Pole piece and battery cell

Abstract

The utility model discloses a pole piece and a battery cell. The pole piece comprises a current collector, a pole lug and a coating, wherein the tab is connected to the current collector. The current collector is coated with the coating, the coating comprises a first region, the first region corresponds to the tab, the first region is provided with a plurality of first accommodating holes, the plurality of first accommodating holes are distributed along the length direction, and the sum of the volumes of the first accommodating holes in unit regions is gradually reduced from two sides of the tab along the length direction. Wherein the mass loss of the pole piece is less than 1%. If the pole piece is an anode pole piece, the plurality of first accommodating holes can increase the area for lithium ion exchange. And if the pole piece is a cathode pole piece, the plurality of first accommodating holes can reduce the volume of the active substance participating in the reaction. Besides, only the first area is punched through control, and the size is gradually reduced from the two sides of the tab along the length direction, so that the influence on the energy density of the battery is reduced to a greater extent while lithium precipitation is not easy to occur near the tab.

Description

Technical Field

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

[0002] Lithium deposition in lithium batteries is a common problem during use. Lithium dendrites formed by the deposition of lithium ions not only increase the thickness of the battery cell but can also puncture the separator, causing a short circuit within the cell. Existing methods typically involve uniformly perforating the electrode coating, but this method significantly reduces the battery's energy density and cannot meet battery demand. Utility Model Content

[0003] The present invention aims to solve at least one of the technical problems existing in the prior art. To this end, the present invention provides a pole piece that can reduce the risk of lithium plating when used in a battery cell without significantly reducing the battery's energy density.

[0004] The utility model also provides a battery core having the above-mentioned electrode piece.

[0005] The utility model also provides another battery core having the above-mentioned electrode piece.

[0006] The pole piece according to the first embodiment of the present invention includes:

[0007] a current collector having a set length direction;

[0008] a tab connected to the current collector;

[0009] A coating is applied on the current collector, the coating including a first area, the first area corresponding to the electrode ear, the first area being provided with a plurality of first accommodating holes, the plurality of first accommodating holes being distributed along the length direction, and the sum of the volumes of the first accommodating holes in a unit area gradually decreasing from both sides of the electrode ear to the length direction.

[0010] The pole piece according to the embodiment of the present invention has at least the following beneficial effects: the first area corresponds to the location of the pole tab, and the first area is provided with a plurality of first accommodating holes. The volume of the first accommodating holes per unit area gradually decreases along the length direction from both sides of the pole tab. If the pole piece is an anode pole piece, the plurality of first accommodating holes can increase the area for lithium ion exchange, making it difficult for lithium to be deposited in the area near the pole tab. If the pole piece is a cathode pole piece, the plurality of first accommodating holes can reduce the volume of the active material participating in the reaction, making it difficult for lithium to be deposited in the area near the pole tab. In addition, by controlling the drilling of holes only in the first area and gradually reducing the volume of the holes along the length direction from both sides of the pole tab, when the pole piece is used in a battery, lithium deposition is not likely to occur near the pole tab, while minimizing the impact on the battery energy density to a large extent.

[0011] According to some embodiments of the present utility model, the apertures of each of the first accommodating holes are equal, and from both sides of the tab to the length direction, the depth of the first accommodating hole gradually decreases.

[0012] According to some embodiments of the present utility model, the length of the first region is L, the thickness of the coating is H, the depth of the first accommodating hole is h, 0 < h < H, the distance between the first accommodating hole and the tab is d, 0 < d < L, and the depth h of the first accommodating hole and the distance d between the hole and the tab satisfy the relational expression: h = (1 - d / L) * 0.9H.

[0013] According to some embodiments of the present utility model, the depths of each of the first accommodating holes are equal, and from both sides of the tab to the length direction, the aperture of the first accommodating hole gradually decreases.

[0014] According to some embodiments of the present utility model, the length of the first region is L, the width is W, the distance between the first accommodating hole and the tab is d, 0 < d < L, the radius of the first accommodating hole is R, and the aperture of the first accommodating hole with the largest radius is R1, 0.005W < R1 < 0.02W; wherein, the radius R of the first accommodating hole and the distance d between the first accommodating hole and the tab satisfy the following relational expression: R = (1 - d / L) * R1.

[0015] According to some embodiments of the present utility model, from both sides of the tab to the length direction, the number of the first accommodating holes per unit area gradually decreases.

[0016] According to some embodiments of the present utility model, the mass loss of the pole piece is less than 1%.

[0017] According to some embodiments of the present utility model, the first region is provided with a plurality of hole groups, each hole group includes a plurality of first accommodating holes arranged at intervals in the width direction, and the plurality of hole groups are arranged at intervals in the length direction. The depths and radii of the first accommodating holes in the same hole group are equal.

[0018] According to some embodiments of the present utility model, the coating further includes a second region corresponding to the bending region of the battery cell. The second region is provided with a plurality of second accommodating holes, and the plurality of second accommodating holes are evenly distributed in the second region.

[0019] According to some embodiments of the present invention, the electrode sheet is a negative electrode sheet, and the coating includes a first coating and a second coating, the first coating and the second coating are respectively connected to both sides of the current collector, the length of the first coating on the current collector is greater than the length of the second coating on the current collector, the apertures of the first accommodating holes on the first coating are equal, and the depths of the first accommodating holes gradually decrease from both sides of the electrode ear along the length direction; the depths of the first accommodating holes on the second coating are equal, and the apertures of the first accommodating holes gradually decrease from both sides of the electrode ear along the length direction.

[0020] According to the second aspect of the present invention, the battery cell includes a diaphragm, a first pole piece and a second pole piece, the diaphragm is arranged between the first pole piece and the second pole piece, and at least one of the first pole piece and the second pole piece is the pole piece provided in the above-mentioned first aspect embodiment.

[0021] The battery cell according to the embodiment of the present invention has at least the following beneficial effects: at least one of the first electrode sheet and the second electrode sheet is the electrode sheet provided by the embodiment of the first aspect above, so that the battery cell has at least all the advantages of the electrode sheet, the first area corresponds to the location of the electrode tab, and the first area is provided with a plurality of first accommodating holes, and the volume of the first accommodating holes per unit area gradually decreases along the length direction from both sides of the electrode tab. If the electrode sheet is an anode electrode sheet, the plurality of first accommodating holes can increase the area for lithium ion exchange, making it less likely for lithium to be deposited in the area near the electrode tab; if the electrode sheet is a cathode electrode sheet, the plurality of first accommodating holes can reduce the volume of the active material involved in the reaction, making it less likely for lithium to be deposited in the area near the electrode tab. In addition, by controlling the drilling only in the first area and gradually reducing the volume of the drilling along the length direction from both sides of the electrode tab, lithium deposition is less likely to occur near the electrode tab while minimizing the impact on the battery energy density to the greatest extent.

[0022] According to the third aspect embodiment of the present utility model, the battery cell includes multiple first pole pieces, multiple second pole pieces and multiple diaphragms. The multiple first pole pieces and the multiple second pole pieces are stacked in sequence, and the diaphragms are arranged between adjacent first pole pieces and second pole pieces. A part of the multiple first pole pieces and the multiple second pole pieces are the pole pieces provided in the above-mentioned first aspect embodiment.

[0023] The battery cell according to the embodiment of the present invention has at least the following beneficial effects: a portion of the plurality of first pole pieces and the plurality of second pole pieces are the pole pieces provided by the embodiment of the first aspect above, so that the battery cell has at least all the advantages of the pole piece, the first region corresponds to the location of the pole piece, the first region is provided with a plurality of first accommodating holes, and the volume of the first accommodating holes per unit region gradually decreases along the length direction from both sides of the pole piece, if the pole piece is an anode pole piece, the plurality of first accommodating holes can increase the area for lithium ion exchange, making it less likely for lithium to be deposited in the area near the pole piece, and if the pole piece is a cathode pole piece, the plurality of first accommodating holes can reduce the volume of the active material involved in the reaction, making it less likely for lithium to be deposited in the area near the pole piece. In addition, by controlling the drilling only in the first region and gradually reducing the volume of the drilling along the length direction from both sides of the pole piece, lithium deposition is less likely to occur near the pole piece, while minimizing the impact on the battery energy density to the greatest extent.

[0024] According to some embodiments of the present invention, the first electrode sheet is a negative electrode sheet, the second electrode sheet is a positive electrode sheet, the coating includes a first coating, a second coating, a third coating, and a fourth coating, the current collector includes a first current collector and a second current collector, the first coating and the second coating are respectively connected to both sides of the first current collector, the length of the first coating on the first current collector is greater than the length of the second coating on the first current collector, the third coating and the fourth coating are respectively connected to both sides of the second current collector, the length of the third coating on the second current collector is greater than the length of the fourth coating on the second current collector The length of the current collector, the apertures of the first accommodating holes on the first coating layer are equal, and the hole depths of the first accommodating holes gradually decrease from both sides of the electrode tab along the length direction; the depths of the first accommodating holes on the second coating layer are equal, and the apertures of the first accommodating holes gradually decrease from both sides of the electrode tab along the length direction; the first accommodating holes are provided on the third coating layer, and the first accommodating holes are not provided on the fourth coating layer, the apertures of the first accommodating holes on the third coating layer are equal, and the hole depths of the first accommodating holes gradually decrease from both sides of the electrode tab along the length direction.

[0025] Additional aspects and advantages of the present invention will be given in part in the following description and will become apparent from the following description or learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The present invention will be further described below with reference to the accompanying drawings and embodiments, wherein:

[0027] Figure 1 Schematic diagram of a pole piece according to an embodiment of the present utility model;

[0028] Figure 2This is a cross-sectional view of a pole piece according to the first embodiment of the present utility model;

[0029] Figure 3 This is a cross-sectional view of a pole piece according to a second embodiment of the present invention;

[0030] Figure 4 This is a schematic diagram of a pole piece according to the third embodiment of the present invention.

[0031] Reference numerals:

[0032] The current collector 100 , the tab 200 , the coating 300 , the hole group 310 , the first accommodating hole 311 , the second accommodating hole 320 , the first region 330 , and the second region 340 . DETAILED DESCRIPTION

[0033] The following describes embodiments of the present invention in detail. Examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended only to explain the present invention and are not to be construed as limiting the present invention.

[0034] In the description of the present invention, it should be understood that descriptions involving orientations, such as up, down, front, back, left, right, etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, they cannot be understood as limitations on the present invention.

[0035] In the description of this utility model, "several" means more than one, "plurality" means more than two, "greater than," "less than," and "exceed" are understood to exclude the number itself, while "above," "below," and "within" are understood to include the number itself. The use of the terms "first" and "second" is solely for the purpose of distinguishing technical features and is not to be construed as indicating or implying relative importance, implicitly specifying the number of the indicated technical features, or implicitly specifying the order of the indicated technical features.

[0036] In the description of the present invention, unless otherwise clearly defined, terms such as setting, installing, connecting, etc. should be understood in a broad sense, and technicians in the relevant technical field can reasonably determine the specific meanings of the above terms in the present invention based on the specific content of the technical solution.

[0037] In the description of the present invention, reference to terms such as "one embodiment," "some embodiments," "illustrative embodiments," "examples," "specific examples," or "some examples" means that the specific features, structures, materials, or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the exemplary expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

[0038] Reference Figures 1 to 4 The first embodiment of the present invention provides a pole piece, including a current collector 100, a pole tab 200 and a coating 300. The current collector 100 has a set length direction. The pole tab 200 is connected to the current collector 100. The coating 300 is applied on the current collector 100, and the coating 300 includes a first area 330. The first area 330 is arranged around the pole tab 200. The first area 330 is provided with a plurality of first accommodating holes 311. The plurality of first accommodating holes 311 are distributed along the length direction. From the two sides of the pole tab 200 to the length direction, the sum of the volumes of the first accommodating holes 311 in the unit area gradually decreases.

[0039] The first region 330 corresponds to the location where the tab 200 is set. The first region 330 is provided with a plurality of first accommodating holes 311. The volume of the first accommodating holes 311 per unit area gradually decreases along the length direction from both sides of the tab 200. If the electrode sheet is an anode electrode sheet, the plurality of first accommodating holes 311 can increase the area of ​​the first region 330 for lithium ion exchange, that is, the bottom wall and side walls of the first accommodating holes 311 can be used for lithium ion exchange, making the area near the tab 200 less likely to undergo lithium deposition. If the electrode sheet is a cathode electrode sheet, the plurality of first accommodating holes 311 can reduce the volume of the cathode active material involved in the reaction, making the area near the tab 200 less likely to undergo lithium deposition. In addition, by controlling the perforation only in the first region 330 and gradually reducing the volume of the perforations along the length direction from both sides of the tab 200, when the electrode sheet is used in a battery, lithium deposition is less likely to occur near the tab 200, while minimizing the impact on the battery energy density.

[0040] The lithium deposition experiment was conducted on the present embodiment and the control group, and the experimental results are shown in Table 1 below:

[0041] Table 1: Lithium precipitation experiment results

[0042]

[0043] Among them, Experimental Group 1 is the solution adopted in this embodiment, while Control Group 1 is a solution with the same total punching volume as Experimental Group 1 but the volume of the first accommodation hole 311 remains unchanged, and Control Group 2 is a solution with the volume of a single first accommodation hole 311 unchanged and a weight loss similar to that of Experimental Group 1. As can be seen from the above table, the punching method in which the sum of the volumes of the first accommodation holes 311 in the unit area decreases in sequence has the same improvement effect on lithium deposition in the corresponding area of the tab 200 as the punching method with the unchanged punching volume, and can also reduce the weight loss and the impact on the battery energy density. When the mass loss is similar, the punching method of this embodiment significantly improves lithium deposition in the battery cell compared with the method of the unchanged punching volume in Control Group 2.

[0044] In addition, since the current needs to flow through the tab 200 and output externally, during the use of the battery cell, the current density in the area near the tab 200 is relatively large, and there are many side reactions, resulting in a relatively fast consumption rate of the electrolyte in the area near the tab 200. Purple spot lithium deposition will occur due to the lack of electrolyte in the later cycle of the battery. And multiple first accommodation holes 311 can accommodate more electrolyte during the electrolyte injection process of the battery cell, enabling the electrolyte to better infiltrate the battery cell through the multiple first accommodation holes 311, thereby providing sufficient electrolyte for the later cycle of the battery cell. For example, the volume of the electrolyte that can be accommodated in the area near the tab 200 of a conventional battery cell is V₁. When the surface layer of the conventional battery cell is depleted in the later cycle, V₁ is almost 0, and purple spots will appear inside the battery cell due to insufficient electrolyte. After the surface of the electrode sheet is punched, the volume of a single first accommodation hole 311 is V₂, and there are n first accommodation holes 311, then the total volume of the electrolyte that can be accommodated is V₁ + nV₂. After V₁ is depleted, V₂ can still provide electrolyte to support the required amount for the later cycle of the battery cell, thereby being able to extend the time of purple spot appearance due to insufficient electrolyte.

[0045] Refer to Figure 2 In some embodiments, the aperture diameters of the first accommodation holes 311 are equal. From both sides of the tab 200 to the length direction, the depth of the first accommodation hole 311 gradually decreases, so that from both sides of the tab 200 to the length direction, the sum of the volumes of the first accommodation holes 311 in the unit area gradually decreases. While making it not easy for lithium deposition to occur in the area near the tab 200, the sum of the volumes of the multiple first accommodation holes 311 in the area far from the tab 200 along the length direction is relatively small, and the impact on the battery energy density can be reduced. Further, the length of the first area 330 is L, the thickness of the coating 300 is H, the depth of the first accommodation hole 311 is h, 0 < h < H, the distance between the first accommodation hole 311 and the tab 200 is d, 0 < d < L, and the depth h of the first accommodation hole 311 and the distance d between the hole and the tab 200 satisfy the relational expression: h = (1 - d / L) * 0.9H.

[0046] Lithium deposition experiments were carried out on the solution of this embodiment and the control group, and the experimental results are shown in Table 2 below:

[0047] Table 2: Results of lithium precipitation experiment 2

[0048]

[0049] Among them, experimental group 2 is the scheme adopted in this embodiment, while control group 4 is a scheme with the same maximum drilling depth as experimental group 2 but unchanged drilling depth, and control group 5 is a scheme with unchanged drilling depth and similar weight loss to experimental group 2. It can be seen from the above table that the punching method with successively decreasing drilling depths has the same improvement effect on lithium deposition in the corresponding area of ​​the tab 200 as the punching method with unchanged drilling depth, and can also reduce weight loss and reduce the impact on battery energy density. When the mass loss is the same, the drilling method of this embodiment significantly improves the lithium deposition of the battery cell compared to the method of control group 2 with unchanged drilling depth. In addition, the drilling method of this embodiment can also significantly improve the charging, rate and low-temperature discharge of the electrode. The experimental results are shown in Table 3 below, where, in addition to the lithium deposition experiment, the electrode was also subjected to discharge and hot box pass tests and other experiments.

[0050] Table 3: Lithium precipitation experiment results

[0051] Punching method capacity 2C discharge capacity (first cycle) Low-temperature discharge at -10 degrees Celsius (first cycle) 3.5C cycle 50cls 4.5C cycle 50cls RT-1000CLS interface Hot box pass rate No punching 5800 84% 76% Slight lithium deposition Severe lithium deposition Severe lithium deposition, large-scale lithium deposition on the main interface, and severe lithium deposition in the corners 30% Example 5800 92.5% 79% No lithium precipitation No lithium precipitation Slight lithium deposition, obvious lithium deposition at the corners, no lithium deposition on the main interface 80%

[0052] Table 3 shows that the punching method of this embodiment can also significantly improve the charging, rate, and low-temperature discharge of the electrode, and can also increase the hot box pass rate. The low-temperature discharge data shows that the punching method of this embodiment improves low-temperature discharge by 3%. The reason is that the internal specific surface area of ​​the perforated channel of this method is large, and there are more lithium ion insertion sites, thus achieving a large benefit. At the same time, the punching method of this embodiment has a 0.5C rate improvement, mainly due to the large number of lithium insertion sites and the rapid lithium ion transmission.

[0053] Reference Figure 3, in some embodiments, the depths of the first accommodating holes 311 are equal. From both sides of the tab 200 towards the length direction, the aperture diameters of the first accommodating holes 311 gradually decrease. As a result, from both sides of the tab 200 towards the length direction, the sum of the volumes of the first accommodating holes 311 in the unit area gradually decreases. While making it difficult for lithium deposition to occur in the area near the tab 200, the sum of the volumes of the multiple first accommodating holes 311 in the area far from the tab 200 along the length direction is small, and the influence on the battery energy density can be reduced. Further, the length of the first region 330 is L, the width is W, the distance between the first accommodating hole 311 and the tab 200 is d, 0 < d < L, the radius of the first accommodating hole 311 is R, and the radius of the first accommodating hole 311 with the largest radius is R1, 0.005W < R1 < 0.02W; wherein, the radius R of the first accommodating hole 311 and the distance d between the first accommodating hole 311 and the tab 200 satisfy the following relational formula: R = (1 - d / L) * R1. Among them, the first accommodating hole 311 with the largest radius is one or more first accommodating holes 311 that are closest to the tab 200 compared with the other first accommodating holes 311. There are many factors determining the aperture diameter of the largest first accommodating hole 311, such as the thickness of the coating 300, the type of active material selected, the design power of the battery cell, etc. After the aperture diameter of the largest first accommodating hole 311 is determined, the aperture diameters of the other first accommodating holes 311 are also determined accordingly.

[0054] Lithium deposition experiments were carried out on the solution of this embodiment and the control group, and the experimental results are shown in Table 4 below:

[0055] Table 4: Lithium deposition experiment results IV

[0056]

[0057] Among them, the experimental group 3 is the solution adopted in this embodiment, the control group 6 is the solution with the same punching depth as the experimental group 3 but the punching radius unchanged, and the control group 7 is the solution with the punching depth unchanged and the weight loss similar to that of the experimental group 4. As can be seen from the above, when the mass loss is the same, the punching method of this embodiment significantly improves the lithium deposition in the battery cell compared with the method with the same punching depth but the unchanged punching radius, and has a better improvement effect on the lithium deposition near the tab 200 compared with the solution with the unchanged punching radius and similar mass loss. In addition, the punching method of this embodiment can also improve the charging of the electrode sheet to a certain extent. The experimental results are shown in Table 5 below. Among them, in addition to the lithium deposition experiment, discharge and hot box passing tests and other experiments were also carried out on the electrode sheet.

[0058] Table 5: Lithium deposition experiment results V

[0059] Punching method capacity 2C discharge capacity (first cycle) Low-temperature discharge at -10 degrees Celsius (first cycle) 3.5C cycle 50cls 4.5C cycle 50cls RT-1000CLS interface Hot box pass rate No punching 5800 84% 76% Slight lithium deposition Severe lithium deposition Severe lithium deposition, large-scale lithium deposition on the main interface, and severe lithium deposition in the corners 30% Example 5800 87% 78% No lithium precipitation Mild lithium deposition Moderate lithium deposition, moderate lithium deposition at corners, moderate lithium deposition on the main interface 80%

[0060] It can be obtained from Table 5 that the punching method of this embodiment can also improve the charging of the electrode sheet to a certain extent and can also improve the passing rate of the hot box.

[0061] Reference Figure 4 In some embodiments, the aperture and depth of each first accommodating hole 311 are equal, and the number of first accommodating holes 311 per unit area gradually decreases from both sides of the pole tab 200 to the length direction, so that the sum of the volumes of the first accommodating holes 311 per unit area from both sides of the pole tab 200 to the length direction gradually decreases, making it less likely for lithium deposition to occur in the area near the pole tab 200. At the same time, the sum of the volumes of the multiple first accommodating holes 311 in the area away from the pole tab 200 along the length direction is smaller, which can reduce the impact on the battery energy density. In addition, the punching method of this embodiment can also improve the charging and rate capabilities of the pole piece. The experimental results are shown in Table 6 below. In addition, in addition to the lithium deposition experiment, the pole piece was also subjected to discharge and hot box pass tests.

[0062] Table 6: Results of lithium precipitation experiment VI

[0063]

[0064] It can be concluded from Table 6 that the punching method of this embodiment can also improve the charging and rate capabilities of the electrode to a certain extent, and can also increase the hot box pass rate.

[0065] It can be understood that, from the above-mentioned multiple embodiments, by changing the aperture and depth of the first accommodating hole 311 and the number of the first accommodating holes 311 per unit area of ​​the first region 330, the volume of the first accommodating holes 311 per unit area can be affected. Therefore, when performing the punching operation, multiple parameters can be changed according to actual needs. It is only necessary to ensure that the sum of the volumes of the first accommodating holes 311 per unit area gradually decreases along the length direction from both sides of the tab 200.

[0066] In some embodiments, the electrode mass loss is less than 1%. By controlling the depth, radius, and density of the holes, the electrode mass loss can be reduced to less than 1%, thereby significantly reducing the impact on battery energy density. Referring to the table of the three lithium deposition experiments above, the mass loss of the experimental groups is less than 1%, which meets the electrode mass loss requirement.

[0067] Reference Figure 4 In some embodiments, the first region 330 is provided with a plurality of hole groups 310, and the hole group 310 includes a plurality of first accommodating holes 311 spaced apart along the width direction. The plurality of hole groups 310 are spaced apart along the length direction, and the hole depth and radius of the first accommodating holes 311 in the same hole group 310 are equal, so that the volume of the first accommodating holes 311 in the plurality of hole groups 310 decreases successively from both sides of the tab 200 to the length direction.

[0068] Reference Figure 1In some embodiments, the coating 300 further includes a second region 340, the second region 340 corresponds to the bending region of the battery cell, and the second region 340 is provided with a plurality of second accommodating holes 320, and the plurality of second accommodating holes 320 are evenly distributed in the second region 340. Specifically, the battery cell is provided with an extension region and two bending regions, and the extension region connects the two bending regions along the width direction. Since the bending region is also prone to lithium deposition, the provision of a plurality of second accommodating holes 320 in the bending region can also prolong the time for lithium deposition to occur in the bending region. The principle is the same as that of providing a plurality of first accommodating holes 311 in the first region 330, and will not be repeated here. Among them, the greater the battery cell rate, the denser the drilling or the larger the aperture of the second accommodating hole 320, and the greater the drilling depth. It can be understood that both the first accommodating hole 311 and the second accommodating hole 320 can be formed by laser drilling.

[0069] Wherein, the coating 300 includes a first coating and a second coating. The length of the first coating on the current collector 100 is greater than the length of the second coating on the current collector 100. After the first coating and the second coating are applied to the current collector 100, the lithium deposition phenomenon on the side of the negative electrode sheet with the first coating is more serious, and the lithium deposition phenomenon on the side of the negative electrode sheet with the second coating is relatively mild. Therefore, in some embodiments, the electrode sheet is a negative electrode sheet, and the coating 300 includes a first coating and a second coating. The first coating and the second coating are respectively connected to both sides of the current collector 100. Wherein, the material of the first coating and the second coating can be the same, so that after being connected to the current collector 100, a negative electrode sheet is formed. The length of the first coating on the current collector 100 is greater than the length of the second coating on the current collector 100. Among them, multiple first accommodating holes 311 are distributed along the length direction, and the sum of the volumes of the first accommodating holes 311 in a unit area gradually decreases from both sides of the pole lug 200 to the length direction. Specifically, the apertures of the first accommodating holes 311 located on the first coating layer are equal, and the hole depths of the first accommodating holes 311 gradually decrease from both sides of the pole lug 200 along the length direction. The depths of the first accommodating holes 311 located on the second coating layer are equal, and the apertures of the first accommodating holes 311 gradually decrease from both sides of the pole lug 200 along the length direction. Specifically, by keeping the aperture of the first accommodating holes 311 unchanged and changing the hole depth, and by changing the hole depth of the first accommodating holes 311 and keeping the aperture unchanged, the charging, rate capability and low-temperature discharge capability of the pole piece can be effectively improved, and lithium plating of the pole piece can also be effectively avoided.

[0070] The following experiments were conducted on the lithium deposition experiments of the present embodiment and the control group. The experimental results are shown in Table 7 below. In addition to the lithium deposition experiments, the electrode pieces were also subjected to discharge and hot box test.

[0071] Table 7: Lithium precipitation test results

[0072]

[0073] It can be concluded from the above table that the processing method of this embodiment can not only effectively avoid the occurrence of lithium plating on the electrode, but also effectively improve the charging, rate capability and low-temperature discharge capability of the electrode.

[0074] A second embodiment of the present invention provides a battery cell (not shown). The battery cell is a square or cylindrical battery cell. The battery cell includes a separator, a first electrode sheet, and a second electrode sheet. The separator is disposed between the first and second electrode sheets. At least one of the first and second electrode sheets is the electrode sheet provided in the first embodiment. This provides the battery cell with at least all the advantages of electrode sheets. The first electrode sheet is an anode electrode sheet, and the second electrode sheet is a cathode electrode sheet. A first region 330 corresponds to the location where the tab 200 is located. The first region 330 is provided with a plurality of first accommodating holes 311. The volume of the first accommodating holes 311 per unit area gradually decreases along the length of the tab 200 from both sides. If the first electrode sheet is the electrode sheet provided in the first embodiment, the plurality of first accommodating holes 311 can increase the area for lithium ion exchange, thereby reducing the occurrence of lithium deposition in the vicinity of the tab 200. If the second electrode sheet is the electrode sheet provided in the first embodiment, the plurality of first accommodating holes 311 can reduce the volume of active material involved in the reaction, thereby reducing the occurrence of lithium deposition in the vicinity of the tab 200. It is understood that both the first and second pole pieces can be the pole pieces provided in the first embodiment described above. Furthermore, by controlling the perforation only in the first region 330 and limiting the pole piece weight loss to less than 1%, lithium deposition near the tab 200 is less likely to occur, while minimizing the impact on battery energy density.

[0075] The third embodiment of the present invention provides a battery cell (not shown in the figure), comprising a plurality of first electrode sheets, a plurality of second electrode sheets, and a plurality of separators. The plurality of first electrode sheets and the plurality of second electrode sheets are stacked in sequence, and the separators are disposed between adjacent first and second electrode sheets. At least a portion of the plurality of first electrode sheets and the plurality of second electrode sheets are the electrode sheets provided in the first embodiment above, which can prolong the time it takes for lithium deposition to occur in at least some of the electrode sheets in the battery cell, thereby extending the overall service life of the battery cell. The battery cell provided in this embodiment is a laminated battery cell, which is manufactured by stacking the first and second electrode sheets, each of which is coated with a separator.

[0076] In some embodiments, the first electrode sheet is a negative electrode sheet, and the second electrode sheet is a positive electrode sheet. The coating 300 includes a first coating, a second coating, a third coating, and a fourth coating. The current collector 100 includes a first current collector and a second current collector. The first coating and the second coating are respectively connected to either side of the first current collector, with the first coating extending longer on the first current collector than the second coating. The third coating and the fourth coating are respectively connected to either side of the second current collector, with the third coating extending longer on the second current collector than the fourth coating. The first and second coatings can be made of the same material, thereby forming a negative electrode sheet with the first current collector. The third and fourth coatings can be made of the same material, thereby forming a positive electrode sheet with the second current collector. The plurality of first receiving holes 311 are distributed along the length direction, with the sum of the volumes of the first receiving holes 311 per unit area gradually decreasing from the sides of the tab 200 toward the length direction. Specifically, the first receiving holes 311 on the first coating have equal diameters, and the depth of the first receiving holes 311 gradually decreases along the length direction from the sides of the tab 200. The depth of each first accommodating hole 311 on the second coating layer is equal, and the diameter of the first accommodating hole 311 gradually decreases along the length direction from both sides of the tab 200. The first accommodating hole 311 is provided on the third coating layer, and is not provided on the fourth coating layer. The diameter of each first accommodating hole 311 on the third coating layer is equal, and the depth of the first accommodating hole 311 gradually decreases along the length direction from both sides of the tab 200. Specifically, this arrangement can effectively solve the problem of lithium deposition in the entire battery cell. At the same time, after drilling holes on the side of the positive electrode sheet with more active material, more storage space for the electrolyte is created. Combined with the greatly increased lithium ion channel of the negative electrode, the two combined have a significant improvement in the late cycle window. In addition, this arrangement can also improve the hot box performance of the battery cell to a certain extent. This is because drilling holes in the negative electrode sheet can reduce the CB value. At the same time, drilling holes in the positive electrode sheet reduces the active material in the positive electrode sheet. During the hot box test of the battery cell, less positive electrode reacts, and the battery cell stability is improved.

[0077] The following experiments were conducted on the present embodiment and the control group. The experimental results are shown in Table 8 below. In addition to the lithium deposition experiment, the electrode was also subjected to discharge and hot box test:

[0078] Table 8: Lithium precipitation test results

[0079]

[0080] It can be concluded from the above table that the battery cells configured using the above embodiments can have great improvements in charging, rate and low-temperature discharge, greatly improving performance. Specifically, by increasing the number of lithium ion channels at the anode, the system stores more electrolyte, and the lithium ion transmission is faster, thereby improving the rate of the battery cells. By punching holes in the cathode, a certain amount of electrolyte is stored in the cathode holes. In the later stage of the cycle, the electrolyte inside the battery cell gradually dries up, and this part of the stored electrolyte can play an important role in this stage. In this way, the battery cells can have great improvements in charging, rate and low-temperature discharge, greatly improving performance.

[0081] The embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the above embodiments. Various modifications can be made within the scope of knowledge possessed by a person skilled in the art without departing from the spirit of the present invention. In addition, the embodiments of the present invention and the features of the embodiments can be combined with each other unless there is a conflict.

Claims

1. A pole piece, characterized in that: Comprising: A current collector having a set length direction and width direction; A tab connected to the current collector; A coating applied to the current collector, the coating including a first region corresponding to the tab, the first region being provided with a plurality of first accommodating holes, the plurality of first accommodating holes being distributed along the length direction, and the sum of the volumes of the first accommodating holes in a unit area gradually decreasing along the length direction from both sides of the tab.

2. The pole piece according to claim 1, characterized in that: The aperture diameters of each of the first accommodating holes are equal, and the depths of the first accommodating holes gradually decrease along the length direction from both sides of the tab.

3. The pole piece according to claim 2, characterized in that: The length of the first region is L, the thickness of the coating is H, the depth of the first accommodating hole is h, 0 < h < H, the distance between the first accommodating hole and the tab is d, 0 < d < L, and the depth h of the first accommodating hole and the distance d between the hole and the tab satisfy the relationship: h = (1 - d / L) * 0.9H.

4. The pole piece according to claim 1, characterized in that: The depths of each of the first accommodating holes are equal, and the aperture diameters of the first accommodating holes gradually decrease along the length direction from both sides of the tab.

5. The pole piece according to claim 4, characterized in that: The length of the first region is L, the width is W, the distance between the first accommodating hole and the tab is d, 0 < d < L, the radius of the first accommodating hole is R, and the aperture diameter of the first accommodating hole with the largest radius is R1, 0.005W < R1 < 0.02W; Wherein, the radius R of the first accommodating hole and the distance d between the first accommodating hole and the tab satisfy the following relationship: R = (1 - d / L) * R1.

6. The pole piece according to claim 1, characterized in that: The aperture diameters and depths of each of the first accommodating holes are equal, and the number of the first accommodating holes in a unit area gradually decreases along the length direction from both sides of the tab.

7. The pole piece according to any one of claims 1 to 6, characterized in that: The mass loss of the pole piece is less than 1%.

8. The pole piece according to any one of claims 1 to 6, characterized in that: The first region is provided with a plurality of hole groups, each hole group including a plurality of first accommodating holes spaced along the width direction, and the plurality of hole groups are spaced along the length direction, and the depths and radii of the first accommodating holes in the same hole group are equal.

9. The pole piece according to any one of claims 1 to 6, characterized in that: The coating further includes a second region corresponding to the bending region of the battery cell, and the second region is provided with a plurality of second accommodating holes, and the plurality of second accommodating holes are uniformly distributed in the second region.

10. The pole piece according to claim 1, characterized in that: The pole piece is a negative pole piece, the coating includes a first coating and a second coating, the first coating and the second coating are respectively connected to both sides of the current collector, the length of the first coating on the current collector is greater than the length of the second coating on the current collector, the aperture diameters of each of the first accommodating holes located on the first coating are equal, and the depths of the first accommodating holes gradually decrease along the length direction from both sides of the tab; the depths of each of the first accommodating holes located on the second coating are equal, and the aperture diameters of the first accommodating holes gradually decrease along the length direction from both sides of the tab.

11. A battery cell, characterized in that: Including a separator, a first pole piece and a second pole piece, the separator is disposed between the first pole piece and the second pole piece, and at least one of the first pole piece and the second pole piece is the pole piece according to any one of claims 1-9.

12. A battery cell, characterized in that: It includes multiple first pole pieces, multiple second pole pieces and multiple diaphragms, the multiple first pole pieces and the multiple second pole pieces are stacked in sequence, the diaphragms are arranged between adjacent first pole pieces and the second pole pieces, and at least a part of the multiple first pole pieces and the multiple second pole pieces are the pole pieces described in any one of claims 1-9.

13. The battery cell according to claim 11 or 12, characterized in that: The first electrode sheet is a negative electrode sheet, and the second electrode sheet is a positive electrode sheet. The coating includes a first coating, a second coating, a third coating, and a fourth coating. The current collector includes a first current collector and a second current collector. The first coating and the second coating are respectively connected to both sides of the first current collector. The length of the first coating on the first current collector is greater than the length of the second coating on the first current collector. The third coating and the fourth coating are respectively connected to both sides of the second current collector. The length of the third coating on the second current collector is greater than the length of the fourth coating on the second current collector. The apertures of the first accommodation holes on the first coating are equal, and the depths of the first accommodation holes gradually decrease from both sides of the electrode tab along the length direction. The depths of the first accommodation holes on the second coating are equal, and the apertures of the first accommodation holes gradually decrease from both sides of the electrode tab along the length direction. The first accommodation holes are provided on the third coating, and the first accommodation holes are not provided on the fourth coating. The apertures of the first accommodation holes on the third coating are equal, and the depths of the first accommodation holes gradually decrease from both sides of the electrode tab along the length direction.

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