Electrode sheet and battery cell

Abstract

An electrode sheet and a battery cell. The electrode sheet comprises a current collector, a tab and a coating, wherein the current collector has a set length direction; the tab is connected to the current collector; and the coating coats the current collector and comprises a first region, the first region corresponds to the tab and is provided with a plurality of first accommodating holes, and the sum of the volumes of the first accommodating holes in a unit region gradually decreases in a direction away from the tab. If the electrode sheet is an anode sheet, the plurality of first accommodating holes can increase the area of lithium ion exchange. If the electrode sheet is a cathode sheet, the plurality of first accommodating holes can reduce the volume of an active material that participates in a reaction. In addition, since the punching of holes is controlled to be merely conducted in the first region and the punching volume gradually decreases in the length direction from both sides of the tab, lithium plating is less liable to occur near the tab, and the influence on the energy density of the battery cell is reduced to a large extent.

Description

A pole piece and a battery cell Technical Field

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

[0002] Lithium deposition is a common problem in lithium-ion batteries 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 address this problem by uniformly perforating the electrode coating. However, this method significantly reduces the energy density of the battery cell and cannot meet the demand for battery cells.

[0003] Summary of the Invention

[0004] 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, when used in a battery cell, can reduce the risk of lithium plating while not significantly reducing the energy density of the battery cell.

[0005] The present invention also provides a battery core having the above-mentioned electrode piece.

[0006] The present invention also provides another battery cell having the above-mentioned electrode piece.

[0007] A pole piece according to an embodiment of the first aspect of the present invention includes:

[0008] A current collector having a set length direction and a set width direction;

[0009] a tab connected to the current collector;

[0010] A coating is applied on the current collector, the coating including a first region corresponding to the electrode tab, the first region being provided with a plurality of first accommodating holes, and the sum of the volumes of the first accommodating holes in a unit region gradually decreasing in a direction away from the electrode tab.

[0011] According to the electrode sheet of the embodiment of the present invention, there are at least the following beneficial effects: the first area corresponds to the location of the electrode tab, and the first area is provided with a plurality of first accommodating holes. In the direction away from the electrode tab, the sum of the volumes of the first accommodating holes in the unit area gradually decreases. 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 difficult for lithium deposition to occur 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 participating in the reaction, making it difficult for lithium deposition to occur 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 holes along the length direction from both sides of the electrode tab, when the electrode sheet is used in a battery cell, lithium deposition is not easy to occur near the electrode tab, while minimizing the impact on the energy density of the battery cell to the greatest extent.

[0012] According to some embodiments of the present invention, the coating includes a plurality of first hole groups, and the plurality of first hole groups are arranged at intervals in the circumferential direction around the tab. Each first hole group includes a plurality of first accommodating holes, and the plurality of first accommodating holes are arranged at intervals in sequence in a direction away from the tab. Along the arrangement direction of the first accommodating holes, the sum of the volumes of the first accommodating holes in a unit area gradually decreases.

[0013] According to some embodiments of the present invention, the aperture diameters of the first accommodating holes are equal, and along the arrangement direction of the first accommodating holes, the hole depths of the first accommodating holes gradually decrease.

[0014] According to some embodiments of the present invention, the length of the first area is L, the width of the electrode plate is W, the thickness of the coating is H, the hole depth of the first accommodating hole is h, 0 < h < H, the distance between the first accommodating hole and the tab is L1, 0 < L1 < L, and the hole depth of the first accommodating hole and the distance between the first accommodating hole and the tab satisfy the relational expression: h = n*(1 - L1 / L)*H, 0.6 ≤ n ≤ 0.9.

[0015] According to some embodiments of the present invention, the coating includes a plurality of second hole groups, each second hole group includes a plurality of first accommodating holes, the plurality of first accommodating holes are arranged at intervals in the circumferential direction around the tab, and the plurality of second hole groups are arranged in sequence in a direction away from the tab. Along the arrangement direction of the second hole groups, the sum of the volumes of the first accommodating holes in a unit area gradually decreases.

[0016] According to some embodiments of the present invention, the aperture diameters of the first accommodating holes are equal, and along the arrangement direction of the second hole groups, the hole depths of the first accommodating holes gradually decrease.

[0017] According to some embodiments of the present invention, the length of the first area is L, the width of the electrode plate is W, the thickness of the coating is H, the hole depth of the first accommodating hole is h, 0 < h < H, the distance between the first accommodating hole and the tab is R0, 0 < R0 < W, and the hole depth of the first accommodating hole and the distance between the first accommodating hole and the tab satisfy the following relational expression: h = n*(1 - R0 / W)*H, 0.5 ≤ n ≤ 0.8.

[0018] According to some embodiments of the present invention, the plurality of first accommodating holes are distributed in the width direction, and along the width direction away from the tab, the sum of the volumes of the first accommodating holes in a unit area gradually decreases.

[0019] According to some embodiments of the present invention, the aperture diameters of the first accommodating holes are equal, and along the width direction away from the tab, the hole depths of the first accommodating holes gradually decrease.

[0020] According to some embodiments of the present invention, the thickness of the coating is H, the width of the electrode is W, the distance from the hole to the top of the electrode is W1, and the relationship between the depth h1 of the first accommodating hole and the width of the electrode satisfies: h1 = n*(1 - W1 / W)*H, where 0.6 ≤ n ≤ 0.8.

[0021] According to some embodiments of the present invention, the apertures of each of the first accommodating holes are equal, and from both sides of the tab to the length direction, the depths of the first accommodating holes gradually decrease.

[0022] According to some embodiments of the present invention, the length of the first region is L, the thickness of the coating is H, the depth h of the first accommodating hole, where 0 < h < H, the distance between the first accommodating hole and the tab is d, where 0 < d < L, and the relationship between the depth h of the first accommodating hole and the distance d between the hole and the tab satisfies: h = (1 - d / L)*n*H, where 0.65 ≤ n ≤ 0.92.

[0023] According to some embodiments of the present invention, the depths of each of the first accommodating holes are equal, and from both sides of the tab to the length direction, the apertures of the first accommodating holes gradually decrease.

[0024] According to some embodiments of the present invention, the length of the first region is L, the width is W, the distance between the first accommodating hole and the tab is d, where 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, where 0.005W < R1 < 0.02W; wherein, the relationship between the radius R of the first accommodating hole and the distance d between the first accommodating hole and the tab satisfies: R = (1 - d / L)*s*R1, where 0.5 ≤ s ≤ 1.

[0025] According to some embodiments of the present invention, from both sides of the tab to the length direction, the number of the first accommodating holes per unit area gradually decreases.

[0026] According to some embodiments of the present invention, the mass loss of the electrode is less than 1%.

[0027] According to some embodiments of the present invention, the first region is provided with a plurality of third hole groups, the third hole group includes a plurality of first accommodating holes arranged at intervals in the width direction, and the plurality of third hole groups are arranged at intervals in the length direction, and the depths and radii of the first accommodating holes in the same third hole group are equal.

[0028] According to some embodiments of the present invention, 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.

[0029] 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.

[0030] 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, 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 in the direction away from 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 holes 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 energy density of the battery cell to the greatest extent.

[0031] According to an embodiment of the third aspect of the present invention, 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 embodiment of the first aspect.

[0032] 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 area corresponds to the location of the pole piece, the first area is provided with a plurality of first accommodating holes, and the sum of the volumes of the first accommodating holes in the unit area gradually decreases in the direction away from 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, so that lithium deposition is not likely to occur in the area near the pole piece. 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, so that lithium deposition is not likely to occur in the area near the pole piece. In addition, by controlling the drilling only in the first area and gradually reducing the volume of the holes along the length direction from both sides of the pole piece, lithium deposition is not likely to occur near the pole piece, while minimizing the impact on the energy density of the battery cell to the greatest extent.

[0033] Additional aspects and advantages of the present invention will be set forth in part in the description which follows and, in part, will be obvious from the description which follows, or may be learned by practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The present invention will be further described below with reference to the accompanying drawings and embodiments, in which:

[0035] FIG1 is a schematic diagram of a pole piece according to an embodiment of the present invention;

[0036] FIG2 is a cross-sectional view of a pole piece according to an embodiment of the present invention, in which the hole diameter remains constant and the hole depths at both ends decrease successively along the length direction of the pole tab;

[0037] FIG3 is a cross-sectional view of a pole piece according to an embodiment of the present invention, in which the hole depth remains constant and the hole diameters at both ends decrease successively along the length direction of the pole tab;

[0038] FIG4 is a schematic diagram of a pole piece in which the hole depth and the hole diameter remain constant and the density of the holes at both ends along the length direction of the pole tab gradually decreases according to an embodiment of the present invention.

[0039] FIG5 is a schematic diagram of a pole piece according to an embodiment of the present invention, in which the hole diameter remains constant and the hole depth decreases gradually along the width direction away from the pole ear.

[0040] FIG6 is a cross-sectional view of the embodiment of FIG5 at position “AA”;

[0041] FIG7 is a schematic diagram of a pole piece with a constant aperture and holes punched along a direction away from the pole lug according to an embodiment of the present invention.

[0042] FIG8 is a cross-sectional view of the embodiment of FIG7 at position “BB”;

[0043] FIG9 is a schematic diagram of a pole piece with a constant aperture and concentrically perforated in a direction away from the pole lug according to an embodiment of the present invention;

[0044] FIG10 is a cross-sectional view of the “CC” position in FIG9 .

[0045] Reference numerals:

[0046] The current collector 100 , the tab 200 , the coating 300 , the third hole group 310 , the first accommodating hole 311 , the second accommodating hole 320 , the first region 330 , the second region 340 , the first hole group 350 , and the second hole group 360 . DETAILED DESCRIPTION

[0047] 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.

[0048] 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.

[0049] In the description of the present invention, "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 "first" and "second" in the description is solely for the purpose of distinguishing technical features and should not 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.

[0050] In the description of the present invention, unless otherwise clearly defined, terms such as setting, installing, and connecting 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.

[0051] 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.

[0052] 1 to 10 , an embodiment of the first aspect of the present invention provides a pole piece, comprising 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 to the current collector 100, and the coating 300 includes a first region 330. The first region 330 is arranged around the pole tab 200, and the first region 330 is provided with a plurality of first accommodating holes 311. The plurality of 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 region gradually decreases from both sides of the pole tab 200 to the length direction.

[0053] The 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 as it moves away from the tab 200. If the electrode sheet is an anode, the plurality of first accommodating holes 311 can increase the area of ​​the first region 330 available for lithium ion exchange. That is, both the bottom and side walls of the first accommodating holes 311 are available for lithium ion exchange, thereby reducing the likelihood of lithium deposition near the tab 200. If the electrode sheet is a cathode, the plurality of first accommodating holes 311 can reduce the volume of the cathode active material involved in the reaction, thereby reducing the likelihood of lithium deposition near the tab 200. Furthermore, by restricting the perforations to the first region 330 and gradually decreasing the perforations along the length of the tab 200 from both sides, the electrode sheet can be used in a battery cell to reduce lithium deposition near the tab 200 while minimizing the impact on the cell's energy density.

[0054] The lithium deposition experiment was conducted on the present embodiment and the control group, and the experimental results are shown in Table 1 below:

[0055] Table 1: Lithium precipitation experiment results

[0056] Among them, experimental group 1 is the scheme adopted in this embodiment, while control group 1 is a scheme in which the total punching volume is the same as that of experimental group 1 but the volume of the first receiving hole 311 remains unchanged, and control group 2 is a scheme in which the volume of a single first receiving hole 311 remains unchanged and the weight loss is 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 receiving holes 311 per unit area decreases successively has the same improvement effect on lithium deposition in the corresponding area of ​​the tab 200 as the punching method in which the punching volume remains unchanged, and can also reduce weight loss and reduce the impact on the energy density of the battery cell. When the mass loss is similar, the punching method of this embodiment significantly improves lithium deposition in the battery cell compared to the method in which the punching volume remains unchanged in control group 2.

[0057] Furthermore, since all current must flow through the tab 200 and be output externally, the current density near the tab 200 is higher during use, leading to more side reactions. This results in faster electrolyte consumption in the area near the tab 200, and purple spots and lithium deposition may occur in the later stages of the battery cell cycle due to a lack of electrolyte. Multiple first accommodating holes 311 can accommodate more electrolyte during the battery cell injection process, allowing the electrolyte to better penetrate the battery cell through the multiple first accommodating holes 311, thereby providing sufficient electrolyte for the later stages of the battery cell cycle. For example, the volume of electrolyte that can be accommodated in the area near the tab 200 of a conventional battery cell is V1. In the later stages of a conventional battery cell cycle, the surface depletion of V1 makes V1 almost zero, and purple spots may appear inside the battery cell due to insufficient electrolyte. When the electrode surface is perforated, the volume of a single first accommodating hole 311 is V2. If n first accommodating holes 311 are provided, the total volume of electrolyte that can be accommodated is V1 + nV2. After V1 is exhausted, V2 can still provide electrolyte to support the amount required for the later cycle of the battery cell, thereby prolonging the time when purple spots appear due to insufficient electrolyte.

[0058] 7 and 8 , in some embodiments, the coating includes a plurality of first hole groups 350 , which are spaced apart in the circumferential direction of the tab 200 . The first hole groups 350 include a plurality of first accommodating holes 311 , which are spaced apart in a direction away from the tab 200 . Along the arrangement direction of the first accommodating holes 311 , the sum of the volumes of the first accommodating holes 311 per unit area gradually decreases, making the area near the tab 200 less susceptible to lithium deposition. At the same time, the sum of the volumes of the plurality of first accommodating holes 311 in areas away from the tab 200 is smaller, thereby reducing the impact on the energy density of the battery cell. The effect of gradually decreasing the sum of the volumes of the first accommodating holes 311 per unit area can be achieved by varying parameters such as the depth of the first accommodating holes 311 in different first hole groups 350 or the diameter of the first accommodating holes 311 in different first hole groups 350 .

[0059] 7 and 8 , in some embodiments, the apertures of the first receiving holes 311 are equal, and the depths of the first receiving holes 311 gradually decrease along the arrangement direction of the first receiving holes 311. The centers of the multiple first receiving holes 311 provided in the same first hole group 350 are all located on the same connecting line (i.e., the dotted line in FIG7 ), and the connecting lines of the multiple first hole groups 350 all intersect at the center of the tab 200. That is, the multiple connecting lines can be regarded as rays emitted from the tab 200, and the hole depths of the first receiving holes 311 gradually decrease along the extension direction of the rays.

[0060] Further, the length of the first region 330 is L, the width of the pole piece is W, the thickness of the coating is H, the depth of the first accommodating hole 311 is h, 0 < h < H, the distance between the first accommodating hole 311 and the tab 200 is L1, L1(0 < L1 < L), and the depth of the first accommodating hole 311 and the distance between the first accommodating hole 311 and the tab 200 satisfy the relational expression: h = n*(1 - L1 / L)*H, 0.6 ≤ n ≤ 0.9. Wherein, n can be selected as 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9 or any other value within 0.6 - 0.9.

[0061] When drilling holes with a gradient along the ray extension direction, experiments were conducted on the influence of lithium deposition on the drilling depth at different rates. The experimental results are shown in Table 2 below:

[0062] Table 2: Lithium Deposition Experiment Results II

[0063] From the experimental results in Table 2, it can be seen that the effect of drilling holes with a gradient along the ray extension direction is good and can be flexibly adjusted according to different products. That is, when the battery cell is a low-rate battery cell, a smaller n value can be selected, while when the battery cell is a high-rate battery cell, a larger n value is required to achieve the purpose of improving lithium deposition.

[0064] Referring to FIGS. 9 and 10, in some embodiments, the coating includes a plurality of second hole groups 360. The second hole group 360 includes a plurality of first accommodating holes 311. The plurality of first accommodating holes 311 are arranged at intervals in the circumferential direction around the tab 200. The plurality of second hole groups 360 are arranged in sequence in the direction away from the tab 200. Along the arrangement direction of the second hole group 360, the sum of the volumes of the first accommodating holes 311 in the unit area gradually decreases. The connection line of the centers of the plurality of first accommodating holes 311 in the second hole group 360 (the dotted line in FIG. 9) is an arc with the center located at the center of the tab 200. That is, the distances from each of the first accommodating holes 311 in the same second hole group 360 to the tab 200 are equal, and the connection lines of the plurality of second hole groups 360 are a plurality of concentric arcs arranged at intervals in the radial direction. By changing the depth of the first accommodating holes 311 in different second hole groups 360, the distance between adjacent second hole groups 360, or the aperture size of the first accommodating holes 311 in different second hole groups 360, the effect that the sum of the volumes of the first accommodating holes 311 in the unit area gradually decreases can be achieved.

[0065] Referring to FIGS. 9 and 10, in some embodiments, the aperture diameters of the first accommodating holes 311 are equal, and along the arrangement direction of the second hole group 360, the hole depths of the first accommodating holes 311 gradually decrease. On the premise that the aperture diameters of the first accommodating holes 311 are equal, the amount of active material removed by the second hole group 360 farther away from the tab 200 is less, so that it can meet the requirement that no lithium deposition occurs in the area near the tab 200 while having a relatively small impact on the energy density of the battery cell. Further, the length of the first region 330 is L, the width of the electrode sheet is W, the thickness of the coating is H, the hole depth of the first accommodating hole 311 is h, 0 < h < H, the distance between the first accommodating hole 311 and the tab 200 is R0 (i.e., the radius of the corresponding concentric arc), 0 < R0 < W, and the hole depth of the first accommodating hole 311 and the distance between the first accommodating hole 311 and the tab 200 satisfy the following relational expression: h = n*(1 - R0 / W)*H, 0.5 ≤ n ≤ 0.8. Here, n can be selected as 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, or any other value within 0.5 - 0.8.

[0066] Lithium deposition experiments were carried out on the solutions of this embodiment and the control group, and the experimental results are shown in Table 3 below:

[0067] Table 3: Lithium deposition experiment results III

[0068] Referring to Table 3, when comparing the way of punching holes with equal depth and the way of punching holes in this embodiment, on the premise of the same improvement in the lithium deposition effect, the loss of active material of the electrode sheet in this embodiment is smaller, and the impact on the energy density of the battery cell is also smaller.

[0069] Referring to FIGS. 5 and 6, in some embodiments, the plurality of first accommodating holes 311 are distributed along the width direction, and along the width direction on the side away from the tab 200, the sum of the volumes of the first accommodating 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 plurality of first accommodating holes 311 in the area far from the tab 200 along the width direction is smaller, and thus the impact on the energy density of the battery cell can be reduced. The effect that the sum of the volumes of the first accommodating holes 311 in the unit area gradually decreases can be achieved by changing the hole depth and / or the aperture size of each first accommodating hole 311.

[0070] In some embodiments, the apertures of the first accommodation holes 311 are equal, and along the width direction away from the side where the tab 200 is located, the depth of the first accommodation holes 311 gradually decreases. Further, the thickness of the coating is H, the width of the electrode sheet is W, the distance from the hole to the top of the electrode sheet is W1, and the relationship between the depth h1 of the first accommodation hole 311 and the width of the electrode sheet satisfies: h1 = n*(1 - W1 / W)*H, where 0.6 ≤ n ≤ 0.8. Here, n can be selected as 0.6, 0.65, 0.7, 0.75, 0.8 or any other value within 0.6 - 0.8. The selection of the value n is related to the charge-discharge rate of the battery cell. Refer to other embodiments in this application for details, which will not be elaborated here.

[0071] The lithium plating experiment was conducted on the solution of this embodiment and the control group, and the experimental results are shown in Table 4 below:

[0072] Table 4: Lithium Plating Experiment Results IV

[0073] Referring to Table 4, on the premise of the same improvement effect on lithium plating, compared with equal-depth drilling, the gradient drilling in the width direction causes less loss of the active material of the electrode sheet and has less impact on the energy density of the battery cell. Moreover, when the maximum drilling depth is relatively deep, the saving effect of the gradient drilling on the active material is more obvious.

[0074] Referring to FIG. 2, in some embodiments, the apertures of the first accommodation holes 311 are equal, and along the length direction from both sides of the tab 200, the depth of the first accommodation holes 311 gradually decreases, so that along the length direction from both sides of the tab 200, the sum of the volumes of the first accommodation holes 311 in the unit area gradually decreases. While making it not easy to occur lithium plating 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 small, and the impact on the energy density of the battery cell can be reduced. Further, the length of the first region 330 is L, the thickness of the coating 300 is H, the depth of the first accommodation hole 311 is h, where 0 < h < H, and the distance between the first accommodation hole 311 and the tab 200 is d, where 0 < d < L. When the battery cell is applied to a high rate (above 3.0C), when the depth h of the first accommodation hole 311 and the distance d between the hole and the tab 200 satisfy the relationship: h = (1 - d / L)*0.9H, the improvement of lithium plating is the best.

[0075] The experiment on the influence of the drilling depth on lithium plating at different rates was conducted, and the experimental results are shown in Table 5 below:

[0076] Table 5: Lithium Plating Experiment Results V

[0077] Referring to FIG. 2, Experiment Result Five is to punch holes in the manner shown in FIG. 2. The apertures of each first accommodating hole 311 are equal. From both sides of the tab 200 to the length direction, the depth of the first accommodating 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 accommodating holes 311 in the unit area gradually decreases. Through Experiment Result Five of lithium deposition analysis, it can be found that the improvement of lithium deposition is also related to the charge-discharge rate of the battery cell. Laser punching of the electrode can also improve the charge-discharge performance of the battery cell. There is a positive correlation between the battery cell rate and the punching depth. That is, when the rate of the battery cell is relatively low, a relatively small punching depth can significantly improve the charging ability and no lithium deposition occurs. After the punching depth increases to a certain extent, there is no obvious improvement in the charge-discharge performance of the battery cell. When the rate of the battery cell is relatively high, a relatively deep punching depth is required to ensure no lithium deposition. Further, the length of the first region 330 is L, the thickness of the coating 300 is H, the depth of the first accommodating hole 311 is h, 0 < h < H, the distance between the first accommodating hole 311 and the tab 200 is d, 0 < d < L. The depth h of the first accommodating hole 311 and the distance d between the hole and the tab 200 satisfy the relationship: h = (1 - d / L) * nH, 0.65 ≤ n ≤ 0.92, where n can be selected as 0.67, 0.70, 0.72, 0.75, 0.78, 0.80, 0.82, 0.85, 0.88, 0.90 or any other value between 0.65 and 0.92.

[0078] Lithium deposition experiments were carried out on the solution of this embodiment and the control group. The experimental results are shown in Table 6 below:

[0079] Table 6: Experiment Result Six of Lithium Deposition

[0080] Among them, the experimental group 20 is the solution adopted in this embodiment, while the control group 12 is a solution with the same maximum punching depth as the experimental group 20 but the punching depth remains unchanged, and the control group 13 is a solution with the punching depth unchanged and the weight loss similar to that of the experimental group 20. It can be seen from the above table that the punching methods with gradually decreasing punching depth and the punching method with unchanged punching depth have the same improvement effect on lithium deposition in the corresponding area of the tab 200, and can also reduce the weight loss and the influence on the energy density of the battery cell. When the mass loss is the same, the punching method of this embodiment can significantly improve lithium deposition in the battery cell compared with the method of the control group 2 with unchanged punching depth.

[0081] Referring to FIG. 3, in some embodiments, the depths of the first accommodating holes 311 are equal. From both sides of the tab 200 to the length direction, the aperture diameters of the first accommodating holes 311 gradually decrease. Thus, from both sides of the tab 200 to 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 plating 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 energy density of the battery cell 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 expression: R = (1 - d / L) * sR1, 0.5 ≤ s ≤ 1. s can be selected as 0.5, 0.6, 0.7, 0.8, 0.9, 1.0 or any other value between 0.5 and 1.0. 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. And 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.

[0082] The lithium plating experiment was carried out on the solution of this embodiment and the control group, and the experimental results are shown in Table 7 below:

[0083] Table 7: Lithium plating experiment results VII

[0084] Among them, the experimental group 21 is the solution adopted in this embodiment, while the control group 14 is the solution with the same punching depth as the experimental group 21 but the punching radius unchanged, and the control group 15 is the solution with the punching depth unchanged and the weight loss similar to the experimental group 21. As can be seen from the above, when the mass loss is the same, the punching method of this embodiment significantly improves the lithium plating of the battery cell compared with the method with the same punching depth but the unchanged punching radius, and the energy density loss is reduced. Compared with the solution with the unchanged punching radius and the similar mass loss, it has a better improvement effect on the lithium plating near the tab 200.

[0085] An experiment was carried out on the influence of the radius R1 of the first accommodating hole 311 on the improvement of lithium plating, and the experimental results are shown in Table 8 below:

[0086] Table 8: Lithium plating experiment results VIII

[0087] Through the lithium deposition experiment results eight, it can be found that the improvement effect of the radius of the first accommodating hole 311 on the lithium deposition of the battery cell first increases and then weakens. When s is between 0.7 and 0.8, the improvement effect is most obvious. When the radius of the first accommodating hole 311 is too large and exceeds a certain value, for example, when it exceeds 0.8, the improvement effect on the lithium deposition of the battery cell will be reduced.

[0088] 4 , in some embodiments, the aperture and depth of each first accommodating hole 311 are equal, and the number of the first accommodating holes 311 per unit area gradually decreases from the two 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 gradually decreases from the two sides of the pole tab 200 to the length direction, making it less likely for lithium deposition to occur in the area near the pole tab 200, while 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 energy density of the battery cell.

[0089] 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.

[0090] 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 the battery cell 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.

[0091] 4 , in some embodiments, a plurality of third hole groups 310 are provided in the first region 330, and the third hole group 310 includes a plurality of first accommodating holes 311 spaced apart along the width direction, and the plurality of third 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 third hole group 310 are equal, so that the volume of the first accommodating holes 311 in the plurality of third hole groups 310 decreases successively from both sides of the tab 200 to the length direction.

[0092] 1 , in 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.

[0093] A second embodiment of the present invention provides a battery cell (not shown in the figure). 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 electrode sheet and the second electrode sheet. At least one of the first electrode sheet and the second electrode sheet is the electrode sheet provided in the first embodiment. This allows the battery cell to have at least all the advantages of the 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 provided. 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 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, making the area near the tab 200 less susceptible to lithium deposition. 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, making the area near the tab 200 less susceptible to lithium deposition. 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 the cell's energy density.

[0094] The third embodiment of the present invention provides a battery cell (not shown in the figure), including multiple first pole pieces, multiple second pole pieces and multiple diaphragms, wherein 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. At least a portion of the multiple first pole pieces and the multiple second pole pieces are the pole pieces provided by the first embodiment above, and the time for lithium deposition to occur in at least some of the pole pieces in the battery cell can be extended, thereby extending the service life of the battery cell as a whole. The battery cell provided in this embodiment is a laminated battery cell, which is made by stacking the first pole piece and the second pole piece, both of which are coated with a diaphragm.

[0095] The embodiments of the present invention are described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the above embodiments. Various changes can be made within the scope of knowledge possessed by ordinary technicians in the relevant technical field without departing from the spirit of the present invention. In addition, the embodiments of the present invention and the features in the embodiments can be combined with each other without 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 accommodation holes, and in a direction away from the tab, the sum of the volumes of the first accommodation holes in a unit area gradually decreases.

2. The pole piece according to claim 1, characterized in that: The coating includes a plurality of first hole groups, the plurality of first hole groups are arranged at intervals in the circumferential direction around the tab, the first hole group includes a plurality of the first accommodation holes, the plurality of first accommodation holes are arranged at intervals in sequence in a direction away from the tab, and in the arrangement direction of the first accommodation holes, the sum of the volumes of the first accommodation holes in a unit area gradually decreases.

3. The pole piece according to claim 2, characterized in that: The aperture diameters of the first accommodation holes are equal, and in the arrangement direction of the first accommodation holes, the hole depths of the first accommodation holes gradually decrease.

4. The pole piece according to claim 3, characterized in that: The length of the first region is L, the width of the pole piece is W, the thickness of the coating is H, the hole depth of the first accommodation hole is h, 0 < h < H, the distance between the first accommodation hole and the tab is L1, 0 < L1 < L, and the depth of the first accommodation hole and the distance between the first accommodation hole and the tab satisfy the relational expression: h = n*(1 - L1 / L)*H, 0.6 ≤ n ≤ 0.

9.

5. The pole piece according to claim 1, characterized in that: The coating includes a plurality of second hole groups, the second hole group includes a plurality of the first accommodation holes, the plurality of first accommodation holes are arranged at intervals in the circumferential direction around the tab, the plurality of second hole groups are arranged in sequence in a direction away from the tab, and in the arrangement direction of the second hole group, the sum of the volumes of the first accommodation holes in a unit area gradually decreases.

6. The pole piece according to claim 5, characterized in that: The aperture diameters of the first accommodation holes are equal, and in the width direction from the tab, the hole depths of the first accommodation holes gradually decrease.

7. The pole piece according to claim 6, characterized in that: The length of the first region is L, the width of the pole piece is W, the thickness of the coating is H, the hole depth of the first accommodation hole is h, 0 < h < H, the distance between the first accommodation hole and the tab is R0, 0 < R0 < W, and the hole depth of the first accommodation hole and the distance between the first accommodation hole and the tab satisfy the following relational expression: h = n*(1 - R0 / W)*H, 0.5 ≤ n ≤ 0.

8.

8. The pole piece according to claim 1, characterized in that: The plurality of first accommodation holes are distributed in the width direction, and in the width direction on the side away from the tab, the sum of the volumes of the first accommodation holes in a unit area gradually decreases.

9. The pole piece according to claim 8, characterized in that: The aperture diameters of the first accommodation holes are equal, and in the width direction on the side away from the tab, the hole depths of the first accommodation holes gradually decrease.

10. The pole piece according to claim 9, characterized in that: The thickness of the coating is H, the width of the pole piece is W, the distance of the hole from the top of the pole piece is W1, and the relational expression between the depth h1 of the first accommodation hole and the width of the pole piece satisfies: h1 = n*(1 - W1 / W)*H, 0.6 ≤ n ≤ 0.

8.

11. The pole piece according to claim 1, characterized in that: The plurality of first accommodation holes are distributed in the length direction, and from both sides of the tab along the length direction, the sum of the volumes of the first accommodation holes in a unit area gradually decreases.

12. The pole piece according to claim 11, characterized in that: The aperture diameters of the first accommodation holes are equal, and from both sides of the tab along the length direction, the hole depths of the first accommodation holes gradually decrease.

13. The pole piece according to claim 12, 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, where 0 < h < H, the distance between the first accommodating hole and the tab is d, where 0 < d < L, and the depth h of the first accommodating hole and the distance d between the hole and the tab satisfy the relation: h = (1 - d / L) * n * H, where 0.65 ≤ n ≤ 0.

92.

14. The pole piece according to claim 11, characterized in that: The depths of the first accommodating holes are equal. Along the length direction from both sides of the tab, the aperture of the first accommodating hole gradually decreases.

15. The pole piece according to claim 14, characterized in that: The length of the first region is L, the width of the electrode tab is W, the distance between the first accommodating hole and the tab is d, where 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, where 0.005W < R1 < 0.02W; Among them, the radius R of the first accommodating hole and the distance d between the first accommodating hole and the tab satisfy the following relation: R = (1 - d / L) * s * R1, where 0.5 ≤ s ≤ 1.

16. The pole piece according to claim 11, characterized in that: The apertures and depths of the first accommodating holes are equal. Along the length direction from both sides of the tab, the number of the first accommodating holes per unit area gradually decreases.

17. The pole piece according to any one of claims 1 to 16, characterized in that: The mass loss of the electrode tab is less than 1%.

18. The pole piece according to any one of claims 11 to 16, characterized in that: A plurality of third hole groups are provided in the first region. Each third hole group includes a plurality of first accommodating holes arranged at intervals in the width direction, and the plurality of third hole groups are arranged at intervals in the length direction. The depths and radii of the first accommodating holes in the same third hole group are equal.

19. The pole piece according to any one of claims 1 to 16, characterized in that: The coating further includes a second region corresponding to the bending region of the battery cell. A plurality of second accommodating holes are provided in the second region, and the plurality of second accommodating holes are evenly distributed in the second region.

20. A battery cell, characterized in that: It includes a separator, a first electrode tab and a second electrode tab. The separator is disposed between the first electrode tab and the second electrode tab, and at least one of the first electrode tab and the second electrode tab is the electrode tab according to any one of claims 1-19.

21. A battery cell, characterized in that: It includes a plurality of first electrode tabs, a plurality of second electrode tabs and a plurality of separators. The plurality of first electrode tabs and the plurality of second electrode tabs are stacked in sequence, the separator is disposed between adjacent first electrode tabs and second electrode tabs, and at least a part of the plurality of first electrode tabs and the plurality of second electrode tabs is the electrode tab according to any one of claims 1-19.

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