Coating composition, electrode sheet and preparation method therefor, secondary battery and electronic device

Abstract

The present application provides a coating composition, an electrode sheet and a preparation method therefor, a secondary battery and an electronic device. The coating composition comprises a first binder and a pore-forming agent, the pore-forming agent has a core-shell structure, and the core-shell structure comprises a shell layer material and a core material, wherein the shell layer material comprises a second binder, and the core material comprises an alkane gas. The coating composition can be used for forming a pore-forming coating in an electrode sheet. The pore-forming coating can be disposed between a current collector and an active material layer. For the pore-forming agent having a core-shell structure in the pore-forming coating, under suitable conditions, the release of alkane gas in the pore-forming agent more easily results in the formation of through-holes in an active material layer as compared to a general pore-forming agent producing a gas by means of decomposition, thereby providing channels for electrolyte infiltration into the active material layer and promoting the infiltration of the electrolyte into the active material layer, which can increase the ionic conductivity of the electrode sheet, reduce polarization in the process of charge / discharge, and improve the rate capability of a battery cell.

Description

Coating composition, electrode plate and preparation method thereof, secondary battery and electronic device Technical Field

[0001] The present application relates to the field of battery technology, and more specifically, to a coating composition, an electrode plate and a preparation method thereof, a secondary battery and an electronic device. Background Art

[0002] Secondary batteries, represented by lithium-ion batteries, are widely used in digital electronic products, energy storage, drones, power tools, electric vehicles, and other products due to their high energy density, long cycle life, high safety, and fast charging capabilities. As the demand for thinner and lighter products becomes increasingly urgent, batteries need to have higher and higher energy density. Increasing the surface density of the electrode plate coating and making the electrode plate thicker, thereby reducing the amount of positive and negative electrode substrates and separators used, is also one of the means by which the industry can improve energy density. However, the increase in the thickness of the electrode plate means that it is difficult for the electrolyte to penetrate the active material layer, the ionic conductivity will be significantly reduced, and the polarization will increase, which will lead to poor rate performance of the battery cell.

[0003] Therefore, it is necessary to improve the wetting of the active material layer in the electrode plate by the electrolyte to improve the ionic conductivity of the electrode plate.

[0004] Summary of the Invention

[0005] The present application provides a coating composition, an electrode plate and a preparation method thereof, a secondary battery and an electronic device. The pore-forming coating formed by the coating composition is more likely to form through holes in the active material layer of the electrode plate, promote the infiltration of the electrolyte into the active material layer, and improve the ionic conductivity, thereby making the battery cell have good rate performance.

[0006] In a first aspect, the present application provides a coating composition for forming pores in an electrode plate, comprising: a first binder and a pore-forming agent, wherein the pore-forming agent has a core-shell structure, and the core-shell structure comprises a shell material and a core material; wherein the shell material comprises a second binder, and the core material comprises an alkane gas.

[0007] According to the present application, the coating composition can be used to form a pore-forming coating in the electrode plate, and the pore-forming coating can be arranged between the current collector and the active material layer. The pore-forming agent with a core-shell structure in the pore-forming coating releases the alkane gas in the pore-forming agent under appropriate conditions. Compared with general decomposition and gas-generating pore-forming agents, it is easier to form through holes in the active material layer, thereby providing a channel for the electrolyte to penetrate into the active material layer, promoting the infiltration of the electrolyte into the active material layer, thereby improving the ionic conductivity of the electrode plate, reducing polarization during charging and discharging, and improving the rate performance of the battery cell.

[0008] In some embodiments, the mass ratio of the pore-forming agent to the first binder is 0.5 to 4; preferably, the mass ratio of the pore-forming agent to the first binder is 2 to 4.

[0009] In some embodiments, the volume average particle size Dv50 of the pore-forming agent satisfies: 5 μm≤Dv50≤50 μm; preferably, Dv50 satisfies: 18 μm≤Dv50≤50 μm.

[0010] In some embodiments, the first binder includes at least one of polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polyacrylonitrile, polyacrylic acid, polyacrylic acid salt, acrylic polymer and polyimide, preferably at least one of polyacrylic acid and polyacrylic acid salt.

[0011] In some embodiments, the pore-forming agent satisfies at least one of the following conditions: 1) the thickness of the shell material is 2 μm to 15 μm, preferably 2 μm to 8 μm; 2) the mass percentage of the core material in the pore-forming agent is 5% to 40%, preferably; 3) the second binder includes at least one of polyacrylonitrile, polyacrylic acid, polymethacrylic acid, polymethyl acrylate and polymethyl methacrylate, preferably at least one of polyacrylonitrile and polymethyl methacrylate; 4) the alkane gas includes at least one of alkane gases having 1 to 4 carbon atoms, preferably at least one of propane and n-butane; 5) the true density of the pore-forming agent is 0.9 g / cm 3 Up to 1.15g / cm 3 , preferably 0.95 g / cm 3 to 1.10g / cm 3 .

[0012] In a second aspect, the present application provides a method for preparing an electrode sheet, comprising the following steps:

[0013] S10: coating the coating composition according to any embodiment of the first aspect on at least one surface of the current collector to form a pore-forming coating on at least one surface of the current collector;

[0014] S20: coating an electrode active slurry on the surface of the current collector coated with the pore-forming coating to form an active material layer on the pore-forming coating;

[0015] S30: Drying the current collector coated with the pore-forming coating layer and the active material layer to release the core material of the pore-forming agent in the pore-forming coating layer to form through-holes in the active material layer.

[0016] In some embodiments, step S10 includes:

[0017] The coating composition according to any embodiment of the first aspect is coated in an island shape on at least one surface of the current collector to form an island-shaped distributed pore-forming coating on at least one surface of the current collector.

[0018] In a third aspect, the present application provides an electrode plate comprising: a current collector, a pore-forming coating and an active material layer, wherein the pore-forming coating is arranged between the current collector and the active material layer; wherein the pore-forming coating comprises a first binder and a second binder, and the active material layer comprises an active material and a third binder; the active material layer is provided with a through hole, and the through hole comprises a second binder at one end close to the current collector.

[0019] In some embodiments, the pore-forming coating is distributed in an island shape on the current collector, and the single-side area S1 of the pore-forming coating and the single-side area S of the current collector satisfy: 0.25≤S1 / S≤0.75.

[0020] In some embodiments, the active material layer is provided with a plurality of pore clusters consisting of a plurality of through holes, the pore spacing between two adjacent through holes in the pore cluster is no more than 30 μm, and the maximum diameter of the pore cluster is 100 μm to 800 μm, preferably the maximum diameter is 200 μm to 500 μm.

[0021] In some embodiments, the cluster spacing between two adjacent pore clusters in the active material layer is 50 μm to 1000 μm, preferably 100 μm to 500 μm.

[0022] In some embodiments, the through hole satisfies at least one of the following conditions: 1) the pore depth H of the through hole and the sum of the thicknesses D of the active material layer and the pore-forming coating layer satisfy: 95% ≤ H / D ≤ 110%, preferably, satisfying: 99% ≤ H / D ≤ 106%; 2) the pore depth H of the through hole is greater than the thickness of the active material layer.

[0023] In some embodiments, the pore-forming coating satisfies at least one of the following conditions: 1) a mass ratio of the first binder to the second binder is 0.1 to 1.0; 2) a thickness of the pore-forming coating is 1 μm to 5 μm.

[0024] In a fourth aspect, the present application provides a secondary battery comprising: a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte;

[0025] At least one of the positive electrode sheet and the negative electrode sheet is an electrode sheet prepared according to the method of any embodiment of the second aspect or an electrode sheet according to any embodiment of the third aspect.

[0026] In a fifth aspect, the present application provides an electronic device comprising: a secondary battery according to any embodiment of the fourth aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments of the present application. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on the drawings without creative work.

[0028] FIG1 is a scanning electron microscope image of the surface after the coating composition is coated in an island shape on the current collector in one embodiment of the present application.

[0029] FIG2 is a scanning electron microscope image of the surface of the active material layer in one embodiment of the present application.

[0030] FIG3 is a scanning electron microscope image of a through-hole cross section of an active material layer in an embodiment of the present application. DETAILED DESCRIPTION

[0031] To make the purpose, technical solutions, and advantages of the embodiments of this application more clear, the technical solutions in the embodiments of this application will be clearly described below in conjunction with the drawings in the embodiments of this application. Obviously, the described embodiments are part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0032] Unless otherwise defined, all technical and scientific terms used in this application have the same meanings as commonly understood by those skilled in the art to which this application belongs. The terms used in the specification of this application are for the purpose of describing specific embodiments only and are not intended to limit this application. The terms "including" and "having" and any variations thereof in the specification and claims of this application and the above-mentioned drawings are intended to cover non-exclusive inclusions. The terms "first" and "second" in the specification and claims of this application or the above-mentioned drawings are used to distinguish different objects, rather than to describe a specific order or a primary-secondary relationship.

[0033] References to "embodiments" in this application mean that a particular feature, structure, or characteristic described in connection with the embodiment may be included in at least one embodiment of the application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor does it constitute an independent or alternative embodiment that is mutually exclusive of other embodiments.

[0034] The term "and / or" in this application simply describes an association between related objects, indicating that three possible relationships exist. For example, A and / or B can represent: A exists alone, A and B exist simultaneously, and B exists alone. In addition, the character " / " in this application generally indicates that the related objects are in an "or" relationship.

[0035] The term "plurality" used in this application refers to two or more (including two).

[0036] As mentioned in the background, one effective way to increase the energy density of battery cells is to increase the areal density of the electrode active material layer. However, since the compaction density of the electrode active material layer cannot be too high, the most direct approach is to increase the thickness of the electrode active material layer. However, the disadvantage of thick electrodes is that the ion transmission path is increased, and the electrolyte does not easily penetrate the active material layer, resulting in reduced ionic conductivity, reduced battery rate discharge capacity, and worsened battery rate performance.

[0037] In this regard, related technologies include mechanically punching holes in the active material layer on the electrode plate to promote the penetration of the electrolyte in the active material layer, so as to improve the ionic conductivity of the electrode plate. However, this method has the disadvantage of causing waste of electrode active materials and increasing production costs. In addition, there are also pore-forming agents such as ammonium bicarbonate added to the active material layer to decompose and produce gas. Although such pore-forming agents can form pores in the active material layer, the problem is that the pores formed by decomposition and gas production are difficult to control, have a high degree of tortuosity, and are not easy to form through-holes that penetrate the active material layer. The effect of promoting the penetration of the electrolyte into the active material layer is limited. At the same time, the residues of such pore-forming agents may have a certain impact on the electrode plate.

[0038] Based on this, the present application provides a coating composition for forming pores in an electrode plate, an electrode plate and a method for preparing the same, a secondary battery, and an electronic device. The coating composition can be used to form a pore-forming coating in the electrode plate, and the pore-forming coating is disposed between the current collector and the active material layer. The core-shell structure of the pore-forming agent in the coating composition is easier to form through holes in the active material layer than general decomposition and gas-generating pore-forming agents, thereby promoting the infiltration of the electrolyte into the electrode plate and improving the rate performance of the battery cell. The specific embodiments provided in this application are described in detail below.

[0039] Coating composition for electrode plate pore formation

[0040] In a first aspect, the present application provides a coating composition for forming pores in an electrode plate, comprising: a first binder and a pore-forming agent, the pore-forming agent having a core-shell structure, the core-shell structure comprising a shell material and a core material; wherein the shell material comprises a second binder, and the core material comprises an alkane gas.

[0041] According to the present application, the coating composition can be used to form a pore-forming coating in the electrode pole piece, and the pore-forming coating can be arranged between the current collector and the active material layer. The first binder in the coating composition is used to bond the pore-forming agent to the current collector to form a pore-forming coating. The pore-forming agent with a core-shell structure in the coating composition releases the alkane gas in the pore-forming agent under appropriate conditions. Compared with general decomposition and gas-producing pore-forming agents, it is easier to form through holes in the active material layer, provide channels for the electrolyte to penetrate into the active material layer, and promote the infiltration of the electrolyte into the active material layer, thereby improving the ionic conductivity of the electrode pole piece, reducing polarization during charging and discharging, and improving the rate performance of the battery cell.

[0042] It is understandable that, compared with the mechanical punching in the related art, on the one hand, it can reduce the waste of active materials, and on the other hand, it will not damage the structure of the active materials during the pore-forming process, thereby improving the stability of the electrode plates. In addition, compared with the use of decomposition gas-generating pore-forming agents (such as ammonium bicarbonate), since decomposition gas production is a continuous process, the gas production gradually increases with the degree of decomposition. In the initial stage of decomposition, the gas production is relatively small, and the tortuosity of the generated pores is relatively high, making it difficult to break through the active material layer to form through-holes. At the same time, there is also the problem of insufficient decomposition residues affecting the performance of the battery cell. The pore-forming agent with a core-shell structure in the above-mentioned coating composition has a shell material of the second binder and an inner core material of an alkane gas. Under appropriate conditions, the shell of the pore-forming agent breaks, and the alkane gas in the core is directly released, resulting in a smaller tortuosity of the generated pores, which is easier to break through the active material layer to form through-holes, so that the electrolyte can infiltrate the active material layer through the through-holes to improve the isolation of the electrode plates. The pore-forming agent improves the ionic conductivity and the rate performance of the battery cell. At the same time, the alkane gas is stable and does not react with other components in the electrode plate, so the consistency of the pore formation is better. In addition, the shell material of the pore-forming agent will be retained in the pore-forming coating, which can improve the adhesion between the active material layer and the current collector and improve the stability of the electrode plate. At the same time, the polymer material group formed by the first binder and the second binder can adsorb the electrolyte, thereby further promoting the electrolyte to penetrate into the side of the active material layer close to the current collector through the through hole, and then the electrolyte is adsorbed and diffused by the pore-forming coating, thereby further improving the infiltration of the electrolyte into the side of the active material layer close to the current collector, thereby improving the ionic conductivity of the electrode plate and improving the rate performance of the battery cell.

[0043] It should be noted that, in the context of this application, the through-holes in the active material layer refer to the holes that penetrate the surface of the active material layer away from the current collector. Alkane gas refers to an alkane that is gaseous at room temperature and pressure.

[0044] In some embodiments, the mass ratio of the pore former to the first binder is 0.5 to 4.

[0045] In some of the above embodiments, the mass ratio of the pore-forming agent and the first binder is further limited. Since the shell material of the pore-forming agent is the second binder, a small amount of the first binder can ensure that the pore-forming coating and the current collector have good adhesion, and the content of the pore-forming agent will affect the pore-forming effect of the pore-forming coating. Therefore, the pore-forming agent and the first binder in the coating composition can be adjusted within a large range and can be selected according to different needs to achieve different pore-forming effects. For example, the mass ratio of the pore-forming agent and the first binder can be 0.5, 0.8, 1, 1.5, 2, 2.5, 3, 3.5, 4, or within the range composed of any of the above values. Further preferably, the mass ratio can be 2 to 4. At this time, the pore-forming coating formed by the coating composition is easier to form through-holes in the active material layer, and the through-holes formed have a suitable pore spacing, which can further promote the penetration of the electrolyte, improve the ionic conductivity of the electrode plate, and improve the rate performance of the battery cell.

[0046] In some embodiments, the volume average particle size Dv50 of the pore former satisfies: 5 μm≤Dv50≤50 μm; preferably, Dv50 satisfies: 18 μm≤Dv50≤50 μm.

[0047] In some of the above embodiments, the volume average particle size Dv50 of the pore former is further limited. The particle size of the pore former will affect the aperture of the through hole. In this case, the through hole obtained has a suitable aperture, which can promote the penetration of the electrolyte while reducing the problem of reduced ionic conductivity caused by local overpressure of the active material in the electrode sheet during rolling. For example, the volume average particle size Dv50 of the pore former can be 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 15μm, 18μm, 20μm, 25μm, 28μm, 30μm, 35μm, 40μm, 45μm, 50μm, or within the range of any of the above values. Further preferably, Dv50 can satisfy: 18μm≤Dv50≤50μm.

[0048] Dv50 has a well-known meaning in the art. Dv50 represents the value below which 50% of the particles in a volume-based particle size distribution have a diameter smaller than this value. Dv50 can be measured using methods and instruments known in the art. For example, it can be measured using a laser particle size analyzer (e.g., Malvern Mastersizer 2000E, UK) in accordance with GB / T 19077-2016, Particle Size Distribution - Laser Diffraction Method.

[0049] In some embodiments, the first binder includes at least one of polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polyacrylonitrile, polyacrylic acid, polyacrylic acid salt, acrylic polymer, and polyimide.

[0050] In some of the above embodiments, the types of first binders are further defined. It is understood that the first binder is not limited to the aforementioned types, and those skilled in the art may select one based on actual needs. Further preferably, the first binder comprises at least one of polyacrylic acid and polyacrylate. This is because polyacrylic acid and polyacrylate have good affinity for the electrolyte and can ionize in the electrolyte to form binding sites for active ions. This can increase the ionic conductivity of the active material layer on the side closest to the current collector, thereby further improving the ionic conductivity of the electrode sheet.

[0051] In some embodiments, the thickness of the shell material in the pore former is 2 μm to 15 μm.

[0052] In some of the above embodiments, the thickness of the shell material in the pore former is further limited. It is understandable that the thickness of the shell material will affect the stability of the pore former. When the thickness of the shell material is 2μm to 15μm, the pore former is more stable and can break under appropriate conditions, quickly release the core material, and more easily form through holes in the active material layer, thereby promoting the penetration of the electrolyte, further improving the ionic conductivity of the electrode plate, and improving the rate performance of the battery cell. For example, the thickness of the shell material in the pore former can be 2μm, 4μm, 6μm, 8μm, 10μm, 12μm, 14μm, 15μm, or within the range of any of the above values. Further preferably, the thickness is 2μm to 8μm.

[0053] The thickness of the shell material has a well-known meaning in the art and can be measured using methods and instruments known in the art. For example, the thickness of the shell material in the pore-forming agent can be measured using a transmission electron microscope.

[0054] In some embodiments, the mass percentage of the core material in the pore-forming agent is 10% to 50%.

[0055] In some of the above-mentioned embodiments, the content of the core material in the pore-forming agent is further limited. The content of the core material in the pore-forming agent affects the gas production and stability of the pore-forming agent. Gas production affects the pore-forming effect. Appropriately increasing the core material content makes it easier to form through-holes in the active material layer, which also affects the pore diameter to a certain extent. It is understood that, while ensuring the stability of the pore-forming agent, pore-forming agents with different core material contents can be selected based on the surface density of the electrode sheet to form through-holes with appropriate pore diameters in the active material layer. Furthermore, while ensuring good pore-forming effect, appropriately reducing the core material content can leave more shell material at the bottom of the through-holes, facilitating electrolyte penetration. For example, the core material content in the pore-forming agent can be 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, or within a range comprised of these values. Further preferably, the core material content in the pore-forming agent can be 20% to 40% by weight. In this case, the pore-forming agent structure is more stable and more easily forms through-holes in the active material layer, promoting electrolyte penetration.

[0056] The content of the core material in the pore-forming agent has a well-known meaning in the art and can be measured using methods and instruments known in the art. For example, the content of the core material in the pore-forming agent can be calculated by measuring the change in pressure of the pore-forming agent before and after gas generation in a closed container using the equal volume method.

[0057] In some embodiments, the second binder includes at least one of polyacrylonitrile, polyacrylic acid, polymethacrylic acid, polymethyl acrylate, and polymethyl methacrylate.

[0058] In some of the above embodiments, the type of the second binder is further limited. It is understood that the second binder is not limited to the above types. Those skilled in the art can select a binder with a certain strength known in the art according to actual needs. Further preferably, the second binder includes at least one of polyacrylonitrile and polymethyl methacrylate. Since the shell material will be retained in the pore-forming coating after the pore-forming agent releases the core material, polyacrylonitrile and polymethyl methacrylate have good affinity with the electrolyte, which can further promote the penetration of the electrolyte. At the same time, polyacrylonitrile and polymethyl methacrylate have high strength and stability, and the polymer structure is relatively dense. The core material in the pore-forming agent is not easy to dissipate, which can improve the stability of the pore-forming agent.

[0059] In some embodiments, the alkane gas includes at least one of alkane gases having 1 to 4 carbon atoms, and preferably the alkane gas includes at least one of propane and n-butane.

[0060] In some embodiments, the true density of the pore former is 0.9 g / cm 3 Up to 1.15g / cm 3, preferably 0.95 g / cm 3 to 1.10g / cm 3 The true density of the pore-forming agent has a well-known meaning in the art, and is the mass of the pore-forming agent per unit volume in an actual absolutely dense state, which can be measured using methods and instruments known in the art.

[0061] In some embodiments, the coating composition further comprises a dispersant, and the dispersant comprises water, dimethylformamide (DMF), diethylformamide, dimethylacetamide (DMAc), N-methylpyrrolidone (NMP), methanol, ethanol, 1-propanol, 2-propanol (isopropanol), 1-butanol (n-butanol), 2-methyl-1-propanol (isobutanol), 2-butanol (sec-butanol), 1-methyl-2-propanol (tert-butanol), pentanol, hexanol, heptanol, octanol, ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, 1,3- At least one of propylene glycol, 1,3-butanediol, 1,5-pentanediol, hexylene glycol, glycerol, trimethylolpropane, pentaerythritol, sorbitol, ethylene glycol monomethyl ether, diethylene glycol monomethyl ether, triethylene glycol monomethyl ether, tetraethylene glycol monomethyl ether, ethylene glycol monoethyl ether, diethylene glycol monoethyl ether, triethylene glycol monoethyl ether, tetraethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, tetraethylene glycol monobutyl ether, acetone, methyl ethyl ketone, methyl propyl ketone, cyclopentanone, ethyl acetate, γ-butyrolactone and ε-propiolactone.

[0062] In some embodiments, the coating composition has a solids content of 20% to 70%.

[0063] Method for preparing electrode sheet

[0064] In a second aspect, the present application provides a method for preparing an electrode sheet, comprising the following steps:

[0065] S10: coating the coating composition according to any embodiment of the first aspect on at least one surface of the current collector to form a pore-forming coating on at least one surface of the current collector;

[0066] S20: coating an electrode active slurry on the surface of the current collector coated with the pore-forming coating to form an active material layer on the pore-forming coating;

[0067] S30: Drying the current collector coated with the pore-forming coating layer and the active material layer to release the core material of the pore-forming agent in the pore-forming coating layer to form through-holes in the active material layer.

[0068] According to the present application, the method uses the coating composition of any embodiment of the first aspect to form a pore-forming coating on at least one surface of a current collector, prepares an active material layer on the pore-forming coating, and releases the core material of the pore-forming agent in the pore-forming coating during the drying process to form through-holes in the active material layer. Therefore, the electrode sheet has the beneficial effects of the first aspect.

[0069] In some embodiments, step S10 includes:

[0070] The coating composition according to any embodiment of the first aspect is coated in an island shape on at least one surface of the current collector to form an island-shaped distributed pore-forming coating on at least one surface of the current collector.

[0071] In some of the above embodiments, the coating method of the pore-forming coating is specifically defined. The island-shaped coating can reduce the coverage area of ​​the pore-forming coating on the current collector. Since the pore-forming coating includes a first binder and a pore-forming agent, the conductivity of the pore-forming coating is poor. Compared with the use of continuous surface coating to form the pore-forming coating, the conductivity of the electrode plate can be improved to achieve the goal of improving the ionic conductivity of the electrode plate without deteriorating its electronic conductivity, thereby further improving the rate performance of the battery cell. On the other hand, the island-shaped distribution of the pore-forming coating is conducive to reducing the thickness of the electrode plate, thereby increasing the energy density of the battery cell.

[0072] It should be noted that in the context of this application, island distribution has a well-known meaning in the art, specifically referring to a discontinuously dispersed distribution. Island coating is a discontinuously dispersed coating. For example, gravure coating can be used to achieve uniform island coating on the current collector.

[0073] In some embodiments, the ratio of the island coating area to the single-side area of ​​the current collector can be 0.25 to 0.75. In this case, the electronic conductivity of the electrode plate is less affected, and the pore-forming coating can form sufficient through-holes in the active material layer to promote electrolyte penetration and improve the ionic conductivity of the electrode plate, thereby obtaining a battery cell with good rate performance.

[0074] In some embodiments, the island spacing between two adjacent islands in the island-shaped pore-forming coating is 50 μm to 1000 μm. The island spacing indicates the density of the distribution of the pore-forming coating on the current collector. The smaller the island spacing, the larger the area of ​​the pore-forming coating required to cover the current collector, and the greater the impact on the electronic conductivity of the electrode plate. The larger the island spacing, the fewer paths for electrolyte penetration, and the less likely the active material layer is to be infiltrated by the electrolyte, thereby affecting the ionic conductivity of the electrode plate. When the island spacing is controlled at 50 μm to 1000 μm, the through-hole distribution in the active material layer is more uniform, which can promote the uniform penetration of the electrolyte into the active material layer when the island coating area is small, thereby better balancing the ionic conductivity and electronic conductivity of the electrode plate, and further improving the rate performance of the battery cell.

[0075] As an example, FIG1 shows a pore-forming coating layer distributed in an island shape on a current collector in one embodiment of the present application. The pore-forming coating layer is evenly distributed in an island shape on the upper layer of the current collector.

[0076] In some embodiments, the coating composition can be obtained by the following method: dispersing the first binder and the pore-forming agent in a dispersant to obtain the coating composition.

[0077] The first binder, pore former and dispersant can be selected according to any embodiment of the first aspect to achieve corresponding beneficial effects.

[0078] In some embodiments, the current collector may be a metal foil or a composite current collector. The composite current collector may include a polymer material base and a metal layer formed on at least one surface of the polymer material base. The composite current collector may be formed by forming a metal material (copper, copper alloy, aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.). As an example, the electrode pole piece is a positive pole piece and the current collector is aluminum foil. As another example, the electrode pole piece is a negative pole piece and the current collector is copper foil.

[0079] In some embodiments, the electrode active slurry can be obtained by the following method: dispersing the active material, the third binder, and the conductive agent in a solvent to obtain the electrode active slurry.

[0080] In some embodiments, the active material may be a positive electrode active material or a negative electrode active material commonly used in the art, and there is no particular limitation on the specific type.

[0081] As an example, the positive electrode active material may include at least one of the following materials: lithium-containing phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, the present application is not limited to these materials, and other traditional materials that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also referred to as NCM 333 ), LiNi 0.5 Co 0.2 Mn 0.3 O2 (also referred to as NCM 523 ), LiNi 0.5 Co 0.25 Mn 0.25 O2 (also referred to as NCM 211 ), LiNi 0.6 Co 0.2 Mn 0.2 O2 (also referred to as NCM 622 ), LiNi 0.8 Co 0.1 Mn 0.1 O2 (also referred to as NCM 811 ), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.15 Al 0.05 O2) and its modified compounds. Examples of olivine-structured lithium-containing phosphates may include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon.

[0082] The negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate. The silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, the present application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0083] In some embodiments, the third binder may be a binder commonly used in the art, and there is no particular limitation on the specific type.

[0084] As an example, the third binder may include at least one of polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polyhexafluoropropylene, polytetrafluoropropylene, polytrifluoropropylene, polyhexafluorobutadiene, polyhexafluoroisobutylene, polytrifluoroethylene, polytrifluorochloroethylene, polytetrafluoroethylene, hydroxyalkyl methyl cellulose, styrene-butadiene rubber, fluorine-based rubber and ethylene propylene diene, wherein the alkyl group in the hydroxyalkyl methyl cellulose includes at least one of methyl, ethyl, propyl and butyl.

[0085] In some embodiments, the conductive agent may be a conductive agent commonly used in the art, and there is no particular limitation on the specific type.

[0086] As an example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0087] In some embodiments, the solvent may include water, dimethylformamide (DMF), diethylformamide, dimethylacetamide (DMAc), N-methylpyrrolidone (NMP), methanol, ethanol, 1-propanol, 2-propanol (isopropanol), 1-butanol (n-butanol), 2-methyl-1-propanol (isobutanol), 2-butanol (sec-butanol), 1-methyl-2-propanol (tert-butanol), pentanol, hexanol, heptanol or octanol, ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, 1,3-propylene glycol, 1 , 3-butylene glycol, 1,5-pentanediol, hexylene glycol, glycerol, trimethylolpropane, pentaerythritol, sorbitol, ethylene glycol monomethyl ether, diethylene glycol monomethyl ether, triethylene glycol monomethyl ether, tetraethylene glycol monomethyl ether, ethylene glycol monoethyl ether, diethylene glycol monoethyl ether, triethylene glycol monoethyl ether, tetraethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, tetraethylene glycol monobutyl ether, acetone, methyl ethyl ketone, methyl propyl ketone, cyclopentanone, ethyl acetate, γ-butyrolactone and ε-propiolactone at least one. As an example, the solvent can be water. As another example, the solvent can be N-methylpyrrolidone.

[0088] In some embodiments, the solid content of the electrode active slurry may be 50 wt % to 80 wt %.

[0089] In some embodiments, the drying temperature can be selected based on the type and thickness of the shell material in the pore-forming agent, as well as the type of dispersant and solvent. At this drying temperature, the core-shell structure of the pore-forming agent is destroyed, releasing the core material, thereby forming through-pores in the active material layer. It should be understood that the process of forming the pore-forming coating in step S10 should be performed below the above-mentioned drying temperature to ensure the stability of the pore-forming agent in the pore-forming coating, so that it is destroyed in step S30 to form through-pores in the active material layer.

[0090] In some embodiments, after the through holes are formed in the active material layer, the electrode plate may be obtained by cold pressing or other steps.

[0091] Electrode plate

[0092] In a third aspect, the present application provides an electrode plate, comprising: a current collector, a pore-forming coating and an active material layer, wherein the pore-forming coating is arranged between the current collector and the active material layer; wherein the pore-forming coating comprises a first binder and a second binder, and the active material layer comprises an active material and a third binder; the active material layer is provided with a through hole, and the through hole comprises a second binder at one end close to the current collector.

[0093] According to the present application, a through hole is provided in the active material layer of the electrode plate, so that the electrolyte can penetrate into the side of the active material layer close to the current collector through the through hole, thereby infiltrating the active material layer. At the same time, the end of the through hole close to the current collector includes a second binder, which cooperates with the polymer material group formed by the first binder in the pore-forming coating to effectively adsorb the electrolyte, thereby promoting the electrolyte to penetrate into the side of the active material layer close to the current collector through the through hole, and then the pore-forming coating adsorbs and diffuses the electrolyte, further improving the infiltration of the electrolyte into the side of the active material layer close to the current collector, thereby improving the ionic conductivity of the electrode plate, and then improving the rate performance of the battery cell.

[0094] At the same time, the first binder and the second binder in the pore-forming coating can enhance the bonding force between the active material layer and the current collector, improve the interface performance between the active material layer and the current collector, and enhance the stability of the electrode sheet.

[0095] In some embodiments, the electrode plate can be prepared according to the method of any embodiment of the second aspect.

[0096] In some embodiments, the current collector, the active material in the active material layer, and the third binder can be selected according to any embodiment of the second aspect.

[0097] In some embodiments, the active material layer further includes a conductive agent, which can be selected according to any embodiment of the second aspect.

[0098] In some embodiments, the first binder and the second binder in the pore-forming coating can be selected according to any embodiment of the first aspect to achieve corresponding beneficial effects.

[0099] In some embodiments, the pore-forming coating is distributed in an island shape on the current collector, and the single-side area S1 of the pore-forming coating and the single-side area S of the current collector satisfy: 0.25≤S1 / S≤0.75.

[0100] In some of the above embodiments, due to the poor conductivity of the pore-forming coating, when S1 / S is controlled to be between 0.25 and 0.75, the pore-forming coating has little effect on the electronic conductivity of the electrode sheet, and the pore-forming coating can form sufficient through-holes in the active material layer, promote the penetration of the electrolyte, and improve the ionic conductivity of the electrode sheet, thereby obtaining a battery cell with good rate performance. For example, S1 / S can be 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.6, 0.7, 0.75, or within the range of any of the above values. Further preferably, S1 / S can be between 0.4 and 0.6.

[0101] In some embodiments, the active material layer is provided with a plurality of pore clusters consisting of a plurality of through holes, the pore distance between two adjacent through holes in the pore clusters is no more than 30 μm, and the maximum diameter of the pore clusters is 100 μm to 800 μm.

[0102] In some of the above embodiments, the island-shaped pore-forming coating can form a plurality of pore clusters consisting of a plurality of through-holes in the active material layer, and the pore spacing between two adjacent through-holes in the pore cluster is not greater than 30 μm. It can be understood that the larger the maximum diameter of the pore cluster, the more channels for electrolyte penetration, and the stronger the ability to promote electrolyte infiltration. By appropriately reducing the maximum diameter of the pore cluster, the number of pore clusters can be increased when the area of ​​the pore-forming coating is constant, which is conducive to the uniform penetration of the electrolyte into the active material layer, so as to further improve the ionic conductivity of the electrode sheet. Therefore, the maximum diameter of the pore cluster can be 100 μm to 800 μm, which can further improve the rate performance of the battery. For example, the maximum diameter of the pore cluster can be 100 μm, 200 μm, 300 μm, 400 μm, 500 μm, 600 μm, 700 μm, 800 μm, or within the range of any of the above values. Further preferably, the maximum diameter can be 200 μm to 500 μm.

[0103] It should be noted that in the context of this application, a pore cluster is a collection of multiple through-holes. Different pore clusters are distinguished by defining the inter-hole spacing between two adjacent through-holes in the pore cluster. The inter-hole spacing between two adjacent through-holes refers to the distance between any through-hole in the pore cluster and the closest through-hole in the pore cluster. The maximum diameter of a pore cluster refers to the distance between the two farthest through-holes in the pore cluster. It is also understood that the maximum diameter of a pore cluster can be adjusted by controlling the island area in the island-shaped pore-forming coating.

[0104] In some embodiments, the cluster spacing between two adjacent pore clusters in the active material layer is 50 μm to 1000 μm.

[0105] In some of the above embodiments, the cluster spacing between two adjacent pore clusters in the active material layer is further defined. The cluster spacing indicates the density of the pore clusters in the active material layer. The smaller the cluster spacing, the larger the pore-forming coating area required to cover the current collector, the greater the impact on the electronic conductivity of the electrode plate, and the tendency to cause local overvoltage during the cold pressing process. The larger the cluster spacing, the fewer paths for electrolyte penetration, and the less likely the active material layer is to be wetted by the electrolyte, thereby affecting the ionic conductivity of the electrode plate. The cluster spacing is controlled to be between 50μm and 1000μm. At this time, the pore clusters in the active material layer are more evenly distributed, which can promote the uniform penetration of the electrolyte into the active material layer when the island coating area is small, thereby better balancing the ionic conductivity and electronic conductivity of the electrode plate, and further improving the rate performance of the battery cell. For example, the cluster spacing may be 50 μm, 100 μm, 200 μm, 300 μm, 400 μm, 500 μm, 600 μm, 700 μm, 800 μm, 900 μm, 1000 μm, or any range thereof. More preferably, the cluster spacing may be 100 μm to 500 μm.

[0106] It should be noted that two adjacent pore clusters refer to any two closest pore clusters in the active material layer, and the cluster spacing refers to the minimum distance between the through-holes in one pore cluster and the through-holes in another pore cluster. It is understood that the cluster spacing can be adjusted by controlling the island spacing of the island-shaped pore-forming coating.

[0107] The maximum diameter of a pore cluster and the intercluster spacing between two adjacent pore clusters in the active material layer can be measured using methods and instruments known in the art. For example, a scanning electron microscope can be used to observe the distribution of through-pores on the surface of the active material layer. Different pore clusters can be distinguished based on the above-mentioned definition of pore clusters, and the maximum diameter of the pore cluster and the intercluster spacing between two adjacent pore clusters in the active material layer can be calculated.

[0108] As an example, FIG2 shows a scanning electron microscope image of the surface of the active material layer in one embodiment of the present application, in which pore clusters consisting of a plurality of through holes are evenly distributed in the active material layer.

[0109] In some embodiments, the pore depth H of the through-pores and the sum of the thicknesses D of the active material layer and the pore-forming coating layer satisfy: 95%≤H / D≤110%.

[0110] In some of the above embodiments, it should be noted that the hole depth H of the through hole refers to the distance from the surface of the active material layer to the interior of the active material layer (in this application, unless otherwise specified, the distance from the surface of the active material layer to the surface of the active material layer away from the current collector, and the interior of the active material layer refers to the current collector side of the active material layer pore). Since the end of the through hole in the active material layer close to the current collector includes a second binder, that is, the through hole penetrates the active material layer, when H / D satisfies 95% to 110%, it means that the tortuosity of the through hole is low, which can reduce the distance for the electrolyte to penetrate into the interior of the active material layer, thereby reducing the ion transmission distance and further improving the ionic conductivity. For example, H / D can be 95%, 95%, 97%, 98%, 99%, 100%, 101%, 102%, 103%, 104%, 105%, 106%, 107%, 108%, 109%, 110%, or within the range of any of the above values. More preferably, H / D can be 99% to 106%.

[0111] The hole depth H of the through hole can be detected by methods and instruments known in the art, such as using a microscope SD scanning imaging method or a scanning electron microscope SEM method to detect the hole depth H of the through hole, thereby calculating H / D.

[0112] In some embodiments, the depth H of the through-holes is greater than the thickness of the active material layer.

[0113] In some of the above embodiments, the hole depth H of the through hole is greater than the thickness of the active material layer, which is conducive to the electrolyte fully infiltrating the interior of the active material layer and improving the ionic conductivity of the electrode plate.

[0114] It should be noted that when the pore-forming coating is distributed in an island shape, the thickness of the active material layer is not uniform. In this case, the thickness of the active material layer is the thickness of the electrode sheet - the thickness of the current collector - the thickness of the pore-forming coating.

[0115] As an example, FIG3 shows a scanning electron microscope image of a cross section of a through hole in an active material layer in an embodiment of the present application. It can be seen that the through hole penetrates the active material layer, and the tortuosity of the through hole is low, and the electrolyte penetration path is short.

[0116] In some embodiments, the mass ratio of the first binder to the second binder is 0.1 to 1. It is understood that when the second binder is derived from a pore former, the mass ratio of the first binder to the second binder can be controlled by controlling the mass ratio of the first binder to the pore former.

[0117] In some embodiments, the pore-forming coating has a thickness of 1 μm to 5 μm. Because the pore-forming coating includes a first binder and a second binder, the resulting polymer material group has an adsorption effect on the electrolyte. Therefore, a pore-forming coating of appropriate thickness can promote the penetration of the electrolyte into the active material layer. However, excessive thickness can affect electronic conductivity and energy density. Therefore, the thickness of the pore-forming coating can be 1 μm to 5 μm. For example, the thickness of the pore-forming coating can be 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, or within a range consisting of any of the above values.

[0118] In some embodiments, the surface density of the active material layer is 8 mg / cm 2 Up to 40 mg / cm 2 The thickness of the active material layer is 25μm to 80μm. Since a thicker active material layer can contain more electrode active material, the amount of positive and negative electrode substrates and separators used in the battery cell can be reduced, thereby improving the energy density. At the same time, the presence of through holes in the electrode sheets can promote the infiltration of the electrolyte into the active material layer. Therefore, the surface density and thickness of the active material layer can be appropriately increased to improve the energy density of the battery cell.

[0119] It should be noted that the definitions of the active material layer and pore-forming coating in the electrode sheet in this application refer to the active material layer and pore-forming coating on the current collector side. When the active material layer and pore-forming coating are provided on both sides of the current collector, if the active material layer and pore-forming coating on either side meet the above-defined ranges, they fall within the scope of protection of this application.

[0120] secondary batteries

[0121] In a fourth aspect, the present application provides a secondary battery comprising: a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte; at least one of the positive electrode sheet and the negative electrode sheet is an electrode sheet prepared according to the method described in any embodiment of the second aspect or an electrode sheet described in any embodiment of the third aspect.

[0122] According to the present application, at least one of the positive or negative electrodes of the secondary battery comprises an electrode sheet prepared according to the method of any embodiment of the second aspect, or an electrode sheet according to any embodiment of the third aspect. The electrode sheet has been described and illustrated in detail above and will not be repeated here. It is understood that the secondary battery of the present application can achieve the beneficial effects of the second and third aspects of the present application.

[0123]

Isolation film

[0124] The separator is placed between the positive and negative electrodes to prevent short circuits between the positive and negative electrodes while allowing active ions to pass through. This application does not impose any particular restrictions on the type of separator; any known porous separator with good chemical and mechanical stability can be used.

[0125] In some embodiments, the material of the isolation membrane can be selected from one or more of, but not limited to, fiberglass, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. Alternatively, the isolation membrane can include polyethylene and / or polypropylene. The isolation membrane can be a single-layer film or a multi-layer composite film. When the isolation membrane is a multi-layer composite film, the materials of each layer can be the same or different. In some embodiments, the isolation membrane can also be provided with a ceramic coating or a metal oxide coating.

[0126]

Electrolyte

[0127] The electrolyte plays a role in conducting active ions between the positive electrode and the negative electrode. The electrolyte that can be used in the secondary electrolyte of this application can be an electrolyte known in the prior art.

[0128] In some embodiments, the electrolyte may include an organic solvent, an electrolyte salt, and optional additives. The types of the organic solvent, the lithium salt, and the additives are not particularly limited and may be selected according to needs.

[0129] In some embodiments, the secondary battery is a lithium-ion battery, and the electrolyte salt may include a lithium salt. As an example, the lithium salt includes, but is not limited to, at least one of LiPF6 (lithium hexafluorophosphate), LiBF4 (lithium tetrafluoroborate), LiClO4 (lithium perchlorate), LiFSI (lithium bis(fluorosulfonyl imide), LiTFSI (lithium bis(trifluoromethanesulfonyl imide), LiTFS (lithium trifluoromethanesulfonate), LiDFOB (lithium difluorooxalatoborate), LiBOB (lithium dioxalatoborate), LiPO2F2 (lithium difluorophosphate), LiDFOP (lithium difluorooxalatophosphate), and LiTFOP (lithium tetrafluorooxalatophosphate). The above lithium salts may be used alone or in combination.

[0130] In some embodiments, the secondary battery is a sodium ion battery, and the electrolyte salt may include a sodium salt. As an example, the sodium salt may be selected from at least one of NaPF6, NaClO4, NaBCl4, NaSO3CF3, and Na(CH3)C6H4SO3.

[0131] In some embodiments, as an example, the organic solvent includes but is not limited to 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), methyl ethyl sulfone (EMS) and diethyl sulfone (ESE). The above organic solvents can be used alone or in combination. Alternatively, two or more organic solvents are used in combination.

[0132] In some embodiments, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high or low temperature performance, etc.

[0133] As an example, the additive includes but is not limited to at least one of fluoroethylene carbonate (FEC), vinylene carbonate (VC), vinyl ethylene carbonate (VEC), diethylene sulfate (DTD), propylene sulfate, vinyl sulfite (ES), 1,3-propane sultone (PS), 1,3-propene sultone (PST), sulfonate cyclic quaternary ammonium salt, succinic anhydride, succinonitrile (SN), adiponitrile (AND), tris(trimethylsilyl) phosphate (TMSP), and tris(trimethylsilyl) borate (TMSB).

[0134] The electrolyte solution can be prepared according to conventional methods in the art. For example, an organic solvent, an electrolyte salt, and optional additives can be uniformly mixed to obtain the electrolyte solution. The order in which the materials are added is not particularly limited. For example, the electrolyte salt and optional additives can be added to the organic solvent and mixed uniformly to obtain the electrolyte solution; alternatively, the electrolyte salt can be added to the organic solvent first, and then the optional additives can be added to the organic solvent and mixed uniformly to obtain the electrolyte solution.

[0135] electronic devices

[0136] A fifth aspect of the present application provides an electronic device comprising the secondary battery according to the fourth aspect of the present application.

[0137] The electronic device of the present application is not particularly limited and can be any electronic device known in the prior art. In some embodiments, the electronic device can include, but is not limited to, a laptop computer, a pen-type computer, a mobile computer, an e-book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a head-mounted stereo headset, a video recorder, an LCD television, a portable cleaner, a portable CD player, a mini-disc, a transceiver, an electronic notepad, a calculator, a memory card, a portable recorder, a radio, a backup power supply, a motor, a car, a motorcycle, a power-assisted bicycle, a bicycle, a lighting fixture, a toy, a game console, a clock, a power tool, a flashlight, a camera, a large household battery, and a lithium-ion capacitor.

[0138] Below, the embodiment of the present application is described. The embodiment described below is exemplary and is only used to explain the present application, and is not to be construed as limiting the present application. Where specific techniques or conditions are not specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. Reagents or instruments used that do not specify the manufacturer are conventional products that can be obtained commercially.

[0139] Performance testing:

[0140] Ionic impedance test: The ionic impedance is calculated by the electrochemical impedance spectroscopy (EIS) curve of the symmetrical battery test. First, take two positive electrode sheets and a diaphragm, inject liquid, and encapsulate to obtain a positive electrode sheet symmetrical battery. The EIS spectrum is obtained by AC impedance test. The test conditions are: frequency range: high frequency 1000KHz, low frequency: 5mHz; disturbance voltage: 10mV; test temperature: 25°C. After the test, the real part of the impedance is used as the horizontal axis and the imaginary part of the impedance is used as the vertical axis to draw a curve, which is the Nyquist Plot. According to the EIS curve, the ionic impedance Rion is calculated using the following formula:

[0141] Rion: Ionic resistance

[0142] R HFR :Rs is the DC resistance, the intersection value of the EIS curve and the horizontal axis

[0143] Z EL |(W LOW →∞): The intersection of the reverse extension line of the EIS curve and the horizontal axis

[0144] Rate performance test: The test temperature is 25℃±3℃. The lithium-ion battery to be tested is charged at a constant current rate of 0.05C to a voltage of 4.50V (i.e., full charge voltage). Then, it is charged at a constant voltage of 4.50V to a current of 0.025C (cut-off current) to fully charge the lithium-ion battery. The battery is left for 10 minutes, and then discharged at a rate of 0.2C to a voltage of 3.0V and left for 5 minutes. The discharge capacity obtained at this time is D0. The lithium-ion battery to be tested is charged at a constant current rate of 0.05C to a voltage of 4.50V (i.e., full charge voltage). Then, it is charged at a constant voltage of 4.50V to a current of 0.025C (cut-off current) to fully charge the lithium-ion battery. The battery is left for 10 minutes, and then discharged at a rate of 3.0C to a voltage of 3.0V and left for 5 minutes. The discharge capacity obtained at this time is D1. Therefore, the 3C discharge rate = D1 / D0.

[0145] Example 1-1

[0146] Preparation of positive electrode sheet:

[0147] (1) Preparation of current collector containing pore-forming coating

[0148] The first binder, pore-forming agent, and deionized water were mixed in a specific ratio and stirred in a vacuum mixer until the mixture was homogeneous, resulting in a pore-forming coating slurry with a solid content of 40%. The mass ratio of the pore-forming agent to the first binder was 3. This slurry was gravure-coated onto a 10μm aluminum foil current collector and dried at 70°C to obtain a current collector containing the pore-forming coating. The first binder was polyacrylic acid, the shell material in the pore-forming agent was polyacrylonitrile, and the core material was propane. The mass percentage of the core material in the pore-forming agent was 20%, the shell thickness was 4μm, and the volume average particle size (Dv50) was 29μm.

[0149] (2) Preparation of positive electrode sheet

[0150] Conductive carbon black and the third binder PVDF were mixed in a certain proportion, and NMP was added to prepare a conductive glue (solid content 7%). After the mixing was completed, the positive electrode active material lithium nickel cobalt manganese oxide was added and continued to be stirred under the action of a vacuum mixer until the system was uniform, and a positive electrode slurry with a solid content of 75% was obtained. The mass ratio of each component was NCM: conductive carbon tube: third binder = 97:1:2; the positive electrode slurry was coated on the 10μm aluminum foil current collector containing the pore-forming coating prepared in (1), dried to form pores, cold pressed, and then cut and welded to the tabs to obtain the positive electrode sheet. The H / D of the positive electrode sheet was tested, as shown in Table 1, and the maximum diameter of the pore clusters on the positive electrode active material layer, the cluster spacing, and the thickness of the pore-forming coating were measured, as shown in Table 2.

[0151] Preparation of the negative electrode: Artificial graphite, styrene-butadiene rubber, and sodium carboxymethyl cellulose were mixed with deionized water and additives in a mass ratio of 96%:2%:2% and stirred evenly to produce a negative electrode slurry. This slurry was then coated onto 6μm copper foil. The slurry was dried, cold-pressed, cut into pieces, and then welded to the tabs to produce the negative electrode.

[0152] Electrolyte preparation: conventional 1.5 mol / L lithium hexafluorophosphate electrolyte was used.

[0153] Preparation of isolation membrane: A 7 μm thick polyethylene (PE) isolation membrane substrate was coated with a 3 μm ceramic coating.

[0154] Preparation of lithium-ion batteries: stack the positive electrode sheet, separator, and negative electrode sheet in order, so that the separator is placed between the positive and negative electrode sheets to act as an isolation, and then wind them to obtain a bare cell; after welding the tabs, place the bare cell in the outer packaging foil aluminum-plastic film, inject the prepared electrolyte into the dried bare cell, and after vacuum packaging, standing, formation, shaping, capacity testing and other processes, a soft-pack lithium-ion battery is obtained.

[0155] Example 1-2 to Example 1-15

[0156] The embodiment is substantially the same as Example 1-1, except that some parameters of the pore-forming coating of the positive electrode sheet are different, as shown in Table 1. The H / D of the positive electrode sheet was tested, as shown in Table 1. It should be noted that the gravure coating method of the pore-forming coating in the above embodiment is the same as that in Example 1-1, so as to obtain a positive electrode sheet with substantially the same maximum diameter of the pore clusters, cluster spacing, and thickness of the pore-forming coating.

[0157] Comparative Example 1-1

[0158] It is substantially the same as Example 1-1, except that no pore-forming coating is used in the positive electrode sheet.

[0159] Comparative Example 1-2

[0160] The same as Example 1-1, the only difference is that the preparation method of the current collector containing the pore-forming coating is different.

[0161] The first binder, ammonium bicarbonate and NMP are mixed in a certain proportion. After the mixing is completed, the mixture is continued to be stirred under the action of a vacuum mixer until the system becomes uniform, and a pore-forming coating slurry with a solid content of 40% is obtained. The mass ratio of ammonium bicarbonate to the first binder is 3; the slurry is gravure coated on a 10μm aluminum foil current collector and dried at 40°C to obtain a current collector containing a pore-forming coating. The first binder is polyacrylic acid, and the volume average particle size Dv50 of ammonium bicarbonate is 29μm. It should be noted that the gravure coating method of the pore-forming coating is the same as that in Example 1-1 to obtain a positive electrode sheet with approximately the same maximum diameter of the pore cluster, cluster spacing, and thickness of the pore-forming coating.

[0162] Performance Testing

[0163] The lithium-ion batteries obtained in Examples 1-1 to 1-15, Comparative Example 1-1 and Comparative Example 1-2 were subjected to rate performance tests, and the ionic impedance of the positive electrode sheets in the above Examples and Comparative Examples was measured. The results are shown in Table 1.

[0164] Table 1

[0165] According to Table 1, the ionic impedance of the positive electrode plate and the 3C discharge rate of the battery in each embodiment are significantly higher than those in each comparative example, indicating that the use of the pore-forming coating can effectively reduce the ionic impedance of the plate, thereby improving the rate performance of the battery. In comparative example 1-1, the positive electrode plate does not use a pore-forming coating, which may make it difficult for the electrolyte to infiltrate the active material layer, resulting in a large ionic impedance of the positive electrode plate and poor rate performance of the battery. In comparative example 1-2, ammonium bicarbonate is used as a pore-forming agent. Due to the high tortuosity of the pores formed by its decomposition and gas production, it is not easy to form through holes in the active material layer, resulting in fewer channels for the electrolyte to penetrate into the active material layer, and the electrolyte is not easy to infiltrate the active material layer, resulting in a large ionic impedance of the positive electrode plate and poor rate performance of the battery. It should be noted that H / D can represent the tortuosity of the through-holes in the active material layer. In each embodiment and comparative example 1-2, H / D is between 0.95 and 1.1, indicating that the tortuosity of the through-holes is low and the path for electrolyte penetration is short. In comparative examples 1-2, only pores with low tortuosity can form through-holes, while the pores formed by the decomposition and gas production of ammonium bicarbonate have high tortuosity, resulting in fewer through-holes in the active material layer.

[0166] According to Examples 1-1 to 1-4, the mass ratio of the pore-forming agent and the first binder in the pore-forming coating layer affects the ionic impedance of the positive electrode sheet, thereby affecting the rate performance of the battery. When the mass ratio of the pore-forming agent and the first binder in the pore-forming coating layer is 0.5 to 4, the rate performance of the battery is better. More preferably, when the mass ratio is 2 to 4, the rate performance of the battery is better.

[0167] According to Examples 1-1, 1-5, and 1-6, the type of shell material in the pore-forming agent will also affect the rate performance of the battery. The possible reason is that the shell material will remain in the pore-forming coating, and polyacrylonitrile has a better ability to adsorb electrolyte than polyacrylate and polymethacrylate, thereby promoting the penetration of the electrolyte and further improving the rate performance of the battery by reducing the ionic impedance of the positive electrode.

[0168] According to Examples 1-1, 1-7, and 1-8, the type of core material in the pore-forming agent also affects the rate performance of the battery. When the alkane gas of the core material is at least one of propane or butane, the rate performance of the battery is better.

[0169] According to Examples 1-1, 1-9 to 1-15, the content of the core material in the pore-forming agent, the shell thickness and the volume average particle size will affect the rate performance of the battery. When the content of the core material is 10% to 50%, the shell thickness is 2μm to 15μm and the volume average particle size Dv50 is 5μm to 50μm, the pore-forming coating can effectively reduce the ionic impedance of the positive electrode sheet and improve the rate performance of the battery.

[0170] Examples 2-1 to 2-11

[0171] It is roughly the same as Example 1-1, except that the gravure coating method of the pore-forming coating is different from that of Example 1-1. The area and the distance between the conductive particles and the coating thickness of the island-shaped pore-forming coating are obtained by controlling the gravure coating, thereby forming pore clusters with different distributions in the positive electrode active material layer, and the thickness of the pore-forming coating. The maximum diameter of the pore clusters on the positive electrode active material layer, the cluster spacing, and the thickness of the pore-forming coating are measured, as shown in Table 2.

[0172] Example 2-11

[0173] It is substantially the same as Example 1-1, except that the pore-forming coating is applied on the entire surface of the aluminum foil current collector.

[0174] Performance Testing

[0175] The lithium-ion batteries obtained in Examples 2-1 to 2-11 were subjected to rate performance tests, and the ionic impedance of the positive electrode sheets in the above examples and comparative examples was measured. The results are shown in Table 2.

[0176] Table 2

[0177] According to Table 2, the ionic impedance of the positive electrode sheets and the rate performance of the batteries in Examples 1-1 and 2-1 to 2-8 are better than those in Example 2-11. The reason for this may be that, on the one hand, the pore-forming coating applied on the entire surface will cause too many through holes in the active material layer, resulting in local overvoltage, thereby increasing the ionic impedance; on the other hand, the first binder and the second binder remaining in the pore-forming coating affect the conductivity of the positive electrode sheet, resulting in poor rate performance of the battery.

[0178] According to Examples 1-1, 2-1 to 2-4, the maximum diameter of the pore cluster in the active material layer has a certain influence on the rate performance of the battery. When the maximum diameter of the pore cluster is 100 μm to 800 μm, the rate performance of the battery is better. More preferably, when the maximum diameter of the pore cluster is 200 μm to 500 μm, the rate performance of the battery is even better.

[0179] According to Examples 1-1, 2-5 to 2-8, the cluster spacing of the pore clusters in the active material layer has a certain influence on the rate performance of the battery. When the cluster spacing is 50 μm to 1000 μm, the battery rate performance is good. More preferably, when the cluster spacing is 100 μm to 500 μm, the battery rate performance is even better. It should also be noted that the maximum diameter of the pore clusters and the cluster spacing affect the rate performance of the battery individually, and both affect the rate performance of the battery by affecting the area of ​​the pore-forming coating.

[0180] According to Examples 1-1, 2-9, and 2-10, the thickness of the pore-forming coating has a certain influence on the rate performance of the battery. When the thickness of the pore-forming coating is between 1 μm and 5 μm, the rate performance of the battery is better.

[0181] It should be noted that, unless there is any conflict, the embodiments and features in the embodiments of this application can be combined with each other.

[0182] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A coating composition for creating pores in an electrode plate, comprising: A first binder and a pore former, the pore former having a core-shell structure, the core-shell structure including a shell material and a core material; wherein, the shell material includes a second binder, and the core material includes an alkane gas.

2. The coating composition according to claim 1, wherein, The mass ratio of the pore former to the first binder is 0.5 to 4; Preferably, the mass ratio of the pore former to the first binder is 2 to 4.

3. The coating composition according to claim 1, wherein, The volume average particle diameter Dv50 of the pore former satisfies: 5 μm ≤ Dv50 ≤ 50 μm; Preferably, Dv50 satisfies: 18 μm ≤ Dv50 ≤ 50 μm.

4. The coating composition according to claim 1, wherein, The first binder includes at least one of polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polyacrylonitrile, polyacrylic acid, polyacrylate, acrylate polymer or polyimide, preferably at least one of polyacrylic acid and polyacrylate.

5. The coating composition according to any one of claims 1 to 4, wherein, The pore former satisfies at least one of the following conditions: 1) The thickness of the shell material is 2 μm to 15 μm, preferably 2 μm to 8 μm; 2) The mass percentage content of the core material in the pore former is 10% to 50%, preferably 20% to 40%; 3) The second binder includes at least one of polyacrylonitrile, polyacrylic acid, polymethacrylic acid, polymethyl acrylate and polymethyl methacrylate, preferably at least one of polyacrylonitrile and polymethyl methacrylate; 4) The alkane gas includes at least one of alkane gases having 1 to 4 carbon atoms, preferably at least one of propane and n-butane; 5) The true density of the pore former is 0.9 g / cm 3 to 1.15 g / cm 3 , preferably 0.95 g / cm 3 to 1.10 g / cm 3 .

6. A method for preparing an electrode plate, comprising the following steps: S10: Coating the coating composition according to any one of claims 1 to 5 on at least one surface of a current collector to form a pore-forming coating on at least one surface of the current collector; S20: Coating an electrode active paste on the surface of the current collector coated with the pore-forming coating to form an active material layer on the pore-forming coating; S30: Drying the current collector coated with the pore-forming coating and the active material layer to release the core material of the pore former in the pore-forming coating, so as to form through holes in the active material layer.

7. The method according to claim 6, wherein, The step S10 includes: Island coating the coating composition according to any one of claims 1 to 5 on at least one surface of a current collector to form an island-distributed pore-forming coating on at least one surface of the current collector.

8. An electrode plate, comprising: A current collector, a pore-forming coating and an active material layer, the pore-forming coating being disposed between the current collector and the active material layer; wherein, the pore-forming coating includes a first binder and a second binder, and the active material layer includes an active material and a third binder; The active material layer is provided with through holes, and one end of the through hole close to the current collector includes a second binder.

9. The electrode plate according to claim 8, wherein, The pore-forming coating is distributed in an island shape on the current collector, and the single-sided area S1 of the pore-forming coating and the single-sided area S of the current collector satisfy: 0.25 ≤ S1 / S ≤ 0.

75.

10. The electrode plate according to claim 8 or 9, wherein, The active material layer is provided with a plurality of pore clusters composed of a plurality of through holes, the pore spacing between two adjacent through holes in the pore cluster is not greater than 30 μm, and the maximum diameter of the pore cluster is 100 μm to 800 μm, preferably the maximum diameter is 200 μm to 500 μm.

11. The electrode plate according to claim 10, wherein, The cluster spacing between two adjacent pore clusters in the active material layer is 50 μm to 1000 μm, preferably 100 μm to 500 μm.

12. The electrode plate according to claim 8, wherein, The through holes satisfy at least one of the following conditions: 1) The hole depth H of the through hole and the sum D of the thicknesses of the active material layer and the pore-forming coating satisfy: 95% ≤ H / D ≤ 110%, preferably, 99% ≤ H / D ≤ 106%; 2) The hole depth H of the through hole is greater than the thickness of the active material layer.

13. The electrode plate according to claim 8, wherein, The pore-forming coating satisfies at least one of the following conditions: 1) The mass ratio of the first binder to the second binder is 0.1 to 1; 2) The thickness of the pore-forming coating is 1 μm to 5 μm.

14. A secondary battery, comprising: A positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte; At least one of the positive electrode sheet or the negative electrode sheet is An electrode sheet prepared by the method according to claim 6 or 7 or an electrode sheet according to any one of claims 8 to 13.

15. An electronic device, comprising: The secondary battery according to claim 14.

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