Battery cell, manufacturing method therefor, battery apparatus and electrical apparatus

Abstract

The present application belongs to the technical field of batteries. Specifically disclosed are a battery cell, a manufacturing method therefor, a battery apparatus, and an electrical apparatus. The battery cell comprises a positive electrode sheet. The positive electrode sheet comprises a positive electrode film layer. The positive electrode film layer comprises a first region close to a current collector and a second region away from the current collector. The first region contains a lithium-nickel transition metal oxide. The second region contains a lithium-containing phosphate and a second carbon nanotube. By reducing the degree of swelling of positive electrode sheets, the design method provided in the present application improves cycle service lives of batteries.

Description

Battery cells and their preparation methods, battery devices and power-consuming devices

[0001] Cross-references to related applications

[0002] This application claims priority to Chinese patent application 202510103795.7, filed on January 22, 2025, entitled “Battery cell and method of preparation thereof, battery device and power device”, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This application relates to the field of batteries, specifically to a battery cell and its preparation method, a battery device, and an electrical device. Background Technology

[0004] With the development of new energy technologies, batteries are being used more and more widely, such as in mobile phones, laptops, electric vehicles, electric cars, energy storage devices, electric airplanes, electric ships, electric toy cars, electric toy ships, electric toy airplanes, and power tools. This places increasingly higher demands on battery performance. Summary of the Invention

[0005] In view of the above problems, this application provides a battery cell and its preparation method, a battery device and an electrical device, which improves the cycle life of the battery by improving the expansion of the electrode.

[0006] In a first aspect, this application provides a battery cell, which includes a positive electrode and a negative electrode;

[0007] The aforementioned positive electrode includes a positive current collector and a positive electrode film layer located on at least one side surface of the positive current collector;

[0008] The aforementioned positive electrode film layer includes a first surface away from the aforementioned positive electrode current collector and a second surface disposed opposite to the aforementioned first surface;

[0009] The distance between the first surface and the second surface is H;

[0010] The region formed extending from the second surface of the above-mentioned positive electrode film to a position of 0.1×H is denoted as the first region of the above-mentioned positive electrode film. The first region includes a first positive electrode active material, which includes a lithium nickel transition metal oxide.

[0011] The region formed extending from the first surface of the aforementioned positive electrode film to a position of 0.1×H is referred to as the second region of the aforementioned positive electrode film. The second region includes a second positive electrode active material and a second carbon nanotube. The second positive electrode active material includes a lithium phosphate material.

[0012] In some embodiments, the average tube length of the second carbon nanotube is greater than or equal to 10 μm.

[0013] In some embodiments, the average length of the second carbon nanotube is 10 μm to 40 μm.

[0014] In some embodiments, the average diameter of the second carbon nanotube is 1 nm to 20 nm.

[0015] In some embodiments, based on the mass of the second region, the mass percentage content of the second carbon nanotube in the second region is 0.05% to 2%.

[0016] In some embodiments, the first region includes a first carbon nanotube.

[0017] In some embodiments, the first carbon nanotube and the second carbon nanotube satisfy any one or more of the following conditions:

[0018] (1) The average tube length of the first carbon nanotube is L1, and the average tube length of the second carbon nanotube is L2, where L1≤L2.

[0019] (2) The average diameter of the first carbon nanotube is D1, and the average diameter of the second carbon nanotube is D2, where D1 ≥ D2.

[0020] (3) The mass percentage content of the first carbon nanotube in the first region is W1; the mass percentage content of the second carbon nanotube in the second region is W2; W1≤W2.

[0021] In some embodiments, the first carbon nanotube and the second carbon nanotube satisfy any one or more of the following conditions:

[0022] (1) The average tube length L1 of the first carbon nanotube is 10μm to 15μm, and the average tube length L2 of the second carbon nanotube is greater than 15μm and less than or equal to 40μm.

[0023] (2) The average diameter D1 of the first carbon nanotube is greater than 2nm and less than or equal to 20nm, and the average diameter D2 of the second carbon nanotube is 1nm to 2nm.

[0024] (3) The mass percentage content W1 of the first carbon nanotube in the first region is 0.05% to 1.0%; the mass percentage content W2 of the second carbon nanotube in the second region is 0.1% to 2.0%.

[0025] In some embodiments, the chemical formula of the aforementioned lithium-nickel transition metal oxide is Li. x N t (Ni a Cob M c ) 1-d M' d O 2-y A y ;

[0026] N includes any one or more of Zn, Al, Na, K, Mg, Nb, Mo, and W;

[0027] M includes any one or more of Mn and Al;

[0028] M' includes any one or more of Zr, Sr, B, Ti, Mg, Sn, and Al;

[0029] A includes any one or more of S, N, B, F, Cl, Br, and I;

[0030] x ranges from 0.2 to 1.2;

[0031] t is 0 to 0.1;

[0032] a ranges from 0.001 to 0.999;

[0033] b is 0.001 to 0.999;

[0034] a+b+c=1,

[0035] 0 ≤ d ≤ 0.1;

[0036] 0 ≤ y < 0.2.

[0037] In some embodiments, based on the total number of moles of transition metals other than lithium in the above-mentioned lithium-nickel transition metal oxide, the nickel content Y in the above-mentioned lithium-nickel transition metal oxide satisfies: Y = a × 100%;

[0038] The above Y ≤ 70%.

[0039] In some embodiments, in the chemical formula of the above-mentioned lithium nickel transition metal oxide, a is 0.001 to 0.7.

[0040] In some embodiments, the chemical formula of the above-mentioned lithium phosphate is Li e Fe 1-y’ M” y’ P 1-m’ C m’ O 4-n’ D n’ ;

[0041] Wherein, M" includes any one or more of Cr, Mg, Ti, Al, Zn, W, Nb, and Zr;

[0042] C includes any one or more of B, S, Si, and N;

[0043] D includes any one or more of S, F, Cl, and Br;

[0044] 0 < e ≤ 1.1;

[0045] 0≤y'<1;

[0046] 0≤m'≤0.1;

[0047] 0≤n'≤0.4.

[0048] In some embodiments, the median particle size Dv50 of the above-mentioned lithium nickel transition metal oxide is 2 μm to 6 μm.

[0049] In some embodiments, the median particle size Dv50 of the lithium phosphate material is 0.5 μm to 2.2 μm.

[0050] In some embodiments, the lithium phosphate material includes lithium phosphate particles and a carbon coating layer, wherein the carbon coating layer coats the lithium phosphate particles and the thickness of the carbon coating layer is 5 nm to 100 nm.

[0051] In some embodiments, the compaction density of the above-mentioned positive electrode film is 1.5 g / cm³. 3 ~2.4g / cm 3 .

[0052] In some embodiments, the cohesive force of the above-mentioned positive electrode film is 150 N / m to 450 N / m.

[0053] In some embodiments, the positive electrode film layer includes an adhesive;

[0054] The aforementioned adhesives include propylene-based polymers;

[0055] The aforementioned propylene-based polymers include any one or more of the following: structural units derived from acrylic monomers, structural units derived from acrylamide monomers, structural units derived from acrylonitrile monomers, and structural units derived from acrylate monomers.

[0056] In some embodiments, based on the mass of the positive electrode film, the mass percentage content of the propylene-based polymer in the positive electrode film is 1% to 3%.

[0057] In some embodiments, the battery cell further includes an electrolyte, which comprises an electrolyte salt and an organic solvent;

[0058] The molar concentration of the above electrolyte salt is ≥0.9 mol / L.

[0059] The second aspect of this application is to provide a method for preparing the battery cell described in the first aspect, comprising the following steps:

[0060] Preparation of the first positive electrode slurry: The first positive electrode active material is dispersed in a solvent and mixed to form the first positive electrode slurry;

[0061] Preparation of the second positive electrode slurry: The second positive electrode active material and the second carbon nanotube dispersion are dispersed in a solvent and mixed to form the second positive electrode slurry;

[0062] Preparation of positive electrode sheet: A first positive electrode slurry is coated on at least one side surface of the positive electrode current collector to obtain a first sub-positive electrode film layer, and a second positive electrode slurry is coated on the side surface of the first sub-positive electrode film layer away from the positive electrode current collector to form a second sub-positive electrode film layer.

[0063] Battery cell preparation: Assemble the negative electrode, positive electrode and separator together.

[0064] In some embodiments, the above-mentioned second carbon nanotube dispersion comprises second carbon nanotubes and a dispersant;

[0065] The above dispersant includes one or more of carboxymethyl cellulose and sodium carboxymethyl cellulose.

[0066] In some embodiments, the mass ratio of the second carbon nanotube to the dispersant in the second carbon nanotube dispersion is 100:(50-250).

[0067] In some embodiments, the solid content of the second carbon nanotube dispersion is 0.6% to 1.5%.

[0068] In some embodiments, the second carbon nanotube dispersion further comprises a surfactant, which includes one or more of glutamic acid surfactants and glycine surfactants.

[0069] In some embodiments, the surfactant content in the second carbon nanotube dispersion is 2% to 5% by mass, based on the mass of the second carbon nanotube dispersion.

[0070] A third aspect of this application is to provide a battery device comprising the battery cell described in the first aspect or the battery cell prepared by the preparation method described in the second aspect.

[0071] A fourth aspect of this application is to provide an electrical device that includes the battery device described in the third aspect.

[0072] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description

[0073] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the scope of this application. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0074] Figure 1 is a schematic diagram of the battery structure of some embodiments of this application;

[0075] Figure 2 is an exploded structural diagram of a battery according to some embodiments of this application;

[0076] Figure 3 is a schematic diagram of the vehicle structure according to some embodiments of this application;

[0077] Figure 4 is a schematic diagram of the structure of a battery pack according to some embodiments of this application;

[0078] Figure 5 is a schematic diagram of the battery structure of some embodiments of this application;

[0079] Figure 6 is a schematic diagram of the structure of a positive electrode sheet according to some embodiments of this application;

[0080] Figure 7 is a schematic diagram of another structure of the positive electrode sheet in some embodiments of this application;

[0081] Figure 8 is a schematic diagram of the structure of the positive electrode sheet of some embodiments of this application before and after recycling;

[0082] The reference numerals in the detailed embodiments are as follows:

[0083] 10000, vehicles;

[0084] 1000, Battery; 2000, Controller; 3000, Motor;

[0085] 100. Battery cell;

[0086] 200. Box body; 210. First part; 220. Second part;

[0087] 10. Secondary batteries;

[0088] 101. Housing; 102. Electrode assembly; 103. Cover plate;

[0089] 1. Negative electrode plate;

[0090] 2. Positive electrode plate; 21. Positive current collector; 22. Positive electrode film;

[0091] 3. Separating membrane;

[0092] 22a, First surface; 22b, Second surface; 22a', Third surface;

[0093] 22A, Area 1; 22B, Area 2;

[0094] 221. First sub-cathode film layer;

[0095] 222. Second positive electrode film layer.

[0096] x-axis: The stacking direction or thickness direction of the electrodes;

[0097] The y-axis direction: the length or width direction of the electrode. Detailed Implementation

[0098] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the battery cell, its preparation method, battery device, and power-consuming 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.

[0099] 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.

[0100] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0101] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0102] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0103] 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.

[0104] 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).

[0105] Unless otherwise specified, in this application, the terms "first," "second," etc., are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features.

[0106] Unless otherwise specified, in this application, the term "multiple" means two or more (including two), similarly, "multiple sets" means two or more (including two sets), and "multiple pieces" means two or more (including two pieces).

[0107] Unless otherwise specified, the technical terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the embodiments of this application and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of this application.

[0108] Batteries, with their advantages of high energy density, long cycle life, and safety and reliability, have been widely used in various products. In recent years, with the significant increase in demand for batteries as an energy source, higher requirements have been placed on battery performance, such as cycle life.

[0109] Lithium-nickel transition metal oxides (LiNiO) offer the advantage of high energy density when used as cathode active materials. However, they suffer from material losses during cycling due to phase transitions, Li-Ni mixing, oxygen release, and structural collapse, resulting in a short lifespan. Lithium-phosphate materials, on the other hand, offer advantages such as high stability, good cycle stability, and long lifespan, but their energy density is lower. To leverage the advantages of both, a physical mixture of LiNiO and lithium-phosphate materials is generally considered as the cathode active material.

[0110] Due to the technical drawback of numerous side reactions between lithium nickel transition metal oxide (LiNi) cathode active materials and the electrolyte, this application aims to mitigate this issue by placing the LiNi Ni LME in the cathode film layer near the current collector and placing lithium phosphate in the cathode film layer away from the current collector. However, the inventors of this application have discovered that during battery charging and discharging, both the lithium phosphate-containing cathode film layer and the lithium Ni Ni LME-containing cathode film layer expand, with the expansion degree of the lithium phosphate-containing cathode film layer being greater than that of the lithium Ni Ni LME-containing cathode film layer. This is detrimental to the battery's cycle life.

[0111] To address the aforementioned technical problems, this application discloses a battery cell and its preparation method, a battery device, and an electrical device.

[0112] First, this application discloses a battery cell, which includes a positive electrode and a negative electrode. The positive electrode includes a positive current collector and a positive electrode film layer located on at least one side surface of the positive current collector. The positive electrode film layer includes a first surface away from the positive current collector and a second surface disposed opposite to the first surface. The distance between the first surface and the second surface is H. The region formed extending from the second surface of the positive electrode film layer to a position of 0.1×H is denoted as the first region of the positive electrode film layer. The first region includes a first positive electrode active material, which includes a lithium nickel transition metal oxide.

[0113] The region formed extending from the first surface of the aforementioned positive electrode film to a position of 0.1×H is referred to as the second region of the aforementioned positive electrode film. The second region includes a second positive electrode active material and a second carbon nanotube. The second positive electrode active material includes lithium phosphate.

[0114] To improve the energy density of the battery, this application uses lithium nickel transition metal oxide as the positive electrode active material. However, during the charging and discharging process, the electronic structure and chemical valence of the transition metal elements in lithium nickel transition metal oxide, especially lithium nickel manganese transition metal oxide, are prone to changes, leading to instability in the material's crystal structure. This causes side reactions between the electrolyte and the lithium nickel transition metal oxide, resulting in manganese dissolution and affecting the battery's cycle performance. This application chooses to place the lithium nickel transition metal oxide in a first region away from the electrolyte (i.e., the first region close to the current collector), while designing a positive electrode film layer containing lithium phosphate in a second region away from the current collector. This design not only obtains high-energy battery cells but also reduces the probability of side reactions between the lithium nickel transition metal oxide and the electrolyte, thereby improving the battery's cycle life.

[0115] However, during battery charging and discharging, both the second region containing lithium phosphate and the first region containing lithium nickel transition metal oxide expand, with the expansion degree of the second region containing lithium phosphate being greater than that of the first region containing lithium nickel transition metal oxide. This is detrimental to battery cycle life. Therefore, this application also selects to add carbon nanotubes with a one-dimensional tubular structure to the second region far from the current collector to linearly wind and bind the lithium phosphate in that region. This reduces the electrode expansion at this location, mitigating the impact of electrode expansion on battery cycle life. Furthermore, compared to using carbon nanotubes to mitigate the expansion of lithium nickel transition metal oxide, this application uses binding carbon nanotubes to mitigate the expansion of lithium phosphate, resulting in a more significant improvement in the expansion of the entire positive electrode film or the battery cell, and a more significant improvement in the cycle life of the battery cell.

[0116] Therefore, the battery cell provided in this application improves the cycle life of the battery by reducing the expansion of the positive electrode sheet. At the same time, it can also improve the uniformity of conductivity of the entire positive electrode sheet, reduce the polarization of the positive electrode sheet, and further improve the cycle life of the battery. Therefore, the design method provided in this application is beneficial to improving the user experience.

[0117] Electrode assembly

[0118] A single battery cell typically includes an electrode assembly. The electrode assembly includes a positive electrode, a negative electrode, and a separator, with the separator positioned between the positive and negative electrodes. During the charging and discharging process of a single battery cell, active ions (such as lithium ions) repeatedly insert and extract between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, prevents short circuits between the positive and negative electrodes while allowing active ions to pass through.

[0119] Battery device

[0120] The battery apparatus mentioned in the embodiments of this application may include one or more battery cell assemblies for providing voltage and capacity. A battery cell assembly may include multiple battery cells connected in series, parallel, or mixed connections via a busbar.

[0121] In some embodiments, a battery cell assembly is typically formed by arranging multiple battery cells.

[0122] As an example, a battery cell assembly can be a battery module, which is formed by arranging and fixing multiple battery cells together to form an independent module. As another example, a battery module can be formed by bundling multiple battery cells together with cable ties.

[0123] In some embodiments, the battery device may be a battery pack, which includes a housing and one or more individual battery cells housed within the housing.

[0124] As an example, the battery cell assembly can be a battery module, which can be housed in a housing by fixing the battery module in the housing.

[0125] As an example, battery cell assemblies can also be housed in a housing by directly fixing multiple battery cells to the housing.

[0126] As an example, the enclosure may include a first enclosure and a second enclosure. The first enclosure and the second enclosure are fastened together to form a closed space inside the enclosure to house the individual battery cells. Here, "closed" refers to covering or closing, and can be either sealed or unsealed. The first enclosure may be a top cover or a bottom plate.

[0127] As an example, the enclosure may include a top cover, a frame, and a bottom plate. The top cover and bottom plate are connected to the frame, creating an enclosed space inside the enclosure to house the individual battery cells.

[0128] In some embodiments, the housing may be part of the vehicle's chassis structure. For example, a portion of the housing may be at least a part of the vehicle's floor, or a portion of the housing may be at least a part of the vehicle's crossbeams and longitudinal beams.

[0129] The battery cell of this application may include an outer packaging. This outer packaging can be used to encapsulate the electrode assembly and electrolyte composed of the aforementioned battery cell. The outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, aluminum shell, steel shell, etc. The outer packaging of the secondary battery can also be a soft pack, such as a pouch-type soft pack. The material of the soft pack can be plastic, including but not limited to polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0130] This application does not impose any particular limitation on the shape of the battery; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 1 shows a square-structured secondary battery 10 as an example.

[0131] According to some embodiments of this application, referring to FIG2, the outer packaging may include a housing 101 and a cover plate 103. The housing 101 may include a bottom plate and side plates connected to the bottom plate, the bottom plate and side plates forming a receiving cavity. The housing 101 has an opening communicating with the receiving cavity, and the cover plate 103 can cover the opening to close the receiving cavity. A positive electrode sheet, a negative electrode sheet, and a separator can be formed into an electrode assembly 102 by a winding process or a stacking process. The electrode assembly 102 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 102. The secondary battery 10 may contain one or more electrode assemblies 102, which can be selected by those skilled in the art according to specific practical needs.

[0132] The electrode assembly 102 provided in this application is beneficial to improving the performance of a secondary battery when applied in a secondary battery. The secondary battery can be a power source for an electrical device or an energy storage unit for an electrical device. The electrical device is applied in the power field, such as 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., but is not limited to the above fields.

[0133] For ease of explanation, some embodiments of this application are illustrated using a vehicle as an example of an electrical device.

[0134] Please refer to Figure 3, which is a structural schematic diagram of a vehicle 10000 provided in some embodiments of this application. The vehicle 10000 can be a gasoline-powered vehicle, a natural gas-powered vehicle, or a new energy vehicle. New energy vehicles can be pure electric vehicles, hybrid electric vehicles, or range-extended electric vehicles, etc. A battery 1000 is installed inside the vehicle 10000, and the battery 10000 can be located at the bottom, front, or rear of the vehicle 10000. The battery 10000 can be used to power the vehicle 10000; for example, the battery 10000 can serve as the operating power source for the vehicle 10000. The vehicle 10000 may also include a controller 2000 and a motor 3000. The controller 2000 is used to control the battery 10000 to supply power to the motor 3000, for example, to meet the power needs of the vehicle 10000 during startup, navigation, and driving.

[0135] In some embodiments of this application, the battery 1000 can not only serve as the operating power source for the vehicle 10000, but also as the driving power source for the vehicle 10000, replacing or partially replacing fuel or natural gas to provide driving power for the vehicle 10000.

[0136] Please refer to Figure 4, which is an exploded view of a battery 1000 provided in some embodiments of this application. The battery 1000 includes a housing 200 and a battery cell 100. A conventional battery cell includes a primary battery or a secondary battery; this application specifically protects a secondary battery 10. The battery cell 100 is housed within the housing 200. The housing 200 provides space for the battery cell 100, and the housing 200 can adopt various structures.

[0137] In some embodiments, the housing 200 may include a first portion 210 and a second portion 220, which overlap each other, and together define a receiving space for accommodating the secondary battery 100. The second portion 220 may be a hollow structure with one open end, and the first portion 210 may be a plate-like structure, with the first portion 210 covering the open side of the second portion 220 so that the first portion 210 and the second portion 220 together define the receiving space; alternatively, the first portion 210 and the second portion 220 may both be hollow structures with one open side, with the open side of the first portion 210 covering the open side of the second portion 220. Of course, the housing 200 formed by the first portion 210 and the second portion 220 may be of various shapes, such as a cylinder, a cuboid, etc.

[0138] In battery 1000, there can be multiple battery cells 100, which can be connected in series, parallel, or in a mixed manner. A mixed connection means that multiple battery cells 100 are connected in both series and parallel configurations. Multiple battery cells 100 can be directly connected in series, parallel, or in a mixed manner, and then the entire assembly of the multiple battery cells 100 is housed within housing 200. Alternatively, battery 1000 can also be composed of multiple battery cells 100 first connected in series, parallel, or in a mixed manner to form battery modules, and then these modules are connected in series, parallel, or in a mixed manner to form a whole, which is also housed within housing 200. Battery 1000 may also include other structures; for example, it may include a busbar component for electrical connection between the multiple battery cells 100.

[0139] battery cell

[0140] This application discloses a battery cell in some embodiments, the battery cell including a positive electrode and a negative electrode; the positive electrode includes a positive current collector and a positive electrode film layer located on at least one side surface of the positive current collector; the positive electrode film layer includes a first surface away from the positive current collector and a second surface disposed opposite to the first surface; the distance between the first surface and the second surface is H; the region formed along the stacking direction of the electrode from the second surface of the positive electrode film layer to a position of 0.1×H is denoted as the first region of the positive electrode film layer, the first region including a first positive electrode active material, the first positive electrode active material including lithium nickel transition metal oxide;

[0141] The region formed extending from the first surface of the aforementioned positive electrode film to a position of 0.1×H is referred to as the second region of the aforementioned positive electrode film. The second region includes a second positive electrode active material and carbon nanotubes. The second positive electrode active material includes lithium phosphate.

[0142] The positive electrode, separator, and negative electrode of this application can be formed into a secondary battery using a winding or stacking process. Specifically, Figure 5 illustrates a stacking method used to form a secondary battery 10. As shown in Figure 5, a negative electrode 1 or a positive electrode 2 is placed between two adjacent separators 3, and the negative electrode 1 and positive electrode 2 are alternately arranged along the stacking direction (x-axis). The number and size of the negative electrode 1 and / or positive electrode 2 can be selected according to actual conditions, and will not be elaborated upon in this application. Furthermore, Figure 5 only illustrates one stacking method; other stacking or winding methods are within the scope of protection of this application.

[0143] As shown in Figure 6, the positive electrode 2 includes a positive current collector 21 and a positive electrode film layer 22 located on at least one surface of the positive current collector 21. Figure 6 illustrates that the positive electrode film layer 22 is disposed on either side of the positive current collector 21, but the positive electrode film layer 22 can also be located on both sides of the positive current collector 21. The positive electrode film layer 22 is formed on the surface of the positive current collector 21 in any manner conventional in the art, such as coating, deposition, etc.

[0144] Figure 6 also illustrates the first surface 22a and the second surface 22b of the positive electrode film 22. The distance between the first surface 22a and the second surface 22b is H, which is the thickness of the positive electrode film 22 on one side of the positive electrode current collector. The measurement of this value H includes any method conventional in the art. In this application, it is measured using a micrometer or a scanning electron microscope.

[0145] To more conveniently describe the characteristics of different regions in the positive electrode film, this application designates the region extending from the second surface 22b of the positive electrode film 22 to a position of 0.1×H along the electrode stacking direction as the first region 22A of the positive electrode film 22; and the region extending from the first surface 22a of the positive electrode film 22 to a position of 0.1×H along the electrode stacking direction as the second region 22B of the positive electrode film 22. The electrode stacking direction also refers to the thickness direction of the electrode. Figure 6 illustrates the x-axis direction, where the positive electrode film region closer to the positive current collector is defined as the first region, and the positive electrode film region farther from the positive current collector is defined as the second region. The 0.1×H position given here is merely for illustrative purposes and its actual numerical range has no explicit meaning.

[0146] Figure 7 illustrates that the positive electrode film layer 22 includes a first sub-positive electrode film layer 221 and a second sub-positive electrode film layer 222. The positive electrode film layer 22 includes a first surface 22a and a second surface 22b. The distance between the first surface 22a and the second surface 22b is H, which means that the thickness of the positive electrode film layer 22 on one side of the positive current collector is H. The measurement of this value H can be done in any way conventional in the art. In this application, it is measured using a micrometer or a scanning electron microscope.

[0147] The first region of this application includes a lithium nickel transition metal oxide, and the second region includes a lithium phosphate. During charging and discharging, the electronic structure and chemical valence of the transition metal elements in the lithium nickel transition metal oxide, especially the lithium nickel manganese transition metal oxide, are prone to change, leading to instability in the material's crystal structure and causing side reactions between the electrolyte and the lithium nickel transition metal oxide. This results in manganese dissolution, affecting the battery's cycle performance. This application places the lithium nickel transition metal oxide in the first region (i.e., the first region close to the current collector) away from the electrolyte, while designing a positive electrode film layer containing lithium phosphate in the second region away from the current collector. This design achieves high-energy battery cells while reducing the probability of side reactions between the lithium nickel transition metal oxide and the electrolyte, thereby improving the battery's cycle life. However, during battery charging and discharging, both the second region containing lithium phosphate and the first region containing lithium nickel transition metal oxide expand, with the second region containing lithium phosphate expanding more than the first region containing lithium nickel transition metal oxide. This is detrimental to the battery's cycle life. Based on this, this application also selects to add carbon nanotubes with one-dimensional tubular structures in the second region away from the current collector to linearly wind and bind the lithium phosphate in the region and increase the cohesive force between the materials in the second region, thereby reducing the electrode expansion at this location to alleviate the impact of electrode expansion on the battery cycle life.

[0148] The carbon nanotubes of this application refer to carbon allotropes, which are hollow tube structures with a diameter of up to several hundred nanometers formed by rolling single or multiple layers of graphene sheets at a certain helical angle. The tube wall of the hollow tube structure includes one or more cylindrical layers of carbon atoms. The microstructure of carbon nanotubes endows them with one-dimensional quantum effects, thus giving them excellent mechanical properties.

[0149] The carbon nanotubes in this application include any one or more of single-walled carbon nanotubes and multi-walled carbon nanotubes.

[0150] The single-walled carbon nanotubes of this application refer to a single cylindrical layer of carbon atoms, while the multi-walled carbon nanotubes of this application refer to two or more layers of carbon atoms connected by intermolecular forces, or a single layer of carbon atoms that is rolled around a hollow cylindrical core several times.

[0151] The lithium-containing phosphate and carbon nanotubes in this application exhibit intermolecular forces. These intermolecular forces, though weaker than intramolecular chemical bonds, play a crucial role in the physical properties of the material. Examples include van der Waals forces. These forces facilitate the attachment of carbon nanotubes to the surface of the lithium-containing phosphate and weaken the interactions between adjacent carbon nanotubes, thereby increasing the uniformity of carbon nanotube dispersion within the lithium-containing phosphate.

[0152] In some embodiments, this application discloses a method for determining that a first region near the positive electrode current collector includes a lithium nickel transition metal oxide and a second region away from the positive electrode current collector includes a lithium phosphate material. The specific steps are as follows:

[0153] 1. In this application, the battery cell is placed in a 1.0 mol / L sodium hydroxide aqueous solution at room temperature for discharge treatment. After discharge, the positive electrode is manually disassembled to obtain the positive electrode sheet. The positive electrode sheet is cut into 6 mm × 6 mm pieces, and the cross-section of the positive electrode sheet is prepared using a cross-section polisher (e.g., JEOL IB-09010CP argon ion cross-section polisher). Then, referring to JY / T010-1996, the longitudinal cross-section of the positive electrode sheet is scanned using a scanning electron microscope (e.g., ZEISS Sigma 300 scanning electron microscope). The thickness of the positive electrode film layer of the positive electrode sheet is measured to be H.

[0154] 2. Using cryo-focused ion beam (FIB) combined with energy-dispersive spectroscopy (EDS) (e.g., the Aquilos 2Cryo-FIB cryo-focused ion beam microscope from Thermo Fisher Scientific), fine slices were made layer by layer at different thicknesses of the positive electrode sheet (the smallest slices could be nanometers in size). The region extending from the upper surface of the positive electrode film (away from the current collector) to a position of 0.1×H was designated as the second region of the positive electrode film, and the region extending from the lower surface of the positive electrode film (near the current collector) to a position of 0.1×H was designated as the first region of the positive electrode film. Five samples were obtained from each of the first and second regions along the thickness direction. Elemental analysis of each sample was performed using energy-dispersive spectroscopy (EDS) to determine that the first region near the positive current collector contained lithium nickel transition metal oxide, and the second region away from the positive current collector contained lithium phosphate material.

[0155] This application selects to add carbon nanotubes with a one-dimensional tubular structure in a second region far from the current collector to linearly wind and bind the lithium phosphate in that region. By reducing the electrode expansion at this location, the impact of electrode expansion on the battery cycle life can be alleviated. At the same time, compared with using carbon nanotubes to alleviate the expansion of lithium nickel transition metal oxides, this application uses carbon nanotubes with binding effect to alleviate the expansion of lithium phosphate, which has a more obvious effect on improving the expansion of the entire positive electrode film or the battery cell, and a more obvious improvement on the cycle life of the battery cell.

[0156] In some embodiments, the average tube length of the second carbon nanotube is greater than or equal to 10 μm. In this application, the average tube length of the second carbon nanotube is greater than or equal to 10 μm. On the one hand, carbon nanotubes with this average tube length have a linear structure, facilitating attachment and entanglement on the surface of lithium-nickel transition metal oxides. On the other hand, carbon nanotubes with this average tube length also possess relatively better mechanical properties. For example, during battery charging and discharging, when the positive electrode active material undergoes volume expansion, the carbon nanotubes entangle and bind the positive electrode active material, increasing the cohesive force between the positive electrode active materials and reducing the degree of expansion.

[0157] The carbon nanotubes of this application possess a one-dimensional tubular structure, which includes structures in two dimensions, wherein the diameter of the one-dimensional tubular structure is at the nanometer level. The length of the one-dimensional tubular structure refers to the distance between one end and the other end of the tubular structure. The length of the one-dimensional tubular structure can be measured using any method commonly used in the art, such as obtaining the length by photographing the carbon nanotubes using a scanning electron microscope or a scanning transmission electron microscope.

[0158] This application discloses a method for determining the length of carbon nanotubes in some embodiments, as follows:

[0159] Sampling was performed according to the above method: In this application, the battery cell was placed in a 1.0 mol / L sodium hydroxide aqueous solution at room temperature for discharge treatment. After discharge, the positive electrode was manually disassembled to obtain the positive electrode sheet. The positive electrode sheet was cut into 6 mm × 6 mm pieces, and the cross-section of the positive electrode sheet was prepared using a cross-section polisher (e.g., JEOL IB-09010CP argon ion cross-section polisher). Then, referring to JY / T010-1996, the longitudinal cross-section of the positive electrode sheet was scanned using a scanning electron microscope (e.g., ZEISS Sigma 300 scanning electron microscope). The thickness of the positive electrode film layer of the positive electrode sheet was measured to be H.

[0160] Cryo-focused ion beam (FIB) microscopy (e.g., the Aquilos 2Cryo-FIB cryo-focused ion beam microscope from Thermo Fisher Scientific) was used to perform fine slicing of the positive electrode sheet at different thicknesses (down to the nanometer scale). The region extending from the upper surface of the positive electrode film (away from the current collector) to a position of 0.1×H is designated as the second region of the positive electrode film, and the region extending from the lower surface of the positive electrode film (closer to the current collector) to a position of 0.1×H is designated as the first region. Five samples were obtained from each of the first and second regions along the thickness direction. This application further discloses the measurement of the five samples from the first region and the five samples from the second region to determine the location and average length of the carbon nanotubes. The specific steps are as follows:

[0161] 1. Following the above method, the first region and the second region were cut to obtain 5 samples each;

[0162] 2. Use a scanning electron microscope (e.g., the Sigma 300 scanning electron microscope from ZEISS, Germany) to scan the above samples and observe whether there are one-dimensional tubular carbon nanotubes in the field of view. If not, continuously adjust the position of the sample in the field of view until one-dimensional tubular carbon nanotubes are observed.

[0163] 3. After observing the one-dimensional tubular structure of carbon nanotubes, adjust the magnification of the scanning electron microscope to 30K / 40K, select 20-50 carbon nanotubes in the field of view, measure their length using the scanning electron microscope and perform length statistics. The average length is the average length (μm) of the carbon nanotube.

[0164] In some embodiments, the average length of the second carbon nanotube is 10 μm to 40 μm.

[0165] The definition and measurement method of the average tube length of carbon nanotubes in this application are the same as those described above, and will not be elaborated further here.

[0166] The longer the carbon nanotubes in this application are, the easier it is for them to attach to, entangle, and bind the positive electrode active material, thereby further improving the cohesive force between the positive electrode active materials. However, it is not easy to achieve good dispersion of carbon nanotubes during the preparation process. Therefore, this application ultimately chose to design and use a second carbon nanotube with an average tube length of 10 μm to 40 μm in the second region.

[0167] In these embodiments, this application discloses that the average tube length of the second carbon nanotube is any one of 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, 21 μm, 22 μm, 23 μm, 24 μm, 25 μm, 26 μm, 27 μm, 28 μm, 29 μm, 30 μm, 31 μm, 32 μm, 33 μm, 34 μm, 35 μm, 36 μm, 37 μm, 38 μm, 39 μm, and 40 μm, or any one of the ranges of both above.

[0168] In some embodiments, the average diameter of the second carbon nanotube is 1 nm to 20 nm.

[0169] The diameter of the carbon nanotubes in this application refers to the outer diameter of the carbon nanotubes. As mentioned above, a carbon nanotube is a hollow tube structure with a diameter of up to several hundred nanometers formed by rolling single or multiple layers of graphene sheets at a certain helical angle. The measurement method for the diameter of the second carbon nanotube includes any method conventional in the art. Specifically, it can be measured using a similar method when measuring the length of the carbon nanotube. As mentioned above, after obtaining samples of different layers at different thickness positions of the positive electrode sheet using cryo-focused ion beam (FIB), these samples are placed in a transmission electron microscope (e.g., a Hitachi HT7800 transmission electron microscope). The magnification of the instrument is adjusted to 100K. 20 to 50 carbon nanotubes are selected in the field of view, and the tube diameter is statistically analyzed. The average tube diameter is taken as the average diameter (nm) of the carbon nanotubes.

[0170] The average diameter of the second carbon nanotube in this application is within the above-mentioned range, which facilitates the attachment and winding of the second carbon nanotube onto the surface of the lithium phosphate material and further enhances the winding and binding of the lithium phosphate material.

[0171] In these embodiments, this application discloses that the average diameter of the second carbon nanotube is any one of 1nm, 2nm, 3nm, 4nm, 5nm, 6nm, 7nm, 8nm, 9nm, 10nm, 11nm, 12nm, 13nm, 14nm, 15nm, 16nm, 17nm, 18nm, 19nm, 20nm or any one of the above ranges.

[0172] In some embodiments, based on the mass of the second region, the mass percentage content of the second carbon nanotube in the second region is 0.05% to 2%.

[0173] The carbon nanotubes of this application not only exert mechanical properties in the positive electrode film layer, but can also act as a conductive agent to partially or completely replace other types of conductive agents. Therefore, in the second region, controlling the content of the second carbon nanotubes within a certain range is beneficial to exert both of the above-mentioned properties.

[0174] In these embodiments, this application discloses that the mass percentage content of the second carbon nanotube in the second region is any one of 0.05%, 0.08%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.5%, 2.0%, or any one of the ranges of both above.

[0175] In some embodiments, the positive electrode film layer further comprises one or more of dot-shaped conductive agents and surface-shaped conductive agents.

[0176] The carbon nanotubes of this application are used to entangle and bind the positive electrode active material in the positive electrode film. At the same time, the carbon nanotubes themselves have excellent conductivity and can also be used as a conductive agent in the positive electrode film. A conductive agent is a substance with conductivity that plays a role in collecting microcurrents between positive electrode active materials and between positive electrode active materials and positive electrode current collectors, so as to reduce the contact resistance of the electrode and accelerate the movement rate of electrons.

[0177] The positive electrode film layer of this application also contains other types of conductive agents. These conductive agents, together with carbon nanotubes, form a conductive network, which helps to improve the uniformity of conductivity of the entire positive electrode sheet, reduce the polarization degree of the positive electrode sheet, and further improve the cycle life of the battery. In these embodiments, this application discloses that the other types of conductive agents include one or more of dot-like conductive agents and planar conductive agents. Specifically, the dot-like conductive agents include one or more of graphite, carbon black, and carbon dots, while the planar conductive agents include graphene.

[0178] The carbon black in this application refers to an industrial product whose main component is elemental carbon, and contains small amounts of oxygen, hydrogen and sulfur.

[0179] The graphene in this application refers to graphene made from sp 2 A planar sheet, one atom thick, composed of bonded carbon atoms, where the carbon atoms are tightly stacked in a honeycomb lattice.

[0180] This application discloses, in some embodiments, conductive agents including carbon black, graphene, and carbon nanotubes. Carbon black primarily functions as a dot-like conductive agent, graphene as a sheet-like conductive agent, and carbon nanotubes as a one-dimensional tubular conductive agent. This facilitates the formation of a conductive network with point, line, and surface structures, thereby improving the conductivity of the conductive agent. Therefore, the conductive agent of this application can exhibit good conductivity with relatively small usage amounts, which helps improve the uniformity of conductivity across the entire positive electrode sheet, reduces the polarization of the positive electrode sheet, and further improves the cycle life of the battery. In some embodiments, this application discloses that the specific surface area of ​​the carbon black is >100 m². 2 / g to further enhance good conductivity.

[0181] The method for determining the specific surface area in this application includes any conventional method in the art, such as the nitrogen adsorption specific surface area analysis method according to GB / T19587-2004, and the calculation of the specific surface area of ​​the porous carbon material using the BET (Brunauer Emmett Teller) method. The testing instrument can be a TRISTAR II 3020 specific surface area and porosity analyzer from Micromeritics, USA.

[0182] This application discloses in these embodiments that the specific surface area of ​​the carbon black is 300 m². 2 / g~3000m2 / g.

[0183] In these embodiments, this application discloses that the specific surface area of ​​the carbon black is 100 m². 2 / g、200m 2 / g、300m 2 / g、381m 2 / g、400m 2 / g、500m 2 / g、600m 2 / g、700m 2 / g、800m 2 / g、900m 2 / g, 1000m 2 / g、1200m 2 / g, 1400m 2 / g, 1600m 2 / g、1800m 2 / g、2000m 2 / g、2200m 2 / g、2400m 2 / g、2600m 2 / g、2800m 2 / g、3000m 2 Either / g or either of the values ​​within the range of the above two.

[0184] In some embodiments, this application discloses that the second region of the positive electrode film contains carbon nanotubes, while the first region does not contain carbon nanotubes. This design reduces the expansion of the positive electrode active material in the second region by utilizing the mechanical properties of carbon nanotubes, thereby further improving the cycle life of the battery.

[0185] In some embodiments, this application also discloses that the second region of the positive electrode film contains a second carbon nanotube, and the first region contains a first carbon nanotube. The second carbon nanotube in the second region may be the same as or different from the first carbon nanotube in the first region. This design not only reduces the expansion of the positive electrode active material in the second region but also reduces the expansion of the positive electrode active material in the first region, thereby improving the cycle life of the battery.

[0186] Specifically, in some embodiments, the first region includes a first carbon nanotube attached to the surface of the lithium nickel transition metal oxide; the second region includes a second carbon nanotube attached to the surface of the lithium phosphate.

[0187] This application uses "first" and "second" to distinguish carbon nanotubes. In fact, the first carbon nanotube and the second carbon nanotube can be the same type of carbon nanotube and meet the above-mentioned numerical ranges for average tube length, tube diameter and content.

[0188] In some embodiments, the first carbon nanotube and the second carbon nanotube satisfy one or more of the following conditions:

[0189] (1) The average tube length of the first carbon nanotube is L1, and the average tube length of the second carbon nanotube is L2, where L1≤L2;

[0190] (2) The average diameter of the first carbon nanotube is D1, and the average diameter of the second carbon nanotube is D2, where D1 ≥ D2.

[0191] (3) The mass percentage content of the first carbon nanotube in the first region is W1; the mass percentage content of the second carbon nanotube in the second region is W2; W1≤W2.

[0192] In some embodiments of this application, different types of carbon nanotubes are selected to be used in the first and second regions of the positive electrode film to match different types of active materials and to better reduce the expansion of the electrode.

[0193] As mentioned above, the second region of the positive electrode film has a higher demand for carbon nanotubes than the first region. Therefore, this application selects to use different types of carbon nanotubes in the first and second regions of the positive electrode film.

[0194] In some embodiments, the first carbon nanotube and the second carbon nanotube satisfy one or more of the following properties:

[0195] (1) The average tube length L1 of the first carbon nanotube is 10μm to 15μm, and the average tube length L2 of the second carbon nanotube is greater than 15μm and less than or equal to 40μm.

[0196] (2) The average diameter D1 of the first carbon nanotube is greater than 2nm and less than or equal to 20nm, and the average diameter D2 of the second carbon nanotube is 1nm to 2nm.

[0197] (3) The mass percentage content W1 of the first carbon nanotube in the first region is 0.05% to 1.0%; the mass percentage content W2 of the second carbon nanotube in the second region is 0.1% to 2.0%.

[0198] This application provides specific parameters for the carbon nanotubes used in the first region and the second region in some embodiments.

[0199] The average length of the first carbon nanotube used in the first region of this application may be any one of 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm or any one of the above two ranges.

[0200] The average diameter of the first carbon nanotube used in the first region of this application may be any one of 2.5nm, 3nm, 4nm, 5nm, 6nm, 7nm, 8nm, 9nm, 10nm, 11nm, 12nm, 13nm, 14nm, 15nm, 16nm, 17nm, 18nm, 19nm, 20nm or any one of the above ranges.

[0201] The mass percentage content of the first carbon nanotubes used in the first region of this application may be any one of 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0% or any one of the above ranges.

[0202] The average length of the second carbon nanotube used in the second region of this application can be any one of 15μm, 16μm, 17μm, 18μm, 19μm, 20μm or any one of the above two ranges.

[0203] The average diameter of the second carbon nanotube used in the second region of this application can be any one of 1 nm, 1.5 nm, 2.0 nm, or any one of the above two ranges.

[0204] The mass percentage content of the second carbon nanotubes used in the second region of this application may be any one of 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.5%, 2.0%, or any one of the above ranges.

[0205] In some embodiments, the chemical formula of the above-mentioned lithium-nickel transition metal oxide is Li x N t (Ni a Co b M c ) 1-d M' d O 2-y A y ;

[0206] N represents a lithium-site doping element, which includes any one or more of Zn, Al, Na, K, Mg, Nb, Mo, and W;

[0207] M includes any one or more of Mn and Al;

[0208] M' includes any one or more of Zr, Sr, B, Ti, Mg, Sn, and Al;

[0209] A represents an oxygen-doped element, which includes any one or more of S, N, B, F, Cl, Br, and I;

[0210] x ranges from 0.2 to 1.2;

[0211] t is 0 to 0.1;

[0212] a ranges from 0.001 to 0.999;

[0213] b is 0.001 to 0.999;

[0214] a+b+c=1,

[0215] 0 ≤ d ≤ 0.1;

[0216] 0 ≤ y < 0.2.

[0217] The lithium-site doping element in this application refers to an external element that is introduced into the crystal lattice of lithium nickel transition oxide and occupies a lithium-ion position, which is beneficial to improving the structural stability of lithium nickel transition oxide.

[0218] The oxygen-doped element in this application refers to an external element that is introduced into the lattice of lithium nickel transition oxide and occupies the oxygen ion position, which is also beneficial to improving the structural stability of lithium nickel transition oxide.

[0219] In these embodiments, this application discloses that x is any one of 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2 or any one of the ranges of both above.

[0220] In these embodiments, this application discloses that t is any one of 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1 or any one of the ranges of both above.

[0221] This application discloses in these embodiments that 'a' is 0.001, 0.002, 0.003, 0.004, 0.005, 0.006, 0.007, 0.008, 0.009, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.2, 0.3, 0.4, 0.5, 0 0.6, 0.7, 0.8, 0.9, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, 0.991, 0.992, 0.993, 0.994, 0.995, 0.996, 0.997, 0.998, 0.999, or any one of the above ranges.

[0222] This application discloses in these embodiments that b is 0.001, 0.002, 0.003, 0.004, 0.005, 0.006, 0.007, 0.008, 0.009, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.2, 0.3, 0.4, 0.5, 0 0.6, 0.7, 0.8, 0.9, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, 0.991, 0.992, 0.993, 0.994, 0.995, 0.996, 0.997, 0.998, 0.999, or any one of the above ranges.

[0223] In these embodiments, this application discloses that d is any one of 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1 or any one of the ranges of both above.

[0224] In these embodiments, this application discloses that y is any one of 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, 0.18, 0.19 or any one of the ranges of both above.

[0225] In some embodiments, 'a' is any one of 0.001 to 0.7 or any one of both ranges. In some embodiments, based on the total moles of transition metals other than lithium in the lithium-nickel transition metal oxide, the nickel content Y in the lithium-nickel transition metal oxide satisfies: Y = a × 100%; Y ≤ 70%.

[0226] In some embodiments of this application, lithium nickel transition metal oxide with relatively low nickel content is selected. On the one hand, this further reduces the side reactions between it and the electrolyte. On the other hand, it is beneficial to use it in combination with carbon nanotubes to further reduce the expansion force of the positive electrode active material itself.

[0227] In these embodiments, this application discloses that, based on the total molar number of transition metals other than lithium in the lithium-nickel transition metal oxide described above, the nickel content Y in the lithium-nickel transition oxide of the first region is any one or more of 70%, 65%, 60%, 50%, 40%, etc.

[0228] In some embodiments, the chemical formula of the above-mentioned lithium phosphate is Li e Fe 1-y’ M” y’ P 1-m’ C m’ O 4-n’ D n’ ;

[0229] Wherein, M” represents the doping element of the iron site, and the doping element of the iron site includes any one or more of Cr, Mg, Ti, Al, Zn, W, Nb and Zr.

[0230] C represents the doping element at the phosphorus site, and the doping element at the phosphorus site includes any one or more of B, S, Si and N.

[0231] D represents the doping element at the oxygen site, and the doping element at the oxygen site includes any one or more of S, F, Cl and Br.

[0232] 0 < e ≤ 1.1;

[0233] 0≤y'<1;

[0234] 0≤m'≤0.1;

[0235] 0≤n'≤0.4.

[0236] The iron-doped element in this application refers to an external element that is introduced into the lattice of lithium phosphate and occupies the iron ion position, which is beneficial to improving the structural stability of lithium phosphate.

[0237] The phosphorus doping element in this application refers to an external element that is introduced into the lattice of lithium phosphate to occupy phosphorus ion positions, which is beneficial to improving the structural stability of lithium phosphate.

[0238] The oxygen-doped element in this application refers to an external element that is introduced into the lattice of lithium phosphate and occupies the oxygen ion position, which is beneficial to improving the structural stability of lithium phosphate.

[0239] The doping elements in the lithium phosphate contained in this application also help to improve the conductivity of the lithium phosphate, thereby synergistically exerting better conductivity together with the carbon nanotube unit.

[0240] In these embodiments, this application discloses that e is any one of 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1 or any one of the ranges of both.

[0241] In these embodiments, this application discloses that y' is any one of 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99 or any one of the above range values.

[0242] In these embodiments, this application discloses that m' is any one of 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1 or any one of the above range values.

[0243] In these embodiments, this application discloses that n' is any one of 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.2, 0.3, 0.4 or any one of the above range values.

[0244] All of the aforementioned positive electrode active materials described in this application can be purchased through commercial channels, and the elemental composition of the purchased products is already indicated. Furthermore, the components of the positive electrode active materials of this application can also be detected by commonly used chemical analysis methods in the art, including but not limited to: complexation titration, precipitation gravimetric method, redox method, differential method, inductively coupled plasma atomic emission spectrometry (ICP-AES), and atomic absorption spectrometry. Among these, ICP-AES and atomic absorption spectrometry are convenient and efficient, and their mechanisms are as follows:

[0245] Plasma emission spectroscopy is an analytical method that uses a high-temperature excitation source generated by plasma as the excitation source for atomic emission spectra. Different elements produce different characteristic spectra. These characteristic spectra are projected onto a grating in a spectrometer through a lens. By controlling a motor to rotate the grating, a transmission mechanism accurately positions the intensity of the characteristic spectral lines of the element to be measured at the exit slit after spectral dispersion. A photomultiplier tube converts this spectral intensity into an electric current. After further circuit processing and conversion, the data is processed by a computer to obtain the analytical results.

[0246] Atomic absorption spectrometry (AAS), also known as atomic absorption spectrophotometry, is an analytical method based on the absorption of characteristic radiation (spectral lines) emitted by atomic vapors of the same type of atom. The analytical process involves irradiating the sample solution with atomized and atomized atomic vapors of the sample solution using characteristic radiation emitted by the same type of atom. The gaseous ground-state atoms of the analyte in the vapor absorb the characteristic radiation lines emitted from the light source. Different elements exhibit selective absorption of these characteristic radiation lines, and the concentration of the analyte in the sample is determined by the degree of radiation attenuation.

[0247] In some embodiments, the median particle size Dv50 of the above-mentioned lithium nickel transition metal oxide is 2 μm to 6 μm.

[0248] In some embodiments, the median particle size Dv50 of the lithium phosphate-containing material is 0.5 μm to 2.2 μm.

[0249] The particle size determination method for the positive electrode active material in this application includes the following steps:

[0250] 1. In this application, the battery cell is placed in a 1.0 mol / L sodium hydroxide aqueous solution at room temperature for discharge treatment. After the discharge is completed, the positive electrode is manually disassembled to obtain the positive electrode sheet. The longitudinal cross-sectional image of the positive electrode sheet is scanned using a scanning electron microscope (e.g., a Sigma 300 scanning electron microscope from ZEISS, Germany) to measure the thickness of the positive electrode film layer of the positive electrode sheet as H.

[0251] The positive electrode sheet was finely sliced ​​layer by layer at different thicknesses using a cryo-focused ion beam (FIB) microscope (e.g., the Aquilos 2Cryo-FIB cryo-focused ion beam microscope from Thermo Fisher Scientific). Different layers of samples were obtained along different thicknesses. The region extending from the upper surface of the positive electrode film (away from the current collector) to the 0.1×H position was designated as the second region of the positive electrode film, and the region extending from the lower surface of the positive electrode film (close to the current collector) to the 0.1×H position was designated as the first region of the positive electrode film. Five samples were obtained by cutting the first and second regions respectively.

[0252] 2. Place each of the above samples into a mixture of water and ethanol (volume ratio of water to ethanol is 10:1), wherein the mass ratio of each positive electrode film sample to the volume of the above mixture (g / ml) is 1:30. Control the temperature of the mixture to be about 40℃, control the stirring speed to be 250r / min, and stir for half an hour.

[0253] After stopping stirring, the above mixture is sieved using a sieve with a pore size of 6m to 10mm to obtain the undersize, which contains positive electrode active material. The undersize is heated to 70℃ to 90℃ and then filtered. The temperature is maintained at 70℃ to 90℃ during the filtration process. After filtration, the filter residue is placed in a crucible as a sample and placed in an electric thermostatic drying oven (e.g., Yijie Technology, model 101-0ES). The temperature of the electric thermostatic drying oven is controlled at about 400℃. The samples are dried until the total mass of the crucible and the sample remains unchanged. The resulting samples are positive electrode active material samples from the first region near the positive electrode current collector and positive electrode active material samples from the second region far away from the positive electrode current collector.

[0254] In this application, the term "Dv50" refers to the particle size at which the cumulative volume distribution number of particles reaches 50% in the particle size distribution curve, and also refers to the median particle size.

[0255] In this application, after obtaining the positive electrode active material sample in the first region near the positive electrode current collector and the positive electrode active material sample in the second region far from the positive electrode current collector, the Dv50 of each positive electrode active material sample is determined using a laser particle size analyzer in accordance with GB / T19077-2016. The testing instrument can be a Mastersizer 3000 laser particle size analyzer from Malvern Instruments Ltd., UK.

[0256] In these embodiments, this application discloses that the median particle size Dv50 of the lithium nickel transition metal oxide is any one of 2 μm, 3 μm, 4 μm, 5 μm, 6 μm or any one of the above two ranges.

[0257] In these embodiments, this application discloses that the median particle size Dv50 of the lithium phosphate is any one of 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1.0 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.7 μm, 1.8 μm, 1.9 μm, 2.0 μm, 2.1 μm, and 2.2 μm, or any one of the above two ranges.

[0258] This application selects a positive electrode active material with a suitable particle size, which can both control the contact area with the electrolyte and allow the positive electrode active material to be well bound by carbon nanotubes.

[0259] In some embodiments, a carbon coating layer is formed on the surface of the lithium phosphate, and the thickness of the carbon coating layer is 5 nm to 100 nm.

[0260] This application selects to form a carbon coating layer on the surface of lithium phosphate, wherein the carbon coating layer can be formed completely or partially on the surface of lithium phosphate. This carbon coating layer can increase the contact area with the electrode material, reduce resistance, thereby improving battery performance, and can also inhibit the dissolution of the positive electrode active material and the peeling off of the structure, thus extending the cycle life of the battery.

[0261] The method for measuring the carbon coating layer in this application includes obtaining transmission electron microscope images containing lithium phosphate, and then measuring them.

[0262] In these embodiments, this application discloses that the thickness of the carbon coating layer formed on the surface of the lithium phosphate is any one of 5nm, 10nm, 15nm, 20nm, 25nm, 30nm, 35nm, 40nm, 45nm, 50nm, 55nm, 60nm, 65nm, 70nm, 75nm, 80nm, 85nm, 90nm, 95nm, and 100nm, or any one of the above two ranges.

[0263] In some embodiments, the compaction density of the above-mentioned positive electrode film is 1.5 g / cm³. 3 ~2.4g / cm 3 .

[0264] The compaction density of the positive electrode film layer in this application can be used to characterize the energy density of the material. The compaction density of the positive electrode film layer = the areal density of the positive electrode film layer / the thickness of the positive electrode film layer. The thickness of the positive electrode film layer includes the distance between the two end faces of the positive electrode film layer along the thickness direction. The areal density of the positive electrode film layer = the weight of a single-sided positive electrode film layer / the area of ​​a single-sided positive electrode film layer. The weight of a single-sided positive electrode film layer can be obtained by weighing, and the area of ​​a single-sided positive electrode film layer can be obtained by using the area calculation formula according to the shape of the film layer. The test method for the compaction density of the positive electrode film layer is given in the test method of the following specific embodiments of this application, and will not be repeated here.

[0265] In these embodiments, this application discloses that the compaction density of the positive electrode film is 1.5 g / cm³. 3 1.8g / cm 3 1.9g / cm 3 2.0g / cm 3 2.1g / cm 3 2.2g / cm 3 2.3g / cm 3 2.4g / cm 3 It can be any one of the above or any one of the range values ​​of any two of the above.

[0266] The cohesive force of the positive electrode film layer described in this application is 150 N / m to 450 N / m.

[0267] The cohesive force of the positive electrode film in this application refers to the bonding force between the material components in the positive electrode film. The magnitude of this cohesive force can be measured by any conventional measurement method in the art, such as by using a tensile testing machine.

[0268] The cohesive force of the positive electrode film layer described in this application is 150 N / m to 450 N / m, which indicates that the positive electrode active material in the positive electrode film layer has a strong bonding force with other auxiliary materials.

[0269] The positive electrode film layer of this application satisfies the above-mentioned cohesive force, thus reducing the degree of electrode expansion.

[0270] In some embodiments, the thickness of the positive electrode film layer of the battery cell in its initial state is h1; the initial state here refers to the battery cell after assembly and before use, or it can refer to the thickness after cold pressing during the preparation of the positive electrode sheet. Since the thickness of the positive electrode film layer changes only to a limited extent before assembly and before use, this application ignores the thickness changes after cold pressing and assembly.

[0271] The above-mentioned battery cell was charged to 3.8V at a constant current of 0.33C at 25°C, and then discharged to 2.0V at a constant current of 0.33C. This was recorded as one cycle. After 500 cycles under this charge and discharge condition, the thickness of the positive electrode film was h2.

[0272] The expansion rate of the above positive electrode film is S = (h2-h1) / h1×100%, and S≤7%.

[0273] As shown in Figure 8, along the stacking direction of the electrode sheets (x-axis direction), in the initial state, the positive electrode film layer 22 of the battery cell has a first surface 22a and a second surface 22b with opposite surfaces, and the distance between the first surface 22a and the second surface 22b is h1. After the battery cell is charged and discharged 500 times at 25°C under the above conditions, the positive electrode sheet 2 has a certain expansion. At this time, the positive electrode film layer 22 has a second surface 22b and a third surface 22a' with opposite surfaces, and the distance between the second surface 22b and the third surface 22a' is h2. According to the calculation formula W=(h2-h1) / h1×100%, the expansion rate S of the positive electrode film layer is calculated to be ≤7%.

[0274] When carbon nanotubes are not added to the second region of the positive electrode film, the expansion rate of the positive electrode film is greater than 7%. Compared with the existing methods, the design method provided in this application is beneficial to reducing the expansion rate of the positive electrode sheet.

[0275] The measurement methods for the distance h1 between the first surface 22a and the second surface 22b and the distance h2 between the second surface 22b and the third surface 22a' mentioned above in this application include any conventional method in the art, such as scanning the positive electrode film layer with a scanning electron microscope to obtain the distance values.

[0276] In some embodiments, the positive electrode film layer includes an adhesive;

[0277] The adhesive includes acrylic-based polymers;

[0278] The propylene-based polymer includes any one or more of the following: structural units derived from acrylic monomers, structural units derived from acrylamide monomers, structural units derived from acrylonitrile monomers, and structural units derived from acrylate monomers.

[0279] In some embodiments, the mass percentage content of the propylene-based polymer is 1% to 3% based on the mass of the positive electrode film.

[0280] The binder in this application refers to a chemical compound, polymer, or mixture that forms a colloidal solution or colloidal slurry in a dispersion medium.

[0281] The term "polymer" in this application refers to an aggregate of chemically homogeneous macromolecules prepared by polymerization reactions, but differing in degree of polymerization, molar mass, and chain length. This term also includes derivatives of such aggregates of macromolecules formed by polymerization reactions, i.e., compounds that can be obtained through reactions of the functional groups in the aforementioned macromolecules, such as addition or substitution, and which may be chemically homogeneous or chemically heterogeneous.

[0282] In some embodiments, the propylene-based polymers of this application include propylene-based copolymers. The copolymers of this application refer to polymerization reactions in which two or more monomers participate, called copolymerization. The polymers formed contain two or more monomer units. Such polymers are called copolymers, also known as copolymers.

[0283] The propylene-based copolymers disclosed in these embodiments are primarily linear binders, which, together with the aforementioned carbon nanotubes, facilitate better binding of the positive electrode active material.

[0284] In these embodiments, this application discloses that the acrylic monomers include one or more of acrylic acid, methacrylic acid, and ethylacrylic acid.

[0285] In these embodiments, this application discloses acrylamide monomers including any one or more of acrylamide, methacrylamide, N-hydroxymethylacrylamide, diacetone acrylamide, N,N-dimethylacrylamide, and N,N-methylenediacrylamide.

[0286] This application discloses in these embodiments that acrylonitrile monomers include any one or more of acrylonitrile, methacrylonitrile, and ethyl acrylonitrile.

[0287] In these embodiments, this application discloses acrylate monomers including any one or more of methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, sec-butyl acrylate, tert-butyl acrylate, n-propyl acrylate, cyclohexyl acrylate, lauryl acrylate, 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, 2-ethylhexyl methacrylate, isobornyl methacrylate, lauryl methacrylate, 2-hydroxyethyl methacrylate, and 2-hydroxypropyl methacrylate.

[0288] In some embodiments, the propylene-based copolymer includes structural units derived from methacrylic acid monomers, structural units derived from N-hydroxymethylacrylamide monomers, structural units derived from acrylonitrile monomers, and structural units derived from n-butyl acrylate monomers. This application discloses in these embodiments that, based on the mass percentage of the propylene-based copolymer, the methacrylic acid monomer content is 20%, the N-hydroxymethylacrylamide monomer content is 35%, the acrylonitrile monomer content is 15%, and the n-butyl acrylate monomer content is 30%.

[0289] In these embodiments, this application discloses that the mass percentage content of propylene-based polymers (propylene-based copolymers) in the above-mentioned positive electrode film layer is any one of 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, and 3.0%, or any one of the above ranges.

[0290] In some embodiments, the battery cell further includes an electrolyte comprising an electrolyte salt and an organic solvent; the molar concentration of the electrolyte salt is ≥0.9 mol / L.

[0291] The use of an electrolyte salt with a molar concentration ≥0.9 mol / L in this application facilitates the formation of a denser and more stable solid electrolyte interphase (SEI) film on the surface of the negative electrode, further reducing side reactions between the negative electrode active material and the electrolyte. This design, when used in conjunction with the design of the positive electrode in this application, helps improve the cycle life of the battery.

[0292] [Positive electrode plate]

[0293] According to some embodiments of this application, as described above, the positive electrode sheet includes a positive current collector and a positive electrode film layer located on at least one side surface of the positive current collector. The positive electrode film layer contains a positive electrode active material.

[0294] The structure and composition of the positive electrode film in this application are as described above, and will not be repeated here.

[0295] In some embodiments of this application, in addition to the aforementioned positive electrode active material, conductive agent, and binder, the positive electrode film layer may also contain, but is not limited to, one or more combinations of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene ternary polymer, PVDF-hexafluoropropylene-tetrafluoroethylene ternary polymer, tetrafluoroethylene-hexafluoropropylene polymer, fluorinated acrylate resin, styrene-butadiene rubber, polyacrylic acid, sodium polyacrylate, polyacrylamide, polyvinyl alcohol, sodium alginate, polymethacrylic acid, and carboxymethyl chitosan. The conductive agent in this application includes one or more of dot-like conductive agents, planar conductive agents, and linear conductive agents. Specifically, the dot-like conductive agent includes one or more of graphite, carbon black, and carbon dots; the planar conductive agent includes graphene; and the linear conductive agent includes carbon fiber.

[0296] The method of forming the positive electrode film layer in this application includes mixing the above-mentioned raw materials with a solvent (such as N-methylpyrrolidone) in a certain mass ratio to form a positive electrode slurry, uniformly coating the positive electrode slurry on both sides of the positive electrode current collector, controlling the coating weight on one side, and after drying, compacting it to a certain compaction density using a cold press to obtain a positive electrode sheet containing the positive electrode film layer.

[0297] [Preparation method of positive electrode sheet]

[0298] According to some embodiments of this application, a method for preparing a positive electrode sheet is disclosed, comprising the following steps:

[0299] Preparation of the first positive electrode slurry: The first positive electrode active material is dispersed in a solvent and mixed to form the first positive electrode slurry;

[0300] Preparation of the second positive electrode slurry: The second positive electrode active material and the second carbon nanotube dispersion are dispersed in a solvent and mixed to form the second positive electrode slurry;

[0301] Preparation of positive electrode sheet: A first positive electrode slurry is coated on at least one side surface of the positive electrode current collector to obtain a first sub-positive electrode film layer, and a second positive electrode slurry is coated on the side surface of the first sub-positive electrode film layer away from the positive electrode current collector to form a second sub-positive electrode film layer;

[0302] Battery cell preparation: Assemble the negative electrode, positive electrode and separator together.

[0303] In some embodiments, the second carbon nanotube dispersion comprises a second carbon nanotube and a dispersant;

[0304] The above dispersant includes one or more of carboxymethyl cellulose and sodium carboxymethyl cellulose.

[0305] The carboxymethyl cellulose and / or sodium carboxymethyl cellulose of this application are mainly used for dispersing carbon nanotubes. Carboxymethyl cellulose refers to a linear polymer derivative of cellulose containing multiple dehydrated glucose units (β-linked pyranose residues), each glucose unit having three hydroxyl groups, with the hydrogen in the hydroxyl groups replaced by carboxymethyl groups. Because this linear polymer derivative contains ether or carboxyl groups, it readily combines with sodium ions to form sodium carboxymethyl cellulose.

[0306] In some embodiments, the mass ratio of the second carbon nanotube to the dispersant in the second carbon nanotube dispersion is 100:(50-250).

[0307] In these embodiments, this application discloses that the mass ratio of the second carbon nanotube to the above-mentioned dispersant is any one or more of 100:50, 100:100, 100:200, and 100:250.

[0308] In some embodiments, the solid content of the second carbon nanotube dispersion is 0.6% to 1.5%.

[0309] The solid content in this application refers to the mass percentage of solid components in a carbon nanotube dispersion, and the determination method includes any method conventional in the art. For specific determination methods in this application, please refer to DB13_T 5025.1-2019:

[0310] Weigh 2g of the dispersion sample into an empty weighing dish with constant mass, spread it evenly, and let its mass before drying be m1. Place the weighing dish containing the sample in an electric thermostatic drying oven at 120℃±2℃ for 3 hours. After cooling, obtain the total mass of the weighing dish and the sample after drying, m20. Place it again in an electric thermostatic drying oven at 120℃±2℃ for 30 minutes. After removing it, weigh m21. Repeat this operation until the difference between the last two weighings is no more than 0.0003g. When calculating, take the average of the last two weighings as m2. Then, the solid content = m2 / m1*100%.

[0311] The solvent in the cathode slurry or carbon nanotube dispersion of this application includes, but is not limited to, N-methylpyrrolidone.

[0312] In these embodiments, this application discloses that the solid content of the second carbon nanotube dispersion is any one of 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, and 1.5%, or any one of the ranges of both of the above.

[0313] In some embodiments, the second carbon nanotube dispersion further comprises a surfactant, which comprises one or more of glutamic acid surfactants and glycine surfactants.

[0314] The glutamic acid surfactants of this application refer to compounds whose anions contain glycine as a hydrophilic group and whose cationic groups contain C8-C20 alkyl groups. Similarly, the glycine surfactants of this application refer to compounds whose anions contain glycine as a hydrophilic group and whose cationic groups contain C8-C20 alkyl groups.

[0315] In some embodiments, the surfactant content in the second carbon nanotube dispersion is 2% to 5% by mass.

[0316] This application contains 2% to 5% by mass of glutamic acid surfactants and / or glycine surfactants in the carbon nanotube dispersion, which is beneficial to further increase the dispersion of carbon nanotubes and improve the solid content of the carbon nanotube dispersion.

[0317] In these embodiments, this application discloses that the mass percentage content of the surfactant in the above-mentioned carbon nanotube dispersion is any one of 2%, 3%, 4%, 5%, or any one of the ranges of both of the above.

[0318] In some embodiments, the preparation of the first positive electrode slurry further includes adding a first carbon nanotube dispersion to the first positive electrode active material.

[0319] In some embodiments, the first carbon nanotube dispersion comprises first carbon nanotubes and a dispersant.

[0320] In some embodiments, the dispersant in the first carbon nanotube dispersion comprises one or more of carboxymethyl cellulose and sodium carboxymethyl cellulose.

[0321] The carboxymethyl cellulose and / or sodium carboxymethyl cellulose of this application are mainly used for dispersing carbon nanotubes. Carboxymethyl cellulose refers to a linear polymer derivative of cellulose containing multiple dehydrated glucose units (β-linked pyranose residues), each glucose unit having three hydroxyl groups, with the hydrogen in the hydroxyl groups replaced by carboxymethyl groups. Because this linear polymer derivative contains ether or carboxyl groups, it readily combines with sodium ions to form sodium carboxymethyl cellulose.

[0322] In some embodiments, the mass ratio of the first carbon nanotube to the dispersant in the first carbon nanotube dispersion is 100:(50-250).

[0323] In these embodiments, this application discloses that the mass ratio of the first carbon nanotube to the above-mentioned dispersant is any one or more of 100:50, 100:100, 100:200, and 100:250.

[0324] In some embodiments, the solid content of the first carbon nanotube dispersion is 0.6% to 1.5%.

[0325] The definition of solid content in this application remains the same as that described above, and will not be repeated here.

[0326] [Negative electrode plate]

[0327] The negative electrode sheet of this application includes a negative current collector and a negative electrode film layer located on one or both surfaces of the negative current collector. Generally, the negative electrode film layer is located on both surfaces of the negative current collector, and is formed by methods such as coating or deposition. In this application, both sides will be used as examples.

[0328] In some embodiments, this application discloses that the compaction density of the negative electrode film layer is ≥1.65 g / cm³. 3 .

[0329] In this application, the compaction density of the negative electrode film can be used to characterize the energy density of the material; however, the compaction density of the negative electrode film is used to evaluate the overall compaction density of the negative electrode sheet. The compaction density of the negative electrode film = areal density of the negative electrode film / thickness of the negative electrode film. The thickness of the negative electrode film includes the distance between the two end faces of the negative electrode film along the thickness direction. The areal density of the negative electrode film = weight of a single positive electrode layer / area of ​​a single positive electrode layer. The weight of a single positive electrode layer can be obtained by weighing, and the area of ​​a single negative electrode layer can be obtained using the area calculation formula based on the shape of the film. In these embodiments, this application lists a compaction density of the negative electrode film ≥ 1.65 g / cm³. 3 .

[0330] This application discloses in some embodiments that the negative electrode film layer includes a negative electrode active material, which comprises one or more of carbonaceous materials, silicon-based materials, silicon-carbon composite materials, tin-based materials and their alloys. The carbonaceous materials in this application include one or more combinations of artificial graphite, natural graphite, soft carbon, and hard carbon. Among them, artificial graphite, natural graphite, soft carbon, and hard carbon include any form of material conventional in the art, and include any manufacturer and model conventional in the art. The silicon-based materials in this application include one or two of silicon-oxygen materials or silicon-carbon materials, or silicon-carbon composites. The tin-based materials and their alloys in this application include, but are not limited to, Li-Sn alloys, Li-Sn-O alloys, Sn, SnO, SnO2, etc. Furthermore, this application is not limited to these materials; other conventional materials that can be used as negative electrode active materials for lithium-ion batteries or sodium-ion batteries can also be used. These negative electrode active materials can be used alone or in combination of two or more.

[0331] In some embodiments, this application discloses that the negative electrode film layer contains a conductive agent, which includes one or more of dot-shaped conductive agents, linear conductive agents, and planar conductive agents. The dot-shaped conductive agents include one or more of conductive carbon black (Super P or Super S), acetylene black, conductive graphite (KS-6 or KS-15 or SFG-6 or SFG-15), and Ketjen black. The linear conductive agents include one or more of single-walled carbon nanotubes, multi-walled carbon nanotubes, and carbon nanofibers. The planar conductive agents include, but are not limited to, graphene.

[0332] In some embodiments, the conductive agent of the negative electrode film layer contains the same carbon nanotubes as those in the positive electrode film layer described above. This design, when used in conjunction with the design of the positive electrode sheet of this application, is beneficial to improving the cycle life of the battery.

[0333] This application discloses in some embodiments that the negative electrode film layer includes a binder and a dispersant. The binder includes, but is not limited to, polyvinyl alcohol, polyethylene glycol, sodium carboxymethyl cellulose, polyethylene oxide, polyacrylic acid, polyacrylamide, sodium alginate, styrene-butadiene rubber (SBR), etc. The dispersant also includes any type conventional in the art, such as cellulose and its salts, specifically including, but not limited to, methylcellulose, carboxymethyl cellulose, hydroxyethyl cellulose, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, etc.

[0334] The method of forming the negative electrode film layer in this application includes mixing the above-mentioned raw materials with a solvent (such as deionized water) in a certain mass ratio to form a negative electrode slurry, defoaming the negative electrode slurry, uniformly coating the negative electrode slurry on both sides of the negative electrode current collector; controlling the coating weight on one side; drying, and compacting it to a certain compaction density using a cold press to obtain a negative electrode sheet containing a negative electrode film layer.

[0335] [Isolation Component]

[0336] Some embodiments of this application disclose isolation elements. This application does not have any particular restrictions on the type of isolation element, and any known porous structure isolation element with good chemical and mechanical stability can be selected.

[0337] In some embodiments, the separator includes a substrate material layer and a coating disposed on the surface of the substrate material layer; the substrate material of the substrate material layer includes one or more of polyethylene, polypropylene, poly(p-phenylene terephthalamide), polyethylene terephthalate, polytetrafluoroethylene, polyacrylonitrile, polyimide, and polyamide; the coating includes a ceramic coating and / or a polymer coating. The substrate material layer has good lithium ion permeability, which is beneficial to lithium ion migration; the coating disposed on the surface of the substrate material layer can further improve the mechanical properties of the separator. Further, the ceramic particles in the ceramic coating include one or more of SiO2, Al2O3, AlOOH, CaO, TiO2, MgO, ZnO, ZrO2, Mg(OH)2, and BaSO4. Furthermore, the polymer material for the polymer coating includes one or more of polyethylene (PE), polypropylene (PP), poly(p-phenylene terephthalamide) (PPTA), polyethylene terephthalate (PET), polytetrafluoroethylene (PTFE), polyacrylonitrile (PAN), polyimide (PI), and polyamide (PA). The polymer coating can be made of the same or different material as the substrate material layer, and the thicknesses of the polymer coating and the substrate material layer can be different; furthermore, the thickness of the polymer coating is less than the thickness of the substrate material layer.

[0338] In other 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.

[0339] Electrolyte

[0340] Some embodiments of this application disclose an electrolyte, which can be liquid, solid, or gel-like. Solid state refers to a solid electrolyte, liquid state to a liquid electrolyte, and gel-like state to a gel electrolyte. The secondary battery of this application uses a liquid electrolyte, i.e., an electrolyte. This electrolyte contains an electrolyte salt and an organic solvent. The electrolyte salt can be any type conventional in the art, including, but not limited to, inorganic metal salts such as RClO4, RAsF6, RPF6, RBF4, RSbF6, RSO3F, RN(FSO2)2, etc.; fluorinated organometallic salts such as RCF3SO3, RN(FSO2)(CF3SO2), RN(CF3SO2)2, RN(C2F5SO2)2, cyclic 1,3-hexafluoropropane disulfonylimide lithium, cyclic 1,2-tetrafluoroethane disulfonylimide lithium, RN(CF3SO2)(C4F9S O2), RC(CF3SO2)3, RPF4(CF3)2, RPF4(C2F5)2, RPF4(CF3SO2)2, RPF4(C2F5SO2)2, RBF2(CF3)2, RBF2(C2F5)2, RBF2(CF3SO2)2, RBF2(C2F5SO2)2, etc.; and metal salts containing dicarboxylic acid complexes, such as lithium bis(oxalate)borate, lithium difluorooxalate borate, lithium tri(oxalate)phosphate, lithium difluorobis(oxalate)phosphate, lithium tetrafluoro(oxalate)phosphate, etc. Here, both the metal and R contain lithium ions.

[0341] According to some embodiments of this application, the concentration of the electrolyte salt in the electrolyte is 0.1 mol / L to 4 mol / L. In these embodiments, this application discloses that the concentration of the electrolyte salt is any one of 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1 mol / L, 1.2 mol / L, 1.5 mol / L, 1.8 mol / L, 2 mol / L, 2.2 mol / L, 2.5 mol / L, 2.8 mol / L, 3 mol / L, 3.2 mol / L, 3.5 mol / L, 3.8 mol / L, and 4 mol / L, or any one of the above ranges.

[0342] As described above, in some embodiments of this application, the molar concentration of the electrolyte salt is selected to be ≥0.9 mol / L, which is beneficial for forming a more dense and stable solid electrolyte interphase (SEI) film on the surface of the negative electrode, further reducing side reactions between the negative electrode active material and the electrolyte. This design approach, when used in conjunction with the design approach of the positive electrode in this application, helps to improve the cycle life of the battery.

[0343] The organic solvents of this application comprise one or more of carboxylic acid esters, carbonates, and ethers. The carboxylic acid esters comprise one or more of ethyl acetate (EA), methyl acetate (MA), ethyl propionate (EP), propyl acetate (PA), methyl propionate (MP), methyl butyrate (MB), ethyl butyrate (EB), and 1,4-butyrolactone (GBL). The carbonates comprise one or more of ethylene carbonate (EC), propylene carbonate (PC), vinylene carbonate, dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl ethyl carbonate (EMC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butyl carbonate (BC), and fluoroethylene carbonate (FEC). The ethers comprise at least one of tetrahydrofuran, dimethyl tetrahydrofuran, tetrahydropyran, dimethyl tetrahydropyran, 1,2-dimethoxyethane, dipropylene glycol dimethyl ether, or dimethyl phthalate. The organic solvents of this application further include one or two of nitrile solvents and sulfone solvents. The nitrile solvents include one or more of acetonitrile (AN), glutaronitrile (GLN), and adiponitrile (ADN). The sulfone solvents include at least one or a combination of two of sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE).

[0344] According to some embodiments of this application, the electrolyte further comprises a film-forming stabilizer, which includes a positive electrode film-forming stabilizer and a negative electrode film-forming stabilizer. The positive electrode film-forming stabilizer comprises carbonate additives and / or sulfate additives. The carbonate additives include one or more of vinylene carbonate (VC), fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), vinyl ethylene carbonate (VEC), and dioctyl carbonate (CC). The sulfate additives include cyclic sulfonate additives and / or sulfated hydrocarbon ester additives; further, the cyclic sulfonate additives include one or more of 1,3-propanesulfonate lactone (PS), propenesulfonate lactone (PES), and 3-fluoro-1,3-propanesulfonate lactone (FPS); the sulfated hydrocarbon ester additives include one or more of vinyl sulfate (DTD), diethyl sulfate (DES), and dimethyl sulfate (DMS). The negative electrode film-forming stabilizer includes one or more of boron lithium salts, phosphorus-containing lithium salts, and sulfur-containing lithium salts; boron-containing lithium salts include one or more of lithium tetrafluoroborate (LiBF4), lithium bis(oxalate)borate (LiBOB), and lithium bis(oxalate)borate (LiDFOB); phosphorus-containing lithium salts include one or more of lithium difluorophosphate (LiPO2F2), lithium fluorophosphate (Li2PO3F), and lithium phosphate (Li3PO4). Sulfur-containing lithium salts include one or more of lithium fluorosulfonate (LiFSO3), lithium sulfate (Li2SO4), and lithium aminosulfonate (LiSO3NH2).

[0345] The following will focus on the battery cell of this application with reference to specific embodiments.

[0346] Unless otherwise specified, the experimental methods used in the following examples are all conventional methods.

[0347] Unless otherwise specified, all materials and reagents used in the following examples are commercially available.

[0348] This application may employ conventional inorganic chemistry techniques within the art. In the following examples, efforts have been made to ensure the accuracy of the figures used (including quantities, temperatures, reaction times, etc.), but some experimental errors and biases should be considered. Temperatures (in degrees Celsius) used in the following examples are expressed in °C, and pressures are at or near atmospheric pressure. All reagents were purchased from AR-grade suppliers, and all reactions were carried out under argon protection. Unless otherwise stated, all reagents were obtained commercially.

[0349] Experimental materials:

[0350] 1. Lithium-nickel transition metal oxides and lithium-containing phosphates: commercially available;

[0351] 2. Carbon nanotube dispersion: Beijing Tiannai Technology Co., Ltd.;

[0352] 3. Acrylic copolymers: Commercially available (including methacrylic acid, N-hydroxymethylacrylamide, acrylonitrile and n-butyl acrylate, based on the mass percentage of the acrylic copolymer, the mass percentage content of methacrylic acid monomer is 20%, the mass percentage content of N-hydroxymethylacrylamide monomer is 35%, the mass percentage content of acrylonitrile monomer is 15%, the mass percentage content of n-butyl acrylate monomer is 30%, and the weight average molecular weight is 500,000);

[0353] 4. Carbon black: Jiangxi Black Cat Carbon Black Co., Ltd.;

[0354] The performance parameters of some experimental materials are listed below:

[0355] Table 1-1 Parameter List of Positive Electrode Active Materials

[0356] Table 1-2 Composition of carbon nanotube dispersion

[0357] The degree of substitution of sodium carboxymethyl cellulose in the carbon nanotube dispersion shown in Tables 1-2 of this application is 0.95, and the weight-average molecular weight is 240,000. The surfactant is a glycine-based surfactant, with glycine as the anion and octadecyl as the cationic surfactant.

[0358] Table 1-3 Parameter List of Carbon Black

[0359] Example 1 (The first region does not contain carbon nanotubes, and the second region does contain carbon nanotubes)

[0360] A battery cell is provided, which includes a positive electrode, a separator and a negative electrode stacked in sequence, and an electrolyte.

[0361] The preparation of the positive electrode sheet includes the following steps:

[0362] (1) Provide carbon nanotube dispersions: as shown in serial number 1-1 in Table 1-2;

[0363] (2) Preparation of the first positive electrode slurry: The lithium-nickel transition metal oxide (LiNi) indicated by serial number A1 in Table 1-1 is prepared. 1.05 Ni 0.7 Co 0.2 Mn 0.1 O2), carbon black (as shown in Serial No. 2-1 of Table 1-3) and polyvinylidene fluoride binder are mixed together, and after stirring with nitrogen-methylpyrrolidone solvent, the first positive electrode slurry is formed.

[0364] (3) Preparation of the second positive electrode slurry: The lithium phosphate (LiFePO4) indicated by serial number B1 in Table 1-1, the above carbon nanotube dispersion and the binder polyvinylidene fluoride are mixed together, and after stirring with nitrogen methyl pyrrolidone solvent, the second positive electrode slurry is formed.

[0365] (4) Preparation of positive electrode sheet: The first positive electrode slurry is coated on the two surfaces of the positive electrode current collector aluminum foil to obtain the first sub-positive electrode film layer. The mass percentage content of each component in the first sub-positive electrode film layer is shown in Table 1-4.

[0366] The second positive electrode slurry is coated on both surfaces of the first sub-positive electrode film to obtain the second sub-positive electrode film. The mass percentage content of each component in the second sub-positive electrode film is shown in Table 1-4.

[0367] This embodiment also provides that the thickness H of the positive electrode film is 0.15 mm, wherein the thicknesses of the first sub-positive electrode film and the second sub-positive electrode film are 0.075 mm, respectively.

[0368] Preparation of negative electrode sheet:

[0369] Graphite, conductive agent carbon black, binder styrene-butadiene rubber (SBR), and thickener sodium carboxymethyl cellulose (CMC-Na) were dissolved in deionized water at a weight ratio of 96.2:1.8:0.8:1.2. The mixture was stirred under vacuum until homogeneous. The negative electrode slurry was then uniformly coated onto both sides of the negative electrode current collector copper foil. The negative electrode was dried in a nine-section oven at sequential temperatures of 100℃ / 100℃ / 95℃ / 85℃ / 85℃ / 80℃ / 80℃ / 80℃ / 60℃. Finally, the negative electrode sheet was compacted using a cold press.

[0370] Preparation of electrolyte:

[0371] In an environment with a water content of less than 10 ppm, non-aqueous organic solvents ethylene carbonate, diethyl carbonate, and dimethyl carbonate are mixed in a volume ratio of 1:1:1 to obtain a solvent. Lithium hexafluorophosphate is added to the solvent to prepare an electrolyte with a lithium hexafluorophosphate concentration of 1 mol / L.

[0372] Provide a separating membrane:

[0373] A porous polyethylene (PE) membrane with a thickness of 13 μm was used as the separator.

[0374] Preparation of battery cells:

[0375] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator acting as a separator between the positive and negative electrodes, and the stacked bare cells are assembled accordingly. The stacked bare cells are placed in an outer packaging shell, dried, and then injected with electrolyte. After vacuum sealing, settling, formation, and shaping, a single battery cell is obtained.

[0376] Example 1-1 (The first region does not contain carbon nanotubes, and the second region contains carbon nanotubes of different contents and types)

[0377] A battery cell is provided, which differs from Example 1 in that: in the preparation of the second positive electrode slurry, the carbon nanotube dispersion shown in 1-1 of Table 1-2 is replaced with 1-3, and the other parts of Example 1-1 are the same as those of Example 1.

[0378] Examples 1-2 (The first region does not contain carbon nanotubes, and the second region contains carbon nanotubes with an average tube length of less than 10 μm)

[0379] A battery cell is provided, which differs from the above-described embodiment 1 in that a second positive electrode slurry is prepared by mixing lithium phosphate (LiFePO4) indicated by serial number B1 in Table 1-1, carbon nanotube dispersions indicated by serial numbers 1-5 described above in this application, and polyvinylidene fluoride binder together, and then stirring with nitrogen-methylpyrrolidone solvent to form a second positive electrode slurry.

[0380] Everything else remains the same as in Example 1.

[0381] Comparative Example 1 (The first region does not contain carbon nanotubes, and the second region does not contain carbon nanotubes)

[0382] A battery cell is provided, which differs from Embodiment 1 described above in that...

[0383] Preparation of the first positive electrode slurry: The lithium-nickel transition metal oxide (LiNi) indicated by serial number A1 in Table 1-1 is used... 1.05 Ni 0.7 Co 0.2 Mn 0.1 O2), carbon black (as shown in Serial No. 2-1 of Table 1-3) and polyvinylidene fluoride binder are mixed together, and after stirring with nitrogen-methylpyrrolidone solvent, the first positive electrode slurry is formed.

[0384] Preparation of the second positive electrode slurry: Lithium phosphate (LiFePO4) indicated by serial number B1 in Table 1-1, carbon black indicated by serial number 2-1 in Table 1-3, and polyvinylidene fluoride binder are mixed together, and then stirred with nitrogen methyl pyrrolidone solvent to form the second positive electrode slurry.

[0385] The first positive electrode slurry is coated on both surfaces of the positive electrode current collector aluminum foil to obtain the first sub-positive electrode film layer. The mass percentage content of each component in the first sub-positive electrode film layer is shown in Table 1-4.

[0386] The second positive electrode slurry is coated on both surfaces of the first sub-positive electrode film to obtain the second sub-positive electrode film. The mass percentage content of each component in the second sub-positive electrode film is shown in Table 1-4.

[0387] This embodiment also provides that the thickness H of the positive electrode film is 0.15 mm, wherein the thicknesses of the first sub-positive electrode film and the second sub-positive electrode film are 0.075 mm, respectively.

[0388] Comparative Example 2 (non-layered design of the positive electrode film, the positive electrode film contains lithium nickel transition metal oxide and uniformly contains carbon nanotubes)

[0389] A battery cell is provided, which differs from Embodiment 1 above in that the first positive electrode slurry and the second positive electrode slurry are the same, both being: lithium nickel transition metal oxide (LiNi) as indicated by serial number A1 in Table 1-1.1.05 Ni 0.7 Co 0.2 Mn 0.1 O2), the carbon nanotube dispersion shown in Table 1-2 (1-1), and the binder polyvinylidene fluoride are mixed together, and then stirred with nitrogen-methylpyrrolidone solvent to form a positive electrode slurry.

[0390] The above-mentioned positive electrode slurry was coated on both surfaces of the positive electrode current collector aluminum foil to obtain a positive electrode film layer with the same thickness as in Example 1.

[0391] Comparative Example 3 (non-layered design of the positive electrode film, the positive electrode film contains lithium phosphate and uniformly contains carbon nanotubes)

[0392] A battery cell is provided, which differs from Embodiment 1 above in that the first positive electrode slurry and the second positive electrode slurry are the same, both of which are formed by mixing lithium phosphate (LiFePO4) indicated by serial number B1 in Table 1-1, carbon nanotube dispersion indicated by serial number 1-1 in Table 1-2, and polyvinylidene fluoride binder together, and then stirring with nitrogen methylpyrrolidone solvent to form the positive electrode slurry.

[0393] The above-mentioned positive electrode slurry was coated on both surfaces of the positive electrode current collector aluminum foil to obtain a positive electrode film layer with the same thickness as in Example 1.

[0394] Comparative Example 4 (The first region contains carbon nanotubes, and the second region does not contain carbon nanotubes)

[0395] A battery cell is provided, which differs from Example 1 above in that the first positive electrode slurry is prepared by: using the lithium-nickel transition metal oxide (LiNi) indicated by serial number A1 in Table 1-1. 1.05 Ni 0.7 Co 0.2 Mn 0.1 O2), the carbon nanotube dispersions shown in Table 1-2 (numbers 1-5) and the binder polyvinylidene fluoride are mixed together, and then stirred with nitrogen-methylpyrrolidone solvent to form the first positive electrode slurry.

[0396] Preparation of the second cathode slurry: The second lithium-nickel transition metal oxide (LiNi) indicated by serial number B1 in Table 1-1 is prepared. 1.05 Ni 0.6 Co 0.2 Mn 0.2 O2), carbon black (as shown in Serial No. 2-1 of Table 1-3), and polyvinylidene fluoride binder are mixed together, and then stirred with nitrogen-methylpyrrolidone solvent to form the second positive electrode slurry.

[0397] Table 1-4 Composition of the positive electrode film

[0398] The test methods for the relevant parameters of each positive electrode in Table 1-4 are illustrated below:

[0399] ①Methods for testing diaphragm resistance:

[0400] The positive electrode sheets prepared in the above embodiments and comparative examples were cut and dried into small circular pieces with a diameter of 10mm at the left, center, and right positions within a certain range. The Yuaneng Technology electrode resistance meter was then powered on and placed at the appropriate position of the probe. The "Start" button was clicked, and the reading was taken after it stabilized. Two positions were tested for each small circular piece, and the average of the six measurements was calculated to obtain the film resistance of the electrode sheet, as shown in Table 2-4.

[0401] ② Method for determining the compaction density of the positive electrode film:

[0402] The positive electrode samples prepared in the above embodiments and comparative examples were used to finely slice the positive electrode samples at different thickness positions using cryo-focused ion beam (FIB) to separate different layer samples along different thickness positions.

[0403] First, the thickness H of each positive electrode film layer was obtained by taking pictures using a scanning electron microscope.

[0404] Let M0 be the mass of the above positive electrode film and S0 be the area measured; then the surface density of the positive electrode film is D = M0 / S0.

[0405] Then the compaction density of the positive electrode film is equal to the surface density D of the positive electrode film / the thickness H of the positive electrode film.

[0406] Similarly, this application obtains multiple positive electrode film samples at different positions along the length of the positive electrode sheet for both the first and second sub-positive electrode film layers. The compaction density value of each positive electrode film sample is measured according to the above measurement method, and then the average value of each compaction density value is taken: (compaction density 1 + compaction density 2 + compaction density 3, ... + compaction density n) / n, which is the compaction density value of the first or second sub-positive electrode film layer.

[0407] ③ Cohesive force test of the positive electrode sheet:

[0408] Equipment used: Instron 336; the specific testing procedure is as follows:

[0409] Cut the positive electrode sheet into a 100mm long and 10mm wide sample. Take a 25mm wide stainless steel plate and attach the sample to it using 11mm wide 3M double-sided tape, ensuring the current collector is bonded to the tape. Roll the sample surface back and forth three times (300mm / min) with a 2000g roller. Then, attach a 10mm wide and 50μm thick tape (model NITTO.NO5000NS) to the surface of the positive electrode film and roll it back and forth three times (300mm / min) with a 2000g roller. Bend the tape 180 degrees and manually peel it 25mm away from the positive electrode film. Fix the sample on an Instron 336 tensile testing machine, ensuring the peeled surface is aligned with the machine's force line (i.e., perform a 180° peel). Pre-stretch at a peeling speed of 100mm / min for 10mm, then allow the tensile testing machine to return to its original position. Finally, peel continuously at 300mm / min to obtain the cohesive force curve. Take the average value of the stable segment as the peeling force F0. Calculate the cohesive force F1 of the tested electrode using the following formula: F1 = F0 / width of the sample. The unit of measurement for F1 is N / m.

[0410] Table 1-5 Performance List of Positive Electrode Sheets

[0411] As shown in Tables 1-5, comparing Examples 1-2 with Comparative Example 4, Examples 1-2 designed to add carbon nanotubes to the lithium phosphate in the second region, while Comparative Example 4 designed to add the same carbon nanotubes to the lithium nickel transition metal oxide in the first region. Through cohesion testing, it can be seen that compared with using carbon nanotubes to bind lithium nickel transition metal oxide, the effect of using carbon nanotubes to bind lithium phosphate in this application is more obvious.

[0412] Comparing Example 1 with Example 1-1, as the carbon nanotube content in the second region increases, the carbon nanotubes enhance their ability to entangle and bind lithium phosphate in the positive electrode film, the bonding force between the various material components in the positive electrode film also increases, and the conductivity of the positive electrode film also becomes stronger.

[0413] Comparing Example 1 with Examples 1-2, the average length of carbon nanotubes also plays a role in their entanglement and binding of the positive electrode active material. Generally speaking, the longer the average length of the carbon nanotubes, the greater the binding effect on the positive electrode active material.

[0414] Example 2-1 (The first and second regions contain the same type and amount of carbon nanotubes)

[0415] A battery cell is provided, which differs from Example 1 in that: when preparing the first positive electrode slurry, carbon black is replaced with the carbon nanotube dispersion shown in Serial No. 1-1 of Table 1-2. All other parts of this Example 2-1 are the same as those of Example 1.

[0416] Example 2-2 (The first and second regions contain different types and amounts of carbon nanotubes)

[0417] A battery cell is provided, which differs from Example 1 in that: when preparing the first positive electrode slurry, carbon black is replaced with carbon nanotube dispersions indicated by serial numbers 1-3 in Table 1-2, while the rest remains the same as in Example 1.

[0418] Examples 2-3 (The first and second regions contain different types and amounts of carbon nanotubes)

[0419] A battery cell is provided, which differs from Example 1 in that: when preparing the first positive electrode slurry, carbon black is replaced with the carbon nanotube dispersion shown in Serial No. 1-I in Table 1-2; when preparing the second positive electrode slurry, the carbon nanotube dispersion shown in Serial No. 1-1 in Table 1-2 is replaced with the carbon nanotube dispersion shown in Serial No. 1-3; all other parts are the same as in Example 1.

[0420] Furthermore, the composition of the positive electrode film layer in this embodiment 2 is shown in Table 2-1 below, and the performance of the positive electrode sheet is illustrated in Table 2-2.

[0421] Table 2-1 Composition of the positive electrode film

[0422] The above positive electrode film was tested according to the above test method, and the results are shown in Table 2-2 below.

[0423] Table 2-2 Performance List of Positive Electrode Sheets

[0424] As can be seen from Examples 1 and 2-1 in Table 2-2, adding carbon nanotubes to both the first region near the current collector and the second region away from the current collector on the positive electrode film layer is beneficial to further enhance the bonding force between the various material components in the positive electrode film layer.

[0425] As can be seen from Examples 2-1, 2-2 and 2-3 in Table 2-2, the second region farther from the current collector has a higher demand for carbon nanotubes than the first region closer to the current collector. Further, based on Examples 2-1 and 2-3, the more carbon nanotubes are added in the second region, the greater the bonding force between the material components in the positive electrode film. Further, based on Examples 2-1 and 2-2, the more carbon nanotubes are added in the first region, the greater the bonding force between the material components in the positive electrode film, but the increase is not significant.

[0426] Example 3-1 (The first and second regions contain different types and amounts of carbon nanotubes)

[0427] A battery cell is provided, which differs from Example 1 in that the preparation of the positive electrode includes the following steps:

[0428] (1) Provide carbon nanotube dispersions: as shown in serial numbers 1-2 and 1-3 in Table 1-2;

[0429] (2) Preparation of the first positive electrode slurry: The lithium-nickel transition metal oxide (LiNi) shown in serial number A2 of Table 1-1 is prepared. 1.05 Ni 0.6 Co 0.2 Mn 0.2 O2), the carbon nanotube dispersion shown in Table 1-2 (numbers 1-3) and the binder polyvinylidene fluoride are mixed together, and after adding nitrogen-methylpyrrolidone solvent and stirring, the first positive electrode slurry is formed.

[0430] (3) Preparation of the second positive electrode slurry: The lithium phosphate (LiFePO4) indicated by serial number B1 in Table 1-1, the carbon nanotube dispersion indicated by serial number 1-2 in Table 1-2 above, and the binder polyvinylidene fluoride are mixed together, and after stirring with nitrogen methyl pyrrolidone solvent, the second positive electrode slurry is formed.

[0431] (4) Preparation of positive electrode sheet: The first positive electrode slurry is coated on both surfaces of the positive electrode current collector aluminum foil to obtain the first sub-positive electrode film layer, wherein the mass percentage content of each component in the first sub-positive electrode film layer is shown in Table 3-1. The other parts of this embodiment are the same as those in Embodiment 1.

[0432] Example 3-2

[0433] A battery cell is provided, which differs from Example 1 in that the preparation of the positive electrode includes the following steps:

[0434] (1) Provide carbon nanotube dispersions: as shown in serial numbers 1-2 and 1-4 in Table 1-2;

[0435] (2) Preparation of the first positive electrode slurry: The lithium-nickel transition metal oxide (LiNi) shown in serial number A3 of Table 1-1 is prepared. 1.05 Ni 0.5 Co 0.2 Mn 0.3 O2), the carbon nanotube dispersions shown in Table 1-2 (numbers 1-4) and the binder polyvinylidene fluoride are mixed together, and then stirred with nitrogen-methylpyrrolidone solvent to form the first positive electrode slurry.

[0436] (3) Preparation of the second positive electrode slurry: The lithium phosphate (LiFePO4) indicated by serial number B1 in Table 1-1, the carbon nanotube dispersion indicated by serial number 1-2 in Table 1-2 above, and the binder polyvinylidene fluoride are mixed together, and after stirring with nitrogen methyl pyrrolidone solvent, the second positive electrode slurry is formed.

[0437] (4) Preparation of positive electrode sheet: The first positive electrode slurry is coated on both surfaces of the positive electrode current collector aluminum foil to obtain the first sub-positive electrode film layer, wherein the mass percentage content of each component in the first sub-positive electrode film layer is shown in Table 3-1. The other parts of this embodiment are the same as those in Embodiment 1.

[0438] Example 3-3

[0439] A battery cell is provided, which differs from Example 1 in that the preparation of the positive electrode includes the following steps:

[0440] (1) Provide carbon nanotube dispersions: as shown in serial numbers 1-2 and 1-4 in Table 1-2;

[0441] (2) Preparation of the first positive electrode slurry: The lithium-nickel transition metal oxide (LiNi) shown in A4 of Table 1-1 is prepared. 1.05 Ni 1 / 3 Co 1 / 3 Mn 1 / 3 O2), the carbon nanotube dispersions shown in Table 1-2 (numbers 1-4) and the binder polyvinylidene fluoride are mixed together, and then stirred with nitrogen-methylpyrrolidone solvent to form the first positive electrode slurry.

[0442] (3) Preparation of the second positive electrode slurry: The lithium phosphate (LiFePO4) indicated by serial number B1 in Table 1-1, the carbon nanotube dispersion indicated by serial number 1-2 in Table 1-2 above, and the binder polyvinylidene fluoride are mixed together, and after stirring with nitrogen methyl pyrrolidone solvent, the second positive electrode slurry is formed.

[0443] (4) Preparation of positive electrode sheet: The first positive electrode slurry is coated on both surfaces of the positive electrode current collector aluminum foil to obtain the first sub-positive electrode film layer, wherein the mass percentage content of each component in the first sub-positive electrode film layer is shown in Table 3-1. The other parts of this embodiment are the same as those in Embodiment 1.

[0444] Examples 3-4

[0445] A battery cell is provided, which differs from Example 1 in that the preparation of the positive electrode includes the following steps:

[0446] (1) Provide carbon nanotube dispersions: as shown in serial numbers 1-3 and 1-4 in Table 1-2;

[0447] (2) Preparation of the first positive electrode slurry: The lithium-nickel transition metal oxide (LiNi) shown in A4 of Table 1-1 is prepared. 1.05 Ni 1 / 3 Co 1 / 3 Mn 1 / 3 O2), the carbon nanotube dispersions shown in Table 1-2 (numbers 1-4) and the binder polyvinylidene fluoride are mixed together, and then stirred with nitrogen-methylpyrrolidone solvent to form the first positive electrode slurry.

[0448] (3) Preparation of the second positive electrode slurry: The lithium phosphate (LiFePO4) indicated by serial number B1 in Table 1-1, the carbon nanotube dispersion indicated by serial number 1-3 in Table 1-2 above, and the binder polyvinylidene fluoride are mixed together, and after stirring with nitrogen methyl pyrrolidone solvent, the second positive electrode slurry is formed.

[0449] (4) Preparation of positive electrode sheet: The first positive electrode slurry is coated on both surfaces of the positive electrode current collector aluminum foil to obtain the first sub-positive electrode film layer, wherein the mass percentage content of each component in the first sub-positive electrode film layer is shown in Table 3-1. The other parts of this embodiment are the same as those in Embodiment 1.

[0450] Furthermore, the composition of the positive electrode film layer in the above embodiment 3 is shown in Table 3-1 below, and the performance of the positive electrode sheet is illustrated in Table 3-2.

[0451] Table 3-1 Composition of the positive electrode film

[0452] The above positive electrode film was tested according to the above test method, and the results are shown in Table 3-2 below.

[0453] Table 3-2 Performance List of Positive Electrode Sheets

[0454] Referring to Examples 3-3 and 3-4 in Table 3-2, it can be seen that, compared to different types of carbon nanotubes, when the average length of the carbon nanotubes does not differ significantly, the content of carbon nanotubes has a greater impact on the bonding force between the various material components in the positive electrode film. Generally speaking, within a certain range, the higher the content, the stronger the bonding force. Furthermore, adding a larger amount of carbon nanotubes in the second region, which is farther from the current collector, is more beneficial for enhancing the bonding force between the various material components in the positive electrode film compared to the first region, which is closer to the current collector.

[0455] As can be seen from Examples 1, 3-1 to 3-3 in Table 3-2, the type of positive active material in the first region has a certain influence on the bonding force between the material components in the positive electrode film, but the influence is not significant.

[0456] Example 4-1

[0457] A battery cell is provided that differs from Example 1 in that the adhesive polyvinylidene fluoride is replaced with the propylene-based copolymer described above (weight-average molecular weight of 500,000), while all other aspects remain the same as in Example 1.

[0458] Table 4-1 Performance List of Positive Electrode Sheets

[0459] As shown in Table 4-1, propylene-based copolymers have a certain positive effect on the bonding force between the components in the positive electrode film. Compared with the binders in the prior art, propylene-based copolymers are beneficial to enhancing the bonding force between the material components in the positive electrode film.

[0460] Example 5-1

[0461] A battery cell is provided, which differs from Example 1 in that the concentration of the electrolyte is 0.85 mol / L, while all other aspects remain the same as Example 1.

[0462] Table 4-2 Performance List of Positive Electrode Sheets

[0463] [Battery Performance Test]

[0464] ④ Capacity retention rate after 500 battery cycles:

[0465] At 25℃, the battery was charged at a constant current of 0.33C to 3.8V, then charged at a constant voltage to a current of 0.05C (corresponding to 100% SOC). After resting for 5 minutes, the battery was discharged at a constant current of 0.33C to the lower limit of 2.0V. The discharge capacity at this point was recorded, which is the discharge capacity of the first cycle. The battery was subjected to a cyclic charge-discharge test using the above method, and the discharge capacity after each cycle was recorded. The battery capacity retention rate (%) after 500 cycles at 25℃ = discharge capacity after 500 cycles / discharge capacity of the first cycle × 100%.

[0466] ⑤ Expansion rate of the positive electrode after 500 battery cycles:

[0467] At 25℃, the secondary battery under test was charged at a constant current of 0.33C to a voltage of 3.8V, then charged at a constant voltage to a current of 0.05C (corresponding to 100% SOC). After resting for 5 minutes, the battery was discharged at a constant current of 0.33C to a voltage of 2.0V. This constitutes one charging cycle. After 500 cycles in the above manner, the battery cell was disassembled in a fully charged state. The thickness of the positive electrode film was measured with a micrometer at this time as h2, and the thickness of the positive electrode film when it was placed in the battery case was h1.

[0468] The formula for calculating the electrode expansion rate S is: S=(h2-h1) / h1×100%.

[0469] The lower the electrode expansion rate, the more effective the expansion reduction and the better the cycle stability of the cell group.

[0470] The test results obtained according to the above test method are shown in Table 5 below.

[0471] Table 5 Battery Performance List

[0472] As can be seen from Examples 1-2 and Comparative Example 4 in Table 5, compared with using carbon nanotubes to alleviate the expansion of lithium nickel transition metal oxide in the first region, this application uses carbon nanotubes with binding effect to alleviate the expansion of lithium phosphate in the second region, which has a more obvious effect on improving the expansion of the entire positive electrode film or the battery cell, and a more obvious effect on improving the cycle life of the battery cell.

[0473] As can be seen from Example 1 and Comparative Examples 1, 2 and 3 in Table 5, this application selects lithium nickel transition metal oxide to be used in the first region near the current collector and lithium phosphate to be used in the second region away from the current collector. Compared with the design method of uniform coating of positive electrode active material, this is also beneficial to reduce the expansion of positive electrode sheet and improve the cycle life of battery.

[0474] As can be seen from Examples 1 and 1-2 in Table 5, the average length of carbon nanotubes plays a role in binding lithium nickel transition metal oxides. Generally speaking, the longer the average length of carbon nanotubes, the more obvious the effect of binding lithium nickel transition metal oxides and improving the cycle life of the battery.

[0475] As can be seen from Examples 1, 2 and 3 in Table 5, adding carbon nanotubes to both the first and second regions simultaneously is beneficial for further improving the cycle life of the battery compared to the design method that only adds them to the second region.

[0476] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and not to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application, and they should all be covered within the scope of the claims and specification of this application. In particular, as long as there is no structural conflict, the various technical features mentioned in the embodiments can be combined in any way. This application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A single battery cell, characterized in that: Including positive electrode plates and negative electrode plates; The positive electrode includes a positive current collector and a positive film layer located on at least one side surface of the positive current collector; The positive electrode film layer includes a first surface away from the positive electrode current collector and a second surface disposed opposite to the first surface; The distance between the first surface and the second surface is H; The region formed extending from the second surface of the positive electrode film to a position of 0.1×H is denoted as the first region of the positive electrode film. The first region includes a first positive electrode active material, which includes a lithium nickel transition metal oxide. The region formed extending from the first surface of the positive electrode film to a position of 0.1×H is denoted as the second region of the positive electrode film. The second region includes a second positive electrode active material and a second carbon nanotube. The second positive electrode active material includes a lithium phosphate material.

2. The battery cell according to claim 1, characterized in that: The average tube length of the second carbon nanotube is greater than or equal to 10 μm.

3. The battery cell according to any one of claims 1 to 2, characterized in that: The average length of the second carbon nanotube is 10 μm to 40 μm.

4. The battery cell according to any one of claims 1 to 3, characterized in that: The average diameter of the second carbon nanotube is 1 nm to 20 nm.

5. The battery cell according to any one of claims 1 to 4, characterized in that: Based on the mass of the second region, the mass percentage content of the second carbon nanotube is 0.05% to 2%.

6. The battery cell according to any one of claims 1 to 5, characterized in that: The first region includes a first carbon nanotube.

7. The battery cell according to claim 6, characterized in that: The first carbon nanotube and the second carbon nanotube satisfy any one or more of the following conditions: (1) The average tube length of the first carbon nanotube is L1, and the average tube length of the second carbon nanotube is L2, where L1≤L2; (2) The average diameter of the first carbon nanotube is D1, and the average diameter of the second carbon nanotube is D2, where D1 ≥ D2. (3) The mass percentage content of the first carbon nanotube in the first region is W1; the mass percentage content of the second carbon nanotube in the second region is W2; W1≤W2.

8. The battery cell according to claim 7, characterized in that: The first carbon nanotube and the second carbon nanotube satisfy any one or more of the following conditions: (1) The average tube length L1 of the first carbon nanotube is 10 μm to 15 μm, and the average tube length L2 of the second carbon nanotube is greater than 15 μm and less than or equal to 40 μm. (2) The average diameter D1 of the first carbon nanotube is greater than 2nm and less than or equal to 20nm, and the average diameter D2 of the second carbon nanotube is 1nm to 2nm. (3) The mass percentage content W1 of the first carbon nanotube in the first region is 0.05% to 1.0%; the mass percentage content W2 of the second carbon nanotube in the second region is 0.1% to 2.0%.

9. The battery cell of any one of claims 1-8, wherein: The positive electrode film layer also contains one or more of dot-shaped conductive agents and surface-shaped conductive agents.

10. The battery cell of any one of claims 1-9, wherein: The chemical formula of the lithium-nickel transition metal oxide is Li x N t (Ni a Co b M c ) 1-d M' d O 2-y A y ; N includes any one or more of Zn, Al, Na, K, Mg, Nb, Mo, and W; M includes any one or more of Mn and Al; M' includes any one or more of Zr, Sr, B, Ti, Mg, Sn, and Al; A includes any one or more of S, N, B, F, Cl, Br, and I; x ranges from 0.2 to 1.2; t is 0 to 0.1; a ranges from 0.001 to 0.999; b is 0.001 to 0.999; a+b+c=1, 0≤d≤0.1； 0≤y＜0.2。 11. The battery cell of claim 10, wherein, a ranges from 0.001 to 0.

7.

12. The battery cell of any one of claims 1-11, wherein: The chemical formula of the lithium-containing phosphate is Li e Fe 1-y’ M” y’ P 1-m’ C m’ O 4-n’ D n’ ; Wherein, M" includes any one or more of Cr, Mg, Ti, Al, Zn, W, Nb, and Zr; C includes any one or more of B, S, Si, and N; D includes any one or more of S, F, Cl, and Br; 0＜e≤1.1； 0≤y’＜1； 0≤m’≤0.1； 0≤n’≤0.4。 13. The battery cell according to any one of claims 1 to 12, characterized in that: The median particle size Dv50 of the lithium-nickel transition metal oxide is 2 μm to 6 μm; and / or; The median particle size Dv50 of the lithium phosphate material is 0.5 μm to 2.2 μm.

14. The battery cell according to any one of claims 1 to 13, characterized in that: The lithium-containing phosphate material includes lithium-containing phosphate particles and a carbon coating layer, wherein the carbon coating layer coats the lithium-containing phosphate particles, and the thickness of the carbon coating layer is 5 nm to 100 nm.

15. The battery cell of any one of claims 1-14, wherein: The compaction density of the positive electrode film is 1.5 g / cm³. 3 ~2.4g / cm 3 ; And / or; the cohesive force of the positive electrode film is 150 N / m to 450 N / m.

16. The battery cell of any one of claims 1-15, wherein: The positive electrode film layer includes an adhesive; The adhesive includes propylene-based polymers; The propylene-based polymers include any one or more of the following: structural units derived from acrylic acid monomers, structural units derived from acrylamide monomers, structural units derived from acrylonitrile monomers, and structural units derived from acrylate monomers.

17. The battery cell of claim 16, wherein: Based on the mass of the positive electrode film, the mass percentage content of the propylene-based polymer is 1% to 3%.

18. The battery cell of any one of claims 1-17, wherein: The battery cell also includes an electrolyte, which comprises an electrolyte salt and an organic solvent; The molar concentration of the electrolyte salt is ≥0.9 mol / L.

19. A method of making the battery cell of claim 1, characterized by: The process includes the following: Preparation of the first positive electrode slurry: The first positive electrode active material is dispersed in a solvent and mixed to form the first positive electrode slurry; Preparation of the second positive electrode slurry: The second positive electrode active material and the second carbon nanotube dispersion are dispersed in a solvent and mixed to form the second positive electrode slurry; Preparation of positive electrode sheet: A first positive electrode slurry is coated on at least one side surface of the positive electrode current collector to obtain a first sub-positive electrode film layer, and a second positive electrode slurry is coated on the side surface of the first sub-positive electrode film layer away from the positive electrode current collector to form a second sub-positive electrode film layer; Battery cell preparation: Assemble the negative electrode, positive electrode and separator together.

20. The method of claim 19, wherein: The second carbon nanotube dispersion comprises second carbon nanotubes and a dispersant; The dispersant comprises one or more of carboxymethyl cellulose and sodium carboxymethyl cellulose.

21. The method of any one of claims 19-20, wherein: In the second carbon nanotube dispersion, the mass ratio of the second carbon nanotube to the dispersant is 100:(50-250).

22. The method of any one of claims 19-21, wherein: The solid content of the second carbon nanotube dispersion is 0.6% to 1.5%.

23. The method of any one of claims 19-22, wherein: The second carbon nanotube dispersion further comprises a surfactant, which includes one or more of glutamic acid surfactants and glycine surfactants.

24. The method of claim 23, wherein: Based on the mass of the second carbon nanotube dispersion, the surfactant content is 2% to 5% by mass.

25. A battery device, characterized by: Includes the battery cell according to any one of claims 1 to 18 or the battery cell prepared by any one of claims 19 to 24.

26. An electrical device, comprising: Includes the battery device as described in claim 25.

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