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 positive electrode active layers arranged on at least one side of the positive electrode current collector, wherein the positive electrode active layers comprise a first active layer and a second active layer; the first active layer comprises a first positive electrode active material and a first binder, the first positive electrode active material comprising a first lithium manganese iron phosphate material; the second active layer comprises a second positive electrode active material and a second binder, the second positive electrode active material comprising a second lithium manganese iron phosphate material; and the mass percentage A1 of the first lithium manganese iron phosphate material in the first active layer, the mass percentage B1 of the first binder in the first active layer, the mass percentage A2 of the second lithium manganese iron phosphate material in the second active layer and the mass percentage B2 of the second binder in the second active layer satisfy the following relationships: A1<A2, and B1<B2. The positive electrode sheet provided by the present application can reduce the internal resistance of a battery and improve the cycling stability of the battery.

Description

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

[0001] This application claims priority to Chinese Patent Application No. 202510106144.3, filed on January 22, 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 in particular relates to a positive electrode, a battery, a battery pack and an electrical device. Background Technology

[0003] In recent years, with the rapid development of the new energy industry, lithium-ion batteries have been widely used. Compared with traditional batteries, lithium-ion batteries have advantages such as high voltage, long life, and environmental friendliness, and are widely used in electronic equipment, automobiles, aerospace and other fields.

[0004] However, existing batteries still suffer from problems such as high internal resistance and poor cycle stability. Summary of the Invention

[0005] The main objective of this application is to provide a positive electrode sheet that, when applied to a battery, can reduce the battery's internal resistance and improve its cycle stability.

[0006] This application also provides a battery including the above-mentioned positive electrode, therefore, the battery has low internal resistance and good cycle stability.

[0007] This application also provides a battery pack including the above-mentioned battery, therefore, the battery pack has low internal resistance and good cycle stability.

[0008] This application also provides an electrical device including the aforementioned battery or battery pack, thus the battery performance of the electrical device is superior.

[0009] In a first aspect, this application provides a positive electrode sheet, including a positive current collector and a positive active layer disposed on at least one side of the positive current collector, the positive active layer including a first active layer disposed on at least one side of the positive current collector and a second active layer disposed on the side of the first active layer opposite to the positive current collector;

[0010] The first active layer includes a first positive electrode active material and a first binder, wherein the first positive electrode active material includes a first lithium manganese iron phosphate material; the second active layer includes a second positive electrode active material and a second binder, wherein the second positive electrode active material includes a second lithium manganese iron phosphate material.

[0011] The mass percentages A1 of the first lithium manganese iron phosphate material in the first active layer, B1 of the first binder in the first active layer, A2 of the second lithium manganese iron phosphate material in the second active layer, and B2 of the second binder in the second active layer satisfy the following relationship:

[0012] A1 < A2, B1 < B2.

[0013] As described above, for the positive electrode, A1 and A2 satisfy: 0.35≤A1 / A2≤0.71.

[0014] As described above for the positive electrode, A1 satisfies 30% ≤ A1 ≤ 50%;

[0015] And / or, A2 satisfies 70% ≤ A2 ≤ 90%.

[0016] As described above, for the positive electrode, B1 and B2 satisfy: 0.5 ≤ B1 / B2 ≤ 0.95.

[0017] In the positive electrode as described above, B1 satisfies 1.5% ≤ B1 ≤ 2.5%;

[0018] And / or, B2 satisfies 1.6% ≤ B2 ≤ 3%.

[0019] As described above, the first active layer further includes a first conductive agent, and the second active layer further includes a second conductive agent. The mass percentage C1 of the first conductive agent in the first active layer and the mass percentage C2 of the second conductive agent in the second active layer satisfy the following relationship: 0.8≤C1 / C2≤1.2.

[0020] As described above for the positive electrode, C1 satisfies 1% ≤ C1 ≤ 5%;

[0021] And / or, C2 satisfies 1% ≤ C2 ≤ 5%.

[0022] As described above, the first positive electrode active material further includes a first ternary positive electrode active material, and the second positive electrode active material further includes a second ternary positive electrode active material.

[0023] As described above, for the positive electrode sheet, X < Y, where X is the mass ratio of the sum of the masses of the first ternary positive electrode active material and the second ternary positive electrode active material to the mass of the positive electrode active layer, and Y is the mass ratio of the sum of the masses of the first lithium manganese iron phosphate material and the second lithium manganese iron phosphate material to the mass of the positive electrode active layer.

[0024] And / or, the sum of the masses of the first ternary cathode active material and the second ternary cathode active material accounts for less than or equal to 35% of the mass of the cathode active layer.

[0025] As described above, the average particle size of the first lithium manganese iron phosphate material is 0.5 μm-1.5 μm;

[0026] And / or, the average particle size of the second lithium manganese iron phosphate material is 0.5 μm-1.5 μm.

[0027] As described above, the positive electrode material has an average particle size of 0.8 μm-1 μm for the first lithium manganese iron phosphate material; and / or, the positive electrode material has an average particle size of 0.8 μm-1 μm for the second lithium manganese iron phosphate material.

[0028] As described above, the average particle size of the first ternary positive electrode active material is 0.5 μm-20 μm.

[0029] And / or, the average particle size of the second ternary cathode active material is 0.5 μm-20 μm.

[0030] As described above, the average particle size of the first ternary positive electrode active material is 2μm-15μm; and / or, the average particle size of the second ternary positive electrode active material is 2μm-15μm.

[0031] As described above, a conductive layer is further provided between the positive current collector and the first active layer, and the conductive layer includes a conductive agent and a binder.

[0032] As described above, the thickness of the conductive layer in the positive electrode is 0.2 μm-1.3 μm.

[0033] Secondly, this application provides a battery including the positive electrode plate as described above.

[0034] Thirdly, this application provides a battery pack including the battery as described above.

[0035] Fourthly, this application provides an electrical device, including the battery or battery pack described above.

[0036] The positive electrode provided in this application has a high mass percentage of the second lithium manganese iron phosphate material in the second active layer 122, which will not affect the conductivity of the battery, and at the same time can reduce the side reaction with the electrolyte and improve the cycle stability of the battery; the first binder in the first active layer 121 has a low mass percentage, which is conducive to electron transport, reduces the internal resistance of the positive electrode, and thus can improve the cycle stability of the lithium-ion battery. Attached Figure Description

[0037] To more clearly illustrate the technical solutions in the embodiments of this application or related technologies, the accompanying drawings used in the description of the embodiments of this application or related technologies are briefly introduced below. Obviously, the drawings described below are merely some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0038] Figure 1 is a schematic diagram of a positive electrode sheet provided in this application;

[0039] Figure 2 is a schematic diagram of a positive electrode sheet provided in this application;

[0040] Figure 3 is a schematic diagram of a battery pack provided in this application;

[0041] Figure 4 is a schematic diagram of the structure of an electronic device provided in this application.

[0042] Reference numerals: 100-Positive electrode sheet; 110-Positive current collector; 120-Positive active layer; 121-First active layer; 122-Second active layer; 130-Conductive layer; 2-Battery; 3-Battery pack; 4-Electrical equipment. Detailed Implementation

[0043] 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.

[0044] In recent years, with the continuous growth of global demand for renewable energy, lithium-ion batteries, as a highly efficient energy storage technology, have received widespread attention and application. Due to their advantages such as high voltage, long lifespan, and environmental friendliness, lithium-ion batteries have become the preferred battery technology in fields such as electronic devices, electric vehicles, and aerospace. The performance of lithium-ion batteries largely depends on the characteristics of their positive electrode active materials. Currently, the most widely used commercially available positive electrode active materials include lithium iron phosphate and ternary materials.

[0045] Lithium iron phosphate (LFP) is favored for its low cost and high safety, but its relatively low energy density limits its application in high-energy-density applications. In contrast, ternary materials offer higher energy densities, but their safety performance is poor, especially under high-temperature or overcharge conditions, where they are prone to thermal runaway. To achieve a balance between safety and energy density, lithium manganese iron phosphate (LFP), a novel phosphate-based cathode material, has attracted attention due to its olivine structure similar to LFP and its higher plateau voltage. LFP can improve battery energy density while maintaining good safety performance. However, its low conductivity and slow kinetics limit its performance in high-rate discharge and fast-charging applications.

[0046] To address these issues, nano-sizing is typically employed to improve conductivity, but this also complicates the manufacturing process. The inventors of this application have discovered that by designing a layered structure for the positive electrode active layer on the surface of the positive electrode current collector and adjusting the proportions of lithium manganese iron phosphate and binder in each layer, the internal resistance of the battery can be reduced simultaneously, while improving cycle stability.

[0047] Based on this, in a first aspect, as shown in FIG1, this application provides a positive electrode sheet 100, including a positive electrode current collector 110 and a positive electrode active layer 120 disposed on at least one side of the positive electrode current collector 110. The positive electrode active layer 120 includes a first active layer 121 disposed on at least one side of the positive electrode current collector 110 and a second active layer 122 disposed on the side of the first active layer 121 opposite to the positive electrode current collector 110. The first active layer 121 includes a first positive electrode active material and a first binder. The first positive electrode active material includes a first lithium manganese iron phosphate material. The second active layer 122 includes a second positive electrode active material and a second binder. The second positive electrode active material includes a second lithium manganese iron phosphate material. The mass percentage A1 of the first lithium manganese iron phosphate material in the first active layer 121, the mass percentage B1 of the first binder in the first active layer 121, the mass percentage A2 of the second lithium manganese iron phosphate material in the second active layer 122, and the mass percentage B2 of the second binder in the second active layer 122 satisfy the following relationship: A1 < A2, B1 < B2.

[0048] The positive electrode active layer 120 of this application can be disposed on at least one side of the positive electrode current collector 110, that is, it can be disposed on any side of the positive electrode current collector 110, or on both the upper and lower sides of the positive electrode current collector 110.

[0049] In the positive electrode 100 of this application, the mass percentage A1 of the first lithium manganese iron phosphate material in the first active layer 121 is less than the mass percentage A2 of the second lithium manganese iron phosphate material in the second active layer 122, and the mass percentage B1 of the first binder in the first active layer 121 is less than the mass percentage B2 of the second binder in the second active layer 122. When this positive electrode 100 is applied to a battery, it can reduce the battery's internal resistance and improve its cycle stability. The reason for this is that the second active layer 122 is far from the positive electrode current collector 110, the mass percentage of the second lithium manganese iron phosphate material in the second active layer 122 is higher, and the second active layer 122 is in contact with the electrolyte. The lithium manganese iron phosphate material has high stability and is less prone to side reactions when in contact with the electrolyte, thus improving the battery's cycle stability. After lithium intercalation / deintercalation, the first lithium manganese iron phosphate material in the first active layer 121 is rapidly transported through the positive electrode active material channels in the second active layer 122, optimizing the interfacial impedance between the positive electrode active materials, thereby reducing polarization during battery charging and discharging, and further improving the battery's cycle stability. Because the binder has electrical insulating properties, a smaller amount of binder can reduce obstacles to electron transport. The first active layer 121 is close to the positive electrode current collector 110. The lower mass percentage of the first binder in the first active layer 121 facilitates electron transport, improves the conductivity of the first active layer 121, reduces the internal resistance of the positive electrode 100, and thus improves the cycle stability of the lithium-ion battery. The higher mass percentage of the second binder in the second active layer 122 improves the mechanical stability and integrity of the positive electrode 100, especially during charge-discharge cycles, which helps to increase the cycle life of the battery.

[0050] The first and second adhesives of this application may be the same or different. For example, they may be polyvinylidene fluoride and / or polyvinylidene chloride polymer materials.

[0051] The positive electrode 100 provided in this application has a high mass percentage of the second lithium manganese iron phosphate material in the second active layer 122, which will not affect the conductivity of the battery, and at the same time can reduce the side reaction with the electrolyte and improve the cycle stability of the battery; the first binder in the first active layer 121 has a low mass percentage, which is conducive to electron transport, reduces the internal resistance of the positive electrode 100, and thus can improve the cycle stability of the lithium-ion battery.

[0052] In some embodiments of this application, A1 and A2 satisfy: 0.35≤A1 / A2≤0.71. For example, A1 / A2 can be a range consisting of 0.35, 0.4, 0.5, 0.6, 0.7, 0.71 or any two of them.

[0053] In this application, the ratio of A1 / A2 meets the above range, and the highly stable lithium manganese iron phosphate material in the second active layer 122 is less prone to side reactions when in contact with the electrolyte, which can improve the cycle stability of the battery.

[0054] In some embodiments of this application, A1 satisfies 30% ≤ A1 ≤ 50%. For example, A1 can be a range consisting of 30%, 35%, 40%, 45%, 50%, or any two of these.

[0055] In some embodiments, A2 satisfies 70% ≤ A2 ≤ 90%, for example, A2 can be a range consisting of 70%, 75%, 80%, 85%, 86%, 87%, 88%, 89%, 90%, or any two of these.

[0056] In this application, the values ​​of A1 and A2 are within the above range, which can further reduce the probability of side reactions occurring when the lithium manganese iron phosphate material in the second active layer 122 comes into contact with the electrolyte, and can also enable the second active layer 122 to maintain good structural stability during charging and discharging, thereby improving the cycle life of the battery.

[0057] In some embodiments of this application, B1 and B2 satisfy: 0.5≤B1 / B2≤0.95. For example, B1 / B2 can be a range consisting of 0.5, 0.6, 0.7, 0.8, 0.9, 0.95 or any two of them.

[0058] In this application, the ratio of B1 / B2 meets the above-mentioned range, that is, the binder content in the first active layer 121 is low, which can reduce the obstacles to electron transport, improve the conductivity of the first active layer 121, reduce the internal resistance of the battery, improve the cycle stability of the battery, and also enable the positive electrode sheet 100 to maintain structural integrity during charging and discharging, reduce the shedding of positive electrode active material and the damage to the electrode structure, thereby improving the cycle life of the battery.

[0059] In some embodiments of this application, B1 satisfies 1.5% ≤ B1 ≤ 2.5%. For example, B1 can be a range consisting of 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, or any two of these.

[0060] In some embodiments, B2 satisfies 1.6% ≤ B2 ≤ 3%, for example, B2 can be a range of 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 3%, or any two of these.

[0061] In this application, the values ​​of B1 and B2 are within the aforementioned range, providing sufficient mechanical strength and structural stability to ensure good adhesion between the positive electrode active material particles and between them and the positive electrode current collector 110. This helps maintain the integrity of the positive electrode sheet 100 during charge-discharge cycles, reducing material shedding and damage to the electrode structure, thereby improving the battery's cycle life. It also minimizes the negative impact on conductivity while providing sufficient adhesion, thus maintaining good conductivity and reducing the battery's internal resistance.

[0062] In some embodiments of this application, the first active layer 121 further includes a first conductive agent, and the second active layer 122 further includes a second conductive agent. The mass percentage C1 of the first conductive agent in the first active layer 121 and the mass percentage C2 of the second conductive agent in the second active layer 122 satisfy the following relationship: 0.8 ≤ C1 / C2 ≤ 1.2. For example, C1 / C2 can be a range of 0.8, 0.9, 1.0, 1.1, 1.2 or any two of them.

[0063] In this application, the C1 / C2 ratio is within the above range, which can improve the conductivity of the first active layer 121, reduce the internal resistance of the battery, and also help to achieve a uniform current distribution in the entire positive electrode 100, reduce local overpotential, and enable the battery to maintain both high energy density and high conductivity.

[0064] The first and second conductive agents in this application may be the same or different. For example, at least one of the conductive agents conventional in the art, such as carbon black, carbon nanotubes, and graphene, may be used.

[0065] In this application, C1 can be greater than C2, C1 can be equal to C2, and C1 can be less than C2.

[0066] In some embodiments of this application, C1 satisfies 1%≤C1≤5%. For example, C1 can be a range of 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or any two of these.

[0067] In some embodiments, C2 satisfies 1% ≤ C2 ≤ 5%, for example, C2 can be a range of 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or any two of these.

[0068] In this application, the values ​​of C1 and C2 are within the aforementioned range, which can improve the overall conductivity of the positive electrode 100, facilitate the rapid transport of electrons in the positive electrode 100, and reduce the internal resistance of the battery. Furthermore, it helps maintain the structural stability of the positive electrode 100 during multiple charge-discharge cycles, reduces the shedding of active material and the expansion or contraction of the positive electrode 100, thereby improving the cycle life of the battery.

[0069] In some embodiments of this application, the first positive electrode active material further includes a first ternary positive electrode active material, and the second positive electrode active material further includes a second ternary positive electrode active material.

[0070] In this application, a ternary cathode active material is introduced into the cathode sheet 100 and used in combination with lithium manganese iron phosphate material. The voltage windows of the two materials are matched, which can overcome the difficulties in the application of lithium manganese iron phosphate material and can take into account the energy density, power and safety performance of the battery.

[0071] In some embodiments of this application, X < Y, where X is the mass ratio of the sum of the masses of the first ternary positive electrode active material and the second ternary positive electrode active material to the mass of the positive electrode active layer 120, and Y is the mass ratio of the sum of the masses of the first lithium manganese iron phosphate material and the second lithium manganese iron phosphate material to the mass of the positive electrode active layer 120.

[0072] In some embodiments, the sum of the masses of the first ternary cathode active material and the second ternary cathode active material accounts for less than or equal to 35% of the mass of the cathode active layer 120. For example, it can be a range of 1%, 5%, 7%, 10%, 15%, 20%, 25%, 30%, 35%, or any two of these.

[0073] In the positive electrode sheet 100 of this application, the mass of the ternary positive electrode active material in the positive electrode active layer 120 is less than the mass of the lithium manganese iron phosphate material. Because lithium manganese iron phosphate material has high thermal stability and safety, and the ternary positive electrode active material can provide higher energy density, the overall safety of the battery can be improved while ensuring energy density, reducing the risk of thermal runaway. At the same time, the structural stability of lithium manganese iron phosphate material is beneficial to improving the cycle life of the battery.

[0074] Where X = (M×H1+N×H2) / (H1+H2), M is the mass percentage of the first ternary cathode active material in the first active layer 121, N is the mass percentage of the second ternary cathode active material in the second active layer 122, H1 is the thickness of the first active layer 121 in μm, and H2 is the thickness of the second active layer 122 in μm.

[0075] Y = (A1×H1+A2×H2) / (H1+H2), where A1 is the mass percentage of the first lithium manganese iron phosphate material in the first active layer 121, A2 is the mass percentage of the second lithium manganese iron phosphate material in the second active layer 122, H1 is the thickness of the first active layer 121 in μm, and H2 is the thickness of the second active layer 122 in μm.

[0076] In some embodiments of this application, the average particle size of the first lithium manganese iron phosphate material is 0.5 μm-1.5 μm, for example, it can be a range of 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm or any combination thereof.

[0077] In some embodiments, the average particle size of the first lithium manganese iron phosphate material is 0.8 μm-1 μm.

[0078] In some embodiments, the average particle size of the second lithium manganese iron phosphate material is 0.5 μm to 1.5 μm, for example, it can be a range of 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm or any combination thereof.

[0079] In some embodiments, the average particle size of the second lithium manganese iron phosphate material is 0.8 μm-1 μm.

[0080] In some embodiments, the chemical formula of the first lithium manganese iron phosphate material is LiMn. a Fe 1-a PO4, where 0.5 ≤ a ≤ 0.8, for example, a can be a range consisting of 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8 or any two of them.

[0081] In some embodiments, the chemical formula of the second lithium manganese iron phosphate material is LiMn b Fe 1-b PO4, where 0.5 ≤ b ≤ 0.8, for example, b can be a range of 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8 or any two of them.

[0082] In this application, the average particle size of the first and second lithium manganese iron phosphate materials falls within the aforementioned range. This increases the specific surface area of ​​the materials, enhances the activity of electrochemical reactions, promotes the rapid insertion and extraction of lithium ions into the electrode materials, and improves the rate performance of the battery. It also helps to shorten the diffusion path of lithium ions and electrons, improves the conductivity of the materials, and reduces the internal resistance of the battery. Furthermore, it maintains the structural integrity of the materials during charging and discharging, reducing material pulverization and electrode structure damage caused by volume changes, thereby improving cycle life.

[0083] The chemical formulas of the first and second lithium manganese iron phosphate materials can optimize the voltage platform and capacity of the materials, further improve the thermal stability of the materials, reduce the risk of thermal runaway, and help maintain the structural stability of the materials in multiple charge-discharge cycles, reduce the shedding of active materials and the expansion or contraction of electrodes, thereby improving the cycle performance of the battery.

[0084] In some embodiments of this application, the average particle size of the first ternary cathode active material is 0.5 μm-20 μm, for example, it can be a range of 0.5 μm, 1 μm, 2 μm, 3 μm, 5 μm, 7 μm, 10 μm, 12 μm, 15 μm, 18 μm, 20 μm or any two of these.

[0085] In some embodiments, the average particle size of the first ternary cathode active material is 2 μm-15 μm.

[0086] In some embodiments, the average particle size of the second ternary cathode active material is 0.5 μm-20 μm, for example, it can be a range of 0.5 μm, 1 μm, 2 μm, 3 μm, 5 μm, 7 μm, 10 μm, 12 μm, 15 μm, 18 μm, 20 μm or any two of these.

[0087] In some embodiments, the average particle size of the second ternary cathode active material is 2 μm-15 μm.

[0088] In some embodiments, the chemical formula of the first ternary cathode active material is LiNi. x Co y Mn zO2, where 0.5≤x≤0.9, for example, x can be a range consisting of 0.5, 0.6, 0.7, 0.8, 0.9 or any two of them; 0.03≤y≤0.15, for example, y can be a range consisting of 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.11, 0.12, 0.13, 0.14, 0.15 or any two of them; 0.01≤z≤0.4, for example, z can be a range consisting of 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4 or any two of them.

[0089] In some embodiments, the chemical formula of the second ternary cathode active material is LiNi. o Co p Mn q O2, where 0.5≤o≤0.9, for example, o can be a range of 0.5, 0.6, 0.7, 0.8, 0.9 or any two of them; 0.03≤p≤0.15, for example, p can be a range of 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.11, 0.12, 0.13, 0.14, 0.15 or any two of them; 0.01≤q≤0.4, for example, q can be a range of 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4 or any two of them.

[0090] In this application, the average particle size of the first and second ternary cathode active materials is within the aforementioned range, providing a good specific surface area. This promotes the rapid insertion and extraction of lithium ions into the electrode materials, improving the rate performance and power density of the battery. It also helps to shorten the diffusion path of lithium ions and electrons, improving the conductivity and ion diffusion rate of the materials, thereby enhancing the overall performance of the battery. Furthermore, it maintains the structural integrity of the materials during charge and discharge, reducing material pulverization and electrode structure damage caused by volume changes, thus improving cycle life.

[0091] The chemical formulas of the first and second ternary cathode active materials described above can optimize the voltage plateau and capacity of the materials, further improve the energy density of the materials, and help improve the stability and safety of the materials, reduce the risk of thermal runaway, help maintain the structural stability of the materials in multiple charge-discharge cycles, reduce the shedding of active materials and the expansion or contraction of electrodes, thereby improving the cycle performance of the battery.

[0092] In some embodiments of this application, as shown in FIG2, a conductive layer 130 is further provided between the positive current collector 110 and the first active layer 121. The conductive layer 130 includes a conductive agent and a binder.

[0093] This application further provides a conductive layer 130 between the positive current collector 110 and the first active layer 121. The conductive layer 130 includes a conductive agent and a binder, wherein the conductive layer 130 can be a continuous or discontinuous layer. The binder may include polyacrylic acid (PAA) and / or polyvinylidene fluoride (PVDF), and the conductive agent may include at least one of styrax, carbon black, and carbon nanotubes.

[0094] The binder can enhance the adhesion between the first active layer 121 and the positive electrode current collector 110, improve the mechanical properties of the positive electrode sheet 100, and reduce material shedding due to volume changes during charge-discharge cycles, which is beneficial to improving the cycle life and reliability of the battery. The conductive agent helps to provide additional electron transport paths between the positive electrode current collector 110 and the first active layer 121, reduce interface resistance, and improve the overall conductivity of the electrode.

[0095] In some embodiments of this application, the thickness of the conductive layer 130 is 0.2 μm to 1.3 μm, for example, it can be a range of 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1.0 μm, 1.1 μm, 1.2 μm, 1.3 μm or any combination thereof.

[0096] The thickness of the conductive layer 130 in this application is within the above-mentioned range, which can provide sufficient mechanical support, enhance the adhesion between the first active layer 121 and the positive electrode current collector 110, and also improve the conductivity of the battery and reduce the internal resistance of the battery.

[0097] The method for preparing the positive electrode 100 in this application may include the following steps:

[0098] 1) Mix lithium manganese iron phosphate material, ternary cathode active material, binder, conductive agent, dispersant and solvent evenly to obtain cathode slurry;

[0099] 2) The positive electrode slurry is coated on at least one surface of the positive electrode current collector 110, and after baking, rolling and cutting, the positive electrode sheet 100 is obtained.

[0100] After obtaining the positive electrode sheet, this application can use photoelectron spectroscopy (EDS) and scanning electron microscopy (SEM) in combination. SEM can be used to determine the first lithium manganese iron phosphate material, the second lithium manganese iron phosphate material, the first ternary positive electrode active material, and the second ternary positive electrode active material particles in the positive electrode sheet. EDS can be used to test the molar ratio of each element in each particle to obtain the chemical composition of the first lithium manganese iron phosphate material, the second lithium manganese iron phosphate material, the first ternary positive electrode active material, and the second ternary positive electrode active material.

[0101] Cut a fixed area of ​​positive electrode sheet and scrape off a small amount of the second active layer powder, denoted as W2. Use ICP to test the Ni and Fe element content. Based on the Fe element content and the chemical composition of the second lithium manganese iron phosphate material, calculate the mass of the second lithium manganese iron phosphate active material in the second active layer as w21. Similarly, based on the Ni element content and the chemical composition of the second ternary positive electrode active material, calculate the mass of the second ternary positive electrode active material in the second active layer as w22. The mass percentage of the second lithium manganese iron phosphate material in the second active layer is A2 = w21 / W2, and the mass percentage of the second ternary positive electrode active material in the second active layer is N = w22 / W2. Likewise, scrape off a small amount of the first active layer powder from the current collector side, denoted as W1. Using the same method, the masses of the first lithium manganese iron phosphate active material and the first ternary cathode active material in the first active layer can be measured as w11 and w12, respectively. The mass percentage of the first lithium manganese iron phosphate material in the first active layer is A1 = w11 / W1, and the mass percentage of the first ternary cathode active material in the first active layer is M = w12 / W1.

[0102] Binder content: Weigh out the first active layer powder with a mass of W3, and use TG-DSC to obtain the mass of the first binder w3 based on the mass loss. The mass percentage of the first binder in the first active layer is B1 = w3 / W3. B2 is measured using the same test method.

[0103] The mass ratio of conductive agent is: C1 = 1 - A1 - B1 - M, C2 = 1 - A2 - B2 - N.

[0104] The ratio of the combined mass of the first and second lithium manganese iron phosphate materials to the mass of the positive electrode active layer is: Y = (w11 + w21) / (W1 + W2).

[0105] The mass ratio of the sum of the first and second ternary cathode active materials to the mass of the cathode active layer: X = (w12 + w22) / (W1 + W2).

[0106] The method for testing the average particle size of the first lithium manganese iron phosphate material and the second lithium manganese iron phosphate material in this application involves placing the positive electrode sheet into the sample chamber of a scanning electron microscope and maintaining the vacuum level to the set requirements. The focus and aperture of the SEM are adjusted until the material particles can be clearly seen. The particle size of multiple (e.g., 100) first lithium manganese iron phosphate particles and second lithium manganese iron phosphate particles are measured, and the average value is calculated to obtain the average particle size of the first lithium manganese iron phosphate material and the average particle size of the second lithium manganese iron phosphate material.

[0107] The method for testing the average particle size of the first ternary cathode active material and the average particle size of the second ternary cathode active material in this application involves placing the cathode sheet into the sample chamber of a scanning electron microscope and maintaining the vacuum level to the set requirements. The focus and aperture of the SEM are adjusted until the material particles can be clearly seen. The particle sizes of multiple (e.g., 100) particles of the first ternary cathode active material and the second ternary cathode active material are measured, and the average values ​​are calculated to obtain the average particle size of the first ternary cathode active material and the average particle size of the second ternary cathode active material.

[0108] The method for testing the thickness of the conductive layer 130 in this application involves cutting the positive electrode sheet into a 0.5cm × 0.5cm positive electrode sheet sample and using a scanning electron microscope to test the thickness of the conductive layer in the positive electrode sheet sample.

[0109] In practice, the positive electrode can be obtained by disassembling the battery and testing it in the manner described above to obtain the parameters.

[0110] In the preparation process of the positive electrode sheet provided in this application, the amount of each substance added, the average particle size, and the thickness of the conductive layer may deviate from the content, average particle size, and thickness of the conductive layer of each substance obtained from the positive electrode sheet obtained after disassembly from the battery. However, these deviations are within the error range. Therefore, the amount of each substance added, the average particle size, and the thickness of the conductive layer in the preparation process of the positive electrode sheet are basically consistent with the content, average particle size, and thickness of the conductive layer of each substance in the positive electrode active layer of the positive electrode sheet.

[0111] Secondly, this application provides a battery 2, including the positive electrode 100 as described above. The battery 2 has advantages corresponding to the positive electrode 100, which will not be elaborated further.

[0112] In addition to the positive electrode 100, the battery 2 of this application also includes a separator, a negative electrode, and an electrolyte. The composition of the negative electrode can refer to conventional negative electrode sheets in the art, and the separator can also be a separator commonly used in the art, such as PP film, PE film, etc.

[0113] The battery 2 of this application can be prepared using conventional methods in the art. Specifically, the positive electrode 100, the separator and the negative electrode can be stacked in sequence, and the cell can be obtained by stacking or winding. Then, the battery 2 can be obtained by baking, liquid injection, formation and packaging.

[0114] Thirdly, this application provides a battery pack 3, as shown in FIG3, which includes the battery 2 as described above. The battery pack 3 has advantages corresponding to the positive electrode 100 described above, which will not be repeated here.

[0115] Fourthly, this application provides an electrical device 4, as shown in FIG4, which includes the battery 2 as described above or the battery pack 3 as described above. The electrical device 4 has advantages corresponding to the positive electrode 100 described above, which will not be elaborated further.

[0116] The electrical equipment 4 in this application can be a conventional electrical equipment in the field, such as power equipment (e.g., electric vehicles), electronic equipment (e.g., computers, mobile phones, digital cameras, printers, fax machines, etc.), wearable devices (e.g., watches, wristbands, VR glasses, etc.), and home appliances (e.g., air conditioners, refrigerators, washing machines, microwave ovens, etc.), etc., without any particular limitation.

[0117] The technical solution of this application will be further described below with reference to specific embodiments.

[0118] Example 1

[0119] The battery preparation method of this embodiment includes the following steps:

[0120] 1) Preparation of the positive electrode:

[0121] Preparation of conductive layer: A certain proportion of PVDF, conductive carbon black and N-methyl-2-pyrrolidone (NMP) as solvent are mixed under uniform stirring, and then coated onto the upper and lower surfaces of the positive electrode current collector Al foil. After drying, a conductive layer is obtained.

[0122] Add LiMn to the mixing tank 0.5 Fe 0.5 PO4 (lithium iron manganese phosphate) and LiNi 0.7 Co 0.1 Mn 0.2 O2 (first ternary cathode active material), carbon black (first conductive agent), PVDF (first binder), and NMP (first solvent) are stirred until uniformly mixed to obtain a first slurry. The mass ratio of the first lithium manganese iron phosphate material, the first ternary cathode active material, the first binder, and the first conductive agent is 30:67.5:1.5:1, denoted as ratio 1. LiMn is added to another mixing tank. 0.5 Fe 0.5 PO4 (lithium iron manganese phosphate) and LiNi0.7 Co 0.1 Mn 0.2 O2 (second ternary cathode active material), carbon nanotubes (second conductive agent), PVDF (second binder), and NMP (second solvent) are stirred until uniformly mixed to obtain a second slurry. The mass ratio of the second lithium manganese iron phosphate material, the second ternary cathode active material, the second binder, and the second conductive agent is 85:10.75:3:1.25, denoted as ratio 2. Low-speed stirring is maintained during the uncoated period to ensure good dispersion of the slurry. The average particle size of the first lithium manganese iron phosphate material is 0.9 μm, the average particle size of the second lithium manganese iron phosphate material is 0.9 μm, the average particle size of the first ternary cathode active material is 8 μm, and the average particle size of the second ternary cathode active material is 9 μm.

[0123] The first and second slurries are simultaneously coated using a dual-die head. The first slurry is applied to the upper and lower surfaces of the aluminum foil current collector, which already has a conductive layer, while the second slurry is applied to the surface of the first slurry facing away from the aluminum foil current collector. The coating width is 100 mm. After baking and curing, the material is rolled to obtain the positive electrode sheet 100. The total mass percentage of NCM in the positive electrode sheet is controlled by the coating thickness. The positive electrode sheet 100 includes a positive current collector 110 and positive active layers 120 disposed on both sides of the positive current collector 110. The positive active layer 120 includes a first active layer 121 disposed on both sides of the positive current collector 110 and a second active layer 122 disposed on the side of the first active layer 121 facing away from the positive current collector 110. The first active layer 121 has a thickness H1 of 30 μm, and the second active layer 122 has a thickness H2 of 50 μm. The first active layer 121 includes a first lithium manganese iron phosphate material, a first ternary cathode active material, a first binder, and a first conductive agent. The second active layer 122 includes a second lithium manganese iron phosphate material, a second ternary cathode active material, a second binder, and a second conductive agent. The mass percentage A1 of the first lithium manganese iron phosphate material in the first active layer 121 is 30 / (30+67.5+1.5+1) = 30%, the mass percentage A2 of the second lithium manganese iron phosphate material in the second active layer 122 is 85 / (85+10.75+3+1.25) = 85%, the mass percentage B1 of the first binder in the first active layer 121 is 1.5 / (30+67.5+1.5+1) = 1.5%, and the mass percentage of the second binder in the second active layer 122 is... The mass percentage of B2 is 3 / (85+10.75+3+1.25) = 3%, the mass percentage of the first conductive agent in the first active layer 121 is C1 = 1 / (30+67.5+1.5+1) = 1%, the mass percentage of the second conductive agent in the second active layer 122 is C2 = 1.25 / (85+10.75+3+1.25) = 1.25%, and the mass percentage of the first ternary cathode active material in the first active layer 121 is M = 67.5 / (30+67.5+1.5+1)

[0124] =67.5%, the mass percentage N of the second ternary cathode active material in the second active layer 122 is 10.75 / (85+10.75+3+1.25)=10.75%. The mass ratio X of the sum of the first and second ternary cathode active materials in the cathode active layer 120 is (67.5%×30+10.75%×50) / (30+50)=32%, and the mass ratio Y of the sum of the first and second lithium manganese iron phosphate materials in the cathode active layer 120 is (30%×30+85%×50) / (30+50).

[0125] =64.4%. A conductive layer 120 is also provided between the positive current collector 110 and the first active layer 121, and the thickness of the conductive layer 130 is 0.2μm.

[0126] 2) Preparation of negative electrode sheet: The negative electrode active material graphite, thickener sodium carboxymethyl cellulose, binder styrene-butadiene rubber, and conductive agent carbon black are mixed in a mass ratio of 97:1:1:1, deionized water is added, and a negative electrode slurry is obtained under the action of a vacuum stirrer; the negative electrode slurry is uniformly coated on a copper foil with a thickness of 8μm; the copper foil is dried at room temperature and then transferred to a 120℃ oven to dry for 1h, and then cold-pressed and slit to obtain the negative electrode sheet.

[0127] 3) Electrolyte preparation: The organic solvent is a mixture containing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC), wherein the mass ratio of EC, EMC, and DEC is 30:30:40. Thoroughly dried LiPF6 is dissolved in the organic solvent in an argon-atmosphere glove box with a water content of <10 ppm. After thorough mixing, the electrolyte is obtained, wherein the concentration of LiPF6 is 1 mol / L.

[0128] 4) Preparation of the isolation membrane: A 12μm thick polypropylene membrane was selected as the isolation membrane.

[0129] 5) Preparation of lithium-ion batteries: The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. After being wound into a square bare cell, it is placed in an aluminum-plastic film, baked at 80°C to remove water, injected with the appropriate electrolyte, and sealed. After processes such as standing, hot and cold pressing, formation, clamping, and capacity testing, a lithium-ion battery (7 positive and 8 negative stacked cells) is obtained.

[0130] Example 2-23

[0131] The preparation methods of the batteries in Examples 2-23 are basically the same as those in Example 1. The difference is that by changing the ratio 1, ratio 2, H1, H2, and the particle size of each material, one or more of the following can be changed: the thickness of A1, A2, B1, B2, C1, C2, X, Y, the conductive layer, and the average particle size of the first lithium manganese iron phosphate material, the second lithium manganese iron phosphate material, the first ternary cathode active material, and the second ternary cathode active material.

[0132] Example 24

[0133] The preparation method of the battery in Example 24 is basically the same as that in Example 1, except that no conductive layer is provided between the positive electrode current collector and the first active layer.

[0134] Comparative Example 1

[0135] The preparation methods of the batteries in Comparative Example 1 and Example 1 are basically the same, except that the positive electrode active layer consists of only one layer and only includes lithium manganese iron phosphate material.

[0136] Comparative Example 2

[0137] The preparation method of the battery in Comparative Example 2 is basically the same as that in Example 1, except that the first active layer and the second active layer only include ternary positive electrode active materials, and B1 = B2, C1 = C2.

[0138] Comparative Example 3

[0139] The preparation method of the battery in Comparative Example 3 is basically the same as that in Example 1, except that A1 = A2 and C1 = C2.

[0140] Comparative Example 4

[0141] The preparation methods of the batteries in Comparative Example 4 and Example 2 are basically the same, except that B1 > B2.

[0142] Comparative Example 5

[0143] The preparation method of the battery in Comparative Example 5 is basically the same as that in Example 1, except that A1 > A2.

[0144] Experimental example:

[0145] 1. DCIR test conditions (room temperature): Charge the battery at 1 / 3C constant current and constant voltage to 4.3V at room temperature, cut off current 0.05C, and discharge at 1 / 3C constant current for 90 minutes at room temperature. At this time, the SOC of the battery is 50%. The termination voltage after standing for 1 hour is V0, and the termination voltage after discharging at 1.5C for 30 seconds is V1. Calculate the internal resistance R. The calculation formula is: R=(V1-V0) / 1.5 (unit mΩ·Ah), which can be used to obtain the DCIR of 50% SOC discharge. Repeat the above test, change the time of the 1 / 3C constant current discharge step at room temperature to 36 minutes, and the DCIR of 80% SOC discharge can be obtained.

[0146] 2. Cycling performance: At 25℃, the above-mentioned lithium-ion battery was subjected to constant current charge-discharge test at a current density of 1C within a voltage window of 2-4.3V. The reversible specific capacity C after 300 cycles was recorded. 300 Capacity retention R relative to the initial capacity C0 循环 =C 300 / C0*100%.

[0147] Table 1

[0148] Table 2

[0149] As shown in Table 1-2, compared with the comparative example, the positive electrode provided in this application has a higher mass percentage of the second lithium manganese iron phosphate material in the second active layer 122, which will not affect the conductivity of the battery, and at the same time can reduce the side reaction with the electrolyte and improve the cycle stability of the battery; the mass percentage of the first binder in the first active layer 121 is lower, which is conducive to electron transport, reduces the internal resistance of the positive electrode, and thus can improve the cycle stability of the lithium-ion battery.

[0150] Finally, it should be noted that other embodiments of this application will readily conceive of by those skilled in the art upon consideration of the specification and practice of the application disclosed herein. This application is intended to cover any variations, uses, or adaptations of this application that follow the general principles of this application and include common knowledge or customary techniques in the art not disclosed herein, and is not limited to the precise structures described above and shown in the accompanying drawings, and various modifications and alterations may be made without departing from its scope. The scope of this application is limited only by the appended claims.

Claims

1. A positive electrode (100), characterized in that, It includes a positive current collector (110) and a positive active layer (120) disposed on at least one side of the positive current collector (110). The positive active layer (120) includes a first active layer (121) disposed on at least one side of the positive current collector (110) and a second active layer (122) disposed on the side of the first active layer (121) opposite to the positive current collector (110). The first active layer (121) includes a first positive electrode active material and a first binder. The first positive electrode active material includes a first lithium manganese iron phosphate material. The second active layer (122) includes a second positive electrode active material and a second binder. The second positive electrode active material includes a second lithium manganese iron phosphate material. The mass percentages A1 of the first lithium manganese iron phosphate material in the first active layer (121), B1 of the first binder in the first active layer (121), A2 of the second lithium manganese iron phosphate material in the second active layer (122), and B2 of the second binder in the second active layer (122) satisfy the following relationships: A1 < A2, B1 < B2.

2. The positive electrode (100) according to claim 1, characterized in that, A1 and A2 satisfy: 0.35≤A1 / A2≤0.

71.

3. The positive electrode (100) according to claim 2, characterized in that, The condition A1 satisfies 30% ≤ A1 ≤ 50%; And / or, A2 satisfies 70% ≤ A2 ≤ 90%.

4. The positive electrode (100) according to any one of claims 1-3, characterized in that, B1 and B2 satisfy the condition: 0.5 ≤ B1 / B2 ≤ 0.

95.

5. The positive electrode (100) according to claim 4, characterized in that, The condition B1 satisfies 1.5% ≤ B1 ≤ 2.5%; And / or, B2 satisfies 1.6% ≤ B2 ≤ 3%.

6. The positive electrode (100) according to any one of claims 1-5, characterized in that, The first active layer (121) further includes a first conductive agent, and the second active layer (122) further includes a second conductive agent. The mass percentage C1 of the first conductive agent in the first active layer (121) and the mass percentage C2 of the second conductive agent in the second active layer (122) satisfy the following relationship: 0.8≤C1 / C2≤1.

2.

7. The positive electrode (100) according to claim 6, characterized in that, The C1 satisfies 1% ≤ C1 ≤ 5%; And / or, C2 satisfies 1% ≤ C2 ≤ 5%.

8. The positive electrode (100) according to any one of claims 1-7, characterized in that, The first positive electrode active material further includes a first ternary positive electrode active material, and the second positive electrode active material further includes a second ternary positive electrode active material.

9. The positive electrode (100) according to claim 8, characterized in that, X < Y, where X is the mass ratio of the sum of the masses of the first ternary positive electrode active material and the second ternary positive electrode active material to the mass of the positive electrode active layer (120), and Y is the mass ratio of the sum of the masses of the first lithium manganese iron phosphate material and the second lithium manganese iron phosphate material to the mass of the positive electrode active layer (120). And / or, the sum of the masses of the first ternary positive electrode active material and the second ternary positive electrode active material accounts for less than or equal to 35% of the mass of the positive electrode active layer (120).

10. The positive electrode (100) according to any one of claims 1-9, characterized in that, The average particle size of the first lithium manganese iron phosphate material is 0.5 μm-1.5 μm; And / or, the average particle size of the second lithium manganese iron phosphate material is 0.5 μm-1.5 μm.

11. The positive electrode (100) according to claim 10, characterized in that, The average particle size of the first lithium manganese iron phosphate material is 0.8 μm-1 μm; And / or, the average particle size of the second lithium manganese iron phosphate material is 0.8 μm-1 μm.

12. The positive electrode (100) according to claim 8 or 9, characterized in that, The average particle size of the first ternary cathode active material is 0.5 μm-20 μm; And / or, the average particle size of the second ternary cathode active material is 0.5 μm-20 μm.

13. The positive electrode (100) according to claim 12, characterized in that, The average particle size of the first ternary cathode active material is 2μm-15μm; And / or, the average particle size of the second ternary cathode active material is 2μm-15μm.

14. The positive electrode (100) according to any one of claims 1-13, characterized in that, A conductive layer (130) is further provided between the positive current collector (110) and the first active layer (121), the conductive layer (130) comprising a conductive agent and a binder.

15. The positive electrode (100) according to claim 14, characterized in that, The thickness of the conductive layer (130) is 0.2μm-1.3μm.

16. A battery (2), characterized in that, Includes the positive electrode (100) as described in any one of claims 1-15.

17. A battery pack (3), characterized in that, Includes the battery (2) as described in claim 16.

18. An electrical appliance (4), characterized in that, Includes the battery (2) of claim 16 or the battery pack (3) of claim 17.

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