Secondary battery, battery module, battery pack, and electric device

Abstract

The invention provides a secondary battery, a battery module, a battery pack and a power utilization device. The secondary battery comprises a positive pole piece, a negative pole piece, an isolating membrane and an electrolyte, the isolating membrane is located between the positive pole piece and the negative pole piece, and the isolating membrane comprises a base material, and a coating disposed on at least one surface of the substrate; the coating comprises organic particles and inorganic particles, the organic particles comprise first organic particles, the inorganic particles form an inorganic particle layer, the first organic particles are embedded in the inorganic particle layer, and protrusions are formed on the surface of the inorganic particle layer; the number average particle size of the first organic particles is greater than or equal to 12 microns; the thickness of the inorganic particle layer is less than or equal to 5 [mu] m, and the volume average particle size Dv50 of the inorganic particles is 0.5-2.5 [mu] m. The secondary battery has good cycle performance and safety performance at the same time.

Description

Technical Field

[0001] The present application belongs to the field of electrochemistry, and more specifically, to secondary batteries, battery modules, battery packs, and electrical devices. Background Art

[0002] In recent years, secondary batteries have been rapidly developed due to their advantages such as light weight and no memory effect, and are widely used in various consumer electronic products and electric vehicles. With the rapid development of the battery industry, people have higher and higher requirements for the performance of secondary batteries. Although technicians have conducted a lot of research on this, the safety performance and electrochemical performance of secondary batteries are still key challenges in the battery field.

[0003] In view of this, it is indeed necessary to provide a secondary battery with better safety performance and electrochemical performance to better meet market demand. Summary of the invention

[0004] In view of the technical problems existing in the background technology, a first aspect of the present application provides a secondary battery, aiming to make the secondary battery have both good cycle performance and safety performance.

[0005] In order to achieve the above-mentioned purpose, the secondary battery provided in the first aspect of the present application includes: a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, wherein the separator is located between the positive electrode sheet and the negative electrode sheet, and the separator includes a substrate and a coating disposed on at least one surface of the substrate. The coating includes organic particles and inorganic particles. The organic particles include a first type of organic particles, the inorganic particles form an inorganic particle layer, the first type of organic particles are embedded in the inorganic particle layer and form protrusions on the surface of the inorganic particle layer. The number average particle size of the first type of organic particles is ≥12μm; the thickness of the inorganic particle layer is ≤5μm, and the volume average particle size Dv50 of the inorganic particles is 0.5μm-2.5μm.

[0006] Compared with the prior art, this application has at least the following beneficial effects:

[0007] The isolation membrane of the present application contains inorganic particles and the first organic particles in the same coating layer. Compared with the isolation membrane having two coating layers, the inorganic particle layer and the organic particle layer, the overall thickness of the isolation membrane is greatly reduced, thereby improving the energy density of the battery; and the organic particles and the inorganic particles form a special coating structure, which can ensure good adhesion and contact interface between the isolation membrane and the electrode plate, thereby improving the cycle performance of the battery; at the same time, when working at high temperature, the isolation membrane coating structure can form a film structure, effectively reducing ion transmission channels and delaying heat spread, thereby further improving the safety performance of the battery.

[0008] In any embodiment of the present application, the ratio of the average height of the protrusions to the thickness of the inorganic particle layer is 4 to 20, and can be 5 to 15. When the ratio of the average height of the protrusions to the thickness of the inorganic particle layer is within the above range, the cycle performance and safety performance of the battery can be further improved.

[0009] In any embodiment of the present application, the average height of the protrusions is ≥10 μm, and can be 12 μm-18 μm. When the average height of the protrusions is within the above range, the cycle 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 15 μm-25 μm. When the number average particle size of the first organic particles is within the above 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 cycle performance and safety performance of the battery can be further improved.

[0012] 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.

[0013] In some embodiments, 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.

[0014] 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.

[0015] In any embodiment of the present application, the isolation film satisfies at least one of the following (1)-(2):

[0016] (1) The mass proportion of the first organic particles in the coating is ≥ 12%, and can be 15%-25%;

[0017] (2) The mass proportion of the inorganic particles in the coating is ≤85%, and can be optionally 60%-75%.

[0018] When the mass proportion of the first organic particles or inorganic particles in the coating is within the above range, the cycle performance and safety performance of the battery can be further improved.

[0019] In any embodiment of the present application, the organic particles further include a second type of organic particles, the second type of organic particles are embedded in the inorganic particle layer and form protrusions on the surface of the inorganic particle layer, and the second type of organic particles are primary particles. When the coating further includes the second type of organic particles, the cycle performance and safety performance of the battery can be further improved.

[0020] In any embodiment of the present application, the number average particle size of the second organic particles is ≤10 μm, and 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 2.5 μm-6 μm. When the number average particle size of the second organic particles is within the above range, the cycle performance and safety performance of the battery can be further improved.

[0021] In any embodiment of the present application, the mass proportion of the second organic particles in the coating is less than 10%, and can be optionally 2%-10%.

[0022] 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 of the modified compounds of the above homopolymers or copolymers;

[0023] 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.

[0024] 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.

[0025] In any embodiment of the present application, the thickness of the inorganic particle layer is ≤5 μm, and can be 1 μm-3 μm. When the thickness of the inorganic particle layer is within the above range, the cycle performance and safety performance of the battery can be further improved.

[0026] In any embodiment of the present application, the volume average particle size Dv50 of the inorganic particles is 0.5 μm-2.5 μm, and can be 0.5 μm-1 μm. When the volume average particle size Dv50 of the inorganic particle layer is within the above range, the cycle performance and safety performance of the battery can be further improved.

[0027] 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).

[0028] In any embodiment of the present application, the isolation film satisfies one or more of the following (1)-(5):

[0029] (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;

[0030] (2) The transverse tensile strength (MD) of the separator is 1500 kg / cm2 -3000kg / cm 2 Optionally, the transverse tensile strength of the isolation film is 1800kg / cm 2 -2500kg / cm 2 ;

[0031] (3) The longitudinal tensile strength (TD) of the separator is 1000 kg / cm 2 -2500kg / cm 2 Optionally, the longitudinal tensile strength of the isolation film is 1400kg / cm 2 -2000kg / cm 2 ;

[0032] (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%;

[0033] (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%.

[0034] In any embodiment of the present application, the inorganic particles and the organic particles form a non-uniform pore structure in the coating.

[0035] 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.

[0036] The second aspect of the present application provides a method for preparing the above-mentioned isolation film, comprising at least the following steps:

[0037] (1) providing a substrate;

[0038] (2) providing a coating slurry, wherein the coating slurry comprises component materials and a solvent, wherein the component materials comprise organic particles and inorganic particles, and wherein the organic particles comprise first organic particles;

[0039] (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;

[0040] Wherein, the isolation film includes: a substrate and a coating arranged on at least one surface of the substrate; the coating includes organic particles and inorganic particles, and the organic particles include a first type of organic particles; the inorganic particles form an inorganic particle layer, and the first type of organic particles are embedded in the inorganic particle layer and form protrusions on the surface of the inorganic particle layer; the number average particle size of the first type of organic particles is ≥12μm, and the ratio of the average height of the protrusions to the thickness of the inorganic particle layer is ≥4.

[0041] In any embodiment of the present application, in the step (2), the organic particles further include second organic particles, the second organic particles are embedded in the inorganic particle layer and form protrusions on the surface of the inorganic particle layer, and the second organic particles are primary particles.

[0042] In any embodiment of the present application, the number average particle size of the second organic particles is ≤10 μm, and 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 2.5 μm-6 μm.

[0043] In any embodiment of the present application, 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%.

[0044] According to the method for preparing an isolation membrane according to the second aspect of the present application, the method satisfies one or more of the following (1)-(7):

[0045] (1) 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; optionally, 12%-30%;

[0046] (2) In step (2), the solid content of the coating slurry is 28%-45%, optionally 30%-38%, based on weight;

[0047] (3) In step (3), the coating is performed by a coating machine, the coating machine comprises a gravure roller, and the line number of the gravure roller is 100LPI-300LPI, and can be 125LPI-190LPI;

[0048] (4) In step (3), the coating speed is 30 m / min-90 m / min, and can be 50 m / min-70 m / min;

[0049] (5) In step (3), the coating line speed ratio is 0.8-2.5, and can be optionally 0.8-1.5;

[0050] (6) In step (3), the drying temperature is 40°C-70°C, and can be 50°C-60°C;

[0051] (7) In step (3), the drying time is 10s-120s, and can be optionally 20s-80s.

[0052] A third aspect of the present application provides a secondary battery, which includes the isolation membrane of the first aspect of the present application or the isolation membrane prepared according to the method of the second aspect of the present application.

[0053] A fourth aspect of the present application provides a battery module, which includes the secondary battery of the third aspect of the present application.

[0054] A fifth aspect of the present application provides a battery pack, which includes the battery module of the fourth aspect of the present application.

[0055] A sixth aspect of the present application provides a device comprising at least one of the secondary battery of the third aspect of the present application, the battery module of the fourth aspect of the present application, or the battery pack of the fifth aspect of the present application.

[0056] The secondary battery, battery module, battery pack and device of the present application include the isolation film provided by the present application, and thus have at least the same advantages as the isolation film of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0057] 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.

[0058] Figure 1-1 It is a schematic structural diagram of an embodiment of the isolation membrane of the present application.

[0059] Figure 1-2 It is a schematic structural diagram of another embodiment of the isolation membrane of the present application.

[0060] Figure 2 The figure is a scanning electron microscope (SEM) picture of an embodiment of the isolation film of the present application.

[0061] Figure 3-1 This is an ion polishing cross-sectional morphology (CP) image of an embodiment of the isolation membrane of the present application.

[0062] Figure 3-2 This is an ion polishing cross-sectional morphology (CP) image of another embodiment of the isolation membrane of the present application.

[0063] Figure 4-1It is a schematic structural diagram of an embodiment of the isolation membrane of the present application.

[0064] Figure 4-2 It is a schematic structural diagram of another embodiment of the isolation membrane of the present application.

[0065] Figure 5 It is a schematic diagram of one embodiment of a secondary battery.

[0066] Figure 6 yes Figure 5 Exploded diagram of .

[0067] Figure 7 is a schematic diagram of one embodiment of a battery module.

[0068] Figure 8 is a schematic diagram of one embodiment of a battery pack.

[0069] Fig. 9 yes Figure 8 Exploded diagram of .

[0070] Fig.10 It is a schematic diagram of one embodiment of a device in which a secondary battery is used as a power source. DETAILED DESCRIPTION

[0071] 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.

[0072] For the sake of 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.

[0073] In the description of this article, it should be noted that, unless otherwise specified, "above" and "below" include the number itself, and "several" in "one or several" means two or more.

[0074] 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).

[0075] 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).

[0076] Secondary battery

[0077] A secondary battery is a battery that can be recharged to activate the active materials after being discharged and continue to be used.

[0078] 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.

[0079] Isolation film

[0080] The present application provides an isolation film, which includes a substrate and a coating disposed on at least one surface of the substrate. The coating includes organic particles and inorganic particles. The organic particles include first organic particles, the inorganic particles form an inorganic particle layer, the first organic particles are embedded in the inorganic particle layer and form protrusions on the surface of the inorganic particle layer. The number average particle size of the first organic particles is ≥12 μm. The ratio of the average height of the protrusions to the thickness of the inorganic particle layer is ≥4.

[0081] 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.

[0082] The isolation membrane of the present application contains inorganic particles and the first organic particles in the same coating. Compared with the isolation membrane having two coatings, the inorganic particle layer and the organic particle layer, the overall thickness of the isolation membrane is greatly reduced, thereby improving the energy density of the battery; and the first organic particles are specially designed, so that the battery containing the isolation membrane of the present application has good cycle performance and safety performance. Without wishing to be confined to any theory, this may be because, since the isolation membrane inorganic coating has sufficient uneven pores, the ion transmission channel can be guaranteed to be unobstructed, and the first organic particles can make the isolation membrane and the electrode plate have good adhesion and contact interface, effectively improving the cycle performance of the battery; at the same time, when working at high temperature, the first organic particles can form a large number of adhesive film structures, which can reduce the ion transmission channel and delay the spread of heat, thereby obtaining good safety performance.

[0083] like Figure 1-1 As shown, the isolation film includes a substrate (A) and a coating (B), the coating (B) includes first organic particles (B1) and inorganic particles (B2), the first organic particles (B1) are secondary particles, and the first organic particles are embedded in the inorganic particle layer formed by the inorganic particles (B2) and form protrusions on the surface of the inorganic particle layer.

[0084] The applicant has further studied and found that when the isolation membrane of the present application optionally satisfies one or more of the following conditions on the basis of the above-mentioned design conditions, the performance of the secondary battery including the isolation membrane of the present application can be further improved.

[0085] In some embodiments, the ratio of the average height of the protrusions to the thickness of the inorganic particle layer is 4-20, and can be optionally 5-15. When the ratio of the average height of the protrusions to the thickness of the inorganic particle layer is within the above range, the cycle performance and safety performance of the battery can be further improved. The inventors have found through extensive research that when the ratio of the two is too small, it is not conducive to gas discharge in the formation process of the battery preparation process. During the battery charging process, the gas will hinder ion transmission, thereby causing black spots on the surface of the negative electrode plate, thereby affecting the cycle performance of the battery; when the ratio of the two is too large, it may cause the ion transmission path to increase, and lithium is easily deposited on the surface of the negative electrode plate during the battery cycle, thereby affecting the safety performance of the battery.

[0086] In some embodiments, the average height of the protrusions is ≥ 10 μm, and can be 12 μm-18 μm. When the average height of the protrusions is within the above range, sufficient bonding force between the separator and the pole piece can be provided, and the risk of wrinkling of the separator during the battery preparation process can be reduced, effectively reducing the probability of short circuits between the positive and negative electrodes, thereby further improving the safety performance of the battery.

[0087] In some embodiments, the particle size of the first organic particles is 8 μm-35 μm. When the particle size of the first organic particles is within the above range, more pore structures can be formed to improve the ion transmission performance of the isolation membrane. It should be noted that in the present application, the particle size of the first organic particles ≥ 8 μm means that among all the first organic particles used, the particle size of a single first organic particle is ≥ 8 μm, for example, 8 μm, 10 μm, 12 μm, etc.

[0088] In some embodiments, the number average particle size of the first organic particles is 15 μm-25 μm. When the number average particle size of the first organic particles is within the above range, the particle size distribution of the first organic particles is relatively uniform, which is conducive to forming a relatively uniform coating interface under the precursor of achieving the technical effect of the present application.

[0089] In some embodiments, the first organic particles are secondary particles. When the first organic particles are secondary particles, it is helpful to form a uniform coating interface. When the separator is used in the battery, it can effectively improve the tab misalignment problem in the battery preparation process, thereby further improving the safety performance of the battery.

[0090] 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.

[0091] In some embodiments, the first organic particles may be formed by agglomeration of primary particles having a particle size of 150 nm to 300 nm.

[0092] In some embodiments, the first organic particles include homopolymers or copolymers of fluorine-containing olefinic monomer units, homopolymers or copolymers of olefinic monomer units, homopolymers or copolymers of unsaturated nitrile monomer units, homopolymers or copolymers of alkylene oxide monomer units, and one or more of the modified compounds of the above homopolymers or copolymers.

[0093] In some embodiments, 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.

[0094] In some embodiments, the first organic particles include one or more of vinylidene fluoride-trifluoroethylene copolymer, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-trifluoroethylene-hexafluoropropylene copolymer, vinylidene fluoride-hexafluoropropylene-acrylic acid copolymer, vinylidene fluoride-hexafluoropropylene-acrylate copolymer, and modified compounds of the above copolymers.

[0095] In some embodiments, the first organic particles are one or more of polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, and modified compounds of the above homopolymers or copolymers.

[0096] In some embodiments, the isolation film satisfies at least one of the following (1)-(2):

[0097] (1) The mass proportion of the first organic particles in the coating is ≥12%, and can be optionally 15%-25%.

[0098] (2) The mass proportion of the inorganic particles in the coating is ≤85%, and can be optionally 60%-75%.

[0099] By selecting the appropriate amount of organic and inorganic particles, the two 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.

[0100] In some embodiments, the organic particles further include a second organic particle, the second organic particle is embedded in the inorganic particle and forms a protrusion on the surface of the inorganic particle layer, and the second organic particle is a primary particle. When the battery is in a normal working environment (e.g., below 45°C), the combination of the first organic particle and the second organic particle can effectively reduce the probability of the organic particles in the coating being swollen in the electrolyte to form a dense and large-area film, so that the isolation film coating has a moderately uneven pore structure, which is convenient for the transmission of active ions, thereby further improving the cycle performance of the battery; in particular, when the battery is in a high-temperature working environment (e.g., above 100°C), the first organic particle and the second organic particle will form a large-area film structure at high temperature, quickly reduce the diffusion channel of the active ions, and delay the time of heat spread, thereby further improving the safety performance of the battery.

[0101] like Figure 1-2 As shown, the isolation film includes a substrate (A) and a coating (B), the coating (B) includes first organic particles (B1), inorganic particles (B2) and second organic particles (B3), the first organic particles (B1) are secondary particles, the second organic particles (B3) are primary particles, the first organic particles (B1) and the second organic particles (B3) are both embedded in the inorganic particle layer formed by the inorganic particles (B2) and form protrusions on the surface of the inorganic particle layer.

[0102] In some embodiments, the number average particle size of the second organic particles is ≤10 μm, and 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 2.5 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. 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 transmission channel of the separator when the battery is working normally, thereby affecting the cycle performance of the battery; if the number average particle size of the second organic particles is too large (for example, greater than 10 μm), after the hot pressing process of the battery preparation, it may cause the isolation membrane and the electrode plate to be too firmly bonded, resulting in poor infiltration of the electrolyte, thereby affecting the cycle performance of the battery.

[0103] In some embodiments, the mass proportion of the second organic particles in the coating is less than 10%; for example, the mass proportion of the second organic particles in the coating is 2%-10%, 3%-8%, 4%-9%, 5%-10%, etc. When the mass proportion of the second organic particles in the coating is controlled within the given range, it helps to ensure that the isolation film coating has a suitable pore structure while ensuring adhesion, thereby further improving the cycle performance and safety performance of the battery.

[0104] In some embodiments, the second organic particles include homopolymers or copolymers of acrylate monomer units, homopolymers or copolymers of acrylic acid monomer units, homopolymers or copolymers of styrene monomer units, polyurethane compounds, rubber compounds, and one or more of the modified compounds of the above homopolymers or copolymers.

[0105] In some embodiments, the second organic particles include copolymers of acrylic acid ester monomer units and styrene monomer units, copolymers of acrylic acid monomer units and styrene monomer units, copolymers of acrylic acid monomer units-acrylic acid ester monomer units-styrene monomer units, copolymers of styrene monomer units 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.

[0106] In some embodiments, the acrylic monomer unit may be selected from one or more of acrylic acid, methacrylic acid, and the like.

[0107] In some embodiments, the styrene monomer unit may be selected from one or more of styrene, methyl styrene, and the like.

[0108] In some embodiments, the unsaturated nitrile monomer unit may be selected from one or more of acrylonitrile, methacrylonitrile, and the like.

[0109] In some embodiments, the second organic particles include butyl acrylate-styrene copolymer, butyl methacrylate-isooctyl methacrylate copolymer, isooctyl methacrylate-styrene copolymer, methacrylate-methacrylic acid-styrene copolymer, methyl acrylate-isooctyl methacrylate-styrene copolymer, butyl acrylate-isooctyl methacrylate-styrene copolymer, butyl acrylate-isooctyl methacrylate-styrene copolymer, butyl methacrylate-isooctyl methacrylate-styrene copolymer, butyl methacrylate-isooctyl methacrylate-styrene copolymer, butyl methacrylate-isooctyl methacrylate-styrene copolymer, styrene-acrylonitrile copolymer, styrene-butadiene-acrylonitrile copolymer, methyl acrylate-styrene-acrylonitrile copolymer, isooctyl methacrylate-styrene-acrylonitrile copolymer, styrene-vinyl acetate copolymer, styrene-vinyl acetate-pyrrolidone copolymer, and one or more of the modified compounds of the above copolymers.

[0110] In some embodiments, the thickness of the inorganic particle layer is ≤5 μm; for example, it can be 0.5 μm-4 μm, 1 μm-3 μm, 0.8 μm-3.5 μm or 1.5 μm-4.5 μm. When the thickness of the inorganic particle layer is controlled within the above range, the battery can have a higher energy density and better safety performance.

[0111] In some embodiments, the volume average particle size Dv50 of the inorganic particles is 0.5 μm-2.5 μm, and can be 0.5 μm-1 μm. When the volume average particle size of the inorganic particles is controlled within the given range, it helps to improve the wettability of the electrolyte in the separator, thereby further improving the cycle performance of the battery.

[0112] In some embodiments, 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). For example, optionally, the inorganic particles are selected from one or more of boehmite (γ-AlOOH) and aluminum oxide (Al2O3).

[0113] According to some embodiments, the coating may further include other organic compounds, for example, a polymer for improving heat resistance (referred to as "heat-resistant glue"), a dispersant, a wetting agent, other types of binders, etc. The above-mentioned other organic compounds are all non-granular substances in the coating. The present application has no particular restrictions on the types of the above-mentioned other organic compounds, and any known material with good improved performance can be selected.

[0114] The embodiments of the present application have no particular restrictions on the material of the substrate, and any known substrate with good chemical stability and mechanical stability can be selected, such as one or more of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The substrate can be a single-layer film or a multi-layer composite film. When the substrate is a multi-layer composite film, the materials of each layer can be the same or different.

[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-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.

[0116] 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 Etc. By controlling the coating weight on one side of the separator per unit area within a given range, the energy density of the battery can be further improved while ensuring the battery cycle performance and safety performance.

[0117] In some embodiments, the isolation film satisfies one or more of the following (1)-(5):

[0118] (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, 170s / 100mL-220s / 100mL;

[0119] (2) The transverse tensile strength (MD) of the separator is 1500 kgf / cm 2 -3000kgf / cm 2Optionally, the transverse tensile strength of the isolation film is 1800kgf / cm 2 -2500kgf / cm 2 ;

[0120] (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 ;

[0121] (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%;

[0122] (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%.

[0123] In any embodiment, 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.

[0124] Related parameter test methods

[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] Figure 2 This is a scanning electron microscope (SEM) image of an embodiment of the isolation film of the present application. Figure 2 It can be seen that the coating of the isolation film includes the first organic particles and the second organic particles, and the first organic particles and the second organic particles are embedded in the inorganic particle layer and form protrusions on the surface of the inorganic particle layer. Figure 2 The particle size and number average particle size of organic particles were measured.

[0127] It should be noted that the height of the protrusion refers to the height of the protrusion formed by the first organic particles in the thickness direction of the inorganic particle layer itself, which is the maximum distance between the "protrusion" and the "surface of the inorganic particle layer facing away from the substrate".

[0128] The average height of the protrusions refers to the arithmetic mean of the heights of the protrusions counted according to the number of protrusions in the isolation film coating.

[0129] According to some embodiments, the average height of the protrusion can be tested using equipment and methods known in the art. For example, it can be tested by ion polishing cross-sectional morphology (CP) images. 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., 6mm×6mm), 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 400g) of flat iron block is used to press for a certain time (e.g., 1h) 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, the sample stage is placed in the sample holder and locked, the argon ion cross-section polisher (e.g., IB-19500CP) is powered on and vacuumed (e.g., 10Pa-4Pa), the argon gas flow rate (e.g., 0.15MPa) and voltage (e.g., 8KV) and polishing time (e.g., 2 hours) are set, the sample stage is adjusted to the swing mode to start polishing, and a scanning electron microscope (e.g., ZEISS Sigma300) is used to finally obtain an ion polishing cross-sectional morphology (CP) image of the sample to be tested. The number and height of the protrusions formed by the organic particles in the ion polishing cross-sectional morphology (CP) image are counted; multiple test samples (e.g., 10) are taken to repeat the above test, and the arithmetic mean of the heights of all protrusions in each test sample (i.e., the ratio of the sum of the heights of each protrusion to the number of protrusions) is taken as the final test result of the average height of the protrusions of the organic particles.

[0130] According to some embodiments, the thickness of the inorganic particle layer can also be tested by the above-mentioned ion polishing cross-sectional morphology (CP) image. In order to ensure the accuracy of the test results, multiple test samples (e.g., 10) can be taken to repeat the above test, and the average value of the thickness of the inorganic particle layer in each test sample is taken as the final test result.

[0131] According to some embodiments, the morphology of the organic particles (eg, primary particle morphology or secondary particle morphology) may also be tested by the above-mentioned ion polishing cross-sectional morphology (CP) image.

[0132] Figure 3-1 and Figure 3-2 This is an ion polishing cross-sectional morphology (CP) picture of the isolation membrane of an embodiment of the present application.

[0133] Depend on Figure 3-1 It can be seen that the coating of the isolation film includes the first type of organic particles, which are secondary particles composed of a plurality of primary particles and have an irregular non-solid spherical cross section. Figure 3-1 The thickness of the inorganic particle layer (a) and the height of the protrusions (b) can be measured simultaneously.

[0134] Depend on Figure 3-2 It can be seen that the coating of the isolation film includes both the first organic particles and the second organic particles. The second organic particles are non-agglomerated primary particles and have a solid spherical cross-section.

[0135] 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.

[0136] 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.

[0137] 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.

[0138] 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.

[0139] According to some embodiments, the spacing 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 center spacing between the inorganic particle and the organic particle is tested as the spacing between the organic particle and the inorganic particle, which is recorded as L2. The above-mentioned organic particles can be the first organic particles or the second organic particles.

[0140] 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 the adjacent organic particles and inorganic 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.

[0141] Similarly, the distance L1 between any two adjacent inorganic particles can also be tested according to the above method.

[0142] The above-mentioned “circumscribed circle” means that the sphere surrounds the irregular body, and the vertices and arc surfaces of the irregular body are on this circle.

[0143] Preparation method of isolation film

[0144] A second aspect of the present application provides a method for preparing an isolation film, the method comprising at least the following steps:

[0145] (1) providing a substrate;

[0146] (2) providing a coating slurry, wherein the coating slurry comprises component materials and a solvent, wherein the component materials comprise organic particles and inorganic particles, and wherein the organic particles comprise first organic particles;

[0147] (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;

[0148] Wherein, the isolation film includes: a substrate and a coating arranged on at least one surface of the substrate; the coating includes organic particles and inorganic particles, the organic particles include the first organic particles; the inorganic particles form an inorganic particle layer, the first organic particles are embedded in the inorganic particle layer and form protrusions on the surface of the inorganic particle layer; the number average particle size of the first organic particles is ≥12μm; the ratio of the average height of the protrusions to the thickness of the inorganic particle layer is ≥4.

[0149] The coating layer may be provided on only one surface of the substrate, or may be provided on both surfaces of the substrate.

[0150] 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).

[0151] 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).

[0152] The present application embodiment has no particular restrictions on the material of the substrate, and any known substrate with good chemical stability and mechanical stability can be selected, such as one or more of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The substrate can be a single-layer film or a multi-layer composite film. When the substrate is a multi-layer composite film, the materials of each layer can be the same or different.

[0153] In some embodiments, in step (2), the solvent may be water, such as deionized water.

[0154] In some embodiments, in step (2), the component material may further include the aforementioned second organic particles. The parameters of the second organic particles can be referred to the aforementioned content and will not be described in detail here.

[0155] 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.

[0156] In some embodiments, in step (2), component materials are added to a solvent and stirred evenly to obtain a coating slurry.

[0157] 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%.

[0158] 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%.

[0159] 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 based on weight. The total dry weight of the component materials is the sum of the dry weights of the component materials.

[0160] In some embodiments, in step (2), the solid content of the coating slurry based on weight can be controlled to be 28%-45%, for example, 30%-38%. 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.

[0161] In some embodiments, in step (3), the coating is performed using a coater.

[0162] 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.

[0163] 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.

[0164] In some embodiments, the coater includes a gravure roll; the gravure roll is used to transfer the coating slurry to the substrate.

[0165] 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.

[0166] In some embodiments, in step (3), the coating speed can be controlled within the range of 30 m / min-90 m / min, such as 50 m / min-70 m / min. When the coating speed is within the above range, it is helpful to adjust the average height of the protrusions so that the ratio of the average height of the protrusions to the thickness of the inorganic particle layer is controlled within the given range; at the same time, it can also effectively reduce the film surface problems of the coating and reduce the probability of uneven coating, thereby further improving the cycle performance and safety performance of the battery.

[0167] 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.

[0168] In some embodiments, in step (3), the drying temperature may be 40°C-70°C, for example, 50°C-60°C.

[0169] In some embodiments, in step (3), the drying time may be 10s-120s, for example, 20s-80s, 20s-40s.

[0170] 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.

[0171] 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.

[0172] The above-mentioned substrate, first organic particles and second organic particles can all be obtained commercially.

[0173] The isolation membrane preparation method of the present application obtains the coating by one-time coating, which greatly simplifies the production process of the isolation membrane; at the same time, the isolation membrane prepared by the above method is used in the battery, which can effectively improve the cycle performance and safety performance of the battery.

[0174] Positive electrode

[0175] 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.

[0176] 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.

[0177] 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.

[0178] 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.

[0179] In some embodiments, the modified compounds of the above materials may be doping-modified and / or surface-coated modified materials.

[0180] The positive electrode film layer may also optionally include a binder, a conductive agent and other optional additives.

[0181] 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.

[0182] 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).

[0183] Negative electrode

[0184] 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.

[0185] 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.

[0186] 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.

[0187] 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.

[0188] The negative electrode film layer may also optionally include a binder, a conductive agent and other optional additives.

[0189] 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.

[0190] 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).

[0191] As an example, other optional auxiliary agents may be thickeners and dispersants (such as sodium carboxymethyl cellulose CMC-Na), PTC thermistor materials, etc.

[0192] Electrolyte

[0193] The present application embodiment has no special restrictions on the selection of the electrolyte, and the electrolyte is used to conduct ions between the positive electrode plate and the negative electrode plate. The electrolyte may include an electrolyte salt and a solvent.

[0194] 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).

[0195] 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).

[0196] 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.

[0197] In some embodiments, the secondary battery of the present application is a lithium ion secondary battery.

[0198] 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.

[0199] In some embodiments, the secondary battery may include an outer package for packaging a positive electrode sheet, a negative electrode sheet, and an electrolyte.

[0200] 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.

[0201] The positive electrode sheet, the negative electrode sheet and the separator can be wound or laminated to form an electrode assembly 52. ​​The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the secondary battery 5 can be one or more, which can be adjusted according to needs.

[0202] In some embodiments, the outer packaging of the secondary battery may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the secondary battery may also be a soft package, such as a bag-type soft package. The material of the soft package may be plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), polybutylene succinate (PBS), etc.

[0203] 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.

[0204] 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.

[0205] Optionally, the battery module 4 may further include a housing having a housing space, and the plurality of secondary batteries 5 are housed in the housing space.

[0206] 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.

[0207] 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.

[0208] Device

[0209] 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.

[0210] The device can select a secondary battery, a battery module or a battery pack according to its usage requirements.

[0211] 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, etc. 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.

[0212] As another example, the device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is usually required to be thin and light, and a secondary battery may be used as a power source.

[0213] The beneficial effects of the present application are further illustrated below in conjunction with embodiments.

[0214] Example

[0215] In order to make the technical problems, technical solutions and beneficial effects solved by the present application clearer, the present application will be further described in detail below in conjunction with the embodiments and drawings. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all of the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is by no means intended to limit the present application and its applications. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field without creative work are within the scope of protection of the present application.

[0216] The materials used in this application are all commercially available.

[0217] For example: the substrate can be purchased from Shanghai Enjie New Materials Co., Ltd.

[0218] Inorganic particles can be purchased from Yishitong Materials Technology Co., Ltd.

[0219] The first organic particles can be purchased from Arkema (Changshu) Chemical Co., Ltd.

[0220] The second type of organic particles can be purchased from Sichuan Yindi Le Technology Co., Ltd.

[0221] Heat-resistant glue can be purchased from Sichuan Yindile Technology Co., Ltd.

[0222] Wetting agents are available commercially from The Dow Chemical Company.

[0223] The dispersant was purchased from Changshu Weiyi Technology Co., Ltd.

[0224] 1. Preparation of isolation membrane

[0225] Isolation film 1

[0226] (1) providing a polyethylene (PE) substrate, for example, the thickness of the substrate is 7 μm and the porosity is 36%;

[0227] (2) Preparation of coating slurry: Inorganic particles of aluminum oxide (Al2O3), the first organic particles of vinylidene fluoride-hexafluoropropylene copolymer (number average molecular weight of 550,000), heat-resistant adhesive acrylic acid-acrylonitrile copolymer: dispersant sodium carboxymethyl cellulose (CMC-Na) and wetting agent silicone modified polyether are mixed uniformly in a proper amount of deionized water at a dry weight ratio of 73:20:5:1.5:0.5 to obtain a coating slurry with a solid content of 35% by weight. Among them, the number average particle size of the first organic particles is 12 μm, and the volume average particle size Dv50 of the inorganic particles of aluminum oxide (Al2O3) is 1 μm.

[0228] (3) The coating slurry prepared in step (2) is coated on two surfaces of a polyethylene (PE) substrate by a coating machine, and then dried, slitting, and other processes are performed to obtain a separator 1. The line number of the gravure roller of the coating machine is 190 LPI, the coating speed is 70 m / min, and the coating line speed ratio is 1.3; the single-side coating weight per unit area of ​​the separator is 2.0 g / m 2 In the isolation film, the first organic particles are embedded in the inorganic particle layer and form protrusions on the surface of the inorganic particle layer. The thickness of the inorganic particle layer is 2 μm, and the ratio of the average height of the protrusions to the thickness of the inorganic particle layer is 5.

[0229] The preparation method of isolation film 2-20 is similar to that of isolation film 1, except that the number average particle size, mass percentage, material type or particle morphology of the first organic particles are adjusted, as shown in Table 1 for details.

[0230] The preparation method of isolation membrane 21-34 is similar to that of isolation membrane 1, except that a second organic particle styrene-vinyl acetate-pyrrolidone copolymer (number average molecular weight of 80,000) is added to the coating, and its number average particle size, mass percentage, and material type are adjusted, see Table 2 for details.

[0231] The properties of the prepared isolation films are summarized in Tables 1 and 2.

[0232] 2. Preparation of batteries

[0233] 1. Preparation of positive electrode sheet

[0234] The positive electrode active material LiNi 0.5 Co 0.2 Mn 0.3O2 (NCM523), conductive agent carbon black (Super P), and 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, slitting, cutting and other processes.

[0235] 2. Preparation of negative electrode sheet

[0236] The negative electrode active material artificial graphite, the conductive agent carbon black (Super P), the binder styrene-butadiene rubber (SBR) and sodium carboxymethyl cellulose (CMC-Na) are mixed uniformly in a proper amount of solvent deionized water at a mass ratio of 96.4:0.7:1.8:1.1 to obtain a negative electrode slurry, and the negative electrode slurry is coated on the negative electrode current collector copper foil, and the negative electrode sheet is obtained through drying, cold pressing, slitting, cutting and other processes.

[0237] 3. Preparation of electrolyte

[0238] 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.

[0239] 4. Isolation film

[0240] The isolation film uses the isolation film 1 prepared by the method described above.

[0241] 5. Preparation of secondary batteries

[0242] 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.

[0243] The preparation methods of the secondary batteries of Examples 2-32 and Comparative Examples 1-2 are similar to the preparation methods of the secondary battery of Example 1, except that different isolation membranes are used. For details, see Tables 1 and 2.

[0244] 3. Performance Test Method

[0245] 1. 45℃ Cycle Performance

[0246] 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 30 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 30 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.

[0247] The cycle capacity retention rate of the battery at 45°C = C1 / C0×100%.

[0248] 2. Heat spread performance

[0249] At 25°C, the secondary batteries prepared in the embodiments and comparative examples were charged at a constant current of 1C to a charging cut-off voltage of 4.2V, then charged at a constant voltage to a current ≤0.05C, and left to stand for 10 minutes; then a metal heating plate was placed close to the surface of the battery, the battery was clamped with a clamp at a position of the battery that did not contact the heating plate, and a 3mm thermal insulation pad was added between the clamp and the battery, and the battery was heated at a constant temperature of 200°C until thermal runaway occurred; the time when thermal runaway occurred was recorded.

[0250] 3. Crack SOH (State of Health) test

[0251] At 25°C, the secondary batteries prepared in the embodiments and comparative examples were charged at a constant current of 0.5C to a charge cut-off voltage of 4.25V, then charged at a constant voltage to a current ≤0.05C, left standing for 30 min, and then discharged at a constant current of 0.33C to a discharge cut-off voltage of 2.8V, left standing for 30 min, and the battery capacity C0 at this time was recorded.

[0252] The battery is subjected to a cyclic charge and discharge test according to this method. When the battery capacity decays by 1% on the basis of C0, the battery is subjected to an X-ray CT test (X-ray computed tomography). When a break is observed at the corner of the positive or negative electrode of the battery, the battery capacity C1 at this time is recorded.

[0253] Crack SOH=C1 / C0×100%

[0254] Tables 1 and 2 show the measured battery performance of each embodiment and comparative example.

[0255]

[0256]

[0257]

[0258]

[0259] As can be seen from Table 1, relative to Comparative Examples 1-2, by making the number average particle size of the first organic particles and the ratio of the average height of the protrusions to the thickness of the inorganic particle layer within the range defined in the present application, the cycle capacity retention rate, Crack SOH improvement and heat spread time of the battery can be significantly improved, and the cycle performance and safety performance of the battery can be improved. In particular, by further optimizing the number average particle size of the first organic particles, the ratio of the average height of the protrusions to the thickness of the inorganic particle layer, the cycle performance and safety performance of the battery can be further improved. As can be seen from Table 2, the use of the second organic particles and the optimization of their number average particle size and other parameters can further improve the cycle performance and safety performance of the battery.

[0260] The inventors also conducted experiments using other amounts and materials of inorganic particles, first organic particles and second organic particles within the scope of the present application, other substrates, other coating process parameters and other process conditions, and obtained similar effects of improving the cycle performance and safety performance of the battery as in Examples 1-32.

[0261] 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, characterized in that: include: A positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, wherein the separator is located between the positive electrode sheet and the negative electrode sheet, and the separator comprises: Base material; and a coating disposed on at least one surface of the substrate; The coating layer includes organic particles and inorganic particles, the organic particles include first organic particles, the inorganic particles form an inorganic particle layer, the first organic particles are embedded in the inorganic particle layer and form protrusions on the surface of the inorganic particle layer; The number average particle size of the first organic particles is ≥12 μm; The thickness of the inorganic particle layer is ≤5 μm, and the volume average particle size Dv50 of the inorganic particles is 0.5 μm-2.5 μm.

2. The secondary battery according to claim 1, wherein The ratio of the average height of the protrusions to the thickness of the inorganic particle layer is 4-20, and can be 5-15.

3. The secondary battery according to any one of claims 1 to 2, wherein: The average height of the protrusions is ≥10 μm, and can be optionally 12 μm-18 μm.

4. The secondary battery according to any one of claims 1 to 3, wherein: The number average particle size of the first organic particles is 8 μm-35 μm, and optionally, the number average particle size of the first organic particles is 15 μm-25 μm.

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 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.

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

8. The secondary battery according to any one of claims 1 to 7, wherein: The isolation film satisfies at least one of the following (1)-(2): (1) The mass proportion of the first organic particles in the coating is ≥ 12%, and can be 15%-25%; (2) The mass proportion of the inorganic particles in the coating is ≤85%, and can be optionally 60%-75%.

9. The secondary battery according to any one of claims 1 to 8, wherein: The organic particles further include second organic particles, the second organic particles are embedded in the inorganic particle layer and form protrusions on the surface of the inorganic particle layer, and the second organic particles are primary particles.

10. The secondary battery according to claim 9, wherein The number average particle size of the second organic particles is ≤10 μm, and 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 2.5 μm-6 μm.

11. The secondary battery according to any one of claims 9 to 10, wherein: The mass percentage of the second organic particles in the coating is less than 10%, and may be 2%-10%.

12. The secondary battery according to any one of claims 9 to 11, 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.

13. The secondary battery according to any one of claims 9 to 12, 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.

14. The secondary battery according to any one of claims 1 to 13, wherein: The thickness of the inorganic particle layer is 1 μm-3 μm.

15. The secondary battery according to any one of claims 1 to 14, wherein: The volume average particle size Dv50 of the inorganic particles is 0.5 μm-1 μm.

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

17. The secondary battery according to any one of claims 1 to 16, 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 kg / cm 2 -3000kg / cm 2 Optionally, the transverse tensile strength of the isolation film is 1800kg / cm 2 -2500kg / cm 2 ; (3) The longitudinal tensile strength (TD) of the separator is 1000 kg / cm 2 -2500kg / cm 2 Optionally, the longitudinal tensile strength of the isolation film is 1400kg / cm 2 -2000kg / 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%.

18. The secondary battery according to any one of claims 1 to 17, wherein: The inorganic particles and the organic particles form a non-uniform pore structure in the coating layer.

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

20. The secondary battery according to any one of claims 1 to 19, wherein: The positive electrode plate includes a positive electrode current collector and a positive electrode film layer located on the positive electrode current collector. The positive electrode film layer includes a positive electrode active material. The positive electrode active material includes one or more of lithium transition metal oxides, lithium-containing phosphates and their respective modified compounds.

21. The secondary battery according to any one of claims 1 to 20, wherein: The negative electrode plate includes a negative electrode current collector and a negative electrode film layer located 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.

22. The secondary battery according to any one of claims 1 to 21, wherein: The electrolyte comprises an electrolyte salt and a solvent, and optionally an additive, The additive includes at least one of a negative electrode film-forming additive and a positive electrode film-forming additive.

23. A battery module comprising the secondary battery according to any one of claims 1 to 22.

24. A battery pack comprising the battery module according to claim 23. 25 . An electrical device comprising at least one of the secondary battery according to claim 1 , the battery module according to claim 23 , or the battery pack according to claim 24 .

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