the glass transition temperature of the shell structure is higher than the glass transition temperature of the core structure, the cycle performance of the battery can be further improved.

[0022] In any embodiment of the present application, the glass transition temperature of the core structure may be -30°C to 20°C; for example, it may be -10°C to 10°C.

[0023] In any embodiment of the present application, the glass transition temperature of the shell structure may be 50°C to 70°C; for example, it may be 55°C to 65°C.

[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 mass proportion of the inorganic particles in the coating is ≤70%, for example, the mass proportion of the inorganic particles in the coating is 60%-70%. When the mass proportion of the inorganic particles is controlled within the given range, the mass energy density of the battery can be further improved while ensuring the safety performance of the isolation membrane.

[0026] In any embodiment of the present application, the mass proportion of the first organic particles in the coating is ≥ 12%, for example, the mass proportion of the first organic particles in the coating is 15%-25%. When the mass proportion of the first organic particles is controlled within the given range, the cycle performance and safety performance of the battery can be improved.

[0027] In any embodiment of the present application, the mass proportion of the second organic particles in the coating is ≤10%, for example, the mass proportion of the second organic particles in the coating is 2%-10%. When the mass proportion of the second organic particles is controlled within the given range, the cycle performance and safety performance of the battery can be improved.

[0028] When the inorganic particles, the first organic particles or the second organic particles are within the above-given range, the three particles can exert a better synergistic effect, thereby further improving the cycle performance and energy density of the battery.

[0029] In any embodiment of the present application, the coating weight per unit area on one side of the isolation film is ≤3.0 g / m 2 ; The single-sided coating weight per unit area on the isolation film is 1.5g / m 2 -2.5g / m 2 When the single-side coating weight per unit area on the separator is within the given range, the energy density of the battery can be further improved while ensuring the battery cycle performance and safety performance.

[0030] In any embodiment of the present application, the air permeability of the isolation membrane may be 100s / 100mL-300s / 100mL; for example, the air permeability of the isolation membrane may be 150s / 100mL-250s / 100mL.

[0031] In any embodiment of the present application, the transverse tensile strength (MD) of the isolation film can be 1500 kgf / cm 2 -3000 kgf / cm 2 For example, the transverse tensile strength of the isolation film can be 1800kgf / cm 2 -2500kgf / cm 2 .

[0032] In any embodiment of the present application, the longitudinal tensile strength (TD) of the isolation film may be 1000 kgf / cm 2 -2500 kgf / cm 2 For example, the longitudinal tensile strength of the isolation film can be 1400kgf / cm 2 -2000kgf / cm 2 .

[0033] In any embodiment of the present application, 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%.

[0034] In any embodiment of the present application, 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%.

[0035] In any embodiment of the present application, the inorganic particles and the organic particles form a non-uniform pore structure in the coating.

[0036] 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.

[0037] The second aspect of the present application provides a method for preparing an isolation film, comprising the following steps: (1) providing a substrate. (2) providing a coating slurry, the coating slurry comprising component materials and a solvent, the component materials comprising inorganic particles and organic particles, the organic particles comprising first organic particles and second 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 to obtain the isolation film. The dried coating comprises the inorganic particles, the first organic particles and the second organic particles. The first organic particles and the second organic particles are embedded in the inorganic particles and form protrusions on the surface of the dried coating. The number average particle size of the first organic particles is ≥8μm. The number average particle size of the second organic particles is ≥2μm, and at least a portion of the second organic particles comprises a core structure and a shell structure.

[0038] In any embodiment of the present application, in 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%.

[0039] In any embodiment of the present application, in step (2), the added mass of the second organic particles accounts for less than 10% of the total dry weight of the component materials, and can be optionally 2%-10%.

[0040] In any embodiment of the present application, in step (2), the solid content of the coating slurry is 28%-45%, optionally 30%-38%, based on weight.

[0041] In any embodiment of the present application, in step (3), 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.

[0042] In any embodiment of the present application, in step (3), the coating speed is 30 m / min-90 m / min, and can be optionally 50 m / min-70 m / min.

[0043] In any embodiment of the present application, in step (3), the coating line speed ratio is 0.8-2.5, and can be optionally 0.8-1.5.

[0044] In any embodiment of the present application, in step (3), the drying temperature is 40°C-70°C, and can be optionally 50°C-60°C.

[0045] In any embodiment of the present application, in step (3), the drying time is 10s-120s, and can be optionally 20s-80s.

[0046] A third aspect of the present application provides a secondary battery, which includes the isolation membrane according to the first aspect of the present application or includes the isolation membrane prepared by the method according to the second aspect of the present application.

[0047] A fourth aspect of the present application provides a battery module, which includes the secondary battery according to the third aspect of the present application.

[0048] A fifth aspect of the present application provides a battery pack, which includes a battery module according to the fourth aspect of the present application.

[0049] The sixth aspect of the present application provides a device comprising at least one of the secondary battery according to the third aspect of the present application, the battery module according to the fourth aspect of the present application, or the battery pack according to the fifth aspect of the present application.

[0050] Since the device of the present application includes at least one of the secondary battery, battery module or battery pack provided in the present application, it has at least the same advantages as the secondary battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] 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.

[0052] Figure 1 It is a schematic structural diagram of an embodiment of the isolation membrane of the present application.

[0053] Figure 2 This is a transmission electron microscope (TEM) image of the second organic particle used in the isolation film of the present application.

[0054] Figure 3 This is an ion polishing cross-sectional morphology (CP) image of an embodiment of the isolation membrane of the present application at a magnification of 3000 times.

[0055] Figure 4 The figure is a scanning electron microscope (SEM) picture of an embodiment of the isolation film of the present application at a magnification of 3000 times.

[0056] Figure 5-1 It is a schematic structural diagram of an embodiment of the isolation membrane of the present application.

[0057] Figure 5-2 It is a schematic structural diagram of another embodiment of the isolation membrane of the present application.

[0058] Figure 6 It is a schematic diagram of one embodiment of a secondary battery.

[0059] Figure 7 yes Figure 6 Exploded diagram of .

[0060] Figure 8 is a schematic diagram of an embodiment of a battery module.

[0061] Fig. 9 is a schematic diagram of one embodiment of a battery pack.

[0062] Fig.10 yes Fig. 9 Exploded diagram of .

[0063] Fig.11 It is a schematic diagram of one embodiment of a device in which a secondary battery is used as a power source. DETAILED DESCRIPTION

[0064] 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.

[0065] 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.

[0066] 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).

[0067] 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.

[0068] 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 various 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).

[0069] Secondary battery

[0070] A secondary battery is a battery that can be recharged to activate the active materials after being discharged and continue to be used.

[0071] 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.

[0072] [Isolation film]

[0073] The embodiment of the present application provides an isolation film, comprising: a substrate and a coating formed on at least one surface of the substrate. The coating comprises inorganic particles and organic particles. The organic particles comprise first organic particles and second organic particles, the first organic particles and the second organic particles are embedded in the inorganic particles and form protrusions on the surface of the coating. The number average particle size of the first organic particles is ≥8 μm. The number average particle size of the second organic particles is ≥2 μm, and at least a portion of the second organic particles comprises a core structure and a shell structure.

[0074] 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 according to 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.

[0075] Without wishing to be limited to any theory, the inventors have found through extensive research that the isolation membrane contains inorganic particles and organic particles in the same coating layer, which can greatly reduce the overall thickness of the isolation membrane compared with the isolation membrane having two coating layers of inorganic particles and organic particles, thereby improving the energy density of the battery; and the organic particles include first organic particles and second organic particles of specific number average particle size and structural design, which can effectively enhance the adhesion between the isolation membrane and the electrode pole piece; at the same time, it can effectively reduce the probability of the second organic particles swelling in the electrolyte to form a large-area adhesive film during normal temperature operation, so that the isolation membrane has a moderate and uneven pore structure to facilitate ion transmission; and the presence of the first organic particles allows the isolation membrane and the pole piece to have appropriate stress release space during the battery cycle, which is beneficial to the gas discharge during the battery formation process, thereby effectively improving the cycle performance and safety performance of the battery.

[0076] The inventors have found through in-depth research that when the isolation membrane of the present application satisfies the above conditions and optionally satisfies one or more of the following conditions, the performance of the secondary battery can be further improved.

[0077] In some embodiments, the number average particle size of the first organic particles is ≥12 μm; the number average particle size of the first organic particles is 15 μm-25 μm. For example, the number average particle size of the first organic particles can be 12 μm-23 μm, 13 μm-22 μm, 15 μm-20 μm, 12 μm-18 μm. When the number average particle size of the first organic particles is within the given range, sufficient gaps can be present between the organic particles, and even if the organic particles swell in the electrolyte, sufficient ion transmission channels can be formed, which can further improve the cycle performance of the battery.

[0078] In some embodiments, the number average particle size of the second organic particles is 3 μm-8 μm; for example, the number average particle size of the second organic particles can be 3 μm-6 μm, 3 μm-5.5 μm, 4 μm-5 μm. When the number average particle size of the second organic particles is within the given range, the cycle performance of the battery can be further improved. If the number average particle size of the second organic particles is too small (for example, less than 2 μm), they are easy to swell in the electrolyte to form a film structure, which will block the ion transmission channel when the battery is working normally, thereby affecting the cycle performance of the battery.

[0079] In some embodiments, the ratio of the number average particle size of the first organic particles to the number average particle size of the second organic particles is ≥ 2; for example, the ratio of the number average particle size of the first organic particles to the number average particle size of the second organic particles may be 2.5 to 4, 3 to 4.5, or 3 to 4. By selecting the ratio of the number average particle size of the first organic particles to the number average particle size of the second organic particles, the cycle performance and safety performance of the battery can be further improved.

[0080] In some embodiments, the first organic particles are secondary particles. When the separator coating includes the first organic particles in the form of secondary particles, it helps to form a uniform coating interface. When the separator is used in a battery, it can effectively improve the tab misalignment problem in the battery preparation process, thereby further improving the safety performance of the battery.

[0081] In some embodiments, the second organic particles are primary particles. When the separator coating includes the second organic particles in the form of primary particles, it is not easy to form a large-area adhesive film structure between the particles, thereby further improving the cycle performance and safety performance of the battery.

[0082] It should be noted that primary particles and secondary particles have the meanings known 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.

[0083] like Figure 1 As shown, the isolation film includes a substrate (A) and a coating (B), the coating (B) includes first organic particles (B1), second organic particles (B2) and inorganic particles (B3), the first organic particles (B1) are secondary particles, the second organic particles (B2) are primary particles, the first organic particles and the second organic particles are both embedded in the inorganic particles (B3) and form protrusions on the surface of the coating (B), and the second organic particles (B2) include a core structure and a shell structure arranged on the surface of the core structure.

[0084] In some embodiments, the first organic particles may 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 modified compounds of the above homopolymers or copolymers.

[0085] 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.

[0086] In some embodiments, the olefin-based monomer unit may be selected from one or more of ethylene, propylene, butadiene, and isoprene.

[0087] In some embodiments, the unsaturated nitrile monomer unit may be selected from one or more of acrylonitrile and methacrylonitrile.

[0088] In some embodiments, the alkylene oxide monomer unit may be selected from one or more of ethylene oxide and propylene oxide.

[0089] In some embodiments, the first organic particles may 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 olefin 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.

[0090] In some embodiments, the first organic particles may 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.

[0091] In some embodiments, the core structure and the shell structure in the second organic particles can be independently selected from 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.

[0092] In some embodiments, the core structure and the shell structure in the second organic particles can be independently selected from one or more of 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 modified compounds of the above copolymers.

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

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

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

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

[0097] In some embodiments, the core structure and the shell structure in the second organic particles can be independently selected from 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 materials.

[0098] In some embodiments, the core structure and the shell structure of the second organic particle may both include one or more of a copolymer of an acrylic acid ester monomer unit and a styrene monomer unit and a modified compound thereof.

[0099] The modified compound of each homopolymer or copolymer is 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 the modified compound.

[0100] In some embodiments, the core structure and the shell structure include the same monomer unit copolymer. The glass transition temperature of the core structure and the shell structure material can be adjusted by adjusting the copolymerization ratio or polymerization process of each monomer unit in a manner known to those skilled in the art.

[0101] In some embodiments, the glass transition temperature of the shell structure is higher than the glass transition temperature of the core structure. Since the shell structure has a higher glass transition temperature, it can effectively reduce the probability of fusion between organic particles to form a continuous adhesive film during the production of the separator, thereby improving the ion transmission channel of the separator; and it can maintain a good bonding ability of the electrode sheet in the electrolyte, so that the electrode sheet and the separator are better fitted. Therefore, it helps to further improve the cycle performance of the battery.

[0102] In some embodiments, the glass transition temperature of the core structure may be -30°C to 20°C; for example, it may be -10°C to 10°C.

[0103] In some embodiments, the glass transition temperature of the shell structure may be 50°C to 70°C; for example, 55°C to 65°C.

[0104] In some embodiments, copolymers including acrylic acid ester monomer units in both the core structure and the shell structure can help reduce the swelling rate of the second organic particles in the electrolyte during operation at room temperature, further avoiding the formation of a large-area film structure, thereby helping to further improve the cycle performance of the battery.

[0105] In some embodiments, the core structure and the shell structure both include a copolymer of acrylic monomer units and styrene monomer units.

[0106] 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).

[0107] In some embodiments, the volume average particle size Dv50 of the inorganic particles is ≤ 2.5 μm; for example, the volume average particle size Dv50 of the inorganic particles can be 0.5 μm-2.5 μm, 1.5 μm-2.5 μm, 0.3 μm-0.7 μm. When the particle size of the inorganic particles is controlled within the given range, it can ensure that the isolation film has good cycle performance and safety performance, and further improve the volume energy density of the battery.

[0108] In some embodiments, the mass proportion of the inorganic particles in the coating is ≤70% (based on the total mass of the coating); for example, the mass proportion of the inorganic particles in the coating may be 60%-70%, 65%-70%. When the mass proportion of the inorganic particles is controlled within the given range, the mass energy density of the battery can be further improved while ensuring the safety performance of the isolation membrane.

[0109] In some embodiments, the mass proportion of the first organic particles in the coating is ≥ 12% (based on the total mass of the coating); for example, the mass proportion of the first organic particles in the coating can be 12%-30%, 15%-30%, 15%-25%, 15%-20%. When the mass proportion of the first organic particles is controlled within the given range, the separator and the pole piece can have sufficient stress release space during the battery cycle, further improving the interface of the electrode pole piece. At the same time, the appropriate mass proportion range can also reduce the consumption of the electrolyte by the separator, thereby further improving the cycle performance and safety performance of the battery.

[0110] In some embodiments, the mass proportion of the second organic particles in the coating is ≤10% (based on the total mass of the coating); for example, the mass proportion of the second organic particles in the coating can be 2%-10%, 3%-8%, 4%-9%, 5%-10%. When the mass proportion of the second organic particles is controlled within the given range, it helps to make the isolation film coating have a suitable pore structure while ensuring adhesion, thereby further improving the cycle performance and safety performance of the battery.

[0111] By selecting appropriate contents of inorganic particles, the first organic particles and the second organic particles, the three can play a better synergistic role, ensuring that the isolation membrane has an appropriate pore structure while ensuring safety performance, while achieving lightweight isolation membrane, thereby further improving the energy density of the battery.

[0112] 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 isolation film can be 1.5 g / m 2 -3.0g / m 2 , 1.5g / m 2 -2.5g / m 2 , 1.8g / m 2 -2.3g / m 2 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's cycle performance and safety performance.

[0113] According to some embodiments, the coating may further include other organic compounds, for example, polymers, dispersants, wetting agents, other types of binders, etc. that improve heat resistance. The above other organic compounds are all non-granular substances in the coating. The present application has no particular restrictions on the types of the above other organic compounds, and any known material with good improved performance can be selected.

[0114] In the embodiments of 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.

[0115] 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-10 μm. When the thickness of the substrate is controlled within the given range, the battery energy density can be further improved while ensuring the battery cycle performance and safety performance.

[0116] In some embodiments, the air permeability of the isolation membrane may be 100s / 100mL-300s / 100mL; for example, the air permeability of the isolation membrane may be 150s / 100mL-250s / 100mL, 170s / 100mL-220s / 100mL.

[0117] 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 1800kgf / cm 2 -2500 kgf / cm 2 .

[0118] In some embodiments, the longitudinal tensile strength (TD) of the separator may be 1000 kgf / cm 2 -2500kgf / cm 2 ; For example, it can be 1400kgf / cm 2 -2000 kgf / cm 2 .

[0119] In some embodiments, 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%.

[0120] 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%.

[0121] 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.

[0122] 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 (e.g., ZEISS Sigma 300) is used to obtain a scanning electron microscope (SEM) image of the isolation film with reference to JY / T010-1996. As an example, the test can be performed according to the following method: a test sample with a length×width=50mm×100mm is randomly selected on the isolation film, and multiple test areas (e.g., 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 (e.g., 500 times when measuring the first type of organic particles and 1000 times when measuring the second type of organic particles) (i.e., the distance between the two farthest points on the organic particles is taken as the particle size of the organic particles), the number and particle size 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 repeat the above test, and the average value of each test sample is taken as the final test result.

[0123] According to some embodiments, the particle structure (including the core structure and the shell structure) of the second organic particle can be tested using equipment and methods known in the art. As an example, the following steps can be followed: select a microgrid of a certain diameter (such as a diameter of 3 mm), place the microgrid with the film surface facing up (the shiny surface, i.e., the film surface, is observed under light), and gently place it on white filter paper; take an appropriate amount of a sample of the second organic particle slurry (such as 10 g) and add it to a beaker, perform ultrasonic oscillation for 10 min-30 min, absorb it with a glass capillary, and then drop 2-3 drops of the sample to be tested onto the microgrid, let it stand for 15 min, place the microgrid with the sample to be tested on the sample stage, and test it with a transmission electron microscope (such as: Hitachi HF-3300S Cs-corrected STEM), and you can get a transmission electron microscope (TEM) image of the sample to be tested.

[0124] Figure 2 is a transmission electron microscope (TEM) image of the second organic particle in the embodiment of the present application. Figure 2 As shown, the second organic particle includes a core structure and a shell structure disposed on the surface of the core structure.

[0125] According to some embodiments, the morphology of organic particles (e.g., primary particle morphology or secondary particle morphology) can be tested using equipment and methods known in the art. For example, it can be tested by using a scanning electron microscope (e.g., ZEISS Sigma 300). As an example, the following steps can be followed: first, the isolation film is cut into a sample to be tested of a certain size (e.g., 6 mm × 6 mm), and the sample to be tested is clamped with two conductive and thermally conductive sheets (e.g., copper foil), and the sample to be tested and the sheet are glued and fixed with glue (e.g., double-sided tape), and a certain mass (e.g., about 400 g) of a flat iron block is used to press for a certain time (e.g., 1 h) to make the gap between the sample to be tested and the copper foil as small as possible, and then the edges are trimmed with scissors, and glued to a sample table with conductive glue, and the sample slightly protrudes from the edge of the sample table. 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 (for example, 10Pa-4Pa), set the argon gas flow rate (for example, 0.15MPa) and voltage (for example, 8KV) and polishing time (for example, 2 hours), adjust the sample stage to the swing mode and start polishing. After polishing, use a scanning electron microscope (such as ZEISS Sigma 300) to obtain the ion polishing cross-sectional morphology (CP) image of the sample to be tested.

[0126] Figure 3 This is a picture of the cross-sectional morphology (CP) of the isolation film of the present application embodiment at a magnification of 3000 times. Figure 3 It can be seen that the coating of the isolation film includes first organic particles and second organic particles; the first organic particles are secondary particles composed of multiple primary particles and have an irregular non-solid spherical cross-section; the second organic particles are non-agglomerated primary particles and have a solid spherical cross-section.

[0127] According to some embodiments, the spacing between any two adjacent inorganic particles refers to: in the SEM image of the isolation membrane, 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 spacing between the two inorganic particles, and is recorded as L1.

[0128] 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.

[0129] The above-mentioned spacing can be measured by instruments known in the art. For example, it can be measured by 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 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 (eg, 10 groups) may be selected from the test sample to repeat the above test, and the average value of the test results of each group may be taken as the final result.

[0130] Similarly, the distance L1 between any two adjacent inorganic particles can also be tested according to the above method.

[0131] Figure 4 : is a scanning electron microscope (SEM) image of the isolation film of the embodiment of the present application at a magnification of 3000 times. Figure 4 It can be seen that the coating of the isolation film includes inorganic particles, first organic particles and second organic particles, the first organic particles are secondary particles, the second organic particles are primary particles, and the first organic particles and the second organic particles are embedded in the inorganic particles and form protrusions on the coating surface. After measuring according to the above method, it can be obtained that L1<L2.

[0132] 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 spectroscopy analysis using instruments and methods known in the art, such as an infrared spectrometer, such as the IS10 Fourier transform infrared spectrometer from Nicolet, USA, and tested in accordance with the general rules for infrared spectroscopy analysis methods of GB / T6040-2002.

[0133] According to some embodiments, the volume average particle size Dv50 of the inorganic particles has a well-known meaning 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 (e.g., Master Size 3000) with reference to GB / T 19077-2016 particle size distribution laser diffraction method.

[0134] 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.

[0135] The present application also provides a method for preparing an isolation film, comprising the following steps:

[0136] (1) providing a substrate;

[0137] (2) providing a coating slurry: the coating slurry comprises component materials and a solvent, the component materials comprise inorganic particles and organic particles, the organic particles comprise first organic particles and second organic particles;

[0138] (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 to obtain the isolation film;

[0139] Wherein, the dried coating includes inorganic particles, first organic particles and second organic particles, the first organic particles and the second organic particles are embedded in the inorganic particles and form protrusions on the surface of the dried coating; the number average particle size of the first organic particles is ≥8μm; the number average particle size of the second organic particles is ≥2μm, and at least a portion of the second organic particles include a core structure and a shell structure.

[0140] like Figure 5-1 As shown, the separator (10) includes a substrate (A) and a coating (B), wherein the coating (B) is disposed on only one surface of the substrate (A).

[0141] like Figure 5-2 As shown, the isolation film (10) includes a substrate (A) and a coating (B), wherein the coating (B) is disposed on both surfaces of the substrate (A).

[0142] In the embodiments of 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.

[0143] In some embodiments, in step (2), the solvent may be water, such as deionized water.

[0144] In some embodiments, in step (2), the component materials may further include other organic compounds, for example, polymers for improving heat resistance, dispersants, wetting agents, and emulsion-like binders. The other organic compounds are all non-granular in the dried coating.

[0145] In some embodiments, in step (2), component materials are added to a solvent and stirred uniformly to obtain a coating slurry.

[0146] In some embodiments, in step (2), the added mass of the first organic particles accounts for more than 12% of the total dry weight of the component materials; for example, 12%-30%, 15%-30%, 15%-25%, 15%-20%, 16%-22%.

[0147] In some embodiments, in step (2), the added mass of the second organic particles is less than 10% of the total dry weight of the component materials, for example, 2%-10%, 3%-7%, 3%-5%.

[0148] An appropriate amount of organic particles can reduce the static electricity generated between the isolation film and the battery winding tool (such as a winding needle) or stacking tool during the battery preparation process, effectively reducing the probability of short circuit between the positive and negative electrodes, thereby improving the manufacturing efficiency of the battery.

[0149] 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.

[0150] 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 weight. When the solid content of the coating slurry is within the above range, the film surface problem 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.

[0151] In some embodiments, in step (3), the coating is performed using a coater.

[0152] 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.

[0153] 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.

[0154] In some embodiments, the coater includes a gravure roll; the gravure roll is used to transfer the coating slurry to the substrate.

[0155] In some embodiments, the line number of the gravure roller can be 100LPI-300LPI, for example, 125LPI-190LPI (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.

[0156] 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, the film surface problem 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.

[0157] 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.

[0158] In some embodiments, in step (3), the drying temperature may be 40°C-70°C, for example, 50°C-60°C.

[0159] In some embodiments, in step (3), the drying time may be 10s-120s, for example, 20s-80s, 20s-40s.

[0160] 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.

[0161] 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.

[0162] The above-mentioned substrate, first organic particles and second organic particles can all be obtained commercially.

[0163] The isolation membrane preparation method of the embodiment 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.

[0164] [Positive electrode]

[0165] 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.

[0166] 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.

[0167] 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.

[0168] 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.

[0169] The modified compounds of the above materials may be doping-modified and / or surface-coated modified materials.

[0170] The positive electrode film layer may also optionally include a binder, a conductive agent and other optional additives.

[0171] 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.

[0172] As an example, the binder can 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).

[0173] [Negative electrode]

[0174] 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.

[0175] 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.

[0176] 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 commercially.

[0177] 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.

[0178] The negative electrode film layer may also optionally include a binder, a conductive agent and other optional additives.

[0179] 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.

[0180] As an example, the binder can 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).

[0181] As examples, other optional auxiliary agents may be thickening and dispersing agents (such as sodium carboxymethyl cellulose CMC-Na), PTC thermistor materials.

[0182] [Electrolyte]

[0183] The secondary battery may include an electrolyte that conducts ions between the positive electrode and the negative electrode. The electrolyte may include an electrolyte salt and a solvent.

[0184] As an example, the electrolyte salt can be selected from one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalatoborate (LiDFOB), lithium dioxalatoborate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorobis(oxalatophosphate) (LiDFOP) and lithium tetrafluorooxalatophosphate (LiTFOP).

[0185] 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), cyclopentane (SF), dimethyl sulfone (MSM), ethyl methyl sulfone (EMS) and diethyl sulfone (ESE).

[0186] 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.

[0187] In some embodiments, the secondary battery may be a lithium ion secondary battery.

[0188] 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 6 The secondary battery 5 is a square structure as an example.

[0189] In some embodiments, the secondary battery may include an outer package for packaging a positive electrode sheet, a negative electrode sheet, and an electrolyte.

[0190] In some embodiments, reference Figure 7 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.

[0191] 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 housing cavity. The electrolyte can be an electrolyte, and the electrolyte is soaked 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.

[0192] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft package, such as a bag-type soft package. The material of the soft package can be plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0193] 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.

[0194] Figure 8 4 is an example of a battery module. Figure 8 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.

[0195] The battery module 4 may further include a housing having a housing space in which the plurality of secondary batteries 5 are housed.

[0196] 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.

[0197] Fig. 9 and Fig.10 1 is a battery pack 1 as an example. Fig. 9 and Fig.10The 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.

[0198] Device

[0199] The present application also provides a device, the device includes at least one of the secondary battery, battery module, or battery pack. The secondary battery, battery module or battery pack can be used as a power source for the device, and can also be used 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), 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), an electric train, a ship and a satellite, and an energy storage system.

[0200] The device can select a secondary battery, a battery module or a battery pack according to its usage requirements.

[0201] Fig.11 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.

[0202] Another example of a device may be a mobile phone, a tablet computer, or a notebook computer. The device is usually required to be thin and light, and a secondary battery may be used as a power source.

[0203] The beneficial effects of the present application are further illustrated below in conjunction with embodiments.

[0204] In order to make the technical problems, technical solutions and beneficial effects solved by the embodiments of the present application clearer, the following will be further described in detail with reference to the embodiments and the accompanying drawings. Obviously, the described embodiments are only a 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.

[0205] 1. Preparation of isolation membrane

[0206] Isolation film 1:

[0207] (1) A PE substrate is provided. For example, the thickness of the substrate is 7 μm and the porosity is 40%.

[0208] (2) Preparation of coating slurry: Inorganic particles of aluminum oxide (Al2O3), first organic particles of vinylidene fluoride-hexafluoropropylene copolymer, second organic particles of styrene-vinyl acetate-pyrrolidone copolymer, dispersant sodium carboxymethyl cellulose (CMC-Na), and wetting agent silicone-modified polyether are mixed uniformly in an appropriate amount of solvent deionized water at a dry weight ratio of 70:20:8:1:1 to obtain a coating slurry with a solid content of 38% (by weight). The volume average particle size Dv50 of the inorganic particles of aluminum oxide (Al2O3) is 1 μm, the first organic particles are secondary particles with a number average particle size of 8 μm, the second organic particles are primary particles with a number average particle size of 4.8 μm, and at least a portion of the second organic particles include a core structure and a shell structure, and the glass transition temperature of the shell structure is 58°C, and the glass transition temperature of the core structure is 20°C.

[0209] (3) The coating slurry prepared in step (2) is coated on two surfaces of the PE substrate by a coating machine, and then dried and cut to obtain a separator 1. The coating machine has a gravure roller with a line number of 125 LPI, a coating speed of 50 m / min, a coating line speed ratio of 1.15, a drying temperature of 50° C., and a drying time of 25 s. The coating weight per unit area on one side of the separator is 2.3 g / m 2 .

[0210] The materials used in the examples can all be obtained commercially. For example:

[0211] The substrate can be purchased from Shanghai Enjie New Materials Co., Ltd.

[0212] Inorganic particles can be purchased from Yishitong Materials Technology Co., Ltd.

[0213] The first organic particles can be purchased from Arkema (Changshu) Chemical Co., Ltd.

[0214] The second type of organic particles can be purchased from Sichuan Yindi Le Technology Co., Ltd.

[0215] The dispersant can be purchased from Changshu Weiyi Technology Co., Ltd.

[0216] Wetting agents are available commercially from The Dow Chemical Company.

[0217] The preparation method of isolation film 2-34 is similar to that of isolation film 1, except that the material types of the first organic particles and the second organic particles, as well as the number average particle sizes of the first organic particles and the second organic particles are adjusted. See Table 1 for details.

[0218] 2. Preparation of batteries

[0219] Example 1

[0220] 1. Preparation of positive electrode sheet

[0221] The positive electrode active material LiNi 0.8 Co 0.1 Mn 0.1 O2 (NCM811), conductive agent carbon black (Super P), binder polyvinylidene fluoride (PVDF) are mixed evenly in a proper amount of solvent N-methylpyrrolidone (NMP) at a mass ratio of 96.2:2.7:1.1 to obtain positive electrode slurry, which is then coated on the positive electrode current collector aluminum foil, and then dried, cold pressed, slit, and cut to obtain positive electrode sheets. The positive electrode surface density is 0.207 mg / mm 2 , compacted density is 3.5g / cm 3 .

[0222] 2. Negative electrode preparation

[0223] 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, which is then coated on the negative electrode current collector copper foil, and then dried, cold pressed, stripped and cut to obtain a negative electrode sheet. The negative electrode surface density is 0.126 mg / mm2 and the compacted density is 1.7 g / cm 3 .

[0224] 3. Isolation film

[0225] The isolation film adopts the isolation film 1 prepared above.

[0226] 4. Preparation of electrolyte

[0227] 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, the concentration of the electrolyte salt is 1.0 mol / L, and the mixture is evenly mixed to obtain an electrolyte solution.

[0228] 5. Preparation of secondary batteries

[0229] The positive electrode sheet, the separator, and the negative electrode sheet are stacked in order, so that the separator is 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, and shaping processes, a secondary battery is obtained.

[0230] The preparation methods of the secondary batteries of Examples 2-26 and Comparative Examples 1-8 are similar to the preparation methods of the secondary battery of Example 1, except that different isolation membranes are used. See Table 1 for details.

[0231] 3. Battery performance test

[0232] 1. 25℃ Cycle Performance

[0233] At 25°C, the secondary batteries prepared in the examples and comparative examples were charged at a constant current of 1C 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 5 minutes, and then discharged at a constant current of 0.33C to a discharge cut-off voltage of 2.8V, left to stand for 5 minutes, and the battery capacity C0 at this time was recorded. According to this method, the battery was charged and discharged for 1500 cycles, and the battery capacity after 1500 cycles was recorded as C1.

[0234] Battery cycle capacity retention rate at 25°C = C1 / C0×100%

[0235] 2. 45℃ Cycle Performance

[0236] At 45°C, the secondary batteries prepared in the examples and comparative examples were charged at a constant current rate of 1C 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 5 minutes, and then discharged at a constant current rate of 0.33C to a discharge cut-off voltage of 2.8V, left to stand for 5 minutes, and the battery capacity at this time was recorded as C0. According to this method, the battery was charged and discharged for 1500 cycles, and the battery capacity at this time was recorded as C1.

[0237] Battery cycle capacity retention rate at 45°C = C1 / C0×100%

[0238] 3. Hot box test

[0239] At 25°C, the secondary batteries prepared in the embodiments and comparative examples were charged at a constant current of 1C to a charge cut-off voltage of 4.2V, then charged at a constant voltage to a current ≤0.05C, and left to stand for 5 min; then, each battery was tested with a fixture in a DHG-9070A DHG series high temperature oven, and the temperature was raised from room temperature to 80°C±2°C at a rate of 5°C / min, and maintained for 30 min; then, the temperature was raised at a rate of 5°C / min, and the temperature was kept for 30 min every time the temperature was raised by 5°C, until the battery cell failed; and the temperature when the battery cell began to fail was recorded.

[0240] Table 1 shows the measured battery performance of each embodiment and comparative example.

[0241]

[0242]

[0243] As can be seen from Table 1, by using the first organic particles and the second organic particles of the specific particle size and structure defined in the present application, the cycle performance and safety performance of the battery can be significantly improved. In particular, by further selecting the number average particle size of the first organic particles and the second organic particles, the ratio between the two, and the type of material, the cycle performance and safety performance can be further improved. In comparison, Comparative Examples 1 and 2 using only the first organic particles and Comparative Examples 3, 4, and 7 in which the second organic particles do not have a core-shell structure are not as good as Examples 1-26 of the present invention in terms of cycle performance and safety performance. Although Comparative Examples 5, 6, and 8 use the second organic particles with a core-shell structure, the number average particle size of the first organic particles or the number average particle size of the second organic particles is not within the range defined in the present application, and therefore good cycle performance and safety performance cannot be obtained.

[0244] 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 drying conditions, and obtained similar effects of improving the cycle performance and safety performance of the battery as in Examples 1-26.

[0245] 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 forming a coating on at least one surface of the substrate; The coating layer comprises inorganic particles and organic particles, the organic particles comprise first organic particles and second organic particles, the first organic particles and the second organic particles are embedded in the inorganic particles and form protrusions on the surface of the coating layer; The number average particle size of the first organic particles is 8-27 μm; The number average particle size of the second organic particles is 2-10 μm, and at least a portion of the second organic particles include a core structure and a shell structure; 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 number average particle size of the first organic particles is ≥12 μm; optionally, the number average particle size of the first organic particles is 15 μm-25 μm.

3. The secondary battery according to any one of claims 1 to 2, wherein: The number average particle size of the second organic particles is 3 μm-8 μm; optionally, the number average particle size of the second organic particles is 3 μm-6 μm.

4. The secondary battery according to any one of claims 1 to 3, wherein: The ratio of the number average particle size of the first organic particles to the number average particle size of the second organic particles is ≥2; optionally, the ratio of the number average particle size of the first organic particles to the number average particle size of the second organic particles is 2.5-4.

5. The secondary battery according to any one of claims 1 to 4, wherein: The first organic particles are secondary particles.

6. The secondary battery according to any one of claims 1 to 5, wherein: The second organic particles are primary particles.

7. The secondary battery according to any one of claims 1 to 6, 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.

8. The secondary battery according to any one of claims 1 to 7, 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.

9. The secondary battery according to any one of claims 1 to 8, wherein: The core structure and the shell structure of the second organic particle are independently selected from 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 core structure and the shell structure in the second organic particles are independently selected from the copolymers of acrylic acid ester monomer units and styrene monomer units, the copolymers of acrylic acid monomer units and styrene monomer units, the copolymers of acrylic acid monomer units-acrylic acid ester monomer units-styrene monomer units, the copolymers of styrene monomer units and unsaturated nitrile monomer units, the 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 secondary battery according to any one of claims 1 to 9, wherein: The core structure and shell structure in the second organic particles are independently selected from 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 materials.

11. The secondary battery according to any one of claims 1 to 10, wherein: The core structure and the shell structure of the second organic particles both include one or more of a copolymer of an acrylic acid ester monomer unit and a styrene monomer unit and a modified compound thereof.

12. The secondary battery according to any one of claims 1 to 11, wherein: The glass transition temperature of the shell structure is higher than the glass transition temperature of the core structure; Optionally, the isolation film satisfies at least one of the following conditions: The glass transition temperature of the core structure is -30°C to 20°C, and may be further -10°C to 10°C; or The glass transition temperature of the shell structure is 50°C to 70°C, and can further be 55°C to 65°C.

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 also satisfies one or more of the following (1)-(4): (1) The mass proportion of the inorganic particles in the coating is ≤70%. Optionally, the mass proportion of the inorganic particles in the coating is 60%-70%; (2) The mass proportion of the first organic particles in the coating is ≥ 12%. Optionally, the mass proportion of the first organic particles in the coating is 15%-25%; (3) The mass proportion of the second organic particles in the coating is ≤10%. Optionally, the mass proportion of the second organic particles in the coating is 2%-10%. (4) Single-sided coating weight per unit area on the isolation film ≤ 3.0 g / m 2 Optionally, the coating weight per unit area on one side of the isolation film is 1.5 g / m 2 -2.5g / m 2 .

15. The secondary battery according to any one of claims 1 to 14, 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; 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%; alternatively, 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%.

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

17. The secondary battery according to any one of claims 1 to 16, 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.

18. The secondary battery according to any one of claims 1 to 17, 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.

19. The secondary battery according to any one of claims 1 to 18, 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.

20. A battery module comprising the secondary battery according to any one of claims 1 to 19. 21 . A battery pack comprising at least one of the secondary battery according to claim 1 to 19 and the battery module according to claim 20.

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

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