Battery monomer and preparation method thereof, battery device and power utilization device

Abstract

The invention relates to a battery monomer and a preparation method thereof, a battery device and a power utilization device. Each single battery comprises a positive pole piece and a negative pole piece, the positive pole piece comprises a positive current collector and a first positive active layer stacked on at least one surface of the positive current collector, and a second positive active layer is further stacked on the surface, deviating from the positive current collector, of the first positive active layer; the first positive electrode active layer contains a first positive electrode active material, the second positive electrode active layer contains a second positive electrode active material, the particle size DV150 of the first positive electrode active material is less than or equal to 1 [mu] m, and the particle size DV250 of the second positive electrode active material is greater than the particle size DV150 of the first positive electrode active material. According to the battery monomer, based on the combined action of the first positive active layer and the second positive active layer of the positive pole piece, the cycle life of the battery can be further prolonged on the premise that the battery has high energy density.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of batteries, and particularly relates to a battery monomer, a preparation method thereof, a battery device and a power utilization device. BACKGROUND

[0002] With the vigorous development of new energy vehicles, the battery driving system becomes an important factor affecting the performance and cost of new energy vehicles, and the battery, due to the characteristics of high energy density, low memory effect and high working voltage, becomes the preferred solution of the power supply in the battery driving system.

[0003] For the battery, with the increase of the compaction density, many processing problems will be caused, for example, the increase of the compaction of the positive active material in the positive electrode sheet, which causes the positive active material particles to be easily broken, the brittleness of the electrode sheet to be deteriorated, and even the problem of broken strip. SUMMARY

[0004] The application aims to provide a battery monomer, a preparation method thereof, a battery device and a power utilization device, and aims to solve the technical problem of how to improve the processing performance of the positive electrode sheet of the battery.

[0005] To achieve the above application purposes, the technical scheme adopted by the application is as follows:

[0006] In a first aspect, the application provides a battery monomer, comprising a positive electrode sheet and a negative electrode sheet, the positive electrode sheet comprising a positive current collector and a first positive active layer stacked on at least one surface of the positive current collector, and a second positive active layer stacked on the surface of the first positive active layer away from the positive current collector; wherein the first positive active layer contains a first positive active material, the second positive active layer contains a second positive active material, the particle size D V1 50 of the first positive active material is less than or equal to 1 μm, and the particle size D V2 50 of the second positive active material is greater than the particle size D V1 50 of the first positive active material.

[0007] By stacking the first positive active layer and the second positive active layer on the surface of the positive current collector in the battery monomer, the first positive active layer close to the positive current collector contains the first positive active material with the particle size D V1 50 less than or equal to 1 μm, and the second positive active layer away from the positive current collector contains the second positive active material with the particle size D V2 50 greater than the particle size D V1 50 of the first positive active material. The first positive active material with the small particle size can act as a buffer, which can reduce the damage of the second positive active material with the large particle size in the second positive active layer to the positive current collector during sheet pressing, thereby improving the processing performance well.

[0008] In some embodiments, the first positive electrode active material comprises monocrystalline particles with a particle size D V1 50 is 200-500 nm.

[0009] The first positive electrode active layer on the side close to the positive electrode current collector uses the monocrystalline particles with the above particle size as a buffer material, which not only has good material stability, but also can well reduce the damage of the second positive electrode active material with large particle size to the positive electrode current collector, thereby improving the strength of the positive electrode sheet.

[0010] In some embodiments, the second positive electrode active material comprises monocrystalline particles with a particle size D V2 50 is 2-10 μm.

[0011] The second positive electrode active layer on the side away from the positive electrode current collector uses the second positive electrode active material with the above particle size, which can make the battery have good charge and discharge performance.

[0012] In some embodiments, the second positive electrode active material comprises monocrystalline particles with a particle size D V2 50 is 2-4 μm and polycrystalline particles with a particle size D V2 50 is 8-10 μm.

[0013] The monocrystalline particles and polycrystalline particles with the above particle sizes used in the second positive electrode active layer can make the monocrystalline particles dispersed between the gaps of the large-particle-size polycrystalline particles, and the particles are not easy to break, while improving the density of the second positive electrode active layer, thereby improving the energy density of the battery.

[0014] In some embodiments, the mass ratio of the monocrystalline particles to the polycrystalline particles in the second positive electrode active material is 5:5-2:8.

[0015] The second positive electrode active layer contains the monocrystalline particles and polycrystalline particles with the above ratio, which not only has good film density, but also makes the battery capacity better.

[0016] In some embodiments, the thickness of the first positive electrode active layer is 2-8 μm;

[0017] And / or, the thickness of the second positive electrode active layer is 50-200 μm.

[0018] The first positive electrode active layer with the above thickness and the second positive electrode active layer with the above thickness can make the battery monomer have better energy density and cycle life.

[0019] In some embodiments, the first positive electrode active layer further contains a first conductive agent, and the first conductive agent comprises first carbon nanotubes;

[0020] And / or, the second positive electrode active layer further contains a second conductive agent, and the second conductive agent comprises second carbon nanotubes.

[0021] Adding a first carbon nanotube to the first positive electrode active layer and / or adding a second conductive agent, including a second carbon nanotube, to the second positive electrode active layer can further improve the conductivity of the positive electrode sheet.

[0022] In some embodiments, the first carbon nanotube includes at least one of single-walled carbon nanotubes and oligo-walled carbon nanotubes, and the diameter of the first carbon nanotube is less than or equal to 20 nm and the aspect ratio is greater than 50.

[0023] And / or, the first carbon nanotube accounts for 1 to 20% of the mass percentage of the first positive electrode active layer.

[0024] The aforementioned sizes and types of first-generation carbon nanotubes can give the positive electrode excellent conductivity, thereby improving the battery's fast-charging performance. The aforementioned proportions of first-generation carbon nanotubes ensure stable conductivity of the positive electrode while having minimal impact on its mechanical properties.

[0025] In some embodiments, the second carbon nanotube includes at least one of single-walled carbon nanotubes and oligo-walled carbon nanotubes, and the second carbon nanotube has a diameter of less than or equal to 15 nm and an aspect ratio greater than 100.

[0026] And / or, the second carbon nanotube accounts for 0.1% to 3% of the mass percentage of the second positive electrode active layer.

[0027] The aforementioned sizes and types of second carbon nanotubes can give the positive electrode excellent conductivity, improving the battery's fast-charging performance. The aforementioned proportions of second carbon nanotubes provide stable conductivity to the positive electrode while having minimal impact on its mechanical properties.

[0028] In some embodiments, the first positive electrode active material includes at least one of lithium phosphate and lithium transition metal oxide;

[0029] And / or, the second positive electrode active material includes at least one of lithium phosphate and lithium transition metal oxide.

[0030] The battery cell formed by the above-mentioned positive electrode active material is a lithium-ion battery cell, which has the characteristics of high energy density and high cycle life.

[0031] In some embodiments, the first positive electrode active material includes a lithium transition metal oxide and a nickel-cobalt-manganese ternary positive electrode material with a manganese content of at least 80%.

[0032] And / or, the second positive electrode active material includes lithium transition metal oxide and includes a nickel-cobalt-manganese ternary positive electrode material with a manganese content of at least 80%.

[0033] The high-nickel-content nickel-cobalt-manganese ternary positive electrode material is used in the first positive electrode active layer and the second positive electrode active layer respectively, so that the battery monomer has higher energy density.

[0034] In a second aspect, the embodiments of the present application provide a preparation method of a battery monomer, comprising:

[0035] The first positive electrode slurry containing the first positive electrode active material and the second positive electrode slurry containing the second positive electrode active material are prepared; wherein the particle size D V1 50 of the first positive electrode active material is less than or equal to 1 μm, and the particle size D V2 50 of the second positive electrode active material is greater than the particle size D V1 50 of the first positive electrode active material.

[0036] The first positive electrode active layer and the second positive electrode active layer are formed in sequence on at least one surface of the positive electrode current collector in a direction away from the surface of the positive electrode current collector by using the first positive electrode slurry and the second positive electrode slurry, to obtain a positive electrode sheet.

[0037] The positive electrode sheet and the negative electrode sheet are assembled to obtain a battery monomer.

[0038] During preparation of the positive electrode sheet, the first positive electrode active layer and the second positive electrode active layer are formed in sequence on the surface of the positive electrode current collector, so that the first positive electrode active layer contains the first positive electrode active material with a particle size D V1 50 less than or equal to 1 μm, and the second positive electrode active layer contains the second positive electrode active material with a particle size D V2 50 greater than the particle size D V1 50 of the first positive electrode active material. The first positive electrode active material with a small particle size can act as a buffer to reduce damage of the second positive electrode active material with a large particle size in the second positive electrode active layer to the positive electrode current collector, and at the same time, increase the overall strength of the positive electrode sheet, thereby reducing the risk of breakage of the positive electrode sheet. Therefore, the obtained positive electrode sheet and the negative electrode sheet are assembled into a battery monomer, so that the obtained battery monomer can further improve the battery cycle life on the premise of having high energy density.

[0039] In a third aspect, the embodiments of the present application provide a battery device, comprising the battery monomer provided in the first aspect of the embodiments of the present application or the battery monomer prepared by the preparation method provided in the second aspect of the embodiments of the present application.

[0040] By using the battery monomer provided in the embodiments of the present application, such a battery device has good cycle life on the premise of high energy density, and thus can better perform charging and discharging.

[0041] In a fourth aspect, an embodiment of the present application provides a power consuming device comprising the battery monomer provided in the first aspect of the present application or the battery device provided in the second aspect of the present application, and the battery monomer or the battery device is used for storing or providing electric energy.

[0042] The power consuming device has a long cycle life and can better consume electric energy by using the battery monomer or the battery device provided in the embodiments of the present application. BRIEF DESCRIPTION OF DRAWINGS

[0043] Various other advantages and benefits will become apparent to those of ordinary skill in the art upon reading the following detailed description of the preferred embodiments. The accompanying drawings are included to provide a better understanding of the preferred embodiments, and are not to be considered limitations of the present application. Moreover, in the drawings, like reference numerals refer to similar components throughout the several views. In the drawings:

[0044] Figure 1 A structural schematic diagram of an embodiment of the battery monomer of the present application;

[0045] Figure 2 A structural schematic diagram of an embodiment of the battery monomer of the present application; Figure 1 A structural schematic diagram of an embodiment of the battery monomer of the present application;

[0046] Figure 3 A structural schematic diagram of an embodiment of the battery module of the present application;

[0047] Figure 4 A structural schematic diagram of an embodiment of the battery pack of the present application;

[0048] Figure 5 A structural schematic diagram of an embodiment of the battery pack of the present application; Figure 4 A structural schematic diagram of an embodiment of the battery pack of the present application;

[0049] Figure 6 A structural schematic diagram of an embodiment of the power consuming device comprising the secondary battery as a power source of the present application;

[0050] Figure 7 A post scanning electron microscope image of the first positive electrode active layer prepared in the positive electrode sheet of the battery monomer of the present application;

[0051] Figure 8 A post scanning electron microscope image of the first positive electrode active layer and the second positive electrode active layer prepared in the positive electrode sheet of the battery monomer of the present application;

[0052] Figure 9 A scanning electron microscope image of the positive electrode sheet prepared in the battery monomer of the comparative example of the present application.

[0053] Legend of reference numerals:

[0054] 10 - battery cell; 11 - housing; 12 - top cover assembly; 13 - electrode assembly; 20 - battery module; 30 - battery pack; 31 - upper case; 32 - lower case. DETAILED DESCRIPTION

[0055] The embodiments of the present application will be described in detail with reference to the drawings. The following embodiments are only used to more clearly illustrate the technical scheme of the present application, and therefore only serve as examples, but cannot be used to limit the protection scope of the present application.

[0056] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present application; the present specification and claims as well as the above description of the drawings may use terms such as "include" and "have" and their derivatives, which are intended to cover inclusive rather than exclusive inclusion.

[0057] In the description of the embodiments of the present application, the technical terms "first", "second", etc. are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features. In the description of the embodiments of the present application, the meaning of "a plurality of" is two or more, unless otherwise explicitly and specifically limited.

[0058] Reference herein to "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the application. The appearance of the phrase in various places in the specification does not necessarily all refer to the same embodiment, nor is it necessarily independent or alternative embodiments to each other. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0059] In the description of the embodiments of the present application, the term "and / or" is only a description of the association relationship of the associated objects, which means that there can be three relationships, for example, A and / or B, which can represent the three cases of A alone, A and B together, and B alone. In addition, the character " / " in this paper generally represents that the front and rear associated objects are a "or" relationship.

[0060] In the description of the embodiments of the present application, the term "a plurality of" refers to two or more (including two), and similarly, "a plurality of groups" refers to two or more groups (including two groups), and "a plurality of pieces" refers to two or more pieces (including two pieces). "At least one" refers to one or more (including one, two, three, etc.).

[0061] In the description of the embodiments of the present application, the orientations or positional relationships indicated by the technical terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like are based on the orientations or positional relationships shown in the drawings, and are only for the convenience of describing the embodiments of the present application and simplifying the description, and therefore cannot be understood as indicating or implying that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the embodiments of the present application.

[0062] In the description of the embodiments of the present application, unless otherwise explicitly specified and limited, the technical terms "mounting", "connecting", "connecting", "fixing" and the like should be understood in a broad sense, for example, can be fixedly connected, or can be detachably connected, or can be integrated; can be mechanically connected, or can be electrically connected; can be directly connected, or can be indirectly connected through an intermediate medium; can be the internal communication of two elements or the interaction relationship between two elements. For those skilled in the art, the specific meanings of the above terms in the embodiments of the present application can be understood according to the specific circumstances.

[0063] With the increasing reduction of traditional energy resources, the development of new energy storage devices is increasingly valued. Among them, the secondary battery can not only be applied to the energy storage power system of hydraulic, thermal, wind and solar power stations, but also be widely used in electric bicycles, electric motorcycles, electric vehicles and other electric vehicles in many fields. With the continuous expansion of the application field of secondary batteries as power batteries, the market demand is also increasing, and the performance requirements of the battery are also increasing.

[0064] For example, lithium ion batteries (LIBs). Increasing the compaction density of the positive active material is an important way to improve the volume energy density of lithium ion batteries. However, with the increase of the compaction density, the positive active material particles are easily broken, and the brittleness of the positive plate is easily deteriorated. For example, when the positive plate is cold-pressed, the increase of the pressure makes the positive active material particles act on the current collector substrate and spread, and larger positive active material particles are easily pressed into the current collector substrate, thereby damaging the current collector, which easily reduces the strength of the current collector and increases the risk of plate breakage.

[0065] Based on this, the embodiments of the present application develop a battery monomer, which uses different particle sizes of first positive active material and second positive active material in the positive plate, which can further improve the processability of the positive plate under the premise of high energy density. The specific technical solutions are as follows.

[0066] Battery monomer and preparation method thereof

[0067] In a first aspect, the embodiments of the present application provide a battery cell, comprising a positive electrode sheet and a negative electrode sheet; the positive electrode sheet comprises a positive electrode current collector and a first positive electrode active layer stacked on at least one surface of the positive electrode current collector, that is, the positive electrode current collector is provided with the first positive electrode active layer on one surface or two surfaces along the thickness direction. The surface of the first positive electrode active layer away from the positive electrode current collector is further provided with a second positive electrode active layer.

[0068] The first positive electrode active layer contains a first positive electrode active material, and the second positive electrode active layer contains a second positive electrode active material. The particle size of the first positive electrode active material is D V1 50 is less than or equal to 1 μm, and the particle size of the second positive electrode active material is D V2 50 is greater than the particle size D V1 50.

[0069] The positive electrode active layer refers to a film layer containing a positive electrode active material on the surface of the positive electrode current collector. The positive electrode active material has active metal ions, and the battery can be charged and discharged through the migration of active metal ions; during the charging and discharging of the battery, the positive electrode active material can realize the embedding and extraction of active metal ions. By stacking the first positive electrode active layer and the second positive electrode active layer on the surface of the positive electrode current collector in the battery cell, the first positive electrode active layer close to the positive electrode current collector contains a first positive electrode active material with a particle size D V1 50 is less than or equal to 1 μm, and the second positive electrode active layer away from the positive electrode current collector contains a second positive electrode active material with a particle size D V2 50 is greater than the particle size D V1 50.

[0070] The above-mentioned first positive electrode active material with small particle size can act as a buffer, and can reduce the damage of the second positive electrode active material with large particle size in the second positive electrode active layer to the positive electrode current collector during sheet pressing, thereby improving the processability and reducing the risk of positive electrode sheet breakage.

[0071] It should be noted that the embodiments of the present application can improve the processability of the positive electrode sheet, thereby improving the overall strength of the positive electrode sheet. The flexibility of the sheet mainly comes from the flexibility of the current collector substrate, and in order to pursue higher volumetric energy density, the sheet compression is getting higher and higher, but higher compression means that a larger pressure roller is needed, so the extrusion of the positive electrode active material and the current collector becomes more intense, which is more likely to cause the current collector to be damaged. Therefore, the embodiments of the present application can reduce the risk of extension and damage of the positive electrode current collector substrate by matching the first positive electrode active material and the second positive electrode active material, increase the strength of the sheet, and improve the cycle life of the battery without reducing the energy density of the entire battery cell.

[0072] The size of the particulate material is referred to as the particle size, the percentage of particles in different particle size intervals in the total amount is referred to as the particle size distribution, and the volume distribution particle size is the particle size calculated in units of particle volume. For example, Dv50 represents the average particle size corresponding to the cumulative volume particle size distribution percentage of 50% in a sample, and in specific embodiments, a particle size tester can be used to test the average particle size. Correspondingly, the volume distribution particle size of the first positive electrode active material is represented by D V1 50, and the volume distribution particle size of the second positive electrode active material is represented by D V2 50.

[0073] For particle size testing of the positive electrode active material of the embodiments of the present application, GB / T 19077-2016 "Particle Size Distribution-Laser Diffraction Method" can be used, and a Mastersizer 2000E laser particle size analyzer from Malvern Instruments Ltd., UK can be used for determination.

[0074] It should be noted that the single crystal and the polycrystal mentioned in the embodiments of the present application are both crystalline substances.

[0075] A single crystal (monocrystalline) refers to ions arranged in order inside a substance, which maintains the same orientation from one end to the other end (for example, a single crystal of a layered oxide), and the single crystal structure exhibits periodicity (the smallest structural unit, unit cell), and has a continuous and regular ordered arrangement in space. Specifically, "single crystal" refers to a primary particle or a dispersed primary particle constituting a non-spherical agglomerate, in which more than 70% of the primary particles are greater than or equal to 1 μm and less than 5 μm, in a unit area (for example, 50 μm x 50 μm) under a 3000-fold field of view of a material scanning electron microscope, with the longest side of the primary particle as the particle size measurement reference.

[0076] A polycrystal (polycrystalline) is a substance composed of many small crystal grains (such as single crystals, quasi-crystals), each crystal grain has its own unique crystal orientation, and these crystal grains are randomly oriented on a macroscopic scale, but the orientation inside each crystal grain is consistent; a polycrystal is generally a secondary particle formed by aggregation of multiple primary particles into a spherical particle state. Specifically, "polycrystal" refers to a primary particle constituting a spherical agglomerate, in which more than 70% of the primary particles are greater than 100 nm and less than 1 μm, in a unit area (for example, 50 μm x 50 μm) under a 3000-fold field of view of a material scanning electron microscope, with the longest side of the primary particle as the particle size measurement reference.

[0077] The above-mentioned primary particle refers to an original particle formed by initial growth of a crystal, and the secondary particle refers to a particle formed by aggregation of primary particles into a spherical particle state.

[0078] In some embodiments, the first positive electrode active material includes a particle size DV1 50 refers to single-crystal particles with a diameter of 200–500 nm. For example, D… V1 50 refers to particles of 200nm, 250nm, 300nm, 350nm, 400nm, and 500nm. Single-crystal particles within this size range are smaller than the particle size of the second positive electrode active material. Using these smaller single-crystal particles as a buffer material in the first positive electrode active layer near the positive electrode current collector not only ensures good material stability but also effectively reduces damage to the positive electrode current collector from the larger-diameter second positive electrode active material, thereby improving the strength of the positive electrode sheet.

[0079] In some embodiments, the first positive electrode active material comprises at least one of lithium phosphate and lithium transition metal oxide. For example, it may be a D-type lithium phosphate and lithium transition metal oxide. V1 50 refers to single-crystal particles with a size of 200–500 nm. A battery cell formed from this first positive electrode active material is a lithium-ion battery cell, which possesses both high energy density and long cycle life.

[0080] In some embodiments, the particle size D of the second positive electrode active material V2 50 is 2–10 μm. For example, D V2 50 refers to particles of 2μm, 3μm, 5μm, 6nm, 8μm, and 10μm. Using the above-mentioned particle sizes of the second positive electrode active material in the second positive electrode active layer on the side away from the positive electrode current collector can give the battery excellent charge and discharge performance.

[0081] In some embodiments, the second positive electrode active material includes a particle size D V2 50 consists of single crystal particles of 2–4 μm and a particle size D V2 50 consists of polycrystalline particles with a diameter of 8–10 μm. Using single-crystal and polycrystalline particles of these sizes in the second positive electrode active layer allows the single-crystal particles to be dispersed between the gaps of the large-diameter polycrystalline particles, making the particles less prone to breakage. This also improves the density of the second positive electrode active layer, thereby increasing the battery's energy density.

[0082] In some embodiments, the mass ratio of single-crystal particles to polycrystalline particles in the second positive electrode active material is 5:5 to 2:8. For example, the mass ratio of single-crystal particles to polycrystalline particles in the second positive electrode active material is 5:5, 4:6, 3:7, 2:8, etc. The presence of single-crystal particles and polycrystalline particles in the second positive electrode active layer in the above-mentioned proportions not only results in good film density but also allows for better utilization of the battery capacity.

[0083] In some embodiments, the second positive electrode active material comprises at least one of lithium phosphate and lithium transition metal oxide. For example, it may be a D-type lithium phosphate and lithium transition metal oxide. V250 is a single crystal particle of 2-4 pm and particle size D V2 50 is a polycrystal particle of 8-10 pm. The battery cell formed by the second positive electrode active material is a lithium ion battery cell, which has the characteristics of high energy density and high cycle life.

[0084] In some embodiments, the first positive electrode active material and the second positive electrode active material are of the same material. For example, the first positive electrode active material includes a lithium transition metal oxide, and includes a nickel-cobalt-manganese ternary positive electrode material with a manganese content of at least 80%, which can be at least one of an 8-series nickel-cobalt-manganese ternary positive electrode material and a 9-series nickel-cobalt-manganese ternary positive electrode material; the second positive electrode active material includes a lithium transition metal oxide, and includes a nickel-cobalt-manganese ternary positive electrode material with a manganese content of at least 80%, which can be at least one of an 8-series nickel-cobalt-manganese ternary positive electrode material and a 9-series nickel-cobalt-manganese ternary positive electrode material. The use of the high-nickel-content nickel-cobalt-manganese ternary positive electrode material in the first positive electrode active layer and the second positive electrode active layer respectively allows the battery cell to have a higher energy density.

[0085] wherein the 8-series nickel-cobalt-manganese ternary positive electrode material can be NCM811, for example, the molecular formula can be LiNi 0.8 Co 0.1 Mn 0.1 O2. The 9-series nickel-cobalt-manganese ternary positive electrode material can have a nickel-cobalt-manganese ratio of 9:0.5:0.5, for example, the molecular formula can be LiNi 0.9 Co 0.05 Mn 0.05 O2.

[0086] In some embodiments, the thickness of the first positive electrode active layer is 2-8 pm; for example, it can be 2 pm, 4 pm, 5 pm, 6 pm, 7 pm, 8 pm, etc. The thickness of the second positive electrode active layer is 50-200 pm; for example, it can be 50 pm, 60 pm, 70 pm, 80 pm, 90 pm, 100 pm, 120 pm, 150 pm, 180 pm, 200 pm, etc.

[0087] The first positive electrode active layer with the above thickness and the second positive electrode active layer with the above thickness can make the battery cell have better energy density and cycle life.

[0088] In some embodiments, the first positive electrode active layer also contains a first conductive agent, and the first conductive agent includes first carbon nanotubes. Carbon nanotubes have good conductivity, so adding first carbon nanotubes to the first positive electrode active layer can further improve the conductivity of the positive electrode sheet.

[0089] In some embodiments, the second positive electrode active layer also contains a second conductive agent, and the second conductive agent includes second carbon nanotubes. Since carbon nanotubes have good conductivity, adding second carbon nanotubes to the second positive electrode active layer can further improve the conductivity of the positive electrode sheet.

[0090] In some embodiments, the first carbon nanotubes include at least one of single-walled carbon nanotubes and few-walled carbon nanotubes. The single-walled carbon nanotubes or the few-walled carbon nanotubes have a tube diameter of less than or equal to 20 nm and an aspect ratio of greater than 50. For example, the first carbon nanotubes can be single-walled carbon nanotubes or few-walled carbon nanotubes with a tube diameter of 0.5 nm to 20 nm and an aspect ratio of 55 to 100. The single-walled carbon nanotubes of the above size category as the first carbon nanotubes can make the positive electrode sheet have good conductivity and can improve the fast charging performance of the battery.

[0091] In some embodiments, the first carbon nanotubes account for 1 to 20 percent of the mass percentage of the first positive electrode active layer. For example, the first carbon nanotubes can account for 1 percent, 3 percent, 5 percent, 10 percent, 12 percent, 15 percent, 18 percent, etc. The first carbon nanotubes in the above proportion make the positive electrode sheet have stable conductivity and have little effect on the mechanical properties of the electrode sheet, and can be well matched with the single-crystal particles with a particle size D V1 50 of 200 to 500 nm to improve the charging performance of the battery.

[0092] In some embodiments, the second carbon nanotubes include at least one of single-walled carbon nanotubes and few-walled carbon nanotubes. The single-walled carbon nanotubes or the few-walled carbon nanotubes have a tube diameter of less than or equal to 15 nm and an aspect ratio of greater than 100. For example, the second carbon nanotubes can be single-walled carbon nanotubes or few-walled carbon nanotubes with a tube diameter of 10 nm to 15 nm and an aspect ratio of 105 to 150. The single-walled carbon nanotubes of the above size category as the second carbon nanotubes can make the positive electrode sheet have good conductivity and can improve the fast charging performance of the battery.

[0093] In some embodiments, the second carbon nanotubes account for 0.1 to 3 percent of the mass percentage of the second positive electrode active layer. For example, the second carbon nanotubes can account for 0.1 percent, 0.3 percent, 0.5 percent, 1 percent, 1.2 percent, 1.5 percent, 2 percent, 2.5 percent, 2.8 percent, etc. The second carbon nanotubes in the above proportion make the positive electrode sheet have stable conductivity and have little effect on the mechanical properties of the electrode sheet, and can be well matched with the single-crystal particles with a particle size D V2 50 of 2 to 4 pm and the polycrystal particles with a particle size D V2 50 of 8 to 10 pm to improve the charging performance of the battery.

[0094] It should be noted that single-walled carbon nanotubes (SWCNTs) can be understood as carbon nanotubes curled from a single layer of graphene carbon atoms, i.e., a tubular structure arranged by only one layer of carbon atoms; few-walled carbon nanotubes (FWNTs) can be understood as carbon nanotubes curled from 2-10 layers of carbon atoms.

[0095] In the embodiments of the present application, the battery monomer can be a secondary battery monomer, which refers to a battery monomer that can be activated by charging after discharging to continue to use. The battery monomer can be a lithium ion battery, a sodium lithium ion battery, a lithium metal battery, a lithium-sulfur battery, etc., and the embodiments of the present application are not limited thereto.

[0096] In the embodiments of the present application, the battery monomer can include a battery shell and an electrode assembly packaged in the battery shell. The shape of the battery monomer is not particularly limited, and it can be cylindrical, square or any other shape. As shown in the square structure of the battery monomer 10. Figure 1

[0097] In some embodiments, as shown in Figure 2 The outer package of the battery monomer 10 can include a shell 11 and a top cover assembly 12. The shell 11 can include a bottom plate and a side plate connected to the bottom plate, which enclose a receiving cavity. The shell 11 has an opening communicating with the receiving cavity, and the top cover assembly 12 is used to cover the opening to close the receiving cavity. The positive electrode sheet, the separator film and the negative electrode sheet contained in the battery monomer of the embodiments of the present application can form an electrode assembly 13 through a winding process. The electrode assembly 13 is packaged in the receiving cavity. The electrolyte is impregnated in the electrode assembly 13. The number of electrode assemblies 13 contained in the battery monomer 10 can be one or more, which can be adjusted according to actual needs.

[0098] The preparation method of the battery monomer 10 is well known. In some embodiments, the positive electrode sheet, the separator film and the negative electrode sheet and the electrolyte can be assembled to form the battery monomer 10. As an example, the positive electrode sheet, the separator film and the negative electrode sheet can be formed into an electrode assembly 13 through a winding process, the electrode assembly 13 is placed in the outer package, the electrolyte is injected after drying, and the battery monomer 10 is obtained after vacuum packaging, standing, formation, shaping and other processes.

[0099] ​In some embodiments, the first positive active layer or the second positive active layer of the positive electrode tab can further include a conductive agent and a binder. As an example, the binder can include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin. At least one of black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0100] In some embodiments, the positive current collector can employ a metal foil, a foam metal, or a composite current collector. For example, as the metal foil, silver surface-treated aluminum or stainless steel, stainless steel, copper, aluminum, nickel, a carbon electrode, a carbon, nickel, or titanium, or the like can be employed. The foam metal can be a foam nickel, a foam copper, a foam aluminum, a foam alloy, or a foam carbon, or the like. The composite current collector can include a polymer material base layer and a metal layer. The composite current collector can be formed by forming a metal material (copper, a copper alloy, nickel, a nickel alloy, titanium, a titanium alloy, silver, and a silver alloy, or the like) on a polymer material base material (such as a base material of polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, polyethylene, or the like).

[0101] In some embodiments, the negative electrode tab can be a negative electrode tab having only a negative current collector, i.e., a metal battery cell corresponding to the negative electrode tab is a metal battery cell without a negative active material. Alternatively, the negative electrode tab includes a negative current collector and a negative active layer disposed on at least one surface of the negative current collector. As an example, the negative current collector has two surfaces opposite in the thickness direction thereof, and the negative active material is disposed on any one or both of the two surfaces of the negative current collector.

[0102] The negative current collector can employ a metal foil, a foam metal, or a composite current collector. For example, as the metal foil, silver surface-treated aluminum or stainless steel, stainless steel, copper, aluminum, nickel, a carbon electrode, a carbon, nickel, or titanium, or the like can be employed. The foam metal can be a foam nickel, a foam copper, a foam aluminum, a foam alloy, or a foam carbon, or the like. The composite current collector can include a polymer material base layer and a metal layer. The composite current collector can be formed by forming a metal material (copper, a copper alloy, nickel, a nickel alloy, titanium, a titanium alloy, silver, and a silver alloy, or the like) on a polymer material base material (such as a base material of polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, polyethylene, or the like). In some embodiments, the material of the positive current collector can be an aluminum foil, and the material of the negative current collector can be a copper foil.

[0103] The negative active layer contains a negative active material. As an example, the negative active material can employ a negative active material for a battery cell known in the art. As an example, the negative active material can include at least one of artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based material, tin-based material, and lithium titanate, etc. The silicon-based material can be selected from at least one of elemental silicon, silicon oxide compound, silicon-carbon composite, silicon-nitrogen composite, and silicon alloy. The tin-based material can be selected from at least one of elemental tin, tin oxide compound, and tin alloy. However, the present application is not limited to these materials, and other conventional materials that can be used as a battery negative active material can also be used. These negative active materials can be used alone or in combination of two or more.

[0104] The negative active layer can also optionally include a binder. The binder can 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). The negative active layer can also optionally include a conductive agent. The conductive agent can be selected from at least one of super conductive carbon, acetylene black, carbon black, ketjen black, carbon dot, carbon nanotube, graphene, and carbon nanofiber. In some embodiments, the negative active layer can also optionally include other auxiliary agents, such as a dispersant, a thickening agent (e.g., sodium carboxymethyl cellulose), etc.

[0105] Specifically, the battery cell can include a wound electrode assembly, specifically including a positive electrode sheet, a negative electrode sheet, and a separator disposed between the positive electrode sheet and the negative electrode sheet. The positive electrode sheet, the separator, and the negative electrode sheet are laminated and wound to form the electrode assembly. During charging and discharging of the battery, active ions are inserted and extracted between the positive electrode sheet and the negative electrode sheet. The electrolyte serves to conduct ions between the positive electrode sheet and the negative electrode sheet. The separator is disposed between the positive electrode sheet and the negative electrode sheet, and mainly serves to prevent short circuiting between the positive and negative electrodes, while allowing the active ions such as lithium ions to pass through.

[0106] In some embodiments, the separator can be a separate component located between the positive electrode sheet and the negative electrode sheet, or can be attached to the surface of the positive / negative electrode sheet. The separator includes a separator film. The present application does not have a particular limitation on the type of separator film, and any known porous structure separator film having good chemical stability and mechanical stability can be used. As an example, the main material of the separator film can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride, ceramic. The separator film can be a single layer film or a multi-layer composite film, and is not particularly limited. When the separator film is a multi-layer composite film, the materials of the respective layers can be the same or different, and are not particularly limited.

[0107] In some embodiments, the battery cell includes an electrolyte that functions to conduct ions between the positive electrode tab and the negative electrode tab.

[0108] In some embodiments, the electrolyte employs an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent. The electrolyte salt can be selected from lithium salts, which are not particularly limited in kind and can be selected as desired. For example, the lithium salt can be selected from one or more of LiPF6, LiClO4, LiBF4, LiClF4, LiAsF6, LiSbF6, LiAlO2, LiAlCl4, LiN(CF3SO2)2, LiN(C2F5SO2)2, LiC(CF3SO2)3, LiCl, LiI, and the like.

[0109] The kind of organic solvent in the electrolyte solution is not particularly limited and can be selected as desired. Specifically, the organic solvent can further include one or more of other kinds of chain carbonates, cyclic carbonates, carboxylic acid esters. The kind of chain carbonates, cyclic carbonates, carboxylic acid esters is not particularly limited and can be selected as desired. The organic solvent can further include one or more of diethyl carbonate, dipropyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, vinyl carbonate, propylene carbonate, butylene carbonate, γ-butyrolactone, methyl formate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, methyl propionate, and tetrahydrofuran.

[0110] In addition, the electrode solution can also use an additive. Specifically, the additive can include a negative electrode film-forming additive, a positive electrode film-forming additive, and can also include an additive capable of improving certain performance of the battery, such as an additive for improving the overcharge performance of the battery, an additive for improving the high-temperature or low-temperature performance of the battery, and the like.

[0111] In a second aspect, the embodiments of the present application provide a preparation method of a battery cell. The preparation method of the battery cell provided by the embodiments of the present application includes the following steps:

[0112] S01: preparing a first positive electrode slurry containing a first positive electrode active material and a second positive electrode slurry containing a second positive electrode active material; wherein the particle size D V1 50 is less than or equal to 1 μm, and the particle size D V2 50 of the second positive electrode active material is greater than the particle size D V1 50 of the first positive electrode active material;

[0113] S02: forming a first positive electrode active layer and a second positive electrode active layer in sequence on at least one surface of the positive electrode current collector in a direction away from the surface of the positive electrode current collector by using the first positive electrode slurry and the second positive electrode slurry, to obtain a positive electrode tab;

[0114] S03: Assembling the positive electrode sheet and the negative electrode sheet to obtain a battery cell.

[0115] During the preparation of the positive electrode sheet, the first positive electrode active layer and the second positive electrode active layer are sequentially formed on the surface of the positive electrode current collector, so that the first positive electrode active layer contains the first positive electrode active material with a particle size D V1 50 less than or equal to 1 pm, the second positive electrode active layer contains the second positive electrode active material with a particle size D V2 50 greater than the particle size D V1 50, the first positive electrode active material with a small particle size can act as a buffer to reduce the damage of the second positive electrode active material with a large particle size in the second positive electrode active layer to the positive electrode current collector, while increasing the overall strength of the positive electrode sheet, thereby reducing the risk of the positive electrode sheet from being broken. Therefore, assembling the obtained positive electrode sheet and the negative electrode sheet into a battery cell can further improve the cycle life of the obtained battery cell under the premise of having high energy density.

[0116] In some embodiments, the first positive electrode active material and the second positive electrode active material of the present application can be prepared by spray pyrolysis (SP). The use of spray pyrolysis method to prepare high-activity oxide precursor can reduce the calcination temperature. However, for nickel-rich positive electrode active materials such as 8-system nickel-cobalt-manganese ternary positive electrode materials or 9-system nickel-cobalt-manganese ternary positive electrode materials, lithium nitrate with low melting point and strong oxidizing property can be introduced as a synthetic raw material lithium salt to manufacture sub-micron and micron single-crystal high-nickel positive electrodes with good dispersion. By changing the amount of lithium nitrate, particle size adjustment and reduction of cation disorder can be achieved.

[0117] For example, the embodiments of the present application can prepare the first positive electrode active material with a particle size D V1 50 of 200-500 nm: single-crystal particle NCM811. It has good lithium ion diffusion kinetics and good electrochemical performance. Coating the above single-crystal particle NCM811 as the first positive electrode active material buffer material on the positive electrode current collector can reduce the risk of damage to the positive electrode sheet by the second positive electrode active material particles.

[0118] In some embodiments, the particle size D V150 The single crystal NCM811 with 200-500 nm as the first positive electrode active material, adding a certain amount of binder and single-walled carbon nanotube dry mixing stirring, and adding an oily solvent wet mixing kneading to prepare the coating slurry of the first positive electrode active layer. The coating slurry of the first positive electrode active layer is coated on the current collector aluminum foil using a transfer coater to prepare a basic positive electrode sheet containing the first positive electrode active layer, and the coating thickness is between 2 μm-8 μm. Then the polycrystal (Dv250 is located at 8-10 μm) and single crystal (Dv250 = 2-4 μm) of NCM811 are mixed, mixed with a conductive agent (single-walled carbon nanotube) and a binder, and a proper amount of solvent is added under the condition of stirring at a speed of 400-1000 r / s, and then wetting, kneading and dispersion treatment are carried out to obtain the coating slurry of the second positive electrode active layer, and the viscosity is adjusted to 8000-13500 mpa·s. The prepared coating slurry of the second positive electrode active layer is coated on the first positive electrode active layer, and then dried in an oven at a temperature of 80-110 ℃, and the thickness of the second positive electrode active layer is 50-200 μm. The final positive electrode sheet has a double-layer structure (i.e. the first positive electrode active layer and the second positive electrode active layer are stacked).

[0119] In some embodiments, since the compaction density and the area density of the electrode sheet after cycling will have a small range of changes compared to the electrode sheet before cycling, in this application, the compaction density and the area density range of the electrode sheet includes the compaction density and the area density of the electrode sheet before and after cycling, for example but not limited to, the compaction density of the positive electrode sheet can be in the range of 3.5-3.7 g / cc, and the area density can be in the range of 1.0-2.0 x 10 -2 g / cm 2 , the compaction density of the negative electrode sheet can be in the range of 1.6-1.8 g / cc, and the area density can be in the range of 0.7-1.4 x 10 -2 g / cm 2 .

[0120] Battery apparatus

[0121] In a third aspect, the embodiments of the present application provide a battery apparatus. The battery apparatus of the embodiments of the present application includes the battery cell provided in the first aspect of the embodiments of the present application or the battery cell prepared by the preparation method provided in the second aspect of the embodiments of the present application. Based on the use of the battery cell of the embodiments of the present application, the battery apparatus of the embodiments of the present application has a good cycle life under the premise of high energy density.

[0122] The battery apparatus mentioned in the embodiments of the present application can include one or more battery cell assemblies for providing voltage and capacity. The battery cell assembly can include a plurality of battery cells connected in series, in parallel, or in a mixed connection through a busbar component.

[0123] In some embodiments, the battery device of the embodiments of the present application can include any one of a battery cell, a battery module, and a battery pack.

[0124] The battery module refers to an assembly of the battery cell 10, i.e., can contain a plurality of the battery cell 10, and the specific number can be adjusted according to the application and capacity of the battery module.

[0125] In some embodiments, Figure 3 is a schematic diagram of the battery module 20 as an example. In the battery module 20, a plurality of battery cells 10 can be arranged in sequence along the length direction of the battery module 20. Of course, other arbitrary arrangements can also be made. Further, the plurality of battery cells 10 can be fixed by fasteners.

[0126] Optionally, the battery module 20 can also include a housing with an accommodation space, and the plurality of battery cells 10 are accommodated in the accommodation space.

[0127] The battery pack refers to an assembly of the battery cell 10 described above, i.e., can contain a plurality of battery cells 10, wherein the plurality of battery cells 10 can be assembled into the battery module 20 described above. The specific number of battery cells 10 or battery modules 20 contained in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0128] As in the embodiments, Figure 4 and Figure 5 is a schematic diagram of the battery pack 30 as an example. In the battery pack 30, a battery box and a plurality of battery modules 20 arranged in the battery box can be included. The battery box includes an upper box body 31 and a lower box body 32, the upper box body 31 is used to cover the lower box body 32, and forms a closed space for accommodating the battery module 20. The plurality of battery modules 20 can be arranged in the battery box in any manner.

[0129] Electric device

[0130] In a fourth aspect, the embodiments of the present application provide an electric device. The electric device of the embodiments of the present application includes the battery cell provided in the first aspect of the embodiments of the present application or the battery device provided in the third aspect of the embodiments of the present application, and the battery cell or the battery device is used to store or provide electric energy. Based on using the battery cell or the battery device of the embodiments of the present application, the electric device of the embodiments of the present application can work safely and for a long time.

[0131] The power consuming device can be, but is not limited to, a mobile device (e.g., a cell phone, a portable device, a notebook computer, etc.), an electric vehicle (e.g., a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, an electric trolley, an electric toy, an electric tool, etc.), an electric train, a ship and a satellite and a spacecraft, an energy storage system, etc. The power consuming device can select the secondary battery cell, the battery module or the battery pack according to its use requirement.

[0132] Figure 6 is a schematic diagram of a power consuming device as an example. The power consuming device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the requirement of high power and high energy density of the power consuming device, a battery pack or a battery module can be used.

[0133] The power consuming device as another example can be a cell phone, a tablet computer, a notebook computer, etc. The power consuming device usually requires thin and light, and a secondary battery can be used as a power source.

[0134] Embodiment

[0135] Hereinafter, the embodiments of the present application are described. The embodiments described below are exemplary and are only used to explain the present application, and cannot be understood as a limitation of the present application. If a specific technology or condition is not specified in the embodiments, the technology or condition described in the literature in the art or according to the product instruction is used. If the reagent or instrument used is not specified by the manufacturer, it is a conventional product that can be obtained by purchase.

[0136] Embodiment 1

[0137] Preparation of battery cell

[0138] 1) Preparation of positive electrode sheet:

[0139] The NCM811 single crystal (molecular formula LiNi 0.8 Co 0.1 Mn 0.1 O2, D V1 50 is 200 nm), a binder (PVDF), and a conductive agent (first oligo-wall carbon nanotube) are dry mixed and stirred at a mass ratio of 96:1:3 for 10 g, and a solvent NMP (N-methyl pyrrolidone) 3.6 g is added for wet mixing and kneading to prepare a first positive electrode slurry.

[0140] The NCM811 polycrystal (D V2 50 is 8 μm) and the NCM811 single crystal (D V250 is 2 μm) 97 g in mass ratio 7:3, mixed with binder (PVDF) 2 g, conductive agent (second oligo-wall carbon nanotube) 1 g, added with 40 g of NMP, stirred and mixed under the condition of 400-1000 r / s, then wetted, kneaded and dispersed to obtain the second positive electrode slurry.

[0141] The first positive electrode slurry is coated on the surface of the positive electrode current collector aluminum foil to form a film, and then the second positive electrode slurry is coated, rolled, and then dried in an oven at a temperature of 110°C to obtain a positive electrode tab. The compaction density of the positive electrode tab is 3.7 g / cc, and the area density is 2.0 x 10 -2 g / cm 2 .

[0142] 2) Preparation of battery negative electrode:

[0143] Graphite (artificial graphite and natural graphite mixed in a mass ratio of 6:4) 96.9 g, binder (polybutadiene rubber) 1.4 g, dispersant (sodium carboxymethyl cellulose) 1.15 g, conductive agent (SP-Li) 0.55 g, mixed and ball milled according to the above mass, then added with 100 g of deionized water, stirred to obtain a negative electrode slurry; the negative electrode slurry is coated on the surface of a copper foil, rolled, and vacuum dried at a temperature of 110°C overnight to obtain a negative electrode tab. The compaction density of the negative electrode tab is 1.8 g / cc, and the area density is 1.4 x 10 -2 g / cm 2 .

[0144] 3) Separator:

[0145] Polyethylene film with a thickness of 13 μm.

[0146] 4) Electrolyte:

[0147] The solvent is ethylene carbonate (EC), diethyl carbonate (DEC) and dimethyl carbonate (DMC) in a volume ratio of 1:1:1, and the lithium salt is 1 mol / L of LiPF6.

[0148] 5) Battery assembly:

[0149] According to the order of "separator-negative electrode tab-separator-positive electrode tab", the positive electrode tab, the negative electrode tab and one end of the two separators are fixed on the discharge roller, and the other end is stacked together and fixed on the winding shaft. The winding shaft is rotated by a motor to wind the positive electrode tab, the negative electrode tab and the two separators to obtain a wound bare cell. The bare cell is placed in an outer packaging shell, and after drying, the electrolyte is injected into the outer packaging shell. After vacuum packaging, standing, formation and shaping, a battery monomer is obtained.

[0150] Example 2-12

[0151] The differences from Example 1 are shown in Table 1 and Table 2.

[0152] Comparative Example 1

[0153] The difference from Example 1 is that the positive electrode tab only has the first positive active layer of Example 1. That is, the whole-layer positive active layer of this Comparative Example 1 only contains the first positive active material. The others are the same as Example 1.

[0154] Comparative Example 2

[0155] The difference from Example 1 is that the positive electrode tab only has the second positive active layer of Example 1. That is, the whole-layer positive active layer of this Comparative Example 2 only contains the second positive active material. The others are the same as Example 1.

[0156] Comparative Example 3

[0157] The difference from Example 1 is that the positive electrode tab includes the first positive active layer and the second positive active layer. But the first positive active material is NCM811 single crystal grain size D V1 = 2 μm. The others are the same as Example 1.

[0158] Table 1

[0159]

[0160]

[0161] Table 2

[0162]

[0163] Performance Test

[0164] 1. Positive electrode tab test

[0165] 1.1) Tab elongation test

[0166] ①Cutting: Lay the tab flat on the horizontal table top, and cut the tab into sections, with each tab about 120 cm long.

[0167] ②Make marks: Make marks on the tab at intervals of 1 m, ensuring that the marks are parallel to the edges of the tab.

[0168] ③Reading: Record the distance between the marks with a steel ruler, and record it as L1.

[0169] ④Measurement: Lay the rolled tab flat on the table top, and measure and record the distance between each pair of mark points on the tab using a meter ruler. The measurement data is estimated to 0.1 mm, and recorded as L2.

[0170] ⑤Calculate elongation: [(L2-L1) / L1]*100%.

[0171] 1.2) Pole piece brittleness test

[0172] ① Sample preparation: Take the pole piece after rolling, cut it into a size of 150mm*15mm.

[0173] ② Test: Fold the pole piece in half, and roll it over the folded area with a roller weighing 5Kg.

[0174] ③ Confirm whether it is transparent: Turn on the light source and observe the folded area of the pole piece. If it is transparent (strip-shaped or pinhole), record the number of roll folds.

[0175] ④ Repeat the test: If there is no transparency, fold the pole piece in the opposite direction and roll it. Observe the transparency.

[0176] ⑤ Repeat steps ③-④ until the folded area of the pole piece is transparent, and record the number of transparent folds.

[0177] ⑥ Take multiple parallel samples and record the number of transparent folds. Take the average.

[0178] 1.3) Pole piece elongation at break test

[0179] ① Sample preparation: Take the pole piece after rolling, cut it into a size of 150mm*15mm.

[0180] ② After sample preparation, use a tensile testing machine to do the tensile test, with an effective tensile area of 50*15mm.

[0181] ③ Adjust the equipment: Set the air pressure to 0.2Mpa, replace the tensile test fixture, and paste 1 layer of yellow wrinkled adhesive on the upper and lower clamps, with a replacement frequency of 1 time per shift, to prevent the pole piece from slipping.

[0182] ④ Sample on equipment: Thread the pole piece through the upper and lower clamps, press the air valve to clamp the upper clamp first, and keep it in a weakly connected state (natural bending state), then clamp the lower clamp.

[0183] ⑤ Test: Click "All Clear", then click "Start". After the test is complete, save the data.

[0184] ⑥ Calculate the elongation at break: If the pole piece is elongated by Xmm at break, then the elongation at break = (X / 50)*100%.

[0185] 1.4) SEM electron microscope observation

[0186] ① Sample preparation: Cut the test pole piece into a size of 1cm*1cm.

[0187] ② Polishing: Take the test sample and polish the fracture surface with argon atoms in the experimental equipment.

[0188] ③As to the observation of the cross-section morphology in the SEM device.

[0189] Figure 7 is the electron micrograph of the first positive active layer prepared in the positive electrode tab of Example 1, Figure 8 is the electron micrograph of the first positive active layer and the second positive active layer prepared in the positive electrode tab of Example 1. Figure 9 is the electron micrograph of Comparative Example 1. From the figure, it can be seen that the positive active material particles in Comparative Example 1 are pressed into the current collector substrate, so that the thickness of the current collector becomes no longer uniform, the current collector is damaged by stretching, and the strength of the tab is reduced. While the current collector of Example 1 is basically not damaged by extrusion.

[0190] 2. Cell test

[0191] 2.1) Energy density test

[0192] The size of the cell model is: 4.0 (mm, thickness, H) * 60 (mm, width, W) * 90 (mm, height, L), i.e. the volume V of the cell is thickness * width * height.

[0193] The cell is placed in an environment of 25±3℃, and after standing for 2h, the cell is charged to full capacity with a constant current and constant voltage of 0.5C rate, the cutoff current is 0.025C, and after standing for 5min, the cell is discharged to the lower limit voltage U with a rate of 0.2C. The volume energy density ED obtained is Q*U / (H*W*L).

[0194] 2.2) Cycle life test

[0195] ①Charging and discharging tests are carried out in the charging and discharging device for the examples and comparative examples.

[0196] ②The cell is placed in an environment of 25±3℃, and after standing for 2h, the cell is charged to full capacity with a constant current and constant voltage of 0.5C rate, the cutoff current is 0.025C, and after standing for 5min, the cell is discharged to the lower limit voltage U with a rate of 1C. Record the capacity C0, C1, and Cn of n cycles.

[0197] ③Calculate the state of health (SOH) of the battery to be 90%, i.e. the cycle number n corresponding to 90% of Cn / C0*100%.

[0198] The test results are shown in Table 3.

[0199] Table 3

[0200]

[0201] The above merely provides preferred embodiments of the application, and is not used to limit the application. Any modification, equivalent replacement, and improvement made within the spirit and principle of the application shall fall within the protection scope of the application.

Claims

1. A battery cell, comprising a positive electrode and a negative electrode, characterized in that, The positive electrode includes a positive current collector and a first positive active layer stacked on at least one surface of the positive current collector. A second positive active layer is further stacked on the surface of the first positive active layer facing away from the positive current collector. The first positive active layer contains a first positive active material, and the second positive active layer contains a second positive active material. The particle size D of the first positive active material is... V1 50 is less than or equal to 1 μm, and the particle size D of the second positive electrode active material V2 50 is greater than the particle size D of the first positive electrode active material V1 50.

2. The battery cell as described in claim 1, characterized in that, The first positive electrode active material includes particles with a diameter D V1 50 refers to single-crystal particles with a diameter of 200–500 nm.

3. The battery cell as described in claim 1 or 2, characterized in that, The particle size D of the second positive electrode active material V2 50 is 2-10 μm.

4. The battery cell according to any one of claims 1-3, characterized in that, The second positive electrode active material includes particles with a diameter D V2 50 consists of single crystal particles of 2–4 μm and a particle size D V2 50 consists of polycrystalline particles of 8–10 μm.

5. The battery cell as described in claim 4, characterized in that, The mass ratio of the single crystal particles to the polycrystalline particles in the second positive electrode active material is 5:5 to 2:

8.

6. The battery cell according to any one of claims 1-5, characterized in that, The thickness of the first positive electrode active layer is 2–8 μm; And / or, the thickness of the second positive electrode active layer is 50–200 μm.

7. The battery cell according to any one of claims 1-6, characterized in that, The first positive electrode active layer also contains a first conductive agent, which includes a first carbon nanotube; And / or, the second positive electrode active layer further contains a second conductive agent, the second conductive agent comprising a second carbon nanotube.

8. The battery cell as described in claim 7, characterized in that, The first carbon nanotube includes at least one of single-walled carbon nanotubes and oligo-walled carbon nanotubes, and the diameter of the first carbon nanotube is less than or equal to 20 nm and the aspect ratio is greater than 50. And / or, the first carbon nanotube accounts for 1 to 20% of the mass percentage of the first positive electrode active layer.

9. The battery cell as described in claim 7, characterized in that, The second carbon nanotube includes at least one of single-walled carbon nanotubes and oligo-walled carbon nanotubes, and the diameter of the second carbon nanotube is less than or equal to 15 nm and the aspect ratio is greater than 100. And / or, the second carbon nanotube accounts for 0.1% to 3% of the mass percentage of the second positive electrode active layer.

10. The battery cell according to any one of claims 1-9, characterized in that, The first positive electrode active material includes at least one of lithium phosphate and lithium transition metal oxide; And / or, the second positive electrode active material includes at least one of lithium phosphate and lithium transition metal oxide.

11. The battery cell as described in claim 10, characterized in that, The first positive electrode active material includes lithium transition metal oxide, and includes a nickel-cobalt-manganese ternary positive electrode material with a manganese content of at least 80%. And / or, the second positive electrode active material includes lithium transition metal oxide and includes a nickel-cobalt-manganese ternary positive electrode material with a manganese content of at least 80%.

12. A method for preparing a single battery cell, characterized in that, include: Prepare a first positive electrode slurry containing a first positive electrode active material and a second positive electrode slurry containing a second positive electrode active material; wherein, the particle size D of the first positive electrode active material is... V1 50 is less than or equal to 1 μm, and the particle size D of the second positive electrode active material V2 50 is greater than the particle size D of the first positive electrode active material V1 50; Along the direction away from the surface of the positive current collector, a first positive active layer and a second positive active layer are sequentially stacked on at least one surface of the positive current collector using the first positive slurry and the second positive slurry to obtain a positive electrode sheet. The positive and negative electrode sheets are assembled to obtain a single battery cell.

13. A battery device, characterized in that, This includes the battery cell as described in any one of claims 1-11 or the battery cell prepared by the preparation method as described in claim 12.

14. An electrical appliance, characterized in that, Includes a battery cell as described in any one of claims 1-11 or a battery device as described in claim 13.

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