Electrode sheet and battery cell

Abstract

The present application provides an electrode sheet and a battery cell. The electrode sheet comprises a current collector and an active material layer arranged on at least one side surface of the current collector; and the electrode sheet comprises a single-sided area, one side of the current collector located in the single-sided area is provided with the active material layer, and the active material layer located in the single-sided area is provided with grooves. By means of forming the grooves on the active material layer located in the single-sided area, the bending degree of the single-sided area of the electrode sheet can be reduced, and when the electrode sheet is used to assemble the battery cell, the adhesion between the single-sided area of the electrode sheet and a separator is improved, thereby shortening a transport pathway of lithium ions of the battery cell during charge and discharge, and alleviating problems such as lithium precipitation and black spots.

Description

A pole piece and a battery cell Technical Field

[0001] The present application relates to the technical field of lithium-ion batteries, and in particular to a pole piece and a battery cell. Background Art

[0002] Lithium-ion batteries have become the primary power source for consumer electronics and electric vehicles due to their numerous advantages. With growing consumer demand, lithium-ion batteries are gradually developing towards fast charging, long life, high energy density, and high safety.

[0003] To increase the energy density of lithium-ion batteries, the compaction density of the electrode is usually increased. However, due to the different stresses on the two sides of the single-sided area of ​​the battery electrode, the electrode bends toward the side without the active material layer. The greater the compaction density, the greater the bend of the electrode. When the electrode is assembled into a battery cell, the greater the bend, the worse the adhesion between the electrode and the separator, creating a gap between the two. This results in a longer lithium ion transmission path during the battery cell's charge and discharge process, which can easily cause problems such as lithium deposition and black spots. Summary of the Invention

[0004] In view of this, the present application provides a pole piece that solves the problems of large pole piece bending and poor adhesion between the pole piece and the diaphragm. The present application also provides a battery cell including the pole piece.

[0005] In order to achieve the above objectives, this application provides the following technical solutions:

[0006] A pole piece includes a current collector and an active material layer provided on at least one side of the current collector, wherein the pole piece includes a single-sided area, and the active material layer is provided on one side of the current collector located in the single-sided area.

[0007] The active material layer located in the single-side area is provided with a groove.

[0008] Optionally, the area of ​​the active material layer in the single-sided region where the groove is set is S1, and the area of ​​the active material layer in the single-sided region is S2, wherein S1 and S2 satisfy: S1 = (0.05-0.7) * S2.

[0009] Optional,

[0010] In a direction perpendicular to the active material layer, the depth of the groove is L, wherein 3 μm≤L≤2000 μm; and / or,

[0011] The outer diameter of the notch of the groove is D, wherein 0.2 mm ≤ D ≤ 5 mm.

[0012] Optionally, the depth of the groove in a direction perpendicular to the active material layer is L, and the bending radius of the pole piece is R, wherein L and R satisfy: L:R≥0.005.

[0013] Optionally, a protrusion is provided on the side of the current collector in the single-sided area facing away from the active material layer, and a protruding direction of the protrusion is the same as a recessed direction of the groove.

[0014] Optionally, the protrusion height of the protrusion is the same as the recessed depth of the groove.

[0015] Optionally, there are at least two protrusions, and a recessed portion is formed between adjacent protrusions.

[0016] Optionally, in a direction perpendicular to the active material layer,

[0017] The depth of the protrusion is M, wherein 2 μm≤M≤1700 μm; and / or,

[0018] The depth of the recessed portion is N, wherein 0.05 mm ≤ N ≤ 1.5 mm.

[0019] Optionally, the bottom of the groove is a plane or an arc surface, and / or

[0020] The side wall of the groove is a plane or an arc surface.

[0021] Optionally, there are at least two grooves, and / or

[0022] The notch of the groove is at least one of circular, polygonal and elliptical.

[0023] A battery cell comprises a negative electrode sheet, a positive electrode sheet and a separator arranged between the negative electrode sheet and the positive electrode sheet, wherein the positive electrode sheet and / or the negative electrode sheet is any one of the electrode sheets described above.

[0024] Optionally, adhesive tape is provided on both sides of the battery cell in the first direction, and the adhesive tape at least covers a portion of the protrusions in the single-sided area.

[0025] Optionally, the single-sided area is located outside the battery cell, and the groove of the single-sided area is recessed in a direction away from the center of the battery cell.

[0026] Optionally, the battery cell further includes a negative electrode tab connected to the negative electrode sheet and a positive electrode tab connected to the positive electrode sheet, and in the second direction, the projection of the groove in the single-sided area overlaps with the projection of at least one of the positive electrode tab and the negative electrode tab.

[0027] Optionally, in the second direction, the projection of the groove of the single-sided area and the projection of the folded section of the diaphragm at least partially overlap.

[0028] Optionally, the battery cell is a wound battery cell, and in the second direction, the projection of the groove in the single-sided area of ​​the positive electrode sheet covers the projection of the end of the active material layer of the negative electrode sheet.

[0029] Optionally, the peeling force between the active material layer and the separator in the single-sided area with the groove is F1, and the peeling force between the active material layer and the separator without the groove is F2, wherein F1 and F2 satisfy: F1>F2.

[0030] Optionally, F1 and F2 satisfy: F1 = (1.1-5) * F2.

[0031] Optionally, the battery cell is a wound battery cell, and the groove is located in a straight section and / or an arc section of the wound battery cell.

[0032] The electrode provided in the present application has a groove formed in the active material layer on a single side, which reduces the bending degree of the electrode on the single side, thereby improving the adhesion between the electrode on the single side and the diaphragm when the electrode is assembled into a battery cell, thereby shortening the transmission path of lithium ions during the charge and discharge process of the battery cell, and reducing problems such as lithium plating and black spots. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are merely embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without any creative work.

[0034] FIG1 is a front view of a pole piece provided by the prior art;

[0035] FIG2 is a front view of a pole piece provided in this embodiment;

[0036] Figure 3 is a top view of the pole piece;

[0037] FIG4 is a partial enlarged view of FIG2;

[0038] FIG5 is a top view of the electrode after the groove is provided;

[0039] FIG6 is a partial enlarged view of the electrode with protrusions;

[0040] Figure 7 is a front view of the battery cell;

[0041] Figure 8 is a schematic diagram of 3D depth synthesis at the groove;

[0042] FIG9 is a line graph showing the capacity ratio and cycle number between the experimental group and the control group;

[0043] FIG10 is a line graph showing the relationship between thickness expansion and cycle number for the experimental group and the control group.

[0044] In Figures 1 to 10: 1-pole sheet, 2-groove, 3-protrusion, 4-positive electrode sheet, 5-negative electrode sheet, 6-separator, 7-positive electrode tab, 8-negative electrode tab, 9-straight section, 10-arc section; 101-single-sided area, 102-double-sided area, 103-current collector, 104-active material layer. DETAILED DESCRIPTION

[0045] The present application provides a pole piece and a battery cell including the pole piece.

[0046] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0047] As shown in Figures 2 to 10, an embodiment of the present application provides a pole piece 1, wherein the pole piece 1 and the diaphragm 6 constitute a battery cell, and the battery cell, the housing, and the components constitute a battery. The battery is installed on an electrical device and provides electrical energy to the electrical device. The pole piece 1 mainly includes a current collector 103 and an active material layer 104 disposed on at least one side of the current collector 103. The pole piece 1 includes a single-sided area 101, and the active material layer 104 is disposed on one side of the current collector 103 located in the single-sided area 101. For example, taking a wound battery cell as an example, the pole piece 1 of the wound battery cell includes a single-sided area 101 and a double-sided area 102. The current collector 103 located in the single-sided area 101 is coated with the active material layer 104 on only one side, and the current collector 103 located in the double-sided area 102 is coated with the active material layer 104 on both sides.

[0048] Specifically, as shown in Figures 2 and 7, a groove 2 is provided in the active material layer 104 located in the single-sided area 101. The provision of the groove 2 can destroy the stress inside the active material layer 104 area of ​​the single-sided area 101, thereby improving the bending degree of the single-sided area 101 after being rolled by the pressure roller. The bending degree of the single-sided area 101 is reduced, and the adhesion between the electrode piece 1 and the diaphragm 6 will be improved after the electrode piece 1 is assembled into a battery cell, so that the electrode piece 1 and the diaphragm 6 provided with the single-sided area 101 are more firmly bonded, and the gap between the electrode piece 1 and the diaphragm 6 can be reduced, or the gap between the electrode piece 1 and the diaphragm 6 can be avoided, thereby avoiding the transmission path of lithium ions from becoming longer during the charging and discharging of the battery, and alleviating or even avoiding problems such as lithium plating or black spots in the battery.

[0049] FIG1 shows a pole piece in the prior art. In the prior art, the active material layer 104 in the single-side area 101 of the pole piece is not provided with grooves.

[0050] It should also be noted that there is no limitation on the type of the electrode 1 , and the electrode 1 can be a positive electrode 4 or a negative electrode 5 .

[0051] In addition, since a groove 2 is opened on the active material layer 104 of the single-sided area 101 of the electrode 1, after the electrode 1 is assembled into a battery cell and the electrolyte is injected, the groove 2 can store more electrolyte, which can also increase the liquid storage capacity of the battery cell, thereby improving the performance of the battery.

[0052] It should also be noted that there is no limitation on the number and arrangement of the grooves 2. One or more grooves 2 can be provided. As shown in Figures 3 and 5, when multiple grooves 2 are provided, the grooves 2 are preferably arranged in an array, which can further alleviate the degree of curvature of the single-sided area 101 of the pole piece 1.

[0053] The electrode 1 of the above structure has a groove 2 formed in the active material layer 104 of the single-sided area 101, which can alleviate the bending degree of the single-sided area 101 of the electrode 1, thereby improving the adhesion between the single-sided area 101 of the electrode 1 and the diaphragm 6 when the electrode 1 is assembled into the battery cell, thereby shortening the transmission path of lithium ions in the battery cell during the charging and discharging process, and alleviating problems such as lithium plating and black spots.

[0054] In some embodiments, the area of ​​the active material layer 104 in the single-sided region 101 where the groove 2 is provided is S1, and the area of ​​the active material layer 104 in the single-sided region 101 is S2, wherein S1 and S2 satisfy the following relationship: S1 = (0.05-0.7) * S2. Specifically, ensuring that S1 and S2 satisfy the above relationship can prevent the groove 2 from being too small, thereby preventing the groove 2 from failing to alleviate the curvature of the electrode 1, and can also prevent the groove 2 from being too large, thereby preventing the energy density of the electrode 1 from being excessively reduced.

[0055] Illustratively, S1 may be 0.05S2, 0.1S2, 0.2S2, 0.3S2, 0.4S2, 0.5S2, 0.6S2, 0.7S2, and so on.

[0056] In some embodiments, as shown in FIG4 , the depth of the groove 2 is L in a direction perpendicular to the active material layer 104 , where 3 μm ≤ L ≤ 2000 μm. Ensuring that the depth of the groove 2 is within the above range can prevent the groove 2 from being too small, which would prevent the groove 2 from failing to alleviate the curvature of the electrode 1 , and can also prevent the problem of the groove 2 being too large causing excessive curvature of the electrode 1 and poor adhesion to the diaphragm 6 . This configuration can greatly alleviate the curvature of the electrode 1 .

[0057] It should be noted that the direction perpendicular to the active material layer 104 is the direction indicated by the double-headed arrow Y in FIG. 4 , and the depth of the groove 2 is the dimension of the groove 2 in the direction indicated by the double-headed arrow Y.

[0058] For example, the depth L of the groove 2 may be 3 μm, 10 μm, 50 μm, 100 μm, 200 μm, 500 μm, 1000 μm, 1500 μm, 2000 μm, etc.

[0059] For example, as shown in Figure 8, the 3D composite depth of groove 2 is shown. The straight line with the number 0.00 is the tangent of the lowest point of groove 2. The gray-white part between the straight line with the number 374.25 and the straight line with the number 0.00 refers to the surface of the pole piece 1. Therefore, the 3D composite depth of groove 2 is specifically 374.25 μm.

[0060] In some embodiments, as shown in FIG4 , the outer diameter of the notch of the groove 2 is D, where 0.2 mm ≤ D ≤ 5 mm. Specifically, ensuring that the groove 2 is within the above range can prevent the outer diameter of the groove 2 from being too small, thereby preventing the groove 2 from failing to alleviate the bending degree of the pole piece 1, and can also prevent the outer diameter of the groove 2 from being too large, thereby reducing the effect of alleviating the bending degree of the pole piece 1. Such a configuration can improve the effect of alleviating the bending degree of the pole piece 1.

[0061] It should be noted that when the slot is circular, the outer diameter of the slot refers to the diameter of the slot; when the slot is non-circular such as polygonal, elliptical or irregular, the outer diameter of the slot refers to the diameter of the circumscribed circle of the slot.

[0062] It should also be noted that, when the notch is a circular notch, the outer diameter of the notch is the dimension of the notch in the direction indicated by the double-headed arrow X in FIG. 2 .

[0063] For example, the outer diameter D of the groove 2 may be 0.2 mm, 0.5 mm, 1 mm, 2 mm, 3 mm, 4 mm, 5 mm, etc.

[0064] In some embodiments, the depth of the groove 2 in the direction perpendicular to the active material layer 104 is L, and the bending radius of the pole piece 1 is R, where L and R satisfy: L:R ≥ 0.005. Specifically, ensuring that the depth of the groove 2 in the direction perpendicular to the active material layer 104 and the bending radius of the pole piece 1 are within the above range can greatly reduce the degree of curvature of the single-sided area 101 of the pole piece 1, thereby alleviating problems such as lithium deposition and black spots in batteries composed of the pole piece 1.

[0065] For example, L:R can be 0.005, 0.008, 0.01, 0.02, 0.03, 0.04, 0.05, 0.08, 0.1, and so on.

[0066] In some embodiments, as shown in FIG6 , a protrusion 3 is provided on the side of the current collector 103 of the single-sided area 101 facing away from the active material layer 104, and the protruding direction of the protrusion 3 is the same as the recessed direction of the groove 2. The protrusion 3 can also alleviate the curvature of the single-sided area 101 of the electrode 1. In this way, when the groove 2 alleviates the curvature of the single-sided area 101 of the electrode 1, the protrusion 3 can also alleviate the above-mentioned curvature, and can avoid excessive reduction of the active material in the active material layer 104, thereby avoiding excessive reduction in the energy density of the battery.

[0067] In some embodiments, the protrusion 3 has the same height as the recessed depth of the groove 2. Exemplarily, ensuring that the protrusion 3 has the same height as the recessed depth of the groove 2 can both alleviate the degree of bending of the electrode 1. Ensuring that the above values ​​are the same can avoid increasing the thickness of the electrode 1 and reducing the energy density of the battery composed of the electrode 1.

[0068] In some embodiments, at least two protrusions 3 are provided, with recesses formed between adjacent protrusions 3. When the electrode 1 provided with the protrusions 3 is assembled into a battery cell, the recesses between adjacent protrusions 3 can also store electrolyte, thereby improving the battery's liquid storage capacity and thereby enhancing the performance of the battery cell.

[0069] In some embodiments, in the direction perpendicular to the active material layer 104, the depth of the protrusion 3 is M, where 2μm≤M≤1700μm, ensuring that the depth of the protrusion 3 is within the above range, which can avoid the protrusion 3 from being too small, and the protrusion 3 from failing to alleviate the degree of bending of the electrode 1, and can also avoid the problem of the protrusion 3 being too deep causing the curvature of the electrode 1 to be too large. Such a setting can alleviate the degree of bending of the electrode 1, so that the electrode 1 forms a regular size of the battery cell.

[0070] For example, the depth of the protrusion 3 may be 2 μm, 5 μm, 10 μm, 50 μm, 100 μm, 200 μm, 500 μm, 1000 μm, 1500 μm, 1700 μm, etc.

[0071] In some embodiments, the depth of the recess is N, where 0.05mm≤N≤1.5mm, ensuring that the depth of the recess is within the above range can avoid the recess being too shallow to increase the liquid storage capacity of the battery cell composed of the electrode 1, and can also avoid the recess being too deep, which will cause the energy density of the battery cell composed of the electrode 1 to decrease. Such a setting can avoid excessive bending of the electrode 1, thereby alleviating problems such as lithium deposition and black spots in the battery composed of the electrode 1.

[0072] Illustratively, the depth of the recess may be 0.05 mm, 0.06 mm, 0.07 mm, 0.08 mm, 0.09 mm, 0.1 mm, 0.12 mm, 0.15 mm, etc.

[0073] In some embodiments, the bottom of the groove 2 is a plane or an arc-shaped surface, and the sidewalls of the groove 2 are plane or arc-shaped surfaces. Here, the shapes of the bottom and sidewalls of the groove 2 are defined. Both the bottom and sidewalls of the groove 2 can be plane or arc-shaped surfaces. Such a configuration of the groove 2 can alleviate the degree of bending of the pole piece 1.

[0074] In some embodiments, at least two grooves 2 are provided, and the notches of the grooves 2 are at least one of circular, polygonal, and elliptical. It should be noted that the shapes of the notches of the at least two grooves 2 can be the same or different. Grooves 2 of different shapes have different capacities for storing electrolyte, and grooves 2 of different shapes have different effects on alleviating the curvature of the electrode 1. Grooves 2 of different shapes can be selected according to the required capacity for storing electrolyte and the required relief of the curvature of the electrode 1.

[0075] In this embodiment, a preferred implementation is provided, in which a plurality of grooves 2 are provided and arranged in an array, so as to reduce the bending degree of the electrode 1 while avoiding excessive reduction in the content of the active material layer 104 at the position where the grooves 2 are provided in the electrode 1.

[0076] A battery cell includes a negative electrode sheet 5, a positive electrode sheet 4, and a separator 6 disposed between the negative electrode sheet 5 and the positive electrode sheet 4, wherein the positive electrode sheet 4 and / or the negative electrode sheet 5 is any of the electrode sheets 1 described above. Since the battery cell includes the electrode sheet 1 described above, the beneficial effects of the electrode sheet 1 are described above and are not further elaborated here.

[0077] In some embodiments, adhesive tape is provided on both sides of the battery cell in the first direction, and the adhesive tape at least partially covers the protrusions 3 of the single-sided area 101. Specifically, after the electrode 1 is assembled into a battery cell, the active material layer 104 of the single-sided area 101 of the electrode 1 faces the center of the battery cell, and the protrusions 3 are located on the side away from the center of the battery cell. The adhesive tape partially covers the protrusions 3 of the single-sided area 101, which can increase the contact area between the adhesive tape and the single-sided area 101, thereby improving the stability of the adhesive tape's adhesion to the single-sided area 101 and making the battery cell more secure.

[0078] It should be noted that the first direction refers to the direction indicated by the double-headed arrow A or the direction indicated by the double-headed arrow B in FIG. 7 .

[0079] In some embodiments, the single-sided region 101 is located outside the battery cell, and the groove 2 of the single-sided region 101 is recessed away from the center of the battery cell. Specifically, the electrode sheet 1 provided with the single-sided region 101 can be a positive electrode sheet 4 or a negative electrode sheet 5. The recessed groove 2 of the single-sided region 101 is recessed away from the center of the battery cell, which can improve the electrolyte storage capacity of the battery cell provided with the electrode sheet 1 and facilitate the transfer of lithium ions between the positive electrode sheet 4 and the negative electrode sheet 5.

[0080] In some embodiments, the battery cell further includes a negative electrode tab 8 connected to the negative electrode sheet 5 and a positive electrode tab 7 connected to the positive electrode sheet 4. In the second direction, the projection of the groove 2 in the single-sided area 101 overlaps with the projection of at least one of the positive electrode tab 7 and the negative electrode tab 8. This arrangement ensures that the area for the groove 2 is sufficient and that the groove 2 is more evenly arranged on the single-sided area 101, thereby better alleviating the degree of curvature of the electrode sheet 1 and alleviating lithium deposition, black spots, and other phenomena in the battery cell.

[0081] It should be noted that the second direction refers to the direction indicated by the double-headed arrow A or the direction indicated by the double-headed arrow B in FIG. 7 .

[0082] Furthermore, in some embodiments, in the second direction, the projection of the groove 2 in the single-sided area 101 and the projection of the folded section of the separator 6 at least partially overlap. This arrangement can further ensure the uniformity of the groove 2 in the single-sided area 101, further ensure the area of ​​the groove 2, and further make the groove 2 more uniform in the single-sided area 101, thereby better alleviating the degree of bending of the electrode 1, thereby alleviating lithium deposition, black spots, and other phenomena in the battery cell.

[0083] It should be understood that the folded section of the separator 6 refers to the section of the separator 6 that extends beyond the positive electrode sheet 4 and the negative electrode sheet 5 at the (winding) starting end.

[0084] In some embodiments, the battery cell is a wound battery cell, and in the second direction, the projection of the groove 2 of the single-sided area 101 of the positive electrode sheet 4 covers the projection of the end of the active material layer 104 of the negative electrode sheet 5, that is, the groove 2 of the single-sided area 101 of the positive electrode sheet 4 exceeds the end of the active material layer 104 of the negative electrode sheet 5. When the above-mentioned electrode sheet 1 is combined into a wound battery cell as the positive electrode sheet 4 and the single-sided area 101 of the positive electrode sheet 4 is located at the outermost circle, referring to the arrangement shown in FIG7 , such an arrangement can alleviate the degree of curvature of the single-sided area 101 of the positive electrode sheet 4. At the same time, the grooves in the active material layer 104 within the positive electrode sheet 4 can reduce the content of the active material on the positive electrode sheet 4, so that the content of the active material in this area is less than the content of the active material layer 104 of the negative electrode sheet 5 corresponding to this area, and lithium deposition in this area can be avoided during the subsequent battery charging and discharging process.

[0085] In some embodiments, the peeling force between the active material layer 104 of the single-sided area 101 with the groove 2 and the diaphragm 6 is F1, and the peeling force between the active material layer 104 and the diaphragm 6 without the groove 2 is F2, wherein F1 and F2 satisfy: F1>F2. Such a setting can improve the stability of the adhesion between the active material layer 104 of the single-sided area 101 with the groove 2 and the diaphragm 6, thereby reducing the gap between the single-sided area 101 with the groove 2 and the active material layer 104 of the other polarity electrode, thereby reducing the transmission path of lithium ions during battery charging and discharging, and improving battery life.

[0086] Furthermore, in some embodiments, F1 and F2 satisfy the following relationship: F1 = (1.1-5) * F2. Specifically, ensuring that F1 and F2 satisfy the above relationship can further reduce the gap between the electrode 1 in the single-sided region 101 and the adjacent electrode due to the bending of the electrode 1, thereby improving the stability of the battery.

[0087] For example, F1 can be 1.1F2, 1.2F2, 1.5F2, 1.8F2, 2F2, 2.5F2, 3F2, 4F2, 4.5F2, 5F2, etc.

[0088] In some embodiments, the battery cell is a wound battery cell, and the groove 2 is located in the straight section 9 and / or arc section 10 of the wound battery cell. This arrangement can further ensure the uniformity of the groove 2 in the single-sided area 101, further ensure the area of ​​the groove 2, and further make the groove 2 more uniform in the single-sided area 101, thereby better alleviating the degree of curvature of the electrode 1, thereby alleviating lithium deposition, black spots, and other phenomena in the battery composed of this battery cell.

[0089] Taking the case where the length of the single-side area 101 of the positive electrode sheet 4 is 120 mm and the width is 80 mm as an example, the following experiment is conducted. The specific steps are as follows:

[0090] In the experimental group, the positive electrode sheet 4 was electrode sheet 1. After normal rolling, a special roller was used to treat the single-side area 101 of the electrode sheet 1 under a pressure of 0.5 MPa before winding, forming a groove 2 on the active material layer 104 of the single-side area 101.

[0091] The depth of groove 2 is 0.3 mm, the diameter is 2 mm, and the total area of ​​groove 2 is about 314 mm 2 Due to the presence of the groove 2 , the active material layer 104 in the single-sided area 101 has a maximum curling height of less than 1 mm when the electrode 1 is laid flat on the experimental table.

[0092] In the normal group, the positive electrode sheet 4 was rolled without any special treatment. When the positive electrode sheet 4 was laid flat on the experimental table, the maximum curling height of the single-side area 101 of the positive electrode sheet 4 was ≥8 mm.

[0093] After winding and capacity separation, the experimental and normal group batteries were disassembled and the peeling force between the positive electrode sheet 4 and the separator 6 was tested. The peeling force F1 between the single-sided area 101 of the positive electrode sheet 4 and the separator 6 in the experimental group battery was 0.032 N / mm, and the peeling force F2 between the other areas without the groove 2 and the separator 6 was 0.015 N / mm.

[0094] The battery cycle performance of the experimental group and the normal group is tested. At 25°C and 2C / 2C charge and discharge conditions, after 700 cycles, the capacity retention rate of the normal group battery is 85.6% (as shown in Figure 9), and the thickness expansion rate is 9.75% (as shown in Figure 10). The capacity retention rate of the experimental group battery is 89.3% (as shown in Figure 9), and the thickness expansion rate is 6.38% (as shown in Figure 10). The performance of the experimental group battery is significantly better than that of the normal group battery.

[0095] The higher thickness expansion rate of the normal group of batteries is mainly due to the bulges at the top and bottom of the battery in the height direction. Disassembly revealed that lithium deposition occurred in the two folds of the outermost circle of the battery (i.e., the top and bottom of the battery in the height direction before the battery was disassembled), while the experimental group of batteries did not have this problem. The analysis is mainly based on the normal group of batteries. The single-sided area 101 has not been treated, and the stress in the coating of the positive electrode 4 still exists, resulting in relatively poor adhesion between the positive electrode 4 and the diaphragm 6. This phenomenon worsens during high-rate cycling, leading to lithium deposition. The experimental group of batteries has indentations in the single-sided coating area. The indentations destroy the stress in the coating of the electrode 1, reduce the curling height of the electrode 1, and make the electrode 1 more "flat", thereby improving the adhesion between it and the diaphragm 6, thereby improving the performance of the battery.

[0096] The basic principles of the present application have been described above in conjunction with specific embodiments. However, it should be noted that the advantages, strengths, and effects mentioned in this application are merely illustrative and not restrictive, and it should not be assumed that these advantages, strengths, and effects are required of each embodiment of this application. In addition, the specific details disclosed above are merely illustrative and facilitating understanding, and are not restrictive. The above details do not limit this application to necessarily being implemented using the above specific details.

[0097] The block diagrams of the devices, devices, equipment, and systems involved in this application are merely illustrative examples and are not intended to require or imply that they must be connected, arranged, or configured in the manner shown in the block diagrams. As will be appreciated by those skilled in the art, these devices, devices, equipment, and systems can be connected, arranged, or configured in any manner. Words such as "include," "comprise," "have," and the like are open-ended words, meaning "including but not limited to," and can be used interchangeably therewith. The words "or" and "and" used herein refer to the words "and / or" and can be used interchangeably therewith, unless the context clearly indicates otherwise. The word "such as" used herein refers to the phrase "such as but not limited to," and can be used interchangeably therewith.

[0098] It should also be noted that in the apparatus, device, and method of the present application, each component or each step can be decomposed and / or recombined, and such decomposition and / or recombination should be regarded as equivalent solutions of the present application.

[0099] The above description of the disclosed aspects is provided to enable any person skilled in the art to make or use the present application. Various modifications to these aspects will be readily apparent to those skilled in the art, and the general principles defined herein may be applied to other aspects without departing from the scope of the present application. Therefore, the present application is not intended to be limited to the aspects shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

[0100] It should be understood that the qualifiers "first", "second", "third", "fourth", "fifth" and "sixth" used in the description of the embodiments of the present application are only used to more clearly illustrate the technical solutions and cannot be used to limit the scope of protection of the present application.

[0101] The above description has been provided for the purpose of illustration and description. Furthermore, this description is not intended to limit the embodiments of the present application to the forms disclosed herein. Although a number of example aspects and embodiments have been discussed above, those skilled in the art will recognize certain variations, modifications, alterations, additions, and sub-combinations thereof.

Claims

1. A pole piece comprising a current collector and an active material layer disposed on at least one side of the current collector, wherein the pole piece comprises a single-sided region, and the active material layer is disposed on one side of the current collector located in the single-sided region, characterized in that: The active material layer located in the single-side area is provided with a groove.

2. The pole piece according to claim 1, characterized in that: The area of ​​the active material layer in the single-sided region where the groove is provided is S1, and the area of ​​the active material layer in the single-sided region is S2, wherein S1 and S2 satisfy: S1 = (0.05-0.7) * S2.

3. The pole piece according to claim 1 or 2, characterized in that: In a direction perpendicular to the active material layer, the depth of the groove is L, wherein 3 μm≤L≤2000 μm; and / or, The outer diameter of the notch of the groove is D, wherein 0.2 mm ≤ D ≤ 5 mm.

4. The pole piece according to any one of claims 1 to 3, characterized in that: The depth of the groove in the direction perpendicular to the active material layer is L, and the bending radius of the pole piece is R, wherein L and R satisfy: L:R≥0.

005.

5. The pole piece according to any one of claims 1 to 4, characterized in that: A protrusion is provided on the side of the current collector in the single-sided area facing away from the active material layer, and a protruding direction of the protrusion is the same as a recessed direction of the groove.

6. The pole piece according to claim 5, characterized in that: The protrusion height is the same as the recess depth of the groove.

7. The pole piece according to claim 5 or 6, characterized in that: At least two protrusions are provided, and a recessed portion is formed between adjacent protrusions.

8. The pole piece according to claim 7, characterized in that: In the direction perpendicular to the active material layer, The depth of the protrusion is M, wherein 2 μm≤M≤1700 μm; and / or, The depth of the recessed portion is N, wherein 0.05 mm ≤ N ≤ 1.5 mm.

9. The pole piece according to any one of claims 1 to 8, characterized in that: The bottom of the groove is a plane or an arc surface, and / or The side wall of the groove is a plane or an arc surface.

10. The pole piece according to any one of claims 1 to 9, characterized in that: There are at least two grooves, and / or The notch of the groove is at least one of circular, polygonal and elliptical.

11. A battery cell, characterized in that: It comprises a negative electrode sheet, a positive electrode sheet and a separator arranged between the negative electrode sheet and the positive electrode sheet, and the positive electrode sheet and / or the negative electrode sheet is the electrode sheet according to any one of claims 1 to 10.

12. The battery cell according to claim 11, characterized in that Adhesive tape is provided on both sides of the battery cell in the first direction, and the adhesive tape at least covers a portion of the protrusions in the single-sided area.

13. The battery cell according to claim 11 or 12, characterized in that: The single-sided area is located outside the battery cell, and the groove in the single-sided area is recessed in a direction away from the center of the battery cell.

14. The battery cell according to any one of claims 11 to 13, characterized in that: The battery cell further includes a negative electrode tab connected to the negative electrode sheet and a positive electrode tab connected to the positive electrode sheet. In the second direction, a projection of the groove in the single-sided area overlaps with a projection of at least one of the positive electrode tab and the negative electrode tab.

15. The battery cell according to any one of claims 11 to 14, characterized in that: In the second direction, a projection of the groove of the single-sided region and a projection of the folded section of the diaphragm at least partially overlap.

16. The battery cell according to any one of claims 11 to 15, characterized in that: The battery cell is a wound battery cell, and in the second direction, the projection of the groove in the single-sided area of ​​the positive electrode sheet covers the projection of the end of the active material layer of the negative electrode sheet.

17. The battery cell according to any one of claims 11 to 16, characterized in that: The peeling force between the active material layer and the separator in the single-sided area with the groove is F1, and the peeling force between the active material layer and the separator without the groove is F2, wherein F1 and F2 satisfy: F1>F2.

18. The battery cell according to claim 17, characterized in that: F1 and F2 satisfy: F1 = (1.1 ~ 5) * F2.

19. The battery cell according to any one of claims 11 to 18, characterized in that: The battery core is a wound battery core, and the groove is located in a straight section and / or an arc section of the wound battery core.

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