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

Abstract

A positive electrode sheet, a battery, a battery pack, and an electric device. The positive electrode sheet comprises a positive electrode current collector, and a first positive electrode active layer and a second positive electrode active layer stacked on at least one side of the positive electrode current collector, wherein the first positive electrode active layer comprises a first positive electrode active material, and the second positive electrode active layer comprises the first positive electrode active material and a second positive electrode active material; the first positive electrode active material comprises at least one of a manganese-based positive electrode active material, an iron-based positive electrode active material and a manganese-iron mixed positive electrode active material; the second positive electrode active material comprises at least one of a ternary positive electrode active material, lithium cobalt oxides, lithium nickel oxides and lithium titanium oxides; and the second positive electrode active layer further comprises a second conductive agent, and the second conductive agent comprises at least two linear conductive agents, and at least one of a sheet-shaped conductive agent and a dot-shaped conductive agent. The positive electrode sheet has a special structure and composition, and thus can effectively ameliorate the impedance growth of a battery and improve the cycle performance thereof.

Description

A positive electrode, a battery, a battery pack, and an electrical device.

[0001] This application claims priority to Chinese Patent Application No. 202510484620.5, filed on April 16, 2025, entitled "A Positive Electrode, Battery, Battery Pack and Electrical Device", the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application belongs to the field of battery technology, and relates to a positive electrode sheet, and more particularly to a positive electrode sheet, a battery, a battery pack and an electrical device. Background Technology

[0003] Lithium-ion batteries have been widely used in electric vehicles (such as electric vehicles, hybrid vehicles, and electric bicycles), energy storage systems (such as home energy storage systems, grid energy storage systems, and renewable energy storage) due to their advantages such as high energy density, high voltage platform, low self-discharge rate, lightweight, no memory effect, environmental friendliness, wide operating temperature range, and flexible design.

[0004] Currently, the main positive electrode active materials in lithium-ion batteries include manganese-based positive electrode materials, iron-based positive electrode materials, manganese-iron hybrid positive electrode materials, ternary positive electrode active materials, and lithium cobalt oxide. The first three materials offer advantages over other positive electrode active materials, such as a high voltage platform, high rate performance, high safety, low cost, and environmental friendliness. However, these materials suffer from varying degrees of manganese and iron ion dissolution during charge and discharge, leading to increased battery impedance, damage to the negative electrode SEI film, and loss of active lithium, thus affecting battery cycle performance. To prevent the dissolution of metal ions, common technical solutions involve coatings on the surface of the positive electrode material, such as complexing agent coatings, CEI films, and carbon coatings. However, these coatings typically do not provide capacity and require additional processing, increasing costs.

[0005] Therefore, how to suppress the dissolution of metal ions in manganese-based cathode materials, iron-based cathode materials, and manganese-iron hybrid cathode materials, improve battery impedance, and enhance battery cycle performance are technical problems that urgently need to be solved in this field. Summary of the Invention

[0006] To address the above deficiencies, this application provides a positive electrode sheet with a special structure and composition that can effectively suppress the dissolution of metal ions in manganese-based positive electrode materials, iron-based positive electrode materials, and manganese-iron mixed-based positive electrode materials, thereby improving battery impedance growth and enhancing battery cycle performance.

[0007] This application also provides a battery including the above-described positive electrode, thus the battery has a low impedance growth rate and a long cycle life.

[0008] This application also provides a battery pack including the above-described positive electrode or the above-described battery, thus the battery pack has a low impedance growth rate and a long cycle life.

[0009] This application also provides an electrical device including the above-mentioned battery or battery pack, thus the electrical device has high endurance and stability.

[0010] The first aspect of this application provides a positive electrode sheet, the positive electrode sheet including a positive current collector, a first positive active layer and a second positive active layer, the first positive active layer being disposed on at least one side of the positive current collector, and the second positive active layer being disposed on the side of the first positive active layer away from the positive current collector;

[0011] The first positive electrode active layer includes a first positive electrode active material, and the second positive electrode active layer includes the first positive electrode active material and a second positive electrode active material;

[0012] The first positive electrode active material includes at least one of manganese-based positive electrode active material, iron-based positive electrode active material, and manganese-iron mixed-based positive electrode active material; the second positive electrode active material includes at least one of ternary positive electrode active material, lithium cobalt oxide, lithium nickel oxide, and lithium titanate.

[0013] The second positive electrode active layer further includes a second conductive agent, which includes at least two linear conductive agents, as well as at least one of sheet-like conductive agents and dot-like conductive agents.

[0014] The positive electrode sheet as described above, wherein the manganese-based positive electrode active material includes at least one of lithium manganese phosphate, lithium-rich manganese-based material, lithium manganese oxide, and lithium nickel manganese oxide; the iron-based positive electrode active material includes lithium iron phosphate; and the manganese-iron mixed-based positive electrode active material includes lithium manganese iron phosphate.

[0015] The positive electrode as described above, wherein the linear conductive agent includes at least one of carbon fiber, single-walled carbon nanotube, multi-walled carbon nanotube, array tube, metal nanowire, and conductive polymer nanowire;

[0016] And / or, the sheet-like conductive agent includes graphene and / or conductive graphite;

[0017] And / or, the dotted conductive agent includes conductive carbon black and / or acetylene black.

[0018] In the positive electrode sheet described above, the linear conductive agent includes a first linear conductive agent and a second linear conductive agent; the diameter of the first linear conductive agent is larger than the diameter of the second linear conductive agent.

[0019] In the positive electrode sheet described above, the diameter ratio of the first linear conductive agent to the second linear conductive agent is 2.5 to 20.

[0020] In the positive electrode sheet described above, the diameter of the linear conductive agent is 0.4 nm to 500 nm, and the aspect ratio is 50 to 1000.

[0021] And / or, the sheet-like conductive agent has a sheet diameter of 0.5 μm to 50 μm and a thickness of 0.3 nm to 200 nm;

[0022] And / or, the particle size of the dotted conductive agent is 15nm to 80nm.

[0023] In the positive electrode as described above, the diameter of the linear conductive agent is 5 nm to 50 nm, and the aspect ratio is 50 to 300.

[0024] As described above, in the positive electrode sheet, based on the total mass of the second conductive agent in the second positive electrode active layer, the total mass content of the linear conductive agent is 25% to 75%, and the total mass content of the other types of second conductive agents is 25% to 75%.

[0025] In the positive electrode sheet as described above, based on the total mass of the first positive electrode active material and the second positive electrode active material in the second positive electrode active layer, the mass content of the second positive electrode active material is 5% to 95%, and the mass content of the first positive electrode active material is 5% to 95%.

[0026] In the positive electrode sheet described above, the mass content of the second positive electrode active layer is 10% to 90% based on the total mass of the second positive electrode active layer and the first positive electrode active layer, and the mass content of the first positive electrode active layer is 10% to 90%.

[0027] In the positive electrode sheet described above, the thickness of the first positive electrode active layer on one side is 5 μm to 104 μm; and / or, the thickness of the second positive electrode active layer on one side is 5 μm to 104 μm.

[0028] The positive electrode sheet as described above further includes a conductive layer disposed between the first positive electrode active layer and the second positive electrode active layer; the conductive layer includes a conductive material, which includes at least one of carbon black, carbon fiber, single-walled carbon nanotubes, multi-walled carbon nanotubes, arrayed tubes, graphene, and conductive graphite.

[0029] In the positive electrode as described above, the thickness of the conductive layer is 1 μm to 3 μm.

[0030] The positive electrode sheet as described above, wherein the electrode further includes a polymer coating disposed on at least one side of the second positive electrode active layer away from the first positive electrode active layer.

[0031] The positive electrode sheet as described above, wherein the thickness of the polymer coating is 0.5 μm to 5 μm; and / or, the polymer in the polymer coating includes at least one of polyimide, polyetherimide, and polyacrylonitrile.

[0032] The positive electrode sheet as described above, wherein the median particle size D50 of the first positive electrode active material is 0.02 μm to 3 μm; and / or, the median particle size D50 of the mixture of the first positive electrode active material and the second positive electrode active material is 0.1 μm to 10 μm.

[0033] The positive electrode sheet as described above, wherein the first positive electrode active layer further includes a first conductive agent, a first binder, and a first dispersant; based on the total mass of the first positive electrode active layer, the mass content of the first conductive agent is 0.5% to 10%, the mass content of the first binder is 0.5% to 10%, the mass content of the first dispersant is 0% to 1%, and the mass content of the first positive electrode active material is 89.5% to 99%.

[0034] And / or, the second positive electrode active layer further includes a second binder and a second dispersant; based on the total mass of the second positive electrode active layer, the mass content of the second conductive agent is 0.5% to 10%, the mass content of the second binder is 0.5% to 10%, the mass content of the second dispersant is 0% to 1%, and the total mass content of the first positive electrode active material and the second positive electrode active material is 89.5% to 99%.

[0035] In the positive electrode sheet described above, the single-sided compaction density of the first positive electrode active layer is 1.8 g / cm³. 3 ~3g / cm 3 ; and / or, the single-sided compaction density of the second positive electrode active layer is 2 g / cm³. 3 ~4.5g / cm 3 .

[0036] A second aspect of this application provides a battery comprising the positive electrode plate described in the first aspect.

[0037] A third aspect of this application provides a battery pack comprising at least two positive electrode plates as described in the first aspect, or batteries as described in the second aspect.

[0038] The fourth aspect of this application provides an electrical device, which includes the battery described in the second aspect or the battery pack described in the third aspect.

[0039] The positive electrode sheet in this application has a special structure and composition, which can not only retain manganese and iron ions dissolved from the first positive electrode active material (including at least one of manganese-based positive electrode active material, iron-based positive electrode active material, and manganese-iron mixed-based positive electrode active material) during charge-discharge cycles, thus improving the cycle performance of the battery, but also reduce the content of the second positive electrode active material (including at least one of ternary positive electrode active material, lithium cobalt oxide, lithium nickel oxide, and lithium titanate) to a certain extent, thereby reducing the risk of thermal runaway and improving battery safety. At the same time, through the combination of special conductive agents, different conductive agents can work synergistically to reduce the contact resistance between different material particles (i.e., the first positive electrode active material and the second positive electrode active material), thereby reducing the rate of increase of DC resistance of the battery and giving the battery higher cycle performance. In addition, it can also optimize the pore structure of the active layer, promote the wetting and diffusion of the electrolyte, and ensure the structural stability of the electrode. Attached Figure Description

[0040] Figure 1 is a cross-sectional structural schematic diagram of the positive electrode sheet of this application in one embodiment;

[0041] Figure 2 is a cross-sectional structural schematic diagram of the positive electrode sheet of this application in another embodiment;

[0042] Figure 3 is a cross-sectional structural diagram of the conductive layer in the positive electrode sheet of this application in one embodiment;

[0043] Figure 4 is a cross-sectional structural diagram of the conductive layer in the positive electrode sheet of this application in another embodiment;

[0044] Figure 5 is a cross-sectional structural diagram of the conductive layer in the positive electrode sheet of this application in another embodiment;

[0045] Figure 6 is a cross-sectional structural diagram of the polymer coating in the positive electrode sheet of this application in one embodiment;

[0046] Figure 7 is a cross-sectional structural diagram of the polymer coating in the positive electrode sheet of this application in another embodiment;

[0047] Figure 8 is a cross-sectional structural diagram of the polymer coating in the positive electrode sheet of this application in another embodiment;

[0048] Figure 9 is a cross-sectional SEM image of the positive electrode sheet in Embodiment 1 of this application;

[0049] Figure 10 is an EDS diagram of the first positive electrode active material in the positive electrode sheet of Embodiment 1 of this application;

[0050] Figure 11 is an EDS diagram of the second positive electrode active material in the positive electrode sheet in Embodiment 1 of this application;

[0051] Figure 12 is a surface SEM image of the second positive electrode active layer in the positive electrode sheet of Embodiment 1 of this application;

[0052] Figure 13 shows the cycle capacity retention curves of the batteries corresponding to the positive electrode sheets in Embodiment 1 and Comparative Example 1 of this application;

[0053] Figure 14 shows the charge-discharge curves of the battery corresponding to the positive electrode in Embodiment 1 of this application;

[0054] Figure 15 shows the charge-discharge curves of the battery corresponding to the positive electrode in Comparative Example 1 of this application;

[0055] Figure 16 shows the discharge DC internal resistance curves of the lithium batteries corresponding to the electrodes in Example 1 and Comparative Example 2 of this application before cycling at 25°C.

[0056] Figure 17 shows the discharge DC internal resistance curves of the lithium batteries corresponding to the electrode sheets in Example 1 and Comparative Example 2 of this application after 300 cycles of charge and discharge at 25°C.

[0057] Figure 18 shows the EDS line scan of manganese element in lithium nickel cobalt aluminum oxide before cycling in the positive electrode sheet of Embodiment 1 of this application;

[0058] Figure 19 shows the EDS line scan of manganese element in lithium nickel cobalt aluminum oxide after cycling of the positive electrode sheet in Example 1 of this application;

[0059] Figure 20 is a schematic diagram of a battery pack provided in this application;

[0060] Figure 21 is a structural schematic diagram of an electrical device provided in this application.

[0061] Explanation of reference numerals in the attached figures: 1-First positive electrode active layer; 2-Second positive electrode active layer; 11-First positive electrode active material; 21-Second positive electrode active material; 3-Positive electrode current collector; 4-Conductive layer; 5-Polymer coating; 6-Battery; 7-Battery pack; 8-Electrical equipment. Detailed Implementation

[0062] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the embodiments of this application. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0063] Among numerous cathode active materials, manganese-based, iron-based, and manganese-iron hybrid cathode materials have been widely used in various technological fields due to their advantages such as high voltage platform, high rate performance, high safety, and low cost. However, these materials suffer from manganese and iron ion dissolution during charge-discharge cycles, leading to a series of problems such as increased battery impedance, damage to the negative electrode SEI film, and loss of active lithium, thus affecting the battery's cycle performance. Currently, coating measures are commonly used to mitigate the dissolution problem of manganese and iron ions in these materials, but this results in capacity loss and increased costs.

[0064] To address the aforementioned issues, the inventors attempted to add a second positive electrode active layer (comprising at least one of ternary positive electrode active materials, lithium cobalt oxide, lithium nickel oxide, and lithium titanate) on the side of the positive electrode active layer (including manganese-based positive electrode materials, iron-based positive electrode materials, and manganese-iron hybrid positive electrode materials, hereinafter referred to as the first positive electrode active material) away from the positive electrode current collector 3. This second positive electrode active layer aims to trap manganese and iron ions dissolved from the first positive electrode active material, reduce the deposition of manganese and iron ions on the negative electrode surface, prevent damage to the SEI film, reduce the loss of active ions, and improve the battery's cycle life. However, the crystal structure of the second positive electrode active material has poor stability and is prone to phase transitions during charging and discharging, accompanied by heat release, which can easily lead to thermal runaway. Furthermore, the particle size of the second positive electrode active material is generally large, resulting in larger pores in the positive electrode active layer. This not only affects the wetting and permeation of the electrolyte but also negatively impacts the stability of the electrode structure, thereby affecting the battery's discharge performance, cycle performance, and safety performance.

[0065] Therefore, the inventors blended the second positive electrode active material with the first positive electrode active material. On the one hand, this can optimize the pore structure of the positive electrode active layer, improve the wettability of the electrolyte, and enhance the stability of the electrode structure, giving the battery better discharge performance, cycle performance, and safety performance. On the other hand, it can also reduce the mass content of the second positive electrode active material, which not only ensures its retention of manganese and iron ions but also reduces the risk of thermal runaway and improves battery safety.

[0066] However, the first and second positive electrode active materials after mixing are different materials. These different materials exhibit inconsistencies in conductivity, lithium-ion diffusion capacity, and charge / discharge volume changes, leading to significant contact resistance between the different material particles. This, in turn, increases the rate of increase in internal resistance during cycling. Therefore, it is necessary to improve the mixed positive electrode active layer to reduce the contact resistance between the different materials, thereby reducing the rate of increase in DC resistance during battery cycling.

[0067] Through extensive research, the inventors discovered that linear conductive agents have better connectivity and conductivity compared to other conductive agents. By using two or more linear conductive agents in combination, and by incorporating at least one of dot-shaped and sheet-like conductive agents, the problem of electrical connection failure at the interface between different materials can be significantly improved, the contact resistance between particles of different materials can be reduced, and the battery can have a lower DC resistance growth rate.

[0068] Among them, linear conductive agents refer to conductive materials that have a significantly extended structure in one dimension (length), while the scales in the other two dimensions (width and height) are within the nanoscale (≤500nm); dot-shaped conductive agents refer to conductive materials that are within the nanoscale (≤100nm) in all three spatial dimensions, usually in the form of particles or spheres; sheet-like conductive agents refer to conductive materials that are in the form of thin sheets, with the scale in one dimension (thickness) within the nanoscale (≤200nm).

[0069] Based on the above analysis, the first aspect of this application provides a positive electrode sheet, which includes a positive current collector 3, a first positive active layer 1, and a second positive active layer 2. The first positive active layer 1 is disposed on at least one side of the positive current collector 3, and the second positive active layer 2 is disposed on the side of the first positive active layer 1 away from the positive current collector 3. The first positive active layer 1 includes a first positive active material 11, and the second positive active layer 2 includes the first positive active material 11 and the second positive active material 21. The first positive active material 11 includes at least one of manganese-based positive active material, iron-based positive active material, and manganese-iron mixed-based positive active material. The second positive active material 21 includes at least one of ternary positive active material, lithium cobalt oxide, lithium nickel oxide, and lithium titanate. The second positive active layer 2 also includes a second conductive agent, which includes at least two linear conductive agents, and at least one of sheet-like conductive agents and dot-like conductive agents.

[0070] As an optional implementation, the second positive electrode active material 21 includes a ternary positive electrode active material. Ternary positive electrode active materials have the advantages of a wide charge / discharge voltage range and high capacity, which can be well matched with the charge / discharge voltage window of the first positive electrode active material and improve the energy density of the cell.

[0071] Figure 1 is a cross-sectional structural schematic diagram of the positive electrode sheet of this application in one embodiment, and Figure 2 is a cross-sectional structural schematic diagram of the positive electrode sheet of this application in another embodiment. In Figures 1 and 2, the positive electrode sheet includes a positive current collector 3, a first positive active layer 1, and a second positive active layer 2. In one embodiment, the first positive active layer 1 is disposed on one side of the positive current collector 3, and the second positive active layer 2 is disposed on the side of the first positive active layer 1 away from the positive current collector 3 (as shown in Figure 1). In another embodiment, the first positive active layer 1 is disposed on both sides of the positive current collector 3, and the second positive active layer 2 is disposed on the side of the first positive active layer 1 away from the positive current collector 3 (as shown in Figure 2). The first positive active layer 1 includes a first positive active material 11, and the second positive active layer 2 includes the first positive active material 11 and the second positive active material 21.

[0072] When a first positive electrode active layer 1 and a second positive electrode active layer 2 are provided on both sides of the positive electrode current collector 3, the first positive electrode active layer 1 and the second positive electrode active layer 2 on both sides of the positive electrode current collector 3 are symmetrically arranged, that is, the thickness of the first positive electrode active layer 1 on both sides is completely consistent with the composition, and the thickness of the second positive electrode active layer 2 on both sides is completely consistent with the composition. This avoids inconsistent capacity performance on both sides of the positive electrode current collector 3, which would reduce the overall performance of the battery. At the same time, it can also simplify the electrode preparation process.

[0073] Specifically, the second conductive agent in the second positive electrode active layer 2 includes at least two types of linear conductive agents and sheet-like conductive agents, or the second conductive agent includes at least two types of linear conductive agents and dot-like conductive agents, or the second conductive agent simultaneously includes at least two types of linear conductive agents, dot-like conductive agents, and sheet-like conductive agents. Wherein, at least two types of linear conductive agents refer to at least two different types of linear conductive agents, or at least two different specifications (such as the diameter, length, and tube diameter (including inner and outer diameter) of the same linear conductive agent).

[0074] It should be noted that the types of the first positive electrode active material 11 in the second positive electrode active layer 2 and the first positive electrode active material 11 in the first positive electrode active layer 1 can be the same or different.

[0075] This application does not specifically limit the material of the positive current collector 3, which can be any of the conventional choices in the art, such as aluminum foil or nickel foil.

[0076] As an optional implementation, the manganese-based positive electrode active material in this application includes lithium manganese phosphate (LMP, LiMn). b PO4 (0 < b ≤ 1), lithium-rich manganese-based cathode, lithium manganese oxide (LMO, molecular formula LiMn2O4), lithium nickel manganese oxide (LNMO, molecular formula LiNi) c Mn 1-cAt least one of O4, 0.5≤c<1); iron-based cathode active materials include lithium iron phosphate (LFP, molecular formula LiFePO4); manganese-iron mixed-based cathode active materials include lithium manganese iron phosphate (LMFP); ternary cathode active materials include at least one of lithium nickel cobalt manganese oxide and lithium nickel cobalt aluminum oxide.

[0077] As an optional implementation method, lithium manganese iron phosphate has the molecular formula LiMn. x Fe y M 1-x-y PO4, 0.2≤x≤0.9, 0.1≤y≤0.5, 0≤1-xy≤0.2, M includes at least one of Al, Cu, Mg, Zn, Ni, Ti, V, Zr, Co, Ga, Sn, Sb, Nb and Ge. The molecular formula of lithium-rich manganese-based compounds is aLi2MnO3·(1-a)LiEO2, where E is a 3d transition metal and / or a 4d transition metal, 0<a<1.

[0078] As an optional implementation, lithium nickel cobalt manganese oxide and lithium nickel cobalt aluminum oxide each independently comprise the chemical composition shown in Formula 2.

[0079] LiNi r Co s E t G 1-r-s-t O2 Formula 2,

[0080] In Equation 2, 0 < r < 1, 0 < s < 1, 0 < t < 1, and 0 ≤ 1 - rst ≤ 0.2, E is selected from Al or Mn, and G includes at least one of Al, Cu, Mg, Zn, Ni, Ti, V, Zr, Co, Ga, Sn, Sb, Nb and Ge.

[0081] This application does not specifically limit the types and specifications of linear conductive agents, sheet conductive agents, and dot conductive agents; conventional materials in the field can be used.

[0082] This application does not specifically limit the source of the above-mentioned manganese-based positive electrode active material, iron-based positive electrode active material, manganese-iron mixed-based positive electrode active material, ternary positive electrode active material, lithium cobalt oxide, lithium nickel oxide, lithium titanate, and second conductive agent (linear conductive agent, sheet conductive agent, and dot conductive agent). Products prepared by commercially available products or conventional preparation methods well known to those skilled in the art are acceptable.

[0083] It is understood that the first positive electrode active layer 1 and the second positive electrode active layer 2 also include a binder and a dispersant. The binders in the first positive electrode active layer 1 and the second positive electrode active layer 2 can be the same or different, and the dispersants can be the same or different. Furthermore, this application does not specifically limit the types of binders and dispersants, which can be the binders and dispersants commonly used in lithium-ion batteries. For example, the binder can be selected from at least one of polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl fluoride, polyethylene, polypropylene, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, and polyimide; the dispersant can be selected from at least one of polyvinylpyrrolidone (PVP), polyacrylic acid (PAA), and polyethylene glycol (PEG).

[0084] The first positive electrode active layer 1 also includes a conductive agent (hereinafter referred to as the first conductive agent). This application does not specifically limit the type of conductive agent in the first positive electrode active layer 1; it can be the same as the second conductive agent in the second positive electrode active layer 2, or it can be a conductive agent commonly used in lithium-ion batteries. For example, the conductive agent can be selected from at least one of carbon black (CB), acetylene black, conductive graphite, carbon fiber (VGCF), carbon nanotubes (CNTs), and graphene (GN). Among them, carbon nanotubes include single-walled carbon nanotubes and multi-walled carbon nanotubes.

[0085] This application does not specify the proportion of each component in the first positive electrode active layer 1 and the second positive electrode active layer 2, and a suitable ratio can be selected according to the actual situation.

[0086] This application does not specify a particular method for preparing the positive electrode. In one embodiment, it can be prepared by the following method:

[0087] The raw materials, including the first positive electrode active material 11, the first conductive agent, the first binder, and the first dispersant, are dispersed in N-methylpyrrolidone (NMP) solvent and thoroughly stirred to form a uniform first positive electrode slurry. The raw materials, including the first positive electrode active material 11, the second positive electrode active material 21, the second conductive agent, the second binder, and the second dispersant, are dispersed in N-methylpyrrolidone (NMP) solvent and thoroughly stirred to form a uniform second positive electrode slurry. The first positive electrode slurry is coated on at least one side of the positive electrode current collector 3, and then the second positive electrode slurry is coated on the coating surface formed by the first positive electrode slurry. After drying, rolling, and slitting, the desired positive electrode sheet is obtained.

[0088] The positive electrode in this application has a special electrode structure and composition. Specifically, a second positive electrode active layer 2 is provided on the side of the first positive electrode active layer 1 away from the positive electrode current collector 3. The first positive electrode active layer 1 includes a first positive electrode active material 11 (including at least one of manganese-based positive electrode active material, iron-based positive electrode active material, and manganese-iron mixed-based positive electrode active material). The second positive electrode active layer 2 includes the first positive electrode active material 11 and a second positive electrode active material 21 (including at least one of ternary positive electrode active material, lithium cobalt oxide, lithium nickel oxide, and lithium titanate). At the same time, the second positive electrode active layer 2 also includes a second conductive agent (including at least two linear conductive agents, and at least one of sheet-like conductive agents and dot-like conductive agents). The second positive electrode active layer 2 can, on the one hand, trap manganese and iron ions dissolved from the first positive electrode active material 11 during charge-discharge cycles, thereby effectively reducing metal deposition on the negative electrode surface, avoiding damage to the SEI film, reducing the loss of active ions, and improving the battery's cycle performance. On the other hand, it can also reduce the content of the second positive electrode active material 21 in the second positive electrode active layer 2 to a certain extent, reducing the risk of thermal runaway, improving battery safety, and optimizing the pore structure of the second positive electrode active layer 2, improving the electrolyte wetting ability and electrode structural stability, further enhancing the battery's cycle performance. The second conductive agent can significantly improve the problem of electrical connection failure between interfaces where different material particles directly contact each other, reducing the contact resistance between different material particles, giving the battery a lower DC resistance growth rate, and thus improving the battery's cycle performance.

[0089] Furthermore, the specific types of linear conductive agents, sheet-like conductive agents, and dot-like conductive agents in the second conductive agent can be selected to reduce the contact resistance between different material particles, thereby enabling the battery to have higher cycle performance.

[0090] In one specific embodiment, the linear conductive agent includes at least one of carbon fiber, single-walled carbon nanotube, multi-walled carbon nanotube, array tube, metal nanowire, and conductive polymer nanowire; the sheet-like conductive agent includes graphene and / or conductive graphite; and the dot-like conductive agent includes conductive carbon black and / or acetylene black.

[0091] It should be noted that carbon nanotubes include single-walled carbon nanotubes, multi-walled carbon nanotubes (MLNTs) and multi-walled carbon nanotubes (CNTs). The diameter A of single-walled carbon nanotubes satisfies: 0.4 nm ≤ A ≤ 3 nm; the diameter B of MLNTs satisfies: 5 nm ≤ B ≤ 20 nm; and the diameter C of CNTs satisfies: 20 nm < C ≤ 150 nm.

[0092] In one specific embodiment, the linear conductive agent includes a first linear conductive agent and a second linear conductive agent; the diameter of the first linear conductive agent is larger than the diameter of the second linear conductive agent.

[0093] In detail, the linear conductive agent in the second conductive agent includes two linear conductive agents with different diameters, namely the first linear conductive agent and the second linear conductive agent.

[0094] When the linear conductive agent includes two linear conductive agents with different diameters, the contact resistance between different positive electrode active material particles can be further reduced, the DC resistance growth rate of the battery can be reduced, and the battery can have higher cycle performance.

[0095] In one specific embodiment, the diameter ratio of the first linear conductive agent to the second linear conductive agent is 2.5 to 20. When the diameter ratio of the first linear conductive agent to the second linear conductive agent is within the aforementioned range, the cycle performance of the battery can be further improved.

[0096] For example, the ratio of diameters can be 2.5, 3, 4, 6, 8, 10, 12, 14, 16, 18, 20 or a range of any two of these values.

[0097] In one specific embodiment, the diameter of the linear conductive agent is 0.4 nm to 500 nm, and the aspect ratio is 50 to 1000; as an optional embodiment, the diameter of the linear conductive agent is 5 nm to 50 nm, and the aspect ratio is 50 to 300. When the linear conductive agent meets the aforementioned size range, the contact resistance between different particles can be further reduced, resulting in a lower DC resistance growth rate and improved battery cycle performance.

[0098] For example, the diameter of the linear conductive agent can be 0.4nm, 1nm, 5nm, 10nm, 50nm, 100nm, 150nm, 200nm, 250nm, 300nm, 350nm, 400nm, 450nm, 500nm, or any two of these values; the aspect ratio can be 50, 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, or any two of these values.

[0099] In one specific embodiment, the sheet-like conductive agent has a sheet diameter of 0.5 μm to 50 μm and a thickness of 0.3 nm to 200 nm. When the sheet-like conductive agent meets the aforementioned size range, the contact resistance between different particles can be further reduced, resulting in a lower DC resistance growth rate and improved battery cycle performance.

[0100] For example, the diameter of the sheet-like conductive agent can be 0.5μm, 1μm, 5μm, 10μm, 15μm, 20μm, 25μm, 30μm, 35μm, 40μm, 45μm, 50μm or any two of these values; the thickness can be 0.3nm, 0.5nm, 1nm, 5nm, 10nm, 50nm, 100nm, 150nm, 200nm or any two of these values.

[0101] In one specific embodiment, the median particle size of the dot-shaped conductive agent is 15 nm to 80 nm. When the dot-shaped conductive agent meets the aforementioned size range, the contact resistance between different particles can be further reduced, resulting in a lower DC resistance growth rate and improved battery cycle performance.

[0102] For example, the median particle size of the dotted conductive agent can be 15nm, 20nm, 25nm, 30nm, 35nm, 40nm, 45nm, 50nm, 55nm, 60nm, 65nm, 70nm, 75nm, 80nm, or any two of these values.

[0103] Furthermore, the mass content of the first positive electrode active material 11 and the second positive electrode active material 21 in the second positive electrode active layer 2, the mass ratio of the first positive electrode active layer 1 and the second positive electrode active layer 2, and the content of various conductive agents in the second conductive agent can be adjusted to give the battery better overall performance.

[0104] In one specific embodiment, based on the total mass of the second conductive agent in the second positive electrode active layer 2, the total mass content of the linear conductive agent is 25% to 75%, and the total mass content of the other types of second conductive agents is 25% to 75%. Within this range, the various conductive agents in the second conductive agent can work together better, combining the advantages of different conductive agents to further reduce the contact resistance between different positive electrode active material particles, reduce the rate of increase of DC resistance during battery cycling, and improve battery performance.

[0105] Specifically, when the second conductive agent includes two or more different specifications of linear conductive agents (e.g., carbon fibers with different diameters and / or lengths), or two or more different types of linear conductive agents (e.g., carbon fibers and single-walled carbon nanotubes), the total mass content of all specifications of linear conductive agents and all types of linear conductive agents in the second conductive agent is between 25% and 75%. Other types of second conductive agents refer to dot-shaped conductive agents and / or sheet-shaped conductive agents. When the second conductive agent includes dot-shaped conductive agents, the mass content of dot-shaped conductive agents in the second conductive agent is 25% to 75%. When the second conductive agent includes sheet-shaped conductive agents, the mass content of sheet-shaped conductive agents in the second conductive agent is 25% to 75%. When the second conductive agent includes both dot-shaped and sheet-shaped conductive agents, the total mass content of sheet-shaped and dot-shaped conductive agents in the second conductive agent is 25% to 75%.

[0106] For example, the total mass content of the linear conductive agent in the second conductive agent can be 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, or 75%, or a range of any two of these values.

[0107] For example, the total mass content of other types of second conductive agents in the second conductive agent can be 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, or 75%, or a range of any two of these values.

[0108] In this application, the surface and cross-section of the positive electrode sheet can be photographed using a scanning electron microscope (SEM) to obtain SEM morphology images. Based on the morphology and size characteristics of each conductive agent (e.g., diameter, aspect ratio, sheet diameter, thickness, particle size, etc.), the types of conductive agents in the first positive electrode active layer 1 and the second positive electrode active layer 2 can be determined. Even when the sizes of the conductive agents are similar, the determination can be made based on the morphology of the conductive agents (e.g., cross-section, tortuosity, roughness, etc.).

[0109] After determining the types of conductive agents contained in the first positive electrode active layer 1 and the second positive electrode active layer 2, a big data AI identification method can be used. This involves establishing a SEM image library of electrode cross-sections containing different proportions of these conductive agents. AI identification and comparison are then used to calculate the density and volume ranges of different conductive agents, thereby determining the mass ratio of each conductive agent in the second positive electrode active layer 2. During the identification process, a large amount of cross-sectional morphological information of electrode sheets containing different proportions and types of conductive agents is needed to ensure the reliability of the statistical results. Therefore, it is necessary to set up positive electrode sheets containing different types and proportions of conductive agents to collect information.

[0110] In one specific embodiment, based on the total mass of the first positive electrode active material 11 and the second positive electrode active material 21 in the second positive electrode active layer 2, the mass content of the second positive electrode active material 21 is 5% to 95%, and the mass content of the first positive electrode active material 11 is 5% to 95%. Within this range, the first positive electrode active material 11 and the second positive electrode active material 21 can work together better, which not only ensures the retention effect of manganese ions and iron ions in the bottom layer of the positive electrode sheet (i.e., the first positive electrode active layer 1), but also gives the second positive electrode active layer 2 a better pore structure, which is beneficial to the wetting and penetration of the electrolyte and improves the stability of the electrode sheet, thereby further improving the discharge performance, cycle performance and safety performance of the battery.

[0111] For example, based on the total mass of the first positive electrode active material 11 and the second positive electrode active material 21 in the second positive electrode active layer 2, the mass content of the second positive electrode active material 21 is 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, or 95%, or a range of any two of these values.

[0112] For example, based on the total mass of the first positive electrode active material 11 and the second positive electrode active material 21 in the second positive electrode active layer 2, the mass content of the first positive electrode active material 11 is 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, or 95%, or a range of any two of these values.

[0113] The "mass content of the first positive electrode active material 11 in the total mass of the first positive electrode active material 11 and the second positive electrode active material 21" and the "mass content of the second positive electrode active material 21 in the total mass of the first positive electrode active material 11 and the second positive electrode active material 21" in this application can be obtained by testing the following methods:

[0114] The electrode and dressing (i.e., the first positive electrode active layer 1 and the second positive electrode active layer 2) were peeled off using adhesive tape to obtain the first positive electrode active layer 1 dressing and the second positive electrode active layer 2 dressing, respectively. The main components of the first positive electrode active layer 1 and the second positive electrode active layer 2 were determined by combining energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), and inductively coupled plasma mass spectrometry (ICP-MS).

[0115] For example, when the first positive electrode active material 11 in the first positive electrode active layer 1 is lithium manganese iron phosphate, and the second positive electrode active material 21 in the second positive electrode active layer 2 is lithium manganese iron phosphate and lithium nickel cobalt aluminum oxide, EDS is used to test the first positive electrode active layer 1 coating and the second positive electrode active layer 2 coating obtained by stripping. The weight percentage of each element in the first positive electrode active layer 1 and the weight percentage of each element in the second positive electrode active layer 2 can be obtained. From the content of each element obtained by the test, it can be analyzed that the first positive electrode active layer 1 contains Mn and Fe elements, which is consistent with the characteristic elements of lithium manganese iron phosphate; the second positive electrode active layer 2 contains not only Mn and Fe elements, but also Ni, Co, and Al elements, which proves that the active main material in the second positive electrode active layer 2 is a mixture of lithium manganese iron phosphate and lithium nickel cobalt aluminum oxide.

[0116] Similarly, XRD testing can be used to test the phase structure of the first positive electrode active layer 1 and the second positive electrode active layer 2 obtained by peeling. This reveals that the active material in the first positive electrode active layer is lithium manganese iron phosphate, and the active material in the second positive electrode active layer 2 is a mixture of lithium manganese iron phosphate and lithium nickel cobalt aluminum oxide. Through XRD refinement, the mass ratio of lithium nickel cobalt aluminum oxide to lithium manganese iron phosphate in the second positive electrode active layer 2 can be calculated. This allows for further calculation of the mass content of the first positive electrode active material 11 in the total mass of the first and second positive electrode active materials 11, as well as the total mass of the second positive electrode active material 21 in the first and second positive electrode active materials 11.

[0117] Similarly, the composition of the second positive electrode active layer 2 dressing obtained by stripping can be tested by ICP to detect the mass percentage content of each element in the dressing (based on the total mass). Using the mass percentage content of the characteristic elements Co and Al in lithium nickel cobalt aluminum oxide, the weight percentage of lithium nickel cobalt aluminum oxide can be calculated, and then the mass ratio of lithium nickel cobalt aluminum oxide to lithium manganese iron phosphate in the second positive electrode active layer 2 can be obtained. This can be further converted to obtain the mass content of the first positive electrode active material 11 in the total mass of the first positive electrode active material 11 and the second positive electrode active material 21, as well as the total mass of the second positive electrode active material 21 in the first positive electrode active material 11 and the second positive electrode active material 21.

[0118] In one specific embodiment, based on the total mass of the second positive electrode active layer 2 and the first positive electrode active layer 1, the mass content of the second positive electrode active layer 2 is 10% to 90%, and the mass content of the first positive electrode active layer 1 is 10% to 90%. Within this range, not only can the retention effect of the second positive electrode active layer 2 on manganese and iron ions be guaranteed, but the pore structure of the outer layer of the positive electrode sheet can also be optimized to improve lithium ion transport.

[0119] For example, based on the total mass of the second positive electrode active layer 2 and the first positive electrode active layer 1, the mass content of the second positive electrode active layer 2 is 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, or 90%, or a range of any two of these values.

[0120] For example, based on the total mass of the second positive electrode active layer 2 and the first positive electrode active layer 1, the mass content of the first positive electrode active layer 1 is 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, or 90%, or a range of any two of these values.

[0121] The "mass content of the first positive electrode active material layer 1 in the total mass of the first positive electrode active material layer 1 and the second positive electrode active material layer 2" and the "mass content of the second positive electrode active material layer 2 in the total mass of the first positive electrode active material layer 1 and the second positive electrode active material layer 2" in this application can be obtained by testing the following methods:

[0122] The thicknesses of the first positive electrode active layer 1 and the second positive electrode active layer 2 in the electrode sheet were measured using a scanning electron microscope (SEM), and the first positive electrode active layer 1 was determined to be d1, and the second positive electrode active layer 2 was determined to be d2. The electrode sheet and the dressing (i.e., the first positive electrode active layer 1 and the second positive electrode active layer 2) were peeled off using adhesive tape to obtain the first positive electrode active layer 1 and the second positive electrode active layer 2, respectively. Using a circular sampler, the first positive electrode active layer 1 and the second positive electrode active layer 2 obtained by peeling are cut into circular sheets of a certain area. The area, thickness and mass of the circular sheet obtained from the first positive electrode active layer 1 are measured and denoted as S1, t1 (t1 < d1) and m1 respectively. The area, thickness and mass of the circular sheet obtained from the second positive electrode active layer 2 are measured and denoted as S2, t2 (t2 < d2) and m2 respectively. Then the compaction density of the first positive electrode active layer ρ1 = m1 / (S1 × t1) and the compaction density of the second positive electrode active layer ρ2 = m2 / (S2 × t2). The weight ratio of the first positive electrode active layer 1 and the second positive electrode active layer 2 is (d1×ρ1):(d2×ρ2). Further calculations yield the mass content of the first positive electrode active material 11 in the total mass of the first positive electrode active material 11 and the second positive electrode active material 21, and the mass content of the second positive electrode active material 21 in the total mass of the first positive electrode active material 11 and the second positive electrode active material 21.

[0123] Furthermore, the thickness of the first positive electrode active layer 1 and the thickness of the second positive electrode active layer 2 will also affect the performance of the electrode, thereby affecting the overall performance of the battery.

[0124] In one specific embodiment, the thickness of the first positive electrode active layer 1 on one side is 5 μm to 104 μm, and the thickness of the second positive electrode active layer 2 on one side is 5 μm to 104 μm. Within this range, the lithium-ion transport path can be shortened to a certain extent, the electrode surface resistance can be reduced, and the kinetic performance of the electrode can be improved; at the same time, a high energy density can be ensured.

[0125] For example, the thickness of one side of the first positive electrode active layer 1 is 5μm, 10μm, 20μm, 30μm, 40μm, 50μm, 60μm, 70μm, 80μm, 90μm, 100μm, 104μm or any two of these values; the thickness of one side of the second positive electrode active layer 2 is 5μm, 10μm, 20μm, 30μm, 40μm, 50μm, 60μm, 70μm, 80μm, 90μm, 100μm, 104μm or any two of these values.

[0126] The thickness of the "first positive electrode active layer 1" and the "thickness of the second positive electrode active layer 2" in this application can be obtained by testing the cross-section of the electrode using SEM.

[0127] Furthermore, the structure of the electrode sheets can be improved to enhance the battery's cycle performance, charge / discharge performance, and safety performance.

[0128] In one specific embodiment, the positive electrode further includes a conductive layer 4, which is disposed between the first positive electrode active layer 1 and the second positive electrode active layer 2. The conductive layer 4 includes a conductive material, which may include at least one of carbon black, carbon fiber, single-walled carbon nanotubes, multi-walled carbon nanotubes, arrayed tubes, graphene, and conductive graphite. As an optional embodiment, the thickness of the conductive layer 4 is 1 μm to 3 μm. By adding the conductive layer 4, the impedance between the first positive electrode active layer 1 and the second positive electrode active layer 2 can be improved, and the electrolyte retention capacity and electrolyte wetting capacity of the electrode can be enhanced, which is beneficial to the penetration and diffusion of the electrolyte, and further improves the cycle performance and charge / discharge capacity of the battery.

[0129] For example, the thickness of the conductive layer 4 can be 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, or any two of these values.

[0130] The "thickness of conductive layer 4" in this application can be tested using the same method as the "thickness of first positive electrode active layer 1" mentioned above, and will not be repeated here.

[0131] It should be noted that when the first positive electrode active layer 1 and the second positive electrode active layer 2 are provided on both sides of the positive electrode current collector 3, the conductive layer 4 can be provided on one side of the positive electrode current collector 3 or on both sides of the positive electrode current collector 3.

[0132] In detail, Figure 3 is a cross-sectional structural diagram of the conductive layer 4 in the positive electrode of this application in one embodiment, Figure 4 is a cross-sectional structural diagram of the conductive layer 4 in the positive electrode of this application in another embodiment, and Figure 5 is a cross-sectional structural diagram of the conductive layer 4 in the positive electrode of this application in yet another embodiment. The positive electrode in Figures 3-5 includes a positive electrode current collector 3, a first positive electrode active layer 1, a second positive electrode active layer 2, and a conductive layer 4.

[0133] In one embodiment, a first positive electrode active layer 1 is disposed on one side of the positive electrode current collector 3, a conductive layer 4 is disposed on the side of the first positive electrode active layer 1 away from the positive electrode current collector 3, and a second positive electrode active layer 2 is disposed on the side of the conductive layer 4 away from the first positive electrode active layer 1 (as shown in Figure 3).

[0134] In another embodiment, a first positive electrode active layer 1 is disposed on one side of the positive electrode current collector 3, a conductive layer 4 is disposed on the side of the first positive electrode active layer 1 away from the positive electrode current collector 3, and a second positive electrode active layer 2 is disposed on the side of the conductive layer 4 away from the first positive electrode active layer 1; a first positive electrode active layer 1 is disposed on the other side of the positive electrode current collector 3, and a second positive electrode active layer 2 is disposed on the side of the first positive electrode active layer 1 away from the positive electrode current collector 3 (as shown in Figure 4).

[0135] In another embodiment, a first positive electrode active layer 1, a conductive layer 4, and a second positive electrode active layer 2 are symmetrically disposed on both sides of the positive electrode current collector 3. The first positive electrode active layer 1 is disposed on both sides of the positive electrode current collector 3, the conductive layer 4 is disposed on both sides of the first positive electrode active layer 1 away from the positive electrode current collector 3, and the second positive electrode active layer 2 is disposed on both sides of the conductive layer 4 away from the first positive electrode active layer 1 (as shown in Figure 5).

[0136] It is understood that the conductive layer 4 also includes an adhesive. This application does not specifically limit the type of adhesive, as long as it can perform an adhesive function. For example, the adhesive in the conductive layer 4 includes at least one of polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl fluoride, polyethylene, polypropylene, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, and polyimide.

[0137] This application does not specify a particular mass ratio of conductive material to adhesive in conductive layer 4, which can be adjusted according to actual conditions. As an optional implementation, the mass ratio of conductive material to adhesive is 1:(0.5 to 4).

[0138] For example, the mass ratio of conductive material to binder can be 1:0.5, 1:1, 1:1.5, 1:2, 1:2.5, 1:3, 1:3.5, 1:4, or any range of two of these ratios.

[0139] In one specific embodiment, the electrode further includes a polymer coating 5, which is disposed on at least one side of the second positive electrode active layer 2 away from the first positive electrode active layer 1; as an optional embodiment, the thickness of the polymer coating 5 is 0.5 μm to 5 μm. By adding the polymer coating 5, side reactions between the active material and the electrolyte can be reduced, further improving the cycle and safety performance of the battery.

[0140] For example, the thickness of the polymer coating 5 can be 0.5μm, 1μm, 1.5μm, 2μm, 2.5μm, 3μm, 3.5μm, 4μm, 4.5μm or 5μm, or a range of any two of these values.

[0141] The "thickness of polymer coating 5" in this application can be tested using the same method as the "thickness of the first positive electrode active layer 1" mentioned above, and will not be repeated here.

[0142] In one specific embodiment, the polymer in the polymer coating 5 includes at least one of polyimide, polyetherimide, and polyacrylonitrile.

[0143] It should be noted that when the first positive electrode active layer 1 and the second positive electrode active layer 2 are provided on both sides of the positive electrode current collector 3, the polymer coating 5 can be provided on one side of the positive electrode current collector 3 or simultaneously on both sides of the current collector.

[0144] In detail, Figure 6 is a cross-sectional structural diagram of the polymer coating 5 in the positive electrode of this application in one embodiment, Figure 7 is a cross-sectional structural diagram of the polymer coating 5 in the positive electrode of this application in another embodiment, and Figure 8 is a cross-sectional structural diagram of the polymer coating 5 in the positive electrode of this application in yet another embodiment. The positive electrode in Figures 6-8 includes a positive electrode current collector 3, a first positive electrode active layer 1, a second positive electrode active layer 2, and a polymer coating 5.

[0145] In one embodiment, a first positive electrode active layer 1 is disposed on one side of the positive electrode current collector 3, a second positive electrode active layer 2 is disposed on the side of the first positive electrode active layer 1 away from the positive electrode current collector 3, and a polymer coating 5 is disposed on the side of the second positive electrode active layer 2 away from the first positive electrode active layer 1 (as shown in Figure 6).

[0146] In another embodiment, the first positive electrode active layer 1 is disposed on both sides of the positive electrode current collector 3, the second positive electrode active layer 2 is disposed on both sides of the first positive electrode active layer 1 away from the positive electrode current collector 3, and the polymer coating 5 is disposed on any side of the second positive electrode active layer 2 away from the first positive electrode active layer 1 (as shown in Figure 7).

[0147] In another embodiment, a first positive electrode active layer 1, a second positive electrode active layer 2, and a polymer coating 5 are symmetrically disposed on both sides of the positive electrode current collector 3. The first positive electrode active layer 1 is disposed on both sides of the positive electrode current collector 3, the second positive electrode active layer 2 is disposed on both sides of the first positive electrode active layer 1 away from the positive electrode current collector 3, and the polymer coating 5 is disposed on both sides of the second positive electrode active layer 2 away from the first positive electrode active layer 1 (as shown in Figure 8).

[0148] Furthermore, the particle size distribution of the first positive electrode active material 11 and the particle size distribution of the mixture of the first positive electrode active material 11 and the second positive electrode active material 21 can be adjusted to further optimize the electrode performance.

[0149] In one specific embodiment, the median particle size D50 of the first positive electrode active material 11 is 0.02 μm to 3 μm. Within this range, the particle size of the first positive electrode active material 11 is relatively moderate. On the one hand, it allows the material particles to have a shorter lithium-ion transport path, reducing lithium-ion transport resistance, and also allows the material particles to have higher mechanical strength, avoiding material breakage due to stress concentration during charging and discharging. On the other hand, this is beneficial to improving the conductivity of the particles, thereby improving the rate performance and safety performance of the material.

[0150] For example, the median particle size D50 of the first positive electrode active material 11 can be 0.02 μm, 0.05 μm, 0.1 μm, 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, or a range of any two of these values.

[0151] In this application, "median particle size D50" refers to the particle size corresponding to a cumulative volume percentage of 50%, which can be obtained by laser particle size analyzer.

[0152] Specifically, the positive electrode needs to be pretreated before testing, including the following steps: The electrode sheet and dressing (i.e., the first positive electrode active layer 1 and the second positive electrode active layer 2) are peeled off using adhesive tape to obtain the first positive electrode active layer 1 dressing and the second positive electrode active layer 2 dressing. The peeled dressings are placed in hydrochloric acid and stirred or sonicated. After solid-liquid separation, the solid is dried, the dried solid is ground, and then dispersed in a solvent (e.g., ethanol, acetone, etc.). The mixture is sonicated to obtain a suspension, and the suspension is centrifuged to obtain the first positive electrode active material 11 and a mixture of the first positive electrode active material 11 and the second positive electrode active material 21, respectively.

[0153] In one specific embodiment, the median particle size D50 of the mixture of the first positive electrode active material 11 and the second positive electrode active material 21 is 0.1 μm to 10 μm. Within this range, the pore structure of the second positive electrode active layer 2 can be further optimized, the wettability of the electrolyte can be improved, and the structural stability of the electrode can be ensured, thereby further improving the kinetic performance and safety performance of the battery.

[0154] For example, the median particle size D50 of the aforementioned mixed material can be 0.1 μm, 0.5 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm or 10 μm, or a range consisting of any two of these values.

[0155] Furthermore, the mass content of each component in the first positive electrode active layer 1 and the second positive electrode active layer 2 can be controlled to improve the overall performance of the electrode.

[0156] In one specific embodiment, the first positive electrode active layer 1 further includes a first conductive agent, a first binder, and a first dispersant; based on the total mass of the first positive electrode active layer 1, the mass content of the first conductive agent is 0.5% to 10%, the mass content of the first binder is 0.5% to 10%, the mass content of the first dispersant is 0 to 1%, and the mass content of the first positive electrode active material 11 is 89.5% to 99%.

[0157] For example, based on the total mass of the first positive electrode active layer 1, the mass content of the first conductive agent is 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10%, or a range consisting of any two of these values; the mass content of the first binder is 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10%, or a range consisting of any two of these values; the mass content of the first dispersant is 0%, 0.2%, 0.4%, 0.6%, 0.8%, or 1%, or a range consisting of any two of these values; and the mass content of the first positive electrode active material 11 is 89.5%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99%, or a range consisting of any two of these values.

[0158] In one specific embodiment, the second positive electrode active layer 2 further includes a second binder and a second dispersant; based on the total mass of the second positive electrode active layer 2, the mass content of the second conductive agent is 0.5% to 10%, the mass content of the second binder is 0.5% to 10%, the mass content of the second dispersant is 0% to 1%, and the total mass content of the first positive electrode active material 11 and the second positive electrode active material 21 is 89.5% to 99%.

[0159] For example, based on the total mass of the second positive electrode active layer 2, the mass content of the second conductive agent is 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10%, or a range consisting of any two of these values; the mass content of the second binder is 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10%, or a range consisting of any two of these values; the mass content of the second dispersant is 0%, 0.2%, 0.4%, 0.6%, 0.8%, or 1%, or a range consisting of any two of these values; and the total mass content of the first positive electrode active material 11 and the second positive electrode active material 21 is 89.5%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99%, or a range consisting of any two of these values.

[0160] In one specific embodiment, the single-sided compaction density of the first positive electrode active layer 1 is 1.8 g / cm³. 3 ~3g / cm 3 Within this range, the single-sided compaction density of the first positive electrode active layer 1 is relatively moderate, which not only helps to improve the battery capacity, but also does not affect the wetting of the electrolyte and the liquid retention capacity of the electrode, thus helping to improve the energy density and cycle performance of the battery.

[0161] For example, the single-sided compaction density of the first positive electrode active layer 1 can be 1.8 g / cm³. 3 2g / cm 3 2.2g / cm 3 2.4g / cm 3 2.6g / cm 3 2.8g / cm 3 Or 3g / cm 3 , or a range consisting of any two of the values.

[0162] The test method for "compact density of the first positive electrode active layer 1" in this application is the same as the test method described above, and will not be repeated here.

[0163] In one specific embodiment, the single-sided compaction density of the second positive electrode active layer 2 is 2 g / cm³. 3 ~4.5g / cm 3 Within this range, the single-sided compaction density of the second positive electrode active layer 2 is relatively moderate. This not only increases the battery capacity but also prevents the pores of the second positive electrode active layer 2 from becoming too small, thus affecting the electrolyte's wetting ability and its own liquid retention capacity. This reduces polarization during battery cycling and helps improve the battery's cycle performance.

[0164] For example, the single-sided compaction density of the second positive electrode active layer 2 can be 2 g / cm³. 32.2g / cm 3 2.4g / cm 3 2.6g / cm 3 2.8g / cm 3 3g / cm 3 4.2g / cm 3 4.4 g / cm 3 Or 4.5g / cm 3 , or a range consisting of any two of the values.

[0165] A second aspect of this application provides a battery 6 that includes the positive electrode plate of the first aspect. Therefore, the battery 6 has high cycle performance.

[0166] Generally, a battery includes an electrolyte, a battery cell, and a package containing the battery cell. The electrolyte is injected into the battery cell within the package. The battery cell includes a positive electrode, a negative electrode, and a separator located between the positive and negative electrodes. The battery cell can be a stacked cell, meaning it is composed of alternating layers of a positive electrode, separator, and negative electrode; or it can be a wound cell, where the positive electrode, separator, and negative electrode are stacked sequentially and then wound to form a cell with a wound structure.

[0167] This application does not specifically limit the structure of the negative electrode. In one embodiment, the negative electrode includes a negative electrode current collector and a negative electrode active layer disposed on at least a portion of the surface of the negative electrode current collector. The negative electrode active layer includes a negative electrode active material, a binder, and a conductive agent.

[0168] This application does not specifically limit the material of the negative electrode current collector, which can be a conventional material in the art. For example, the negative electrode current collector can be any of copper foil, nickel foam, or copper foam.

[0169] This application does not specifically limit the type of negative electrode active material, which can be any negative electrode active material commonly used in batteries. For example, the negative electrode active material can be selected from at least one of graphite, hard carbon, soft carbon, mesophase carbon microspheres, silicon-based negative electrode materials (mainly including silicon suboxide and silicon-carbon negative electrodes), and tin-based negative electrode materials (mainly including tin and tin alloys).

[0170] This application does not specifically limit the type of binder in the negative electrode; it can be any binder commonly used in current battery negative electrodes. For example, the binder can be selected from at least one of carboxymethyl cellulose, styrene-butadiene rubber, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide, polyimide, polyvinyl alcohol, and sodium polyacrylate.

[0171] This application does not specifically limit the type of conductive agent in the negative electrode; it can be any conductive agent commonly used in current battery negative electrodes. For example, the conductive agent can be selected from at least one of natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, and graphene.

[0172] This application does not specifically limit the preparation method of the negative electrode. In one embodiment, the negative electrode can be prepared by a method including the following steps:

[0173] The negative electrode active material, conductive agent, and binder are dispersed in deionized water and thoroughly stirred to form a uniform negative electrode slurry. The negative electrode slurry is then uniformly coated onto the negative electrode current collector, and after drying, rolling, and slitting, a negative electrode sheet is obtained.

[0174] This application does not specify the amount of negative electrode active material, conductive agent, and binder, which can be adjusted according to the actual situation.

[0175] This application does not specifically limit the composition of the electrolyte, which may include one or more solvents commonly used in current battery electrolytes, as well as lithium salts commonly used in current battery electrolytes. For example, the solvent may include at least one of ethylene carbonate, propylene carbonate, butene carbonate, fluoroethylene carbonate (FEC), dimethyl carbonate (DMC), diethyl carbonate (DEC), difluoroethylene carbonate (DFEC), dipropyl carbonate, ethyl methyl carbonate (EMC), ethyl acetate, ethyl propionate, propyl acetate, propyl propionate, sulfolane, and γ-butyrolactone; the lithium salt may include at least one of lithium hexafluorophosphate (LiPF6), lithium bis(fluorosulfonyl)imide (LiFSI), and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI).

[0176] This application does not specifically limit the material of the separator; it can be any separator material commonly used in batteries. For example, the separator can be selected from any of the following: polypropylene separator (PP), polyethylene separator (PE), polypropylene / polyethylene double-layer composite membrane (PP / PE), polyimide electrospun separator (PI), polypropylene / polyethylene / polypropylene triple-layer composite membrane (PP / PE / PP), cellulose nonwoven fabric separator, and separator with ceramic coating.

[0177] A third aspect of this application provides a battery pack 7, as shown in FIG20, which includes a positive electrode sheet of the first aspect or a battery 6 of the second aspect. This battery pack 7 has advantages corresponding to the aforementioned positive electrode, which will not be elaborated further.

[0178] Generally, the battery pack 7 includes multiple batteries 6 as described above. These batteries 6 are connected as individual cells to form the battery pack 7. These batteries 6 can be electrically connected by conventional methods in the art, such as series connection, parallel connection, or a combination of these connection methods, without any particular limitation.

[0179] A fourth aspect of this application provides an electrical device 8, as shown in FIG21, which includes a battery 6 of the second aspect or a battery pack 7 of the third aspect. This electrical device has advantages corresponding to the above-mentioned positive electrode, which will not be elaborated here.

[0180] The electrical equipment 8 in this application can be a conventional electrical equipment in the field, such as power equipment (e.g., electric vehicles, electric cars), electronic equipment (e.g., mobile phones, tablets, laptops, digital cameras, etc.), wearable devices (e.g., watches, bracelets, VR glasses, etc.), and there are no special restrictions on it.

[0181] The positive electrode provided in this application will be described in detail below through specific embodiments.

[0182] Example 1

[0183] Lithium manganese iron phosphate (molecular formula LiMn) 0.6 Fe 0.4 PO4 (D50 of 0.06 μm), coarse multi-walled carbon nanotubes (diameter of 50 nm, aspect ratio of 50), polyvinylidene fluoride (PVDF), polyvinylpyrrolidone (PVP), and N-methylpyrrolidone (NMP) were mixed in a mass ratio of 100:2:2.5:0.2:60, and the first positive electrode active slurry was obtained after uniform mixing.

[0184] Lithium nickel cobalt aluminum oxide (molecular formula LiNi) 0.7 Co 0.2 Al 0.1 O2, D50 is 3.77μm), lithium manganese iron phosphate (molecular formula is LiMn) 0.6 Fe 0.4 The following materials were mixed in a mass ratio of 60:40:0.75:0.5:0.75:2.5:0.2:55: PO4 (D50 of 0.06 μm), coarse multi-walled carbon nanotubes (50 nm in diameter and 50 aspect ratio of the first linear conductive agent), fine multi-walled carbon nanotubes (10 nm in diameter and 300 aspect ratio of the second linear conductive agent), carbon black (median particle size of 40 nm), polyvinylidene fluoride (PVDF), polyvinylpyrrolidone (PVP), and N-methylpyrrolidone (NMP) to obtain the second positive electrode active slurry.

[0185] The first positive electrode active slurry prepared above is coated on one side of the positive electrode current collector aluminum foil, and then the second positive electrode active slurry is coated on the coating surface formed by the first positive electrode coating. After drying, a single-sided coated electrode sheet is obtained. The single-sided coated electrode sheet is reversed and coated on the other side of the aluminum foil using the same method as described above. The surface density of each coating layer on both sides is consistent. After drying, it is rolled and cut to obtain the positive electrode sheet of this embodiment.

[0186] The areal density of both the first and second positive electrode active layers in this positive electrode sheet is 125 g / m². 2 The single-sided compaction density of the first positive electrode active layer is 2.4 g / cm³. 3 The single-sided compaction density of the second positive electrode active layer is 2.78 g / cm³. 3 The thickness of the first positive electrode active layer on one side is 52.4 μm, and the thickness of the second positive electrode active layer on one side is 44.9 μm. Based on the total mass of the second positive electrode active layer and the first positive electrode active layer, the mass content of the second positive electrode active layer is 50%, and the mass content of the first positive electrode active layer is 50%. The D50 of the mixed material of lithium nickel cobalt aluminum oxide and lithium manganese iron phosphate in the second positive electrode active layer is 2.3 μm.

[0187] Example 2

[0188] The preparation method of the positive electrode in this embodiment is basically the same as that in Example 1, except that:

[0189] In the second positive electrode active slurry, lithium nickel cobalt aluminum oxide is replaced with lithium nickel cobalt manganese oxide (molecular formula LiNi). 0.7 Co 0.1 Mn 0.2 O2, D50 is 3.68μm), and the mass ratio of lithium manganese iron phosphate to lithium nickel cobalt manganese oxide is adjusted to 5:95, that is, based on the total mass of lithium manganese iron phosphate and lithium nickel cobalt manganese oxide, the mass content of lithium manganese iron phosphate is 5% and the mass content of lithium nickel cobalt manganese oxide is 95%.

[0190] In the second positive electrode active slurry, the mass ratio of the first linear conductive agent multi-walled carbon nanotube coarse tube, the second linear conductive agent multi-walled carbon nanotube fine tube, and carbon black is adjusted to 1:0.5:0.5, that is, based on the total mass of the conductive agent, the mass content of multi-walled carbon nanotube coarse tube is 50%, the mass content of multi-walled carbon nanotube fine tube is 25%, and the mass content of carbon black is 25%.

[0191] The single-sided compaction density of the first positive electrode active layer is 2.4 g / cm³. 3 The single-sided compaction density of the second positive electrode active layer is 3.4 g / cm³. 3The thickness of the first positive electrode active layer on one side is 93.75 μm, and the thickness of the second positive electrode active layer on one side is 7.35 μm. Based on the total mass of the first and second positive electrode active layers, the mass content of the first positive electrode active layer is 90%, and the mass content of the second positive electrode active layer is 10%. The D50 of the mixed material of lithium nickel cobalt aluminum oxide and lithium manganese iron phosphate in the second positive electrode active layer is 3.46 μm, and other parameters remain unchanged.

[0192] Example 3

[0193] The preparation method of the positive electrode in this embodiment is basically the same as that in Example 1, except that:

[0194] In the second positive electrode active slurry, lithium nickel cobalt aluminum oxide is replaced with lithium nickel cobalt manganese oxide (molecular formula LiNi). 0.7 Co 0.1 Mn 0.2 O2, D50 is 3.68μm), and the mass ratio of lithium manganese iron phosphate to lithium nickel cobalt manganese oxide is adjusted to 50:50, that is, based on the total mass of lithium manganese iron phosphate and lithium nickel cobalt manganese oxide, the mass content of lithium manganese iron phosphate is 50% and the mass content of lithium nickel cobalt manganese oxide is 50%.

[0195] In the second positive electrode active slurry, the mass ratio of the first linear conductive agent multi-walled carbon nanotube coarse tube, the second linear conductive agent multi-walled carbon nanotube fine tube, and carbon black is adjusted to 0.5:1:0.5, that is, based on the total mass of the conductive agent, the mass content of multi-walled carbon nanotube coarse tube is 25%, the mass content of multi-walled carbon nanotube fine tube is 50%, and the mass content of carbon black is 25%.

[0196] The single-sided compaction density of the first positive electrode active layer is 2.4 g / cm³. 3 The single-sided compaction density of the second positive electrode active layer is 3.1 g / cm³. 3 The thickness of the first positive electrode active layer on one side is 52.1 μm, and the thickness of the second positive electrode active layer on one side is 40.3 μm. The D50 of the mixed material of lithium nickel cobalt aluminum oxide and lithium manganese iron phosphate in the second positive electrode active layer is 1.12 μm, and other parameters remain unchanged.

[0197] Example 4

[0198] The preparation method of the positive electrode in this embodiment is basically the same as that in Example 1, except that:

[0199] In the second positive electrode active slurry, lithium nickel cobalt aluminum oxide is replaced with lithium nickel cobalt manganese oxide (molecular formula LiNi). 0.7 Co 0.1 Mn 0.2O2, D50 is 3.68μm), and the mass ratio of lithium manganese iron phosphate to lithium nickel cobalt manganese oxide is adjusted to 95:5, that is, based on the total mass of lithium manganese iron phosphate and lithium nickel cobalt manganese oxide, the mass content of lithium manganese iron phosphate is 95% and the mass content of lithium nickel cobalt manganese oxide is 5%.

[0200] In the second positive electrode active slurry, the mass ratio of the first linear conductive agent multi-walled carbon nanotube coarse tube, the second linear conductive agent multi-walled carbon nanotube fine tube, and carbon black is adjusted to 0.75:0.75:0.5, that is, based on the total mass of the conductive agent, the mass content of multi-walled carbon nanotube coarse tube is 37.5%, the mass content of multi-walled carbon nanotube fine tube is 37.5%, and the mass content of carbon black is 25%.

[0201] The single-sided compaction density of the first positive electrode active layer is 2.4 g / cm³. 3 The single-sided compaction density of the second positive electrode active layer is 2.45 g / cm³. 3 The thickness of the first positive electrode active layer on one side is 10.5 μm, and the thickness of the second positive electrode active layer on one side is 91.84 μm. Based on the total mass of the first and second positive electrode active layers, the mass content of the first positive electrode active layer is 10%, and the mass content of the second positive electrode active layer is 90%. The D50 of the mixed material of lithium nickel cobalt aluminum oxide and lithium manganese iron phosphate in the second positive electrode active layer is 0.14 μm, and other parameters remain unchanged.

[0202] Example 5

[0203] The preparation method of the positive electrode in this embodiment is basically the same as that in Example 2, except that:

[0204] In both the first positive electrode active material and the second positive electrode active slurry, lithium manganese iron phosphate is replaced with lithium-rich manganese-based material (chemical formula 0.8Li2MnO3·0.2LiMnO2, D50 is 0.6μm);

[0205] Meanwhile, the coarse multi-walled carbon nanotubes were replaced with array tubes (25 nm in diameter and 500 aspect ratio), and the mass ratio of the first linear conductive agent array tube, the second linear conductive agent multi-walled carbon nanotube fine tube, and carbon black was adjusted to 0.5:0.5:1. That is, based on the total mass of the conductive agent, the mass content of the array tube was 25%, the mass content of the multi-walled carbon nanotube fine tube was 25%, and the mass content of carbon black was 50%.

[0206] The single-sided compaction density of the first positive electrode active layer is 2.53 g / cm³. 3 The single-sided compaction density of the second positive electrode active layer is 3.4 g / cm³. 3The thickness of the first positive electrode active layer on one side is 88.93 μm, and the thickness of the second positive electrode active layer on one side is 7.35 μm. The D50 of the mixed material of lithium nickel cobalt aluminum oxide and lithium manganese iron phosphate in the second positive electrode active layer is 3.48 μm, and other parameters remain unchanged.

[0207] Example 6

[0208] The preparation method of the positive electrode in this embodiment is basically the same as that in Example 3, except that:

[0209] In both the first positive electrode active material and the second positive electrode active slurry, lithium manganese iron phosphate is replaced with lithium-rich manganese-based material (chemical formula 0.8Li2MnO3·0.2LiMnO2, D50 is 0.6μm);

[0210] The coarse multi-walled carbon nanotubes were replaced with carbon fibers (200 nm in diameter and 200 aspect ratio), and the mass ratio of the first linear conductive agent carbon fiber, the second linear conductive agent multi-walled carbon nanotube fine tube, and carbon black was adjusted to 0.5:0.5:1. That is, based on the total mass of the conductive agent, the mass content of carbon fiber was 25%, the mass content of multi-walled carbon nanotube fine tube was 25%, and the mass content of carbon black was 50%.

[0211] The single-sided compaction density of the first positive electrode active layer is 2.53 g / cm³. 3 The single-sided compaction density of the second positive electrode active layer is 3.01 g / cm³. 3 The thickness of the first positive electrode active layer on one side is 49.41 μm, and the thickness of the second positive electrode active layer on one side is 41.53 μm. The D50 of the mixed material of lithium nickel cobalt aluminum oxide and lithium manganese iron phosphate in the second positive electrode active layer is 1.56 μm, and other parameters remain unchanged.

[0212] Example 7

[0213] The preparation method of the positive electrode in this embodiment is basically the same as that in Example 4, except that:

[0214] In both the first positive electrode active material and the second positive electrode active slurry, lithium manganese iron phosphate is replaced with lithium-rich manganese-based material (chemical formula 0.8Li2MnO3·0.2LiMnO2, D50 is 0.6μm);

[0215] The coarse multi-walled carbon nanotubes were replaced with single-walled carbon nanotubes (1 nm in diameter and 1000 aspect ratio), and the mass ratio of the second linear conductive agent single-walled carbon nanotubes, the first linear conductive agent multi-walled carbon nanotubes, and carbon black was adjusted to 0.5:0.5:1. That is, based on the total mass of the conductive agent, the mass content of single-walled carbon nanotubes was 25%, the mass content of multi-walled carbon nanotubes was 25%, and the mass content of carbon black was 50%.

[0216] The single-sided compaction density of the first positive electrode active layer is 2.53 g / cm³. 3 The single-sided compaction density of the second positive electrode active layer is 2.57 g / cm³. 3 The thickness of the first positive electrode active layer on one side is 9.88 μm, and the thickness of the second positive electrode active layer on one side is 87.55 μm. The D50 of the mixed material of lithium nickel cobalt aluminum oxide and lithium manganese iron phosphate in the second positive electrode active layer is 0.67 μm, and other parameters remain unchanged.

[0217] Example 8

[0218] The preparation method of the positive electrode in this embodiment is basically the same as that in Example 2, except that:

[0219] In both the first and second positive electrode active materials, lithium manganese iron phosphate is replaced with lithium manganese phosphate (chemical formula LiMnPO4, D50 1.3μm), and lithium nickel cobalt manganese oxide is replaced with lithium nickel cobalt aluminum oxide (chemical formula LiNi). 0.7 Co 0.2 Al 0.1 O2 (D50 is 3.77μm);

[0220] The mass ratio of the first linear conductive agent multi-walled carbon nanotube coarse tube, the second linear conductive agent multi-walled carbon nanotube fine tube, and carbon black was adjusted to 0.7:0.7:0.6. That is, based on the total mass of the conductive agent, the mass content of multi-walled carbon nanotube coarse tube is 35%, the mass content of multi-walled carbon nanotube fine tube is 35%, and the mass content of carbon black is 30%.

[0221] The single-sided compaction density of the first positive electrode active layer is 2.61 g / cm³. 3 The single-sided compaction density of the second positive electrode active layer is 3.4 g / cm³. 3 The thickness of the first positive electrode active layer on one side is 86.2 μm, and the thickness of the second positive electrode active layer on one side is 7.36 μm. The D50 of the mixed material of lithium nickel cobalt aluminum oxide and lithium manganese iron phosphate in the second positive electrode active layer is 3.64 μm, and other parameters remain unchanged.

[0222] Example 9

[0223] The preparation method of the positive electrode in this embodiment is basically the same as that in Example 3, except that:

[0224] In both the first and second positive electrode active materials, lithium manganese iron phosphate is replaced with lithium manganese phosphate (chemical formula LiMnPO4, D50 1.3μm), and lithium nickel cobalt manganese oxide is replaced with lithium nickel cobalt aluminum oxide (chemical formula LiNi). 0.7 Co 0.2 Al 0.1 O2 (D50 is 3.77μm);

[0225] Meanwhile, the coarse multi-walled carbon nanotubes were replaced with array tubes (25 nm in diameter and 500 aspect ratio), and the mass ratio of the first linear conductive agent array tube, the second linear conductive agent multi-walled carbon nanotube fine tube, and carbon black was adjusted to 0.7:0.7:0.6, that is, the mass content of the array tube was 35%, the mass content of the multi-walled carbon nanotube fine tube was 35%, and the mass content of carbon black was 30%.

[0226] The single-sided compaction density of the first positive electrode active layer is 2.6 g / cm³. 3 The single-sided compaction density of the second positive electrode active layer is 2.98 g / cm³. 3 The thickness of the first positive electrode active layer on one side is 48.07 μm, and the thickness of the second positive electrode active layer on one side is 41.95 μm. The D50 of the mixed material of lithium nickel cobalt aluminum oxide and lithium manganese iron phosphate in the second positive electrode active layer is 2.52 μm, and other parameters remain unchanged.

[0227] Example 10

[0228] The preparation method of the positive electrode in this embodiment is basically the same as that in Example 4, except that:

[0229] In both the first and second positive electrode active materials, lithium manganese iron phosphate is replaced with lithium manganese phosphate (chemical formula LiMnPO4, D50 1.3μm), and lithium nickel cobalt manganese oxide is replaced with lithium nickel cobalt aluminum oxide (chemical formula LiNi). 0.7 Co 0.2 Al 0.1 O2 (D50 is 3.77μm);

[0230] The coarse multi-walled carbon nanotubes were replaced with carbon fibers (200 nm in diameter and 200 aspect ratio), and the mass ratio of the first linear conductive agent carbon fiber, the second linear conductive agent multi-walled carbon nanotube fine tube, and carbon black was adjusted to 0.7:0.7:0.6, that is, the mass content of carbon fiber was 35%, the mass content of multi-walled carbon nanotube fine tube was 35%, and the mass content of carbon black was 30%.

[0231] The single-sided compaction density of the first positive electrode active layer is 2.61 g / cm³. 3 The single-sided compaction density of the second positive electrode active layer is 2.67 g / cm³. 3 The thickness of the first positive electrode active layer on one side is 9.6 μm, and the thickness of the second positive electrode active layer on one side is 84.27 μm. The D50 of the mixed material of lithium nickel cobalt aluminum oxide and lithium manganese iron phosphate in the second positive electrode active layer is 1.36 μm, and other parameters remain unchanged.

[0232] Example 11

[0233] The preparation method of the positive electrode in this embodiment is basically the same as that in Example 3, except that:

[0234] In both the first positive electrode active material and the second positive electrode active slurry, lithium manganese iron phosphate is replaced with lithium manganese oxide (chemical formula LiMn2O4, D50 is 1.3μm), and the second positive electrode active slurry also includes lithium cobalt oxide (chemical formula LiCoO2, D50 is 1.1μm). Then the mass ratio of lithium manganese oxide, lithium nickel cobalt manganese oxide and lithium cobalt oxide in the second positive electrode active slurry is 25:50:25.

[0235] The coarse carbon nanotubes were replaced with single-walled carbon nanotubes (1 nm in diameter and 1000 aspect ratio), and the mass ratio of single-walled carbon nanotubes, multi-walled carbon nanotubes, and carbon black was adjusted to 0.5:0.5:1. That is, based on the total mass of the conductive agent, the mass content of the second linear conductive agent, single-walled carbon nanotubes, was 25%, the mass content of the first linear conductive agent, multi-walled carbon nanotubes, was 25%, and the mass content of carbon black was 50%.

[0236] The single-sided compaction density of the first positive electrode active layer is 2.57 g / cm³. 3 The single-sided compaction density of the second positive electrode active layer is 2.99 g / cm³. 3 The thickness of the first positive electrode active layer on one side is 48.64 μm, and the thickness of the second positive electrode active layer on one side is 41.8 μm. The D50 of the mixed material of lithium nickel cobalt aluminum oxide and lithium manganese iron phosphate in the second positive electrode active layer is 2.5 μm, and other parameters remain unchanged.

[0237] Example 12

[0238] The preparation method of the positive electrode in this embodiment is basically the same as that in Example 1, except that the positive electrode in this embodiment also includes a conductive layer 4, and the specific preparation method is as follows:

[0239] The conductive layer slurry is obtained by uniformly mixing the conductive material (carbon black), binder (PVDF), and solvent (NMP) at a mass ratio of 100:0.1:70.

[0240] The first positive electrode active slurry from Example 1 is coated on one side of the aluminum foil of the positive electrode current collector. Then, the conductive layer slurry prepared above is coated on the coating surface formed by the first positive electrode coating. Then, the second positive electrode active slurry from Example 1 is coated on the coating surface formed by the conductive layer slurry. After drying, a single-sided coated electrode sheet is obtained. The single-sided coated electrode sheet is reversed and coated on the other side of the aluminum foil using the same method as described above. The surface density of each coating layer on both sides is consistent. After drying, it is rolled and cut to obtain the positive electrode sheet of this example. The thickness of the conductive layer 4 is 2 μm, and other parameters remain unchanged.

[0241] Example 13

[0242] The preparation method of the positive electrode in this embodiment is basically the same as that in Example 1, except that the positive electrode in this embodiment also includes a polymer coating 5, and the specific preparation method is as follows:

[0243] The first positive electrode active slurry from Example 1 is coated on one side of the aluminum foil of the positive electrode current collector. Then, the second positive electrode active slurry is coated on the coating surface formed by the first positive electrode coating. Then, the polymer material polyimide is coated on the coating surface formed by the second positive electrode active slurry. After drying, a single-sided coated electrode sheet is obtained. The single-sided coated electrode sheet is reversed and coated on the other side of the aluminum foil using the same method as described above. The surface density of each coating layer on both sides is consistent. After drying, it is rolled and cut to obtain the positive electrode sheet of this example. The thickness of the polymer coating 5 is 1 μm, and other parameters remain unchanged.

[0244] Example 14

[0245] The preparation method of the positive electrode in this embodiment is basically the same as that in Example 1, except that:

[0246] In the second positive electrode active slurry, lithium nickel cobalt aluminum oxide is replaced with lithium nickel oxide (chemical formula NiCoO2, D50 is 3.3μm);

[0247] The single-sided compaction density of the first positive electrode active layer is 2.4 g / cm³. 3 The single-sided compaction density of the second positive electrode active layer is 2.9 g / cm³. 3 The thickness of the first positive electrode active layer on one side is 52.08 μm, and the thickness of the second positive electrode active layer on one side is 43.1 μm. The D50 of the mixed material of lithium nickel cobalt aluminum oxide and lithium manganese iron phosphate in the second positive electrode active layer is 1.35 μm, and other parameters remain unchanged.

[0248] Example 15

[0249] The preparation method of the positive electrode in this embodiment is basically the same as that in Example 1, except that:

[0250] In the second positive electrode active slurry, lithium nickel cobalt aluminum oxide is replaced with lithium titanate (chemical formula Li4Ti5O). 12 (D50 is 0.98μm);

[0251] The single-sided compaction density of the first positive electrode active layer is 2.4 g / cm³. 3 The single-sided compaction density of the second positive electrode active layer is 2.6 g / cm³. 3The thickness of the first positive electrode active layer on one side is 53 μm, and the thickness of the second positive electrode active layer on one side is 48.08 μm. The D50 of the mixed material of lithium nickel cobalt aluminum oxide and lithium manganese iron phosphate in the second positive electrode active layer is 0.65 μm, and other parameters remain unchanged.

[0252] Example 16

[0253] The preparation method of the positive electrode sheet in this embodiment is basically the same as that in Example 1. The difference is that the mass ratio of the first linear conductive agent multi-walled carbon nanotube coarse tube, the second linear conductive agent multi-walled carbon nanotube fine tube, and carbon black in the second positive electrode active slurry is adjusted to 0.4:0.4:1.2. That is, based on the total mass of the conductive agent, the mass content of multi-walled carbon nanotube coarse tube is 20%, the mass content of multi-walled carbon nanotube fine tube is 20%, and the mass content of carbon black is 60%.

[0254] Example 17

[0255] The preparation method of the positive electrode sheet in this embodiment is basically the same as that in Example 1. The difference is that the mass ratio of the first linear conductive agent multi-walled carbon nanotube coarse tube, the second linear conductive agent multi-walled carbon nanotube fine tube, and carbon black in the second positive electrode active slurry is adjusted to 1.6:0.2:0.2. That is, based on the total mass of the conductive agent, the mass content of multi-walled carbon nanotube coarse tube is 80%, the mass content of multi-walled carbon nanotube fine tube is 10%, and the mass content of carbon black is 10%.

[0256] Example 18

[0257] The preparation method of the positive electrode in this embodiment is basically the same as that in Example 1. The difference is that in the second positive electrode active slurry, the mass ratio of lithium manganese iron phosphate and lithium nickel cobalt aluminum oxide is adjusted to 3:97. That is, based on the total mass of lithium manganese iron phosphate and lithium nickel cobalt manganese oxide, the mass content of lithium manganese iron phosphate is 3% and the mass content of lithium nickel cobalt manganese oxide is 97%.

[0258] The single-sided compaction density of the first positive electrode active layer is 2.4 g / cm³. 3 The single-sided compaction density of the second positive electrode active layer is 3.4 g / cm³. 3 The thickness of the first positive electrode active layer on one side is 52.4 μm, and the thickness of the second positive electrode active layer on one side is 36.76 μm. The D50 of the mixed material of lithium nickel cobalt aluminum oxide and lithium manganese iron phosphate in the second positive electrode active layer is 3.55 μm, and other parameters remain unchanged.

[0259] Example 19

[0260] The preparation method of the positive electrode sheet in this embodiment is basically the same as that in Example 1. The difference is that, based on the total mass of the first positive electrode active layer and the second positive electrode active layer, the mass content of the first positive electrode active layer is 95% and the mass content of the second positive electrode active layer is 5%.

[0261] The single-sided compaction density of the first positive electrode active layer is 2.4 g / cm³. 3 The single-sided compaction density of the second positive electrode active layer is 2.78 g / cm³. 3 The thickness of the first positive electrode active layer on one side is 98.9 μm, and the thickness of the second positive electrode active layer on one side is 4.5 μm; other parameters remain unchanged.

[0262] Example 20

[0263] The preparation method of the positive electrode sheet in this embodiment is basically the same as that in Example 1. The difference is that, based on the total mass of the first positive electrode active layer and the second positive electrode active layer, the mass content of the first positive electrode active layer is 5% and the mass content of the second positive electrode active layer is 95%.

[0264] The single-sided compaction density of the first positive electrode active layer is 2.4 g / cm³. 3 The single-sided compaction density of the second positive electrode active layer is 2.78 g / cm³. 3 The thickness of the first positive electrode active layer on one side is 5.2 μm, and the thickness of the second positive electrode active layer on one side is 85.4 μm; other parameters remain unchanged.

[0265] Comparative Example 1

[0266] Lithium manganese iron phosphate (molecular formula LiMn) 0.6 Fe 0.4 PO4 (D50 of 0.06 μm), coarse multi-walled carbon nanotubes (diameter of 50 nm, aspect ratio of 50), polyvinylidene fluoride (PVDF), polyvinylpyrrolidone (PVP), and N-methylpyrrolidone (NMP) were mixed in a mass ratio of 100:2:2.5:0.2:60, and the positive electrode active slurry was obtained after uniform mixing.

[0267] The positive electrode active slurry prepared above is coated on one side of the positive electrode current collector aluminum foil, and after drying, a single-sided coated electrode sheet is obtained; the single-sided coated electrode sheet is reversed and coated on the other side of the aluminum foil using the same method as described above, with the surface density of each coating layer on both sides being consistent, and then dried; after drying, it is rolled and cut to obtain the positive electrode sheet of this embodiment;

[0268] The areal density of the positive electrode active layer in this positive electrode is 250 g / m². 2 The single-sided compaction density of the positive electrode active layer is 2.4 g / cm³. 3 Furthermore, the thickness of the positive electrode active layer on one side is 105 μm.

[0269] Comparative Example 2

[0270] The preparation method of the electrode in this comparative example is basically the same as that in Example 1, except that:

[0271] If the second positive electrode active slurry does not include the second linear conductive agent carbon nanotubes, then the mass ratio of the first linear conductive agent multi-walled carbon nanotubes to carbon black is 0.75:1.25, and other parameters remain unchanged.

[0272] Comparative Example 3

[0273] The preparation method of the electrode in this comparative example is basically the same as that in Example 1, except that:

[0274] The second positive electrode active slurry does not include lithium manganese iron phosphate. Therefore, the mass ratio of lithium nickel cobalt aluminum oxide, the first linear conductive agent multi-walled carbon nanotube coarse tube, the second linear conductive agent multi-walled carbon nanotube fine tube, carbon black, polyvinylidene fluoride (PVDF), polyvinylpyrrolidone (PVP), and N-methylpyrrolidone (NMP) is 100:0.75:0.5:0.75:2.5:0.2:50.

[0275] The single-sided compaction density of the first positive electrode active layer is 2.4 g / cm³. 3 The single-sided compaction density of the second positive electrode active layer is 3.45 g / cm³. 3 The thickness of the first positive electrode active layer on one side is 52.08 μm, and the thickness of the second positive electrode active layer on one side is 36.23 μm; other parameters remain unchanged.

[0276] Comparative Example 4

[0277] The preparation method of the electrode in this comparative example is basically the same as that in Example 1, except that:

[0278] The second positive electrode active slurry does not include the second linear conductive agent multi-walled carbon nanotubes (fine tubes) and the first linear conductive agent multi-walled carbon nanotubes (coarse tubes). Therefore, the mass ratio of lithium nickel cobalt aluminum oxide, lithium manganese iron phosphate, carbon black, polyvinylidene fluoride (PVDF), polyvinylpyrrolidone (PVP), and N-methylpyrrolidone (NMP) is 60:40:2:2.5:0.2:55.

[0279] Comparative Example 5

[0280] The preparation method of the electrode in this comparative example is basically the same as that in Example 1, except that:

[0281] If the second positive electrode active slurry does not include the first linear conductive agent multi-walled carbon nanotube coarse tube, then the mass ratio of lithium nickel cobalt aluminum oxide, lithium manganese iron phosphate, the second linear conductive agent multi-walled carbon nanotube fine tube, carbon black, polyvinylidene fluoride (PVDF), polyvinylpyrrolidone (PVP), and N-methylpyrrolidone (NMP) is 60:40:0.75:1.25:2.5:0.2:55.

[0282] Test case

[0283] 1. The electrode sheet prepared in Example 1 above was subjected to SEM testing. The test results are shown in Figure 9.

[0284] Figure 9 is a cross-sectional SEM image of the positive electrode sheet in Embodiment 1 of this application. In Figure 9, the upper and lower electrode layers can be clearly distinguished. The darker upper layer is the second positive electrode active layer, and the lighter lower layer is the first positive electrode active layer. This is due to the difference in conductivity between the upper and lower electrode layers. The conductive agent in the upper active layer has a more concentrated density and better conductivity, while the conductive agent in the lower active layer has a more dispersed density and weaker conductivity, resulting in the difference in brightness. Thus, the single-sided thickness of the second positive electrode active layer can be measured to be approximately 44.9 μm, and the single-sided thickness of the first positive electrode active layer is approximately 52.4 μm.

[0285] 2. Use adhesive tape to peel off the electrode prepared in Example 1 above to obtain the first positive electrode active layer dressing and the second positive electrode active layer dressing respectively. Perform EDS test on the dressings respectively. The test results are shown in Table 1 and Figures 10 and 11.

[0286] Table 1

[0287] From Table 1 and Figures 10-11, we can see that:

[0288] The second positive electrode active layer contains the characteristic elements Ni, Co, and Al (wt% > 0.2%) of lithium nickel cobalt aluminum oxide (NCA), indicating that it contains NCA; the first positive electrode active layer contains Mn and Fe (wt% > 1%), which is consistent with the characteristic elements of lithium manganese iron phosphate (LMFP); at the same time, the second positive electrode active layer also contains Mn and Fe elements, indicating that the active material of the second positive electrode active layer is a mixture of lithium manganese iron phosphate and lithium nickel cobalt aluminum oxide. Figure 10 is an EDS diagram of the first positive electrode active layer in the positive electrode sheet of Example 1 of this application, and Figure 11 is an EDS diagram of the second positive electrode active layer in the positive electrode sheet of Example 1 of this application.

[0289] 3. The surface of the positive electrode sheet prepared in Example 1 above was subjected to SEM test to obtain the surface SEM image of the second positive electrode active layer. The test results are shown in Figure 12.

[0290] Figure 12 is a surface SEM image of the second positive electrode active layer in the positive electrode sheet of Embodiment 1 of this application. As can be seen in Figure 12, two kinds of linear conductive agents (coarse multi-walled carbon nanotubes and fine multi-walled carbon nanotubes) and dot conductive agents (carbon black) are clearly present in the second positive electrode active layer.

[0291] 4. The positive electrodes prepared in the above examples and comparative examples are used to fabricate batteries, and the electrochemical performance of the prepared batteries is tested. Specifically, the following steps are included:

[0292] The prepared electrode sheets were cut into rectangles of 3.2 cm (length) × 2.6 cm (width) and tabs were led out. A 3.4 cm (length) × 2.8 cm (width) graphite sheet was used as the negative electrode. Dry cells were fabricated by stacking the positive electrode, separator, and negative electrode in that order. The dry cells were then placed in a 4 cm × 9 cm aluminum-plastic shell, electrolyte was injected, and the shell was vacuum-sealed. Formation, aging, and capacity testing were then performed to prepare a lithium battery. The electrolyte consisted of lithium hexafluorophosphate (LiPF6), ethylene carbonate (EC), dimethyl carbonate (DMC), fluoroethylene carbonate (FEC), and dimethyl carbonate (PC) in a mass ratio of 11.3:23.05:24:0.5:1.

[0293] 1) Cyclic performance test

[0294] The lithium battery prepared above was charged at 25°C at a constant current rate of 1 / 3C to 4.35V, and then charged at a constant voltage rate with a cutoff current rate of 0.02C. After standing for 10 minutes, it was discharged at a constant current rate of 1 / 3C to 2V, and the initial discharge capacity was recorded as C0. The battery was cycled 300 times according to the aforementioned charge and discharge mechanism, and the discharge capacity at the 300th cycle was recorded as C1. The cycle capacity retention rate (%) = (C1 / C0) × 100%. The test results are shown in Table 2 and Figures 13-15.

[0295] Figure 13 shows the cycle capacity retention curves of the batteries corresponding to the electrodes in Example 1 and Comparative Example 1 of this application. As can be seen from Figure 13, compared with the positive electrode (i.e., LMFP single-layer positive electrode) in Comparative Example 1, the lithium battery prepared using the positive electrode (i.e., LMFP|&NCA double-layer positive electrode) in Example 1 has a higher capacity retention rate within 300 cycles at room temperature, and the difference further increases with the increase of the number of cycles.

[0296] Figure 14 shows the charge-discharge curve of the battery corresponding to the electrode in Example 1 of this application, and Figure 15 shows the charge-discharge curve of the battery corresponding to the electrode in Comparative Example 1 of this application. As can be seen from Figures 14 and 15, compared with the positive electrode in Comparative Example 1 (i.e., LMFP single-layer positive electrode), the lithium battery prepared using the positive electrode in Example 1 (i.e., LMFP|&NCA double-layer positive electrode) has a higher average voltage and less capacity decay during cycling.

[0297] 2) Internal resistance test

[0298] The lithium batteries before and after cycling were subjected to DC internal resistance tests, and the test methods are as follows:

[0299] The battery was placed in a room temperature environment of 25℃ and charged to 4.35V at a rate of 1 / 3C0. Then, it underwent constant voltage charging with a cutoff current rate of 0.05C0 to obtain a 100% SOC battery. After resting for 10 minutes (as the start of the cycle), it was discharged at a constant current rate of 1 / 3C0 to obtain 0.1C0 of capacity. After resting for 60 minutes, the initial voltage at the last second of the resting period was recorded as V0. Then, it was discharged at a constant current rate of 1.5C0 for 30 seconds, and the final voltage at the last second of the discharge was recorded as V1. After resting for 10 minutes, it was charged at a constant current rate of 1 / 3C0 to obtain 0.0125C0 of capacity (as the end of the cycle). The DC internal resistance is then (V0-V1) / (1.5C0). Nine cycles were performed from the start to the end of the cycle. From the first to the ninth cycle, the obtained internal resistance (DCIR) values ​​correspond to 90%, 80%, 70%, 60%, 50%, 40%, 30%, 20%, and 10% SOC of the battery, respectively.

[0300] The test results are shown in Table 2 and Figures 16-17.

[0301] Figure 16 shows the discharge DC internal resistance curves of the lithium batteries corresponding to the electrodes in Example 1 and Comparative Example 2 of this application before cycling at 25°C; Figure 17 shows the discharge DC internal resistance curves of the lithium batteries corresponding to the electrodes in Example 1 and Comparative Example 2 of this application after 300 charge-discharge cycles at 25°C. The horizontal axis represents SOC (State of Charge), in %; the vertical axis represents DCIR, in mΩ·Ah. The comparison shows that the lithium battery in Example 1 exhibits a smaller increase in DC internal resistance during cycling, especially between 30% SOC and 70% SOC. This demonstrates that a special conductive agent combination can effectively suppress the excessively rapid increase in electrode ohms.

[0302] 3) Safety

[0303] The battery was charged at room temperature (25°C) with a constant current rate of 1 / 3C to 4.35V, followed by constant voltage charging with a cutoff current rate of 0.02C. After full charging, a Φ5mm high-temperature resistant steel needle was inserted into the battery at a speed of 1mm / s from a direction perpendicular to the narrow side of the pouch battery (with the needle remaining inside the battery). The battery was considered passed if it did not catch fire or explode. Ten batteries were tested in each embodiment and comparative example, and the number of batteries passing in each group was recorded. If six batteries passed in a group, it was recorded as 6 / 10 PASS. The test results are shown in Table 2.

[0304] Table 2

[0305] As shown in Table 2:

[0306] Compared to Comparative Examples 1-5, the lithium batteries in Examples 1-20 achieve higher cycle performance, lower DC internal resistance change rate, and higher safety, exhibiting superior overall performance. Specifically, Example 3 achieved a 78% cycle capacity retention rate at room temperature, a 3.03% DC internal resistance change rate at 40% SOC after 300 cycles at room temperature, and a 9 / 10 pass rate for needle penetration. In contrast, Comparative Example 3 achieved only a 59% cycle capacity retention rate, a 13.79% DC internal resistance change rate at 40% SOC, lower safety, and a 4 / 10 pass rate for needle penetration. While the lithium batteries in Comparative Examples 1, 2, 4, and 5 demonstrate high safety, their room temperature cycle performance and DC internal resistance change rate are poor. Therefore, the positive electrode sheet in this application can effectively improve battery impedance growth and cycle performance, while also enhancing needle penetration safety.

[0307] 5. The lithium batteries in Example 1 and Comparative Example 1 were cycled 300 times at room temperature (25°C) according to the charge-discharge mechanism in the cycle performance test. The lithium batteries after cycling were disassembled to obtain the corresponding negative electrode sheets. The concentration of manganese in the negative electrode sheets was detected by inductively coupled plasma spectrometry (ICP). The test results are shown in Table 3.

[0308] Table 3

[0309] As shown in Table 3:

[0310] Compared to the lithium battery in Comparative Example 1, the lithium battery in Example 1 had a lower manganese content in the negative electrode after 300 cycles, indicating that the positive electrode in Example 1 can effectively reduce the dissolution of manganese in the positive electrode.

[0311] 6. The lithium battery in Example 1 was cycled 300 times at room temperature (25°C) according to the aforementioned charge-discharge mechanism. The lithium battery before and after the cycle was disassembled to obtain the corresponding positive electrode. The cross-section of the positive electrode was photographed using scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS), and the manganese element line scan of the lithium nickel cobalt aluminum oxide particles was performed (it is known that NCA particles contain almost no Mn element). The test results are shown in Figures 18 and 19.

[0312] Figure 18 shows the EDS line scan of manganese in the positive electrode of LiFePO4 nickel cobalt aluminum oxide before cycling in Example 1 of this application, and Figure 19 shows the EDS line scan of manganese in the positive electrode of LiFePO4 nickel cobalt aluminum oxide after cycling in Example 1 of this application. As can be seen from Figures 18 and 19, the Mn signal of the LiFePO4 nickel cobalt aluminum oxide material in the positive electrode of Example 1 is enhanced during charge-discharge cycling. This indicates that the manganese dissolved from lithium manganese iron phosphate is captured by LiFePO4 nickel cobalt aluminum oxide, thereby reducing the dissolution of manganese from the positive electrode. Similarly, ternary materials also have the effect of capturing and retaining iron ions dissolved from LMFP.

[0313] The above embodiments are only used to illustrate the technical solutions of this application, and are not intended 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. Such 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.

Claims

1. A positive electrode plate, characterized in that, The positive electrode sheet includes a positive current collector (3), a first positive active layer (1), and a second positive active layer (2). The first positive active layer (1) is disposed on at least one side of the positive current collector (3), and the second positive active layer (2) is disposed on the side of the first positive active layer (1) away from the positive current collector (3). The first positive electrode active layer (1) includes a first positive electrode active material (11), and the second positive electrode active layer (2) includes the first positive electrode active material (11) and the second positive electrode active material (21). The first positive electrode active material (11) includes at least one of manganese-based positive electrode active material, iron-based positive electrode active material, and manganese-iron mixed-based positive electrode active material; the second positive electrode active material (21) includes at least one of ternary positive electrode active material, lithium cobalt oxide, lithium nickel oxide, and lithium titanate. The second positive electrode active layer (2) further includes a second conductive agent, which includes at least two linear conductive agents, as well as at least one of sheet-like conductive agents and dot-like conductive agents.

2. The positive electrode sheet according to claim 1, characterized in that, The manganese-based cathode active material includes at least one of lithium manganese phosphate, lithium-rich manganese-based material, lithium manganese oxide, and lithium nickel manganese oxide; the iron-based cathode active material includes lithium iron phosphate; and the manganese-iron mixed-based cathode active material includes lithium manganese iron phosphate.

3. The positive electrode sheet according to claim 1 or 2, characterized in that, The linear conductive agent includes at least one of carbon fiber, single-walled carbon nanotube, multi-walled carbon nanotube, array tube, metal nanowire, and conductive polymer nanowire. And / or, the sheet-like conductive agent includes graphene and / or conductive graphite; And / or, the dotted conductive agent includes conductive carbon black and / or acetylene black.

4. The positive electrode sheet according to any one of claims 1-3, characterized in that, The linear conductive agent includes a first linear conductive agent and a second linear conductive agent; the diameter of the first linear conductive agent is larger than the diameter of the second linear conductive agent.

5. The positive electrode sheet according to claim 4, characterized in that, The diameter ratio of the first linear conductive agent to the second linear conductive agent is 2.5 to 20.

6. The positive electrode sheet according to any one of claims 1-5, characterized in that, The diameter of the linear conductive agent is 0.4 nm to 500 nm, and the aspect ratio is 50 to 1000. And / or, the sheet-like conductive agent has a sheet diameter of 0.5 μm to 50 μm and a thickness of 0.3 nm to 200 nm; And / or, the median particle size of the dotted conductive agent is 15 nm to 80 nm.

7. The positive electrode sheet according to claim 6, characterized in that, The linear conductive agent has a diameter of 5 nm to 50 nm and an aspect ratio of 50 to 300.

8. The positive electrode sheet according to any one of claims 1-7, characterized in that, Based on the total mass of the second conductive agent in the second positive electrode active layer (2), the total mass content of the linear conductive agent is 25% to 75%, and the total mass content of the other types of second conductive agents is 25% to 75%.

9. The positive electrode sheet according to any one of claims 1-8, characterized in that, Based on the total mass of the first positive electrode active material (11) and the second positive electrode active material (21) in the second positive electrode active layer (2), the mass content of the second positive electrode active material (21) is 5% to 95%, and the mass content of the first positive electrode active material (11) is 5% to 95%.

10. The positive electrode sheet according to any one of claims 1-9, characterized in that, Based on the total mass of the second positive electrode active layer (2) and the first positive electrode active layer (1), the mass content of the second positive electrode active layer (2) is 10% to 90%, and the mass content of the first positive electrode active layer (1) is 10% to 90%.

11. The positive electrode sheet according to any one of claims 1-10, characterized in that, The thickness of the first positive electrode active layer (1) on one side is 5 μm to 104 μm; and / or, the thickness of the second positive electrode active layer (2) on one side is 5 μm to 104 μm.

12. The positive electrode sheet according to any one of claims 1-11, characterized in that, The positive electrode sheet further includes a conductive layer (4), which is disposed between the first positive electrode active layer (1) and the second positive electrode active layer (2); the conductive layer (4) includes a conductive material, which includes at least one of carbon black, carbon fiber, single-walled carbon nanotube, multi-walled carbon nanotube, array tube, graphene, and conductive graphite.

13. The positive electrode sheet according to claim 12, characterized in that, The thickness of the conductive layer (4) is 1 μm to 3 μm.

14. The positive electrode sheet according to any one of claims 1-13, characterized in that, The positive electrode also includes a polymer coating (5), which is disposed on at least one side of the second positive electrode active layer (2) away from the first positive electrode active layer (1).

15. The positive electrode sheet according to claim 14, characterized in that, The thickness of the polymer coating (5) is 0.5 μm to 5 μm; And / or, the polymer in the polymer coating (5) includes at least one of polyimide, polyetherimide, and polyacrylonitrile.

16. The positive electrode sheet according to any one of claims 1-15, characterized in that, The median particle size D50 of the first positive electrode active material (11) is 0.02 μm to 3 μm; and / or, the median particle size D50 of the mixture of the first positive electrode active material (11) and the second positive electrode active material (21) is 0.1 μm to 10 μm.

17. The positive electrode sheet according to any one of claims 1-16, characterized in that, The first positive electrode active layer (1) further includes a first conductive agent, a first binder and a first dispersant; based on the total mass of the first positive electrode active layer (1), the mass content of the first conductive agent is 0.5% to 10%, the mass content of the first binder is 0.5% to 10%, the mass content of the first dispersant is 0 to 1%, and the mass content of the first positive electrode active material (11) is 89.5% to 99%. And / or, the second positive electrode active layer (2) further includes a second binder and a second dispersant; based on the total mass of the second positive electrode active layer (2), the mass content of the second conductive agent is 0.5% to 10%, the mass content of the second binder is 0.5% to 10%, the mass content of the second dispersant is 0% to 1%, and the total mass content of the first positive electrode active material (11) and the second positive electrode active material (21) is 89.5% to 99%.

18. The positive electrode sheet according to any one of claims 1-17, characterized in that, The single-sided compaction density of the first positive electrode active layer (1) is 1.8 g / cm³. 3 ~3g / cm 3 ; and / or, the single-sided compaction density of the second positive electrode active layer (2) is 2 g / cm³. 3 ~4.5g / cm 3 .

19. A battery (6), characterized in that, The battery includes the positive electrode sheet as described in any one of claims 1-18.

20. A battery pack (7), characterized in that, The battery pack includes at least two positive electrode plates as described in any one of claims 1-18, or the battery (6) as described in claim 19.

21. An electrical appliance (8), characterized in that, The electrical equipment includes the battery (6) of claim 19 or the battery pack (7) of claim 20.

Images