Electrode sheet and preparation method therefor, battery, and electric device

Abstract

An electrode sheet and a preparation method therefor, a battery, and an electric device. The electrode sheet comprises an electrode current collector and an electrode coating located on the surface of at least one side of the electrode current collector; the electrode coating comprises an electrode active material; in the length direction of the electrode coating, the electrode coating comprises a central region and edge regions located on two opposite sides of the central region; and the OI value of the electrode active material in the central region is less than the OI value of the electrode active material in the edge regions.

Description

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

[0001] This application claims priority to Chinese Patent Application No. 202411644875.5, filed on November 15, 2024, entitled “An electrode sheet and its preparation method, a battery and an electrical device thereof”, the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to the field of batteries, specifically to an electrode sheet and its preparation method, a battery, and an electrical device. Background Technology

[0003] Electrode sheets are a crucial component of batteries, and the electrode materials within them significantly impact battery performance, including cycle life. In related technologies, uneven current density on the electrode sheets during battery cycling can lead to lithium plating and subsequent cycle drops during long cycles, resulting in low cycle life and requiring immediate solutions. Summary of the Invention

[0004] The purpose of this application is to provide an electrode sheet and its preparation method, a battery and an electrical device, which can effectively improve the battery's cycle life and other performance characteristics, and overcome the defects of the prior art.

[0005] In a first aspect, this application discloses an electrode sheet, including an electrode current collector and an electrode coating located on at least one side surface of the electrode current collector, the electrode coating including an electrode active material; along the length direction of the electrode coating, the electrode coating includes a central region and edge regions located on opposite sides of the central region, the OI value of the electrode active material in the central region being less than the OI value of the electrode active material in the edge regions.

[0006] According to one embodiment of this application, the OI value of the electrode active material in the central region is 0.001 to 200, preferably 0.1 to 30; and / or, the width of the central region in the length direction of the electrode coating is greater than or equal to 1 cm.

[0007] According to one embodiment of this application, each edge region includes a plurality of sub-regions distributed along the length direction of the electrode coating, wherein in every two adjacent sub-regions, the OI value of the electrode active material in the sub-region closer to the center region is less than the OI value of the electrode active material in the sub-region farther from the center region.

[0008] According to one embodiment of this application, the ratio of the OI value of the electrode active material in the central region to the OI value of the electrode active material in the sub-region closest to the central region is 0.3 to 0.9; and / or, in every two adjacent sub-regions, the ratio of the OI value of the electrode active material in the sub-region closer to the central region to the OI value of the electrode active material in the sub-region farther from the central region is 0.3 to 0.9; and / or, the OI value of the electrode active material in any one sub-region is 0.001 to 200, preferably 0.1 to 30; and / or, the width of any one sub-region in the length direction of the electrode coating is greater than or equal to 1 cm.

[0009] According to one embodiment of this application, the length of the electrode coating is 1 cm to 10 m.

[0010] According to one embodiment of this application, the electrode sheet is a negative electrode sheet, and the electrode active material includes graphite.

[0011] According to one embodiment of this application, the electrode sheet is a positive electrode sheet, and the electrode active material includes a positive electrode ternary material and / or lithium iron phosphate.

[0012] According to one embodiment of this application, the porosity of the electrode coating is 20% to 40%; and / or, the compaction density of the electrode coating is 1.3 g / cm³. 3 ~2g / cm 3 ; and / or, the areal density of the electrode coating is 200 g / m³. 2 ~800g / m 2 .

[0013] Secondly, this application discloses a method for preparing the above-mentioned electrode sheet. The method includes the following steps: coating a slurry containing the electrode active material onto the surface of the electrode current collector to form a wet film on the surface of the electrode current collector; wherein, along the length direction of the electrode coating, the wet film includes a central region and edge regions located on opposite sides of the central region; then, applying a magnetic field of a preset intensity to the central region and the edge regions of the wet film respectively, and inducing the electrode active material in the central region and the edge regions of the wet film to reach a preset OI value respectively through magnetic field induction; wherein, the intensity of the magnetic field applied to the central region of the wet film is greater than the intensity of the magnetic field applied to the edge regions of the wet film; then, drying and rolling are performed to obtain the electrode sheet.

[0014] According to one embodiment of this application, the strength of the magnetic field applied to the central region of the wet film is 0.1T to 20T, preferably 0.2T to 2T.

[0015] According to one embodiment of this application, the edge region of the wet film includes a plurality of sub-regions distributed along the length direction of the wet film, wherein in every two adjacent sub-regions, the intensity of the magnetic field applied to the sub-region closer to the central region is greater than the intensity of the magnetic field applied to the sub-region farther from the central region.

[0016] According to one embodiment of this application, the strength of the magnetic field applied to any of the sub-regions of the wet film is 0.1T to 20T, preferably 0.2T to 2T.

[0017] Thirdly, this application discloses a battery comprising the above-described electrode sheet or an electrode sheet prepared according to the above-described electrode sheet preparation method.

[0018] According to one embodiment of this application, the battery includes a cell, the cell including a positive electrode and a negative electrode, at least one of the positive electrode and the negative electrode being the aforementioned electrode or an electrode prepared according to the aforementioned electrode preparation method; the positive electrode includes a positive electrode tab located at one end of the length direction of the cell; the negative electrode includes a negative electrode tab located at the other end of the length direction of the cell.

[0019] Fourthly, this application discloses an electrical device, which includes the aforementioned battery.

[0020] In conjunction with the above technical solutions, the electrode sheet, its preparation method, battery, and electrical equipment provided in this application have an OI value in the electrode coating of the electrode sheet that is lower than the OI value in the electrode active material in the edge region. By designing the OI value by region, the particle structure of the electrode active material in the electrode sheet is arranged in a way that facilitates the uniform distribution of current in the electrode sheet, improving the impedance of different regions in the electrode sheet, balancing the problem of uneven current caused by the uneven impedance of different regions in the electrode sheet, thereby improving the uniformity of current density of the electrode sheet during battery cycling, avoiding problems such as lithium plating and cycle failure caused by uneven current density of the electrode sheet, and thus improving the cycle life and other performance of the battery. Attached Figure Description

[0021] Figure 1 is a schematic diagram of the structure of an electrode sheet according to an embodiment of this application;

[0022] Figure 2 is a plan view of the electrode coating according to an embodiment of this application;

[0023] Figure 3 is a cross-sectional SEM image of the negative electrode coating of Example 1;

[0024] Figure 4 is a cross-sectional SEM image of the negative electrode coating in Comparative Example 1.

[0025] Figure 5 is a schematic diagram of the stacked structure of the positive electrode, separator and negative electrode in a battery cell according to an embodiment of this application.

[0026] Explanation of reference numerals in the attached figures: 1: Electrode coating; 2: Electrode current collector; 11: Central region; 12: Edge region; 121: First sub-region; 122: Second sub-region; 123: Third sub-region; L0: Width of the central region; L1: Width of the first sub-region; L2: Width of the second sub-region; L3: Width of the third sub-region; 101: First side 101; 102: Second side 102; 3: Positive electrode plate; 31: Positive electrode tab; 4: Negative electrode plate; 41: Negative electrode tab; 5: Separator. Detailed Implementation

[0027] To enable those skilled in the art to better understand the solutions of this application, a further detailed description of this application is provided below. The specific embodiments listed below are merely descriptions of the principles and features of this application; the examples are only for explaining this application and are not intended to limit its scope. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of this application.

[0028] In related technologies, during battery cycling, factors such as uneven current density on the electrode plates can lead to lithium plating and cycle failure during long cycles, resulting in low battery cycle life, which urgently needs to be addressed.

[0029] Specifically, the "rocking chair" energy storage mechanism of lithium batteries determines their relatively low power density. During charging and discharging, lithium ions need to be repeatedly inserted and extracted between the positive and negative electrode materials. Therefore, the diffusion rate of lithium ions in the electrode active material determines the battery's charging and discharging speed and other performance characteristics. Currently, the main approach is to shorten the diffusion path of lithium ions in the electrode active material by structural design, such as nano-sizing the electrode active material or forming a porous structure. However, these methods are difficult to apply in actual industrial production due to considerations of mass manufacturing costs and process complexity.

[0030] Through long-term research, the inventors of this application have discovered that during the charging and discharging test of batteries, the electrode sheets generally suffer from uneven current density. The reason for this is that, due to factors such as the structure and manufacturing process of the electrode sheets, the impedance of different regions of the electrode sheets is usually different, which leads to uneven current density of the electrode sheets during the charging and discharging process of the battery. Specifically, the impedance of the central region of the electrode sheet along its length is usually higher than that of the edge region, which makes the current density of the central region of the electrode sheet lower than that of the edge region, resulting in uneven current density of the electrode sheets during the charging and discharging process of the battery.

[0031] For example, electrode sheets are usually made by coating, that is, the electrode paste used to form the electrode coating is coated on one side of the electrode current collector to form the electrode coating and thus the electrode sheet is made. During the coating process, the electrode paste has a certain fluidity, which inevitably causes the thickness of different areas of the electrode coating to be different. In particular, the thickness of the electrode coating in the central area is higher than that in the edge area. This will cause the impedance of the central area to be greater than that in the edge area, and consequently, the current density in the central area will be lower than that in the edge area, resulting in uneven current density of the electrode sheet during battery charging and discharging.

[0032] For example, as shown in Figure 5, the electrode plates in the battery cell include positive electrode plates and negative electrode plates. The positive electrode plate includes a positive electrode tab, which is located at one end of the length direction of the battery cell. The negative electrode plate includes a negative electrode tab, which is located at the other end of the length direction of the battery cell. For either the positive or negative electrode plate (hereinafter referred to as electrode plate), the impedance of the area closer to the tab is relatively smaller. Since the positive and negative electrode tabs are respectively located at opposite ends of the length direction of the battery cell, the impedance of the edge area of ​​the electrode plate in its length direction is less than the impedance of its center area. Consequently, the current density in the center area of ​​the electrode plate is less than the current density in the edge area, resulting in uneven current density of the electrode plate during the charging and discharging process of the battery.

[0033] Uneven current density on the electrode sheets can easily lead to surface lithium plating and subsequent cycle drops during long-term battery cycling, affecting the battery's cycle life. Therefore, improving current density uniformity through reasonable electrode sheet structure design, thereby improving battery cycle life and other performance characteristics, is a significant challenge.

[0034] In view of this, embodiments of this application provide an electrode sheet, as shown in Figures 1 and 2. The electrode sheet includes an electrode current collector 2 and an electrode coating 1 located on at least one side surface of the electrode current collector 2. The electrode coating 1 includes an electrode active material. Along the length direction of the electrode coating 1, the electrode coating 1 includes a central region 11 and edge regions 12 located on opposite sides of the central region 11. The OI value of the electrode active material in the central region 11 is less than the OI value of the electrode active material in the edge regions 12.

[0035] According to the inventors' research and analysis, the different OI values ​​in different regions of the electrode coating 1 result in different orientation angles of the electrode active material particles in different regions of the electrode coating 1, thus forming different lengths of ion transport channels. In the above-mentioned electrode sheet structure system, by controlling the OI value of the electrode active material in the central region 11 to be lower than the OI value of the electrode active material in the edge region 12, the orientation degree of the electrode active material is adjusted at the particle level in different regions, constructing an electrode coating 1 with an ordered stacking of electrode active material particles and crystal structures in specific regions. This can improve the layer performance of the electrode sheet, form an ordered ion transport channel, and optimize the resistivity and ion diffusion capacity of the electrode sheet, thereby improving the uneven distribution of current at the battery level and the resulting poor battery cycle performance, thus improving the cycle life of the battery. At the same time, it can reduce battery impedance and improve the fast charging and dynamic performance of the battery.

[0036] Specifically, by making the OI value of the electrode active material in the central region 11 lower than that in the edge region 12, the ion transport capacity and conductivity of the central region 11 can be improved. This addresses the issues of the impedance of the central region being higher than that of the edge region and the resulting uneven current density caused by factors such as the structure and coating process of the electrode sheet. For example, it improves the problem of the thickness of the electrode coating in the central region being greater than that in the edge region due to factors such as the coating process, which leads to the impedance of the central region being greater than that in the edge region, and the resulting current density in the central region being lower than that in the edge region, thus causing uneven current density of the electrode sheet during battery charging and discharging. It also improves the problem of the impedance of the central region being greater than that in the edge region due to the presence of positive and negative electrode tabs at opposite ends of the cell's length direction, while the central region is not equipped with tabs, which leads to the current density in the central region being lower than that in the edge region, and the resulting uneven current density of the electrode sheet during battery charging and discharging.

[0037] Referring again to Figures 1 and 2, the electrode sheet (electrode coating 1) has a first side 101 and a second side 102 opposite each other in its length direction. The distance from the middle position (dashed line in Figure 2) of the electrode coating 1 in its length direction to the outer edge of the first side 101 of the electrode coating 1 is basically equal to the distance from the outer edge of the second side 102 of the electrode coating 1. The central region 11 of the electrode coating 1 is basically bisected by the middle position M of the electrode coating 1 (that is, the dashed line M in Figure 2 is the center line of the central region 11). That is, the central region 11 of the electrode coating 1 is the region that extends from the middle position M of the electrode coating 1 to the first side 101 and the second side 102 by a distance L0 / 2, where L0 is the width of the central region 11 of the electrode coating 1 in the length direction of the electrode coating 1.

[0038] Referring again to Figures 1 and 2, for any edge region 12 located on either side of the central region 11 of the electrode coating 1, it can be a sub-region. In this case, the electrode coating 1 includes a sub-region (edge ​​region 12), a central region 11, and another sub-region (edge ​​region 12) distributed sequentially along its length. For any sub-region, the OI values ​​of each region are basically uniform.

[0039] In some optional embodiments, as shown in Figures 1 and 2, for an edge region 12 located on either side of the central region 11 of the electrode coating 1, it includes multiple sub-regions distributed along the length direction of the electrode coating 1. In every two adjacent sub-regions, the OI value of the electrode active material in the sub-region closer to the central region 11 is less than the OI value of the electrode active material in the sub-region farther from the central region 11. At this time, the OI value of the electrode coating 1 shows a gradient decreasing trend in the direction from the edge region 12 to the central region 11. In this way, by changing the orientation degree of the electrode active material particles at different regional particle levels, it is beneficial to further improve the layer performance of the electrode sheet, optimize the resistivity, ion diffusion ability and other properties of the electrode sheet, thereby improving the problem of uneven current distribution at the battery level, and thus improving the cycle life and other performance of the battery.

[0040] In the aforementioned electrode sheet, for any side of the central region 11 of the electrode coating 1, the edge region 12 extends to the outer edge of the electrode coating 1 in the length direction. Specifically, the edge region 12 consists of n sub-regions, where n is an integer greater than or equal to 2, for example, n≥3. The sub-regions distributed along the direction from the central region 11 to the edge region 12 of the electrode coating 1 are, in sequence, the first sub-region 121, the second sub-region 122, ..., the nth sub-region. The first sub-region 121 is the sub-region closest to the central region 11 of the electrode coating 1, and the nth sub-region is the sub-region furthest from the central region 11 of the electrode coating 1. The edge of the nth sub-region away from the central region 11 is the outer edge of the electrode coating 1.

[0041] As shown in Figures 1 and 2, the first sub-region 121 is in direct contact with the central region 11, and every two adjacent sub-regions are in direct contact. Specifically, the first sub-region 121 is the region extending L1 distance away from the center line M from the cutoff edge of the central region 11 (i.e., the width of the first sub-region 121 in the length direction of the electrode coating 1 is L1), the second sub-region 122 is the region extending L2 distance away from the center line M from the cutoff edge of the first sub-region 121 (i.e., the width of the second sub-region 122 in the length direction of the electrode coating 1 is L2), the third sub-region 123 is the region extending L3 distance away from the center line M from the cutoff edge of the second sub-region 122 (i.e., the width of the third sub-region 123 in the length direction of the electrode coating 1 is L3)... the nth sub-region is the region extending L... n The region (i.e., the nth sub-region) has a width of L along the length of electrode coating 1. n That is, the length L of electrode coating 1 is L = L0 + 2 × (L1 + L2 + ... + L... n ).

[0042] For example, the number of sub-regions of the edge region 12 located on either side of the central region 11 of the electrode coating 1 can be 2 (n=2), 3 (n=3), 4 (n=4), 5 (n=5), 6 (n=6), etc., but is not limited to this.

[0043] In contrast, for any edge region 12 located on either side of the central region 11 of the electrode coating 1, the more sub-regions there are and the smaller the width of a single sub-region along the length of the electrode coating 1, the better it is to improve the problem of uneven current distribution on the electrode sheet, thereby improving the cycle life and other performance of the battery. However, this will increase the difficulty of electrode sheet preparation and the complexity of the preparation process to a certain extent. Therefore, considering the electrode sheet preparation process and battery performance, in some optional embodiments, the width of any sub-region along the length of the electrode coating 1 is greater than or equal to 1 cm, for example, a range of 1 cm, 10 cm, 30 cm, 50 cm, 80 cm, 100 cm, 120 cm, 140 cm, 150 cm, 180 cm, 200 cm, 230 cm, 250 cm, 500 cm, 800 cm, 1000 cm, 2000 cm, 3000 cm, 4000 cm, 5000 cm or any combination thereof.

[0044] In some embodiments, the length of the electrode coating 1 can be from 1 cm to 10 m. As an optional implementation, the length of the electrode coating 1 can be from 10 cm to 5000 cm, for example, 1 cm, 10 cm, 30 cm, 50 cm, 80 cm, 100 cm, 120 cm, 140 cm, 150 cm, 180 cm, 200 cm, 230 cm, 250 cm, 500 cm, 800 cm, 1000 cm, 2000 cm, 3000 cm, 4000 cm, 5000 cm, or any combination thereof. By making the OI value of the electrode active material in the central region 11 of the electrode coating 1 smaller than the OI value of the electrode active material in the edge region 12, the problem of uneven current density of the electrode sheet during battery cycling can be improved, while also facilitating the preparation of the electrode sheet and improving the preparation efficiency and yield.

[0045] Taking into account factors such as the electrode sheet fabrication process and battery performance, the width L0 of the central region 11 of the electrode coating 1 along the length of the electrode coating 1 can be greater than or equal to 1 cm, for example, a range of 1 cm, 10 cm, 30 cm, 50 cm, 80 cm, 100 cm, 120 cm, 140 cm, 150 cm, 180 cm, 200 cm, 230 cm, 250 cm, 500 cm, 800 cm, 1000 cm, 2000 cm, 3000 cm, 4000 cm, 5000 cm or any two of these ranges. This is beneficial for improving the uniformity of current distribution on the electrode sheet, facilitating the fabrication of the electrode sheet, and improving the fabrication efficiency and yield of the electrode sheet.

[0046] In the aforementioned electrode sheet, the electrode active material exists in the form of particles, as shown in Figure 1. The smaller the OI value of the electrode active material, the higher the verticality of the electrode active material particles. This helps to reduce tortuosity, reduce ion transport paths, and reduce ion transport resistance. In this embodiment, by designing different OI values ​​for different regions, the OI value gradient of the electrode active material in the electrode coating 1 decreases from the edge of the electrode coating 1 towards the center position M of the electrode coating 1. This results in the electrode active material particles (crystal structure) in the entire electrode coating 1 exhibiting an ordered stacking, which can effectively solve the problem of uneven current density of the electrode sheet during battery cycling, reduce the temperature difference between the central and edge regions of the electrode sheet, and improve the cycle life and other performance characteristics of the battery.

[0047] In the embodiments of this application, the shape of the electrode active material can be spherical, near-spherical, or other regular or irregular shapes.

[0048] Specifically, the OI value of the electrode active material in the central region 11 of the electrode coating 1 can be 0.001 to 200, for example, a range of 0.001, 0.01, 0.1, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 30, 50, 80, 100, 130, 150, 180, 200 or any two of these. As an optional implementation, the OI value of the electrode active material in the central region 11 of the electrode coating 1 can be 0.1 to 30, which is beneficial to further improve the uniformity of current density of the electrode sheet during battery cycling and improve the cycle life and other performance of the battery.

[0049] Further research revealed that the ratio of the OI value of the electrode active material in the central region 11 of the electrode coating 1 to the OI value of the electrode active material in the sub-region closest to the central region 11 can be 0.3 to 0.9, for example, within the range of 0.3, 0.35, 0.38, 0.4, 0.43, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, or any combination thereof. This is beneficial for further improving the uniformity of current density of the electrode sheet during battery cycling, improving the cycle life and other performance characteristics of the battery, while also facilitating the preparation of the electrode sheet and improving its preparation efficiency and yield.

[0050] Furthermore, in each pair of adjacent sub-regions, the ratio of the OI value of the electrode active material in the sub-region closer to the center region 11 to the OI value of the electrode active material in the sub-region farther from the center region 11 can be 0.3 to 0.9, for example, a range of 0.3, 0.35, 0.38, 0.4, 0.43, 0.45, 0.5, 0.55, 0.6, 0.65, 0.67, 0.7, 0.75, 0.8, 0.85, 0.87, 0.9 or any combination thereof. This is beneficial for further improving the uniformity of current density of the electrode sheet during battery cycling, improving the cycle life and other performance of the battery, and at the same time facilitating the preparation of the electrode sheet and improving the preparation efficiency and yield of the electrode sheet.

[0051] Specifically, the OI value of the electrode active material in any sub-region can be 0.001 to 200. As an optional implementation, the OI value of the electrode active material in any sub-region can be 0.1 to 30, which is beneficial to further improve the uniformity of current density of the electrode sheet during battery cycling and improve the battery's cycle life and other performance.

[0052] Furthermore, the porosity of the electrode coating 1 can be 20% to 40%, for example, 20%, 21%, 23%, 25%, 28%, 30%, 31%, 33%, 35%, 38%, 40%, or any combination thereof, which is beneficial to further improve the battery's cycle life and other performance.

[0053] In this embodiment of the application, the porosity of the electrode coating 1 on the electrode sheet can be measured by mercury intrusion porosimetry.

[0054] Furthermore, the compaction density of the electrode coating 1 described above can be 1.3 g / cm³. 3 ~2g / cm 3 For example, 1.3g / cm 3 1.4g / cm 3 1.5g / cm 3 1.6g / cm 3 1.7g / cm 3 1.8g / cm 3 1.9g / cm 3 2g / cm 3 or a range of any two of them, which is beneficial for further improving battery performance such as cycle life.

[0055] Furthermore, the areal density of the electrode coating 1 described above can be 200 g / m³. 2 ~800g / m 2 For example, 200g / m 2 210g / m 2 220g / m 2 230g / m 2 240g / m 2 250g / m 2 280g / m 2 300g / m 2 400g / m 2 500g / m 2 600g / m 2 700g / m 2 800g / m 2 or a range of any two of them, which is beneficial for further improving battery performance such as cycle life.

[0056] In some embodiments, the electrode sheet can be a negative electrode sheet, and correspondingly, the electrode current collector 2 is a negative electrode current collector, the electrode coating 1 is a negative electrode coating (negative electrode active material layer), and the electrode active material is a negative electrode active material, which may include graphite, such as artificial graphite and / or natural graphite. Specifically, the electrode coating 1 may include primary graphite particles and / or secondary graphite particles.

[0057] In this embodiment, by controlling the OI value of the negative electrode active material (graphite) particles in the central region 11 of the negative electrode coating to be less than the OI value of the negative electrode active material (graphite) particles in the edge region 12, a negative electrode sheet with ordered stacking of negative electrode active material particles and crystal structure is constructed. This can effectively improve the current density uniformity and other properties of the negative electrode sheet during battery cycling, which is beneficial to the performance of the negative electrode sheet under high areal density and compaction density conditions, and improve the cycle life and other performance of the battery.

[0058] The embodiments of this application may employ conventional negative electrode current collectors in the art, for example, negative electrode current collectors may include copper foil.

[0059] In other embodiments, the electrode sheet is a positive electrode sheet, and correspondingly, the electrode current collector 2 is a positive electrode current collector, the electrode coating 1 is a positive electrode coating (positive electrode active material layer), and the electrode active material is a positive electrode active material, which may include a positive electrode ternary material and / or lithium iron phosphate, wherein the positive electrode ternary material includes, for example, nickel cobalt manganese ternary material and / or nickel cobalt aluminum ternary material.

[0060] In this embodiment, by controlling the OI value of the positive active material (such as lithium iron phosphate) particles in the central region 11 of the positive electrode coating to be less than the OI value of the positive active material particles in the edge region 12, a positive electrode sheet with ordered stacking of positive active material particles and crystal structure is constructed. This can effectively improve the properties of the positive electrode sheet such as the uniformity of current density during battery cycling, which is beneficial to the performance of the positive electrode sheet under high areal density and compaction density conditions, and improve the cycle life and other performance of the battery.

[0061] The embodiments of this application may employ conventional positive current collectors in the art, for example, positive current collectors may include aluminum foil.

[0062] In this embodiment, an electrode coating 1 can be provided on one side surface of the electrode current collector 2, or an electrode coating 1 can be provided on both sides of the electrode current collector 2. When an electrode coating 1 is provided on both sides of the electrode current collector 2, the electrode coating 1 on one side surface can be an electrode coating 1 designed for the different OI values ​​of the aforementioned regions (i.e., the OI value of the electrode active material in the central region 11 is less than the OI value of the electrode active material in the edge region 12), or the electrode coating 1 on both sides of the electrode current collector 2 can be an electrode coating 1 designed for the different OI values ​​of the aforementioned regions.

[0063] Generally, the electrode coating 1 also includes a conductive agent and a binder. Based on the total mass of the electrode coating 1, the mass fraction of the electrode active material (i.e., the ratio of the mass of the electrode active material to the total mass of the electrode coating 1) can be 70% to 99%, for example, 70%, 75%, 80%, 85%, 90%, 93%, 95%, 97%, 99%, or any combination thereof. The mass fraction of the conductive agent can be 0.5% to 15%, for example, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 8%, 10%, 13%, 15%, or any combination thereof. The mass fraction of the binder can be 0.5% to 15%, for example, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 8%, 10%, 13%, 15%, or any combination thereof.

[0064] In this embodiment, the conductive agent in the electrode coating 1 can be a conventional conductive material in the art, such as one or more of carbon black, carbon nanotubes (CNT), acetylene black, graphene, Ketjen black, and carbon fiber.

[0065] In this embodiment, the binder in the electrode coating 1 can be a conventional adhesive material in the art. For example, when the electrode sheet is a negative electrode sheet, the binder may include one or more of the following: carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide-imide, polyvinyl alcohol, and sodium polyacrylate. When the electrode sheet is a positive electrode sheet, the binder may include one or more of the following: polyvinylidene fluoride (PVDF), polyvinylidene fluoride, polyvinyl fluoride, polyethylene, polypropylene, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, ethylene oxide-containing polymers, polyvinylpyrrolidone, and polyurethane.

[0066] This application embodiment also provides a method for preparing the above-mentioned electrode sheet, comprising the following steps: coating a slurry containing electrode active material onto the surface of an electrode current collector to form a wet film on the surface of the electrode current collector; wherein, along the length direction of the electrode coating, the wet film includes a central region and edge regions located on opposite sides of the central region; then, applying a magnetic field of a preset intensity to the central region and the edge regions of the wet film respectively, thereby inducing the electrode active material in the central region and the edge regions of the wet film to reach a preset OI value; wherein, the intensity of the magnetic field applied to the central region of the wet film is greater than the intensity of the magnetic field applied to the edge regions of the wet film; then, drying and rolling are performed to form an electrode coating on the wet film, thereby obtaining the electrode sheet.

[0067] In the preparation process of the above electrode sheet, the orientation of the electrode active material in each region is modified by magnetic induction of the electrode active material orientation under different magnetic field strengths, so that the OI value of the electrode active material in the central region is less than that of the electrode active material in the edge region. Combined with subsequent drying and rolling processes, an electrode sheet with an ordered stacking of the crystal structure of the electrode active material in the electrode coating is obtained.

[0068] To give a further example, the negative electrode is the main body of lithium storage. Graphite is usually used as the main negative electrode active material. Magnetic force is a non-contact force that can apply a magnetic field to the graphite main material to make it oriented and orderly. Specifically, the orientation degree (OI value) of the graphite can be controlled by conditions such as the magnitude of the magnetic field strength applied to each region. By applying magnetic fields of different strengths to different regions of the wet film, the graphite in each region will be oriented under the magnetic field. The deflection angle of the graphite particles under the action of different magnetic field strengths is different, thus making the graphite in each region have different orientation degrees.

[0069] In this embodiment, the magnetic field strength applied to the central region of the wet film is greater than that applied to the edge region of the wet film, so that the OI value of the graphite in the central region of the electrode coating is less than that of the graphite in the edge region. The graphite in the electrode coating forms an ordered ion transport channel through this oriented ordered arrangement structure, which helps to reduce the impedance of the electrode sheet and improve the problem of uneven current distribution in the electrode sheet during battery cycling, thereby improving the cycle life and other performance of the battery.

[0070] Specifically, during the preparation of the negative electrode, the intensity of the magnetic field applied to the central region of the wet film can be 0.1T to 20T. As an optional implementation, the intensity of the magnetic field applied to the central region of the wet film can be 0.2T to 2T.

[0071] Specifically, the edge region of the wet film includes multiple sub-regions distributed along the length of the wet film. In each pair of adjacent sub-regions, the magnetic field strength applied to the sub-region closer to the center is greater than the magnetic field strength applied to the sub-region farther from the center. This results in the negative electrode sheet having an edge region of the electrode coating that includes multiple sub-regions distributed along the length of the electrode coating. In each pair of adjacent sub-regions, the OI value of the electrode active material in the sub-region closer to the center is less than the OI value of the electrode active material in the sub-region farther from the center.

[0072] Specifically, the strength of the magnetic field applied to any sub-region of the wet film can be 0.1T to 20T. As an optional implementation, the strength of the magnetic field applied to any sub-region of the wet film can be 0.2T to 2T.

[0073] In the preparation process of the above electrode sheet, after drying and rolling, the wet film on the surface of the electrode current collector forms the electrode coating. The central region of the wet film forms the central region of the electrode coating, and the edge region of the wet film forms the edge region of the electrode coating. When the edge region of the wet film includes multiple sub-regions, each sub-region of the wet film forms the corresponding sub-region of the electrode coating.

[0074] In this embodiment of the application, when electrode coatings are formed on both the front and back surfaces of the electrode current collector, a slurry containing electrode active material can be coated on one side surface of the electrode current collector first, and then induced and dried by a magnetic field. Then, a slurry containing electrode active material can be coated on the other side surface of the electrode current collector, and then induced and dried by a magnetic field. Finally, the electrode sheet is rolled to obtain an electrode sheet.

[0075] In this embodiment, a conventional magnetic field application method can be used to apply a magnetic field to each area of ​​the wet film. Specifically, a gaussmeter can be used to detect the magnetic field strength on the surface of the wet film, and the measured value is the magnetic field strength experienced by the wet film.

[0076] In the embodiments of this application, drying (baking) and rolling can also be conventional operations in the art, and there are no special restrictions on them.

[0077] In this embodiment, a slurry containing electrode active materials can be prepared using conventional methods in the art. For example, when the electrode sheet is a negative electrode sheet, the components used to form the negative electrode coating, such as the negative electrode active material, conductive agent, and binder, can be dispersed in a first solvent, such as deionized water and / or N-methylpyrrolidone (NMP), to prepare a negative electrode slurry (i.e., a slurry containing electrode active materials). This slurry is then coated onto the surface of the negative electrode current collector, and after processes such as magnetic field induction, drying, and rolling, a negative electrode sheet is obtained. When the electrode sheet is a positive electrode sheet, the components used to form the positive electrode coating, such as the positive electrode active material, conductive agent, and binder, can be dispersed in a second solvent, such as N-methylpyrrolidone (NMP), to prepare a positive electrode slurry (i.e., a slurry containing electrode active materials). This slurry is then coated onto the surface of the positive electrode current collector, and after processes such as magnetic field induction, drying, and rolling, a positive electrode sheet is obtained.

[0078] In practice, a slurry containing electrode active materials can be prepared at a temperature of 20–45°C; and conventional coating equipment in the field, such as continuous coating equipment, can be used to coat the slurry containing electrode active materials onto the surface of the electrode current collector.

[0079] This application also provides a battery, including the above-described electrode sheet or an electrode sheet prepared according to the above-described electrode sheet preparation method. This battery has advantages corresponding to the above-described electrode sheet, which will not be described in detail here.

[0080] The battery in this application embodiment can be a lithium-ion battery (such as a lithium-ion power battery), a solar cell, or other novel energy storage battery.

[0081] Generally, a battery includes an electrolyte, a cell, and a package that encapsulates the cell. The electrolyte is injected into the cell within the package, as shown in Figure 5. The cell includes a positive electrode 3, a negative electrode 4, and a separator 5 located between the positive electrode 3 and the negative electrode 4.

[0082] In this embodiment of the application, at least one of the positive electrode 3 and the negative electrode 4 is an electrode sheet designed for the different OI values ​​of the aforementioned regions. That is, the positive electrode 3 can be an electrode sheet designed for the different OI values ​​of the aforementioned regions (i.e., the OI value of the positive active material in the central region of the positive electrode coating is less than the OI value of the positive active material in the edge region), or the negative electrode 4 can be an electrode sheet designed for the different OI values ​​of the aforementioned regions (i.e., the OI value of the negative active material in the central region of the negative electrode coating is less than the OI value of the negative active material in the edge region), or both the positive electrode 3 and the negative electrode 4 are electrode sheets designed for the different OI values ​​of the aforementioned regions.

[0083] Referring again to Figure 5, the positive electrode plate 3 includes a positive electrode tab 31, which is connected to the positive current collector. The positive electrode tab 31 is located at one end of the positive electrode plate 3 along its length (which is also the length of the positive current collector).

[0084] Referring again to Figure 5, the negative electrode plate 4 includes a negative electrode tab 41, which is connected to the negative electrode current collector. The negative electrode tab 41 is located at one end of the negative electrode plate 4 along its length (which is also the length of the negative electrode current collector).

[0085] Referring again to Figure 5, in the battery cell, the positive electrode tab 31 and the negative electrode tab 41 are located at opposite ends along the length of the battery cell; that is, the positive electrode tab 31 is located at one end along the length of the battery cell, and the negative electrode tab 41 is located at the other end along the length of the battery cell. The length directions of the battery cell, the positive electrode 3, and the negative electrode 4 are parallel to each other.

[0086] In this embodiment, the positive electrode tab 31 can be provided on the positive electrode sheet 3 in a conventional manner in the art. For example, the positive electrode tab 31 can be welded to the positive current collector or extended outward from the positive current collector. There are no particular limitations on this.

[0087] In this embodiment, the negative electrode tab 41 can be provided on the negative electrode sheet 4 in a conventional manner in the art. For example, the negative electrode tab 41 can be welded to the negative electrode current collector, or it can be formed by extending outward from the negative electrode current collector. There are no particular limitations on this.

[0088] Specifically, the battery cell can be a laminated battery cell, that is, the battery cell is composed of positive electrode 3, separator 5 and negative electrode 4 stacked alternately.

[0089] The electrolyte in this application embodiment can be a conventional electrolyte in the art. For example, the electrolyte is a non-aqueous electrolyte, which may specifically include an organic solvent and an electrolyte salt. The organic solvent may include, for example, ethylene carbonate and / or diethyl carbonate. When the battery is a sodium-ion battery, the electrolyte salt may include a lithium salt, such as lithium hexafluorophosphate (LiPF6), but is not limited thereto.

[0090] In this embodiment, the separator 5 is used to separate the positive electrode 3 and the negative electrode 4 to prevent the positive electrode 3 and the negative electrode 4 from short-circuiting due to contact. Conventional separators in the art can be used in this embodiment, and there are no special restrictions.

[0091] In this embodiment, the battery cell can be packaged using conventional encapsulation (shell) materials in the art, and the battery can be a conventional battery type and structure in the art. For example, the battery can be a blade battery, but it is not limited to this.

[0092] The embodiments of this application can assemble components such as the positive electrode 3, the separator 5, and the negative electrode 4 into a battery using conventional methods in the art, and there are no particular limitations on this.

[0093] This application also provides an electrical device including the battery described above. This electrical device has advantages corresponding to the electrode plates described above, which will not be elaborated further.

[0094] The electrical equipment used in the embodiments of this application can be conventional electrical equipment in the art, such as power equipment (e.g., electric vehicles, electric cars), electronic equipment (e.g., mobile phones, tablets, laptops, digital cameras, etc.), wearable devices (e.g., watches, bracelets, VR glasses, etc.), energy storage power stations, etc., and there are no special limitations on this.

[0095] In this embodiment of the application, the position and width of the central region and each sub-region in the electrode coating, as well as the number of sub-regions, can be measured by means of scanning electron microscopy (SEM), XRD analysis, etc. For example, by using SEM to inspect the surface of the electrode coating, the position and width of the central region, the number of sub-regions, and the position and width of each sub-region can be determined based on the different gray levels and colors (such as darker or whiter) exhibited by each region. Alternatively, the OI value of different regions can be tested by XRD, and the different regions of the electrode coating can be determined based on the OI value measurement results.

[0096] In this embodiment, X-ray diffraction (XRD) analysis can be performed on each region of the electrode coating to measure the OI value of the electrode active material in each region. Taking the OI value of the negative electrode active material as an example, the OI value represents the orientation degree of the crystal structure of the negative electrode active material particles. In the XRD analysis results of a certain region of the electrode coating, I1 is the XRD peak intensity of the direction in which active ions (such as lithium ions) are embedded in the crystal structure of the negative electrode active material particles, and I2 is the XRD peak intensity of the crystal direction perpendicular to I1, where active ions are less likely to be embedded (that is, the crystal direction in which active ions are less likely to be embedded is perpendicular to the direction in which active ions are embedded in the crystal structure of the negative electrode active material particles). Then, the orientation value of the internal crystal structure of the negative electrode active material particles (i.e., the OI value of the negative electrode active material) = I2 / I1, and the OI value > 0. Taking the negative electrode sheet using graphite as the negative electrode active material as an example, XRD analysis was performed on each region of the negative electrode coating. In the XRD analysis results, I1 is the peak intensity of the 110 crystal direction of graphite, I2 is the peak intensity of the 004 crystal direction of graphite, and the OI value of graphite = I2 / I1. The OI value of graphite can characterize the degree of order of the arrangement of graphite particles crystal structure (the smaller the OI value, the higher the degree of order (perpendicularity)).

[0097] Furthermore, taking the positive electrode sheet using lithium iron phosphate as the positive electrode active material as an example, XRD analysis was performed on each region of the positive electrode coating. In the XRD analysis results, I1 is the 020 crystal orientation peak intensity of lithium iron phosphate, I2 is the 200 crystal orientation peak intensity of lithium iron phosphate, and the OI value of lithium iron phosphate = I2 / I1.

[0098] In this embodiment of the application, the process of testing the areal density of the electrode coating may include: taking an electrode sheet sample, testing the total mass m1 of the electrode sheet sample and the surface area S of one side of the electrode sheet sample in the thickness direction; then scraping off the electrode coating on the electrode sheet sample, testing the mass m2 of the obtained electrode current collector, and then the areal density of the electrode coating = (m1-m2) / S.

[0099] In this embodiment, the compaction density of the electrode coating = the areal density of the electrode coating / the total thickness of the electrode coating. The testing process for the areal density of the electrode coating is as described above. The testing process for the total thickness of the electrode coating may include: taking an electrode sheet sample and testing the total thickness T1 of the electrode sheet sample (T1 = total thickness of the electrode coating + thickness of the electrode current collector; when both the front and back surfaces of the electrode current collector are respectively provided with electrode coatings, the total thickness of the electrode coating = the thickness of the electrode coating on one side of the electrode current collector + the thickness of the electrode coating on the other side of the electrode current collector); then scraping off the electrode coating on the electrode sheet sample and testing the thickness T2 of the obtained electrode current collector. Then the total thickness of the electrode coating = T1 - T2.

[0100] In practice, a micrometer can be used to measure the average thickness T1 of the electrode sheet and the average thickness T2 of the electrode current collector.

[0101] In practice, the battery can be disassembled to obtain the electrode sheet, and then the OI value of different regions in the electrode coating of the electrode sheet, as well as the areal density and compaction density of the electrode coating, can be tested.

[0102] The present application will be further described below through specific embodiments. In the following embodiments, the relevant testing processes such as magnetic field strength, areal density and compaction density of electrode coating, XRD test of graphite (graphite OI value = I2 / I1, I1 is the peak intensity of graphite in the 110 crystal direction, and I2 is the peak intensity of graphite in the 004 crystal direction), and XRD test of lithium iron phosphate (lithium iron phosphate OI value = I2 / I1, I1 is the peak intensity of lithium iron phosphate in the 020 crystal direction, and I2 is the peak intensity of lithium iron phosphate in the 200 crystal direction) are as described above, and will not be repeated below.

[0103] Example 1

[0104] 1. Preparation of negative electrode sheet

[0105] (1) Mix graphite, carbon black, CMC and SBR in a mass ratio of 100:1:1.6:3.3, add deionized water and NMP, stir evenly, and prepare a negative electrode slurry;

[0106] (2) A continuous coating device is used to coat the negative electrode paste onto one side surface of the copper foil. A magnetic field with a strength of H0 = 0.552T is applied to the central region (width L0 = 50cm) of the formed wet film; a magnetic field with a strength of H1 = 0.38T is applied to the first sub-region (width L1 = 150cm) closest to the center of the wet film; a magnetic field with a strength of H2 = 0.254T is applied to the second sub-region (width L2 = 230cm) located on the side away from the center of the first sub-region; and a magnetic field with a strength of H2 is applied to the side away from the center of the second sub-region. A magnetic field with a strength of H3 = 0.119T was applied to the third sub-region (L3 = 140cm) on one side of the domain. The orientation of graphite in each region was induced by the applied magnetic field. The induction time was about 5 minutes. During the induction, the magnetic field was kept uniform and stable. After the induction was completed, the wet film was dried to form a coating layer. As shown in Figure 2, there are three sub-regions on opposite sides of the central region, namely the first, second and third sub-regions. During the magnetic field induction process, a magnetic field was applied to each sub-region according to the above magnetic field strength.

[0107] (3) Then, the coating, magnetic field induction and drying process of step (2) above is repeated on the other side of the copper foil to form a coating layer on both the front and back surfaces of the copper foil. After rolling, a negative electrode sheet with a negative electrode coating formed on both the front and back surfaces of the copper foil is obtained.

[0108] The structure of the negative electrode sheet is shown in Figures 1 and 2. The negative electrode coating on either side of the copper foil includes a central region 11 and edge regions 12 on opposite sides of the central region. Each edge region 12 on either side of the central region has three sub-regions, namely the first sub-region 121, the second sub-region 122, and the third sub-region 123, which are distributed sequentially along the direction from the central region 11 to the edge region 12 (the outer edge of the third sub-region 123 away from the central region is the outer edge of the negative electrode coating on one side in its length direction). The length of the central region 11 in the width direction of the positive electrode coating and the length of each sub-region in the width direction of the positive electrode coating are basically equal to the width of the negative electrode sheet.

[0109] Among them, the width of the central region 11 of the negative electrode coating is L0 = 50cm along the length of the negative electrode coating, the width of the first sub-region 121 along the length of the negative electrode coating is L1 = 150cm, the width of the second sub-region 122 along the length of the negative electrode coating is L2 = 230cm, and the width of the third sub-region 123 along the length of the negative electrode coating is L3 = 140cm.

[0110] The OI value of graphite in each region of the negative electrode coating, the areal density of the negative electrode coating, the compaction density of the negative electrode coating, and the porosity of the negative electrode coating are measured and are shown in Table 1.

[0111] 2. Preparation of the positive electrode sheet

[0112] Lithium iron phosphate, CNT, carbon black, and PVDF were mixed in a mass ratio of 100:0.3:0.5:2.5, and NMP was added. The mixture was stirred evenly to prepare a positive electrode slurry.

[0113] A positive electrode slurry is coated onto both sides of an aluminum foil. After drying and rolling, a positive electrode coating is formed on both sides of the aluminum foil, thus producing a positive electrode sheet. The areal density of the positive electrode coating is 500 g / m³. 2 .

[0114] 3. Battery assembly

[0115] Positive electrode, separator, and negative electrode are alternately stacked to form a stacked cell, and electrolyte is injected to assemble it into a pouch battery (design capacity of 120Ah). The electrolyte composition is as follows: the organic solvent is a mixture of ethylene carbonate and diethyl carbonate in a 1:1 volume ratio, and the LiPF6 concentration in the electrolyte is 1 mol / L. The stacked structure of the positive electrode 3, separator 5, and negative electrode 4 in the stacked cell is shown in Figure 5. The positive electrode tab 31 of the positive electrode 3 is located at one end of the length direction of the cell, and the negative electrode tab 41 of the negative electrode 4 is located at the other end of the length direction of the cell.

[0116] Example 2: The difference from Example 1 is that the magnetic field strength applied to the central region of the wet film is H0 = 0.431T, the magnetic field strength applied to the first sub-region is H1 = 0.32T, the magnetic field strength applied to the second sub-region is H2 = 0.263T, and the magnetic field strength applied to the third sub-region is H3 = 0.1T. The OI values ​​of graphite in each region of the negative electrode coating in the obtained electrode sheet are shown in Table 1; the remaining steps and conditions are the same as in Example 1.

[0117] Example 3: The difference from Example 1 is that the magnetic field strength applied to the central region of the wet film is H0 = 0.33T, the magnetic field strength applied to the first sub-region is H1 = 0.272T, the magnetic field strength applied to the second sub-region is H2 = 0.16T, and the magnetic field strength applied to the third sub-region is H3 = 0T. The OI values ​​of graphite in each region of the negative electrode coating in the obtained electrode sheet are shown in Table 1; the remaining steps and conditions are the same as in Example 1.

[0118] Comparative Example 1: The difference from Example 1 is that no magnetic field is applied during the preparation of the negative electrode sheet (i.e., in Comparative Example 1, after the negative electrode slurry is coated on both the front and back surfaces of the copper foil, it is dried and rolled to form a negative electrode coating and obtain a negative electrode sheet); the remaining steps and conditions are the same as in Example 1.

[0119] Comparative Example 2: The difference from Example 1 is that, during the preparation of the negative electrode sheet, the magnetic field strength applied to the central region of the wet film is H0 = 0.1T, the magnetic field strength applied to the first sub-region is H1 = 0.263T, the magnetic field strength applied to the second sub-region is H2 = 0.32T, and the magnetic field strength applied to the third sub-region is H3 = 0.431T. The OI values ​​of graphite in each region of the negative electrode coating in the obtained negative electrode sheet are shown in Table 1; the remaining steps and conditions are the same as in Example 1.

[0120] Comparative Example 3: The difference from Example 1 is that, during the preparation of the negative electrode sheet, the same magnetic field with a strength of 0.36T is applied to the entire area of ​​the wet film so that the OI value of graphite in each area of ​​the formed negative electrode coating is basically the same (the OI value of graphite in each area is about 20.2, see Table 1 for details); the remaining steps and conditions are the same as in Example 1.

[0121] Example 4

[0122] The difference between Example 4 and Example 1 is that a magnetic field is applied during the preparation of the positive electrode, but no magnetic field is applied during the preparation of the negative electrode. The remaining steps and conditions are the same as in Example 1.

[0123] The specific preparation process of the positive and negative electrode sheets in Example 4 is as follows:

[0124] 1. Preparation of negative electrode sheet

[0125] Graphite, carbon black, CMC, and SBR were mixed in a mass ratio of 100:1:1.6:3.3, and deionized water and NMP were added. The mixture was stirred evenly to prepare a negative electrode slurry.

[0126] The negative electrode slurry is coated on both the front and back surfaces of a copper foil. After drying and rolling, a negative electrode coating is formed on both the front and back surfaces of the copper foil, thus producing a negative electrode sheet.

[0127] 2. Preparation of the positive electrode sheet

[0128] (1) Mix lithium iron phosphate, CNT, carbon black and PVDF in a mass ratio of 100:0.3:0.5:2.5, add NMP, stir evenly, and prepare a positive electrode slurry;

[0129] (2) A positive electrode slurry is coated on one side of an aluminum foil using a continuous coating equipment. A magnetic field with a strength of H0 = 0.552T is applied to the central region (width L0 = 50cm) of the formed wet film, a magnetic field with a strength of H1 = 0.38T is applied to the first sub-region (width L1 = 150cm) closest to the central region of the wet film, a magnetic field with a strength of H2 = 0.254T is applied to the second sub-region (width L2 = 230cm) located on the side away from the central region of the first sub-region, and a magnetic field with a strength of H3 = 0.119T is applied to the third sub-region (L3 = 140cm) located on the side away from the central region of the second sub-region. The orientation of graphite in each region is induced by the applied magnetic field. The induction time is about 5 minutes. During the induction, the magnetic field is kept uniform and stable. After the induction is completed, the wet film is dried to form a coating layer.

[0130] (3) Then, the coating, magnetic field induction and drying process of step (2) above is repeated on the other side of the aluminum foil to form coating layers on both the front and back surfaces of the aluminum foil. After rolling, a positive electrode sheet with a positive electrode coating formed on both the front and back surfaces of the aluminum foil is obtained.

[0131] The structure of the positive electrode sheet is shown in Figures 1 and 2. The positive electrode coating on either side of the aluminum foil includes a central region 11 and edge regions 12 on opposite sides of the central region 11. Each edge region 12 on either side of the central region 11 has three sub-regions, namely the first sub-region 121, the second sub-region 122, and the third sub-region 123, which are distributed sequentially along the direction from the central region 11 to the edge region 12 (the outer edge of the third sub-region 123 away from the central region 11 is the outer edge of the positive electrode coating on one side in its length direction). The length of the central region 11 in the width direction of the positive electrode coating and the length of each sub-region in the width direction of the positive electrode coating are basically equal to the width of the positive electrode sheet.

[0132] Among them, the width of the central region 11 of the positive electrode coating along the length of the positive electrode coating is L0 = 50cm, the width of the first sub-region 121 along the length of the positive electrode coating is L1 = 150cm, the width of the second sub-region 122 along the length of the positive electrode coating is L2 = 230cm, and the width of the third sub-region 123 along the length of the positive electrode coating is L3 = 140cm.

[0133] The measured OI value of lithium iron phosphate in each region of the positive electrode coating, the areal density of the positive electrode coating, the compaction density of the positive electrode coating, and the porosity of the positive electrode coating are shown in Table 2.

[0134] Comparative Example 4: The difference from Example 4 is that no magnetic field is applied during the preparation of the positive electrode sheet (i.e., in Comparative Example 3, after the positive electrode slurry is coated on both the front and back surfaces of the copper foil, it is dried and rolled to form a positive electrode coating and obtain a positive electrode sheet); the remaining steps and conditions are the same as in Example 4.

[0135] Comparative Example 5: The difference from Example 4 is that, during the preparation of the positive electrode sheet, the magnetic field strength applied to the central region of the wet film is H0 = 0.1T, the magnetic field strength applied to the first sub-region is H1 = 0.263T, the magnetic field strength applied to the second sub-region is H2 = 0.32T, and the magnetic field strength applied to the third sub-region is H3 = 0.431T. The OI values ​​of lithium iron phosphate in each region of the positive electrode coating in the obtained positive electrode sheet are shown in Table 2; the remaining steps and conditions are the same as in Example 4.

[0136] Comparative Example 6: The difference from Example 4 is that, during the preparation of the positive electrode, the same magnetic field with a strength of 0.32T is applied to the entire area of ​​the wet film so that the OI value of lithium iron phosphate in each area of ​​the formed negative electrode coating is basically the same (the OI value of lithium iron phosphate in each area is about 3.2, see Table 2 for details); the remaining steps and conditions are the same as in Example 1.

[0137] The DC impedance (DCIR) and long-cycle performance (number of cycles when capacity decays to 80%) of the batteries in each embodiment and comparative example were tested according to the following procedure. The results are shown in Tables 1 and 2.

[0138] (1) 50% SOC DC internal resistance test: At 25℃, the state of charge of the above soft pack battery was adjusted to 50% SOC, and then charged at 1.5C for 30s. The voltage drop of the soft pack battery was recorded, and its DC impedance DCIR was calculated.

[0139] (2) Long cycle test: At 25℃, discharge at 0.5C constant current to 2.0V, charge at 0.5C constant current to 3.8V, charge at 0.2C constant current to 3.8V, and continue cycling until the SOC is reduced to 80% of the original value. Record the number of cycles (see the number of long cycle cycles in Table 1 and Table 2).

[0140] Table 1

[0141] Table 2

[0142] As can be seen from Table 1, compared with Comparative Example 1, Examples 1 to 3 perform regional OI value regulation on the negative electrode sheet, so that the graphite OI value of the negative electrode coating decreases in a gradient from the edge region to the center region, which can significantly reduce the DC internal resistance of the battery and improve the long cycle life of the battery. At the same time, as can be seen from Examples 1 to 3, the lower the graphite OI value of each region, the lower the DC internal resistance of the battery and the better the long cycle effect.

[0143] Furthermore, as can be seen from Example 1 and Comparative Example 2, the graphite OI value in the negative electrode of Comparative Example 2 is designed in the opposite direction to that of Example 1 (the graphite OI value of the negative electrode coating increases in a gradient from the edge region to the center region), resulting in a significant decrease in its cycle performance. Compared to Comparative Example 2, the long cycle life of Example 1 is significantly improved. The reason for this is that in Example 1, by controlling the graphite OI value of the central region 11 to be lower than that of the edge region 12, the ion transport capability of the central region 11 can be improved, the conductivity of the central region 11 can be reduced, and the problem of the impedance of the central region 11 being higher than that of the edge region 12, caused by factors such as the structure and coating process of the negative electrode, as well as the resulting uneven current density of the negative electrode, can be improved. Specifically, it can improve the situation where the thickness of the negative electrode coating in the central region 11 is greater than that in the edge region 12 due to factors such as the coating process, thereby making the impedance of the central region 11 greater than that in the edge region 12. The first example addresses the issues of impedance in the central region 11 being lower than that in the edge region 12, leading to uneven current density in the negative electrode during battery charging and discharging. It also addresses the problem of the central region 11 having a higher impedance than the edge region 12 due to the absence of tabs at both ends of the cell's length, resulting in a lower current density in the central region 11 compared to the edge region 12, and consequently uneven current density in the negative electrode during charging and discharging. This improves battery cycle life and other performance characteristics. However, the second example, with its reverse design, struggles to reduce the impedance of the central region 11 and balance the current density between the central and edge regions 12. It fails to effectively overcome the uneven current distribution in the negative electrode during charging and discharging, resulting in a poor cycle life for the battery.

[0144] Furthermore, in Comparative Example 3, during the preparation of the negative electrode sheet, the same magnetic field was applied to each region of the wet film used to form the negative electrode coating, so as to reduce the OI value of graphite in the negative electrode coating by magnetic field induction. Although this can reduce the internal resistance of the battery to a certain extent, the OI value of graphite in each region of the negative electrode coating is basically the same (around 20.2). Due to the uneven current distribution of the negative electrode coating during the battery charging and discharging process, the cycle life of the battery is poor. In contrast to Comparative Example 3, Examples 1 to 3 can significantly improve the cycle life of the battery while maintaining a low internal resistance.

[0145] Taking Example 1 and Comparative Example 1 as examples, the cross-sections of the negative electrode coating in Example 1 and Comparative Example 1 were observed using an electron microscope (SEM) (the arrangement of graphite particles in the negative electrode coating was observed by SEM). The SEM image of the cross-section of the negative electrode coating in Example 1 is shown in Figure 3, and the SEM image of the cross-section of the negative electrode coating in Comparative Example 1 is shown in Figure 4. As can be seen from Figures 3 and 4, the deflection angles of the graphite particles in the negative electrode coatings of Example 1 and Comparative Example 1 are significantly different. The verticality of the graphite particles in the negative electrode coating of Example 1 is significantly improved, and the tortuosity is reduced, which reduces the resistivity and liquid phase diffusion resistance of the electrode sheet, thereby reducing the impedance and improving the uniformity of current distribution of the electrode sheet during battery cycling, thus improving the cycle life and other performance characteristics of the battery.

[0146] As can be seen from Table 2, compared with Comparative Example 4, Example 4 regionally modulates the OI value of the positive electrode, so that the OI value of lithium iron phosphate in the positive electrode coating decreases in a gradient from the edge region to the center region, which can significantly reduce the DC internal resistance of the battery and improve the long cycle life of the battery.

[0147] Furthermore, as can be seen from Examples 4 and 5, the lithium iron phosphate OI value in the positive electrode of Comparative Example 5 is designed in the opposite direction to that of Example 4 (the lithium iron phosphate OI value of the positive electrode coating increases in a gradient from the edge region to the center region), resulting in a significant decrease in its cycle performance. Compared to Comparative Example 4, the long cycle life of Example 4 is significantly improved. The reason for this is that in Example 1, by controlling the lithium iron phosphate OI value of the central region 11 to be lower than that of the edge region 12, the ion transport capacity of the central region 11 can be improved, the conductivity of the central region 11 can be reduced, and the problem of the impedance of the central region 11 being higher than that of the edge region 12 due to factors such as the structure and coating process of the positive electrode sheet, as well as the resulting uneven current density of the positive electrode sheet, can be improved. Specifically, it can improve the problem of the thickness of the positive electrode coating in the central region 11 being greater than that in the edge region 12 due to factors such as the coating process, thereby making the impedance of the central region 11 greater than that in the edge region 12. The first example addresses the issues of uneven current density in the positive electrode during battery charging and discharging due to the lower impedance of the central region 11 compared to the edge region 12, caused by the presence of positive and negative electrodes at opposite ends of the cell's length. This leads to a higher impedance in the central region 11 compared to the edge region 12, resulting in a lower current density in the central region 11 and uneven current density in the edge region 12. This, in turn, improves the battery's cycle life and other performance characteristics. However, the second example, a reverse design, struggles to reduce the impedance of the central region 11 and balance the current density between the central and edge regions 12. It fails to effectively overcome the uneven current distribution in the positive electrode during charging and discharging, resulting in a poor cycle life for the battery.

[0148] Furthermore, in Comparative Example 6, during the preparation of the negative electrode sheet, the same magnetic field was applied to each region of the wet film used to form the positive electrode coating to induce a reduction in the OI value of lithium iron phosphate in the positive electrode coating. Although this could reduce the internal resistance of the battery to some extent, the OI value of lithium iron phosphate in each region of the positive electrode coating was basically the same (around 0.32). Due to the uneven current distribution of the positive electrode coating during the battery charging and discharging process, the cycle life of the battery was poor. In contrast to Comparative Example 6, Example 4 was able to significantly improve the cycle life of the battery while maintaining a lower internal resistance.

[0149] Finally, it should be noted that 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. An electrode sheet, characterized by, The electrode includes an electrode current collector (2) and an electrode coating (1) located on at least one side surface of the electrode current collector (2), the electrode coating (1) comprising an electrode active material; Along the length direction of the electrode coating (1), the electrode coating (1) includes a central region (11) and edge regions (12) located on opposite sides of the central region (11), wherein the OI value of the electrode active material in the central region (11) is less than the OI value of the electrode active material in the edge regions (12).

2. The electrode sheet according to claim 1, characterized in that, The OI value of the electrode active material in the central region (11) is 0.001 to 200; And / or, the width L0 of the central region (11) in the length direction of the electrode coating (1) is greater than or equal to 1 cm.

3. The electrode pad of claim 2, wherein The OI value of the electrode active material in the central region (11) is 0.1 to 30.

4. The electrode pad of claim 1, wherein Each of the edge regions (12) includes a plurality of sub-regions distributed along the length direction of the electrode coating (1), wherein in every two adjacent sub-regions, the OI value of the electrode active material of the sub-region closer to the center region (11) is less than the OI value of the electrode active material of the sub-region farther from the center region (11).

5. The electrode pad of claim 4, wherein The ratio of the OI value of the electrode active material in the central region (11) to the OI value of the electrode active material in the sub-region closest to the central region (11) is 0.3 to 0.9; And / or, in every two adjacent sub-regions, the ratio of the OI value of the electrode active material in the sub-region closer to the central region to the OI value of the electrode active material in the sub-region farther from the central region is 0.3 to 0.9; And / or, the OI value of the electrode active material in any of the sub-regions is 0.001 to 200; And / or, the width of any of the sub-regions in the length direction of the electrode coating is greater than or equal to 1 cm.

6. The electrode pad of claim 5, wherein The OI value of the electrode active material in any of the sub-regions is 0.1 to 30.

7. The electrode sheet according to any one of claims 1 to 6, characterized by The length of the electrode coating (1) is 1cm to 10m.

8. The electrode sheet according to any one of claims 1 to 6, characterized by The electrode sheet is a negative electrode sheet (4), and the electrode active material includes graphite.

9. The electrode pad according to any one of claims 1 to 6, characterized in that The electrode sheet is a positive electrode sheet (3), and the electrode active material includes a positive ternary material and / or lithium iron phosphate.

10. The electrode sheet according to any one of claims 1 to 6, characterized by The porosity of the electrode coating (1) is 20% to 40%; and / or the compacted density of the electrode coating (1) is 1.3 g / cm 3 ~ 2 g / cm 3 ; and / or the areal density of the electrode coating (1) is 200 g / m 2 ~ 800 g / m 2 .

11. A method of producing the electrode sheet as claimed in any one of claims 1 to 10, characterized by, Includes the following steps: A slurry containing the electrode active material is applied to the surface of the electrode current collector (2) to form a wet film on the surface of the electrode current collector (2); wherein, along the length direction of the electrode coating (1), the wet film includes a central region (11) and edge regions (12) located on opposite sides of the central region (11); Then, a magnetic field of a preset intensity is applied to the central region (11) and the edge region (12) of the wet film, respectively, and the electrode active materials in the central region (11) and the edge region (12) of the wet film are induced by the magnetic field to reach a preset OI value; wherein, the intensity of the magnetic field applied to the central region (11) of the wet film is greater than the intensity of the magnetic field applied to the edge region (12) of the wet film. Then, the electrode sheet is dried and rolled to obtain the electrode sheet.

12. The method of producing an electrode sheet according to claim 11, wherein The strength of the magnetic field applied to the central region (11) of the wet film is 0.1T to 20T.

13. The method of producing an electrode sheet according to claim 12, wherein The strength of the magnetic field applied to the central region (11) of the wet film is 0.2T to 2T.

14. The method of producing an electrode sheet according to any one of claims 11 to 13, characterized by, The edge region (12) of the wet film includes a plurality of sub-regions distributed along the length of the wet film. In every two adjacent sub-regions, the magnetic field applied to the sub-region closer to the center region (11) is greater than the magnetic field applied to the sub-region farther from the center region (11).

15. The method of claim 14, wherein the electrode sheet is prepared by a method comprising: The strength of the magnetic field applied to any of the sub-regions of the wet film is 0.1T to 20T.

16. The method of claim 15, wherein the electrode sheet is prepared by a method comprising: The strength of the magnetic field applied to any of the sub-regions of the wet film is 0.2T to 2T.

17. A battery, wherein, This includes the electrode sheet as described in any one of claims 1-10 or the electrode sheet prepared according to the method described in any one of claims 11-16.

18. The battery of claim 17, wherein, The battery includes a cell, the cell includes a positive electrode (3) and a negative electrode (4), at least one of the positive electrode (3) and the negative electrode (4) is an electrode sheet as described in any one of claims 1-10 or an electrode sheet prepared according to the method of preparing an electrode sheet as described in any one of claims 11-16; The positive electrode includes a positive electrode tab (31), which is located at one end of the battery cell along its length. The negative electrode includes a negative electrode tab (41), which is located at the other end of the cell along its length.

19. An electrical device, comprising: Includes the battery as described in claim 17 or 18.

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