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

Abstract

Provided in the present application are a positive electrode sheet, a battery, a battery pack, and an electric device. The positive electrode sheet comprises a positive electrode current collector, a first positive electrode active layer, a second positive electrode active layer, and a third positive electrode active layer, wherein the first positive electrode active layer is disposed on one side of the positive electrode current collector, the third positive electrode active layer is disposed on the other side of the positive electrode current collector, and the second positive electrode active layer is disposed on the side of the first positive electrode active layer away from the positive electrode current collector; the first positive electrode active layer comprises a first positive electrode active material, the second positive electrode active material comprises a second positive electrode active material, and the third positive electrode active layer comprises a third positive electrode active material; the first positive electrode active material comprises primary particles and secondary particles, the third positive electrode active material comprises primary particles and secondary particles, and the second positive electrode active material comprises primary particles. The positive electrode sheet can improve the energy density of the battery, and also has relatively high rate capability and cycle performance.

Description

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

[0001] This application claims priority to Chinese Patent Application No. 202510123530.3, filed on January 24, 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 lithium-ion 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, as a clean and recyclable new energy battery, have advantages such as high energy density, high voltage platform, wide operating temperature range, low self-discharge, and no memory effect, and are widely used in portable electronic devices, electric vehicles, robots, aerospace, energy storage systems, and other fields. However, in order to further improve the battery life of electrical devices and support longer use, higher requirements are placed on the energy density (mass energy density, volumetric energy density) of lithium-ion batteries.

[0004] Currently, increasing the compaction density of the positive electrode is commonly used to improve battery energy density. However, as the compaction density of the positive electrode increases, the porosity inside the electrode gradually decreases, affecting electrolyte wetting and ion diffusion, increasing internal resistance, and leading to a decline in rate performance and cycle performance. Therefore, achieving high energy density in a battery often comes at the cost of compromised rate and cycle performance, making it impossible to achieve both simultaneously.

[0005] Therefore, how to improve battery energy density while taking into account its rate performance and cycle performance is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0006] To address the aforementioned shortcomings, this application provides a positive electrode that not only improves the energy density of the battery but also possesses high rate performance and cycle performance.

[0007] This application provides a battery including the above-mentioned positive electrode, thus the battery not only has high energy density, but also high rate performance and cycle performance.

[0008] This application provides a battery pack including the aforementioned battery, which can thus achieve higher energy density, rate performance, and cycle performance.

[0009] This application provides an electrical device including the aforementioned battery or battery pack, which thus has high endurance and discharge capacity, as well as a long service life.

[0010] This application provides a positive electrode sheet, the positive electrode sheet comprising a positive current collector, a first positive active layer, a second positive active layer, and a third positive active layer; the first positive active layer is disposed on one side of the positive current collector, the third positive active layer is disposed on the other side of the positive current collector, and the second positive active layer is disposed on the side of the first positive active layer away from the positive current collector; the first positive active layer comprises a first positive active material, the second positive active layer comprises a second positive active material, and the third positive active layer comprises a third positive active material; the first positive active material comprises primary particles and secondary particles, the third positive active material comprises primary particles and secondary particles, and the second positive active material comprises primary particles.

[0011] The positive electrode sheet as described above satisfies: 1≤H2 / H1≤2.5, where H1 is the thickness of the first positive electrode active layer and H2 is the thickness of the second positive electrode active layer.

[0012] As described above, the thickness H1 of the first positive electrode active layer satisfies: 20μm≤H1≤38μm; and / or, the thickness H2 of the second positive electrode active layer satisfies: 35μm≤H2≤50μm; and / or, the thickness H3 of the third positive electrode active layer satisfies: 58μm≤H3≤70μm.

[0013] The positive electrode sheet as described above further includes a fourth positive electrode active layer, which is disposed on the side of the third positive electrode active layer away from the positive electrode current collector; the fourth positive electrode active layer includes a fourth positive electrode active material, which includes primary particles.

[0014] In the positive electrode sheet described above, the average particle size of the primary particles in the fourth positive electrode active material is 0.3–3 μm.

[0015] The positive electrode sheet as described above, wherein the primary particles in the fourth positive electrode active layer comprise a chemical composition of Li x4 (Ni a4 Co b4 Mn c4 ) 1-d4 E d4 O2, wherein 0.95≤x4≤1.05, 0<a4<1, 0<b4<1, 0<c4<1, and a4+b4+c4=1, 0≤d4≤0.1, and E includes at least one of Ti, Zr, and Al.

[0016] The positive electrode sheet as described above satisfies: 1≤H2 / H1≤2.5, 1≤H4 / H3≤2.5, where H1 is the thickness of the first positive electrode active layer, H2 is the thickness of the second positive electrode active layer, H3 is the thickness of the third positive electrode active layer, and H4 is the thickness of the fourth positive electrode active layer.

[0017] In the positive electrode sheet as described above, the thickness H1 of the first positive electrode active layer satisfies: 20μm≤H1≤38μm; and / or, the thickness H2 of the second positive electrode active layer satisfies: 35μm≤H2≤50μm; and / or, the thickness H3 of the third positive electrode active layer satisfies: 20μm≤H3≤35μm; and / or, the thickness H4 of the fourth positive electrode active layer satisfies: 40μm≤H4≤50μm.

[0018] The positive electrode sheet as described above, wherein the average particle size of the primary particles in the first positive electrode active material is 0.3 to 3 μm; and / or, the average particle size of the primary particles in the second positive electrode active material is 0.3 to 3 μm; and / or, the average particle size of the primary particles in the third positive electrode active material is 0.3 to 3 μm.

[0019] The positive electrode sheet as described above, wherein the first positive electrode active layer satisfies: 1≤α1 / β1≤3, preferably 1.5≤α1 / β1≤2, where α1 is the number of secondary particles in the first positive electrode active layer and β1 is the number of primary particles in the first positive electrode active layer; and / or, the third positive electrode active layer satisfies: 1≤α2 / β2≤3, preferably 1.5≤α2 / β2≤2, where α2 is the number of secondary particles in the third positive electrode active layer and β2 is the number of primary particles in the third positive electrode active layer.

[0020] In the positive electrode sheet described above, the average particle size of the secondary particles in the first positive electrode active layer is 5 to 10 μm; and / or, the average particle size of the secondary particles in the third positive electrode active layer is 5 to 10 μm.

[0021] In the positive electrode sheet described above, the primary and secondary particles in the first positive electrode active material each independently comprise a chemical composition of Li. x1 (Ni a1 Co b1 Mn c1 ) 1-d1 M d1 O2, wherein 0.95≤x1≤1.05, 0<a1<1, 0<b1<1, 0<c1<1, and a1+b1+c1=1, 0≤d1≤0.1, M includes at least one of Ti, Zr, and Al; and / or, the primary particles in the second positive electrode active material include the chemical composition Li x2 (Nia2 Co b2 Mn c2 ) 1-d2 A d2 O2, wherein 0.95≤x2≤1.05, 0<a2<1, 0<b2<1, 0<c2<1, and a2+b2+c2=1, 0≤d2≤0.1, A includes at least one of Ti, Zr, and Al; and / or, the primary and secondary particles in the third positive electrode active material each independently include the chemical composition Li. x3 (Ni a3 Co b3 Mn c3 ) 1-d3 G d3 O2, wherein 0.95≤x3≤1.05, 0<a3<1, 0<b3<1, 0<c3<1, and a3+b3+c3=1, 0≤d3≤0.1, and G includes at least one of Ti, Zr, and Al.

[0022] The positive electrode sheet described above has a compaction density of 2.88–3.7 g / cm³. 3 The preferred concentration is 3.2–3.7 g / cm³. 3 ; and / or, the areal density of the positive electrode is 350–450 g / m³. 2 Preferably 400-420 g / m 2 .

[0023] A second aspect of this application provides a battery comprising the positive electrode plate described in the first aspect.

[0024] A third aspect of this application provides a battery pack comprising the battery described in the second aspect.

[0025] 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.

[0026] The positive electrode sheet provided in this application adopts a special multi-layer structure design. Specifically, along the thickness direction of the current collector, from the side closest to the positive current collector to the side furthest away from it, a first positive electrode active layer and a second positive electrode active layer are sequentially stacked on one side of the positive current collector, and a third positive electrode active layer is disposed on the other side of the positive current collector. The second positive electrode active layer includes primary particles, exhibiting high structural stability. Disposing of the second positive electrode active layer on one side of the first positive electrode active layer effectively improves the structural stability of the electrode sheet. Furthermore, since both the first and third positive electrode active layers include primary and secondary particles, this positive electrode sheet can balance high compaction density and structural stability, thereby effectively improving the energy density and cycle stability of the battery. Attached Figure Description

[0027] Figure 1 is a schematic diagram of the structure of the positive electrode sheet of this application in one embodiment;

[0028] Figure 2 is a schematic diagram of the structure of the positive electrode sheet in one embodiment of this application.

[0029] Explanation of reference numerals in the attached figures: 1-First positive electrode active layer; 2-Second positive electrode active layer; 3-Third positive electrode active layer; 4-Fourth positive electrode active layer; 5-Positive electrode current collector. Detailed Implementation

[0030] 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.

[0031] With the rapid development of technology, higher demands are being placed on the battery life of electronic devices. Since battery energy density is directly related to the battery life of these devices, further improvements in battery energy density are needed to meet these higher requirements. Currently, increasing the compaction density of the positive electrode is a common method to effectively improve battery energy density, allowing the electrode to accommodate more active material per unit volume. However, as compaction density increases, the porosity of the electrode gradually decreases, making it difficult for the electrolyte to wet the battery and hindering lithium-ion diffusion, thus affecting the battery's rate performance and cycle performance.

[0032] To address the aforementioned issues, the inventors discovered through research that secondary particles in the positive electrode active material are formed by the agglomeration and stacking of primary particles. This structure facilitates particle stacking during compaction, effectively increasing the compaction density of the electrode. However, this particle structure exhibits poor stability, affecting the battery's cycle performance; moreover, it can result in excessively low porosity in the electrode structure, hindering lithium-ion transport and reaction, thus impacting the battery's rate performance and cycle performance.

[0033] Primary particles possess high structural stability. Therefore, the inventors mixed secondary particles with primary particles and coated them onto both sides of the positive electrode current collector, forming positive electrode active layers on both sides of the current collector (hereinafter, the positive electrode active layer formed on one side of the positive electrode current collector is referred to as the first positive electrode active layer, and the positive electrode active layer formed on the other side of the positive electrode current collector is referred to as the third positive electrode active layer). The primary particles in the first and third positive electrode active layers can provide support, preventing the secondary particles from breaking. This improves the structural stability of the electrode while maintaining high compaction, resulting in higher cycle performance. Moreover, the mixed primary particles can also increase the porosity of the electrode to a certain extent, achieving good electrolyte wetting, reducing lithium-ion migration resistance, and ensuring the rate performance and cycle performance of the battery. Simultaneously, another positive electrode active layer containing primary particles is set on the side of the first positive electrode active layer away from the positive electrode current collector (as described below, a second positive electrode active layer set on the side of the first positive electrode active layer away from the positive electrode current collector). This further improves the structural stability of the electrode while maintaining energy density, thereby further enhancing the cycle performance of the battery.

[0034] Based on the above analysis, the first aspect of this application provides a positive electrode sheet, which includes a positive current collector, a first positive active layer, a second positive active layer, and a third positive active layer; the first positive active layer is disposed on one side of the positive current collector, the third positive active layer is disposed on the other side of the positive current collector, and the second positive active layer is disposed on the side of the first positive active layer away from the positive current collector; the first positive active layer includes a first positive active material, the second positive active layer includes a second positive active material, and the third positive active layer includes a third positive active material; the first positive active material includes primary particles and secondary particles, the third positive active material includes primary particles and secondary particles, and the second positive active material includes primary particles.

[0035] Figure 1 is a schematic diagram of the structure of the positive electrode sheet in one embodiment. In Figure 1, the first positive electrode active layer 1 and the third positive electrode active layer 3 are respectively disposed on both sides of the positive electrode current collector 5, and a second positive electrode active layer 2 is also disposed on one side of the first positive electrode active layer 1.

[0036] It should be noted that the primary particles in the first positive electrode active layer 1, the primary particles in the second positive electrode active layer 2, and the primary particles in the third positive electrode active layer 3 may have the same or different chemical compositions and structures; the secondary particles in the first positive electrode active layer 1 and the secondary particles in the third positive electrode active layer 3 may have the same or different chemical compositions and structures.

[0037] It is understood that in this application, the primary particles in the first positive electrode active layer 1 refer to the primary particles of the first positive electrode active material, and the secondary particles refer to the secondary particles of the first positive electrode active material; the primary particles in the second positive electrode active layer 2 refer to the primary particles of the second positive electrode active material; and the primary particles in the third positive electrode active layer 3 refer to the primary particles of the third positive electrode active material, and the secondary particles refer to the secondary particles of the third positive electrode active material.

[0038] The first positive electrode active material in this application includes a ternary material. When the first positive electrode active material is a ternary material, the primary particles of the first positive electrode active material refer to the primary particles of the ternary material, and the secondary particles of the first positive electrode active material refer to the secondary particles of the ternary material.

[0039] The second positive electrode active material in this application includes ternary materials. When the second positive electrode active material is a ternary material, the primary particles of the second positive electrode active material refer to the primary particles of the ternary material.

[0040] The third positive electrode active material in this application includes ternary materials. When the third positive electrode active material is a ternary material, the primary particles of the third positive electrode active material refer to the primary particles of the ternary material, and the secondary particles of the third positive electrode active material refer to the secondary particles of the ternary material.

[0041] This application does not specifically limit the type of positive current collector 5, and conventional positive current collectors in the art, such as aluminum foil, can be used.

[0042] This application does not specify the thickness of the first positive electrode active layer 1, the second positive electrode active layer 2, and the third positive electrode active layer 3; the appropriate thickness of the positive electrode active layer can be selected according to the actual situation.

[0043] The positive electrode sheet provided in this application has a special structure. The first positive electrode active layer 1 and the third positive electrode active layer 3, disposed on both sides of the positive electrode current collector 5, include primary particles and secondary particles. The secondary particles achieve a high compaction density, while the primary particles have high structural stability, acting as structural supports in the electrode sheet and improving its structural stability. Simultaneously, they can, to a certain extent, prevent the electrode structure from having excessively low porosity, improve electrolyte wettability, and reduce lithium-ion transport resistance. A second positive electrode active layer 2, including primary particles, is also disposed on one side of the first positive electrode active layer 1. This structure further enhances the structural stability of the electrode sheet, improving battery cycle performance while maintaining energy density. Furthermore, because the primary particles in the first positive electrode active layer 1, the second positive electrode active layer 2, and the third positive electrode active layer 3 have high structural integrity, the structural stability of the material can be maintained under high-voltage charge-discharge conditions, reducing the risk of structural collapse. Therefore, the positive electrode sheet in this application can achieve both high rate performance and high cycle performance while ensuring high energy density.

[0044] Furthermore, the thicknesses of the first positive electrode active layer 1, the second positive electrode active layer 2, and the third positive electrode active layer 3 can be controlled to ensure a balanced improvement in compaction density, rate performance, and cycle performance.

[0045] The thickness of the second positive electrode active layer 2 needs to be moderate. This not only ensures sufficient support and effectively improves the structural stability of the electrode, but also helps to increase the overall compaction density of the electrode and reduce the loss of battery energy density. Similarly, the thicknesses of the first positive electrode active layer 1 and the third positive electrode active layer 3 also need to be moderate. This ensures not only a high energy density, but also avoids negatively impacting the structural stability of the electrode.

[0046] In one specific embodiment, the positive electrode sheet satisfies: 1 ≤ H2 / H1 ≤ 2.5, where H1 is the thickness of the first positive electrode active layer 1 and H2 is the thickness of the second positive electrode active layer 2. When the positive electrode sheet satisfies the above relationship, the rate performance and cycle performance of the battery can be further improved without affecting the energy density of the battery.

[0047] For example, H2 / H1 is 1, 1.25, 1.5, 1.75, 2, 2.25 or 2.5, or a range of any two of these values.

[0048] In one specific embodiment, the thickness H1 of the first positive electrode active layer 1 satisfies: 20μm ≤ H1 ≤ 38μm. Within this range, the thickness of the first positive electrode active layer 1 is suitable and can further improve the rate performance and cycle performance of the battery.

[0049] For example, H1 is 20μm, 22μm, 24μm, 26μm, 28μm, 30μm, 32μm, 34μm, 36μm or 38μm, or a range of any two of these values.

[0050] In one specific embodiment, the thickness H2 of the second positive electrode active layer 2 satisfies: 35μm≤H2≤50μm. Within this range, the thickness of the second positive electrode active layer 2 is suitable, which can further improve the cycle performance of the battery and reduce the loss of energy density.

[0051] For example, H2 is 35μm, 38μm, 40μm, 42μm, 44μm, 46μm, 48μm or 50μm, or a range of any two of these values.

[0052] In one specific embodiment, the thickness H3 of the third positive electrode active layer 3 satisfies: 58μm≤H3≤70μm. Within this range, the thickness of the third positive electrode active layer 3 is suitable, which can give the electrode high structural stability, reduce energy density loss, and give the battery high cycle stability.

[0053] For example, H3 is 58μm, 60μm, 62μm, 64μm, 66μm, 68μm or 70μm, or a range of any two of these values.

[0054] In one specific embodiment, the positive electrode sheet satisfies: 120μm≤H1+H2+H3≤160μm. Within this range, the overall thickness of the positive electrode active layer in the electrode sheet is relatively moderate, which not only provides high energy density but also avoids the increase in battery internal resistance caused by excessive thickness, thereby improving the battery's rate performance.

[0055] For example, H1+H2+H3 is 120μm, 125μm, 130μm, 135μm, 140μm, 145μm, 150μm, 155μm or 160μm, or a range consisting of any two of these values.

[0056] Furthermore, another positive electrode active layer can be provided on the side of the third positive electrode active layer 3 away from the positive electrode current collector 5. This positive electrode active layer includes primary particles, which can further improve the structural stability of the electrode and ensure the transport and reaction of lithium ions, so that the battery has higher cycle performance and rate performance.

[0057] In one specific embodiment, the positive electrode sheet further includes a fourth positive electrode active layer, which is disposed on the side of the third positive electrode active layer 3 away from the positive electrode current collector 5; the fourth positive electrode active layer includes a fourth positive electrode active material, which includes primary particles.

[0058] Figure 2 is a schematic diagram of the structure of the positive electrode sheet in one embodiment. In Figure 2, the first positive electrode active layer 1 and the third positive electrode active layer 3 are respectively disposed on both sides of the positive electrode current collector 5, the 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 5, and the fourth positive electrode active layer 4 is disposed on the side of the third positive electrode active layer 3 away from the positive electrode current collector 5.

[0059] By setting a fourth positive electrode active layer 4 on one side of the third positive electrode active layer 3, the structural stability of the electrode can be further improved while ensuring the high energy density of the battery, thereby giving the battery higher cycle performance.

[0060] It should be noted that the chemical composition and structure of the primary particles in the fourth positive electrode active material layer 4 may be the same as or different from those in the first positive electrode active layer 1, the second positive electrode active layer 2, or the third positive electrode active layer 3.

[0061] It is understood that, in this application, the primary particles in the fourth positive electrode active material layer 4 refer to the primary particles of the fourth positive electrode active material.

[0062] The fourth positive electrode active material in this application includes ternary materials. When the fourth positive electrode active material is a ternary material, the primary particles of the fourth positive electrode active material refer to the primary particles of the ternary material.

[0063] Furthermore, the average particle size of the primary particles in the fourth positive electrode active material can be controlled to improve ion diffusion and reaction rates while ensuring the stability of the electrode structure, thereby improving the rate performance and cycle performance of the battery.

[0064] In one specific embodiment, the average particle size of the primary particles in the fourth cathode active material is 0.3–3 μm. Within this range, the smaller particle size of the primary particles in the fourth cathode active material can improve ion diffusion and reaction rates, thereby enabling the battery to have higher rate performance and cycle performance.

[0065] For example, the average particle size of the primary particles in the fourth positive electrode active material is 0.3 μm, 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm or 3 μm, or a range of any two of these values.

[0066] The "average particle size" in this application can be obtained through SEM testing. The specific testing method includes the following steps:

[0067] Based on the positive electrode sheet, a 2cm*2cm section of the positive electrode sheet was cut and magnified 5000 times under a cross-section polisher-scanning electron microscope (CP-SEM) to obtain a CP-SEM image. The long side dimensions (i.e., the dimensions of the longest part of the primary particle) and the long side dimensions (i.e., the dimensions of the longest part of the secondary particle) of 100 primary particles were counted separately. The data distribution was then statistically analyzed, and the average value of the long side dimensions of the primary particles was calculated to obtain the average particle size of the primary particles. The average value of the long side dimensions of the secondary particles was also calculated to obtain the average particle size of the secondary particles.

[0068] In one specific embodiment, the primary particles in the fourth positive electrode active layer 4 comprise a chemical composition of Li. x4 (Ni a4 Co b4 Mn c4 )1-d4 E d4 O2, wherein 0.95≤x4≤1.05, 0<a4<1, 0<b4<1, 0<c4<1, and a4+b4+c4=1, 0≤d4≤0.1, and E includes at least one of Ti, Zr, and Al. This can further improve the battery's energy density, charging efficiency, and cycle life.

[0069] Furthermore, the thicknesses of the first positive electrode active layer 1, the second positive electrode active layer 2, the third positive electrode active layer 3, and the fourth positive electrode active layer 4 can be controlled to ensure a balanced improvement in compaction density, rate performance, and cycle performance.

[0070] In one specific embodiment, the positive electrode sheet satisfies: 1≤H2 / H1≤2.5, 1≤H4 / H3≤2.5, where H1 is the thickness of the first positive electrode active layer 1, H2 is the thickness of the second positive electrode active layer 2, H3 is the thickness of the third positive electrode active layer 3, and H4 is the thickness of the fourth positive electrode active layer 4. When the positive electrode sheet satisfies the above relationships, a balanced improvement in compaction density, rate performance, and cycle performance can be achieved, while also reducing energy density loss.

[0071] For example, H2 / H1 is 1, 1.25, 1.5, 1.75, 2, 2.25 or 2.5, or a range of any two of these values.

[0072] For example, H4 / H3 is 1, 1.25, 1.5, 1.75, 2, 2.25 or 2.5, or a range of any two of these values.

[0073] In one specific embodiment, the thickness H1 of the first positive electrode active layer 1 satisfies: 20μm≤H1≤38μm. Within this range, the thickness of the first positive electrode active layer 1 is suitable, enabling the battery to have a high energy density while ensuring the stability of the electrode structure.

[0074] For example, H1 is 20μm, 22μm, 24μm, 26μm, 28μm, 30μm, 32μm, 34μm, 36μm or 38μm, or a range of any two of these values.

[0075] In one specific embodiment, the thickness H2 of the second positive electrode active layer 2 satisfies: 35μm≤H2≤50μm. Within this range, the thickness of the second positive electrode active layer 2 is relatively moderate, which further improves the structural stability of the electrode while ensuring the energy density of the battery, thus enabling the battery to have high cycle performance.

[0076] For example, H2 is 35μm, 38μm, 40μm, 42μm, 44μm, 46μm, 48μm or 50μm, or a range of any two of these values.

[0077] In one specific embodiment, the thickness H3 of the third positive electrode active layer 3 satisfies: 20μm≤H6≤35μm. Within this range, the thickness of the third positive electrode active layer 3 is suitable, which can not only reduce the loss of energy density, but also maintain the structural stability of the electrode, enabling the battery to have high cycle performance.

[0078] For example, H3 is 20μm, 23μm, 25μm, 27μm, 29μm, 31μm, 33μm or 35μm, or a range of any two of these values.

[0079] In one specific embodiment, the thickness H4 of the fourth positive electrode active layer 4 satisfies: 40μm≤H4≤50μm. Within this range, the thickness of the fourth positive electrode active layer 4 is relatively moderate, which can not only improve the structural stability of the electrode, but also ensure the overall compaction density of the electrode and reduce energy density loss.

[0080] For example, H4 is 40μm, 42μm, 44μm, 46μm, 48μm or 50μm, or a range of any two of these values.

[0081] In one specific embodiment, the positive electrode sheet satisfies: 120μm≤H1+H2+H3+H4≤170μm. Within this range, the overall thickness of the positive electrode active layer in the positive electrode sheet is relatively moderate, which can not only improve the energy density of the battery to a certain extent, but also avoid the increase in battery internal resistance caused by excessive thickness of the positive electrode active layer, thereby improving the rate performance of the battery.

[0082] For example, H1+H2+H3+H4 is 120μm, 125μm, 130μm, 135μm, 140μm, 145μm, 150μm, 155μm, 160μm, 165μm or 170μm, or a range consisting of any two of these values.

[0083] Furthermore, the particle size of the primary particles in the first positive electrode active layer 1, the second positive electrode active layer 2, and the third positive electrode active layer 3 can be controlled to make the primary particle size smaller, thereby improving ion diffusion and reaction rate, and enabling the battery to have higher rate performance and cycle performance.

[0084] In one specific embodiment, the average particle size of the primary particles in the first positive electrode active material is 0.3 to 3 μm; the average particle size of the primary particles in the second positive electrode active material is 0.3 to 3 μm; and the average particle size of the primary particles in the third positive electrode active material is 0.3 to 3 μm.

[0085] For example, the average particle size of the primary particles in the first positive electrode active material is 0.3 μm, 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm or 3 μm, or a range of any two of these values.

[0086] For example, the average particle size of the primary particles in the second positive electrode active material is 0.3 μm, 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, or 3 μm, or a range consisting of any two of these values.

[0087] For example, the average particle size of the primary particles in the third positive electrode active material is 0.3 μm, 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm or 3 μm, or a range of any two of these values.

[0088] When the average particle size of the primary particles in the first, second, and third positive electrode active materials is within the aforementioned range, the smaller particle size of the primary particles can improve the wettability of the electrolyte in the corresponding layer and the diffusion rate of ions, thereby further improving the rate performance and cycle performance of the battery.

[0089] Furthermore, the ratio of secondary to primary particles in the first positive electrode active layer 1 and the third positive electrode active layer 3 also significantly affects the compaction density, rate performance, and structural stability of the electrode. A suitable ratio of secondary to primary particles helps to increase the compaction density of the electrode, thereby improving the energy density of the battery. It also enhances the structural stability of the electrode, resulting in higher cycle stability. Therefore, it is necessary to regulate the ratio of secondary to primary particles.

[0090] In one specific embodiment, the first positive electrode active layer satisfies: 1 ≤ α1 / β1 ≤ 3, preferably 1.5 ≤ α1 / β1 ≤ 2, where α1 is the number of secondary particles in the first positive electrode active layer, and β1 is the number of primary particles in the first positive electrode active layer. Within this range, the positive electrode sheet can have higher compaction density and structural stability, as well as a higher lithium-ion diffusion rate, which can further improve the battery's energy density, rate performance, and cycle stability.

[0091] Specifically, the number ratio of secondary particles to primary particles can be further adjusted by adjusting the mass ratio of secondary particles to primary particles during the preparation process, so that the number ratio of secondary particles to primary particles is within the aforementioned range.

[0092] For example, α1 / β1 is 1, 1.5, 2, 2.5 or 3, or a range consisting of any two of these values.

[0093] The "α1 / β1" in this application can be determined by SEM testing of the cross-section of the positive electrode, including the following steps:

[0094] Based on the positive electrode sheet, a 2cm*2cm portion of the positive electrode sheet was cut out and magnified 10,000 times under a cross-section polisher-scanning electron microscope (CP-SEM) to obtain a CP-SEM image. The number of primary and secondary particles in the first positive electrode active layer was counted to obtain α1 and β1.

[0095] In one specific embodiment, the third positive electrode active layer satisfies: 1 ≤ α2 / β2 ≤ 3, preferably 1.5 ≤ α2 / β2 ≤ 2, where α2 is the number of secondary particles in the third positive electrode active layer, and β2 is the number of primary particles in the third positive electrode active layer. Within this range, the compaction density and structural stability of the positive electrode sheet can be further improved, and the lithium-ion diffusion rate can be increased, enabling the battery to have higher energy density, rate performance, and cycle stability.

[0096] Specifically, the number ratio of secondary particles to primary particles in the slurry corresponding to the third positive electrode active layer can be further adjusted during the preparation process, so that the number ratio of secondary particles to primary particles is within the aforementioned range.

[0097] For example, α2 / β2 is 1, 1.5, 2, 2.5 or 3, or a range of any two of these values.

[0098] The “α2 / β2” in this application can be obtained by SEM testing of the cross-section of the positive electrode. The specific method is the same as the test method of α1 and β1 mentioned above, and will not be repeated here.

[0099] Furthermore, the average particle size of the secondary particles in the first positive electrode active layer 1 and the third positive electrode active layer 3 also significantly affects the battery's cycle performance and rate performance. A suitable secondary particle size helps improve its mechanical strength, preventing material cracking and breakage during cycling, especially under high-voltage charge and discharge conditions, due to continuous expansion and contraction of the particles, thus reducing capacity loss. Simultaneously, it also helps achieve a suitable specific surface area, avoiding material agglomeration and side reactions with the electrolyte due to increased surface energy, effectively reducing the battery's internal resistance. Therefore, the average particle size of the secondary particles also needs to be within a suitable range.

[0100] In one specific embodiment, the average particle size of the secondary particles in the first positive electrode active layer 1 is 5–10 μm; the average particle size of the secondary particles in the third positive electrode active layer 3 is 5–10 μm. Within this range, the particle size of the secondary particles in the first positive electrode active layer 1 and the third positive electrode active layer 3 is relatively moderate, which not only has high ion transport and reaction rates, but also good mechanical strength and conductivity, resulting in high structural stability and electronic conductivity of the electrode, further improving the cycle performance and rate performance of the battery.

[0101] For example, the average particle size of the secondary particles in the first positive electrode active layer 1 is 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm, 9.5 μm or 10 μm, or a range consisting of any two of these values.

[0102] For example, the average particle size of the secondary particles in the third positive electrode active layer 3 is 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm, 9.5 μm or 10 μm, or a range consisting of any two of these values.

[0103] In one specific embodiment, the primary particles and secondary particles in the first positive electrode active material each independently comprise the chemical composition Li. x1 (Ni a1 Co b1 Mn c1 ) 1-d1 M d1 O2, where 0.95≤x1≤1.05, 0<a1<1, 0<b1<1, 0<c1<1, and a1+b1+c1=1, 0≤d1≤0.1, and M includes at least one of Ti, Zr, and Al. This can further improve the battery's energy density, charging efficiency, and cycle life.

[0104] It should be noted that the chemical composition of the primary and secondary particles in the first positive electrode active material can be the same or different, as long as the above-mentioned chemical composition is met.

[0105] In one specific embodiment, the primary particles in the second positive electrode active material comprise a chemical composition of Li. x2 (Ni a2 Co b2 Mn c2 ) 1-d2 A d2O2, where 0.95≤x2≤1.05, 0<a2<1, 0<b2<1, 0<c2<1, and a2+b2+c2=1, 0≤d2≤0.1, and A includes at least one of Ti, Zr, and Al. This can further improve the battery's energy density, charging efficiency, and cycle life.

[0106] In one specific embodiment, the primary and secondary particles in the third positive electrode active material each independently comprise the chemical composition Li. x3 (Ni a3 Co b3 Mn c3 ) 1-d3 G d3 O2, where 0.95≤x3≤1.05, 0<a3<1, 0<b3<1, 0<c3<1, and a3+b3+c3=1, 0≤d3≤0.1, and G includes at least one of Ti, Zr, and Al. This allows for further improvement in the battery's energy density, charging efficiency, and cycle life.

[0107] It should be noted that the chemical composition of the primary and secondary particles in the third positive electrode active material can be the same or different, as long as the above-mentioned chemical composition is met.

[0108] Furthermore, in order to further improve the electrochemical performance of the battery, the positive electrode active material can be screened, or the compaction density and areal density of the positive electrode sheet can be controlled.

[0109] In one specific embodiment, the compaction density of the positive electrode sheet is 2.88–3.7 g / cm³. 3 The preferred concentration is 3.2–3.7 g / cm³. 3 The areal density of the positive electrode is 350–450 g / m³. 2 Preferably 400-420 g / m 2 .

[0110] It should be noted that "area density" in this application refers to the mass of the coating in a unit area positive electrode sheet, where the mass refers to the total mass of the coating within a unit area on both sides of the positive electrode current collector; similarly, "compacted density" refers to the mass of the coating in a unit volume positive electrode sheet, where the mass refers to the total mass of the coating within a unit volume on both sides of the positive electrode current collector.

[0111] For example, the compaction density of the positive electrode is 2.88 g / cm³. 3 2.96 g / cm 3 3.04 g / cm 3 3.20g / cm 3 3.28g / cm 3 3.36 g / cm 33.44 g / cm 3 3.52g / cm 3 3.60g / cm 3 Or 3.7g / cm 3 , or a range consisting of any two of the values.

[0112] For example, the areal density of the positive electrode is 350 g / cm³. 3 360g / cm 3 370g / cm 3 380g / cm 3 390g / cm 3 400g / cm 3 410g / cm 3 420g / cm 3 430g / cm 3 440g / cm 3 Or 450g / cm 3 , or a range consisting of any two of the values.

[0113] When the compaction density and areal density of the positive electrode are within the aforementioned range, the battery can have a high energy density without negatively impacting its rate performance and cycle performance.

[0114] It is understood that the first positive electrode active layer 1, the second positive electrode active layer 2, the third positive electrode active layer 3 and the fourth positive electrode active layer 4 also include conductive agents, and the conductive agents in each active layer can be the same or different.

[0115] In one specific embodiment, the conductive agent includes graphite sheets and / or carbon nanotubes; wherein the diameter of the carbon nanotubes is 10–50 nm, and the diameter of the graphite sheets is 1–30 μm. By using graphite sheets and / or carbon nanotubes of the aforementioned sizes as conductive agents, a sufficient conductive network can be formed in the active layer, effectively connecting more active materials, significantly improving the conductivity of the electrode, reducing the electrode impedance, and thereby further improving the energy density and rate performance of the battery.

[0116] This application does not specify the mass content of the conductive agent in the first positive electrode active layer 1, the second positive electrode active layer 2, the third positive electrode active layer 3, and the fourth positive electrode active layer 4. The appropriate conductive agent content can be selected according to the actual situation.

[0117] Furthermore, the first positive electrode active layer 1, the second positive electrode active layer 2, the third positive electrode active layer 3, and the fourth positive electrode active layer 4 also include a binder. The binder in each positive electrode active layer can be the same or different. This application does not specifically limit the type of binder, and conventional binders in the art can be used, such as polyvinylidene fluoride (PVDF), polyacrylic acid, polyvinyl acid, etc.

[0118] This application does not specify the mass content of the binder in the first positive electrode active layer 1, the second positive electrode active layer 2, the third positive electrode active layer 3, and the fourth positive electrode active layer 4. The appropriate binder content can be selected according to the actual situation.

[0119] This application does not specifically limit the preparation method of the positive electrode sheet. In one embodiment, the positive electrode sheet is prepared by a method including the following process:

[0120] 1) The first positive electrode active material, binder, conductive agent and solvent are uniformly mixed to obtain the first positive electrode active slurry;

[0121] 2) The second positive electrode active material, binder, conductive agent and solvent are uniformly mixed to obtain the second positive electrode active slurry;

[0122] 3) The third positive electrode active material, binder, conductive agent and solvent are uniformly mixed to obtain the third positive electrode active slurry;

[0123] 4) The first positive electrode active slurry and the second positive electrode active slurry are sequentially coated on one side of the positive electrode current collector. After drying, an electrode sheet coated with the first positive electrode active layer 1 and the second positive electrode active layer 2 is obtained. Subsequently, the third positive electrode active slurry is coated on the other side of the positive electrode current collector. After drying, cold pressing and slitting, a positive electrode sheet is obtained.

[0124] This application does not specifically limit the solvents in the first, second, and third positive electrode active slurries, which may be the same or different; and conventional solvents in the art may be used, such as N-methylpyrrolidone (NMP), acetone, ethylene glycol, etc.

[0125] This application does not specify the specific parameters for drying, such as drying temperature of 100℃~130℃ and drying time of not less than 2 hours.

[0126] The second aspect of this application provides a battery including the positive electrode of the first aspect, thereby the battery having higher energy density, rate performance and cycle performance.

[0127] As is conceivable, the battery in this application also includes a negative electrode, a separator, and an electrolyte.

[0128] This application does not specifically limit the electrolyte, and may include solvents and lithium salts commonly used in lithium-ion battery electrolytes. For example, the solvent may include at least one of ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), fluoroethylene carbonate (FEC), ethyl acetate, ethyl propionate, propyl acetate, and propyl propionate; the lithium salt may include at least one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium dioxolaneborate (LiBOB), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and lithium bis(fluorosulfonyl)imide (LiFSI).

[0129] This application does not specifically limit the separator, and it can be any of the separator materials commonly used in lithium-ion batteries, such as polypropylene separator (PP), polyethylene separator (PE), polypropylene / polyethylene double-layer composite membrane (PP / PE), polypropylene / polyethylene / polypropylene triple-layer composite membrane (PP / PE / PP), and separator with ceramic coating.

[0130] This application does not specifically limit the composition and structure of the negative electrode sheet. In one embodiment, the negative electrode sheet 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 conductive agent, and a binder.

[0131] The negative electrode current collector can be a conventional negative electrode current collector in this field, such as copper foil.

[0132] The negative electrode active material may include carbon negative electrode active material and / or silicon negative electrode active material, wherein the carbon negative electrode active material includes at least one of natural graphite, artificial graphite, hard carbon, soft carbon, and carbon black; and the silicon negative electrode active material includes at least one of elemental silicon, silicon-based composite material, and silicon alloy.

[0133] The binder may include at least one of polyvinylidene fluoride (PVDF), sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), and nitrile rubber (NBR).

[0134] The conductive agent may include at least one of acetylene black, Ketjen black, graphite, graphene, and carbon nanotubes.

[0135] This application does not specify the mass content of negative electrode active material, binder and conductive agent in the negative electrode active layer, and appropriate mass ratio can be selected according to actual needs.

[0136] This application does not specify the method of battery preparation. For example, the positive electrode, separator and negative electrode are wound or stacked to obtain a bare cell, the bare cell is packaged, and the battery is obtained after drying, liquid injection, resting, formation and secondary sealing.

[0137] The third aspect of this application provides a battery pack including the battery of the second aspect, and thus the battery pack has high energy density, rate performance and cycle performance.

[0138] The fourth aspect of this application provides an electrical device, including the battery of the second aspect or the battery pack of the third aspect. Therefore, this electrical device has high battery life, long service life, and high discharge capacity.

[0139] This application does not specifically limit the type of electrical equipment. For example, it can be any device that requires a battery to power it, such as a mobile phone, tablet computer, electric vehicle, electric car, robot, drone, etc.

[0140] The positive electrode sheet provided in this application will be described in detail below through specific embodiments.

[0141] Example 1

[0142] 1) Preparation of positive electrode sheet

[0143] The first positive electrode active material, LiNi, consists of primary particles (average particle size 0.3 μm) and secondary particles (average particle size 5 μm). 0.8 Co 0.1 Mn 0.1 O4, polyvinylidene fluoride (PVDF) binder, and carbon nanotubes (10 nm in diameter) conductive agent are mixed in a mass ratio of 98:1:1 and added to N-methylpyrrolidone (NMP). The mixture is stirred evenly under vacuum to obtain the first positive electrode active slurry.

[0144] The second positive electrode active material, LiNi, includes primary particles (average particle size 0.4 μm). 0.8 Co 0.1 Mn 0.1 O4, polyvinylidene fluoride (PVDF) binder, and graphite flakes (5 μm in diameter) conductive agent are mixed in a mass ratio of 98:1:1 and added to N-methylpyrrolidone (NMP). The mixture is stirred evenly under vacuum to obtain the second positive electrode active slurry.

[0145] The first positive electrode active material, LiNi, consists of primary particles (average particle size 0.4 μm) and secondary particles (average particle size 5 μm). 0.8 Co 0.1 Mn 0.1 O4, polyvinylidene fluoride (PVDF) binder, and carbon nanotubes (10 nm in diameter) conductive agent are mixed in a mass ratio of 98:1:1 and added to N-methylpyrrolidone (NMP). The mixture is stirred evenly under vacuum to obtain the third positive electrode active slurry.

[0146] The first positive electrode active slurry and the second positive electrode active slurry were sequentially laminated onto one side of a positive electrode current collector aluminum foil with a thickness of 13 μm. After drying at 120°C, the third positive electrode active slurry was coated onto the other side of the aluminum foil. After drying at 120°C, the positive electrode sheet of this embodiment was obtained by cold pressing and slitting.

[0147] The compaction density of this positive electrode is 3.0 g / cm³. 3 The surface density is 350 g / m³ 2 The thickness of the first positive electrode active layer is 20 μm, the thickness of the second positive electrode active layer is 38 μm, and the thickness of the third positive electrode active layer is 58 μm. CP-SEM testing of the positive electrode sheet showed that the ratio of secondary particles to primary particles in the first positive electrode active layer is 1, and the ratio of secondary particles to primary particles in the third positive electrode active layer is also 1.

[0148] 2) Preparation of negative electrode sheet

[0149] The negative electrode active material graphite, thickener sodium carboxymethyl cellulose, binder styrene-butadiene rubber, and conductive agent carbon black were mixed in a mass ratio of 97:1:1:1. Deionized water was added, and the negative electrode active slurry was obtained under the action of a vacuum stirrer. The negative electrode active slurry was uniformly coated on the surface of a copper foil with a thickness of 8 μm. After drying at room temperature, it was transferred to a 120°C oven for drying for 1 hour. Then, it was cold-pressed and slit to obtain the negative electrode sheet of this embodiment.

[0150] 3) Diaphragm

[0151] A 12μm thick polypropylene membrane was selected as the separator.

[0152] 4) Preparation of electrolyte

[0153] In an argon-atmosphere glove box with a water content of <10ppm, thoroughly dried LiPF6 was dissolved in an organic solvent and mixed thoroughly to obtain an electrolyte; wherein the concentration of LiPF6 was 1mol / L; the organic solvent included ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) in a volume ratio of 20:20:60.

[0154] 5) Preparation of lithium-ion batteries

[0155] 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 moisture, injected with the electrolyte, and sealed. After processes such as standing, hot and cold pressing, formation, clamping, and capacity testing, the lithium-ion battery of this embodiment is obtained.

[0156] Example 2

[0157] The preparation method of the lithium-ion battery in this embodiment is basically the same as that in Example 1, except that:

[0158] In step 1), the chemical composition of the first positive electrode active material, the second positive electrode active material, and the third positive electrode active material is LiNi. 0.89 Co 0.07 Mn 0.04 The first positive electrode active material has an average primary particle size of 0.45 μm and an average secondary particle size of 6.5 μm, with a secondary particle to primary particle ratio of 1.8. The third positive electrode active material is identical to the first positive electrode active material. The second positive electrode active material has an average primary particle size of 0.45 μm. The second positive electrode active layer has a thickness of 40 μm, and the third positive electrode active layer has a thickness of 60 μm. The compaction density of the positive electrode sheet in this embodiment is 3.5 g / cm³. 3 The surface density is 420 g / m³ 2 .

[0159] Example 3

[0160] The preparation method of the lithium-ion battery in this embodiment is basically the same as that in Example 1, except that:

[0161] In step 1), the chemical composition of the first positive electrode active material, the second positive electrode active material, and the third positive electrode active material is LiNi. 0.50 Co 0.2 Mn 0.3 The first positive electrode active material has an average primary particle size of 1 μm and an average secondary particle size of 7 μm, with a secondary particle to primary particle ratio of 1.5. The third positive electrode active material is identical to the first positive electrode active material. The second positive electrode active material has an average primary particle size of 0.5 μm. The second positive electrode active layer has a thickness of 45 μm, and the third positive electrode active layer has a thickness of 65 μm. The compaction density of the positive electrode sheet in this embodiment is 3.5 g / cm³. 3 The surface density is 430 g / m³ 2 .

[0162] Example 4

[0163] The preparation method of the lithium-ion battery in this embodiment is basically the same as that in Example 1, except that:

[0164] In step 1), the average particle size of the primary particles in the first positive electrode active material is 2 μm, the average particle size of the secondary particles is 8 μm, and the ratio of the number of secondary particles to the number of primary particles is 3; the third positive electrode active material is the same as the first positive electrode active material; the average particle size of the primary particles in the first positive electrode active material is 0.7 μm; the thickness of the second positive electrode active layer is 50 μm, and the thickness of the third positive electrode active layer is 70 μm; the compaction density of the positive electrode sheet in this embodiment is 3.2 g / cm³. 3 The surface density is 450 g / m³ 2 .

[0165] Example 5

[0166] The preparation method of the lithium-ion battery in this embodiment is basically the same as that in Example 1, except that:

[0167] In step 1), the average particle size of the primary particles in the first positive electrode active material is 0.8 μm, the average particle size of the secondary particles is 6 μm, and the ratio of the number of secondary particles to the number of primary particles is 2; the third positive electrode active material is the same as the first positive electrode active material; the average particle size of the primary particles in the second positive electrode active material is 0.8 μm; the thickness of the second positive electrode active layer is 40 μm, and the thickness of the third positive electrode active layer is 60 μm; the compaction density of the positive electrode sheet in this embodiment is 3.5 g / cm³. 3 The surface density is 420 g / m³ 2 .

[0168] Example 6

[0169] The preparation method of the lithium-ion battery in this embodiment is basically the same as that in Example 1, except that:

[0170] In step 1), the average particle size of the primary particles in the first positive electrode active material is 3 μm, the average particle size of the secondary particles is 6 μm, and the ratio of the number of secondary particles to the number of primary particles is 2; the average particle size of the primary particles in the second positive electrode active material is 1 μm; the average particle size of the primary particles in the third positive electrode active material is 3 μm, the average particle size of the secondary particles is 10 μm, and the ratio of the number of secondary particles to the number of primary particles is 2; the thickness of the second positive electrode active layer is 40 μm, and the thickness of the third positive electrode active layer is 60 μm; the compaction density of the positive electrode sheet in this embodiment is 3.5 g / cm³. 3 The surface density is 420 g / m³ 2 .

[0171] Example 7

[0172] The preparation method of the lithium-ion battery in this embodiment is basically the same as that in Example 5, except that:

[0173] In step 1), the average particle size of the primary particles in the first positive electrode active material is 0.8 μm, the average particle size of the secondary particles is 6 μm, and the ratio of the number of secondary particles to primary particles is 3; the average particle size of the primary particles in the second positive electrode active material is 0.8 μm; the average particle size of the primary particles in the third positive electrode active material is 0.8 μm, the average particle size of the secondary particles is 6 μm, and the ratio of the number of secondary particles to primary particles is 2; the thickness of the second positive electrode active layer is 40 μm, and the thickness of the third positive electrode active layer is 60 μm; the compaction density of the positive electrode sheet in this embodiment is 3.5 g / cm³. 3 The surface density is 420 g / m³ 2 .

[0174] Example 8

[0175] The preparation method of the lithium-ion battery in this embodiment is basically the same as that in Example 2, except that:

[0176] The positive electrode sheet also includes a fourth positive electrode active layer, the formulation of which is the same as that of the second positive electrode active slurry. The first and second positive electrode active slurries are sequentially laminated onto one side of a 13μm thick aluminum foil used as a positive electrode current collector, and dried at 120°C. The third and fourth positive electrode active slurries are then sequentially laminated onto the other side of the aluminum foil, dried at 120°C, and cold-pressed and slit to obtain the positive electrode sheet of this embodiment. In this embodiment, the thickness of the third positive electrode active layer is 20μm, and the thickness of the fourth positive electrode active layer is 40μm. The compaction density of the positive electrode sheet is 3.3 g / cm³. 3 The surface density is 400 g / m³ 2 .

[0177] Example 9

[0178] The preparation method of the lithium-ion battery in this embodiment is basically the same as that in Example 1, except that:

[0179] The thickness of the first positive electrode active layer in the positive electrode sheet is 35 μm, the thickness of the second positive electrode active layer is 35 μm, and the thickness of the third positive electrode active layer is 70 μm; the compaction density of the positive electrode sheet is 3.2 g / cm³. 3 The surface density is 450 g / m³ 2 .

[0180] Example 10

[0181] The preparation method of the lithium-ion battery in this embodiment is basically the same as that in Example 1, except that:

[0182] The thickness of the first positive electrode active layer in the positive electrode sheet is 20 μm, the thickness of the second positive electrode active layer is 50 μm, and the thickness of the third positive electrode active layer is 70 μm; the compaction density of the positive electrode sheet is 3.2 g / cm³. 3 The surface density is 450 g / m³ 2 .

[0183] Example 11

[0184] The preparation method of the lithium-ion battery in this embodiment is basically the same as that in Example 1, except that:

[0185] The average particle size of the primary particles in the second positive electrode active material is 0.8 μm; the average particle size of the primary particles in the third positive electrode active material is 1 μm, and the average particle size of the secondary particles is 8.5 μm; the compaction density of the positive electrode sheet in this embodiment is 3.0 g / cm³. 3 The surface density is 350 g / m³ 2 .

[0186] Example 12

[0187] The preparation method of the lithium-ion battery in this embodiment is basically the same as that in Example 1, except that:

[0188] The average particle size of the primary particles in the first positive electrode active material is 3.2 μm; the average particle size of the primary particles in the third positive electrode active material is 4 μm; the compaction density of the positive electrode sheet in this embodiment is 3.0 g / cm³. 3 The surface density is 350 g / m³ 2 .

[0189] Example 13

[0190] The preparation method of the lithium-ion battery in this embodiment is basically the same as that in Example 1, except that:

[0191] The average particle size of the primary particles in the second positive electrode active material is 3.5 μm; the compaction density of the positive electrode sheet in this embodiment is 3.0 g / cm³. 3 The surface density is 350 g / m³ 2 .

[0192] Example 14

[0193] The preparation method of the lithium-ion battery in this embodiment is basically the same as that in Example 1, except that:

[0194] The average particle size of the primary particles in the second positive electrode active material is 0.1 μm; the compaction density of the positive electrode sheet in this embodiment is 3.0 g / cm³. 3 The surface density is 350 g / m³ 2 .

[0195] Example 15

[0196] The preparation method of the lithium-ion battery in this embodiment is basically the same as that in Example 1, except that:

[0197] The ratio of secondary particles to primary particles in the first positive electrode active layer is 0.8, and the ratio of secondary particles to primary particles in the third positive electrode active layer is also 0.8; the compaction density of the positive electrode sheet in this embodiment is 2.9 g / cm³. 3 The surface density is 350 g / m³ 2 .

[0198] Example 16

[0199] The preparation method of the lithium-ion battery in this embodiment is basically the same as that in Example 1, except that:

[0200] The ratio of secondary particles to primary particles in the first positive electrode active layer is 3.2, and the ratio of secondary particles to primary particles in the third positive electrode active layer is also 3.2; the compaction density of the positive electrode sheet in this embodiment is 2.9 g / cm³. 3 The surface density is 350 g / m³ 2 .

[0201] Example 17

[0202] The preparation method of the lithium-ion battery in this embodiment is basically the same as that in Example 1, except that:

[0203] The thickness of the first positive electrode active layer in the positive electrode sheet is 15 μm, the thickness of the second positive electrode active layer is 50 μm, and the thickness of the third positive electrode active layer is 65 μm; the compaction density of the positive electrode sheet in this embodiment is 3.5 g / cm³. 3 The surface density is 430 g / m³ 2 .

[0204] Example 18

[0205] The preparation method of the lithium-ion battery in this embodiment is basically the same as that in Example 1, except that:

[0206] The thickness of the first positive electrode active layer in the positive electrode sheet is 35 μm, the thickness of the second positive electrode active layer is 30 μm, and the thickness of the third positive electrode active layer is 65 μm; the compaction density of this positive electrode sheet is 3.5 g / cm³. 3 The surface density is 430 g / m³ 2 .

[0207] Comparative Example 1

[0208] The preparation method of the lithium-ion battery in this comparative example is basically the same as that in Example 1, except that the preparation of the positive electrode sheet is different, specifically including:

[0209] Polycrystalline cathode active material LiNi 0.8 Co 0.1 Mn 0.1 O4 (average particle size 10 μm), polyvinylidene fluoride (PVDF) binder, and graphite flakes (5 μm diameter) conductive agent were mixed at a mass ratio of 98:1:1 and added to N-methylpyrrolidone (NMP). The mixture was stirred evenly under vacuum to obtain a positive electrode active slurry. This positive electrode active slurry was coated onto both functional surfaces of a 13 μm thick aluminum foil current collector. After drying at 120 °C, cold pressing, and slitting, the positive electrode sheet of this comparative example was obtained. The compacted density of the positive electrode sheet in this comparative example was 3.5 g / cm³. 3 The surface density is 350 g / m³ 2 The thickness of the positive active layer on both sides of the positive current collector is 58 μm.

[0210] Comparative Example 2

[0211] The preparation method of the lithium-ion battery in this comparative example is basically the same as that in Example 1, except that the preparation of the positive electrode sheet is different, specifically including:

[0212] A single-crystal positive electrode active material NCM811 (average particle size of 3 μm), a binder polyvinylidene fluoride, and a conductive agent graphite sheet (sheet diameter of 5 nm) were mixed at a mass ratio of 98:1:1 and added to N-methylpyrrolidone (NMP). The mixture was stirred evenly under vacuum to obtain a positive electrode active slurry. This positive electrode active slurry was coated onto both functional surfaces of a 13 μm thick aluminum foil current collector. After drying at 120 °C, cold pressing, and slitting, the positive electrode sheet of this comparative example was obtained. The compaction density of the positive electrode sheet in this comparative example was 3.3 g / cm³. 3 The surface density is 350 g / m³ 2 The thickness of the positive active layer on both sides of the positive current collector is 58 μm.

[0213] Comparative Example 3

[0214] The preparation method of the lithium-ion battery in this comparative example is basically the same as that in Example 1, except that:

[0215] There are no primary particles in the first and third positive electrode active layers, and everything else remains unchanged; the compacted density of the positive electrode sheet in this comparative example is 2.9 g / cm³. 3 The surface density is 350 g / m³ 2 .

[0216] Comparative Example 4

[0217] The preparation method of the lithium-ion battery in this comparative example is basically the same as that in Example 1, except that:

[0218] The positive electrode sheet does not include the second positive electrode active layer. The thickness of the first positive electrode active layer is 58 μm, the thickness of the third positive electrode active layer is 58 μm, and other parameters remain unchanged. The compaction density of the positive electrode sheet in this comparative example is 3.1 g / cm³. 3 The surface density is 350 g / m³. 2 .

[0219] The basic parameters are shown in Tables 1, 2 and 3.

[0220] Table 1

[0221] Table 2

[0222] Table 3

[0223] Experimental Example

[0224] 1. The electrochemical performance of the lithium-ion batteries prepared in the above examples and comparative examples was tested, including the following steps:

[0225] 1) Volumetric energy density

[0226] In a 25°C constant temperature chamber, the battery was charged at a 1C rate to 4.25V, and then charged at a constant voltage of 4.25V until the cutoff current was 0.01C, at which point the battery was fully charged. Subsequently, the fully charged battery was discharged at a 1C rate to 2.5V, and the discharge capacity of the lithium-ion battery was recorded.

[0227] The surface area S and the total thickness T of the positive electrode active material layer in the positive electrode sheet were measured.

[0228] The reversible capacity C per unit area of ​​the positive electrode active material layer is then expressed as C (mAh / cm²). 2 = Discharge capacity of lithium-ion battery / Surface area S of positive electrode active material layer.

[0229] The volumetric energy density (Wh / L) of a lithium-ion battery = reversible capacity per unit area of ​​the positive electrode active material C / total thickness T of the positive electrode active material layer.

[0230] 2) Battery DC internal resistance

[0231] The battery was discharged to 2.0V at a constant current of 0.33C (0.6A) at room temperature, and then charged to 50% SOC (charging capacity 0.9A) at a constant current of 0.33C. It was then discharged at a constant current of 1.5C (2.7A) for 30s, and the voltage before and after discharge was recorded. The discharge DC internal resistance DCIR (mΩ) is calculated as [(voltage before discharge - voltage after discharge) / discharge current] * 1000.

[0232] 3) Cyclic performance

[0233] At 25°C, the lithium-ion battery was charged at a 1C rate to a cutoff voltage of 4.25V, and then discharged at a 1C rate to a cutoff voltage of 2.5V. This was repeated to perform a full charge-discharge cycle test until the capacity of the lithium-ion battery decreased to 80% of its initial capacity. The number of cycles was recorded.

[0234] 4) Capacity retention rate

[0235] The lithium-ion battery was placed in a constant temperature chamber at 25°C and left to stand for 6 hours until the temperature stabilized. It was then charged to 3.7V at a constant current of 1 / 3C, left to rest for 30 minutes, and then discharged to 2.0V at a constant current of 1 / 3C, left to rest for 30 minutes. This charge-discharge cycle was repeated 3 times, and the capacity of the last discharge was recorded as the actual capacity C0. Subsequently, it was charged to 3.7V at a constant current of 4C, left to rest for 30 minutes, and then discharged to 2.0V at a constant current of 0.33C, left to rest for 30 minutes. The capacity of the last discharge was recorded as the actual capacity C1. The capacity retention rate (%) is calculated as (C1 / C0) × 100%.

[0236] The test results are shown in Table 4.

[0237] Table 4

[0238] As shown in Table 4:

[0239] Compared to Comparative Examples 1-4, the lithium-ion batteries in Examples 1-18 exhibit better overall performance. Specifically, the lithium-ion battery in Example 8 has a low DC internal resistance of 75 mΩ, correspondingly achieving a capacity retention rate of 94.6%, a cycle life of 3167 cycles, and a volumetric energy density of 645 Wh / L. Therefore, the positive electrode in this application not only improves the battery's energy density but also possesses high rate performance and cycle life.

[0240] Compared to Example 1, Example 8 adds a fourth positive electrode active layer to the positive electrode sheet, located on the surface of the third positive electrode active layer. Correspondingly, the lithium-ion battery in Example 8 exhibits higher rate performance and cycle performance compared to Example 1, with a rate capacity retention rate as high as 94.6% and a cycle life of 3167 cycles. Although the DC internal resistance (DCIR) increases and the volumetric energy density decreases, both are within acceptable ranges and represent a good level. Therefore, it can be seen that by adding a fourth positive electrode active layer, the battery can achieve higher rate performance and cycle performance.

[0241] Compared to Example 1, in Example 12, the average particle size of the primary particles in the first positive electrode active material and the average particle size of the primary particles in the third positive electrode active material are both outside the range of 0.3–3 μm. Correspondingly, the rate performance and cycle performance in Example 12 are both reduced, with a rate capacity retention of 90.5%, a cycle count of 2845, and almost no change in volumetric energy density. Furthermore, the DC internal resistance (DCIR) also increases to 81 mΩ. Therefore, it can be seen that further control over the average particle size of the primary particles in the first and third positive electrode active materials can further improve the rate performance and cycle performance of the battery.

[0242] Compared to Example 1, the average particle size of the primary particles in the second positive electrode active material in Examples 13 and 14 is not between 0.3 and 3 μm; correspondingly, the rate performance and cycle performance both decrease, while the volumetric energy density remains almost unchanged; and the DC internal resistance (DCIR) also increases. Therefore, it can be seen that further control of the average particle size of the primary particles in the second positive electrode active material can further improve the rate performance and cycle performance of the battery.

[0243] Compared to Example 1, the ratio of secondary particles to primary particles in the first positive electrode active layer and the ratio of secondary particles to primary particles in the third positive electrode active material in Examples 15 and 16 are not between 1 and 3. Correspondingly, the volumetric energy density, rate performance, and cycle performance all decrease, while the DC internal resistance (DCIR) increases. Therefore, by controlling the ratio of secondary particles to primary particles in the first and third positive electrode active layers, the energy density, rate performance, and cycle stability of the battery can be effectively improved.

[0244] Compared to Example 1, in Examples 17 and 18, the thickness ratio H2 / H1 of the second positive electrode active layer to the first positive electrode active layer is not between 1 and 2.5. Correspondingly, the rate performance and cycle performance decrease, and the DC internal resistance (DCIR) increases. Although the volumetric energy density fluctuates, it remains within an acceptable range. Therefore, by controlling the thickness ratio H2 / H1 of the second positive electrode active layer to the first positive electrode active layer in the positive electrode sheet, the rate performance and cycle performance of the battery can be further improved without negatively impacting the battery's energy density.

[0245] 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, wherein, The positive electrode sheet includes a positive current collector, a first positive active layer, a second positive active layer, and a third positive active layer; the first positive active layer is disposed on one side of the positive current collector, the third positive active layer is disposed on the other side of the positive current collector, and the second positive active layer is disposed on the side of the first positive active layer away from the positive current collector; the first positive active layer includes a first positive active material, the second positive active layer includes a second positive active material, and the third positive active layer includes a third positive active material; the first positive active material includes primary particles and secondary particles, the third positive active material includes primary particles and secondary particles, and the second positive active material includes primary particles.

2. The positive electrode according to claim 1, wherein, The positive electrode sheet satisfies: 1≤H2 / H1≤2.5, where H1 is the thickness of the first positive electrode active layer and H2 is the thickness of the second positive electrode active layer.

3. The positive electrode according to claim 1 or 2, wherein, The thickness H1 of the first positive electrode active layer satisfies: 20μm≤H1≤38μm; and / or the thickness H2 of the second positive electrode active layer satisfies: 35μm≤H2≤50μm; and / or the thickness H3 of the third positive electrode active layer satisfies: 58μm≤H3≤70μm.

4. The positive electrode sheet according to claim 1, wherein, The positive electrode sheet further includes a fourth positive electrode active layer, which is disposed on the side of the third positive electrode active layer away from the positive electrode current collector; the fourth positive electrode active layer includes a fourth positive electrode active material, which includes primary particles.

5. The positive electrode according to claim 4, wherein, The average particle size of the primary particles in the fourth positive electrode active material is 0.3–3 μm.

6. The positive electrode according to claim 4 or 5, wherein, The primary particles in the fourth positive electrode active layer include those with the chemical composition Li. x4 (Ni a4 Co b4 Mn c4 ) 1-d4 E d4 O2, wherein 0.95≤x4≤1.05, 0<a4<1, 0<b4<1, 0<c4<1, and a4+b4+c4=1, 0≤d4≤0.1, and E includes at least one of Ti, Zr, and Al.

7. The positive electrode according to any one of claims 4-6, wherein, The positive electrode sheet satisfies: 1≤H2 / H1≤2.5, 1≤H4 / H3≤2.5, where H1 is the thickness of the first positive electrode active layer, H2 is the thickness of the second positive electrode active layer, H3 is the thickness of the third positive electrode active layer, and H4 is the thickness of the fourth positive electrode active layer.

8. The positive electrode according to any one of claims 4-7, wherein, The thickness H1 of the first positive electrode active layer satisfies: 20μm≤H1≤38μm; and / or, the thickness H2 of the second positive electrode active layer satisfies: 35μm≤H2≤50μm; and / or, the thickness H3 of the third positive electrode active layer satisfies: 20μm≤H3≤35μm; and / or, the thickness H4 of the fourth positive electrode active layer satisfies: 40μm≤H4≤50μm.

9. The positive electrode according to any one of claims 1-8, wherein, The average particle size of the primary particles in the first positive electrode active material is 0.3–3 μm; and / or, the average particle size of the primary particles in the second positive electrode active material is 0.3–3 μm; and / or, the average particle size of the primary particles in the third positive electrode active material is 0.3–3 μm.

10. The positive electrode according to any one of claims 1-9, wherein, The first positive electrode active layer satisfies: 1≤α1 / β1≤3, preferably 1.5≤α1 / β1≤2, where α1 is the number of secondary particles in the first positive electrode active layer and β1 is the number of primary particles in the first positive electrode active layer; and / or, the third positive electrode active layer satisfies: 1≤α2 / β2≤3, where α2 is the number of secondary particles in the third positive electrode active layer and β2 is the number of primary particles in the third positive electrode active layer.

11. The positive electrode according to any one of claims 10, wherein, 1.5≤α2 / β2≤2。 12. The positive electrode according to any one of claims 1-11, wherein, The average particle size of the secondary particles in the first positive electrode active layer is 5–10 μm; and / or, the average particle size of the secondary particles in the third positive electrode active layer is 5–10 μm.

13. The positive electrode according to any one of claims 1-12, wherein, The primary and secondary particles in the first positive electrode active material each independently comprise the chemical composition Li. x1 (Ni a1 Co b1 Mn c1 ) 1-d1 M d1 O2, wherein 0.95≤x1≤1.05, 0<a1<1, 0<b1<1, 0<c1<1, and a1+b1+c1=1, 0≤d1≤0.1, M includes at least one of Ti, Zr, and Al; and / or, the primary particles in the second positive electrode active material include the chemical composition Li x2 (Ni a2 Co b2 Mn c2 ) 1-d2 A d2 O2, wherein 0.95≤x2≤1.05, 0<a2<1, 0<b2<1, 0<c2<1, and a2+b2+c2=1, 0≤d2≤0.1, A includes at least one of Ti, Zr, and Al; and / or, the primary and secondary particles in the third positive electrode active material each independently include the chemical composition Li. x3 (Ni a3 Co b3 Mn c3 ) 1-d3 G d3 O2, wherein 0.95≤x3≤1.05, 0<a3<1, 0<b3<1, 0<c3<1, and a3+b3+c3=1, 0≤d3≤0.1, and G includes at least one of Ti, Zr, and Al.

14. The positive electrode according to any one of claims 1-13, wherein, The compaction density of the positive electrode sheet is 2.88–3.7 g / cm³. 3 ; and / or, the areal density of the positive electrode is 350–450 g / m³. 2 .

15. The positive electrode according to claim 14, wherein, The compaction density of the positive electrode sheet is 3.2–3.7 g / cm³. 3 ; and / or, the areal density of the positive electrode is 400–420 g / m³. 2 .

16. A battery, wherein, The battery includes the positive electrode sheet as described in any one of claims 1-15.

17. A battery pack, wherein, The battery pack includes the battery of claim 16.

18. An electrical appliance, wherein, The electrical equipment includes the battery of claim 16 or the battery pack of claim 17.

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