Positive electrode sheet, secondary battery, battery module, battery pack, and electric device

Abstract

The application provides a positive electrode sheet, a secondary battery provided with the positive electrode sheet, and a battery module, a battery pack and a power utilization device. The positive electrode sheet of the application comprises a positive electrode current collector and a positive electrode film layer, the positive electrode film layer comprises a first positive electrode film layer and a second positive electrode film layer, wherein the first positive electrode film layer is arranged on at least one surface of the positive electrode current collector and comprises a first positive electrode active material, the first positive electrode active material comprises a hollow particle material, the second positive electrode film layer is arranged on the first positive electrode film layer and comprises a second positive electrode active material, and the second positive electrode active material comprises a solid particle material. Through the positive electrode sheet of the application, the Li + The diffusion path in the active material is increased; the BET of the active material is increased, so that the reaction area of the active material is increased; the capacity and the compaction density of the battery cell are increased, and the energy density of the battery cell is effectively improved.

Description

Technical Field

[0001] This invention relates to the field of batteries, and more particularly to a positive electrode, a secondary battery having the positive electrode, a battery module, a battery pack, and an electrical device. Background Technology

[0002] Lithium-ion batteries (LIBs) are widely used in consumer electronics, electric vehicles, and energy storage applications due to their long cycle life, wide operating temperature range, and high energy and power density. To meet the demands of electric vehicle customers for longer driving ranges on a single charge, it is necessary to increase the energy density of electric vehicle batteries.

[0003] As a method to improve energy density, existing technologies increase the areal loading of active materials by using thicker electrodes, thereby reducing the weight ratio of inactive materials (current collectors, separators, and electrolytes, etc.). However, simply increasing the electrode thickness increases the transport distance of ions and electrons, leading to severe polarization and poor electrochemical performance. Especially at high current densities, the active material near the current collector layer does not react sufficiently, while the active material near the separator layer overreacts and undergoes excessive delithiation, causing the layered structure to collapse. The microstructure manifests as particle breakage, resulting in severe deterioration of electrical performance.

[0004] Existing methods for preparing thick electrodes generally suffer from immature processes, high costs, and the need to sacrifice other properties, making it difficult to achieve the desired results. Therefore, how to increase the electrode thickness without sacrificing the electrochemical performance of the battery cell is the current focus of thick electrode research. Summary of the Invention

[0005] This application is made in view of the above-mentioned technical problems, and its purpose is to provide a positive electrode, a secondary battery having the positive electrode, a battery module, a battery pack, and an electrical device. The positive electrode of this application can help reduce lithium ion concentration (Li₂O₃). + The diffusion path in the active material improves the kinetic performance of the secondary battery; it increases the specific surface area (BET) of the active material, thereby increasing the reaction area of ​​the active material; and it can also increase the compaction density of the positive electrode sheet, effectively improving the energy density of the cell.

[0006] To achieve the above objectives, a first aspect of this application is to provide a positive electrode sheet, wherein...

[0007] The positive electrode sheet includes: a positive current collector and a positive electrode film layer, wherein the positive electrode film layer includes a first positive electrode film layer and a second positive electrode film layer, wherein...

[0008] The first positive electrode film layer is disposed on at least one surface of the positive electrode current collector and includes a first positive electrode active material, wherein the first positive electrode active material includes hollow particulate material.

[0009] The second positive electrode film layer is disposed on the first positive electrode film layer and includes a second positive electrode active material, wherein the second positive electrode active material includes solid particulate material.

[0010] The positive electrode film is composed of two layers of positive electrode materials with different particle morphologies: the first layer is the first positive electrode film layer, which is placed on the current collector and is the bottom layer near the current collector. It is a coating with hollow particles formed by hollow particle materials; the second layer is the second positive electrode film layer, which is placed on the first positive electrode film layer and is the top layer near the separator. It is a coating with a solid structure formed by solid particle materials.

[0011] The advantage of this double-layer structure is that the hollow structure of the first layer, being close to the current collector layer, helps to reduce Li. + The diffusion path in active materials, and since the BET of solid granular materials generally does not exceed 1m. 2 / g, hollow structures can improve the BET of materials, increasing it to 2m. 2 / g or more, greatly increasing the reaction area of ​​the active material; the second layer, due to its proximity to the diaphragm and anode, Li + The migration path is relatively short, and its core structure can increase the cell capacity and compaction density, effectively improving the energy density of the cell.

[0012] In some embodiments, the number of hollow particles in the hollow particulate material is 70% or more of the total number of particles in the first positive electrode active material. If the number of hollow particles in the total number of particles in the first positive electrode active material is less than 70%, the rate performance will decrease. Therefore, by ensuring that the proportion of hollow particles in the particles of the first positive electrode active material is within the range of 70% or more, the rate performance can be improved.

[0013] In some embodiments, the median volumetric particle size of the hollow particles is 1–15 μm, optionally 3–9 μm; and / or the median volumetric particle size of the solid particles is 1–15 μm, optionally 3–9 μm. If the median volumetric particle size of the hollow particles exceeds 15 μm, it will cause a decrease in rate performance. If it is less than 1 μm, the material synthesis is more difficult and the compaction density is lower, which is not conducive to improving energy density. Therefore, by keeping the median volumetric particle size of the hollow particles in the range of 1–15 μm, both energy density and rate performance are taken into account. From the viewpoint of comprehensively considering various performance aspects, the median volumetric particle size of the hollow particles is preferably 3–9 μm. Furthermore, the median volumetric particle size of the hollow particles in the first positive electrode active material particles is preferably comparable to, and more preferably equal to, the median volumetric particle size of the solid particles in the second positive electrode active material particles. This can effectively improve the rate performance of the battery cell, while the higher compaction density of the electrode sheet is beneficial to improving the energy density of the battery cell.

[0014] In some embodiments, the ratio of the volume median particle size of the hollow particles to the volume median particle size of the solid particles (the ratio of the volume median particle size of the hollow particles to the volume median particle size of the solid particles) is 0.5 to 2. If the ratio exceeds 2, it will result in a lower electrode compaction density, which in turn will lead to a lower energy density. If it is lower than 0.5, it will result in poor kinetics. Therefore, by keeping the ratio of the volume median particle size of the hollow particles to the volume median particle size of the solid particles within the range of 0.5 to 2, better kinetics and higher energy density can be obtained.

[0015] In some embodiments, the ratio of the hollow particle diameter to the median volume diameter of the hollow particles (hollow particle diameter / median volume diameter) is 0.1 to 0.5. If the ratio exceeds 0.5, it will result in low compaction density of the electrode, making the particles prone to breakage under high compaction density. If it is below 0.1, it will cause a decrease in rate performance. Therefore, by keeping the ratio of the hollow particle diameter to the median volume diameter within the range of 0.1 to 0.5, both compaction density and rate performance can be balanced.

[0016] In some embodiments, the BET of the hollow particulate material is 1–3 m. 2 / g, the BET of the solid granular material is 0.1~1m 2 / g.

[0017] In some embodiments, the weight ratio of the first positive electrode film to the second positive electrode film is 1:9 to 9:1. If the weight ratio of the first positive electrode film to the second positive electrode film exceeds 9:1, it will result in a lower electrode compaction density; if it is lower than 1:9, it will cause a reduction in rate performance. Therefore, by keeping the weight ratio of the first positive electrode film to the second positive electrode film within the range of 1:9 to 9:1, both compaction density and rate performance can be balanced.

[0018] In some embodiments, the thickness of the first positive electrode film is 100-200 μm; and / or the thickness of the second positive electrode film is 100-200 μm.

[0019] In some embodiments, the ratio of the thickness of the first positive electrode film to the thickness of the second positive electrode film is 0.5 to 2. If the ratio exceeds 2, the electrode compaction density will be low, resulting in low energy density. If it is below 0.5, the rate performance will decrease. Therefore, by keeping the ratio of the thickness of the first positive electrode film to the thickness of the second positive electrode film within the range of 0.5 to 2, both compaction density and rate performance can be balanced.

[0020] A second aspect of this application is to provide a secondary battery comprising the electrode plates described in the first aspect of this application.

[0021] A third aspect of this application is to provide a battery module comprising a secondary battery as described in the second aspect of this application.

[0022] A fourth aspect of this application is to provide a battery pack that includes the battery module described in the third aspect of this application.

[0023] The fifth aspect of this application is to provide an electrical device comprising at least one of the secondary battery described in the second aspect of this application, the battery module described in the third aspect of this application, and the battery pack described in the fourth aspect of this application.

[0024] The positive electrode sheet according to this application can help reduce Li... + The diffusion pathway in the active material improves the kinetic performance of the secondary battery; it increases the BET of the active material, thereby increasing the reaction area of ​​the active material; and it can also increase the compaction density of the positive electrode sheet, effectively improving the energy density of the cell. Attached Figure Description

[0025] Figure 1a This is a schematic diagram of the structure of the positive electrode sheet according to one embodiment of this application; Figure 1b yes Figure 1a A magnified view of the hollow particulate material contained in the first positive electrode film layer.

[0026] Figure 2a This is a SEM image of the positive electrode sheet according to another embodiment of this application; Figure 2b yes Figure 2a A magnified view of the hollow particulate material contained in the first positive electrode film layer.

[0027] Figure 3 This is a SEM image of the positive electrode sheet of Comparative Example 1 of this application.

[0028] Figure 4 This is a SEM image of the positive electrode of Comparative Example 2 of this application.

[0029] Figure 5 This is a SEM image of the positive electrode of Comparative Example 3 of this application.

[0030] Figure 6 This is a schematic diagram of a secondary battery according to one embodiment of this application.

[0031] Figure 7 yes Figure 6 The diagram shown is an exploded view of a secondary battery according to one embodiment of this application.

[0032] Figure 8 This is a schematic diagram of a battery module according to one embodiment of this application.

[0033] Figure 9 This is a schematic diagram of a battery pack according to one embodiment of this application.

[0034] Figure 10 yes Figure 9 The diagram shown is an exploded view of a battery pack according to one embodiment of this application.

[0035] Figure 11 This is a schematic diagram of an electrical device that uses a secondary battery as a power source according to one embodiment of this application.

[0036] Explanation of reference numerals in the attached figures:

[0037] 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Secondary battery; 51 Casing; 52 Electrode assembly; 53 Top cover assembly Detailed Implementation

[0038] The following detailed description, with appropriate reference to the accompanying drawings, specifically discloses embodiments of the positive electrode, secondary battery, battery module, battery pack, and electrical device of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0039] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60–120 and 80–110 are listed for a specific parameter, it is also expected that ranges of 60–110 and 80–120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1–3, 1–4, 1–5, 2–3, 2–4, and 2–5. In this application, unless otherwise stated, the numerical range "a–b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0~5" indicates that all real numbers between "0~5" have been listed in this article; "0~5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0040] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0041] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0042] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0043] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: 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).

[0044] Positive electrode sheet

[0045] In one embodiment of this application, a positive electrode sheet is provided. The positive electrode sheet includes: a positive current collector and a positive electrode film layer, the positive electrode film layer including a first positive electrode film layer and a second positive electrode film layer, wherein the first positive electrode film layer is disposed on at least one surface of the positive current collector and includes a first positive electrode active material, the first positive electrode active material including hollow particulate material; the second positive electrode film layer is disposed on the first positive electrode film layer and includes a second positive electrode active material, the second positive electrode active material including solid particulate material.

[0046] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, a first positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector, and then a second positive electrode film layer is disposed on the first positive electrode film layer.

[0047] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0048] In some embodiments, the first positive electrode film layer includes a first positive electrode active material, and the second positive electrode film layer includes a second positive electrode active material. The first positive electrode active material and the second positive electrode active material are two positive electrode active materials with different particle morphologies for use in the battery.

[0049] As an example, the first positive electrode active material may include at least one of the following materials: a hollow particulate material composed of a lithium phosphate with an olivine structure, a hollow particulate material composed of a lithium transition metal oxide, and a hollow particulate material composed of a modified compound of a lithium phosphate or lithium transition metal oxide with an olivine structure. The second positive electrode active material may include at least one of the following materials: a solid particulate material composed of a lithium phosphate with an olivine structure, a solid particulate material composed of a lithium transition metal oxide, and a solid particulate material composed of a modified compound of a lithium phosphate or lithium transition metal oxide with an olivine structure.

[0050] However, the first and second positive electrode active materials of this application are not limited to these materials. Other conventional materials that can be used as positive electrode active materials for batteries can also be used, as long as the first positive electrode active material has hollow particles and the second positive electrode active material has solid particles. These positive electrode active materials can be used alone or in combination of two or more. Examples of lithium transition metal oxides 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 LiNi1 / 3Co1 / 3Mn1 / 3O2 (also referred to as NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM523), LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM211), LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM811), lithium nickel cobalt aluminum oxide (such as LiNi) 0.85 Co 0.15 Al 0.05 At least one of O2 and its modified compounds. Examples of lithium phosphates with an olivine structure include, but are not limited to, lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites.

[0051] As a schematic diagram of the structure of the positive electrode sheet in one embodiment of this application, refer to... Figure 1a The positive electrode sheet has a double positive electrode film with different particle morphologies. The first positive electrode film with a hollow particle structure is disposed on the positive electrode current collector, and the second positive electrode film with a solid particle structure is disposed on the first positive electrode film.

[0052] When the above conditions are met, it is beneficial to reduce the diffusion path of Li+ in the active material and to make good use of the energy of the active material in the thick electrode, which has the advantages of high energy density and better rate performance.

[0053] like Figure 1aAs shown, in the first positive electrode active material, from the viewpoint of reducing the diffusion path of lithium ions in the first positive electrode film layer near the current collector, the number of hollow particles is more than 70% of the total number of particles in the first positive electrode active material.

[0054] In this application, the size of particles is collectively referred to as particle size. Typically, the particle size of spherical particles is expressed as diameter; the particle size of cubic particles is expressed as side length; for irregular particles, the diameter of a sphere with the same behavior can be used as the equivalent diameter of the particle. Particle size is commonly expressed using indicators such as median particle size (D50) and specific surface area (BET).

[0055] Specifically, the median particle size (D50) is the diameter (particle size value) of a single particle in a sample. If 50% of the particles are larger than this diameter and 50% are smaller than this particle size value, then this diameter is called the median particle size (D50). The median particle size (D50) is used to represent the average particle size of the particles in this application.

[0056] Furthermore, specific surface area (BET) is the sum of the surface areas of particles per unit mass. The specific surface area of ​​particles is related to particle size; the smaller the particle size, the larger the specific surface area.

[0057] Reference Figure 1b Let's take the hollow particles in the first positive electrode film layer as an example for detailed explanation: Let the radius of the hollow particle be R1 and the radius of the hollow part be R2. The hollow particle is a spherical particle, and the surface area and volume of the hollow particle are calculated based on the spherical shape.

[0058] The formula for calculating the diameter of hollow particles is D = 2R1.

[0059] The median particle size (D50) of hollow particles is the diameter (particle size value) of a selected hollow particle in the sample. If 50% of the hollow particles are larger than this diameter and 50% are smaller than this particle size value, this diameter is called the median particle size (D50) of the hollow particles. The median particle size (D50) of hollow particles is used to represent the average particle size of the hollow particles in this application. The first positive electrode active material of this application is mainly composed of hollow spherical particles. From the viewpoint of reducing the diffusion path of lithium ions in the first positive electrode film layer near the current collector, the volume median particle size of the hollow particles is 1–15 μm, preferably 3–9 μm.

[0060] like Figure 1b As shown, the ratio of the hollow diameter of the hollow particle to the median particle size of the hollow particle is calculated by the formula R2 / R1. From the perspective of both reducing the diffusion path of lithium ions in the first positive electrode film layer near the current collector and ensuring the reaction area of ​​the reactive material, this ratio is 0.1 to 0.5.

[0061] In addition, the second positive electrode active material of this application is mainly composed of solid spherical particles. From the viewpoint of increasing the compaction density of the electrode and increasing the cell capacity, the median particle size of the solid particles is 1 to 15 μm, preferably 3 to 9 μm.

[0062] Furthermore, from the viewpoint of balancing lithium-ion diffusion paths, cell capacity, and compaction density, the ratio of the median volumetric diameter of the hollow particles to the median volumetric diameter of the solid particles is 0.5 to 2. Moreover, from the viewpoint of improving the rate performance of the cell, increasing the compaction density, and improving the energy density of the cell, it is preferable that the median volumetric diameter of the hollow particles is the same as that of the solid particles, that is, the ratio of the median volumetric diameters is 1.

[0063] From the perspective of increasing the reaction area of ​​the active material, the BET of the hollow particle material of the first positive electrode active material in this application is 1-3m. 2 / g; the BET of the solid granular material of the second positive electrode active material is 0.1~1m. 2 / g.

[0064] Furthermore, the first positive electrode film layer and the second positive electrode film layer of this application are simultaneously coated using a coating device, and the weight ratio of the first positive electrode film layer to the second positive electrode film layer is 1:9 to 9:1. Moreover, considering both compaction density and energy density, it is preferable that the weight of the first positive electrode film layer and the weight of the second positive electrode film layer are the same, that is, the weight ratio of the two is 1:1.

[0065] From the perspective of balancing energy density and kinetics, the thickness of the first positive electrode film is 100–200 μm; and / or the thickness of the second positive electrode film is 100–200 μm. The thickness ratio of the first positive electrode film to the second positive electrode film is 0.5–2. Furthermore, based on test results, it is preferable that the thickness of the first positive electrode film and the thickness of the second positive electrode film are the same, that is, it is preferable that the thickness ratio of the two is 1.

[0066] In some embodiments, the first positive electrode film layer and the second positive electrode film layer may optionally include an adhesive. As an example, the adhesive may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0067] In some embodiments, the first positive electrode film layer and the second positive electrode film layer may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0068] In some embodiments, the positive electrode sheet can be prepared by dispersing the components used to prepare the positive electrode sheet, such as the first positive electrode active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a first positive electrode slurry; and dispersing the second positive electrode slurry, conductive agent, binder and any other components in a solvent (e.g., N-methylpyrrolidone) to form a second positive electrode slurry; coating the first positive electrode slurry onto the positive electrode current collector, and simultaneously coating the second positive electrode slurry onto the first positive electrode slurry, with the two coating processes performed and completed simultaneously; after drying, cold pressing, slitting, die cutting and other processes, the positive electrode sheet can be obtained.

[0069] Secondary batteries

[0070] In one embodiment of this application, a secondary battery is provided.

[0071] The secondary battery of this application includes: a positive electrode as described in the first aspect of this application, a negative electrode, an electrolyte, and a separator. During the charging and discharging process, active ions repeatedly insert and extract between the positive and negative electrode. The electrolyte acts as a conductor of ions between the positive and negative electrode. The separator is disposed between the positive and negative electrode, primarily to prevent short circuits between the positive and negative electrodes, while also allowing ions to pass through. The negative electrode, electrolyte, and separator are described in detail below.

[0072] [Negative electrode plate]

[0073] The negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector, wherein the negative electrode film layer includes the negative electrode active material described above in this application.

[0074] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0075] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0076] In some embodiments, the negative electrode active material may be a negative electrode active material known in the art for use in batteries. As an example, 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, etc. 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, this 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.

[0077] In some embodiments, the negative electrode film layer may optionally include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0078] In some embodiments, the negative electrode film may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0079] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0080] In some embodiments, the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto a negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0081] [Electrolytes]

[0082] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific restrictions on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel, or entirely solid.

[0083] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0084] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0085] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0086] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0087] [Isolation membrane]

[0088] In some embodiments, the secondary battery also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0089] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0090] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0091] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0092] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0093] This application does not impose any particular limitation on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 6 This is an example of a square-structured secondary battery 5.

[0094] In some implementations, refer to Figure 7 The outer packaging may include a housing 51 and a cover 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 can be placed over the opening to close the receiving cavity. A positive electrode, a negative electrode, and a separator can be formed into an electrode assembly 52 using a winding or stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The secondary battery 5 may contain one or more electrode assemblies 52, which can be selected by those skilled in the art according to specific practical needs.

[0095] Battery Module

[0096] In some implementations, the secondary batteries can be assembled into a battery module, and the number of secondary batteries contained in the battery module can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery module.

[0097] Figure 8 This is battery module 4, used as an example. (See reference...) Figure 8 In battery module 4, multiple secondary batteries 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple secondary batteries 5 can be fixed in place using fasteners.

[0098] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of secondary batteries 5 are received.

[0099] Battery pack

[0100] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0101] Figure 9 and Figure 10 This is battery pack 1 as an example. (See reference...) Figure 9 and Figure 10The battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3, with the upper body 2 covering the lower body 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0102] Electrical appliances

[0103] In addition, this application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack provided in this application. The secondary battery, battery module, or battery pack can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0104] As the electrical device, a secondary battery, battery module, or battery pack can be selected according to its usage requirements.

[0105] Figure 11 This is an example of an electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the secondary battery for this device, a battery pack or battery module can be used.

[0106] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a rechargeable battery as their power source.

[0107] Example

[0108] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0109] <Example 1>

[0110] 1) Preparation of the first positive electrode slurry

[0111] The first positive electrode active material (D50: 8μm), conductive agent SP, and binder polyvinylidene fluoride (PVDF) shown in Table 1 were thoroughly mixed in an N-methylpyrrolidone (NMP) solvent system at a weight ratio of 97:2:1. The viscosity was then tested. The viscosity was 3000-10000 mPa·s at 12 rpm, which is a suitable viscosity range for coating. The first positive electrode slurry was thus prepared.

[0112] 2) Preparation of the second positive electrode slurry

[0113] The second active material (D50: 8μm), conductive agent SP, and polyvinylidene fluoride (PVDF) as a binder were mixed thoroughly in an N-methylpyrrolidone (NMP) solvent system at a weight ratio of 97:2:1. The viscosity was then tested. The viscosity was 3000-10000 mPa·s at 12 rpm, which is a suitable viscosity range for coating. The second positive electrode slurry was thus prepared.

[0114] 3) Preparation of positive electrode sheet

[0115] A first positive electrode slurry is coated onto one surface of an aluminum foil serving as the positive electrode current collector using a dual-cavity coating apparatus. Simultaneously, a second positive electrode slurry is coated onto the first positive electrode slurry. The two coating processes are performed and completed concurrently, thereby forming a first positive electrode film and a second positive electrode film. The weight of the first positive electrode film is 125 g / cm³. 2 The weight of the second positive electrode film is 125 g / cm³. 2 After coating, the solvent NMP is dried in the coating machine oven, and then the positive electrode sheet is prepared by cold pressing, slitting and die cutting processes.

[0116] 4) Preparation of negative electrode sheet

[0117] A mixture of 95 wt% negative electrode active material (artificial graphite), 1.0 wt% conductive agent (conductive carbon black), 2.0 wt% binder (styrene-butadiene rubber (SBR)), and 2.0 wt% thickener (sodium carboxymethyl cellulose (CMC)) was prepared by mixing with deionized water and stirring. The mixture was then coated onto copper foil on both sides. After coating, the foil was dried, cold-pressed, slit, and sheeted to obtain the negative electrode sheet.

[0118] 5) Battery manufacturing

[0119] The prepared positive electrode, separator, and negative electrode are stacked in sequence, with the separator placed between the positive and negative electrode to provide isolation. At the same time, the bare cell is wound up. Then, it is welded, packaged, and injected with electrolyte before undergoing formation, degassing, and final sealing processes to finally obtain a secondary battery.

[0120] <Examples 2-26>

[0121] In Examples 2-26, the same preparation method as in Example 1 was used, with the following changes as shown in Table 1: median volumetric particle size (D50) of the hollow particles of the first positive electrode active material, median volumetric particle size (D50) of the solid particles of the second positive electrode active material, "D50 of hollow particles / D50 of solid particles", "Number of hollow particles / Total number of particles", "Hollow diameter of hollow particles / D50 of hollow particles", "BET of the first positive electrode active material", "BET of the second positive electrode active material", "Weight ratio of the first positive electrode film to the second positive electrode film", "Thickness of the first positive electrode film and the second positive electrode film", and "Thickness ratio of the first positive electrode film to the second positive electrode film".

[0122] <Comparative Example 1>

[0123] In Comparative Example 1, the same preparation method as in Example 1 was used, except that, as shown in Table 1, only the first positive electrode active material was used to form the first positive electrode film layer, and there was no second positive electrode film layer.

[0124] <Comparative Example 2>

[0125] In Comparative Example 2, the same preparation method as in Example 1 was used, except that, as shown in Table 1, only the second positive electrode active material was used to form the second positive electrode film layer, and there was no first positive electrode film layer.

[0126] <Comparative Example 3>

[0127] In Comparative Example 3, the same preparation method as in Example 1 was used, except that the positions of the first positive electrode film layer and the second positive electrode film layer were interchanged during the preparation process. That is, the second positive electrode film layer was formed on the aluminum foil (near the bottom current collector), and the first positive electrode film layer was formed on the second positive electrode film layer (near the top separator).

[0128] The following is a detailed description of the relevant parameter testing process involved in Examples 1 to 26 and Comparative Examples 1 to 3 of this application.

[0129] I. Volume Median Particle Size (D50) Test

[0130] Equipment model: Malvern 3000 (MasterSizer 3000) laser particle size analyzer; Reference standard procedure: GB / T19077-2016 / ISO 13320:2009; Specific test procedure: Take an appropriate amount of the sample to be tested (the sample concentration should be 8-12% opacity), add 20 ml of deionized water, and simultaneously incubate for 5 minutes (53 kHz / 120 W) to ensure complete dispersion of the sample. Then, according to GB / T19077-2016 / ISO 13320:2009, the first positive electrode active material and the second positive electrode active material of Examples 1-26 and Comparative Examples 1-3 are measured. The test results are shown in Table 1.

[0131] II. Median Diameter Test

[0132] The hollow diameter of hollow particles was determined by cross-sectional electron microscopy (TEM) images. Specifically, the cross-sectional morphology of coated electrode samples was photographed, a random area was selected, and the hollow diameters of all hollow particles within the field of view were counted. The longest diameter was used as the standard. The average of all hollow particle diameters was then calculated.

[0133] III. Morphological Test

[0134] The positive electrode sheets of Examples 1-26 and Comparative Examples 1-3 were tested using a ZEISS Sigma 300 scanning electron microscope, and then the morphology of the samples was observed according to standard JY / T010-1996. The specific observation results are as follows.

[0135] like Figure 2a As shown, by observing the morphology of the positive electrode sheet of Embodiment 1 of this application, it can be confirmed that the positive electrode sheet of this application forms a double-layer film. The bottom layer, near the current collector, forms a first positive electrode film layer, mainly composed of hollow particles; above the first positive electrode film layer, near the separator, forms a second positive electrode film layer, mainly composed of solid particles. Figure 2b As shown, the hollow particles contained in the first positive electrode film are nearly spherical in shape, and the BET of the first positive electrode film material is increased through the hollow structure.

[0136] The positive electrode sheets of Examples 2 to 26 of this application were observed to have the same morphology in the same way. It was observed that the positive electrode sheets of this application have a double film layer. The bottom layer is a first positive electrode film layer near the current collector, which is mainly composed of hollow particles. The second positive electrode film layer is formed above the first positive electrode film layer near the separator, which is mainly composed of solid particles.

[0137] like Figure 3As shown, by observing the morphology of the positive electrode sheet of Comparative Example 1 of this application, it can be confirmed that the positive electrode sheet of Comparative Example 1 only has a single layer of film, that is, only the bottom layer near the current collector forms a first positive electrode film mainly composed of hollow particles, and there is no second positive electrode film composed of solid particles.

[0138] like Figure 4 As shown, by observing the morphology of the positive electrode sheet of Comparative Example 2 of this application, it can be confirmed that the positive electrode sheet of Comparative Example 2 only has a single layer of film, that is, only the top layer near the separator forms a second positive electrode film mainly composed of solid particles, and there is no first positive electrode film composed of hollow particles.

[0139] like Figure 5 As shown, by observing the morphology of the positive electrode sheet of Comparative Example 3 of this application, it can be confirmed that although the positive electrode sheet of Comparative Example 3 also forms a double-layer film, it forms a second positive electrode film mainly composed of solid particles near the current collector at the bottom layer, and a first positive electrode film mainly composed of hollow particles is formed above the second positive electrode film near the separator. That is, the position of the double-layer film is completely opposite to that of this application.

[0140] IV. Specific Surface Area (BET) Test

[0141] The first and second positive electrode active materials of Examples 1-26 and Comparative Examples 1-3 were tested using a Mach-McGemini VII 2390 fully automated surface area and porosity analyzer. Approximately 7g of sample was placed in a 9cc long tube with a bulb, degassed at 150°C for 15min, and then placed in the main unit for BET data testing. The results are shown in Table 1.

[0142] V. Battery Performance Testing

[0143] The positive electrode sheets obtained in Examples 1-26 and Comparative Examples 1-3 were subjected to the following battery performance tests. The test results are shown in Table 2.

[0144] (1) Discharge rate test

[0145] The battery cell was left to stand at 25℃ for 30 minutes, then discharged at a constant current of 0.33C to 3.0V. After standing at 25℃ for 1 hour, it was charged at a constant current of 0.33C to 4.3V, then charged at a constant voltage with a cutoff current of 0.05C. After standing at 25℃ for 30 minutes, it was discharged at a constant current of 0.33C to 3.0V, yielding the initial capacity C0. After standing at 25℃ for 1 hour, it was charged at a constant current of 0.33C to 4.3V, then charged at a constant voltage with a cutoff current of 0.05C. After standing at 25℃ for 30 minutes, it was discharged at 1C to 3.0V, yielding the capacity C1 at 1C. After standing at 25℃ for 1 hour, it was charged at a constant current of 0.33C to 4.3V, then charged at a constant voltage with a cutoff current of 0.05C. After standing at 25℃ for 30 minutes, it was discharged at 2C to 3.0V, yielding the capacity C2 at 2C. The capacity retention rate at 1C is C1 / C0, and the capacity retention rate at 2C is C2 / C0.

[0146] (2) Capacity test

[0147] The cell was left to stand at 25℃ for 30 minutes, then discharged at 0.33C to 3.0V. After standing at 25℃ for 30 minutes, it was charged at a constant current of 0.33C to 4.3V, then charged at a constant voltage with a cutoff current of 0.05C. After standing at 25℃ for 30 minutes, it was discharged at 0.33C to 3.0V, thus obtaining the cell capacity C.

[0148] (3) DC Impedance (DCR) Test

[0149] First, the battery cell is calibrated according to the capacity test above (2) to obtain the capacity C0. The battery cell is left to stand for 30 minutes at 25℃, charged to 4.3V with a constant current of 0.33C0, charged with a constant voltage, and cut off with a cutoff current of 0.05C0. It is left to stand for 5 minutes at 25℃, and discharged to 0.5C0 with a constant current of 0.33C0. At this time, it is 50% SOC. Then it is discharged at a rate of 2C0 for 30 seconds. The voltage before 2C0 discharge is V1, and the voltage after 30 seconds of discharge is V2. The formula for calculating DCR is as follows:

[0150] R = (V1 - V2) / 2C0

[0151] Table 1

[0152]

[0153] Table 2

[0154]

[0155] As can be seen from Tables 1 and 2:

[0156] Compared to Comparative Examples 1-3, the positive electrode sheets in Examples 1-26, which have a double-layer electrode film consisting of a first positive electrode film layer made of hollow material and a second positive electrode film layer made of solid material as described in this application, exhibit better overall rate performance, lower DCR, and higher battery capacity. Therefore, lithium-ion batteries made using the positive electrode sheets of this invention possess better kinetic performance, providing a solution for the application of thick electrode sheets in batteries.

[0157] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A positive electrode plate, wherein, The positive electrode sheet includes: a positive current collector and a positive electrode film layer, wherein the positive electrode film layer includes a first positive electrode film layer and a second positive electrode film layer, wherein... The first positive electrode film layer is disposed on at least one surface of the positive electrode current collector and includes a first positive electrode active material, wherein the first positive electrode active material includes hollow particulate material. The second positive electrode film layer is disposed on the first positive electrode film layer and includes a second positive electrode active material, wherein the second positive electrode active material includes solid particulate material. In the first positive electrode active material, the number of hollow particles accounts for 70%-80% of the total number of particles in the first positive electrode active material. The thickness of the first positive electrode film is 100~200μm. The thickness of the second positive electrode film is 100~200μm.

2. The positive electrode sheet according to claim 1, wherein, The median volumetric particle size of the hollow particles is 1~15μm; and / or, The median volumetric particle size of the solid particles is 1~15μm.

3. The positive electrode sheet according to claim 1 or 2, wherein, The median volumetric particle size of the hollow particles is 3~9 μm; and / or, The median particle size of the solid particles is 3~9μm.

4. The positive electrode sheet according to claim 1 or 2, wherein, The ratio of the median volume diameter of the hollow particles to the median volume diameter of the solid particles is 0.5 to 2.

5. The positive electrode sheet according to claim 1 or 2, wherein, The ratio of the hollow diameter of the hollow particle to the median volume diameter of the hollow particle is 0.1 to 0.

5.

6. The positive electrode sheet according to claim 1 or 2, wherein, The BET of the hollow granular material is 1~3m. 2 / g, the BET of the solid granular material is 0.1~1m 2 / g.

7. The positive electrode sheet according to claim 1 or 2, wherein, The weight ratio of the first positive electrode film to the second positive electrode film is 1:9 to 9:

1.

8. A secondary battery, wherein, The secondary battery includes the positive electrode sheet according to any one of claims 1 to 7.

9. A battery module, wherein, The battery module includes the secondary battery as described in claim 8.

10. A battery pack, wherein, The battery pack includes the battery module as described in claim 9.

11. An electrical appliance, wherein, The electrical device includes at least one selected from the secondary battery of claim 8, the battery module of claim 9, and the battery pack of claim 10.

Images