Electrode sheet and battery cell

Abstract

The present application relates to the technical field of battery electrode sheets, and discloses an electrode sheet and a battery cell. The electrode sheet has a length direction, a width direction and a thickness direction, and comprises a current collector, a first active layer and a second active layer. The current collector has a first side surface and a second side surface that are opposite to each other in the thickness direction. The first active layer is coated on the first side surface, a first slot is formed in the first active layer, and a tab connecting portion is formed in the first slot. The second active layer is coated on the second side surface, and a second slot is formed in the second active layer. The first slot and the second slot are distributed in a staggered manner in the length direction, and / or the first slot and the second slot are distributed in a staggered manner in the width direction. The side edges of the first slot and the second slot are provided with transition portions, and the transition portions ensure smooth transition between the active layers and the current collector at the side edges of the slots, reducing the ductility difference of the current collector between the slot positions and other regions of the electrode sheet, thereby effectively preventing the cracking and breakage of the electrode sheet during calendering.

Description

An electrode and a single cell Technical Field

[0001] This application relates to the field of battery electrode technology, and in particular to an electrode and a single battery cell. Background Technology

[0002] To improve battery charging speed, battery electrodes typically employ a centrally located tab or multiple tab designs. Currently, high-energy laser technology is used to clean and remove the active coating of the electrodes, thereby forming tab welding grooves on localized surfaces of the electrode foil.

[0003] As battery energy density continues to increase, the thickness of electrode foil is becoming thinner, and the coating and compaction densities are also increasing accordingly. However, during the rolling process, there is a difference in elongation between the active coating and the electrode foil in the groove area, which can easily lead to cracking and breakage of the electrode.

[0004] Application content

[0005] The technical problem to be solved by this application is that during the rolling process, the difference in elongation between the active coating and the electrode foil in the groove area can easily lead to cracking and breakage of the electrode.

[0006] To address the aforementioned technical problems, this application provides a technical solution for an electrode sheet:

[0007] Electrodes, having pairwise orthogonal length, width, and thickness directions, including:

[0008] A current collector having a first side surface and a second side surface opposite each other along the thickness direction;

[0009] A first active layer is coated on the first side surface. The first active layer has a first groove, and a tab connection portion is provided in the first groove.

[0010] A second active layer is coated on the second side surface, and the second active layer has a second groove.

[0011] The first slot and the second slot are staggered in the length direction, and / or the first slot and the second slot are staggered in the width direction;

[0012] The first groove has a first transition portion and a second transition portion on two opposite side edges in the length direction, and the second groove has a third transition portion and a fourth transition portion on two opposite side edges in the length direction.

[0013] Along the length direction, the thickness of the first transition portion gradually decreases as it approaches the current collector, and the thickness of the third transition portion gradually decreases as it approaches the current collector; along the length direction, the thickness of the second transition portion gradually increases as it moves away from the current collector, and the thickness of the fourth transition portion gradually increases as it moves away from the current collector.

[0014] Furthermore, the current collector has a first edge extending along the length direction and close to the first groove and the second groove, a first excess material portion exists between the first groove and the first edge of the current collector, and a second excess material portion exists between the second groove and the first edge of the current collector.

[0015] Furthermore, the first groove also has a first bottom edge and a second bottom edge opposite to each other along the length direction, and the second groove also has a third bottom edge and a fourth bottom edge opposite to each other along the length direction; in the length direction, the first bottom edge and the third bottom edge are arranged at intervals, and / or the second bottom edge and the fourth bottom edge are arranged at intervals.

[0016] Furthermore, the distance between the first bottom edge and the second bottom edge in the length direction is D1, the dimension of the tab connection in the length direction is D2, and the distance between the first bottom edge and the third bottom edge in the length direction is d1, satisfying d1≤(D1-D2) / 2.

[0017] Furthermore, 0.1mm≤d1≤3mm.

[0018] Furthermore, the first groove also has a fifth bottom edge that is away from the first surplus material portion along the width direction, and the second groove also has a sixth bottom edge that is away from the second surplus material portion along the width direction; the fifth bottom edge and the sixth bottom edge are arranged at intervals along the width direction.

[0019] Furthermore, the distance between the fifth bottom edge and the sixth bottom edge in the width direction is d2, which satisfies 0.2mm≤d2≤2mm.

[0020] Furthermore, the first transition portion includes at least two first stepped portions, which are stacked along the thickness direction and arranged one by one away from the current collector in the length direction; the second transition portion includes at least two second stepped portions, which are stacked along the thickness direction and arranged one by one away from the current collector in the length direction.

[0021] The third transition portion includes at least two third step portions, which are stacked along the thickness direction and arranged one by one close to the current collector in the length direction; the fourth transition portion includes at least two fourth step portions, which are stacked along the thickness direction and arranged one by one close to the current collector in the length direction.

[0022] Furthermore, the first transition portion further includes a first chamfer portion, which is disposed on the first stepped portion away from the current collector; the second transition portion further includes a second chamfer portion, which is disposed on the second stepped portion away from the current collector.

[0023] The third transition portion further includes a third chamfer portion, which is disposed on the third stepped portion away from the current collector; the fourth transition portion further includes a fourth chamfer portion, which is disposed on the fourth stepped portion away from the current collector.

[0024] Furthermore, the opening size of the first groove is larger than the opening size of the second groove.

[0025] Furthermore, the electrode connecting part is provided with an electrode, the thickness of which is H; along the length direction, the distance between the electrode and the first transition portion and the second transition portion of the first groove is L1, and the distance between the projection of the electrode on the second side and the third transition portion and the fourth transition portion of the second groove is L2, satisfying: H < L2 < 1.5 * H, L2 < L1 < 2 * L2.

[0026] To address the aforementioned technical problems, this application provides a technical solution for a single-cell battery:

[0027] A single cell includes: electrodes;

[0028] Electrodes, having pairwise orthogonal length, width, and thickness directions, including:

[0029] A current collector having a first side surface and a second side surface opposite each other along the thickness direction;

[0030] A first active layer is coated on the first side surface. The first active layer has a first groove, and a tab connection portion is provided in the first groove.

[0031] A second active layer is coated on the second side surface, and the second active layer has a second groove.

[0032] The first slot and the second slot are staggered in the length direction, and / or the first slot and the second slot are staggered in the width direction;

[0033] The first groove has a first transition portion and a second transition portion on its two opposite side edges in the length direction, and the second groove has a third transition portion and a fourth transition portion on its two opposite side edges in the length direction.

[0034] Along the length direction, the thickness of the first transition portion gradually decreases as it approaches the current collector, and the thickness of the third transition portion gradually decreases as it approaches the current collector; along the length direction, the thickness of the second transition portion gradually increases as it moves away from the current collector, and the thickness of the fourth transition portion gradually increases as it moves away from the current collector.

[0035] Furthermore, the current collector has a first edge extending along the length direction and close to the first groove and the second groove, a first excess material portion exists between the first groove and the first edge of the current collector, and a second excess material portion exists between the second groove and the first edge of the current collector.

[0036] Furthermore, the first groove also has a first bottom edge and a second bottom edge opposite to each other along the length direction, and the second groove also has a third bottom edge and a fourth bottom edge opposite to each other along the length direction; in the length direction, the first bottom edge and the third bottom edge are arranged at intervals, and / or the second bottom edge and the fourth bottom edge are arranged at intervals.

[0037] Furthermore, the distance between the first bottom edge and the second bottom edge in the length direction is D1, the dimension of the tab connection in the length direction is D2, and the distance between the first bottom edge and the third bottom edge in the length direction is d1, satisfying d1≤(D1-D2) / 2.

[0038] Furthermore, 0.1mm≤d1≤3mm.

[0039] Furthermore, the first groove also has a fifth bottom edge that is away from the first surplus material portion along the width direction, and the second groove also has a sixth bottom edge that is away from the second surplus material portion along the width direction; the fifth bottom edge and the sixth bottom edge are arranged at intervals along the width direction.

[0040] Furthermore, the distance between the fifth bottom edge and the first bottom edge in the width direction is d2, which satisfies 0.2mm≤d2≤2mm.

[0041] Furthermore, the first transition portion includes at least two first stepped portions, which are stacked along the thickness direction and arranged one by one away from the current collector in the length direction; the second transition portion includes at least two second stepped portions, which are stacked along the thickness direction and arranged one by one away from the current collector in the length direction.

[0042] The third transition portion includes at least two third step portions, which are stacked along the thickness direction and arranged one by one close to the current collector in the length direction; the fourth transition portion includes at least two fourth step portions, which are stacked along the thickness direction and arranged one by one close to the current collector in the length direction.

[0043] Furthermore, the first transition portion further includes a first chamfer portion, which is disposed on the first stepped portion away from the current collector; the second transition portion further includes a second chamfer portion, which is disposed on the second stepped portion away from the current collector.

[0044] The third transition portion further includes a third chamfer portion, which is disposed on the third stepped portion away from the current collector; the fourth transition portion further includes a fourth chamfer portion, which is disposed on the fourth stepped portion away from the current collector.

[0045] Furthermore, the opening width of the first groove is greater than the opening width of the second groove.

[0046] Furthermore, the electrode connecting part is provided with an electrode, the thickness of which is H; along the length direction, the distance between the electrode and the first transition portion and the second transition portion of the first groove is L1, and the distance between the projection of the electrode on the second side and the third transition portion and the fourth transition portion of the second groove is L2, satisfying: H < L2 < 1.5 * H, L2 < L1 < 2 * L2.

[0047] Compared with the prior art, the electrode and single cell of this application have the following advantages: the electrode adopts a structure combining a current collector, a first active layer and a second active layer. The current collector has a first side and a second side opposite to each other along the thickness direction. The first active layer is coated on the first side and the second active layer is coated on the second side. The first active layer and the second active layer can improve the conductivity of the electrode and reduce the internal resistance of the battery, thereby improving the overall performance of the single cell.

[0048] The first active layer has a first groove, in which a tab connection portion is reserved for matching the tab, enabling electrical connection between the tab and the first side of the current collector, and allowing the tab to be smoothly led out of the current collector along the width direction. Correspondingly, the second active layer has a second groove; the first groove and the second groove are staggered in the length direction, and / or staggered in the width direction. It is precisely this staggered arrangement of the first groove and the second groove in the length direction and / or width direction that reduces the thickness difference between the current collector and the first and second active layers at the first and second grooves.

[0049] Meanwhile, the first groove has a first transition portion and a second transition portion on its two opposite side edges along its length, and the second groove has a third transition portion and a fourth transition portion on its two opposite side edges along its length. Along the length direction, the thickness of the first transition portion gradually decreases as it approaches the current collector, and the thickness of the third transition portion gradually decreases as it approaches the current collector; conversely, the thickness of the second transition portion gradually increases as it moves away from the current collector, and the thickness of the fourth transition portion gradually increases as it moves away from the current collector. This ensures a smooth transition between the first active layer at the two side edges of the first groove and the second active layer at the two side edges of the second groove with the current collector, reducing the difference in ductility between the current collector in the first and second grooves and the current collector in other areas. This effectively prevents electrode cracking and strip breakage due to ductility differences during rolling. Furthermore, it reduces the cleaning area of ​​the grooves, i.e., the area of ​​the first and second active layers to be removed in the first and second grooves, which helps reduce dust generation and improve Hi-pot throughput and K-value yield. Simultaneously, the staggered arrangement of the first and second grooves on both sides of the current collector helps reduce the cell thickness and avoids lithium plating during cycling. Attached Figure Description

[0050] Figure 1 is a cross-sectional schematic diagram of the electrode sheet in the thickness direction in an embodiment of this application;

[0051] Figure 2 is a top view of the electrode in Figure 1;

[0052] Figure 3 is a cross-sectional schematic diagram of the electrode sheet in the thickness direction in another embodiment of this application;

[0053] Figure 4 is a top view of the electrode in Figure 3;

[0054] Figure 5 is a top view of the electrode sheet in another embodiment 2 of this application;

[0055] Figure 6 is a cross-sectional schematic diagram of the electrode sheet in the thickness direction in another embodiment three of this application;

[0056] In the figure: 1-current collector, 11-first side surface, 12-second side surface, 13-first edge, 2-first active layer, 20-first groove, 200-tab connection part, 21a-first bottom edge, 21b-second bottom edge, 22-first excess material part, 23-fifth bottom edge, 24a-first transition part, 24b-second transition part, 241a-first stepped part, 241b-second stepped part, 242a-first chamfered part, 24 2b-Second chamfered portion, 3-Second active layer, 30-Second groove, 31a-Third bottom edge, 31b-Fourth bottom edge, 32-Second surplus material portion, 33-Sixth bottom edge, 34a-Third transition portion, 34b-Fourth transition portion, 341a-Third step portion, 341b-Fourth step portion, 342a-Third chamfered portion, 342b-Fourth chamfered portion, 4-Electrode tab, X-Length direction, Y-Width direction, Z-Thickness direction. Detailed Implementation

[0057] The specific embodiments of this application will be described in further detail below with reference to the accompanying drawings and examples. The following examples are used to illustrate this application, but are not intended to limit the scope of this application.

[0058] In the description of this application, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," and "counterclockwise" used to indicate orientation or positional relationships are based on the orientation or positional relationships shown in the accompanying drawings and are used only for the convenience of describing this application and simplifying the description, and are not intended to indicate or imply that the equipment or components referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application.

[0059] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0060] In this application, unless otherwise expressly specified and limited, the terms "installation," "connection," "joining," "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0061] As shown in Figures 1 and 2, an electrode sheet according to an embodiment of this application has two orthogonal length directions X, width directions Y and thickness directions Z, including: a current collector 1, a first active layer 2 and a second active layer 3. The current collector 1 has a first side surface 11 and a second side surface 12 that are opposite to each other along the thickness direction Z. The first active layer 2 is coated on the first side surface 11, and the first active layer 2 has a first groove 20, in which an electrode tab connection portion 200 is provided.

[0062] A second active layer 3 is coated on the second side surface 12, and the second active layer 3 has a second groove 30; the first groove 20 and the second groove 30 are staggered in the length direction X, and / or the second groove 30 and the second groove 30 are staggered in the width direction Y; the two opposite side edges of the first groove 20 in the length direction X are respectively provided with a first transition portion 24a and a second transition portion 24b, and the two opposite side edges of the second groove 30 in the length direction X are respectively provided with a third transition portion 34a and a fourth transition portion 34b.

[0063] Along the length direction X, the thickness of the first transition portion 24a gradually decreases as it approaches the current collector 1, and the thickness of the third transition portion 34a gradually decreases as it approaches the current collector 1; along the length direction X, the thickness of the second transition portion 24b gradually increases as it moves away from the current collector 1, and the thickness of the fourth transition portion 34b gradually increases as it moves away from the current collector 1.

[0064] The electrode adopts a structure consisting of a current collector 1, a first active layer 2, and a second active layer 3. The current collector 1 has a first side 11 and a second side 12 opposite to each other along the thickness direction Z. The first active layer 2 is coated on the first side 11, and the second active layer 3 is coated on the second side 12. The first active layer 2 and the second active layer 3 can improve the conductivity of the electrode and reduce the internal resistance of the battery, thereby improving the overall performance of the single cell.

[0065] The first active layer 2 has a first groove 20, in which a tab connection portion 200 for matching the tab is reserved. This allows for electrical connection between the tab and the first side 11 of the current collector 1, and facilitates the tab's smooth extension outwards along the width direction Y of the current collector 1. Correspondingly, the second active layer 3 has a second groove 30. The first groove 20 and the second groove 30 are staggered in the length direction X, and / or staggered in the width direction Y. It is this staggered arrangement of the first groove 20 and the second groove 30 in the length direction X and / or the width direction Y that reduces the direct difference in thickness between the current collector 1 and the first active layer 2 and the second active layer 3 at the first and second grooves.

[0066] Meanwhile, the first groove 20 has a first transition portion 24a and a second transition portion 24b respectively on its two opposite side edges in the length direction X, and the second groove 30 has a third transition portion 34a and a fourth transition portion 34b respectively on its two opposite side edges in the length direction X. Along the length direction X, the thickness of the first transition portion 24a gradually decreases as it approaches the current collector 1, and the thickness of the third transition portion 34a gradually decreases as it approaches the current collector 1; along the length direction X, the thickness of the second transition portion 24b gradually increases as it moves away from the current collector 1, and the thickness of the fourth transition portion 34b gradually increases as it moves away from the current collector 1. This ensures a smooth transition between the first active layer 2 at the two side edges of the first groove 20 and the second active layer 3 at the two side edges of the second groove 30 and the current collector 1, thereby reducing the difference in ductility between the current collector in the first groove 20 and the second groove 30 and the current collector 1 in other areas. This effectively prevents the electrode from cracking and breaking due to differences in ductility during rolling. Furthermore, it can reduce the cleaning area of ​​the slot imprint, that is, the area of ​​the first and second active layers to be removed in the first and second slots, which helps to reduce dust generation and improve Hi-pot throughput and K-value yield. At the same time, the staggered arrangement of the first and second slots on both sides of the current collector helps to reduce the cell thickness and avoid lithium plating during the cycling process.

[0067] In this embodiment, the current collector 1 has a first edge 13 extending along the length direction X and close to the first groove 20 and the second groove 20. There is a first excess material portion 22 between the first groove 20 and the first edge 13 of the current collector 1, and there is a second excess material portion 32 between the second groove 30 and the first edge 13 of the current collector 1. Specifically, the width of the first excess material portion 22 and the second excess material portion 32 are each designed to be any size between 0.1 mm and 1 mm.

[0068] Furthermore, the first groove 20 also has a first bottom edge 21a and a second bottom edge 21b opposite each other along the length direction X, and the second groove 30 also has a third bottom edge 31a and a fourth bottom edge 31b opposite each other along the length direction X; the first bottom edge 21a and the third bottom edge 31a are arranged alternately along the length direction X. As a further preferred embodiment, the first bottom edge 21a and the second bottom edge 31a are arranged alternately along the length direction X, and the second bottom edge 21b and the fourth bottom edge 31b are arranged coincidentally along the length direction X. That is, the first groove 20 and the second groove 30 have one bottom edge misaligned and the other bottom edge flush, which can improve the electrode damage caused by the difference in ductility.

[0069] To meet different usage requirements, another embodiment of the electrode sheet in this application differs from the above embodiment in that, in the length direction X, the first bottom edge 21a and the third bottom edge 31a are arranged alternately, and the second bottom edge 21b and the fourth bottom edge 31b are arranged alternately, as shown in Figures 3 and 4. That is, the first groove 20 and the second groove 30 are designed with both bottom edges staggered, which can also protect the electrode sheet during the rolling process.

[0070] The distance between the first bottom edge 21a and the second bottom edge 21b in the length direction X is D1, the dimension of the electrode connecting part 200 in the length direction X is D2, and the distance between the first bottom edge 21a and the third bottom edge 31a in the length direction X is d1, satisfying d1≤(D1-D2) / 2. By controlling the misalignment range of the first groove 20 and the second groove 30 to be moderate, the electrode connecting part 200 is centered in the length direction X in the overlapping part of the first groove 20 and the second groove 30, ensuring the accuracy of the electrode welding position.

[0071] Specifically, 0.1mm ≤ d1 ≤ 3mm. For example, the distance d1 between the first bottom edge 21a and the third bottom edge 31a in the length direction X can be selected as 0.1mm, 0.2mm, 0.5mm, 1mm, 2mm, 3mm, or any other size between 0.1mm and 3mm. If the distance d1 is too small, it will be difficult to effectively protect the electrode sheet during the rolling process.

[0072] Furthermore, the first groove 20 also has a fifth bottom edge 23 that is away from the first surplus material portion 22 along the width direction Y, and the second groove 30 also has a sixth bottom edge 33 that is away from the second surplus material portion 32 along the width direction Y, with the fifth bottom edge 23 and the sixth bottom edge 33 being arranged to overlap.

[0073] Another embodiment of the electrode sheet in this application, as shown in Figure 5, has its first bottom edge 21a and second bottom edge 21b of the first groove 20 arranged at intervals along the length direction X with the third bottom edge 31a and fourth bottom edge 31b of the second groove 30, respectively. That is, the first groove 20 and the second groove 30 are designed with opposite bottom edges staggered. Furthermore, the first groove 20 also has a fifth bottom edge 23 extending away from the first excess material portion 22 along the width direction Y, and the second groove 30 also has a sixth bottom edge 33 extending away from the second excess material portion 32 along the width direction Y; the fifth bottom edge 23 and the sixth bottom edge 33 are arranged at intervals along the width direction Y. Specifically, the distance between the fifth bottom edge 23 and the sixth bottom edge 33 in the width direction Y is d2, satisfying 0.2mm ≤ d2 ≤ 2mm. The second groove 20 and the second groove 30 are also staggered in the width direction Y, increasing the staggered area of ​​the two grooves and further improving the protective effect of the electrode sheet.

[0074] As a further preferred embodiment, the first transition portion 24a includes at least two first step portions 241a, which are stacked along the thickness direction Z and arranged sequentially away from the current collector 1 in the length direction X; the second transition portion 24b includes at least two second step portions 241b, which are stacked along the thickness direction Z and arranged sequentially away from the current collector 1 in the length direction X; the third transition portion 34a includes at least two third step portions 341a, which are stacked along the thickness direction Z and arranged sequentially closer to the current collector 1 in the length direction X; the fourth transition portion 34b includes at least two fourth step portions 341b, which are stacked along the thickness direction Z and arranged sequentially closer to the current collector 1 in the length direction X. This multi-level stepped design achieves a smooth transition in the extensibility of the current collector 1 in the first groove 20 and the second groove 30 of the electrode compared to the current collector 1 in other regions.

[0075] The first transition portion 24a further includes a first chamfered portion 242a, which is disposed on the first stepped portion 241a away from the current collector 1; the second transition portion 24b further includes a second chamfered portion 242b, which is disposed on the second stepped portion 241b away from the current collector 1; the third transition portion 34a further includes a third chamfered portion 342a, which is disposed on the third stepped portion 341a away from the current collector 1; the fourth transition portion 34b further includes a fourth chamfered portion 342b, which is disposed on the fourth stepped portion 341b away from the current collector 1. The first chamfered portion 242a, the second chamfered portion 242b, the third chamfered portion 342a, and the fourth chamfered portion 342b improve the structural smoothness of the first active layer and the second active layer at the groove position, and prevent the risk of puncturing the current collector 1 due to the presence of sharp corners during the rolling process.

[0076] In this design, the first transition portion 24a, the second transition portion 24b, the third transition portion 34a, and the fourth transition portion 34b are equivalent to multiple small steps, making the side edges of the first groove 20 and the second groove 30 closer to arcs. Compared to having only one step, the current collector 1 transitions more smoothly with the first active layer 2 and the second active layer 3. This solves the problem of tape breakage and improves the Hi-pot throughput and K-value yield. Furthermore, a first excess material portion 22 is reserved between the first groove 20 and the first edge 13 of the current collector 1, and a second excess material portion 32 is reserved between the second groove 30 and the first edge 13 of the current collector 1. The reserved excess material portions are not die-cut, which can prevent the side edge areas of the first groove 20 and the second groove 30 from being torn during tape feeding, thus preventing tape breakage.

[0077] The statistics of the number of times the band broke during testing are as follows:

[0078] Keeping the parameters of the winding equipment for producing battery cells unchanged (PPM (Piece Per Minutes) is 6, i.e., 6 cells are produced per minute), the electrode sheet of this application with a length of 3000m, a thickness of 85μm, and a width of 80mm is selected, wherein the current collector is an 8μm thick aluminum foil, the active layer coating material is lithium cobalt oxide, and the tape speed is 300mm / s. The number of tape breaks during the tape travel process of the 3000m electrode sheet during production by the winding equipment is counted, and the tape break frequency is calculated as: number of tape breaks / total tape travel length, with the unit being: number of tape breaks / km.

[0079] Hi-pot test (High Potential Test): Primarily used to test the internal insulation performance of lithium batteries. The principle is to apply a high voltage (typically between 25V and 250V) between the positive and negative terminals of the cell and measure the leakage current to evaluate the internal resistance. For bare cells produced by the winding equipment of this application (made from the electrode sheets of this application, 80mm in length, 60mm in width, and 4.5mm in thickness), a pressure of 0.2MPa is applied to the entire bare cell, and then a Hi-pot tester (Wuxi Lead Intelligent Equipment Co., Ltd.) is used to apply a 50V voltage to the positive and negative terminals of the bare cell, recording its internal resistance. An internal resistance > 2MΩ is considered a good product, and the proportion of cells with an internal resistance > 2MΩ is the Hi-pot yield.

[0080] K-value (referring to the voltage drop of the cell per unit time, measured in mV / h, and is an indicator used to measure the self-discharge rate of lithium batteries) test: The finished cell used in this test was made from the above-mentioned bare cell, aluminum-plastic film (DNP, model: EL35H) and electrolyte (Shenzhen Xinzhoubang Technology Co., Ltd., model: EL2), with a length of 82mm, a width of 61mm, and a thickness of 4.7mm. Step 1: After storing the finished battery cell at 45℃±2℃ for 2 days and at 25℃±2℃ for 2 days, test the OCV (Open Circuit Voltage)1 of the finished battery cell at room temperature (25℃±2℃) using a voltage tester (Wuxi Lead Intelligent Equipment Co., Ltd.), with the unit being mV; Step 2: After storing the finished battery cell at 25℃±2℃ for 2 days, test the OCV2 of the finished battery cell at room temperature (25℃±2℃), with the unit being mV. K value = (OCV1-OCV2) / 48h. A K value < 0.06mV / h indicates a good product. The proportion of K values ​​< 0.06mV / h is the K value yield.

[0081] Based on the above examples, it can be seen that any two or three of the following three features, when combined: setting a transition section at the edge of the slot, misaligning the edge of the slot, and die-cutting at the top of the slot (without leaving any excess material), can significantly improve the problem of tape breakage and increase the Hi-pot throughput and K-value yield.

[0082] Another embodiment of the electrode sheet in this application differs from the above embodiment in that, as shown in FIG. 6, the opening size of the first groove 20 is larger than the opening size of the second groove 30. Specifically, the electrode connecting part 200 is provided with an electrode tab 4, the thickness of the electrode tab 4 is H; along the length direction X, the minimum distance between the electrode tab 4 and the side edge of the first groove 20 is L1, and the minimum distance between the projection of the electrode tab 4 on the second side surface 12 and the side edge of the second groove 30 is L2, satisfying: H < L2 < 1.5 * H, L2 < L1 < 2 * L2.

[0083] The purpose of its design is to ensure that the tab 4 is accommodated in the first groove 20 along the thickness direction Z of the electrode sheet, and not to waste too much active material around the second groove 30, thereby improving the energy density (ED) of the battery cell. At the same time, it can also accelerate the release of edge stress caused by the first groove 20 and the second groove 30, which are misaligned according to mechanical principles, to prevent the strip from breaking during the production process.

[0084] The specific embodiments of the single cell in this application include electrode sheets, wherein the electrode sheets are the same as those in the specific embodiments of the electrode sheets in the above-mentioned applications, and will not be repeated here.

[0085] The above description is only a preferred embodiment of this application. It should be noted that for those skilled in the art, several improvements and substitutions can be made without departing from the technical principles of this application, and these improvements and substitutions should also be considered within the scope of protection of this application.

Claims

1. An electrode sheet having pairwise orthogonal length directions (X), width directions (Y), and thickness directions (Z), characterized in that, include: A current collector (1) having a first side surface (11) and a second side surface (12) opposite each other along the thickness direction (Z); A first active layer (2) is coated on the first side surface (11). The first active layer (2) has a first groove (20) and a tab connection part (200) is provided in the first groove (20). A second active layer (3) is coated on the second side surface (12), and the second active layer (3) has a second groove (30). The first groove (20) and the second groove (30) are staggered in the length direction (X), and / or the first groove (20) and the second groove (30) are staggered in the width direction (Y); The first groove (20) has a first transition portion (24a) and a second transition portion (24b) on its two opposite side edges in the length direction (X), and the second groove (30) has a third transition portion (34a) and a fourth transition portion (34b) on its two opposite side edges in the length direction (X). Along the length direction (X), the thickness of the first transition portion (24a) gradually decreases as it approaches the current collector (1), and the thickness of the third transition portion (34a) gradually decreases as it approaches the current collector (1); along the length direction (X), the thickness of the second transition portion (24b) gradually increases as it moves away from the current collector (1), and the thickness of the fourth transition portion (34b) gradually increases as it moves away from the current collector (1).

2. The electrode sheet according to claim 1, characterized in that, The current collector (1) has a first edge (13) extending along the length direction (X) and close to the first groove (20) and the second groove (30), a first excess material portion (22) exists between the first groove (20) and the first edge (13) of the current collector (1), and a second excess material portion (32) exists between the second groove (30) and the first edge (13) of the current collector (1).

3. The electrode sheet according to claim 1 or 2, characterized in that, The first groove (20) also has a first bottom edge (21a) and a second bottom edge (21b) opposite each other along the length direction (X), and the second groove (30) also has a third bottom edge (31a) and a fourth bottom edge (31b) opposite each other along the length direction (X); in the length direction (X), the first bottom edge (21a) and the third bottom edge (31a) are spaced apart, and / or, the second bottom edge (21b) and the fourth bottom edge (31b) are spaced apart.

4. The electrode sheet according to claim 3, characterized in that... The distance between the first bottom edge (21a) and the second bottom edge (21b) in the length direction (X) is D1, the size of the tab connection part (200) in the length direction (X) is D2, and the distance between the first bottom edge (21a) and the third bottom edge (31a) in the length direction (X) is d1, satisfying d1≤(D1-D2) / 2.

5. The electrode sheet according to claim 4, characterized in that, 0.1mm≤d1≤3mm.

6. The electrode sheet according to claim 2, characterized in that, The first groove (20) also has a fifth bottom edge (23) that is away from the first surplus material portion (22) along the width direction (Y), and the second groove (30) also has a sixth bottom edge (33) that is away from the second surplus material portion (32) along the width direction (Y); the fifth bottom edge (23) and the sixth bottom edge (33) are arranged at intervals along the width direction (Y).

7. The electrode sheet according to claim 6, characterized in that, The distance between the fifth bottom edge (23) and the sixth bottom edge (33) in the width direction (Y) is d2, which satisfies 0.2mm≤d2≤2mm.

8. The electrode sheet according to any one of claims 1 to 7, characterized in that, The first transition portion (24a) includes at least two first stepped portions (241a), which are stacked along the thickness direction (Z) and arranged one by one away from the current collector (1) in the length direction (X); the second transition portion (24b) includes at least two second stepped portions (241b), which are stacked along the thickness direction (Z) and arranged one by one away from the current collector (1) in the length direction (X); The third transition portion (34a) includes at least two third step portions (341a), which are stacked along the thickness direction (Z) and arranged one by one close to the current collector (1) in the length direction (X); the fourth transition portion (34b) includes at least two fourth step portions (341b), which are stacked along the thickness direction (Z) and arranged one by one close to the current collector (1) in the length direction (X).

9. The electrode sheet according to claim 8, characterized in that, The first transition portion (24a) further includes a first chamfer portion (242a), which is disposed on the first stepped portion (241a) away from the current collector (1); the second transition portion (24b) further includes a second chamfer portion (242b), which is disposed on the second stepped portion (241b) away from the current collector (1); The third transition portion (34a) further includes a third chamfer portion (342a), which is disposed on the third stepped portion (341a) away from the current collector (1); the fourth transition portion (34b) further includes a fourth chamfer portion (342b), which is disposed on the fourth stepped portion (341b) away from the current collector (1).

10. The electrode sheet according to any one of claims 1 to 9, characterized in that, The opening size of the first groove (20) is larger than the opening size of the second groove (30).

11. The electrode according to claim 10, characterized in that, The electrode connecting part (200) is provided with an electrode (4), the thickness of the electrode (4) is H; along the length direction (X), the distance between the electrode (4) and the first transition part (24a) and the second transition part (24b) of the first groove (20) is L1, and the distance between the projection of the electrode (4) on the second side surface (12) and the third transition part (34a) and the fourth transition part (34b) of the second groove (30) is L2, satisfying: H < L2 < 1.5 * H, L2 < L1 < 2 * L2.

12. A single-cell battery, characterized in that, Includes the electrode sheet as described in any one of claims 1 to 11.

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