Positive electrode sheet, electrode assembly, battery cell, battery, and electric device

Abstract

The application discloses a positive electrode sheet, an electrode assembly, a battery monomer, a battery and an electric equipment. The positive electrode sheet comprises a positive current collector and a positive active material layer arranged on at least one side of the positive current collector. The positive active material layer comprises carbon nanotubes and halloysite nanotubes. The mass content of the halloysite nanotubes is 0.05% to 1.00% based on the mass of the positive active material layer. In the application, the electronic conductivity and the ionic conductivity of the positive electrode sheet can be improved by adding the carbon nanotubes and the halloysite nanotubes with the mass content in the range, the direct current impedance of the battery can be reduced, the capacity retention rate of the battery can be improved, and the short-term performance and the cycle performance of the battery can be significantly improved.

Description

Technical Field

[0001] This application relates to the field of battery technology, and more specifically, to a positive electrode sheet, electrode assembly, battery cell, battery, and electrical device. Background Technology

[0002] In recent years, with the increasing demand for clean energy and the rapid development of the new energy field, batteries have been widely used in energy storage power systems such as hydropower, thermal power, wind power, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, and many other fields. Due to the significant advancements in battery technology, higher requirements have been placed on their electrochemical performance and other aspects.

[0003] To further meet user needs and improve user experience, improving the short-term and cycle performance of batteries has become an urgent technical problem to be solved. Summary of the Invention

[0004] In view of the above problems, this application provides a positive electrode sheet, electrode assembly, battery cell, battery, and electrical device, which can improve the short-term performance and cycle performance of the battery.

[0005] The embodiments of this application are implemented as follows:

[0006] In a first aspect, embodiments of this application provide a positive electrode sheet, including a positive current collector and a positive active material layer disposed on at least one side of the positive current collector. The positive active material layer includes carbon nanotubes and halloysite nanotubes, wherein the mass content of halloysite nanotubes is 0.05%-1.00% based on the mass of the positive active material layer.

[0007] In the technical solution of this application embodiment, the positive electrode active material layer includes carbon nanotubes. These carbon nanotubes have a three-dimensional structure and can form a conductive network in the positive electrode sheet, improving the electronic conductivity of the positive electrode sheet. The positive electrode active material layer also includes halloysite nanotubes, with a mass content of 0.05%-1.00%. Halloysite nanotubes within this mass content range can form an ion-conducting network in the positive electrode sheet, improving its ionic conductivity. Therefore, in this application, the combination of carbon nanotubes and halloysite nanotubes within the aforementioned mass content range can effectively promote the formation of both the conductive and ion-conducting networks in the positive electrode sheet. These two interacting networks can effectively improve the electronic and ionic conductivity of the positive electrode sheet, reduce the DC impedance of the battery, improve the battery's capacity retention rate, and thus effectively improve the battery's short-term performance and cycle performance.

[0008] In some embodiments, the mass content of halloysite nanotubes is 0.20%-0.50% based on the mass of the positive electrode active material layer. In this embodiment, the mass content of halloysite nanotubes meets a certain lower limit requirement to avoid insufficient addition of halloysite nanotubes, ensuring that the halloysite nanotubes can form a good ion-conducting network in the positive electrode sheet; the mass content of halloysite nanotubes also meets a certain upper limit requirement to avoid excessive addition of halloysite nanotubes, because further increasing the addition amount of halloysite nanotubes can easily lead to agglomeration, making it difficult to fully disperse in the positive electrode sheet, thus reducing the effect of reducing the DC resistance of the battery and improving the capacity retention rate, thereby affecting the short-term performance and cycle performance of the battery.

[0009] In some embodiments, halloysite nanotubes are linear and / or carbon nanotubes are curved. In this embodiment, linear halloysite nanotubes and / or curved carbon nanotubes can effectively form an interactive conductive network and ion-conducting network in the positive electrode, thus improving the short-term performance and cycle performance of the battery cell.

[0010] In some embodiments, the porosity of the positive electrode sheet is 18%-19%. In this embodiment, halloysite nanotubes and carbon nanotubes have tubular structures, which can increase the porosity of the positive electrode sheet, which is beneficial for the storage and transport of lithium ions, and thus helps to improve the short-term performance and cycle performance of the battery cell.

[0011] In some embodiments, the ionic conductivity of the positive electrode is 0.08-0.16 S / m. In this embodiment, halloysite nanotubes have a tubular structure with a positively charged interior and a negatively charged exterior, which facilitates the adsorption and transport of lithium ions and effectively improves the ionic conductivity of the positive electrode, thus contributing to improved short-term and cycle performance of the battery cell.

[0012] In some embodiments, the average diameter of halloysite nanotubes is 10-20 nm.

[0013] In some embodiments, the average length of halloysite nanotubes is 200-500 nm.

[0014] In some embodiments, the volume average particle size Dv50 of halloysite nanotubes is 5-10 μm.

[0015] In the above embodiments, halloysite nanotubes whose average diameter, average length, and volume average particle size meet the above range can improve the lithium-ion transport efficiency, thus benefiting the short-term performance and cycle performance of battery cells.

[0016] In some embodiments, the mass content of carbon nanotubes is 0.05%-0.70% based on the mass of the positive electrode active material layer. In this embodiment, the mass content of carbon nanotubes meets a certain lower limit requirement to avoid insufficient addition of carbon nanotubes, ensuring that the carbon nanotubes can form a conductive network well in the positive electrode sheet; the mass content of carbon nanotubes also meets a certain upper limit requirement to avoid excessive addition of carbon nanotubes, because further increasing the amount of carbon nanotubes will easily cause them to agglomerate and fail to disperse sufficiently, reducing the effect of reducing the DC resistance of the battery and improving the capacity retention rate, which will affect the short-term performance and cycle performance of the battery.

[0017] In some embodiments, the average diameter of the carbon nanotubes is 2-15 nm.

[0018] In some embodiments, the average length of the carbon nanotubes is 200 nm to 1 μm.

[0019] In the above embodiments, carbon nanotubes with average diameter and / or average length satisfying the above range can form a conductive network in the positive electrode sheet, thereby improving the electronic conductivity of the positive electrode sheet, which is beneficial to improving the short-term performance and cycle performance of the battery cell.

[0020] Secondly, embodiments of this application provide an electrode assembly, including a positive electrode as described in the above embodiments.

[0021] Thirdly, embodiments of this application provide a battery cell including the electrode assembly as described in the above embodiments.

[0022] Fourthly, embodiments of this application provide a battery, including a battery cell as described in the above embodiments.

[0023] Fifthly, embodiments of this application provide an electrical device, including a battery cell as described in the above embodiments or a battery as described in the above embodiments.

[0024] 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

[0025] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 Structural schematic diagrams of vehicles provided for some embodiments of this application

[0027] Figure 2 Exploded views of batteries provided for some embodiments of this application;

[0028] Figure 3 Exploded views of a single battery cell provided in some embodiments of this application;

[0029] Figure 4 This is a schematic diagram of the structure of an electrode assembly provided in some embodiments of this application;

[0030] Figure 5 This is a schematic diagram of the structure of a first type of positive electrode sheet provided in some embodiments of this application;

[0031] Figure 6 This is a schematic diagram of the structure of a second type of positive electrode sheet provided in some embodiments of this application.

[0032] icon:

[0033] 1000 - Vehicles;

[0034] 100 - Battery; 200 - Controller; 300 - Motor;

[0035] 10-Box body; 11-First part; 12-Second part; 13-Accommodation space;

[0036] 20-Battery cell; 21-Casing; 22-Electrode assembly; 23-Electrode terminal; 24-Pressure relief structure;

[0037] 211-Shell; 212-Cover; 213-Sealed space;

[0038] 221 - Positive electrode; 222 - Negative electrode; 223 - Separator membrane;

[0039] 2211 - Positive current collector; 2212 - Positive active material layer. Detailed Implementation

[0040] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0041] The embodiments of the technical solution of this application will now be described in detail with reference to the accompanying drawings. These embodiments are only used to more clearly illustrate the technical solution of this application and are therefore merely examples, and should not be used to limit the scope of protection of this application.

[0042] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the drawings are intended to cover non-exclusive inclusion.

[0043] In the description of the embodiments of this application, the technical terms "first", "second", etc. are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features.

[0044] In the description of the embodiments of this application, the technical terms "inner" and "outer" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the embodiments of this application and simplifying the description, and do not 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.

[0045] In the description of the embodiments of this application, the technical term "and / or", such as "feature 1 and / or feature 2", refers to three cases: feature 1 alone, feature 2 alone, and feature 1 plus feature 2.

[0046] In the description of the embodiments of this application, unless otherwise stated, "multiple" in "one or more" means two or more.

[0047] In the description of the embodiments of this application, unless otherwise expressly specified and limited, the technical terms such as "installation," "connection," "joining," and "fixing" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in the embodiments of this application according to the specific circumstances.

[0048] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0049] In the embodiments of this application, the same reference numerals denote the same components, and for the sake of brevity, detailed descriptions of the same components are omitted in different embodiments. It should be understood that the height, length, width, and other dimensions of various components in the embodiments of this application shown in the accompanying drawings, as well as the overall height, length, width, and other dimensions of the integrated device, are merely illustrative and should not constitute any limitation on this application.

[0050] Currently, power batteries still suffer from high impedance, especially under fast charging conditions. Taking lithium-ion batteries as an example, high impedance degrades both short-term and cycle performance. Disassembling the battery revealed that the resistance of the positive electrode accounts for 47% of the total internal resistance of the battery.

[0051] To improve impedance issues, some technical solutions involve altering the synthesis method of the positive electrode active material, thereby changing its morphology and increasing the ionic conductivity of the positive electrode. However, the steps involved in changing the material morphology in these solutions are generally quite complex. These complex production steps and processes reduce production efficiency and increase production costs, hindering large-scale adoption.

[0052] Based on the above considerations, adding highly conductive ion-additives to the positive electrode is relatively simple and easy to implement. In some technical solutions, halloysite nanotubes are added to the positive electrode. Halloysite nanotubes can promote lithium-ion transport in the electrolyte, thereby reducing DC resistance and improving capacity retention. However, in the above technical solutions, halloysite nanotubes themselves are not conductive and cannot significantly improve the electronic conductivity of the positive electrode. Therefore, using halloysite nanotubes alone has a very limited effect on reducing DC resistance and improving capacity retention in the battery.

[0053] Building upon this foundation, the applicant, through in-depth research, discovered that adding carbon nanotubes and halloysite nanotubes to the positive electrode plate is beneficial. Carbon nanotubes, with their high conductivity, can form a three-dimensional network structure, enabling the formation of a conductive network within the positive electrode plate. Halloysite nanotubes, with their tubular structure, positively charged interior and negatively charged exterior, can form an ion-conducting network within the positive electrode plate. This interaction of conductive and ion-conducting networks helps improve the electronic and ionic conductivity of the positive electrode plate, while reducing its impedance.

[0054] Based on this, this application provides a positive electrode sheet, the active material layer of which includes carbon nanotubes and halloysite nanotubes. The impedance of the positive electrode sheet can be reduced by improving the electronic conductivity of carbon nanotubes and the ionic conductivity of halloysite nanotubes, thereby effectively improving the impedance and performance of the battery.

[0055] From a market perspective, the application of power batteries is becoming increasingly widespread. Power batteries are not only used in energy storage systems such as hydropower, thermal power, wind power, and solar power plants, but also extensively in electric vehicles such as electric bicycles, electric motorcycles, and electric cars, as well as in military equipment and aerospace. With the continuous expansion of the application areas of power batteries, the market demand is also constantly increasing.

[0056] For ease of explanation, the following embodiments use a vehicle as an example of an electrical device according to an embodiment of this application.

[0057] See Figure 1 , Figure 1 This is a schematic diagram of the structure of a vehicle 1000 provided in some embodiments of this application. The vehicle 1000 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 100 is disposed inside the vehicle 1000, and the battery 100 can be located at the bottom, front, or rear of the vehicle 1000. The battery 100 can be used to power the vehicle 1000; for example, the battery 100 can serve as the operating power source for the vehicle 1000. The vehicle 1000 may also include a controller 200 and a motor 300. The controller 200 is used to control the battery 100 to supply power to the motor 300, for example, to meet the power needs of the vehicle 1000 during startup, navigation, and driving.

[0058] In some embodiments of this application, the battery 100 can not only serve as the operating power source for the vehicle 1000, but also as the driving power source for the vehicle 1000, replacing or partially replacing fuel or natural gas to provide driving power for the vehicle 1000.

[0059] In this application, battery 100 refers to a single physical module comprising multiple battery cells 20 to provide higher voltage and capacity, which may be in the form of a battery pack, battery module, etc. Battery 100 may include a housing 10 for encapsulating the multiple battery cells 20, the housing 10 preventing liquids or other foreign objects from affecting the charging or discharging of the battery cells 20.

[0060] See Figure 2 , Figure 2This is an exploded view of a battery 100 provided in some embodiments of this application. The battery 100 includes a housing 10 and a plurality of battery cells 20, which are housed within the housing 10. The housing 10 is used to house the battery cells 20 and can have various structures. In some embodiments, the housing 10 may include a first portion 11 and a second portion 12, which overlap each other, defining a receiving space 13 for accommodating the battery cells 20. The second portion 12 may be a hollow structure with one open end, and the first portion 11 may be a plate-like structure, overlapping the open side of the second portion 12 to form a housing 10 with the receiving space 13; alternatively, the first portion 11 and the second portion 12 may both be hollow structures with one open side, overlapping the open side of the second portion 12 to form a housing 10 with the receiving space 13. Of course, the first portion 11 and the second portion 12 can have various shapes, such as cylinders, cuboids, etc.

[0061] In battery 100, multiple battery cells 20 can be connected in series, parallel, or in a mixed configuration. A mixed configuration means that multiple battery cells 20 are connected in both series and parallel configurations. Multiple battery cells 20 can be directly connected in series, parallel, or in a mixed configuration, and then the entire assembly of the multiple battery cells 20 is housed within the housing 10. Alternatively, multiple battery cells 20 can first be connected in series, parallel, or in a mixed configuration to form modules, and then these modules can be connected in series, parallel, or in a mixed configuration to form a whole, which is also housed within the housing 10. Battery 100 may also include other structures; for example, multiple battery cells 20 can be electrically connected through a busbar component to achieve parallel, series, or mixed configurations of the multiple battery cells 20.

[0062] The battery cell 20 refers to the smallest unit that makes up the battery pack. The battery cell 20 can be a secondary battery 100 or a primary battery 100; it can also be a lithium-sulfur battery 100, a sodium-ion battery 100 or a magnesium-ion battery 100, but is not limited to these.

[0063] See Figure 3 The battery cell 20 may include a housing 21, an electrode assembly 22 and an electrolyte, with the electrode assembly 22 and the electrolyte both housed within the housing 21.

[0064] The outer casing 21 may include a housing 211 and a cover 212. The housing 211 is an assembly that fits with the cover 212 to form an internal sealed space 213 of the battery cell 20, wherein the formed sealed space 213 can be used to accommodate the electrode assembly 22, electrolyte, and other components. The cover 212 is a component that covers the opening of the housing 211 to isolate the internal environment of the battery cell 20 from the external environment. The shape of the cover 212 may be adapted to the shape of the housing 211 to fit the housing 211, and functional components such as electrode terminals 23 and pressure relief structures 24 may also be provided on the cover 212. A sealing ring may be provided between the opening of the housing 211 and the cover 212 to achieve a seal between the housing 211 and the cover 212.

[0065] The housing 211 and cover 212 can be of various shapes and sizes, such as cuboids, cylinders, and hexagonal prisms. Specifically, the shapes of the housing 211 and cover 212 can be determined according to the specific shape and size of the electrode assembly 22. The materials of the housing 211 and cover 212 can be various, such as, but not limited to, metals like copper, iron, aluminum, stainless steel, and aluminum alloys. The materials of the sealing ring can be various, such as, but not limited to, materials resistant to electrolyte corrosion, high toughness, and fatigue resistance, such as PP (polypropylene), PC (polycarbonate), and PET (polyethylene terephthalate). A plating layer can be formed on the outer surface of the housing 211, and the plating layer material can be various, such as, but not limited to, corrosion-resistant materials like Ni and Cr.

[0066] See Figure 4 The electrode assembly 22 can be composed of a positive electrode 221, a negative electrode 222, and a separator 223. The battery cell 20 mainly relies on the movement of metal ions between the positive electrode 221 and the negative electrode 222 to operate. The positive electrode 221 includes a positive current collector 2211 and a positive active material layer 2212 disposed on the surface of the positive current collector 2211. The material of the positive current collector 2211 can be aluminum, and the positive active material in the positive active material layer 2212 can be lithium cobalt oxide, lithium iron phosphate, ternary lithium, lithium manganese oxide, lithium-rich manganese-based materials, lithium-sulfur, etc. The negative electrode 222 includes a negative current collector and a negative active material layer disposed on the surface of the negative current collector. The material of the negative current collector can be copper, and the negative active material in the negative active material layer can be carbon, silicon, etc. Furthermore, the electrode assembly 22 can be a wound structure or a stacked structure; the embodiments of this application are not limited to these.

[0067] The positive electrode sheet proposed in the embodiments of this application will be described in detail below.

[0068] See Figure 5 and Figure 6In a first aspect, embodiments of this application provide a positive electrode 221, including a positive current collector 2211 and a positive active material layer 2212 disposed on at least one side of the positive current collector 2211. The positive active material layer 2212 includes carbon nanotubes and halloysite nanotubes, wherein, based on the mass of the positive active material layer 2212, the mass content of halloysite nanotubes is 0.05%-1.00%.

[0069] In the positive electrode 221, a positive electrode active material layer 2212 can be formed on one side surface of the positive electrode current collector 2211, such as... Figure 5 As shown; alternatively, positive electrode active material layers 2212 can be respectively disposed on both sides of the positive electrode current collector 2211, such as Figure 6 As shown.

[0070] The positive electrode active material can be a lithium-containing active material, a sodium-containing active material, or an active material containing both lithium and sodium.

[0071] Carbon nanotubes are one-dimensional carbon nanomaterials, primarily composed of several to dozens of layers of coaxial cylindrical tubes formed by hexagonally arranged carbon atoms. The radial dimension of carbon nanotubes is on the nanometer scale, and the axial dimension is on the micrometer scale. The carbon atoms are arranged in sp... 2 Hybridization is the dominant process. Carbon nanotubes can include single-walled carbon nanotubes, double-walled carbon nanotubes, and multi-walled carbon nanotubes, etc.

[0072] Halloysite nanotubes are tubular aluminosilicate natural nanomaterials. The chemical formula of halloysite nanotubes can be Al₂O₃·2SiO₂·nH₂O (n = 0 or 2). Halloysite nanotubes can include a bilayer structure, consisting of an inner layer and an outer layer. The inner layer can be alumina, and the outer layer can be silicon oxide. The inner alumina layer can be octahedral and may contain a certain amount of hydroxyl groups, making it positively charged. The outer silicon oxide layer can be tetrahedral and may contain a small amount of Si-OH groups, making it negatively charged.

[0073] Based on the mass of the positive electrode active material layer 2212, the mass content of halloysite nanotubes can be the mass percentage of halloysite nanotubes added during the preparation of the positive electrode slurry 221, expressed as a percentage. As an example, the mass content of halloysite nanotubes can be, for example, but not limited to, any one of 0.05%, 0.10%, 0.20%, 0.30%, 0.40%, 0.50%, 0.60%, 0.70%, 0.80%, 0.90%, or 1.00%, or a range between any two.

[0074] The unique curved tubular structure of carbon nanotubes can form a three-dimensional network structure in the positive electrode 221. The high conductivity of carbon nanotubes facilitates electron transport within the conductive network. Halloysite nanotubes can form an ion-conducting network in the positive electrode 221, shortening the path for lithium ions in the electrolyte to transport into the interior of the positive electrode 221. The unique straight tubular structure of halloysite nanotubes and the electrical difference between the inner and outer layers further promote the adsorption and transport of lithium ions in the ion-conducting network, improving lithium ion mobility.

[0075] In some embodiments, the mass content of halloysite nanotubes is 0.20%-0.50% based on the mass of the positive electrode active material layer 2212.

[0076] Based on the mass of the positive electrode active material layer 2212, the mass content of halloysite nanotubes can be the mass percentage of halloysite nanotubes added during the preparation of the positive electrode slurry 221, expressed as a percentage. As an example, the mass content of halloysite nanotubes can be, for example, but not limited to, any one of 0.20%, 0.30%, 0.40%, 0.50%, or a range between any two.

[0077] In this embodiment, the mass content of halloysite nanotubes meets a certain lower limit requirement to avoid insufficient addition of halloysite nanotubes, ensuring that the halloysite nanotubes can form a good ion-conducting network in the positive electrode 221. The mass content of halloysite nanotubes also meets a certain upper limit requirement to avoid excessive addition of halloysite nanotubes. This is because further increasing the amount of halloysite nanotubes will cause them to agglomerate and fail to disperse sufficiently in the positive electrode 221. This would reduce the DC resistance of the battery cell 20 and decrease its capacity retention, thus affecting the short-term performance and cycle performance of the battery cell 20.

[0078] In some embodiments, halloysite nanotubes are linear; and / or carbon nanotubes are curved.

[0079] Halloysite nanotubes are linear because they can be observed to have a straight structure or morphology in electron microscopy images.

[0080] The bending shape of carbon nanotubes can be observed in electron micrographs, showing a bent structure or morphology.

[0081] In this embodiment, linear halloysite nanotubes and / or curved carbon nanotubes can effectively form an interactive conductive network and an ion-conducting network in the positive electrode 221, which is beneficial to improving the short-term performance and cycle performance of the battery cell 20.

[0082] In some embodiments, the porosity of the positive electrode 221 is 18%-19%.

[0083] The porosity of the positive electrode 221 can be expressed as the ratio of the volume of pores in the positive electrode 221 to its total volume, expressed in percentage (%). The porosity of the positive electrode 221 can be measured using test methods known in the art. For example, the test can be performed using the AccuPycⅡ1340 true density meter according to the WI-PCA-080 true density method, as per the national standard GB / T 24586-2009.

[0084] As an example, the porosity of the positive electrode 221 can be, for example, but not limited to, any one of 18.0%, 18.1%, 18.2%, 18.3%, 18.4%, 18.5%, 18.6%, 18.7%, 18.8%, 18.9%, 19.0% or a range between any two.

[0085] In this embodiment, halloysite nanotubes and carbon nanotubes have tubular structures, which can increase the porosity of the positive electrode 221, thus improving the short-term performance and cycle performance of the battery cell 20.

[0086] In some embodiments, the positive electrode 221 has an ionic conductivity of 0.08-0.16 S / m.

[0087] The ionic conductivity of the positive electrode 221 can be a physical quantity characterizing the ability of ions to conduct electricity, with units of S / m. The ionic conductivity of the positive electrode 221 can be measured using test methods known in the art. As an example, electrochemical impedance spectroscopy can be performed using a VMP3 electrochemical co-workstation, referring to standard WI-ATC-2013.

[0088] As an example, the ionic conductivity of the positive electrode 221 can be, for example, but not limited to, any one of 0.08 S / m, 0.09 S / m, 0.10 S / m, 0.11 S / m, 0.12 S / m, 0.13 S / m, 0.14 S / m, 0.15 S / m, 0.16 S / m, or a range between any two.

[0089] In this embodiment, halloysite nanotubes have a tubular structure with a positive charge inside and a negative charge outside, which can facilitate the adsorption and transport of lithium ions and effectively improve the ionic conductivity of the positive electrode 221. Therefore, it is beneficial to improve the short-term performance and cycle performance of the battery cell 20.

[0090] In some embodiments, the average diameter of halloysite nanotubes is 10-20 nm.

[0091] The average diameter of halloysite nanotubes can be the average of the diameters of multiple halloysite nanotubes, measured in nm. The average diameter of halloysite nanotubes can be measured using methods known in the art. For example, the average diameter can be obtained by statistically analyzing and calculating the results from SEM and TEM tests using Nano Measurer software.

[0092] As an example, the average diameter of halloysite nanotubes can be, for example, but not limited to, any one of 10 nm, 11 nm, 12 nm, 13 nm, 14 nm, 15 nm, 16 nm, 17 nm, 18 nm, 19 nm, 20 nm, or a range between any two.

[0093] In this embodiment, the average diameter of the halloysite nanotubes meets a certain lower limit requirement to prevent the average diameter from being too small, which could accelerate the lithium-ion transport rate. The average diameter of the halloysite nanotubes also meets a certain upper limit requirement to prevent the average diameter from being too large. If the average diameter of the halloysite nanotubes increases further, the number of halloysite nanotubes per unit area decreases, reducing the effectiveness of improving the ionic conductivity of the positive electrode 221, thereby affecting the reduction of the DC impedance of the battery cell 20 and the improvement of the capacity retention rate of the battery cell 20.

[0094] In some embodiments, the average length of halloysite nanotubes is 200-500 nm.

[0095] The average length of halloysite nanotubes can be the average of the lengths of multiple halloysite nanotubes, measured in nm. The average length of halloysite nanotubes can be measured using methods known in the art. For example, the average length can be obtained by statistically analyzing and calculating the results from SEM and TEM tests using Nano Measurer software.

[0096] As an example, the average length of halloysite nanotubes can be, for example, but not limited to, any one of 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, 450 nm, 500 nm, or a range between any two.

[0097] In this embodiment, the average length of the halloysite nanotubes meets a certain lower limit requirement to prevent the average length of the halloysite nanotubes from being too small, which could accelerate the lithium-ion transport rate. The average length of the halloysite nanotubes also meets a certain upper limit requirement to prevent the average length from being too large. If the average length of the halloysite nanotubes further increases, the lithium-ion transport path will also increase accordingly, reducing the effectiveness of improving the ionic conductivity of the positive electrode 221, thereby affecting the reduction of the DC impedance of the battery cell 20 and the improvement of the capacity retention rate of the battery cell 20.

[0098] In some embodiments, the volume average particle size Dv50 of halloysite nanotubes is 5-10 μm.

[0099] The volume average particle size (Dv50) of halloysite nanotubes can be defined as the particle size corresponding to a cumulative volume percentage of 50% for halloysite nanotube materials. The volume average particle size (Dv50) of halloysite nanotubes can be measured using methods known in the art. For example, GB / T 19077-2016 can be referenced, and characterization testing can be performed using a Malvern laser particle size analyzer, such as the Malvern Mastersizer-3000.

[0100] As an example, the volume average particle size Dv50 of halloysite nanotubes is, for example, but not limited to, any one of 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm or a range between any two.

[0101] In this embodiment, the volume average particle size Dv50 of halloysite nanotubes meets the above range, which can shorten the lithium ion transport path, improve the lithium ion transport efficiency, and help improve the short-term performance and cycle performance of the battery cell 20.

[0102] In some embodiments, the mass content of carbon nanotubes is 0.05%-0.70% based on the mass of the positive electrode active material layer 2212.

[0103] Based on the mass of the positive electrode active material layer 2212, the mass content of carbon nanotubes can be the percentage of carbon nanotubes added during the preparation of the positive electrode slurry 221, expressed as a percentage. As an example, the mass content of carbon nanotubes can be, for example, but not limited to, any one of 0.05%, 0.10%, 0.20%, 0.30%, 0.40%, 0.50%, 0.60%, or 0.70%, or a range between any two.

[0104] In this embodiment, the mass content of carbon nanotubes meets a certain lower limit requirement to avoid insufficient addition of carbon nanotubes, thus enabling the carbon nanotubes to form a conductive network effectively. The mass content of carbon nanotubes also meets a certain upper limit requirement to avoid excessive addition of carbon nanotubes, because further increasing the amount of carbon nanotubes will cause them to agglomerate and fail to disperse sufficiently. This would reduce the DC resistance of the battery cell 20 and decrease its capacity retention, thus affecting the short-term performance and cycle performance of the battery cell 20.

[0105] In some embodiments, the average diameter of the carbon nanotubes is 2-15 nm.

[0106] In some embodiments, the average length of the carbon nanotubes is 200 nm to 1 μm.

[0107] The average diameter of a carbon nanotube can be the average of the diameters of multiple carbon nanotubes, measured in nm. As an example, the average diameter of a carbon nanotube can be, for example, but not limited to, any one of 2 nm, 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, 10 nm, 11 nm, 12 nm, 13 nm, 14 nm, or 15 nm, or a range between any two.

[0108] The average length of a carbon nanotube can be the average of the lengths of multiple carbon nanotubes, in nm or μm. As an example, the average length of a carbon nanotube can be, for example, but not limited to, a point value of 200 nm, 300 nm, 400 nm, 500 nm, 600 nm, 700 nm, 800 nm, 900 nm, 1 μm, or a range between any two.

[0109] The average diameter and average length of carbon nanotubes can be measured using testing methods known in the art. For example, the average diameter and average length can be obtained by statistically analyzing and calculating the results from SEM and TEM tests using Nano Measurer software.

[0110] In the above embodiments, carbon nanotubes with average diameter and / or average length satisfying the above range can form a conductive network better, improve the electronic conductivity of the positive electrode, and thus benefit the short-term performance and cycle performance of the battery cell.

[0111] Secondly, embodiments of this application provide an electrode assembly 22, including a positive electrode 221 as described in the above embodiments.

[0112] Thirdly, embodiments of this application provide a battery cell 20, including an electrode assembly 22 as described in the above embodiments.

[0113] Fourthly, embodiments of this application provide a battery 100, including a battery cell 20 as described in the above embodiments.

[0114] Fifthly, embodiments of this application provide an electrical device, including a battery cell 20 as described in the above embodiments or a battery 100 as described in the above embodiments.

[0115] According to some embodiments of this application, the positive electrode 221 includes a positive current collector 2211 and a positive active material layer 2212 disposed on at least one side of the positive current collector 2211. The positive active material layer 2212 includes, for example, carbon nanotubes and halloysite nanotubes, wherein, based on the mass of the positive active material layer 2212, the mass content of halloysite nanotubes is 0.05-1.00%.

[0116] Based on the positive electrode 221 provided in the embodiments of this application, the material composition and morphology can be confirmed by inductively coupled plasma (ICP), energy dispersive X-ray spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS), and the carbon nanotubes and halloysite nanotubes and their mass content in the positive electrode 221 can be calculated in reverse.

[0117] The following specific embodiments are provided to better illustrate this application.

[0118] I. Preparation of battery cells

[0119] Preparation of the positive electrode sheet

[0120] NCM622, conductive carbon, polyvinylidene fluoride (PVDF), carbon nanotubes, and halloysite nanotubes (in some comparative examples, carbon nanotubes and / or halloysite nanotubes are omitted if they are unavailable) were prepared in a specific mass ratio, dissolved in N-methylpyrrolidone (NMP), stirred for 4 hours, and the viscosity was adjusted to 10000 mPa·s with NMP. The slurry was stirred evenly, coated onto aluminum foil, and dried at 90°C. After cold pressing and slitting, the positive electrode sheet was obtained.

[0121] Preparation of the negative electrode sheet

[0122] The active material artificial graphite, conductive agent carbon black, binder styrene-butadiene rubber (SBR), and thickener sodium carboxymethyl cellulose (CMC) are dissolved in deionized water at a weight ratio of 96.2:0.8:0.8:1.2 and mixed evenly to prepare a negative electrode slurry. The negative electrode slurry is coated evenly on copper foil once or multiple times and dried at 90°C. After cold pressing and slitting, the negative electrode sheet is obtained.

[0123] Preparation of Electrolyte

[0124] In an argon atmosphere glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), the organic solvents ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed evenly at a volume ratio of 3 / 7. 12.5% ​​LiPF6 lithium salt was added and dissolved in the organic solvent and stirred evenly to obtain the electrolyte of Example 1.

[0125] Preparation of the separating membrane

[0126] Polyethylene film is used as the separation membrane.

[0127] [Preparation of Lithium-ion Batteries]

[0128] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide insulation. Then, the electrodes are wound, tabs are welded, and the cells are housed in an aluminum casing. After baking at 105°C to remove moisture, electrolyte is injected and the casing is sealed, resulting in a non-charged battery cell. This non-charged battery cell then undergoes a series of processes including settling, hot and cold pressing, formation, shaping, and capacity testing to obtain a lithium-ion battery cell.

[0129] II. Testing Methods

[0130] [Ion Conductivity Test]

[0131] Electrochemical impedance spectroscopy can be performed using the VMP3 electrochemical co-workstation, referring to the standard WI-ATC-2013.

[0132] The specific testing method is as follows: (1) Bake the aluminum-plastic film, electrode, and separator at 60°C for 4 hours before use; (2) Prepare the die, 23*35*2mm; (3) Cut the electrode into small pieces slightly larger than the die size with ceramic scissors and place them on the die for punching. Take out the punched electrode with tweezers for later use; (4) Then make the electrode into a single-layer symmetrical cell; (5) Place the symmetrical cell in an electrochemical workstation to test EIS, set the frequency to 0.5Hz-200kHz, and the disturbance voltage to 10mV; (6) Calculate the ionic resistance Rion of the electrode through the intersection of the two straight lines of EIS; (7) Electrode ionic conductivity = d (electrode thickness) / (Rion * A (electrode area)).

[0133] Porosity Test

[0134] You can refer to the national standard GB / T 24586-2009 and use the AccuPycⅡ1340 true density meter to conduct the test according to the WI-PCA-080 true density method.

[0135] Electrode porosity testing utilizes the displacement method of a small-molecule diameter inert gas (helium), combined with Archimedes' principle and Bohr's law (PV = nRT), to accurately measure the true volume of the material being tested, thereby obtaining the porosity of the sample.

[0136] Calculation formulas: Apparent volume V2 = S * H ​​* A; Porosity P = (V2 - V1) / V2 * 100%

[0137] Where: S - area, cm 2 H - Thickness, cm; A - Number of samples, EA; V1 - True volume of the sample, cm³ 3 V2 – Apparent volume of the sample, cm³ 3 P—Porosity of the sample, %.

[0138] [Average Diameter and Average Length Test]

[0139] Based on the SEM and TEM test results, the Nano Measurer software was used to statistically analyze and calculate the results to obtain the average diameter and length.

[0140] SEM testing was conducted in accordance with the testing standards of JY / T 010-1996, using a Sigma 300 scanning electron microscope and energy dispersive spectroscopy (EDS) instrument, and following the WI-PCA-053 standard guidelines for surface micro-area morphology analysis.

[0141] TEM testing was performed according to GB / T 34002-2017, using a 200kV field emission scanning transmission electron microscope JEOL JEM-F200. The STEM-HAADF resolution was 0.16nm@200kV; the EDS energy resolution was MnKa 133eV, and the accelerating voltages were 200kV and 80kV.

[0142]

Volume Average Particle Size Dv50 Test

[0143] The national standard GB / T 19077-2016 can be referenced, and a Malvern laser particle size analyzer can be used for characterization testing, such as the Malvern Mastersizer-3000.

[0144] DC Impedance Reduction Rate Test

[0145] At 25°C, the capacity of the above lithium-ion battery was tested at a charging rate of 0.33C and a discharging rate of 0.33C. Then, the cell was adjusted to 50% SOC and charged and discharged at a 4C rate for 60 seconds. The DC resistance of the first 30 seconds of each discharge was extracted.

[0146] The rate of decrease in DC impedance of a lithium-ion battery = [(DC resistance - DC resistance of Comparative Example 1) / DC resistance of Comparative Example 1] × 100%.

[0147] In this embodiment, a higher DC impedance reduction rate means better short-term performance of the battery cell.

[0148] [Capacity Retention Rate Test]

[0149] At 25°C, the lithium-ion battery was charged at a constant current of 1 / 3C to 3.65V, then charged at a constant voltage of 3.65V to a current of 0.05C. After resting for 5 minutes, it was discharged at a rate of 1 / 3C to 2.5V. This constitutes one charge-discharge cycle, and the discharge capacity of this cycle is the discharge capacity of the first cycle. The lithium-ion battery was subjected to the above steps for charge-discharge cycle testing, and the discharge capacity of the 800th cycle was recorded.

[0150] The capacity retention rate of a lithium-ion battery after 800 cycles = (discharge capacity of the 800th cycle / discharge capacity of the first cycle) × 100%.

[0151] In this embodiment of the application, a higher capacity retention rate means better cycle performance of the battery cell.

[0152] III. Experimental Conditions and Test Results

[0153] The types, mass content, morphology, and performance test results of the additives used in the positive electrode active material layer of each experimental group are shown in Tables 1 and 2. Among them, the performance test results of the battery cells include the DC impedance reduction rate and capacity retention rate of the battery cells.

[0154] Table 1

[0155]

[0156] Table 2

[0157]

[0158] According to Tables 1 and 2:

[0159] In Examples 1-25, the positive electrode active material layer all included carbon nanotubes and halloysite nanotubes with a mass content of 0.05%-1.00%. Compared with Comparative Example 1, which did not include carbon nanotubes and halloysite nanotubes in its positive electrode active material layer, the ionic conductivity and porosity of the positive electrode sheet were significantly improved, and the DC impedance reduction rate and capacity retention rate of the battery cell were also significantly improved. This indicates that the battery cells in Examples 1-25 have significantly improved short-term performance and cycle performance. In Comparative Example 2, no halloysite nanotubes were added to the positive electrode active material layer, but carbon nanotubes with the same mass content as in Examples 1-11 were added. However, the ionic conductivity and porosity of the positive electrode sheet were still much lower than those in Examples 1-11, and the resulting battery cells had poor DC impedance and capacity retention rates. This indicates that adding carbon nanotubes alone to the positive electrode active material layer has limited effect on improving the short-term performance and cycle performance of the battery cells. Compared to Comparative Example 2, Comparative Example 3 added 1.50% halloysite nanotubes to the positive electrode active material layer. Excessive halloysite nanotubes agglomerated within the positive electrode sheet and could not be fully dispersed, indicating that adding excessive halloysite nanotubes to the positive electrode active material layer not only failed to improve the DC impedance reduction rate and capacity retention of the battery cell, but actually worsened the effect. Comparative Example 4 included 0.30% halloysite nanotubes in its positive electrode active material layer, but did not include carbon nanotubes. Compared to Example 4, the positive electrode sheet exhibited poorer ionic conductivity and porosity, and the effect of adding halloysite nanotubes alone to the positive electrode active material layer on improving the DC impedance and capacity retention of the battery cell was also limited.

[0160] In Examples 1-11, the mass content of carbon nanotubes in the positive electrode active material layer was 0.30%. Specifically, in Examples 1-4, when the mass content of halloysite nanotubes was in the range of 0.05%-0.30%, the ionic conductivity and porosity of the positive electrode gradually increased with the gradual increase in the halloysite nanotube mass content, and the DC impedance reduction rate and capacity retention rate of the battery cell also gradually improved. In Examples 5-11, when the mass content of halloysite nanotubes was in the range of 0.40%-1.00%, although the ionic conductivity and porosity of the positive electrode decreased to some extent with the gradual increase in the halloysite nanotube mass content, the resulting battery cell still exhibited a significantly improved DC impedance reduction rate and capacity retention rate.

[0161] In Examples 4 and 12-15, the mass content of halloysite nanotubes in the positive electrode active material layer was 0.30%. Among them, in Examples 4 and 12-14, when the mass content of carbon nanotubes in the positive electrode active material layer was in the range of 0.05%-0.70%, the resulting battery cells had better DC impedance reduction rate and capacity retention rate, exhibiting superior short-term performance and cycle performance.

[0162] In Examples 16-25, the positive electrode active material layer comprised 0.30% halloysite nanotubes and 0.30% carbon nanotubes by mass. In Examples 17-19, when the average diameter of the halloysite nanotubes was in the range of 10-20 nm and the volume average particle size Dv50 was in the range of 6.3-8.9 μm, the resulting battery cells exhibited better DC impedance reduction and capacity retention. In Examples 22-24, when the average length of the halloysite nanotubes was in the range of 200-500 nm and the volume average particle size Dv50 was in the range of 6.4-8.2 μm, the DC impedance reduction and capacity retention of the resulting battery cells were significantly improved.

Claims

1. A positive electrode sheet, comprising a positive current collector and a positive active material layer disposed on at least one side of the positive current collector, characterized in that, The positive electrode active material layer includes carbon nanotubes and halloysite nanotubes, wherein the mass content of the halloysite nanotubes is 0.05%-1.00% based on the mass of the positive electrode active material layer.

2. The positive electrode sheet according to claim 1, characterized in that, Based on the mass of the positive electrode active material layer, the mass content of the halloysite nanotubes is 0.20%-0.50%.

3. The positive electrode sheet according to claim 1 or 2, characterized in that, The halloysite nanotubes are linear; and / or The carbon nanotubes are curved.

4. The positive electrode sheet according to any one of claims 1-3, characterized in that, The porosity of the positive electrode sheet is 18%-19%.

5. The positive electrode sheet according to any one of claims 1-4, characterized in that, The positive electrode has an ionic conductivity of 0.08-0.16 S / m.

6. The positive electrode sheet according to any one of claims 1-5, characterized in that, The halloysite nanotubes have an average diameter of 10-20 nm.

7. The positive electrode sheet according to any one of claims 1-6, characterized in that, The halloysite nanotubes have an average length of 200-500 nm.

8. The positive electrode sheet according to any one of claims 1-7, characterized in that, The volume average particle size Dv50 of the halloysite nanotubes is 5-10 μm.

9. The positive electrode sheet according to any one of claims 1-8, characterized in that, Based on the mass of the positive electrode active material layer, the mass content of the carbon nanotubes is 0.05%-0.70%.

10. The positive electrode sheet according to any one of claims 1-9, characterized in that, The average diameter of the carbon nanotubes is 2-15 nm.

11. The positive electrode sheet according to any one of claims 1-10, characterized in that, The average length of the carbon nanotubes is 200 nm - 1 μm.

12. An electrode assembly, characterized in that, Includes the positive electrode sheet as described in any one of claims 1-11.

13. A single battery cell, characterized in that, Includes the electrode assembly as described in claim 12.

14. A battery, characterized in that, Includes the battery cell as described in claim 13.

15. An electrical appliance, characterized in that, This includes the battery cell as described in claim 13 or the battery as described in claim 14.

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