Electrode sheet and battery cell

Abstract

An electrode sheet, comprising a first surface and a second surface which are oppositely arranged, a first active substance layer being provided on each of the first surface and the second surface. The electrode sheet has a first direction and a second direction, bright regions and dark regions being alternately arranged on the first active material layer in the first direction of the electrode sheet, the bright regions extending in the second direction of the electrode sheet, and the edges of the bright regions in the second direction being within the edge of the electrode sheet in the second direction. In the electrode sheet, the width of gap lithium strips is shortened to be smaller than the width of the first active substance layer, such that the lithium strips are prevented from extending out of the edge of the first electrode sheet, thereby solving the problem of lithium burrs on the edge of the first electrode sheet. Further provided is a battery cell, which comprises said electrode sheet and further comprises a second electrode sheet having a third surface and a fourth surface which are oppositely arranged, a second active layer being provided on each of the third surface and the fourth surface.

Description

Electrode sheet and battery cell Technical Field

[0001] The present application relates to the field of battery technology, and in particular to an electrode plate and a battery cell.

[0002] Background of the Invention

[0003] Silicon materials have a high theoretical specific capacity, making them an ideal material for replacing graphite anodes and increasing the energy density of lithium-ion batteries. However, in practical applications, silicon materials also have a significant shortcoming: the coulombic efficiency of the first charge and discharge cycle is lower than that of graphite anodes (the initial efficiency of silicon-based anodes is generally around 70%). An effective method is to pre-fill the electrode with lithium to replenish the irreversible capacity consumed in the first cycle, improve the initial efficiency of silicon-doped batteries, and thus increase the battery's energy density.

[0004] The most direct way to replenish lithium is to use interstitial lithium strips to directly laminate with the electrode. However, the current lithium replenishment method easily causes edge lithium burrs on the edge of the electrode, and these edge lithium burrs have the risk of piercing the diaphragm and causing safety hazards.

[0005] Summary of the Invention

[0006] In view of this, in order to address the technical problem in the related art that edge lithium burrs exist on the edges of the pole pieces that have undergone the lithium replenishment process, the present application provides an electrode pole piece and a battery cell. By shortening the width of the gap lithium strip to make it smaller than the width of the pole piece, the lithium strip of the gap lithium strip is avoided from extending to the outside of the edge of the pole piece, thereby solving the problem of edge lithium burrs on the edge of the pole piece.

[0007] In order to achieve the above objectives, this application provides the following technical solutions:

[0008] An electrode pad comprises: a first surface and a second surface arranged opposite to each other, a first active material layer being provided on the first surface and the second surface respectively; the electrode pad has a first direction and a second direction; bright areas and dark areas are alternately provided on the first active material layer along the first direction of the electrode pad, the bright areas extend along the second direction of the electrode pad, and the edges of the bright areas in the second direction are within the edges of the electrode pad in the second direction.

[0009] Optionally, the distance between the edge of the bright area in the second direction and the edge of the electrode plate in the second direction is 0.1-2 mm.

[0010] Optionally, there is a height difference between the surfaces of the bright area and the dark area, and the height difference ranges from 0.1 to 30 μm.

[0011] The electrode plate provided in the present application shortens the width of the gap lithium strip to make it smaller than the width of the first active material layer on the electrode plate, thereby avoiding the lithium strip of the gap lithium strip extending to the outside of the edge of the electrode plate, solving the problem of edge lithium burrs on the edge of the electrode plate, and avoiding the risk of edge lithium burrs failing to fit with the side end surface of the plate and becoming free in the battery cell and piercing the diaphragm to cause a safety hazard.

[0012] The present application also provides a battery cell, comprising the electrode plate of any of the above embodiments, and further comprising a second plate, wherein the second plate comprises a third surface and a fourth surface arranged opposite to each other, and a second active material layer is respectively provided on the third surface and the fourth surface.

[0013] Optionally, the edge of the bright area on the electrode plate in the second direction exceeds the edge of the second active material layer in the second direction, or the edge of the bright area on the electrode plate in the second direction is flush with the edge of the second active material layer in the second direction.

[0014] Optionally, a distance between an edge of the bright area on one side in the second direction and an edge of the second active material layer on the same side in the second direction is greater than or equal to 0.1 mm.

[0015] Optionally, a plurality of tabs are provided on one side of the second direction of the second active material layer, an insulating layer is further provided between the second active material layer and the plurality of tabs, and the insulating layer overlaps with an edge of the bright area on one side of the plurality of tabs.

[0016] Optionally, a diaphragm is provided between the electrode plate and the second electrode plate, and at least one side edge of the diaphragm in the second direction exceeds two side edges of the bright area in the second direction by at least 0.5 mm.

[0017] Optionally, both side edges of the bright area in the second direction extend beyond both side edges of the second active material layer in the second direction by at least 0.1 mm.

[0018] The battery cell provided in this application is used for lithium batteries, which can improve the battery's initial efficiency, energy density and cycle performance, and can avoid safety hazards caused by edge lithium burrs.

[0019] BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the technical solutions in the embodiments of the present application or related technologies, the following briefly introduces the drawings required for use in the embodiments or related technical descriptions. Obviously, the drawings described below are merely embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without any creative work.

[0021] FIG1 is a schematic diagram showing the first active material layer on the first surface and the second surface of the first electrode in the prior art where lithium is replenished on the entire surface through interstitial lithium strips.

[0022] FIG2 is a schematic diagram of a first surface of a first electrode sheet covered with interstitial lithium strips in the prior art.

[0023] FIG3 is a schematic diagram of the first electrode after the lithium replenishment process in this application.

[0024] FIG4 is a schematic diagram of the interlayer structure of each layer after the first pole piece of FIG3 is wound into a battery core.

[0025] FIG5 is a schematic diagram of the boundary between the bright area and the dark area on the surface of the first pole piece in FIG3 .

[0026] FIG6 is a schematic diagram showing the processing process of the first pole piece and the second pole piece of the multi-tab wound battery cell.

[0027] FIG7 is a schematic diagram of the first pole piece structure of a multi-electrode wound battery cell.

[0028] FIG8 is a schematic diagram of the second pole piece structure of a multi-electrode wound battery cell.

[0029] Figure 9 is a schematic diagram of the interlayer alignment structure of a multi-electrode wound battery cell.

[0030] In Figures 1 to 9: 1. First pole piece; 11. Copper foil; 12. First active material layer; 121. Head boundary of first active layer; 122. Bottom boundary of first active layer; 123. Cutting boundary of first active layer; 2. Second pole piece; 21. Aluminum foil; 22. Second active material layer; 221. Head boundary of second active layer; 23. Insulating ceramic layer; 231. Head boundary of insulating layer; 232. Bottom boundary of insulating layer; 3. Diaphragm; 4. Gap lithium strip; 41. Lithium strip; 42. Edge lithium burr; 431. Head boundary of lithium strip layer; 432. Bottom boundary of lithium strip layer.

[0031] Modes for Carrying Out the Invention

[0032] The present application provides an electrode plate and a battery cell, the structure of which shortens the width of the gap lithium strip to make it smaller than the width of the first active material layer on the electrode plate, thereby avoiding the lithium strip of the gap lithium strip extending to the outside of the edge of the electrode plate, solving the problem of edge lithium burrs on the edge of the electrode plate, and avoiding the risk of edge lithium burrs failing to fit with the side end surface of the plate and becoming free in the battery cell and piercing the diaphragm, causing a safety hazard.

[0033] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0034] Using interstitial lithium ribbons to directly laminate with the electrode is the most direct way to replenish lithium. However, in actual operation, in order to fully cover the electrode with the interstitial lithium ribbon, the interstitial lithium ribbon often exceeds the electrode in the width direction, which results in edge lithium burrs on the edge of the electrode after the lithium replenishment process. The greater the surface density of the interstitial lithium ribbon, the more difficult it is to remove the edge lithium burrs. These edge lithium burrs fail to fit with the side end faces of the electrode and cannot form an active lithium source. Instead, they are free in the battery cell and have the risk of piercing the diaphragm and causing safety hazards.

[0035] The structure of the electrode plate in the prior art is shown in Figure 1-2, where the x direction in the figure is the first direction of the electrode plate, that is, the first plate 1, and the y direction is the second direction of the first plate 1. In the prior art, the gap lithium strip 4 completely covers the second direction of the first plate 1 and is wider than the first plate 1; as shown in Figure 2, the gap lithium strip 4 includes a plurality of lithium strips 41 distributed along its first direction, and the lithium strips 41 extend along the second direction of the gap lithium strip 4, and there is a gap between two adjacent lithium strips 41. It can be seen from Figure 2 that the lithium strips 41 and the gap appear alternately along the first direction of the gap lithium strip 4, and the lithium strips 41 form a lithium replenishment area on the first plate 1, and the gap between the two adjacent lithium strips 41 is a non-lithium replenishment area on the first plate 1. The lithium replenishment area and the non-lithium replenishment area are characterized as bright areas and dark areas on the surface of the first plate 1.

[0036] The first active material layer 12 on the first surface of the first electrode piece 1 and the first active material layer 12 on the second surface of the first electrode piece 1 are both connected with a gap lithium strip 4, and the gap lithium strip 4 completely covers the first active material layer 12 on the first surface and the second surface. In order to achieve this requirement, it is necessary to make the width of the gap lithium strip 4 greater than the width of the first electrode piece 1, that is, there is a portion of the gap lithium strip 4 that exceeds the second direction edge of the first electrode piece 1. Therefore, there is a problem of edge lithium burrs 42 on the edge of the first electrode piece 1. The edge lithium burrs 42 are easy to be freed in the battery cell and pierce the diaphragm 3 in the subsequent process, causing safety hazards.

[0037] As shown in FIG3 , the present application provides an electrode plate, namely, the first electrode plate 1 in this embodiment. In this embodiment, the first electrode plate 1 is a negative electrode plate, and the first electrode plate 1 includes a copper foil 11 (not shown in FIG3 , but see FIG9 ) and two first active material layers 12 provided on the upper surface (i.e., the first surface) and the lower surface (i.e., the second surface) of the copper foil 11.

[0038] The interstitial lithium strip 4 includes a plurality of lithium strips 41 distributed along a first direction thereof. The lithium strips 41 extend along a second direction of the interstitial lithium strip 4 , and there is a gap between two adjacent lithium strips 41 .

[0039] The first active material layer 12 is covered and connected with a gap lithium strip 4, and the lithium strip strip 41 extends along the second direction of the first electrode 1, that is, the second direction of the gap lithium strip 4 covered and connected to the first electrode 1 is consistent with the second direction of the first electrode 1, and the edge of the gap lithium strip 4 is within the edge of the first active material layer 12, that is, the size of the gap lithium strip 4 in at least the second direction is smaller than the size of the first active material layer 12 in the second direction.

[0040] The electrode plate provided in the present application shortens the width of the gap lithium strip 4 to make it smaller than the width of the first active material layer 12, thereby avoiding the lithium strip 41 of the gap lithium strip 4 from extending to the outside of the edge of the first electrode plate 1 in the second direction, solving the problem of edge lithium burrs 42 on the edge of the first electrode plate 1, and avoiding the risk of the edge lithium burrs 42 failing to fit with the side end surface of the electrode plate and becoming free in the battery cell and piercing the diaphragm 3, causing a safety hazard.

[0041] As shown in FIG3 , in order to avoid edge lithium burrs 42 on the edge of the first electrode 1 and to avoid short circuit caused by contact between the edge lithium burrs 42 and the second electrode 2 or the aluminum-plastic film, considering the processing technology, preferably, the distance between the two side edges of the second direction of the gap lithium strip 4 and the two side edges of the second direction of the first active material layer 12 is 0.1–2 mm.

[0042] As shown in Figure 5, using a 3D microscope to synthesize a high-definition 3D image, it can be observed that the lithium strips 41 of the interstitial lithium strips 4 are embedded in the first active material layer 12 after the injection cycle, causing the first active material layer 12 to form alternating bright and dark areas along the first direction of the first electrode 1. These alternating bright and dark areas are formed due to lithium replenishment and non-replenishment. These alternating bright and dark areas can be observed under a 3D microscope, and can be used to characterize the lithium replenishment area on the first active material layer 12, thereby distinguishing between lithium replenishment and non-replenishment areas.

[0043] A 3D microscope was used to synthesize a 3D high-definition 3D image, and a two-point height difference measurement tool was used to measure the presence of relatively obvious interface features at the boundary between the bright and dark areas on the first active material layer 12. That is, there was a height difference between the surfaces of the bright and dark areas. The size of the difference varied depending on the thickness of the coated lithium strip, and the height difference generally ranged from 0.1–30 μm.

[0044] As shown in Figure 4, the present application also provides a battery cell, including the above-mentioned electrode plate, that is, the first plate 1, and also including a second plate 2. In this embodiment, the second plate 2 is a positive plate, and the positive plate includes an aluminum foil 21, and two second active material layers 22 respectively arranged on the upper surface (that is, the third surface) and the lower surface (that is, the fourth surface) of the aluminum foil 21.

[0045] The second pole piece 2 can be wound together with the first pole piece 1 to form a battery core, or the second pole piece 2 can be stacked with the first pole piece 1 to form a battery core. In this embodiment, the second pole piece 2 and the first pole piece 1 are wound together to form a battery core.

[0046] The battery cell provided in the present application is used for lithium batteries, which can improve the battery's initial efficiency, energy density and cycle performance, and can avoid the safety hazards caused by edge lithium burrs 42.

[0047] The second electrode piece 2 has a first direction and a second direction corresponding to the first electrode piece 1. The edge of the gap lithium strip 4 in the second direction on the first electrode piece 1 exceeds the edge of the second active material layer 22 in the second direction, or the edge of the gap lithium strip 4 in the second direction on the first electrode piece 1 is at least flush with the edge of the second active material layer 22 in the second direction, so as to ensure that the second active material layer 22 is completely covered by the width of the gap lithium strip 4 in the second direction, thereby ensuring that there are sufficient lithium ions from the first electrode piece 1 through the diaphragm 3 to reach the second active material layer 22 of the second electrode piece 2 during the charge and discharge cycle.

[0048] In order to ensure that the second active material layer 22 of the second electrode 2 is completely covered by the width of the gap lithium strip 4 on the first electrode 1 in the second direction, and taking into account the processing technology, preferably, the distance between the two side edges of the gap lithium strip 4 in the second direction exceeds the two side edges of the second direction of the second active material layer 22 by at least 0.1 mm, that is, greater than or equal to 0.1 mm.

[0049] As shown in FIG. 6-9 , in one embodiment, a plurality of tabs are provided on one side of the second direction of the second active material layer 22 .

[0050] The lithium replenishment process of the first electrode sheet 1 of the multi-electrode wound battery cell used in high-power models is often arranged after rolling and slitting and before die-cutting (Figure 6 shows the process route of lithium replenishment, die-cutting, etc. for the first and second electrode sheets 1 and 2 of the multi-electrode battery cell).

[0051] The wound cell die-cutting process generally uses laser die-cutting. To avoid safety hazards caused by laser cutting of the gap lithium strip 4 layers, the width of the gap lithium strip 4 is set to be smaller than the width of the first active material layer 12 on the first electrode 1.

[0052] Specifically, after lithium replenishment, the distance between the edge of the interstitial lithium strip 4 in the second direction and the edge of the first active material layer 12 in the second direction of the first electrode 1 is greater than 0.5 mm, while the distance between the edge of the interstitial lithium strip 4 in the second direction and the edge of the first active material layer 12 in the second direction of the first electrode 1 after laser die-cutting is greater than 0.1 mm. After laser die-cutting, the first electrode 1 needs to be cut in the center and then wound together with the second electrode 2 and the separator 3 to prepare a core.

[0053] As shown in Figure 7, after cutting, a plurality of tabs are provided on one side of the second direction of the first active material layer 12, and the edge of the first active material layer 12 in the second direction close to the tab side is the first active layer head boundary 121, and correspondingly, the edge of the first active material layer 12 in the second direction away from the tab side is the first active layer bottom boundary 122, and the edge of the first active material in the second direction after cutting is the first active layer cutting boundary 123.

[0054] Similarly, the edge of the gap lithium strip 4 in the second direction close to the pole ear side is the lithium strip layer head boundary 431, and correspondingly, the edge of the gap lithium strip 4 in the second direction away from the pole ear side is the lithium strip layer bottom boundary 432. Since the first pole piece 1 is cut in the center, the bottom boundary 122 of the first active layer is flush with the bottom boundary 432 of the lithium strip layer.

[0055] As shown in Figure 8, a plurality of pole tabs are provided on one side of the second direction of the second active material layer 22, and the edge of the second direction of the second active material layer 22 close to the pole tab is the second active layer head boundary 221; an insulating layer is also provided between the second active layer head boundary 221 and the pole tab, specifically an insulating ceramic layer 23, and after the battery cell is wound, in order to ensure the insulation effect and avoid contact between the gap lithium strip 4 in the bright area and the second pole piece, the insulating ceramic layer 23 overlaps with the edge of the bright area on the pole tab side, that is, as shown in Figure 9, the edge of the gap lithium strip 4 in the second direction on the pole tab side, that is, the lithium strip layer head boundary 431 is set between the two edges of the second direction of the insulating ceramic layer 23, that is, between the insulating layer head boundary 231 and the insulating layer bottom boundary 232.

[0056] It is worth noting that within the wound battery cell structure, the relative positions between the layers are such that, in order to ensure that the second active material layer 22 is completely covered by the width of the gap lithium strip 4 in the second direction, the first active layer head boundary 121 and the first active layer bottom boundary 122 both exceed the second active layer head boundary 221 and the second active layer bottom boundary, and the lithium strip layer head boundary 431 and the lithium strip layer bottom boundary 432 also both exceed the second active layer head boundary 221 and the second active layer bottom boundary.

[0057] The lithium replenishment process for wound battery pole sheets used in multi-pole or single-pole cells is often arranged after roll-pressing and slitting. Figure 4 shows a schematic diagram of the inter-layer alignment structure of wound battery cells used in multi-pole or single-pole cells.

[0058] As shown in Figure 4, in another embodiment, x is the first direction of the first electrode sheet 1, that is, the unfolding direction of the battery cell, y is the second direction of the first electrode sheet 1, that is, the height direction of the battery cell, and a diaphragm 3 is provided between the first electrode sheet 1 and the second electrode sheet 2. Generally, in order to improve battery safety, the battery needs to be wound to meet the coverage requirements, and the two side edges of the diaphragm 3 in the second direction each exceed the two side edges of the second direction of the first active material layer 12 by at least 0.5 mm.

[0059] Furthermore, to ensure that the second active material layer 22 is completely covered by the width of the interstitial lithium strip 4 in the second direction, the two side edges of the first active material layer 12 in the second direction extend at least 0.1 mm beyond the two side edges of the second active material layer 22 in the second direction. In other words, in the wound cell, the second-direction edge of the first electrode sheet 1 is not accompanied by the second electrode sheet 2. This portion is not fully charged during the charge-discharge cycle and does not require lithium replenishment. Therefore, the width of the interstitial lithium strip 4 can be smaller than the width of the first active material on the first electrode sheet 1.

[0060] The basic principles of this application have been described above in conjunction with specific embodiments. However, it should be noted that the advantages, strengths, and effects mentioned in this application are merely illustrative and non-restrictive, and should not be construed as necessarily possessed by each embodiment of this application. Furthermore, the specific details disclosed above are provided for illustrative purposes and to facilitate understanding, not for limitation. These details do not necessarily limit this application to the use of these specific details.

[0061] The block diagrams of the devices, devices, equipment, and systems involved in this application are merely illustrative examples and are not intended to require or imply that they must be connected, arranged, or configured in the manner shown in the block diagrams. As will be appreciated by those skilled in the art, these devices, devices, equipment, and systems can be connected, arranged, or configured in any manner. Words such as "include," "comprise," "have," and the like are open-ended words, meaning "including but not limited to," and can be used interchangeably therewith. The words "or" and "and" used herein refer to the word "or" and can be used interchangeably therewith, unless the context clearly indicates otherwise. The word "such as" used herein refers to the phrase "such as but not limited to," and can be used interchangeably therewith.

[0062] It should also be noted that in the apparatus, device, and method of the present application, each component or each step can be decomposed or recombined, and such decomposition or recombination should be regarded as equivalent solutions of the present application.

[0063] The above description of the disclosed aspects is provided to enable any person skilled in the art to make or use the present application. Various modifications to these aspects will be readily apparent to those skilled in the art, and the general principles defined herein may be applied to other aspects without departing from the scope of the present application. Therefore, the present application is not intended to be limited to the aspects shown herein, but rather to be accorded the widest scope consistent with the principles and novel features disclosed herein.

[0064] It should be understood that the qualifiers "first", "second", "third", "fourth", "fifth" and "sixth" used in the description of the embodiments of the present application are only used to more clearly illustrate the technical solutions and cannot be used to limit the scope of protection of the present application.

[0065] The above description has been provided for the purpose of illustration and description. Furthermore, this description is not intended to limit the embodiments of the present application to the forms disclosed herein. Although a number of example aspects and embodiments have been discussed above, those skilled in the art will recognize certain variations, modifications, alterations, additions, and sub-combinations thereof.

Claims

1. An electrode sheet, characterized in that, Comprising: A first surface and a second surface which are oppositely arranged, and first active material layers are respectively arranged on the first surface and the second surface; The electrode tab has a first direction and a second direction; Bright regions and dark regions are alternately arranged on the first active material layer along the first direction of the electrode tab, the bright regions extend along the second direction of the electrode tab, and the edges of the bright regions in the second direction are within the edges of the electrode tab in the second direction.

2. The electrode sheet according to claim 1, characterized in that, The distance between the edge of the bright region in the second direction and the edge of the electrode tab in the second direction is 0.1 - 2 mm.

3. The electrode sheet according to claim 1 or 2, characterized in that, There is a height difference between the surfaces of the bright region and the dark region, and the range of the height difference is 0.1 - 30 μm.

4. A battery cell, characterized in that, Comprising the electrode tab according to any one of claims 1 - 3, and further comprising a second tab, the second tab includes a third surface and a fourth surface which are oppositely arranged, and second active material layers are respectively arranged on the third surface and the fourth surface.

5. The battery cell according to claim 4, characterized in that, The edge of the bright region on the electrode tab in the second direction extends beyond the edge of the second active material layer in the second direction.

6. The battery cell according to claim 4, wherein The edge of the bright region on the electrode tab in the second direction is flush with the edge of the second active material layer in the second direction.

7. The battery cell according to claim 4 or 5, characterized in that, The distance between the edge of the bright region on one side in the second direction and the edge of the second active material layer on the same side in the second direction is greater than or equal to 0.1 mm.

8. The battery cell according to any one of claims 4 to 7, characterized in that, A plurality of tabs are arranged on one side of the second active material layer in the second direction, and an insulating layer is further arranged between the second active material layer and the plurality of tabs, and the insulating layer overlaps with the edge of the bright region on the side of the plurality of tabs.

9. The battery cell according to any one of claims 4 to 8, characterized in that, A separator is arranged between the electrode tab and the second tab, and at least one side edge of the separator in the second direction extends beyond the side edges of the bright region in the second direction by at least 0.5 mm.

10. The battery cell according to claim 9, characterized in that, The side edges of the bright region in the second direction each extend beyond the side edges of the second active material layer in the second direction by at least 0.1 mm.

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