Pole piece manufacturing method and pole piece

Abstract

The invention discloses a pole piece manufacturing method and a pole piece, and relates to the technical field of batteries. The pole piece manufacturing method comprises the steps that a current collector is obtained, the current collector is provided with a coating area, and the coating area comprises an edge area and a middle area located on the inner side of the edge area; the coating area of the current collector is coated with active substance slurry, the active substance slurry comprises an active substance material and a dispersing agent, and the amount of the active substance material in the unit area of the edge area is lower than the amount of the active substance material in the unit area of the middle area; and drying the active substance slurry. When the active material slurry is coated, the amount of the active material in the unit area of the middle area is larger than the amount of the active material in the unit area of the edge area, so that the surface density of the active material in the edge area and the surface density of the active material in the middle area after drying tend to be consistent; and the thickness of the active material layer of the pole piece tends to be consistent, so that the problem of edge bulging is solved.

Description

Technical Field

[0001] This application relates to the field of battery technology, and more specifically, to electrode fabrication methods and electrodes. Background Technology

[0002] The electrode fabrication method in related technologies involves coating an active material slurry onto a current collector and then drying it, causing the dispersant in the slurry to evaporate and leaving the active material to form an active material layer. However, during the drying process, the active material slurry on the electrode dries at a faster rate at the edges than in the center. This causes the dispersant to flow from the center to the edges, carrying a certain amount of active material with it. Consequently, after drying, the edge areas of the electrode are thicker than the center areas, a phenomenon known as edge bulging. Edge bulging affects the performance of the electrode.

[0003] Therefore, this application is hereby submitted. Summary of the Invention

[0004] The purpose of this application is to provide a method for making electrode sheets and electrode sheets.

[0005] This application is implemented as follows: In a first aspect, this application provides a method for manufacturing electrode sheets, comprising: A current collector is obtained, the current collector having a coating area, the coating area including an edge area and a central area located inside the edge area; An active substance slurry is coated in the coating area of ​​the current collector, wherein the active substance slurry includes an active substance material and a dispersant, and the amount of active substance material per unit area in the edge area is lower than the amount of active substance material per unit area in the central area. Dry the active substance slurry.

[0006] In an optional embodiment, the step of coating the active substance slurry in the coating area of ​​the current collector includes: The first active substance slurry is applied to the central region; A second active substance slurry is applied to the edge area; The active material in the first active material slurry is the same as that in the second active material slurry, but the amount of active material in the first active material slurry per unit area is greater than that in the second active material slurry per unit area.

[0007] In an optional embodiment, the coating thickness of the first active substance slurry and the second active substance slurry is the same, and the mass fraction of the active substance material in the second active substance slurry is lower than the mass fraction of the active substance material in the first active substance slurry.

[0008] In an optional embodiment, the active material in both the first active material slurry and the second active material slurry is a positive electrode active material, the mass fraction of the active material in the first active material slurry is 52%~58%, and the mass fraction of the active material in the second active material slurry is 45%~53%.

[0009] In an optional embodiment, the active material in both the first active material slurry and the second active material slurry is a negative electrode active material, the mass fraction of the active material in the first active material slurry is 48%~53%, and the mass fraction of the active material in the second active material slurry is 36%~47%.

[0010] In an optional embodiment, the mass fraction of active material in the first active material slurry and the second active material slurry is equal, and the coating thickness of the first active material slurry is greater than the coating thickness of the second active material slurry.

[0011] In an optional embodiment, the step of coating the active substance slurry in the coating area of ​​the current collector includes: A first active substance slurry of uniform thickness is applied to the central and edge areas; A second active substance slurry is applied to the central region; The active material in the first active material slurry is the same as that in the second active material slurry.

[0012] In an optional embodiment, the active material in the active material slurry is a positive electrode active material, and the areal density of the active material layer composed of the active material after drying is 160 g / m³. 2 ~200g / m 2 ; Alternatively, the active material in the active material slurry is a negative electrode active material, and the areal density of the active material layer composed of the active material after drying is 70 g / m³. 2 ~110g / m 2 .

[0013] In an optional implementation, the width of the edge region is 10mm to 30mm.

[0014] Secondly, this application provides an electrode sheet, which is prepared by any of the electrode sheet manufacturing methods described in the foregoing embodiments.

[0015] This application has the following beneficial effects: The electrode fabrication method provided in this application includes: obtaining a current collector having a coating area, the coating area including an edge area and a central area located inside the edge area; coating an active material slurry in the coating area of ​​the current collector, wherein the active material slurry includes an active material and a dispersant, and the amount of active material per unit area in the edge area is lower than the amount of active material per unit area in the central area; and drying the active material slurry. In this application, by coating the active material slurry with a greater amount of active material per unit area in the central area than in the edge area, the active material in the central area is carried to the edge area by the dispersant during the subsequent drying process, ultimately making the areal density of the active material in the edge area and the central area more consistent, and the thickness of the active material layer of the electrode also more consistent, thereby improving the problem of edge bulging. Attached Figure Description

[0016] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a flowchart of an embodiment of the electrode fabrication method in this application; Figure 2 This is a schematic diagram of the coating area, edge area, and central area on the current collector in one embodiment of this application.

[0018] Explanation of key component symbols: 100 - current collector; 110 - coating area; 111 - edge area; 112 - central area. Detailed Implementation

[0019] In related technologies, during the drying of the active material slurry on the current collector in electrode fabrication, the dispersant in the edge region of the slurry layer evaporates rapidly, while the evaporation rate in the central region is relatively slower. This causes the dispersant to flow from the central region to the edge region during drying, carrying a certain amount of active material with it. Since the slurry thickness is often uniform during coating, the content of active material per unit area is essentially the same at different locations. However, the active material diffuses from the central region to the edge region during drying, resulting in a thicker layer of active material at the edge of the electrode after drying—a phenomenon known as edge bulging. While it is theoretically feasible to change the temperature field distribution to make the drying rate of the edge region the same as that of the central region, achieving high precision in temperature field control is difficult, thus increasing the technological complexity. Related technologies thin the edges of the active material layer on the electrode to eliminate edge bulging. However, this can easily lead to a reduction in the total amount of active material in the electrode, causing the cell design capacity to fail to meet the design target. At the same time, since the degree of electrode thinning is difficult to control, and both positive and negative electrodes undergo thinning operations during the production process, inconsistent thinning often results in an excess or deficiency of negative electrode at the edges of the positive and negative electrodes, which in turn causes lithium plating abnormalities and affects the safety performance of the cell.

[0020] Therefore, this application provides an electrode fabrication method. By making the amount of active material per unit area in the central region greater than that in the edge region during the coating process, the phenomenon of active material migrating from the central region to the edge region during the drying process can make the thickness of the final active material layer more uniform at the edge and center, thereby improving the bulging edge problem.

[0021] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0022] The features and performance of this application will be further described in detail below with reference to the embodiments.

[0023] Figure 1 This is a flowchart illustrating an electrode fabrication method according to one embodiment of this application. The electrode fabrication method provided in this embodiment can be used to fabricate both positive and negative electrode sheets. Figure 1 As shown, the electrode manufacturing method includes: Step S100: Obtain current collector 100. Current collector 100 has a coating area 110. The coating area 110 includes an edge area 111 and a central area 112 located inside the edge area 111.

[0024] Figure 2 This is a schematic diagram of the coating area 110, edge area 111, and central area 112 on the current collector 100 in one embodiment of this application. Figure 2 As shown, in this embodiment, the coating area 110 is the area on the current collector 100 used for coating the active material slurry, and it is also the area on the final electrode where the active material layer is formed. The edge area 111 is the area extending along the edge of the coating area 110. The width of the edge area 111 can be selected from 10mm to 30mm, for example, any value among 10mm, 15mm, 20mm, 25mm, and 30mm, or any value between any two values. It should be understood that the width direction of the edge area 111 is perpendicular to the extension direction of the corresponding edge of the coating area 110. In this embodiment, the coating area 110 is smaller than the surface of the current collector 100, that is, there is a gap between the edge area 111 and the edge of the current collector 100; in other optional embodiments, the coating area 110 may also be distributed over the entire surface of the current collector 100.

[0025] When it is necessary to prepare a positive electrode sheet, a positive current collector is obtained. The type of positive current collector includes, but is not limited to, aluminum foil and carbon-coated composite aluminum foil. When it is necessary to prepare a negative electrode sheet, the obtained current collector 100 is a negative current collector. The type of negative current collector includes, but is not limited to, copper foil, carbon-coated composite copper foil, and PP composite copper foil.

[0026] In step S200, an active substance slurry is coated in the coating area 110 of the current collector 100, wherein the active substance slurry includes an active substance material and a dispersant, and the amount of active substance material per unit area in the edge region 111 is lower than the amount of active substance material per unit area in the central region 112.

[0027] It should be understood that, in the preparation of the positive electrode sheet, the active material in the active material slurry is a positive electrode active material, including but not limited to lithium iron phosphate, ternary materials, and lithium cobalt oxide; in the preparation of the negative electrode sheet, the active material in the active material slurry is a negative electrode active material, including but not limited to graphite and hard carbon. Dispersants include deionized water and N-methylpyrrolidone (NMP).

[0028] By setting the amount of active material per unit area in the edge region 111 to be lower than that in the middle region 112, the diffusion of active material to the edge during the subsequent drying process can make the areal density of active material in the middle region 112 and the edge region 111 more consistent, thereby improving the problem of drum edge.

[0029] Optionally, step S200 includes the following steps: Step S201: Apply the first active substance slurry to the central region 112; Step S202: Apply a second active material slurry to the edge region 111.

[0030] The active material in the first active material slurry is the same as that in the second active material slurry, but the amount of active material in the first active material slurry per unit area is greater than that in the second active material slurry per unit area.

[0031] It should be understood that in this embodiment, steps S201 and S202 are performed in separate steps; the order of steps S201 and S202 can be reversed, for example, the second active substance slurry is applied first, and then the first active substance slurry is applied.

[0032] In an optional embodiment, the coating thickness of the first active material slurry and the second active material slurry is the same, and the mass fraction of the active material in the second active material slurry is lower than that in the first active material slurry. Optionally, when the active materials in both the first and second active material slurries are positive electrode active materials, the mass fraction of the active material in the first active material slurry is 52% to 58%, for example, any value among 52%, 53%, 54%, 55%, 56%, 57%, and 58%, or a value between any two values; the mass fraction of the active material in the second active material slurry is 45% to 53%, for example, any value among 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%, and 53%, or a value between any two values. Optionally, when both the active material in the first active material slurry and the second active material slurry is a negative electrode active material, the mass fraction of the active material in the first active material slurry is 48% to 53%, for example, any value among 48%, 49%, 50%, 51%, 52%, and 53%, or the value between any two values; the mass fraction of the active material in the second active material slurry is 36% to 47%, for example, any value among 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, and 47%, or the value between any two values.

[0033] In another optional embodiment, the mass fraction of active material in the first active material slurry and the second active material slurry is equal, and the coating thickness of the first active material slurry is greater than that of the second active material slurry. For example, the mass fraction of active material in both the first and second active material slurries is 52% to 58%, and the coating thickness of the first active material slurry is 5% to 20% greater than that of the second active material slurry.

[0034] In steps S201 and S202 above, the central region 112 and the edge region 111 are coated in stages, that is, one of the central region 112 and the edge region 111 is coated in the first step, and the other of the central region 112 and the edge region 111 is coated in the second step; optionally, the two steps can also be performed simultaneously. In other embodiments, the order of the two coating steps can be adjusted. For example, in other embodiments, step S200 may include: Step S211: Apply a first active material slurry of uniform thickness to the central region 112 and the edge region 111; Step S212: Apply the second active material slurry to the central region 112.

[0035] The active material in the first active material slurry is the same as that in the second active material slurry.

[0036] In this embodiment, step S211 can be considered as the first coating, and step S212 can be considered as the second coating. Since the central region 112 undergoes one more coating step than the edge region 111, the amount of active material per unit area in the central region 112 is greater than that in the edge region 111. In steps S211 and S212, the concentrations of the active material in the first and second active material slurries can be the same or different.

[0037] Optionally, when the active material is a positive electrode active material, the coating amount of the active material slurry is based on the areal density of the active material layer formed after drying being 160 g / m². 2 ~200g / m 2 Design is then performed. Optionally, when the active material is a negative electrode active material, the coating amount of the active material slurry is based on a surface density of 70 g / m² for the active material layer formed after drying. 2 ~110g / m 2 To carry out the design.

[0038] Step S300: Dry the active substance slurry.

[0039] After drying, the electrode sheet is obtained.

[0040] The table below shows the process parameters and the thickness parameters of the active material layer of the electrode sheet when different mass fractions of active material are used in the edge region 111 during the fabrication of the positive electrode sheet.

[0041]

[0042] In the table above, the solid content of the slurry in the central region 112 is the mass fraction of the active material in the active material slurry coated in the central region 112; the solid content of the slurry in the edge region 111 is the mass fraction of the active material in the active material slurry coated in the edge region 111. In the embodiment shown in the table above, the coating thicknesses of the central region 112 and the edge region 111 are the same. It can be seen that when the solid content of the active material slurry in the edge region 111 and the central region 112 is the same (both are 55%), the final active material layer has a large difference in thickness between the edge and the center, reaching 8 μm; while as the solid content of the slurry in the edge region 111 decreases, the blistering phenomenon is alleviated.

[0043] The table below shows the process parameters and the thickness parameters of the active material layer of the electrode sheet when different mass fractions of active material are used in the edge region 111 during the fabrication of the negative electrode sheet.

[0044]

[0045] In the embodiments shown in the table above, the coating thickness of the central region 112 and the edge region 111 is consistent. It can be seen that when the solid content of the active material slurry in the edge region 111 and the central region 112 is consistent (both are 50%), the final active material layer has a large difference in thickness between the edge and the center, reaching 9 μm; while as the solid content of the slurry in the edge region 111 decreases, the bulging phenomenon is alleviated.

[0046] In summary, the electrode fabrication method provided in this application includes: obtaining a current collector 100, the current collector 100 having a coating region 110, the coating region 110 including an edge region 111 and a central region 112 located inside the edge region 111; coating an active material slurry in the coating region 110 of the current collector 100, wherein the active material slurry includes an active material and a dispersant, the amount of active material per unit area in the edge region 111 is lower than the amount of active material per unit area in the central region 112; and drying the active material slurry. In this application, by ensuring that the amount of active material per unit area in the central region 112 is greater than that in the edge region 111 during the coating of the active material slurry, the active material in the central region 112 is carried to the edge region 111 by the dispersant during the subsequent drying process. This results in the areal density of the active material in the edge region 111 and the central region 112 becoming more consistent, and the thickness of the active material layer of the electrode also becoming more consistent, thereby improving the problem of bulging edges.

[0047] The above are merely preferred embodiments of this application and are not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for manufacturing electrode sheets, characterized in that, include: A current collector is obtained, the current collector having a coating area, the coating area including an edge area and a central area located inside the edge area; An active substance slurry is coated in the coating area of ​​the current collector, wherein the active substance slurry comprises an active substance material and a dispersant, and the amount of the active substance material per unit area in the edge region is lower than the amount of the active substance material per unit area in the central region; The active substance slurry is dried.

2. The electrode fabrication method according to claim 1, characterized in that, The step of coating the current collector with an active substance slurry includes: A first active substance slurry is applied to the central region; A second active substance slurry is applied to the edge region; The active material in the first active material slurry is the same as that in the second active material slurry, and the amount of active material in the first active material slurry per unit area is greater than that in the second active material slurry per unit area.

3. The electrode fabrication method according to claim 2, characterized in that, The first active substance slurry and the second active substance slurry have the same coating thickness, and the mass fraction of the active substance material in the second active substance slurry is lower than the mass fraction of the active substance material in the first active substance slurry.

4. The electrode fabrication method according to claim 3, characterized in that, Both the first and second active material slurries contain positive electrode active material materials. The mass fraction of the active material in the first active material slurry is 52% to 58%, and the mass fraction of the active material in the second active material slurry is 45% to 53%.

5. The electrode fabrication method according to claim 3, characterized in that, Both the first and second active material slurries contain negative electrode active materials. The mass fraction of the active material in the first active material slurry is 48% to 53%, and the mass fraction of the active material in the second active material slurry is 36% to 47%.

6. The electrode fabrication method according to claim 2, characterized in that, The mass fraction of active material in the first active material slurry and the second active material slurry is equal, and the coating thickness of the first active material slurry is greater than the coating thickness of the second active material slurry.

7. The electrode fabrication method according to claim 1, characterized in that, The step of coating the current collector with an active substance slurry includes: A first active substance slurry of uniform thickness is applied to the central region and the edge region; A second active substance slurry is applied to the central region; The active material in the first active material slurry is the same as that in the second active material slurry.

8. The method for manufacturing an electrode according to any one of claims 1-7, characterized in that, The active material in the active material slurry is a positive electrode active material, and the areal density of the active material layer composed of the active material after drying is 160 g / m³. 2 ~200g / m 2 ; Alternatively, the active material in the active material slurry is a negative electrode active material, and the areal density of the active material layer composed of the active material after drying is 70 g / m³. 2 ~110g / m 2 .

9. The method for manufacturing an electrode according to any one of claims 1-7, characterized in that, The width of the edge region is 10mm to 30mm.

10. An electrode sheet, characterized in that, The electrode is prepared by the electrode manufacturing method according to any one of claims 1-9.

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