An electrode sheet and its preparation method, a battery and an electrical device thereof

Abstract

This application relates to the field of batteries, specifically to an electrode sheet and its preparation method, a battery, and an electrical device. The electrode sheet of this application comprises a current collector, a conductive buffer layer, and an active layer stacked sequentially. At least one of the conductive buffer layer and the active layer comprises a carbon material, including one or more of graphite, soft carbon, and fullerene. The electrode sheet of this application can mitigate the squeezing effect of the active material in the active layer on the current collector, reducing the current collector's elongation, thereby narrowing the elongation difference between the current collector and the active layer, and improving the problems of active layer edge collapse and winding breakage.

Description

Technical Field

[0001] This application relates to the field of batteries, specifically to an electrode sheet and its preparation method, a battery, and an electrical device. Background Technology

[0002] In battery chemical reactions, electron transfer is typically achieved using active materials in the electrodes. These active materials are usually bonded to one or both surfaces of the current collector. A common method for bonding the active material to the current collector is to prepare an electrode active slurry by combining the active material with binders, conductive agents, etc. This slurry is then coated onto one or both surfaces of the current collector, followed by drying and cold pressing to form an active layer containing the active material on the current collector surface. After cold pressing, the electrode can be further processed through winding or other processes.

[0003] In actual production, the active layer often collapses during the cold pressing process, which in turn leads to breakage problems (winding strip breakage) in the winding process, seriously reducing the quality of the electrode sheet and thus affecting the battery performance. Summary of the Invention

[0004] In view of the above problems, this application provides an electrode sheet and its preparation method, a battery and an electrical device, which can alleviate the problems of active layer collapse and winding breakage during the processing of the electrode sheet.

[0005] In a first aspect, this application provides an electrode comprising a current collector, a conductive buffer layer, and an active layer stacked sequentially, wherein at least one of the conductive buffer layer and the active layer comprises a carbon material, and the carbon material comprises one or more of graphite, soft carbon, and fullerene.

[0006] In the technical solution of this application embodiment, a conductive buffer layer is provided between the current collector and the active layer, and carbon materials such as graphite, soft carbon, and fullerene are provided in at least one of the conductive buffer layer and the active layer. These carbon materials have special structures and properties, and can undergo internal structural slippage and / or interparticle slippage under pressure.

[0007] Specifically, in graphite crystals, carbon atoms are arranged in an ordered and anisotropic manner, with carbon atoms in the same layer arranged in sp... 2Hybridization forms covalent bonds, with each carbon atom connected to three other atoms by three covalent bonds. The layers are primarily bonded by molecular bonds, resulting in weak molecular attraction between layers. Therefore, graphite is characterized by its soft particle texture and weak van der Waals forces between particles, leading to relative slippage between layers during cold pressing. Similarly, fullerene also has a layered structure, with layers primarily bonded by molecular bonds and weak molecular attraction between layers, resulting in relative slippage between layers during cold pressing. Soft carbon refers to amorphous carbon materials that can be graphitized at temperatures above 2500℃, i.e., amorphous carbon that is easily graphitized at high temperatures. The microcrystalline structure of soft carbon has lattice fringes, which are parallel straight fringes. The structure contains a large amount of amorphous carbon, resulting in a relatively loose and disordered crystal structure, making it prone to interlayer slippage during cold pressing.

[0008] Therefore, when the conductive buffer layer contains carbon material, it can mitigate the squeezing effect of the active material in the active layer on the current collector, reduce the current collector's elongation, thereby narrowing the elongation difference between the current collector and the active layer, and improving the problems of active layer edge collapse and winding breakage. Similarly, when the active layer contains carbon material, the combined effect of the conductive buffer layer and the carbon material can also mitigate the squeezing effect of the active material in the active layer on the current collector, ultimately improving the problems of active layer edge collapse and winding breakage.

[0009] Meanwhile, since the conductive buffer layer acts as a barrier between the active layer and the current collector, the active material in the active layer does not directly contact the current collector, which can improve the damage of the active material to the current collector during the cold pressing process.

[0010] In some embodiments, the Dv50 of the carbon material is 0.4–1.5 μm, and optionally 0.7–0.9 μm.

[0011] In some embodiments, the Dv90 of the carbon material is 1–4 μm, and optionally 1–3 μm.

[0012] The carbon material used in this embodiment has a small particle size, which is beneficial for forming an extremely thin conductive buffer layer. Since carbon materials typically have a lower energy density than the active materials in the active layer, a thinner conductive buffer layer, when it contains carbon material, is more conducive to reducing the energy density loss of the electrode. Alternatively, the small particle size of the carbon material allows for good dispersion within the active layer.

[0013] In some embodiments, the conductive buffer layer comprises the carbon material, wherein the mass content of the carbon material in the conductive buffer layer is greater than or equal to 5% and less than 100%, optionally 14% to 56%. With appropriate dosage, the structural characteristics of the carbon material can be fully utilized to improve the problems of active layer edge collapse and winding breakage caused by large current collector elongation, and to reduce damage to the current collector; it also helps to reduce the energy density loss of the electrode.

[0014] In some embodiments, the active layer comprises the carbon material, and the mass content of the carbon material in the active layer is 1% to 5%, optionally 3% to 5%. When the active layer comprises carbon material, considering that these carbon materials typically have lower energy densities than the active materials in the active layer, controlling the carbon material content in the active layer within an appropriate range is beneficial for reducing the energy density loss of the electrode.

[0015] In some embodiments, the thickness of the conductive buffer layer is 3–6 μm; optionally, it is 3–4 μm. Since carbon materials typically have a lower energy density than the active materials in the active layer, when the conductive buffer layer contains carbon materials, an extremely thin conductive buffer layer is advantageous for reducing the energy density loss of the electrode (with a fixed electrode compaction density and thickness, the smaller the thickness of the conductive buffer layer, the larger the thickness of the active layer, the more active materials in the active layer, and the greater the energy density of the electrode).

[0016] Secondly, this application provides a method for preparing an electrode, comprising the steps of: preparing a conductive buffer layer on the surface of a current collector; preparing an active layer on the surface of the conductive buffer layer; wherein at least one of the conductive buffer layer and the active layer comprises a carbon material, the carbon material comprising one or more of graphite, soft carbon, and fullerene.

[0017] The embodiments of this application can obtain an electrode sheet comprising a current collector, a conductive buffer layer and an active layer stacked sequentially on the surface of the current collector, which is a simple preparation method.

[0018] In some embodiments, the step of preparing the conductive buffer layer includes: providing a primer slurry and coating the primer slurry onto the surface of the current collector.

[0019] In some embodiments, the viscosity of the primer slurry is 100–1000 mPa / s (25°C), optionally 300–600 mPa / s. A suitable slurry viscosity facilitates the fabrication of the conductive buffer layer.

[0020] Thirdly, this application provides a battery comprising the above-described electrode sheet, or comprising an electrode sheet prepared by the above-described method.

[0021] The electrode of this application embodiment, with the help of carbon material and conductive buffer layer, can reduce the elongation of the current collector, improve the problem of active layer edge collapse and winding breakage, and minimize current collector damage. Therefore, this electrode has excellent structural stability. Applying the electrode of this application embodiment to a battery will help improve the battery's cycle stability.

[0022] Fourthly, this application provides an electrical device, which includes the battery described above.

[0023] The battery disclosed in this application can be used to provide power to various electrical devices.

[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 in the embodiments of this application, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 The diagram shows the structure of the current collector and active layer in a conventional electrode (left) and the electrode structure of the embodiment of this application (right).

[0027] Figure 2 This is a schematic diagram of a battery module according to one embodiment of this application;

[0028] Figure 3 This is a schematic diagram of a battery pack according to one embodiment of this application;

[0029] Figure 4 for Figure 3 An exploded view of a battery pack according to one embodiment of this application is shown;

[0030] Figure 5 This is a schematic diagram of a battery according to one embodiment of this application;

[0031] Figure 6 for Figure 5 An exploded view of a battery according to one embodiment of this application is shown;

[0032] Figure 7 This is a schematic diagram of an electrical device in which a battery is used as a power source, according to one embodiment of this application.

[0033] Figure label:

[0034] 1-Battery pack; 2-Upper housing; 3-Lower housing; 4-Battery module; 5-Battery cell; 51-Housing; 52-Electrode assembly; 53-Cover plate. Detailed Implementation

[0035] 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.

[0036] 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.

[0037] In the description of the embodiments of this application, technical terms such as "first" and "second" 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. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0038] 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.

[0039] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0040] In the description of the embodiments of this application, the term "at least one" refers to one or more, and "more than one" refers to two or more. "At least one of the following" or similar expressions refer to any combination of these items, including any combination of a single item or a plurality of items. For example, "at least one of a, b, or c", or "at least one of a, b, and c", can both mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be a single item or multiple items.

[0041] It should be understood that in the various embodiments of this application, the order of the above processes does not imply the order of execution. Some or all steps may be executed in parallel or sequentially. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

[0042] The weights of the relevant components mentioned in the embodiments of this application can refer not only to the specific content of each component, but also to the proportional relationship between the weights of the components. Therefore, any scaling up or down of the content of the relevant components according to the embodiments of this application is within the scope disclosed in the embodiments of this application. Specifically, the mass described in the embodiments of this application can be a mass unit known in the chemical industry, such as μg, mg, g, or kg.

[0043] Traditional electrodes typically consist of a current collector and an active layer disposed on one or two surfaces of the current collector, such as... Figure 1 As shown in the left figure. In the battery chemical reaction process, electron and ion transfer is typically achieved using the active material in the electrode active layer. A common method for combining the active layer with the current collector is to prepare an electrode active slurry by combining the active material with binders, conductive agents, etc. This slurry is then coated onto one or both surfaces of the current collector, followed by drying and cold pressing to form an active layer containing the active material on the current collector surface. After cold pressing, the electrode can be further processed through winding or other processes.

[0044] The active materials in the active layer do not slide under pressure. Therefore, during cold pressing, the active materials are squeezed together, applying pressure to the current collector. Commonly used current collectors include metal current collectors, such as aluminum foil and copper foil. While these current collectors are difficult to stretch individually under the rollers of a cold pressing machine, they tend to stretch significantly under the pressure of the active materials. This large difference in stretching between the current collector and the active layer reduces the adhesion at the edges, making the active layer prone to edge collapse. This, in turn, leads to tape breakage during the winding process, severely reducing electrode quality and affecting battery performance. Furthermore, many active materials have irregular angular structures, which can easily damage the current collector and further degrade battery performance.

[0045] In related technologies, a primer slurry is typically applied between the active layer and the current collector, and then dried to form a primer layer. The main components of traditional anode primer slurries include sodium carboxymethyl cellulose, conductive carbon black, and binders, while the main components of cathode primer slurries include modified polyacrylate, calcium hydroxide, and conductive carbon black. However, these primer layers only increase the adhesion between the current collector and the active layer, and improve the conductivity of the electrode. They do not alleviate the current collector's elongation problem during the cold pressing process, and are insufficient to improve issues such as active layer collapse, winding breakage, and damage to the current collector. This may be because these traditional primer layers themselves have high hardness. When the active layer contains hard carbon or other active materials with high hardness, which do not undergo structural slippage under pressure and have angular structures, the mutual compression of these active materials during cold pressing applies pressure to the primer layer. This pressure, after being transmitted through the high-hardness primer layer, still acts on the current collector, causing significant elongation of the current collector and ultimately leading to active layer collapse, winding breakage, and other problems. At the same time, the angular structure of these active materials may also pierce the base coating, thereby coming into contact with the current collector and causing damage to it.

[0046] To address the issues of active layer collapse and winding breakage caused by the large elongation of the current collector (macroscopically manifested as large overall elongation of the electrode), embodiments of this application incorporate a conductive buffer layer between the active layer of the electrode and the current collector, such as... Figure 1 As shown in the right figure, a specific carbon material is added to at least one of the conductive buffer layer and the active layer. These carbon materials can undergo internal structural slippage and / or interparticle slippage under pressure. Therefore, during cold pressing, these carbon materials can mitigate the squeezing effect of the active material in the active layer on the current collector, preventing excessive elongation of the current collector and thus improving the problems of active layer edge collapse and winding breakage caused by excessive current collector elongation.

[0047] The present application is further illustrated below with reference to embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the present application.

[0048] The first aspect of this application provides an electrode sheet, which includes a current collector, a conductive buffer layer and an active layer stacked sequentially, wherein at least one of the conductive buffer layer and the active layer contains a carbon material, which includes one or more of graphite, soft carbon and fullerene.

[0049] The term "sequentially stacked" refers to the sequential overlapping of two or more objects. In this embodiment, the electrode includes a current collector, a conductive buffer layer, and an active layer stacked sequentially. Specifically, in one direction of the electrode, the current collector, conductive buffer layer, and active layer are stacked in the order of current collector → conductive buffer layer → active layer; conversely, in the opposite direction, the current collector, conductive buffer layer, and active layer are stacked in the order of active layer → conductive buffer layer → current collector. Therefore, "including sequentially stacked current collector, conductive buffer layer, and active layer" is equivalent to "including sequentially stacked active layer, conductive buffer layer, and current collector."

[0050] Considering that the current collector typically has two surfaces, the conductive buffer layer can be disposed on one or both surfaces of the current collector. When the conductive buffer layer is disposed on one surface of the current collector, in one direction of the electrode, the current collector, conductive buffer layer, and active layer overlap in the order of current collector → conductive buffer layer → active layer; in the opposite direction, they overlap in the order of active layer → conductive buffer layer → current collector. When the conductive buffer layer is disposed on both surfaces of the current collector, the current collector, conductive buffer layer, and active layer overlap in the order of active layer → conductive buffer layer → current collector → conductive buffer layer → active layer, resulting in a sandwich structure for the electrode.

[0051] In this embodiment, a conductive buffer layer is provided between the current collector and the active layer, and carbon materials such as graphite, soft carbon, and fullerene are provided in at least one of the conductive buffer layer and the active layer. These carbon materials have special structures and properties, and can undergo internal structural slippage and / or interparticle slippage under pressure.

[0052] Specifically, in graphite crystals, carbon atoms are arranged in an ordered and anisotropic manner, with carbon atoms in the same layer arranged in sp... 2Hybridization forms covalent bonds, with each carbon atom connected to three other atoms by three covalent bonds. The layers are primarily bonded by molecular bonds, resulting in weak molecular attraction between layers. Therefore, graphite is characterized by its soft particle texture and weak van der Waals forces between particles, leading to relative slippage between layers during cold pressing. Similarly, fullerene also has a layered structure, with layers primarily bonded by molecular bonds and weak molecular attraction between layers, resulting in relative slippage between layers during cold pressing. Soft carbon refers to amorphous carbon materials that can be graphitized at temperatures above 2500℃, i.e., amorphous carbon that is easily graphitized at high temperatures. The microcrystalline structure of soft carbon has lattice fringes, which are parallel straight fringes. The structure contains a large amount of amorphous carbon, resulting in a relatively loose and disordered crystal structure, making it prone to interlayer slippage during cold pressing.

[0053] Therefore, when the conductive buffer layer contains carbon material, it can mitigate the squeezing effect of the active material in the active layer on the current collector, reduce the current collector's elongation, thereby narrowing the elongation difference between the current collector and the active layer, and improving the problems of active layer edge collapse and winding breakage. Similarly, when the active layer contains carbon material, the combined effect of the conductive buffer layer and the carbon material can also mitigate the squeezing effect of the active material in the active layer on the current collector, ultimately improving the problems of active layer edge collapse and winding breakage.

[0054] Meanwhile, since the conductive buffer layer acts as a barrier between the active layer and the current collector, the active material in the active layer does not directly contact the current collector, which can improve the damage of the active material to the current collector during the cold pressing process.

[0055] In some implementations, graphite may include one or more of artificial graphite and natural graphite.

[0056] In graphite crystals, carbon atoms are arranged in an ordered and anisotropic manner, with carbon atoms in the same layer arranged in sp... 2 Hybridization forms covalent bonds, with each carbon atom connected to three other atoms by three covalent bonds. The layers are primarily bonded by molecular bonds, with relatively weak molecular attraction between layers. Therefore, graphite particles are soft, and van der Waals forces interact between them. During cold pressing, the structure slips, mitigating the compression of the current collector by the active material in the active layer, reducing the current collector's elongation, and ultimately improving the problems of active layer collapse and winding breakage. Furthermore, the regular morphology of graphite minimizes damage to the current collector. In addition, graphite is easy to process and utilize; its electrical conductivity also improves the conductivity of the electrode.

[0057] In some embodiments, the Dv50 of the carbon material is 0.4 to 1.5 μm, optionally 0.7 to 0.9 μm, for example, any one of the following values ​​or a range between any two: 0.4 μm, 0.45 μm, 0.5 μm, 0.55 μm, 0.6 μm, 0.65 μm, 0.7 μm, 0.75 μm, 0.8 μm, 0.85 μm, 0.9 μm, 0.95 μm, 1 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, and 1.5 μm.

[0058] In some embodiments, the Dv90 of the carbon material is 1 to 4 μm, optionally 1 to 3 μm, for example, any one of 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm or a range between any two.

[0059] The particle size distribution of a material is usually expressed as the percentage of particles within different size ranges relative to the total particle size. There are various benchmarks for determining particle size distribution, such as number distribution, length distribution, area distribution, volume distribution, and weight distribution. Volume distribution is typically determined using laser methods. Dv50 and Dv90 are specific particle size distributions derived from volume distribution. Dv50 represents the particle size corresponding to 50% of the volume distribution, and Dv90 represents the particle size corresponding to 90% of the volume distribution.

[0060] The carbon material used in this embodiment has a small particle size, which is beneficial for forming an extremely thin conductive buffer layer. Since carbon materials typically have a lower energy density than the active materials in the active layer, a thinner conductive buffer layer, when it contains carbon material, is more conducive to reducing the energy density loss of the electrode. Alternatively, the small particle size of the carbon material allows for good dispersion within the active layer.

[0061] In some embodiments, the conductive buffer layer comprises carbon material, with the carbon material comprising at least 5% and less than 100% by mass, optionally between 14% and 56%. For example, the mass content of the carbon material in the conductive buffer layer can be any one of 5%, 14%, 15%, 18%, 20%, 25%, 28%, 30%, 35%, 40%, 45%, 50%, 55%, 56%, 60%, 70%, 80%, 90%, 95%, or 98%, or a range between any two. With appropriate amounts, the structural characteristics of the carbon material can be fully utilized to mitigate the squeezing effect of the active material in the active layer on the current collector, reduce the current collector's elongation, improve the problem of active layer edge collapse and winding breakage, and reduce damage to the current collector; it also helps to reduce the energy density loss of the electrode.

[0062] In some embodiments, the active layer comprises carbon material, with a mass content of 1% to 5%, optionally 3% to 5%, for example, any one of 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, or 5%, or a range between any two. When the active layer comprises carbon material, considering that these carbon materials typically have a lower energy density than the active material in the active layer, controlling the carbon material content in the active layer within an appropriate range is beneficial for reducing the energy density loss of the electrode.

[0063] In some embodiments, the thickness of the conductive buffer layer is 3–6 μm, optionally 3–4 μm, for example, any one of 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm, or a range between any two. Typically, the thickness of the conductive buffer layer can be measured using a micrometer, laser thickness gauge, or thickness scanning thickness gauge. Since carbon materials generally have a lower energy density than the active materials in the active layer (for example, the sodium storage density of hard carbon is 380–450 mAh / g, while that of soft carbon is only 160–240 mAh / g), when the conductive buffer layer contains carbon material, an extremely thin conductive buffer layer is advantageous in reducing the energy density loss of the electrode (with a fixed electrode compaction density and thickness, the smaller the thickness of the conductive buffer layer, the larger the thickness of the active layer, the more active material in the active layer, and the greater the energy density of the electrode).

[0064] In some embodiments, the thickness of the active layer is 100–200 μm, optionally 130–150 μm, for example, any one of 100 μm, 110 μm, 120 μm, 130 μm, 140 μm, 150 μm, 160 μm, 170 μm, 180 μm, 190 μm, and 200 μm, or a range between any two. The thickness of the active layer can be measured using a micrometer, a laser thickness gauge, or a thickness scanning thickness gauge. In the electrode of the embodiments of this application, the active layer can be set to a larger thickness, which is beneficial to increasing the total amount of active material in the active layer, thereby reducing the energy density loss of the electrode due to the incorporation of carbon materials.

[0065] In some embodiments, the compaction density of the electrode sheet is 0.8–1 g / cm³. 3 The optional concentration is 0.9–1 g / cm³. 3 For example, 0.8g / cm 3 0.82 g / cm 3 0.84 g / cm 3 0.85g / cm 3 0.9g / cm 3 0.92g / cm 30.93g / cm 3 0.94 g / cm 3 0.96 g / cm 3 0.98g / cm 3 1g / cm 3 The compaction density of the electrode can be any one of the point values ​​or any range between the two. The compaction density of the electrode can be obtained using a compaction density meter, while also referring to relevant standards such as GB / T 24533-2019. In the case of a relatively thin conductive buffer layer in this embodiment, by controlling the electrode compaction density to a low level, the damage to the current collector by the active material in the active layer can be improved.

[0066] In some embodiments, the active layer comprises an active material, which includes, but is not limited to, one or more of hard carbon, Prussian blue compounds, layered oxides, and polyanionic compounds.

[0067] Hard carbon refers to carbon that is difficult to graphitize even at temperatures above 2500℃. It is typically prepared from hard carbon precursors, such as the thermal decomposition of polymer materials. Hard carbon precursors are often rich in heteroatoms such as hydrogen, oxygen, and nitrogen, making it difficult for carbon atoms to form sp atoms during heat treatment. 2 Hybridization results in a graphitization temperature typically above 2500℃. Hard carbon particles are inherently hard and brittle, with dispersed crystals, large lattice spacing, and irregular, multi-faceted structures. The particles are primarily connected by relatively weak mechanical rivets. The lamellar structure of hard carbon contains strong COC chemical bonds, meaning there are multiple cross-linked structures between layers, resulting in strong interlayer bonding. Therefore, hard carbon structures do not slip during cold pressing.

[0068] Prussian blue compounds, including iron-based and manganese-based Prussian blue compounds, have a stable cubic crystal structure and are not prone to structural slip under pressure.

[0069] Layered oxides include, but are not limited to, iron-based layered oxides, manganese-based layered oxides, iron-manganese-based layered oxides, and one or more of iron-based layered oxides, manganese-based layered oxides, and iron-manganese-based layered oxides doped with transition metal elements (such as Ti, Cu, Ni). For example, iron-based layered oxides include, but are not limited to, NaFeO2; manganese-based layered oxides include, but are not limited to, NaMnO2; and iron-manganese-based layered oxides include, but are not limited to, Na… x Fe y Mn 1-y O2 (x=0.2~1, y=0.1~0.9, such as Na 0.67 Fe 0.5 Mn 0.5 O2, Na 0.67 Fe 0.45 Mn 0.65O2). The atoms in layered oxides have strong interactions, good structural stability, and are not prone to structural slippage under pressure.

[0070] Polyanionic compounds can include, but are not limited to, one or more of phosphates, pyrophosphates, fluorophosphates, and mixed phosphates. Phosphates include, but are not limited to, one or more of Na3V2(PO4)3 and Na4MnV(PO4)3; pyrophosphates include, but are not limited to, one or more of NaFeP2O7, NaMnP2O7, and NaCoP2O7; fluorophosphates include, but are not limited to, NaVPO4F; and mixed phosphates include, but are not limited to, one or more of Na4Fe3(PO4)2P2O7 and Na4Mn3(PO4)2P2O7. Polyanionic electrode materials possess a stable polyhedral framework structure and are not prone to structural slippage under pressure.

[0071] Therefore, during the cold pressing process, these active materials are squeezed against each other, applying pressure to the current collector. Under the pressure of the active materials, the current collector area coated with the active materials tends to stretch significantly, resulting in a large difference in stretch between the current collector and the active layer. This reduces the adhesion between the current collector and the edge of the active layer, making the active layer prone to edge collapse. Consequently, this leads to strip breakage during the winding process, severely reducing the quality of the electrode. Furthermore, the angular structure of the active materials can easily damage the current collector. This application's embodiments address this issue by incorporating a conductive buffer layer and adding carbon material to the electrode with such active materials, thus improving the aforementioned problems of active layer edge collapse and strip breakage.

[0072] In some embodiments, the mass content of the active material in the active layer is 85% to 90%, optionally 85% to 87%, for example, any one of 85%, 86%, 87%, 88%, 89%, or 90%, or a range between any two. The active material participates in electron and ion transfer during electrochemical reactions, affecting the energy density and other electrochemical properties of the electrode. At an appropriate active material content, it helps to improve the electrochemical performance of the electrode.

[0073] In some embodiments, the conductive buffer layer and the active layer may each independently contain a conductive agent. When the conductive buffer layer contains carbon material, it may or may not contain a conductive agent. Adding a conductive agent to the conductive buffer layer enhances electron transport between the active layer and the current collector, improving the electrode's conductivity. In the active layer, the conductive agent enhances electron transport within the active layer and between the active layer and the conductive buffer layer, further improving the electrode's conductivity.

[0074] In some embodiments, the conductive agents in the conductive buffer layer and the active layer are independently selected from one or more of the following: acetylene black, carbon nanotubes, conductive carbon black (super-P, sp), Ketjen black, carbon fiber, and graphene. These conductive agents have excellent conductivity and are readily available. For example, the conductive carbon black used in conventional processes typically comprises primary particles with a diameter of about 40 nm agglomerated into primary aggregates of 150–200 nm, which are often used to disperse around the active material to form a multi-branched conductive network, thereby reducing the physical internal resistance of the battery and improving electronic conductivity; or it can be applied to the primer to improve the conductivity between the active material and the current collector.

[0075] In some embodiments, the mass content of the conductive agent in the conductive buffer layer is 0% to 56%, optionally 20% to 42%, for example, any one of 0%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 42%, 45%, 50%, 55%, 56%, or a range between any two. Adding a conductive agent to the conductive buffer layer can enhance electron transport between the active layer and the current collector, thereby improving the conductivity of the electrode.

[0076] In some embodiments, the mass content of the conductive agent in the active layer includes, but is not limited to, 1% to 5%, optionally 2% to 3%, for example, any one of 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or a range between any two, and may also be set to other contents as needed. Adding an appropriate amount of conductive agent to the active layer can enhance electron transport within the active layer and between the active layer and the conductive buffer layer, thereby improving the conductivity of the electrode.

[0077] In some embodiments, the conductive buffer layer and the active layer each independently further comprise an adhesive. In the conductive buffer layer, the adhesive enhances the bonding strength between the conductive buffer layer and the current collector, between the conductive buffer layer and the active layer, and between the materials within the conductive buffer layer. In the active layer, the adhesive enhances the bonding strength between the conductive buffer layer and the active layer, and between the materials within the active layer.

[0078] In some embodiments, the adhesives in the conductive buffer layer and the active layer independently include one or more of oil-soluble adhesives, water-soluble adhesives, and emulsion adhesives. Oil-soluble adhesives include one or more of polyvinylidene fluoride, polyimide, polytetrafluoroethylene, polybutylene acrylate, and polyacrylonitrile. Water-soluble adhesives include one or more of carboxymethyl cellulose, carboxymethyl cellulose salts, polyacrylic acid, polyacrylate, polyvinyl alcohol, sodium alginate, and cyclodextrin. Emulsion adhesives include one or more of styrene-butadiene rubber, vinyl acetate resin, acrylic resin, and chlorinated rubber.

[0079] In some embodiments, the adhesive content in the conductive buffer layer is 35% to 45% by mass, optionally 40% to 42%, for example, any one of 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, or a range between any two.

[0080] In some embodiments, the mass content of the adhesive in the active layer is independently included, but is not limited to, 0.5% to 10%, or 5% to 9%, for example, any one of 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or any range between two, and may also be set to other contents as needed.

[0081] In some embodiments, the conductive buffer layer and the active layer may optionally include a thickener, such as carboxymethyl cellulose (CMC), independently. The mass content of the thickener in the conductive buffer layer and the active layer is independently, but not limited to, 0.5% to 5%, or, for example, 1% to 5%, such as any one of 0.5%, 1%, 2%, 3%, 4%, and 5%, or a range between any two, and may also be set to other contents as needed. By adding a thickener, the viscosity of the slurry related to the conductive buffer layer and the active layer can be adjusted, making it easier to process and manufacture.

[0082] In some embodiments, the current collector includes, but is not limited to, metal current collectors, carbon current collectors, conductive resin current collectors, and composite current collectors of metal and resin, and more specifically, copper, aluminum, nickel, titanium, iron and their respective alloys, stainless steel, carbon fiber, carbon nanotubes (CNTs), graphite, etc. The current collector on the electrode is used to bond with the active layer and to transport electrons in the battery chemical reaction.

[0083] In some embodiments, the thickness of the current collector includes, but is not limited to, 6–13 μm, optionally 6–10 μm, such as any one of 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, and 13 μm, or a range between any two. The thickness of the current collector can be measured using a micrometer, laser thickness gauge, or thickness scanning thickness gauge. A smaller current collector thickness is beneficial for reducing the electrode mass and meeting market requirements for lightweight electrodes.

[0084] In some embodiments, the electrode includes one or both of a positive electrode and a negative electrode. The technical solutions of the embodiments of this application are applicable to different electrode types and have good applicability.

[0085] A second aspect of this application provides a method for preparing an electrode, comprising the steps of: preparing a conductive buffer layer on the surface of a current collector; preparing an active layer on the surface of the conductive buffer layer; wherein at least one of the conductive buffer layer and the active layer comprises a carbon material, the carbon material comprising one or more of graphite, soft carbon, and fullerene.

[0086] The embodiments of this application can obtain an electrode sheet comprising a current collector, a conductive buffer layer and an active layer stacked sequentially on the surface of the current collector, which is a simple preparation method.

[0087] In some embodiments, the step of preparing the conductive buffer layer includes: providing a primer slurry and coating the primer slurry onto the surface of the current collector.

[0088] In some embodiments, the viscosity of the primer slurry is 100–1000 mPa / s (25°C), optionally 300–600 mPa / s, for example, any point value or a range between 100 mPa / s, 200 mPa / s, 300 mPa / s, 400 mPa / s, 500 mPa / s, 600 mPa / s, 700 mPa / s, 800 mPa / s, 900 mPa / s, and 1000 mPa / s. The viscosity can be obtained by testing with a viscometer under specific conditions. A suitable slurry viscosity facilitates the fabrication of the conductive buffer layer.

[0089] In some embodiments, the primer slurry may contain carbon materials. The primer slurry may also contain one or more of an adhesive and a conductive agent. The preparation method of the primer slurry includes mixing one or more of the adhesive and conductive agent with the carbon material and dispersing them with a solvent to obtain the primer slurry; or dispersing one or more of the adhesive and conductive agent with a solvent to obtain the primer slurry. The mixing process may employ one or both of dry mixing and wet mixing methods. During the mixing process, a rotation speed of 200–1200 rpm may be used for 5–30 minutes. The solvents used include, but are not limited to, one or more of water, NMP (N-methylpyrrolidone), DMF (dimethylformamide), EGDME (ethylene glycol dimethyl ether), EC (ethylene carbonate), mineral oil, ethanol, and acetone. The dispersion time with the solvent may be set to 30–90 minutes. The dispersion process may be assisted by stirring, or it may not require stirring.

[0090] In some embodiments, the step of preparing the active layer includes: providing an active slurry containing an active material and coating the active slurry onto the surface of the conductive buffer layer.

[0091] In some embodiments, the solid content of the active slurry is 45% to 55%, optionally 50% to 55%, for example, any one of 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%, 54%, or 55%, or a range between any two. This solid content can be obtained by measuring the moisture content using a moisture meter; or by using a drying method, i.e., calculating the solid content by weighing the slurry before and after drying. A suitable solid content in the active slurry is beneficial for the processing and fabrication of the active layer.

[0092] In some embodiments, the viscosity of the active slurry is 4000–15000 mPa / s (25°C), optionally 8000–12000 mPa / s, for example, any point value or a range between 4000 mPa / s, 6000 mPa / s, 8000 mPa / s, 10000 mPa / s, 12000 mPa / s, 14000 mPa / s, and 15000 mPa / s. The viscosity can be obtained by testing with a viscometer under specific conditions. A suitable slurry viscosity is beneficial for the fabrication of the active layer.

[0093] In some embodiments, the active slurry may contain carbon materials. The active slurry may also contain one or more of a binder and a conductive agent. The preparation method of the active slurry includes mixing one or more of the binder and conductive agent with the active material and dispersing it with a solvent to obtain the active slurry; or mixing one or more of the binder and conductive agent with the active material and the carbon material and dispersing it with a solvent to obtain the active slurry. The mixing process may employ one or both of dry mixing and wet mixing methods. During the mixing process, a rotation speed of 200–1200 rpm may be used for 5–30 minutes. The solvents used include, but are not limited to, one or more of water, NMP (N-methylpyrrolidone), DMF (dimethylformamide), EGDME (ethylene glycol dimethyl ether), EC (ethylene carbonate), mineral oil, ethanol, and acetone. The dispersion time with the solvent may be set to 30–90 minutes. The dispersion process may be assisted by stirring, or it may not require stirring.

[0094] In some embodiments, the coating methods used in the steps of preparing the conductive buffer layer and preparing the active layer may be independently one or more of printing, spin coating, and roll coating.

[0095] In some embodiments, the preparation method of the electrode further includes a drying step of the conductive buffer layer and / or active layer. After the base coating slurry and / or active slurry are applied, they typically need to be dried to evaporate the solvent, forming a solid conductive buffer layer and / or active layer, and enhancing the bonding force between the conductive buffer layer, the active layer, and the current collector. In practice, the base coating slurry can be applied to the surface of the current collector and then dried; then, the active slurry can be applied to the surface of the conductive buffer layer and dried a second time. Alternatively, the active slurry can be directly applied after the base coating slurry is applied to the surface of the current collector, followed by drying. That is, the drying of the conductive buffer layer and the active layer can be performed sequentially or simultaneously. The drying methods include, but are not limited to, one or more of heating, air cooling, natural drying, and freeze drying.

[0096] In some embodiments, the electrode preparation method further includes a shaping step. The shaping method includes one or both of cold pressing and hot pressing, optionally including cold pressing. By performing shaping processes such as cold pressing or hot pressing on the electrode, the density of the electrode can be improved and the bonding force between the conductive buffer layer, the active layer, and the current collector can be enhanced. The pressure used in the shaping step can include 20–80T, for example, any one of 20T, 30T, 40T, 50T, 60T, 70T, and 80T, or a range between any two. In some embodiments, the electrode preparation method further includes a cutting step. Depending on actual needs, the electrode is cut into various required shapes to suit different application scenarios.

[0097] A third aspect of this application provides a battery comprising the above-described electrode sheet, or comprising an electrode sheet prepared by the above-described method.

[0098] The electrode of this application embodiment, with the help of carbon material and conductive buffer layer, can reduce the elongation of the current collector, improve the problem of active layer collapse and winding breakage, and minimize damage to the current collector. Therefore, this electrode has excellent structural stability. When the electrode with stable structure of this application embodiment is applied to a battery, the electrode is less prone to active layer shedding and pulverization during battery charging and discharging, which will help improve the battery's cycle stability.

[0099] In some embodiments, the battery of this application includes one or more of a primary battery and a secondary battery. Batteries can be classified as primary batteries and secondary batteries based on whether they can be recharged and reused. A primary battery cannot be recharged to restore its original state after discharge, while a secondary battery can be reactivated by charging after discharge to allow the active materials to be reused. The electrode sheets of this application can be applied to both primary and secondary batteries, thus having a wide range of applications.

[0100] In some embodiments, the battery of this application includes one or more of the following: battery cell, battery module, and battery pack. When the battery is a rechargeable battery, it is classified into battery cell, battery module, and battery pack according to different packaging forms. The battery cell is the most basic unit of a rechargeable battery, including electrode components and an electrolyte. The electrode components typically consist of a positive electrode, a negative electrode, and a separator. The battery cell mainly relies on the movement of metal ions in the electrolyte between the positive and negative electrodes to function. In some battery packaging technologies, multiple battery cells can be integrated into a battery module, and then the battery module is installed in a battery housing to form a battery pack. In other battery packaging technologies, multiple battery cells can be directly installed in a housing to form a battery pack, eliminating the intermediate state of the battery module, thereby reducing the weight of the battery pack and increasing the energy density of the battery.

[0101] In some embodiments, the battery may include one or more of sodium-ion batteries, lithium-ion batteries, lithium-sulfur batteries, sodium-lithium-ion batteries, and magnesium-ion batteries.

[0102] In some embodiments, the battery of this application includes the above-mentioned electrode sheet, which can be a positive electrode sheet, a negative electrode sheet, or both a positive electrode sheet and a negative electrode sheet.

[0103] In some implementations, the battery also includes an electrolyte. The electrolyte can serve as a carrier for ion transport within the battery.

[0104] In some embodiments, the electrolyte may be a solid electrolyte, including but not limited to polymer electrolytes and inorganic solid electrolytes. The electrolyte may also be an electrolyte solution. The electrolyte solution may include a solvent and a metal salt dissolved in the solvent.

[0105] The solvent in the electrolyte may include non-aqueous organic solvents, such as one or more of ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), and ethyl butyrate (EB), preferably two or more.

[0106] Metal salts can include one or more of sodium salts and lithium salts.

[0107] Sodium salts may include one or more of the following: sodium hexafluorophosphate (NaPF6), sodium chlorate (NaClO4), sodium chloride (NaCl), sodium tetrafluoroborate (NaBF4), sodium nitrate (NaNO3), sodium cyanide (NaCN), sodium bisulfate (NaHSO4), sodium bis(trifluoromethylsulfonyl)imide (NaTFSI), and sodium bis(fluorosulfonyl)imide (NaFSI).

[0108] Lithium salts may include one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalate borate (LiDFOB), lithium bis(oxalate borate) (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorooxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP), for example, one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium bis(oxalate borate) (LiBOB), lithium difluorooxalate borate (LiDFOB), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and lithium bis(fluorosulfonyl)imide (LiFSI).

[0109] The electrolyte may also optionally contain other additives, such as vinylene carbonate (VC), ethylene ethylene carbonate (VEC), fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), trifluoromethyl ethylene carbonate (TFPC), succinic anionyl (SN), adiponitrile (ADN), glutaronitrile (GLN), hexanetrionitrile (HTN), 1,3-propanesulfonyl lactone (1,3-PS), vinyl sulfate (DTD), methylene disulfonate (MMDS), and 1-propene-1,3-sulfonyl lactone. One or more of the following, but not limited to: (PST), 4-methyl ethylene sulfate (PCS), 4-ethyl ethylene sulfate (PES), 4-propyl ethylene sulfate (PEGLST), propylene sulfate (TS), 1,4-butane sulpholactone (1,4-BS), ethylene sulfite (DTO), dimethyl sulfite (DMS), diethyl sulfite (DES), sulfonate cyclic quaternary ammonium salts, tris(trimethylsilane) phosphate (TMSP), and tris(trimethylsilane) borate (TMSB).

[0110] In some embodiments, the battery also includes a separator stacked between the positive and negative electrodes. In some batteries, a separator is required to separate the positive and negative electrodes, preventing electrons from freely passing through and thus preventing short circuits, while allowing ions in the electrolyte to freely pass between the positive and negative electrodes.

[0111] The separator can be any known porous separator with electrochemical and mechanical stability, including but not limited to one or more single-layer or multi-layer films of glass fiber, non-woven fabric, polyethylene (PE), polypropylene (PP) and polyvinylidene fluoride (PVDF).

[0112] A battery cell is obtained by alternately stacking positive and negative electrode sheets, with a separator between them for isolation. Alternatively, the cells can be wound to form a battery cell. The cell is then placed in a casing, filled with electrolyte, and sealed to obtain a single battery cell. Multiple battery cells are integrated to form a battery module, which provides higher voltage and capacity and has specific output functions. The battery module is then installed in a battery housing, often with the addition of a battery management system, to form a battery pack, typically provided to the user. Alternatively, multiple battery cells can be directly installed in a housing to form a battery pack.

[0113] refer to Figure 2 This is an example of a battery module 4. In the battery module 4, multiple battery cells 5 can be arranged sequentially along the length of the battery module 4. Of course, they can also be arranged in any other way. Furthermore, the multiple battery cells 5 can be fixed in place by fasteners.

[0114] Optionally, the battery module 4 may also include a housing with a receiving space in which multiple battery cells 5 are received.

[0115] refer to Figure 3 and Figure 4 This is exemplified by a battery pack 1. The battery pack 1 may include a battery compartment and multiple battery modules 4 disposed within the battery compartment. The battery compartment includes an upper housing 2 and a lower housing 3, with the upper housing 2 covering the lower housing 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery compartment.

[0116] In some embodiments, the battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly consisting of a positive electrode, a negative electrode, and a separator, as well as the electrolyte.

[0117] The outer packaging of a battery can be a hard shell, such as a hard plastic shell, aluminum shell, or steel shell. It can also be a soft pack, such as a pouch. The material of the soft pack can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0118] The battery can be cylindrical, square, or any other shape. For example, Figure 5 This is a square-shaped battery as an example.

[0119] In some implementations, refer to Figure 6 The outer packaging may include a housing 51 and a cover 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 can be placed over the opening to close the receiving cavity. A positive electrode, a negative electrode, and a separator can be formed into an electrode assembly 52 via a winding process or a stacking process. One or more electrode assemblies 52 are encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52.

[0120] This application also provides an electrical device including the battery described above. The battery disclosed in this application can be used to provide power to various electrical devices. These devices may include, but are not limited to, mobile phones, tablets, laptops, electric toys, power tools, electric vehicles, electric cars, ships, spacecraft, etc. Electric toys may include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc. Spacecraft may include airplanes, rockets, space shuttles, and spacecraft, etc. As for the aforementioned electrical devices, individual battery cells, battery modules, or battery packs can be selected according to their usage requirements.

[0121] Figure 7 This is an example of an electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the device's requirements for high power and high energy density, a battery pack or battery module can be used.

[0122] The following description is based on specific embodiments.

[0123] Example 1

[0124] This embodiment provides an electrode sheet comprising an active layer, a conductive buffer layer, a current collector, and an active layer stacked sequentially. Specifically, the electrode sheet includes a current collector, conductive buffer layers are disposed on both surfaces of the current collector, and an active layer is disposed on the surface of the conductive buffer layer. The current collector is a 6 μm thick Cu foil; the conductive buffer layer comprises 3%, 41%, and 56% by mass of carboxymethyl cellulose (CMC), a binder (styrene-butadiene rubber, SBR), and graphite (Dv50 = 0.8 μm, Dv90 = 2 μm), with a total thickness of 3 μm; the active layer comprises 90%, 3%, and 7% by mass of hard carbon, a conductive agent (conductive carbon black, sp), and the binder SBR, with a total thickness of 142 μm.

[0125] In this embodiment, the method for preparing the electrode includes the following steps:

[0126] 1) Mix CMC, SBR and graphite at 1200 rpm for 5 min according to the ratio, then add water and continue dispersing for 60 min to prepare a primer slurry with a viscosity controlled at 100 mPa / s (25℃, Borelfeld DV2T viscometer, rotor No. 63).

[0127] 2) Using gravure printing technology, the prepared base coating slurry is applied to the Cu foil and dried to form a conductive buffer layer on both surfaces of the Cu foil.

[0128] 3) Mix hard carbon, SP and SBR binder according to the ratio, add water to prepare an active slurry with a solid content of 55%, coat the active slurry on the surface of the conductive buffer layer, and obtain the electrode sheet after drying and cold pressing.

[0129] Example 2

[0130] This embodiment provides an electrode sheet, which differs from Embodiment 1 only in that graphite is replaced with an equal mass of soft carbon (Dv50 = 0.8 μm, Dv90 = 2 μm). Everything else is the same as in Embodiment 1.

[0131] Example 3

[0132] This embodiment provides an electrode sheet, which differs from Embodiment 1 in that: sp is added to the conductive buffer layer while the graphite content is reduced. Specifically, in this embodiment, the conductive buffer layer contains CMC, SBR, graphite (Dv50 = 0.8 μm, Dv90 = 2 μm) and sp at mass contents of 3%, 41%, 14%, and 42%, respectively. Everything else is the same as in Embodiment 1.

[0133] Example 4

[0134] This embodiment provides an electrode sheet, which differs from Embodiment 3 in that the mass content of graphite in the conductive buffer layer is increased, while the mass content of sp in the conductive buffer layer is reduced. Specifically, in this embodiment, the conductive buffer layer comprises CMC, SBR, graphite (Dv50 = 0.8 μm, Dv90 = 2 μm), and sp with mass contents of 3%, 41%, 28%, and 28%, respectively. Everything else is the same as in Embodiment 3.

[0135] Example 5

[0136] This embodiment provides an electrode sheet, which differs from Embodiment 4 in that the Cu foil is replaced with a 13 μm thick Al foil. Everything else is the same as in Embodiment 4.

[0137] Example 6

[0138] This embodiment provides an electrode sheet, which differs from Embodiment 4 in that the graphite particle size is reduced. Specifically, the graphite particle size in the conductive buffer layer of this embodiment is: Dv50 = 0.4 μm, Dv90 = 1 μm. Everything else is the same as in Embodiment 4.

[0139] Example 7

[0140] This embodiment provides an electrode sheet, which differs from Embodiment 4 in that the graphite particle size is increased. This increased graphite particle size also leads to a greater thickness of the conductive buffer layer. Specifically, the graphite particle size in the conductive buffer layer of this embodiment is: Dv50 = 1.5 μm, Dv90 = 4 μm, and the total thickness of the conductive buffer layer is 6 μm. Everything else is the same as in Embodiment 4.

[0141] Example 8

[0142] This embodiment provides an electrode sheet, which differs from Embodiment 4 in that graphite is replaced with an equal mass of soft carbon (Dv50 = 0.8 μm, Dv90 = 2 μm). Everything else is the same as in Embodiment 4.

[0143] Example 9

[0144] This embodiment provides an electrode sheet, which differs from Embodiment 4 in that the conductive buffer layer simultaneously contains graphite, soft carbon, and sp. Specifically, in this embodiment, the conductive buffer layer comprises CMC, SBR, graphite (Dv50 = 0.8 μm, Dv90 = 2 μm), soft carbon (Dv50 = 0.8 μm, Dv90 = 2 μm), and sp in mass percentages of 3%, 41%, 18%, 18%, and 20%, respectively. Everything else is the same as in Embodiment 4.

[0145] Example 10

[0146] This embodiment provides an electrode sheet, including a current collector, with conductive buffer layers disposed on both surfaces of the current collector, and an active layer disposed on the surface of the conductive buffer layer. The current collector is a 6 μm thick Cu foil; the conductive buffer layer comprises 3%, 41%, and 56% by mass of CMC, SBR, and sp; the active layer comprises 1%, 89%, 3%, and 7% by mass of graphite (Dv50 = 0.8 μm, Dv90 = 2 μm), hard carbon, sp, and SBR, with a total thickness of 142 μm.

[0147] In this embodiment, the method for preparing the electrode includes the following steps:

[0148] 1) Mix CMC, SBR and sp at 1200 rpm for 5 min according to the ratio, then add water and continue dispersing for 60 min to prepare a primer slurry with a viscosity controlled at 100 mPa / s (25℃, Bollerfeld DV2T viscometer, rotor No. 63).

[0149] 2) Using gravure printing technology, the prepared base coating slurry is applied to the Cu foil and dried to form a conductive buffer layer on both surfaces of the Cu foil.

[0150] 3) Mix graphite, hard carbon, sp and SBR in proportion, add water to prepare an active slurry with a solid content of 55%, coat the active slurry on the surface of the conductive buffer layer, and obtain the electrode sheet after drying and cold pressing.

[0151] Example 11

[0152] This embodiment provides an electrode sheet, which differs from Embodiment 10 in that the mass content of graphite in the active layer is increased. Specifically, in this embodiment, the active layer comprises graphite (Dv50 = 0.8 μm, Dv90 = 2 μm), hard carbon, sp, and SBR with mass contents of 3%, 87%, 3%, and 7%, respectively. Everything else is the same as in Embodiment 10.

[0153] Example 12

[0154] This embodiment provides an electrode sheet, which differs from Embodiment 10 in that the mass content of graphite in the active layer is increased. Specifically, in this embodiment, the active layer comprises 5%, 85%, 3%, and 7% by mass of graphite (Dv50 = 0.8 μm, Dv90 = 2 μm), hard carbon, sp, and SBR, respectively. Everything else is the same as in Embodiment 10.

[0155] Example 13

[0156] This embodiment provides an electrode sheet, which differs from Embodiment 11 in that the Cu foil is replaced with a 13 μm thick Al foil. Everything else is the same as in Embodiment 11.

[0157] Example 14

[0158] This embodiment provides an electrode sheet, which differs from Embodiment 11 in that graphite is replaced with an equal mass of soft carbon (Dv50 = 0.8 μm, Dv90 = 2 μm). Everything else is the same as in Embodiment 11.

[0159] Example 15

[0160] This embodiment provides an electrode sheet, which differs from Embodiment 14 in that the Cu foil is replaced with a 13 μm thick Al foil. Everything else is the same as in Embodiment 14.

[0161] Comparative Example 1

[0162] This comparative example provides an electrode sheet, the main difference between which is that neither the conductive buffer layer nor the active layer contains graphite or soft carbon.

[0163] Specifically, the electrode in this comparative example includes a current collector, with conductive buffer layers disposed on both surfaces of the current collector, and an active layer disposed on the surface of the conductive buffer layer. The current collector is a 6 μm thick Cu foil; the conductive buffer layer comprises CMC, SBR, and sp with mass contents of 3%, 41%, and 56%, respectively, with a total thickness of 3 μm; the active layer comprises hard carbon, sp, and SBR with mass contents of 90%, 3%, and 7%, respectively, with a total thickness of 142 μm.

[0164] Comparative Example 2

[0165] This comparative example provides an electrode sheet that differs from Comparative Example 1 in that the Cu foil is replaced with a 13 μm thick Al foil. Everything else is the same as Comparative Example 1.

[0166] Comparative Example 3

[0167] This comparative example provides an electrode sheet, the main difference between which is that it does not contain a conductive buffer layer, nor does it contain graphite or soft carbon.

[0168] Specifically, the electrode in this comparative example includes a current collector, and active layers are disposed on both surfaces of the current collector. The current collector is a 6 μm thick Cu foil; the active layer contains 90%, 3%, and 7% by mass of hard carbon, sp, and SBR, respectively, with a total thickness of 142 μm.

[0169] Comparative Example 4

[0170] This comparative example provides an electrode sheet that differs from Comparative Example 3 in that the Cu foil is replaced with a 13 μm thick Al foil. Everything else is the same as Comparative Example 3.

[0171] The electrode compositions of each embodiment and comparative example are shown in the table below.

[0172] Table 1. Electrode Composition

[0173]

[0174]

[0175]

[0176] The compaction density of the electrodes in each embodiment and comparative example was fixed at 0.93 g / cm³. 3The elongation rate was tested (the elongation rate of the electrode largely depends on the elongation rate of the current collector, therefore the elongation rate of the electrode can reflect the elongation rate of the current collector). Using these electrodes with fixed compaction density as the negative electrode and NaFeO2 as the positive electrode, and employing a PP separator, the negative electrode, positive electrode, and separator were wound to form a bare cell. The cell was then packaged in an aluminum-plastic film package, subjected to a top-side sealing process, and then injected with electrolyte (1 mol / L NaPF6; EC, DMC = 1:1, v:v). After further processing including settling, shaping, and formation, a sodium-ion battery pouch was obtained, and initial efficiency and cycle performance tests were conducted. The results are shown in the table below.

[0177] Table 2. Electrode Performance Test Results

[0178]

[0179]

[0180] In Table 2, the elongation ratio 1 refers to the percentage of the elongation of the electrode in each embodiment compared to the elongation of the electrode in Comparative Example 1 (or Comparative Example 2) when using the same current collector.

[0181] For example, in Example 1, the current collector used was a 6μm thick Cu foil, and its electrode elongation was 1.20%; while in Comparative Example 1, the current collector was also a 6μm thick Cu foil, and its electrode elongation was 2.80%. Therefore, the elongation ratio 1 corresponding to Example 1 = elongation of electrode in Example 1 / elongation of electrode in Comparative Example 1 * 100% = 1.20% / 2.80% * 100% = 42.86%. Similarly, in Example 5, the current collector used was a 13μm thick Al foil, and its electrode elongation was 0.38%; while in Comparative Example 2, the current collector was also a 13μm thick Al foil, and its electrode elongation was 2.10%. Therefore, the elongation ratio 1 corresponding to Example 5 = elongation of electrode in Example 5 / elongation of electrode in Comparative Example 2 * 100% = 0.38% / 2.10% * 100% = 18.10%.

[0182] The elongation ratio 2 refers to the percentage of the elongation of each embodiment, comparative example 1, and comparative example 2 compared to the elongation of comparative example 3 (or comparative example 4) when using the same current collector.

[0183] For example, in Example 1, the current collector used was a 6μm thick Cu foil, and its electrode elongation was 1.20%; while in Comparative Example 3, the current collector was also a 6μm thick Cu foil, and its electrode elongation was 3.40%. Therefore, the elongation ratio 2 corresponding to Example 1 = elongation of electrode in Example 1 / elongation of electrode in Comparative Example 3 * 100% = 1.20% / 3.40% * 100% = 35.29%. Similarly, in Example 5, the current collector used was a 13μm thick Al foil, and its electrode elongation was 0.38%; while in Comparative Example 4, the current collector was also a 13μm thick Al foil, and its electrode elongation was 3.80%. Therefore, the elongation ratio 2 corresponding to Example 5 = elongation of electrode in Example 5 / elongation of electrode in Comparative Example 4 * 100% = 0.38% / 3.80% * 100% = 10.00%.

[0184] The test results show that:

[0185] The electrodes of Comparative Examples 3 and 4 employ a traditional electrode structure, with the active layer fabricated only on the current collector. This active layer contains no graphite or soft carbon, and its compaction density is 0.93 g / cm³. 3 The electrodes exhibit high elongation (reaching 3.40% and 3.80%), making them prone to edge collapse and winding breakage; their cycle performance is also poor (the capacity drops to 80% after 450 and 580 cycles at 45℃). While Comparative Examples 1 and 2, based on Comparative Examples 3 and 4, added a conductive buffer layer containing CMC, binder, and SP between the current collector and the active layer, this conductive buffer layer had only a small effect on improving the electrode's elongation (55.26%–82.35% of Comparative Examples 3 and 4), and edge collapse and winding breakage were still common, indicating structural instability. Consequently, the cycle performance of the electrodes was not effectively improved.

[0186] In contrast, Examples 1-15, by setting a conductive buffer layer between the current collector and the active layer, and adding graphite and soft carbon to the conductive buffer layer or the active layer, effectively reduced the elongation of the electrode. Under the same compaction density, the elongation was reduced to 0.38%–1.50%. Comparatively, this elongation was only 8.82%–44.12% of Comparative Examples 3 and 4, and 10.71%–66.67% of Comparative Examples 1 and 2. Such a low elongation effectively improved the problems of electrode edge collapse and winding breakage, while also improving the electrode's cycling performance, resulting in the capacity only decreasing to 80% after 870–1360 cycles at 45°C.

[0187] More specifically, Examples 1 to 9 incorporated a conductive buffer layer between the active layer and the current collector. In Examples 1 and 2, the conductive buffer layer contained up to 56% graphite or soft carbon by mass, resulting in a decrease in electrode elongation to 1.20% and 1.50%, respectively, while increasing the number of cycles at 45°C with 80% capacity retention to 870 and 980 cycles, respectively. Examples 3 to 9, by reducing the graphite or soft carbon content in the conductive buffer layer and adding sp to it, further reduced the electrode elongation to 0.30%–0.90%, which is only 10.71%–32.14% of Comparative Examples 1 and 2, and 8.82%–26.47% of Comparative Examples 3 and 4.

[0188] Examples 1 through 9 simultaneously demonstrate that the elongation of the electrode sheet is highly correlated with the mass content of graphite (or soft carbon) in the conductive buffer layer. Within a certain range, the elongation of the electrode sheet initially decreases and then increases as the content of graphite (or soft carbon) in the conductive buffer layer decreases. For example, in Examples 4 through 9, the content of graphite (or soft carbon) in the conductive buffer layer is lower than in Examples 1 and 3, and the elongation of the electrode sheet is also lower than in Examples 1 and 3; in Example 3, the content of graphite in the conductive buffer layer is further lower than in Examples 4 through 9, and the elongation of the electrode sheet increases slightly. Meanwhile, Examples 5 through 7 show that the elongation of the electrode sheet is correlated with the particle size of graphite (or soft carbon). Within a certain range, the elongation of the electrode sheet decreases as the particle size of graphite (or soft carbon) increases. Therefore, the elongation of the electrode sheet can be further optimized by optimizing the particle size of graphite (or soft carbon). However, in Examples 1 to 9, the electrodes containing graphite (or soft carbon) in the conductive buffer layer all had lower elongation than those without graphite (or soft carbon).

[0189] Examples 10-15 involved placing a conventional conductive buffer layer between the active layer and the current collector, while adding a certain amount of graphite or soft carbon to the active layer. This resulted in a decrease in the electrode elongation to 0.80%-1.50%, and an increase in the number of cycles with 80% capacity retention at 45°C to 1054-1145 cycles, showing a significant improvement compared to Comparative Examples 1-4. Furthermore, Examples 10-12 demonstrate a strong correlation between the electrode elongation and the mass content of graphite (or soft carbon) in the active layer. Within a certain range, the electrode elongation decreases with increasing graphite (or soft carbon) content in the active layer.

[0190] In addition, analysis of the first-efficiency results revealed that in Examples 1-15, a conductive buffer layer was provided between the current collector and the active layer, and graphite or soft carbon was added to the conductive buffer layer or the active layer. The resulting electrodes exhibited high first-efficiency, which was similar to that of common sodium-ion batteries using hard carbon negative electrodes. This indicates that the provision of the conductive buffer layer, graphite, and soft carbon did not cause significant degradation in the first-efficiency.

[0191] In summary, by setting a conductive buffer layer between the current collector and the active layer of the electrode, and adding graphite or soft carbon to at least one of the conductive buffer layer and the active layer, the elongation of the electrode can be effectively reduced. Furthermore, by adjusting the content of graphite and soft carbon in the conductive buffer layer and the active layer, the elongation of the electrode can be further optimized. In practice, reducing the elongation of the electrode can effectively improve its stability, mitigate edge collapse and winding breakage issues, and thus improve the cycle performance of the battery.

[0192] Appendix: The relevant performance testing methods are as follows:

[0193] 1) Electrode elongation

[0194] Take three anode plates, remove the tab area, and mark three points horizontally at three-meter intervals along the direction of the plates. The length of each mark should be accurate to 0.1mm, and denoted as a (a1, a2, a3). Adjust the left and right gaps of the cold press and the tonnage of the pressure rollers (20T~79T) to ensure that the cold-pressed thickness meets the set compaction density. Measure the length b of the marked points on the cold-pressed plates (b1, b2, b3). That is, the cold-pressed elongation (η) η=(b / a-1)*100%.

[0195] 2) First effect

[0196] First-cycle efficiency, also known as first-cycle coulombic efficiency, is the ratio of the first-cycle charge capacity D0 to the first-cycle discharge capacity C0 of a secondary battery (specifically a sodium-ion battery in this embodiment of the application) during the first-cycle charge and discharge process.

[0197] The specific testing method is as follows:

[0198] At 25°C, the sodium-ion battery is charged at a constant current rate of 0.2C for 1 hour, and the corresponding capacity is recorded as IGC0; then it is discharged at a rate of 0.1C to 1.5V, and the corresponding capacity is recorded as AGD0; after standing for 5 minutes, the sodium-ion battery is charged again at a rate of 0.5C to 4.2V, and the corresponding capacity is recorded as AGC0; after standing for 5 minutes, it is discharged at a rate of 0.1C to 1.5V, and the corresponding capacity is recorded as AGD1; where C0 is IGC0 - AGD0 + AGC0; D0 is AGD1; initial efficiency = D0 / C0*100%.

[0199] 3) 45℃ cycle

[0200] At 45°C, the sodium-ion battery was charged to 4.2V at a rate of 0.5C, then charged at a constant voltage until the current dropped below 0.05C, and finally discharged to 1.5V at a rate of 1C. Cyclic tests were performed using this full charge-discharge cycle until the lithium-ion battery's discharge capacity decreased to 80% of its initial capacity, and the number of cycles at this point was recorded.

[0201] 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. An electrode sheet, characterized in that, The electrode comprises a current collector, a conductive buffer layer, and an active layer stacked sequentially. The conductive buffer layer comprises a binder, a thickener, a conductive agent, and a carbon material. The conductive agent comprises one or more of carbon nanotubes, conductive carbon black, carbon fibers, and graphene. The carbon material comprises one or more of graphite and soft carbon. The carbon material in the conductive buffer layer has a mass content of 14% to 56%; The Dv50 of the carbon material is 0.4~1.5μm; The carbon material has a Dv90 of 1~4μm.

2. The electrode according to claim 1, characterized in that, The Dv50 of the carbon material is 0.7~0.9μm; And / or, the Dv90 of the carbon material is 1~3μm.

3. The electrode according to claim 1 or 2, characterized in that, The active layer contains the carbon material, and the carbon material in the active layer has a mass content of 1% to 5%.

4. The electrode according to claim 3, characterized in that, The carbon material in the active layer has a mass content of 3% to 5%.

5. The electrode sheet according to claim 1 or 2, characterized in that, The thickness of the conductive buffer layer is 3~6μm.

6. The electrode according to claim 5, characterized in that, The thickness of the conductive buffer layer is 3~4μm.

7. A method for preparing an electrode sheet, characterized in that, The process includes the following steps: preparing a conductive buffer layer on the surface of the current collector; preparing an active layer on the surface of the conductive buffer layer; wherein the conductive buffer layer comprises an adhesive, a thickener, a conductive agent, and a carbon material, wherein the conductive agent comprises one or more of carbon nanotubes, conductive carbon black, carbon fibers, and graphene, and the carbon material comprises one or more of graphite and soft carbon. The carbon material in the conductive buffer layer has a mass content of 14% to 56%; The Dv50 of the carbon material is 0.4~1.5μm; The carbon material has a Dv90 of 1~4μm.

8. The preparation method according to claim 7, characterized in that, The step of preparing the conductive buffer layer includes: providing a primer slurry and coating the primer slurry onto the surface of the current collector.

9. The preparation method according to claim 8, characterized in that, The viscosity of the primer slurry at 25°C is 100~1000mPa / s.

10. The preparation method according to claim 8 or 9, characterized in that, The viscosity of the primer slurry at 25°C is 300~600 mPa / s.

11. A battery, characterized in that, The battery includes the electrode as described in any one of claims 1 to 6.

12. An electrical appliance, characterized in that, The electrical device includes the battery as described in claim 11.

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