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 base material (A) and a coating layer (B) provided on at least one surface of the base material (A); the coating (B) comprises inorganic particles (B3) and organic particles, the organic particles comprise first organic particles (B1) and second organic particles (B2), the first organic particles (B1) and the second organic particles (B2) are embedded in the inorganic particles (B3), and protrusions are formed on the surface of the coating (B); the first organic particles (B1) are secondary particles, the number of the first organic particles (B1) in the coating (B) is recorded as A, the second organic particles (B2) are primary particles, the number of the second organic particles (B2) in the coating (B) is recorded as B, and the isolating membrane meets the condition that A / B is larger than or equal to 0.05 and smaller than 1.

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 features such as light weight, no pollution, and no memory effect.

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

[0004] Therefore, how to make the battery have good rate performance, storage performance and safety performance at the same time 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 good rate performance, storage performance and safety performance.

[0006] In order to achieve the above-mentioned purpose, the isolation film provided in the first aspect of the present application includes: a substrate and a coating disposed on at least one surface of the substrate. The coating includes inorganic particles and organic particles. The organic particles include first organic particles 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 first organic particles are secondary particles, and the number of the first organic particles in the coating is recorded as A, the second organic particles are primary particles, and the number of the second organic particles in the coating is recorded as B, then the isolation film satisfies: 0.05≤A / B<1.

[0007] Compared with the prior art, the present application at least has the following beneficial effects:

[0008] The isolation membrane of the present application contains inorganic particles and organic particles in the same coating, which greatly reduces the thickness of the isolation membrane, thereby improving the energy density of the battery; and the organic particles include a first organic particle and a second organic particle in a specific distribution state and quantity ratio range, which can not only effectively improve the adhesion between the isolation membrane and the electrode plate, but also reduce the wrinkling of the isolation membrane during the battery cycle, so that the battery can take into account both safety performance and rate performance.

[0009] In any embodiment of the present application, the isolation film satisfies: 0.2≤A / B≤0.6; optionally, 0.25≤A / B≤0.5. When A / B is within the given range, the rate performance, storage performance and safety performance of the battery can be further improved.

[0010] In any embodiment of the present application, the number average particle size of the first organic particles is ≥8 μm; optionally, the number average particle size of the first organic particles is 12 μm-25 μm. When the number average particle size of the first organic particles is within the given range, the rate performance of the battery can be further improved.

[0011] In any embodiment of the present application, the number average particle size of the second organic particles is ≥ 2 μm; optionally, the number average particle size of the second organic particles is 3 μm-7 μm. When the number average particle size of the second organic particles is within the given range, the rate performance and safety performance of the battery can be further improved.

[0012] 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 ≥ 2.0; 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 2.5-4.0. When the ratio of the number average particle size of the first organic particles to the second organic particles is within the given range, the rate performance and safety performance of the battery can be further improved.

[0013] In any embodiment of the present application, the mass proportion of the inorganic particles in the coating is ≤75%. Optionally, the mass proportion of the inorganic particles in the coating is 60%-75%.

[0014] In any embodiment of the present application, 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%.

[0015] In any embodiment of the present application, 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%.

[0016] 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.

[0017] 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 Optionally, the coating weight per unit area on one side of the isolation film is 1.5 g / m 2 -3.0g / m2 When the coating weight per unit area on one side of 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.

[0018] In any embodiment of the present application, the first organic particles include homopolymers or copolymers of fluorine-containing olefinic monomer units, homopolymers or copolymers of olefinic monomer units, homopolymers or copolymers of unsaturated nitrile monomer units, homopolymers or copolymers of alkylene oxide monomer units, and one or more modified compounds of the above homopolymers or copolymers.

[0019] In any embodiment of the present application, the first organic particles include polytetrafluoroethylene, polychlorotrifluoroethylene, polyvinyl fluoride, polyvinylidene fluoride, polyethylene, polypropylene, polyacrylonitrile, polyethylene oxide, copolymers of different fluorine-containing 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.

[0020] In any embodiment of the present application, the first organic particles include one or more of vinylidene fluoride-trifluoroethylene copolymer, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-trifluoroethylene-hexafluoropropylene copolymer, vinylidene fluoride-hexafluoropropylene-acrylic acid copolymer, vinylidene fluoride-hexafluoropropylene-acrylate copolymer, and modified compounds of the above copolymers.

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

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

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

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

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

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

[0027] kgf / cm 2 -2500 kgf / cm 2 .

[0028] In any embodiment of the present application, the longitudinal tensile strength (TD) of the separator is 1000 kgf / cm 2 -2500kgf / cm 2 Optionally, the longitudinal tensile strength of the isolation film is 1400

[0029] kgf / cm 2 -2000 kgf / cm 2 .

[0030] In any embodiment of the present application, the transverse elongation at break of the isolation film is 50%-200%; optionally, the transverse elongation at break of the isolation film is 100%-150%.

[0031] In any embodiment of the present application, the longitudinal elongation at break of the isolation film is 50%-200%; optionally, the longitudinal elongation at break of the isolation film is 100%-150%.

[0032] In any embodiment of the present application, the inorganic particles and the organic particles form a non-uniform pore structure in the coating.

[0033] 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.

[0034] 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, wherein the coating slurry comprises component materials and a solvent, wherein the component materials comprise inorganic particles and organic particles, wherein the organic particles comprise 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 first organic particles are secondary particles, and the number of the first organic particles in the dried coating is recorded as A, the second organic particles are primary particles, and the number of the second organic particles in the dried coating is recorded as B, then the isolation film satisfies: 0.05≤A / B<1.

[0035] 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%.

[0036] 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%.

[0037] In any embodiment of the present application, in step (2), the solid content of the coating slurry is 28%-45%, and can be optionally 30%-38%.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] In any embodiment of the present application, in step (3), the drying time is 10s-120s, and can be optionally 20s-80s.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] The device of the present application includes at least one of the secondary battery, battery module or battery pack provided in the present application, and thus has at least the same advantages as the secondary battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] 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.

[0049] Figure 1 It is a schematic structural diagram of an embodiment of the isolation membrane of the present application.

[0050] Figure 2-1 This is a scanning electron microscope (SEM) image of an embodiment of the isolation film of the present application at a magnification of 500 times.

[0051] Figure 2-2 This is a scanning electron microscope (SEM) picture of an embodiment of the isolation film of the present application at a magnification of 3000 times.

[0052] 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.

[0053] Figure 4-1 It is a schematic structural diagram of an embodiment of the isolation membrane of the present application.

[0054] Figure 4-2 It is a schematic structural diagram of another embodiment of the isolation membrane of the present application.

[0055] Figure 5 It is a schematic diagram of one embodiment of a secondary battery.

[0056] Figure 6 yes Figure 5 Exploded diagram of .

[0057] Figure 7 is a schematic diagram of one embodiment of a battery module.

[0058] Figure 8 is a schematic diagram of one embodiment of a battery pack.

[0059] Fig. 9 yes Figure 8 Exploded diagram of .

[0060] Fig.10 is a schematic diagram of one embodiment of a device in which a secondary battery is used as a power source. DETAILED DESCRIPTION

[0061] 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.

[0062] 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.

[0063] 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.

[0064] 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).

[0065] 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).

[0066] Secondary battery

[0067] A secondary battery is a battery that can be recharged to activate the active materials after being discharged and continue to be used.

[0068] 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.

[0069] [Isolation film]

[0070] The isolation film provided in the present application includes: a substrate and a coating disposed on at least one surface of the substrate. The coating includes inorganic particles and organic particles. The organic particles include first organic particles 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 first organic particles are secondary particles, and the number of the first organic particles in the coating is recorded as A, the second organic particles are primary particles, and the number of the second organic particles in the coating is recorded as B, then the isolation film satisfies: 0.05≤A / B<1.

[0071] The isolation film of the present application includes inorganic particles, specific first organic particles and second organic particles in the same coating layer, which can further improve the battery's rate performance, high temperature storage performance and puncture safety performance while ensuring that the battery has a high energy density.

[0072] 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.

[0073] Without wishing to be limited to any theory, the inventors have found through extensive research that the isolation membrane of the present application contains inorganic particles and organic particles in the same coating layer. Compared with the isolation membrane having two coating layers, the thickness of the isolation membrane is greatly reduced, thereby improving the energy density of the battery; at the same time, the organic particles include a first organic particle and a second organic particle, and the morphology and quantity ratio of the first organic particle and the second organic particle are specially designed. On the one hand, the first organic particle is a secondary particle, which helps to form a uniform coating interface and can effectively improve the problem of misalignment of the tabs in the battery preparation process, thereby improving the safety performance of the battery; the second organic particle is a primary particle, and the particles and the particles are closely connected. On the other hand, it is not easy to form a large-area film structure between the organic particles, thereby further improving the rate performance and safety performance of the battery; on the other hand, the combination of the two can effectively improve the wettability and distribution uniformity of the electrolyte, and further improve the high-temperature storage performance of the battery; in particular, when the battery encounters a foreign object piercing during use, the second organic particles can instantly wrap the foreign object and the exposed copper foil or aluminum foil to form a first polymer insulating layer, effectively reducing the probability of short circuit between the positive and negative electrodes and improving the safety performance of the battery. As the temperature around the foreign object increases, the first organic particles will form a more solid second polymer insulating layer around the first polymer insulating layer, thereby further improving the safety performance of the battery.

[0074] When A / B is too small (for example, less than 0.05), it may be that there are too few first organic particles or too many second organic particles. When there are too few first organic particles, the isolation membrane is not easy to form a strong second polymer insulation layer when the battery is used in a harsh environment, thus affecting the safety performance of the battery; when there are too many second organic particles, excessive adhesion may occur between the isolation membrane and the electrode plate, causing excessive consumption of the electrolyte, and reduced wettability and uniformity of the electrolyte, thereby affecting the storage performance of the battery.

[0075] When A / B is too large (for example, greater than 1), it may be that there are too many first organic particles or too few second organic particles. When there are too many first organic particles, the ion transmission path may be too long, thus affecting the battery's rate performance; when there are too few second organic particles, when the battery is in a harsh operating environment, the isolation membrane is not easy to form the first polymer insulating layer instantly, which greatly increases the risk of battery short circuit, thereby affecting the battery's safety performance.

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

[0077] In some embodiments, the isolation film may satisfy: 0.05≤A / B≤0.95, 0.1≤A / B<1, 0.15≤A / B<1, 0.15≤A / B≤0.8, 0.2≤A / B≤0.85, 0.2≤A / B≤0.6, 0.25≤A / B≤0.5, 0.3≤A / B≤0.75, 0.3≤A / B≤0.6, 0.3≤A / B≤0.5, 0.3≤A / B≤0.45. When A / B is within the given range, the rate performance, storage performance and safety performance of the battery can be further improved.

[0078] 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).

[0079] In some embodiments, the number average particle size of the first organic particles is ≥ 8 μm; for example, the number average particle size of the first organic particles can be 10 μm-20 μm, 10.5 μm-18 μm, 12 μm-25 μm, 12 μm-18 μm, 13 μm-20 μm, 15 μm-22 μm. When the number average particle size of the first organic particles is within the given range, sufficient gaps can be formed between the organic particles, and even if the organic particles swell in the electrolyte, sufficient ion transmission channels can be formed, which can further improve the rate performance of the battery.

[0080] In some embodiments, the number average particle size of the second organic particles is ≥ 2 μm; for example, the number average particle size of the second organic particles can be 3 μm-8 μm, 2.5 μm-7 μm, 3 μm-7 μm, 3 μm-6 μm, 3.5 μm-6 μm. When the number average particle size of the second organic particles is within the given range, the rate performance and safety performance of the battery can be further improved.

[0081] 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 ≥ 2.0; 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 2.0-5.0, 2.0-4.5, 2.0-4.0, 2.5-4.0, 3.0-4.0. 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 rate performance and safety performance of the battery can be further improved.

[0082] 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.

[0083] 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.

[0084] 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.

[0085] In some embodiments, the olefin-based monomer unit may be selected from one or more of ethylene, propylene, butadiene, and isoprene.

[0086] In some embodiments, the unsaturated nitrile monomer unit may be selected from one or more of acrylonitrile and methacrylonitrile.

[0087] In some embodiments, the alkylene oxide monomer unit may be selected from one or more of ethylene oxide and propylene oxide.

[0088] 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.

[0089] 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.

[0090] In some embodiments, the second organic particles may include homopolymers or copolymers of acrylate monomer units, homopolymers or copolymers of acrylic acid monomer units, homopolymers or copolymers of styrene monomer units, polyurethane compounds, rubber compounds, and one or more of modified compounds of the above homopolymers or copolymers.

[0091] In some embodiments, the second organic particles may include a copolymer of an acrylic acid ester monomer unit and a styrene monomer unit, a copolymer of an acrylic acid monomer unit and a styrene monomer unit, a copolymer of an acrylic acid monomer unit-an acrylic acid ester monomer unit-a styrene monomer unit, a copolymer of a styrene monomer unit and an unsaturated nitrile monomer unit, a copolymer of a styrene monomer unit-an olefin monomer unit-an unsaturated nitrile monomer unit, and one or more of the modified compounds of the above copolymers.

[0092] 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.

[0093] In some embodiments, the acrylic monomer unit may be selected from one or more of acrylic acid and methacrylic acid.

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

[0095] In some embodiments, the unsaturated nitrile monomer unit may be selected from one or more of acrylonitrile and methacrylonitrile.

[0096] In some embodiments, the second organic particles may include butyl acrylate-styrene copolymer, butyl methacrylate-isooctyl methacrylate copolymer, isooctyl methacrylate-styrene copolymer, methacrylate-methacrylic acid-styrene copolymer, methyl acrylate-isooctyl methacrylate-styrene copolymer, butyl acrylate-isooctyl methacrylate-styrene copolymer, butyl acrylate-isooctyl methacrylate-styrene copolymer, butyl methacrylate-isooctyl methacrylate-styrene copolymer, butyl methacrylate-isooctyl methacrylate-styrene copolymer, butyl methacrylate-isooctyl methacrylate-styrene copolymer, styrene-acrylonitrile copolymer, styrene-butadiene-acrylonitrile copolymer, methyl acrylate-styrene-acrylonitrile copolymer, isooctyl methacrylate-styrene-acrylonitrile copolymer, styrene-vinyl acetate copolymer, styrene-vinyl acetate-pyrrolidone copolymer, and one or more of the modified compounds of the above copolymers.

[0097] 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 a modified compound thereof.

[0098] In some embodiments, the number average molecular weight of the first organic particles is 300,000-800,000, such as 400,000-650,000.

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

[0100] In some embodiments, the 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).

[0101] 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, 0.5 μm-1 μm. When the volume average particle size of the inorganic particles is controlled within the given range, it can ensure that the battery has good cycle performance and safety performance, and further improves the volume energy density of the battery.

[0102] In some embodiments, the mass proportion of the inorganic particles in the coating is ≤75% (based on the total mass of the coating); for example, the mass proportion of the inorganic particles in the coating may be 60%-75%, 60%-70%, 65%-75%. When the mass proportion of the inorganic particles is controlled within the given range, it can ensure that the battery has good safety performance and further improves the mass energy density of the battery.

[0103] 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%, 16%-18%. When the mass proportion of the first organic particles is controlled within the given range, it is easier to achieve the above-mentioned A / B range of the present application. At the same time, the appropriate mass proportion range can also reduce the consumption of the electrolyte by the separator, thereby further improving the storage performance and safety performance of the battery.

[0104] 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 may be 2%-10%, 3%-7%, or 3%-5%. When the mass proportion of the second organic particles is controlled within the given range, it is easier to achieve the above-mentioned A / B range of the present application, and at the same time, it is also helpful to make the isolation film have a suitable pore structure under the premise of ensuring adhesion, thereby further improving the rate performance and safety performance of the battery.

[0105] 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 uneven pore structure while ensuring safety performance, while achieving lightweight isolation membrane, thereby further improving the energy density of the battery.

[0106] In some embodiments, the coating weight per unit area on one side of the isolation film is ≤3.0 g / m 2 For example, the coating weight per unit area on one side of the isolation film can be 1.5 g / m 2 -3.0g / m2 , 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 battery energy density can be improved while further taking into account the battery rate performance and safety performance.

[0107] In some embodiments, the coating may further include other organic compounds, for example, a polymer for improving heat resistance (referred to as "heat-resistant glue"), a dispersant, a wetting agent, other types of binders, etc. The above-mentioned other organic compounds are all non-granular substances in the coating. The present application has no particular restrictions on the types of the above-mentioned other organic compounds, and any known material with good improved performance can be selected.

[0108] 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.

[0109] In some embodiments, the thickness of the substrate is ≤10 μm; for example, the thickness of the substrate may be 5 μm-10 μm, 5 μm-9 μm, or 7 μm-9 μm. When the thickness of the substrate is controlled within the given range, the energy density of the battery can be further improved while ensuring the battery rate performance and safety performance.

[0110] 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.

[0111] In some embodiments, the longitudinal tensile strength (TD) of the separator may be 1000 kgf / cm 2 -2500kgf / cm 2 For example, the longitudinal tensile strength of the isolation film can be 1400kgf / cm 2 -2000 kgf / cm 2 .

[0112] 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%.

[0113] 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 .

[0114] 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%.

[0115] 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.

[0116] According to some embodiments, the number ratio of the first organic particles to the second organic particles can be tested by methods known in the art, for example, it can be measured by a scanning electron microscope. As an example, the test method for the number ratio of the first organic particles to the second organic particles can be: the isolation film is made into a test sample with a length × width = 50 mm × 100 mm; the organic particles in the coating are tested using a scanning electron microscope (such as ZEISS Sigma300). The test can refer to JY / T010-1996. A plurality of (for example, 5) different areas are randomly selected from the test sample for scanning test, and the number of the first organic particles or the second organic particles in the test area is counted at a certain magnification (for example, 500 times or 1000 times), the average value of the number of the first organic particles in each test area is recorded as A, the average value of the number of the second organic particles in each test area is recorded as B, and the value of A / B is calculated. In order to ensure the accuracy of the test results, multiple test samples (for example, 10) can be taken to repeat the above test, and the average value of A / B calculated for each test sample is taken as the final test result.

[0117] Figure 2-1 : is a scanning electron microscope (SEM) image of the isolation film of the embodiment of the present application at a magnification of 500 times. Figure 2-1 In the present invention, the number A of the first organic particles in the coating layer and the number B of the second organic particles in the coating layer can be counted according to the method given above.

[0118] 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.

[0119] 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.

[0120] 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.

[0121] Similarly, the distance L1 between any two adjacent inorganic particles can also be tested according to the above method.

[0122] Figure 2-2 : 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 2-2 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.

[0123] 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, the test can be performed 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), the sample to be tested is clamped with two conductive and thermally conductive sheets (e.g., copper foil), the sample to be tested and the sheet are glued and fixed with glue (e.g., double-sided tape), a flat iron block of a certain mass (e.g., 400 g) is used to press for a certain time (e.g., 1 hour) 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 stage with conductive glue, with the sample slightly protruding from the edge of the sample stage. Then put the sample stage into the sample holder and lock it, turn on the power of the argon ion cross-section polisher (such as IB-19500CP) and evacuate (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.

[0124] 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.

[0125] 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.

[0126] 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 an 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.

[0127] 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.

[0128] 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.

[0129] The present application also provides a method for preparing an isolation film, comprising the following steps:

[0130] (1) providing a substrate;

[0131] (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;

[0132] (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 it to obtain the isolation film;

[0133] Among them, the dried coating includes 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 first organic particles are secondary particles, and the number of the first organic particles in the dried coating is recorded as A, the second organic particles are primary particles, and the number of the second organic particles in the dried coating is recorded as B, then the isolation film satisfies: 0.05≤A / B<1.

[0134] like Figure 4-1 As shown, the separator includes a substrate (A) and a coating (B), wherein the coating (B) is disposed on only one surface of the substrate (A).

[0135] like Figure 4-2 As shown, the isolation film includes a substrate (A) and a coating (B), and the coating (B) is disposed on both surfaces of the substrate (A).

[0136] 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.

[0137] In some embodiments, in step (2), the solvent may be water, such as deionized water.

[0138] 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 other types of binders. The other organic compounds are all non-granular in the dried coating.

[0139] In some embodiments, in step (2), component materials are added to a solvent and stirred evenly to obtain a coating slurry.

[0140] 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%.

[0141] 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%.

[0142] When the added mass of the first organic particles or the second organic particles is within the above range, it is helpful to control the quantity ratio of the first organic particles to the second organic particles within the given range. At the same time, the appropriate content of organic particles can reduce the static electricity generated between the separator and the battery winding tool (such as a winding needle) or the lamination 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.

[0143] 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.

[0144] In some embodiments, in step (2), the solid content of the coating slurry can be controlled within the range of 28%-45%, for example, 30%-38%. When the solid content of the coating slurry is within the above range, the film surface problems of the coating can be effectively reduced and the probability of uneven coating can be reduced, thereby further improving the cycle performance and safety performance of the battery.

[0145] In some embodiments, in step (3), the coating is performed using a coater.

[0146] 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.

[0147] 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.

[0148] In some embodiments, the coater includes a gravure roll; the gravure roll is used to transfer the coating slurry to the substrate.

[0149] 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 number ratio of the first organic particles to the second organic particles within the given range, thereby further improving the cycle performance and safety performance of the isolation film.

[0150] In some embodiments, in step (3), the coating speed can be controlled within the range of 30 m / min-90 m / min, such as 50 m / min-70 m / min. When the coating speed is within the above range, it helps to control the quantity ratio of the first organic particles to the second organic particles within the given range; and can effectively reduce the film surface problem of the coating and reduce the probability of uneven coating, thereby further improving the cycle performance and safety performance of the battery.

[0151] 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.

[0152] In some embodiments, in step (3), the drying temperature may be 40°C-70°C, for example, 50°C-60°C.

[0153] In some embodiments, in step (3), the drying time may be 10s-120s, for example, 20s-80s, 20s-40s.

[0154] 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.

[0155] 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.

[0156] The above-mentioned substrate, first organic particles and second organic particles can all be obtained commercially.

[0157] The isolation membrane preparation method of the present application obtains the coating by one-time coating, which greatly simplifies the production process of the isolation membrane; at the same time, the isolation membrane prepared by the above method is used in the battery, which can effectively improve the battery's rate performance, storage performance and safety performance.

[0158] [Positive electrode]

[0159] In the secondary battery, the positive electrode plate includes a positive electrode current collector and a positive electrode film layer disposed on the positive electrode current collector, and the positive electrode film layer includes a positive electrode active material.

[0160] 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.

[0161] 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.

[0162] 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.

[0163] In some embodiments, the modified compounds of the above materials may be doping-modified and / or surface-coated modified materials.

[0164] The positive electrode film layer may also optionally include a binder, a conductive agent and other optional additives.

[0165] 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.

[0166] 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).

[0167] [Negative electrode]

[0168] In the secondary battery, the negative electrode plate includes a negative electrode current collector and a negative electrode film layer disposed on the negative electrode current collector, and the negative electrode film layer includes a negative electrode active material.

[0169] 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.

[0170] 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.

[0171] 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.

[0172] The negative electrode film layer may also optionally include a binder, a conductive agent and other optional additives.

[0173] 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.

[0174] 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).

[0175] As examples, other optional auxiliary agents may be thickening and dispersing agents (such as sodium carboxymethyl cellulose CMC-Na), PTC thermistor materials.

[0176] [Electrolyte]

[0177] 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.

[0178] 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).

[0179] 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).

[0180] 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.

[0181] In some embodiments, the secondary battery may be a lithium ion secondary battery.

[0182] The embodiment of the present application has no particular limitation on the shape of the secondary battery, which may be cylindrical, square or any other shape. Figure 5 The secondary battery 5 is a square structure as an example.

[0183] In some embodiments, the secondary battery may include an outer package for packaging a positive electrode sheet, a negative electrode sheet, and an electrolyte.

[0184] In some embodiments, reference Figure 6 The outer package may include a shell 51 and a cover plate 53. The shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity.

[0185] 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.

[0186] 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).

[0187] 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.

[0188] Figure 7 4 is an example of a battery module. Figure 7 In the battery module 4, the plurality of secondary batteries 5 may be arranged in sequence along the length direction of the battery module 4. Of course, they may also be arranged in any other manner. Further, the plurality of secondary batteries 5 may be fixed by fasteners.

[0189] In some embodiments, the battery module 4 may further include a housing having a receiving space, and the plurality of secondary batteries 5 may be received in the receiving space.

[0190] 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.

[0191] Figure 8 and Fig. 9 1 is a battery pack 1 as an example. Figure 8 and Fig. 9 The battery pack 1 may include a battery box and a plurality of battery modules 4 disposed in the battery box. The battery box includes an upper box body 2 and a lower box body 3. The upper box body 2 can cover the lower box body 3 and form a closed space for accommodating the battery modules 4. The plurality of battery modules 4 can be arranged in the battery box in any manner.

[0192] Device

[0193] 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, etc.), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship and a satellite, an energy storage system, etc.

[0194] The device can select a secondary battery, a battery module or a battery pack according to its usage requirements. Fig.10 The device is used as an example. The device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. In order to meet the device's requirements for high power and high energy density of secondary batteries, a battery pack or a battery module can be used.

[0195] 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.

[0196] The beneficial effects of the present application are further illustrated below in conjunction with embodiments.

[0197] Example

[0198] In order to make the technical problems, technical solutions and beneficial effects solved by the present application clearer, the following will be further described in detail with reference to the embodiments and drawings. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all 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 application. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field without creative work belong to the scope of protection of the present application.

[0199] 1. Preparation of isolation membrane

[0200] Isolation film 1:

[0201] (1) providing a PE substrate, for example, the thickness of the substrate is 7 μm and the porosity is 40%;

[0202] (2) Preparation of coating slurry: Inorganic particles of aluminum oxide (Al2O3), the first organic particles of vinylidene fluoride-hexafluoropropylene copolymer (number average molecular weight of 550,000), the second organic particles of butyl methacrylate-isooctyl acrylate-styrene copolymer (number average molecular weight of 80,000), dispersant sodium carboxymethyl cellulose (CMC-Na), wetting agent silicone modified polyether and heat-resistant adhesive acrylic acid-acrylonitrile copolymer are mixed uniformly in an appropriate amount of solvent deionized water at a dry weight ratio of 71:12:10:1.5:0.5:5 to obtain a coating slurry with a solid content of 38% (by weight). Among them, 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 15.0 μm, and the second organic particles are primary particles with a number average particle size of 4.8 μm.

[0203] (3) The coating slurry prepared in step (2) is coated on two surfaces of the PE substrate by a coating machine, and a separation film 1 is obtained by drying, slitting and other processes. The aforementioned coating formulation process or coating process can be assisted to adjust the number ratio A / B of the first organic particles and the second organic particles to 0.05. For example, the line number of the gravure roller of the coating machine is 125 LPI, the coating speed is 50 m / min, the coating line speed ratio is 1.15, the drying speed is 50°C, and the drying time is 25 s. In the separation film, the first organic particles and the second organic particles are embedded in the inorganic particles and form protrusions on the coating surface.

[0204] The materials used in the examples can be obtained commercially, for example:

[0205] The substrate can be purchased from Shanghai Enjie New Materials Co., Ltd.

[0206] Inorganic particles can be purchased from Yishitong Materials Technology Co., Ltd.

[0207] The first organic particles can be purchased from Arkema (Changshu) Chemical Co., Ltd.

[0208] The second type of organic particles can be purchased from Sichuan Yindi Le Technology Co., Ltd.

[0209] Heat-resistant glue can be purchased from Sichuan Yindile Technology Co., Ltd.

[0210] Wetting agents are available commercially from The Dow Chemical Company.

[0211] The dispersant can be purchased from Changshu Weiyi Technology Co., Ltd.

[0212] The preparation method of isolation film 2-40 is similar to that of isolation film 1, except that the number average particle size, mass percentage, material type, etc. of the first organic particles and the second organic particles are adjusted, as shown in Table 1 for details.

[0213] 2. Preparation of batteries

[0214] Example 1

[0215] 1. Preparation of positive electrode sheet

[0216] The positive electrode active material LiNi 0.5 Co 0.2 Mn 0.3 O2 (NCM523), 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, and the positive electrode slurry is coated on the positive electrode current collector aluminum foil, and the positive electrode sheet is obtained through drying, cold pressing, striping, cutting and other processes. Optionally, the surface density of a single side of the positive electrode sheet is 0.207 mg / mm 2 The compaction density of the positive electrode is 3.5g / cm 3 .

[0217] 2. Preparation of negative electrode sheet

[0218] 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, slit, cut and other processes are performed to obtain a negative electrode sheet. The negative electrode surface density is 0.126 mg / mm 2 , compacted density is 1.7g / cm 3 .

[0219] 3. Isolation film

[0220] The isolation film adopts the isolation film 1 prepared above.

[0221] 4. Preparation of electrolyte

[0222] 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.

[0223] 5. Preparation of secondary batteries

[0224] The positive electrode sheet, the separator, and the negative electrode sheet are stacked in order, so that the separator is placed between the positive and negative electrode sheets to play an isolating role, and then they are wound to obtain an electrode assembly; the electrode assembly is placed in an outer package, and the prepared electrolyte is injected into the dried secondary battery. After vacuum packaging, standing, formation, shaping and other processes, a secondary battery is obtained.

[0225] The preparation methods of the secondary batteries of Examples 2-36 and Comparative Examples 1-4 are similar to the preparation methods of the secondary battery of Example 1, except that different isolation membranes are used. See Table 2 for details.

[0226] 3. Battery performance test

[0227] 1. 2C rate performance test

[0228] At 25°C, the secondary batteries of the embodiments and comparative examples were charged to 4.20V at a constant current of 0.33C, then charged to a current of 0.05C at a constant voltage, and left to stand for 5 minutes. The charging capacity at this time was recorded as the first charging capacity. After standing for 5 minutes, the secondary batteries were discharged to 2.8V at a constant current of 0.33C, and left to stand for 30 minutes. The secondary batteries were then charged to 4.20V at a constant current of 2C, then charged to a current of 0.05C at a constant voltage, and left to stand for 5 minutes. The charging capacity at this time was recorded.

[0229] Battery capacity retention rate at 2C charge rate (%) = 2C charge capacity / 0.33C charge capacity × 100%

[0230] 60℃ high temperature storage performance test

[0231] At 25°C, the secondary battery prepared in each embodiment and comparative example is charged to a charge cut-off voltage of 4.2V at a rate of 1C, then charged to a current of 0.05C at a constant voltage, left to stand for 5 minutes, and then discharged to a discharge cut-off voltage of 2.8V at a rate of 0.33C at a constant current to obtain the initial capacity of the battery. Then at 25°C, the battery is charged to a charge cut-off voltage of 4.2V at a rate of 1C, then charged to a current of 0.05C at a constant voltage, at which time the battery is fully charged, and the fully charged battery is placed in a thermostat at 60°C for storage. The battery is taken out every 7 days, and discharged to a discharge cut-off voltage of 2.8V at a rate of 0.33C at 25°C, left to stand for 5 minutes, then charged to a charge cut-off voltage of 4.2V at a rate of 1C, then charged to a current of 0.05C at a constant voltage, left to stand for 5 minutes, and then discharged to a constant current of 0.33C at a rate of 0.33C to test the capacity of the battery at this time. The number of days of storage is recorded until the capacity decays to 80% of the initial capacity. (It should be noted that each time the battery is taken out and the capacity is tested, it is necessary to charge the battery at a rate of 1C to a charge cut-off voltage of 4.2V, then charge it at a constant voltage to a current of 0.05C to keep the battery in a fully charged state, and then store it in a 60°C constant temperature box.)

[0232] 3. Shallow puncture test

[0233] At 25°C, the secondary batteries prepared in each embodiment and comparative example (each embodiment and comparative example takes several) are charged at a constant current rate of 1C to a charge cut-off voltage of 4.2V, and then charged at a constant voltage to a current of ≤0.05C, and left to stand for 10 minutes; the battery is peeled on the large surface, clamped with a clamp, and then punctured with a 1mm steel needle at a speed of 0.1mm / s until the battery has thermal runaway, and the puncture depth at this time is recorded as L0;

[0234] Take another battery and repeat the above steps, except that the puncture depth is controlled at L0-0.1mm and the battery is observed for 1 hour.

[0235] If the battery has thermal runaway during the above observation period, take another battery and repeat the above steps, except that the puncture depth is controlled at L0-0.2mm;

[0236] And so on, until the battery does not experience thermal runaway during the observation period, the puncture depth at this time is recorded as L, which is the puncture depth for safe use of the battery.

[0237]

[0238]

[0239] Table 2

[0240]

[0241] As can be seen from Table 1, by making the number ratio of the first organic particles and the second organic particles within the range specified in the present application, the rate performance, storage performance and safety performance of the battery can be significantly improved. In particular, by further optimizing the number average particle size, number average particle size ratio or material type of the first organic particles and the second organic particles, the rate performance, storage performance and safety performance of the battery can be further improved. In comparison, Comparative Examples 1-4 do not meet the requirements of the present application, so the battery cannot simultaneously take into account good rate performance, storage performance and safety performance.

[0242] The inventors also conducted experiments using other amounts and materials of inorganic particles, first organic particles and second organic particles within the scope of the present application, other substrates, other coating process parameters and other process conditions, and obtained similar effects of improving the cycle performance and safety performance of the battery as in Examples 1-36.

[0243] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any technician familiar with the technical field can easily think of various equivalent modifications or replacements within the technical scope disclosed in the present application, and these modifications or replacements should be included in the protection scope of the present application. Therefore, the protection scope of the present application shall be based on the protection scope of the claims.

Claims

1. A secondary battery comprising a positive electrode sheet, a separator and a negative electrode sheet; The isolation film comprises: Base material; and a coating disposed on at least one surface of the substrate; The coating layer comprises inorganic particles and organic particles, 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 first organic particles are secondary particles, and the number of the first organic particles in the coating is recorded as A, the second organic particles are primary particles, and the number of the second organic particles in the coating is recorded as B, then the isolation film satisfies: 0.05≤A / B<1; 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 isolation film satisfies: 0.2≤A / B≤0.6; optionally, 0.25≤A / B≤0.

5.

3. The secondary battery according to claim 1 or 2, wherein: The number average particle size of the first organic particles is ≥8 μm; optionally, the number average particle size of the first organic particles is 12 μm-25 μm.

4. The secondary battery according to any one of claims 1 to 3, wherein: The number average particle size of the second organic particles is ≥2 μm; optionally, the number average particle size of the second organic particles is 3 μm-7 μm.

5. The secondary battery according to any one of claims 1 to 4, 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 ≥2.0; 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.

0.

6. The secondary battery according to any one of claims 1 to 5, 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 ≤75%. Optionally, the mass proportion of the inorganic particles in the coating is 60%-75%; (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) The coating weight per unit area on one side of the isolation film is ≤3.0g / m 2 Optionally, the coating weight per unit area on one side of the isolation film is 1.5 g / m 2 -3.0g / m 2 .

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 second organic particles include one or more of homopolymers or copolymers of acrylate monomer units, homopolymers or copolymers of acrylic acid monomer units, homopolymers or copolymers of styrene monomer units, polyurethane compounds, rubber compounds, and modified compounds of the above homopolymers or copolymers; Optionally, the second organic particles include copolymers of acrylic acid ester monomer units and styrene monomer units, copolymers of acrylic acid monomer units and styrene monomer units, copolymers of acrylic acid monomer units-acrylic acid ester monomer units-styrene monomer units, copolymers of styrene monomer units and unsaturated nitrile monomer units, copolymers of styrene monomer units-olefin monomer units-unsaturated nitrile monomer units, and one or more of the modified compounds of the above copolymers.

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

11. The secondary battery according to any one of claims 1 to 10, 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).

12. The secondary battery according to any one of claims 1 to 11, 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 -3000 kgf / cm 2 Optionally, the transverse tensile strength of the isolation film is 1800 kgf / cm 2 -2500 kgf / cm 2 ; (3) The longitudinal tensile strength (TD) of the separator is 1000 kgf / cm 2 -2500 kgf / cm 2 Optionally, the longitudinal tensile strength of the isolation film is 1400 kgf / cm 2 -2000 kgf / cm 2 ; (4) The transverse elongation at break of the isolation film is 50%-200%. Optionally, the transverse elongation at break of the isolation film is 100%-150%; (5) The longitudinal elongation at break of the isolation film is 50%-200%. Optionally, the longitudinal elongation at break of the isolation film is 100%-150%.

13. The secondary battery according to any one of claims 1 to 12, wherein: The inorganic particles and the organic particles form a non-uniform pore structure in the coating layer.

14. The secondary battery according to any one of claims 1 to 13, 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.

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

16. The secondary battery according to any one of claims 1 to 15, 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.

17. A battery module comprising the secondary battery according to any one of claims 1 to 16. 18 . A battery pack comprising at least one of the secondary battery according to claim 1 to 16 and the battery module according to claim 17 .

19. A device comprising at least one of the secondary battery of any one of claims 1 to 16, the battery module of claim 17, or the battery pack of claim 18.

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