Electrode sheet, cell and terminal device

Abstract

An electrode sheet (100), a cell (200) and a terminal device (300). The electrode sheet (100) comprises a current collector (10) and a first active material layer (20). The surface of the first active material layer (20) facing away from the current collector (10) is provided with a plurality of first grooves (21) that are arranged at equal intervals in a second direction. When viewed in a first direction, each first groove (21) extends from one side of the first active material layer (20) in a third direction to the other side of the first active material layer (20) in the third direction. The extension direction of each first groove (21) is inclined relative to the second direction, and the extension directions of the plurality of first grooves (21) are parallel to each other. The included angle between the extension direction of the first grooves (21) and the second direction is θ, 0＜θ＜90°. The spacing between each two adjacent first grooves (21) in the second direction is W2,θ and W2 satisfying the following relationship: 0.5≤1 / (W2×tanθ)≤1.5, and the unit of W2 being mm. The arrangement of the first grooves (21) helps to reduce the risk of lithium plating in the cell (200).

Description

Electrode sheets, cells and terminal devices Technical Field

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

[0002] In existing wound battery cells, the corners of the cell correspond to the bending sections of the electrode assembly. During cell cycling, due to electrode expansion and other reasons, the electrodes located at the bending sections will squeeze the electrolyte out of the corners of the cell, resulting in less electrolyte at the corners and causing lithium plating at the corners. Summary of the Invention

[0003] In view of the above situation, this application provides an electrode that helps to reduce the risk of lithium plating.

[0004] An embodiment of this application provides an electrode, which includes a current collector and a first active material layer. The thickness direction of the current collector is a first direction, the length direction of the current collector is a second direction, and the width direction of the current collector is a third direction. The first active material layer is disposed on one side of the current collector in the first direction. A plurality of first grooves are provided on the surface of the first active material layer facing away from the current collector, arranged at equal intervals along the second direction. Viewed along the first direction, each first groove extends from one side of the first active material layer in the third direction to the other side in the third direction. The extension direction of each first groove is inclined relative to the second direction, and the extension directions of the plurality of first grooves are parallel to each other. The angle between the extension directions of the first grooves and the second direction is θ, where 0 < θ < 90°. The distance between two adjacent first grooves in the second direction is W2, and θ and W2 satisfy the following relationship: 0.5 ≤ 1 / (W2 × tanθ) ≤ 1.5.

[0005] In the above-mentioned electrode, a plurality of first grooves arranged at equal intervals along the second direction are provided on the surface of the first active material layer facing away from the current collector. The first grooves can increase the area of the first active material layer wetted by the electrolyte, enabling the first active material layer to be in full contact with the electrolyte. When the electrode forms a wound battery cell, on the one hand, the first grooves at the corners of the battery cell can store the electrolyte, and on the other hand, they can form a transmission channel for the electrolyte to supply the electrolyte to the corners of the battery cell, reducing the risk of lithium deposition caused by less electrolyte at the corners of the battery cell. 1 / (W2×tanθ) represents the number of intersections between the corners of the battery cell and the first grooves per unit distance. When the number of intersections is small, the number of first grooves at the corners of the battery cell will be small, unable to meet the supply amount of the electrolyte at the corners of the battery cell, and thus lithium deposition will occur at the corners of the battery cell. When the number of intersections is large, the number of first grooves will be excessive, and the arrangement of the first grooves will be too dense, which is a redundant design without additional benefits and will result in a loss of the energy density of the electrode. By limiting 0.5≤1 / (W2×tanθ)≤1.5, the risk of lithium deposition can be reduced, and it is beneficial to improve the energy density of the electrode.

[0006] In some embodiments of the present application, 1 / 2<1 / (sinθ×2)<K / 2, and 1<K<2.

[0007] When the electrode forms a wound battery cell, during the cycling process of the battery cell, along the third direction, the middle position of the electrode is most likely to lack electrolyte, and the distance for the electrolyte to be transmitted from one end of the first groove to the middle position is the longest transmission distance of the electrolyte. The longest transmission distance of the electrolyte satisfies the following relationship: (W1 / 2) / sinθ.

[0008] In the extreme case where θ = 90°, the extending direction of the first groove is the same as the third direction. At this time, the minimum value of the longest transmission distance of the electrolyte satisfies the following relationship: W1 / 2. The maximum value of the longest transmission distance of the electrolyte is limited by the flow rate of the electrolyte. The flow rate of the electrolyte is related to the viscosity of the electrolyte, the coating weight of the first active material layer, and the compaction density of the first active material layer. Considering the influence of these three variables, a parameter K is defined, and 1<K<2. When the viscosity of the electrolyte is greater, and / or the coating weight of the first active material layer is greater, and / or the compaction density of the first active material layer is greater, the value of K is smaller. The maximum value of the longest transmission distance of the electrolyte satisfies the following relationship: K×W1 / 2.

[0009] The longest transmission distance of the electrolyte is between the minimum value and the maximum value, W1 / 2<(W1 / 2) / sinθ<K×W1 / 2. Simplifying gives: 1 / 2<1 / (sinθ×2)<K / 2. By limiting 1 / 2<1 / (sinθ×2)<K / 2, the risk of lack of electrolyte at the middle position of the electrode can be reduced, and further the risk of lithium deposition can be reduced.

[0010] In some embodiments of this application, the width W1 of the current collector in the third direction, the angle θ between the extension direction of the first groove and the second direction, and the spacing W2 between two adjacent first grooves in the second direction satisfy the following relationship: 30 ≤ (W1×W2×tanθ) / (sinθ×2) ≤ 100. (W1×W2×tanθ) / (sinθ×2) represents the ratio of the longest electrolyte transmission distance to the number of intersections per unit distance between the corner of the cell and the first groove. When the electrodes form a wound cell, a small ratio of the longest electrolyte transmission distance to the number of intersections results in a shorter longest electrolyte transmission distance. Simultaneously, the large number of first grooves at the corners of the cell constitutes a redundant design without additional benefit, leading to a loss of electrode energy density and increased production costs. When the ratio of the longest electrolyte transport distance to the number of intersections is large, the longest electrolyte transport distance is long. Simultaneously, the number of first grooves at the cell corners is insufficient to meet the electrolyte supply requirements at these corners, leading to lithium plating. By limiting the value to 30 ≤ (W1 × W2 × tanθ) / (sinθ × 2) ≤ 100, the risk of lithium plating and production costs can be reduced, and the energy density of the electrode can be improved.

[0011] In some embodiments of this application, along the first direction, the thickness h1 of the first active material layer and the depth h2 of the first groove satisfy the following relationship: 1 / 6≤h2 / h1≤3 / 4, so as to increase the area of ​​the first active material layer wetted by the electrolyte, and facilitate the formation of electrolyte transport channels and reduce the loss of energy density of the electrode.

[0012] In some embodiments of this application, viewed along the extension direction of the first groove, the first groove includes a bottom wall and two side walls connected to both sides of the bottom wall. Each side wall is inclined relative to the bottom wall, and an opening is formed at the end of each side wall away from the bottom wall. Along the first direction, the projection of the bottom wall lies within the projection of the opening, forming a groove structure that is wider at the top and narrower at the bottom. This facilitates the entry of electrolyte into the first groove from the opening and reduces the etching of the first active material layer at the bottom wall, thereby reducing the loss of energy density of the electrode. Furthermore, the inclined arrangement of each side wall relative to the bottom wall helps to increase the area of ​​the first active material layer wetted by the electrolyte, ensuring sufficient contact between the first active material layer and the electrolyte.

[0013] In some embodiments of this application, the electrode includes two first active material layers, which are respectively disposed on both sides of the current collector along a first direction to improve the energy density of the electrode.

[0014] In some embodiments of this application, along a first direction, the projection of a first groove in one first active material layer is parallel to the projection of a first groove in another first active material layer, to facilitate processing.

[0015] In some embodiments of this application, along a first direction, the projection of a first groove in one first active material layer intersects with the projection of a first groove in another first active material layer.

[0016] In some embodiments of this application, along the first direction, the thickness H1 of the current collector satisfies: 3μm≤H1≤15μm, in order to meet the structural strength requirements of the current collector and reduce the space waste caused by the large thickness of the current collector, which is beneficial to improving the energy density of the electrode.

[0017] Embodiments of this application also provide a battery cell, which includes an electrode assembly comprising a positive electrode, a separator, and a negative electrode wound together. The positive or negative electrode can be any of the electrode types described in the above embodiments.

[0018] The electrode assembly includes a first straight section, a first bent section, a second straight section, and a second bent section connected in sequence. The first straight section and the second straight section are arranged opposite each other along the thickness direction of the battery cell, and the first bent section and the second bent section are arranged opposite each other along the width direction of the battery cell. Multiple first grooves are provided on the electrode plates located at the first bent section and / or the second bent section.

[0019] Embodiments of this application also provide a terminal device, which includes the battery cell described in the above embodiments.

[0020] In the aforementioned electrode, cell, and terminal device, the surface of the first active material layer facing away from the current collector is provided with a plurality of first grooves arranged at equal intervals along a second direction. The first grooves provide channels for the electrolyte to wet the first active material layer, increasing the area of ​​the first active material layer wetted by the electrolyte and ensuring sufficient contact between the first active material layer and the electrolyte. When the electrode forms a wound cell, the first grooves located at the corners of the cell can store electrolyte and form electrolyte transport channels to replenish the electrolyte at the corners, reducing the risk of lithium plating due to insufficient electrolyte at the corners. 1 / (W²×tanθ) represents the number of intersections between the cell corner and the first grooves per unit distance. When the number of intersections is small, the number of first grooves at the cell corners will be insufficient to meet the electrolyte replenishment needs at the cell corners, leading to lithium plating at the cell corners. When the number of intersections is large, it leads to an overabundance of first grooves. The excessively dense arrangement of these first grooves constitutes a redundant design with no additional benefit, resulting in a loss of electrode energy density. By limiting the value to 0.5 ≤ 1 / (W²×tanθ) ≤ 1.5, the risk of lithium plating can be reduced, and the loss of electrode energy density can be minimized as much as possible. Attached Figure Description

[0021] Figure 1 is a schematic diagram of the electrode structure in one embodiment of this application.

[0022] Figure 2 is a schematic diagram of the structure of an electrode sheet in one embodiment of this application, viewed along a first direction.

[0023] Figure 3 is a schematic diagram of the structure of a wound battery cell with electrode sheets in one embodiment of this application.

[0024] Figure 4 is a schematic diagram of the structure of the electrode sheet of another embodiment of this application as viewed along the first direction.

[0025] Figure 5 is a schematic diagram of the structure of the two first active material layers of the electrode in one embodiment of this application.

[0026] Figure 6 is a schematic diagram of the battery cell structure in one embodiment of this application.

[0027] Figure 7 is a schematic diagram of the structure of a terminal device in one embodiment of this application.

[0028] Key Component Symbols: Electrode 100, Cell 200, Terminal Device 300, Current Collector 10, First Active Material Layer 20, First Groove 21, Bottom Wall 211, Side Wall 212, Opening 213, First Reference Line E, Second Reference Line F, Third Reference Line G, Middle Position M, Electrode Assembly 30, Positive Electrode 31, Separator 32, Negative Electrode 33, First Straight Section 30A, First Bending Section 30B, Second Straight Section 30C, Second Bending Section 30D, First Direction Z, Second Direction X, Third Direction Y

[0029] The following detailed description, in conjunction with the accompanying drawings, will further illustrate this application. Detailed Implementation

[0030] The technical solutions of the embodiments of this application will be described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments.

[0031] It should be noted that when a component is considered to be "connected" to another component, it can be directly connected to the other component or may also have a component that is centrally located. When a component is considered to be "set" on another component, it can be directly set on the other component or may also have a component that is centrally located.

[0032] When one value is considered "equal" to another, it means that they are equal within a set deviation range, which is within 5%. In other words, if at least one of the two values ​​fluctuates within the set deviation range, they are considered approximately equal even if their values ​​are not equal. Similarly, when one value is considered to have a "1:1" ratio with another, it means that they are equal within a set deviation range, which is within 5%. Again, if at least one of the two values ​​fluctuates within the set deviation range, they are considered equal in ratio even if their values ​​are not equal.

[0033] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein in the specification of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items. The term "overlap" as used herein refers to the overlapping of the projected portions of two components or the coincidence of the projected portions of two components.

[0034] An embodiment of this application provides an electrode, which includes a current collector and a first active material layer. The thickness direction of the current collector is a first direction, the length direction of the current collector is a second direction, and the width direction of the current collector is a third direction. The first active material layer is disposed on one side of the current collector in the first direction. A plurality of first grooves are provided on the surface of the first active material layer facing away from the current collector, arranged at equal intervals along the second direction. Viewed along the first direction, each first groove extends from one side of the first active material layer in the third direction to the other side in the third direction. The extension direction of each first groove is inclined relative to the second direction, and the extension directions of the plurality of first grooves are parallel to each other. The angle between the extension directions of the first grooves and the second direction is θ, where 0 < θ < 90°. The distance between two adjacent first grooves in the second direction is W2, and θ and W2 satisfy the following relationship: 0.5 ≤ 1 / (W2 × tanθ) ≤ 1.5.

[0035] In the aforementioned electrode, the surface of the first active material layer facing away from the current collector has multiple first grooves arranged at equal intervals along a second direction. These first grooves increase the area of ​​the first active material layer wetted by the electrolyte, ensuring sufficient contact between the first active material layer and the electrolyte. When the electrode forms a wound battery cell, the first grooves located at the corners of the cell can store electrolyte and form electrolyte transport channels, replenishing the electrolyte at the corners and reducing the risk of lithium plating due to insufficient electrolyte at the corners. 1 / (W²×tanθ) represents the number of intersections between the corner of the cell and the first grooves per unit distance. A small number of intersections results in fewer first grooves at the corners, insufficient electrolyte replenishment, and consequently, lithium plating at the corners. A large number of intersections leads to an excess of first grooves, resulting in an overly dense arrangement, a redundant design with no additional benefit, and a loss of electrode energy density. By limiting the value to 0.5≤1 / (W2×tanθ)≤1.5, the risk of lithium plating can be reduced, and the energy density of the electrode can be improved.

[0036] The embodiments of this application will be further described below with reference to the accompanying drawings.

[0037] Please refer to Figure 1. An embodiment of this application provides an electrode 100, which is used to form an electrode assembly for use in a secondary battery. A secondary battery is a battery that can be used again after being discharged by recharging to activate the active material.

[0038] The electrode 100 includes a current collector 10 and a first active material layer 20. The current collector 10 is used to collect current. The first active material layer 20 is used to generate current and collect the current onto the current collector 10. Specifically, the first active material layer 20 is coated onto the surface of the current collector 10 by means of extrusion coating, transfer coating, spray coating, etc. Optionally, the electrode 100 is negatively polarized or positively polarized.

[0039] The thickness direction of the current collector 10 is the first direction Z, the length direction of the current collector 10 is the second direction X, and the width direction of the current collector 10 is the third direction Y. The first direction Z, the second direction X, and the third direction Y are all perpendicular to each other. The length and width directions of the current collector 10 refer to two dimensions of its surface. The length direction is the primary dimension (i.e., the direction with the larger dimension), while the width direction is the secondary dimension (i.e., the direction with the smaller dimension). Typically, the length direction is consistent with the coating direction of each material layer (e.g., the first active material layer 20) during the electrode 100 processing, while the width direction is perpendicular to the length direction.

[0040] Please refer to Figure 2. The first active material layer 20 is disposed on one side of the current collector 10 in the first direction Z. The surface of the first active material layer 20 facing away from the current collector 10 has a plurality of first grooves 21 arranged at equal intervals along the second direction X. Viewed along the first direction Z, each first groove 21 extends from one side of the first active material layer 20 in the third direction Y to the other side in the third direction Y. The extension direction of each first groove 21 is inclined relative to the second direction X, and the extension directions of the plurality of first grooves 21 are parallel to each other. The first grooves 21 can increase the area of ​​the first active material layer 20 wetted by the electrolyte, allowing the first active material layer 20 to fully contact the electrolyte. When the electrode 100 constitutes a wound battery cell, the first grooves 21 located at the corners of the battery cell can, on the one hand, store electrolyte, and on the other hand, form electrolyte transport channels to replenish electrolyte at the corners of the battery cell, reducing the risk of lithium plating caused by insufficient electrolyte at the corners of the battery cell.

[0041] Optionally, the first groove 21 is formed by laser etching of the surface of the first active material layer 20 away from the current collector 10.

[0042] Please refer to Figure 2. The angle θ between the extension direction of the first groove 21 and the second direction X, and the distance W2 between two adjacent first grooves 21 in the second direction X, satisfy the following relationship: 0.5≤1 / (W2×tanθ)≤1.5.

[0043] The specific derivation process is as follows:

[0044] A first reference line E extends along a third direction Y from one side of the first active material layer 20 to the other side of the first active material layer 20. A second reference line F extends along the extension direction of the first groove 21 from one side of the first active material layer 20 to the other side of the first active material layer 20. One end of the first reference line E is connected to one end of the second reference line F, and the other end of the first reference line E and the other end of the second reference line F are connected by a third reference line G. The first reference line E, the second reference line F, and the third reference line G form a right triangle.

[0045] The length of the first reference line E is equal to the width W1 of the current collector 10 in the third direction Y. The angle between the extension direction of the second reference line F and the second direction X is equal to the angle θ between the extension direction of the first groove 21 and the second direction X. The number of first grooves 21 passing through the first reference line E is the same as the number of first grooves 21 passing through the third reference line G.

[0046] The number of first grooves 21 passing through the third reference line G can be obtained by the ratio of the length of the third reference line G to the distance W2 between two adjacent first grooves 21 in the second direction X. The length of the third reference line G satisfies the following relationship: W1 / tanθ. The number of first grooves 21 passing through the third reference line G satisfies the following relationship: (W1 / tanθ) / W2. Furthermore, the number of first grooves 21 passing through the first reference line E satisfies the following relationship: (W1 / tanθ) / W2. The number of intersections between the first reference line E and the first grooves 21 at a unit distance satisfies the following relationship: (W1 / tanθ) / W2 / W1. Simplifying, we get: 1 / (W2×tanθ). The units of W2 and W1 are both mm.

[0047] Referring to Figure 3, when the electrode 100 forms a wound cell, the first reference line E is located at the corner of the cell. The number of intersections between the first reference line E and the first groove 21 per unit distance is the number of intersections between the corner of the cell and the first groove 21 per unit distance. When the number of intersections is small (less than 0.5), the number of first grooves 21 at the corner of the cell will be insufficient to meet the electrolyte supply requirements at the corner, leading to lithium plating at the corner. When the number of intersections is large (greater than 1.5), the number of first grooves 21 will be excessive, resulting in an overly dense arrangement of the first grooves 21, which is a redundant design without additional benefit and will reduce the energy density of the electrode 100. By limiting 0.5 ≤ 1 / (W2×tanθ) ≤ 1.5, the risk of lithium plating can be reduced, and the energy density of the electrode 100 can be improved.

[0048] Furthermore, the above formula can reduce the error caused by measuring the width W1 of the current collector 10 in the third direction Y, thereby improving accuracy.

[0049] Please refer to Figure 4. It should be noted that when the two endpoints E' of the first reference line E in the third direction Y coincide with two different first grooves 21, the two endpoints of the first reference line E in the third direction Y are considered as one intersection point to conform to the above formula.

[0050] Please refer to Figure 2. In some embodiments, parameter K is defined in relation to the following three conditions: a) the coating weight of the first active material layer 20; b) the compaction density of the first active material layer 20; and c) the viscosity of the electrolyte in contact with the first active material layer 20. The greater the coating weight of the first active material layer 20, the smaller the value of parameter K; the greater the compaction density of the first active material layer 20, the smaller the value of parameter K; and the greater the viscosity of the electrolyte, the smaller the value of parameter K. Considering the respective value ranges of the three conditions, parameter K satisfies 1 < K < 2.

[0051] Optionally, the value of K is one of 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, and any other value within the range of 1 < K < 2.

[0052] In some embodiments, the angle θ between the extending direction of the first groove 21 and the second direction X and the parameter K satisfy the following relationship: 1 / 2 < 1 / (sinθ × 2) < K / 2.

[0053] The specific derivation process is as follows:

[0054] When the electrode sheet 100 forms a wound battery cell, during the cycling of the battery cell, along the third direction Y, the middle position M of the electrode sheet 100 is most likely to lack electrolyte, and the distance for the electrolyte to be transmitted from one end of the first groove 21 to the middle position M is the longest transmission distance of the electrolyte. The longest transmission distance of the electrolyte satisfies the following relationship: (W1 / 2) / sinθ.

[0055] In the extreme case where θ = 90°, the extending direction of the first groove 21 is the same as the third direction Y. At this time, the minimum value of the longest transmission distance of the electrolyte satisfies the following relationship: W1 / 2. The maximum value of the longest transmission distance of the electrolyte is limited by the flow rate of the electrolyte. The flow rate of the electrolyte is related to the viscosity of the electrolyte, the coating weight of the first active material layer, and the compaction density of the first active material layer. Considering the influence of these three variables, the parameter K is defined, and 1 < K < 2. When the viscosity of the electrolyte is greater, and / or, the coating weight of the first active material layer is greater, and / or, the compaction density of the first active material layer is greater, the value of K is smaller. The maximum value of the longest transmission distance of the electrolyte satisfies the following relationship: K × W1 / 2.

[0056] The longest transmission distance of the electrolyte is between the minimum value and the maximum value, W1 / 2 < (W1 / 2) / sinθ < K × W1 / 2. Simplifying gives: 1 / 2 < 1 / (sinθ × 2) < K / 2. By limiting 1 / 2 < 1 / (sinθ × 2) < K / 2, the risk of the middle position M of the electrode sheet 100 lacking electrolyte is reduced, and thus the risk of lithium plating is reduced.

[0057] Moreover, through the above formula, the error caused by measuring the width W1 of the current collector 10 in the third direction Y can be reduced, improving the accuracy.

[0058] Please continue to refer to FIG. 2. In some embodiments, the width W1 of the current collector 10 in the third direction Y, the angle θ between the extending direction of the first groove 21 and the second direction X, and the pitch W2 between two adjacent first grooves 21 in the second direction X satisfy the following relationship:

[0059] 30 ≤ (W1 × W2 × tanθ) / (sinθ × 2) ≤ 100.

[0060] The specific derivation process is as follows:

[0061] The longest transmission distance of the electrolyte satisfies the following relationship: (W1 / 2) / sinθ. The number of intersections per unit distance between the corner of the cell 200 and the first groove 21 satisfies the following relationship: 1 / (W2×tanθ). The ratio of the longest transmission distance of the electrolyte to the number of intersections per unit distance between the corner of the cell 200 and the first groove 21 satisfies the following relationship: (W1×W2×tanθ) / (sinθ×2).

[0062] When the electrode 100 forms a wound cell, if the ratio of the longest electrolyte transport distance to the number of intersections is small (less than 30), the longest electrolyte transport distance will be short. Simultaneously, the number of first grooves 21 at the cell corners will be large, constituting a redundant design with no additional benefit, resulting in a loss of energy density for the electrode 100 and increased production costs. Conversely, if the ratio is large (greater than 100), the longest electrolyte transport distance will be long, but the number of first grooves 21 at the cell corners will be small, insufficient to replenish the electrolyte at the corners, leading to lithium plating at the cell corners. By limiting the value to 30 ≤ (W1 × W2 × tanθ) / (sinθ × 2) ≤ 100, the risk of lithium plating and production costs can be reduced, and the energy density of the electrode 100 can be improved.

[0063] Referring again to Figure 1, in some embodiments, along the first direction Z, the thickness h1 of the first active material layer 20 and the depth h2 of the first groove 21 satisfy the following relationship: 1 / 6 ≤ h2 / h1 ≤ 3 / 4. When h2 / h1 is small (less than 1 / 6), the area of ​​the first active material layer 20 wetted by the electrolyte is small, which is not conducive to the formation of electrolyte transport channels. When h2 / h1 is large (greater than 3 / 4), the energy density of the electrode 100 will be lost. By limiting 1 / 6 ≤ h2 / h1 ≤ 3 / 4, the area of ​​the first active material layer 20 wetted by the electrolyte can be increased, which is conducive to the formation of electrolyte transport channels and reduces the loss of energy density of the electrode 100.

[0064] Optionally, h2 / h1 can take any value from 1 / 6, 1 / 3, 5 / 12, 1 / 2, 7 / 12, 2 / 3, 3 / 4, and any other value within the range of 1 / 6≤h2 / h1≤3 / 4.

[0065] Referring to Figure 1, in some embodiments, viewed along the extending direction of the first groove 21, the first groove 21 includes a bottom wall 211 and two side walls 212 connected to both sides of the bottom wall 211. Each side wall 212 is inclined relative to the bottom wall 211, and an opening 213 is formed at the end of each side wall 212 away from the bottom wall 211. Along the first direction Z, the projection of the bottom wall 211 lies within the projection of the opening 213, forming a groove structure that is wider at the top and narrower at the bottom. This facilitates the entry of electrolyte into the first groove 21 from the opening 213 and reduces the etching of the first active material layer 20 at the bottom wall 211, thereby reducing the energy density loss of the electrode 100. Furthermore, the inclined arrangement of each side wall 212 relative to the bottom wall 211 helps to increase the area of ​​the first active material layer 20 wetted by the electrolyte, ensuring sufficient contact between the first active material layer 20 and the electrolyte.

[0066] It is understood that in other embodiments, at least one sidewall 212 is provided with an arc surface to reduce the first active material layer 20 etched at the sidewall 212 and reduce the loss of energy density of the electrode 100.

[0067] Please refer to Figure 5. In some embodiments, the electrode 100 includes two first active material layers 20, which are respectively disposed on both sides of the current collector 10 along the first direction Z to improve the energy density of the electrode 100.

[0068] Each first active material layer 20 has a plurality of first grooves 21 arranged at equal intervals along the second direction X on the surface opposite to the current collector 10, to further increase the area of ​​the first active material layer 20 wetted by the electrolyte, so as to ensure sufficient contact between the first active material layer 20 and the electrolyte. When the electrode 100 constitutes a wound battery cell, the first grooves 21 located at the corners of the battery cell can store electrolyte on the one hand, and form electrolyte transport channels on the other hand, so as to replenish electrolyte at the corners of the battery cell, reducing the risk of lithium plating due to insufficient electrolyte at the corners of the battery cell.

[0069] In some embodiments, along the first direction Z, the projection of each first groove 21 of one first active material layer 20 is parallel to the projection of a first groove 21 of another first active material layer 20, in order to facilitate processing.

[0070] Optionally, along the first direction Z, the projection of each first groove 21 of one first active material layer 20 coincides with the projection of a first groove 21 of another first active material layer 20.

[0071] In some embodiments, along the first direction Z, the projection of each first groove 21 of one first active material layer 20 intersects with the projection of a first groove 21 of another first active material layer 20.

[0072] Please continue to refer to Figure 1. In some embodiments, along the first direction Z, the thickness H1 of the current collector 10 satisfies: 3μm≤H1≤15μm, so as to meet the structural strength requirements of the current collector 10 and reduce the space waste caused by the large thickness of the current collector 10, which is beneficial to improving the energy density of the electrode 100.

[0073] Optionally, H1 can be any value within the range of 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, or any other value within the range of 3μm≤H1≤15μm.

[0074] Optionally, the current collector 10 is a metal current collector or a composite current collector.

[0075] Referring to Figures 3 and 6, an embodiment of this application also provides a battery cell 200. The battery cell 200 includes an electrode assembly 30 for converting chemical energy into electrical energy. The electrode assembly 30 includes a positive electrode 31, a separator 32, and a negative electrode 33 wound together, wherein the positive electrode 31 or the negative electrode 33 is the electrode 100 as described in any of the above embodiments.

[0076] In some embodiments, the electrode assembly 30 includes a first straight section 30A, a first bent section 30B, a second straight section 30C, and a second bent section 30D connected in sequence. The first straight section 30A and the second straight section 30C are disposed opposite each other along the thickness direction of the cell 200, and the first bent section 30B and the second bent section 30D are disposed opposite each other along the width direction of the cell 200. The electrode 100 has a plurality of first grooves 21 at the portions of the first bent section 30B and / or the second bent section 30D.

[0077] Referring to Figure 7, one embodiment of this application also provides a terminal device 300, which includes the battery cell 200 from any of the above embodiments. Optionally, the terminal device 300 may be a vehicle, mobile phone, portable device, laptop computer, ship, spacecraft, electric toy, or power tool, etc.

[0078] The following describes the specific implementation of the battery cell 200 in the embodiments and comparative examples.

[0079] Example 1:

[0080] The battery cell is 200, with a capacity of 4Ah. The assembly process is as follows:

[0081] (1) Preparation of negative electrode sheet: The negative electrode active materials artificial graphite, conductive carbon black (Super P), styrene-butadiene rubber (SBR), and CMC (sodium carboxymethyl cellulose) are mixed in a weight ratio of 97:0.5:1.3:1.2 (the addition ratio can be adjusted), and deionized water is added as a solvent to prepare a slurry with a weight percentage of 50 wt%, and stirred evenly. The slurry is uniformly coated on one surface of a copper foil (negative electrode current collector, Cu with a thickness of 6 μm), and then dried at 110 °C to obtain a negative electrode sheet with a single-sided coating of negative electrode active material. When preparing a double-sided coated negative electrode sheet, the above steps are repeated on the other surface of the negative electrode sheet to obtain a negative electrode sheet with a double-sided coating of negative electrode active material. The coated electrode sheet is then cold-pressed to a thickness of 105 μm, and a first groove is formed on the surface of the negative electrode active material layer away from the negative electrode current collector by laser etching. Then, negative electrode tabs are welded on the copper foil. The material of the negative electrode tabs is nickel or nickel-plated copper.

[0082] (2) Preparation of the positive electrode sheet: Lithium cobalt oxide (LiCoO2), conductive carbon black (Super P), CNTs (carbon nanotubes), and polyvinylidene fluoride (PVDF) were mixed in a weight ratio of 97.5:0.5:0.5:1.5. N-methylpyrrolidone (NMP) was added as a solvent to prepare a slurry with a solid content of 75 wt%, and the mixture was stirred evenly. The slurry was uniformly coated on one surface of an aluminum foil (positive electrode current collector), and then dried at 90°C to obtain a positive electrode sheet with a single-sided coating of positive electrode active material. When preparing a double-sided coated positive electrode sheet, the above coating steps were repeated on the other surface of the aluminum foil. The coated electrode sheet was then cold-pressed to a thickness of 95 μm, and positive electrode tabs were welded onto the aluminum foil. The material of the positive electrode tabs was aluminum.

[0083] (3) Preparation of electrolyte: In a dry argon atmosphere, ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) are first mixed in a mass ratio of EC:EMC:DEC = 30:50:20 to form a basic organic solvent. Then, lithium salt lithium hexafluorophosphate (LiPF6) is added to the basic organic solvent to dissolve and mix evenly to obtain an electrolyte with a lithium salt concentration of 1.15 mol / L.

[0084] (4) Preparation of the isolation membrane: A 7μm thick porous polyethylene polymer film was used as the isolation membrane.

[0085] (5) Preparation of electrode assembly: The positive electrode, the separator and the negative electrode are wound and arranged.

[0086] (6) Assembly of electrode assembly: Place the punched aluminum-plastic film in the assembly fixture with the punched surface facing up, place the electrode assembly in the punch, and apply external force to press it tight. Then cover the electrode assembly with another punched aluminum-plastic film with the punched surface facing down, and heat seal the two aluminum-plastic films around their perimeter by hot pressing to obtain the assembled electrode assembly.

[0087] (7) Electrolyte injection and encapsulation: Electrolyte is injected into the assembled electrode assembly, and after vacuum encapsulation, standing, hot pressing formation, shaping and other processes, a secondary battery is obtained.

[0088] Cyclic performance test pass rate:

[0089] Twenty cells from each sample group were subjected to a 25°C cycle test. Cells that could maintain a capacity retention rate (discharge capacity of the cell after 800 cycles divided by the discharge capacity of the cell in the first cycle) greater than 80% were considered to have passed the test. The number of cells that passed the test was divided by the total number of cells (20) and the cycle performance test pass rate was recorded.

[0090] 25℃ Cyclic Test Procedure:

[0091] Using a battery performance testing machine (brand: Xinweier; model: CT-4008W-5V6A-80CH), the battery was charged to a full charge voltage of 4.5V with a current of 4A (charging rate 1C), then charged at a constant voltage to a cutoff current of 200mA (0.05C), and then left to stand for 10 minutes. Then, it was discharged to a voltage of 3V with a current of 2A (0.5C), and left to stand for 10 minutes. This process is recorded as one cycle, and the discharge capacity of one cycle is recorded. Then, the charging and discharging process is repeated.

[0092] Table 1 Note: / indicates that there is no data for this experiment.

[0093] In Comparative Example 1, the electrode 100 is not provided with a groove; in Comparative Example 2, the electrode 100 is provided with a groove, and the extension direction of the groove is perpendicular to the second direction X, that is, the included angle θ is 90°; in Comparative Examples 1 to 4 and Examples 2 to 13, all parameters except those involved in Table 1 are the same as those in Example 1.

[0094] As can be seen from the comparison of Comparative Examples 1, 2 to 4, and Examples 1 to 13, the grooves on the electrode can significantly improve the pass rate of the cycle performance test of the cell 200.

[0095] As can be seen from the comparison of Comparative Examples 2 and 3 to 4 and Examples 1 to 13, when the angle θ between the first groove 21 and the second direction X is set to 0 < θ < 90°, the cycle performance test pass rate of the cell 200 is further improved compared with the case of θ = 90°.

[0096] As can be seen from the comparison of Comparative Examples 3 to 4 and Examples 1 to 5, when the value of θ is constant, the number of intersection points 1 / (W2×tanθ) between the corner of the cell 200 and the first groove 21 at a unit distance will affect the pass rate of the cycle performance test of the cell 200. Specifically, when 1 / (W²×tanθ) ≤ 1.00, the pass rate of the cycle performance test of cell 200 gradually increases with the increase of 1 / (W²×tanθ) value, and the increase is relatively large; when 1 / (W²×tanθ) > 1.00, the increase of the pass rate of the cycle performance test of cell 200 gradually slows down with the increase of 1 / (W²×tanθ) value; when 1 / (W²×tanθ) ≥ 1.50, the pass rate of the cycle performance test of cell 200 can be stably maintained at 100%. With the increase of 1 / (W²×tanθ), there is no further benefit to the cycle performance of cell 200, and the increase in the number of first grooves 21 will cause redundant design, increase manufacturing costs, and cause a loss of energy density of electrode 100. When 0.5 ≤ 1 / (W²×tanθ) ≤ 1.5, the pass rate of the cycle performance test of cell 200 can reach more than 75%, which is the optimal range for the value of 1 / (W²×tanθ).

[0097] As can be seen from the comparison of Examples 3, 6, and 7, when the number of intersection points 1 / (W2×tanθ) between the corner of the cell 200 and the first groove 21 at a unit distance is constant, the pass rate of the cycle performance test of the cell 200 decreases when 1 / (sinθ×2)≥2 / K.

[0098] A comparison of Examples 3 and 8-13 shows that, when the number of intersections (1 / (W2×tanθ)) between the corner of the cell 200 and the first groove 21 at a unit distance is constant, if the ratio (W1×W2×tanθ) / (sinθ×2) of the longest electrolyte transmission distance to the number of intersections (W1×W2×tanθ) / (sinθ×2) is greater than 100, the longest electrolyte transmission distance is longer, and the cycle performance test pass rate of the cell 200 shows a downward trend. However, when (W1×W2×tanθ) / (sinθ×2) is less than 30, as shown in Table 1 (28), the arrangement of the first grooves 21 is too close. Although this is beneficial for the transmission and storage of electrolyte at the corner of the cell 200, it does not help the cycle performance of the cell 200 and is a redundant design. Furthermore, an excessive number of first grooves 21 will also lead to a loss of energy density.

[0099] In summary, in the aforementioned electrode 100, battery cell 200, and terminal device 300, the surface of the first active material layer 20 facing away from the current collector 10 is provided with a plurality of first grooves 21 arranged at equal intervals along the second direction X. The first grooves 21 increase the area of ​​the first active material layer 20 wetted by the electrolyte, ensuring sufficient contact between the first active material layer 20 and the electrolyte. When the electrode 100 constitutes a wound battery cell, the first grooves 21 located at the corners of the battery cell can, on the one hand, store electrolyte, and on the other hand, form electrolyte transport channels to replenish the electrolyte at the corners of the battery cell, reducing the risk of lithium plating due to insufficient electrolyte at the corners. 1 / (W²×tanθ) represents the number of intersection points per unit distance between the corner of the battery cell and the first grooves 21. When the number of intersection points is small (less than 0.5), the number of first grooves 21 at the corners of the cell is insufficient, failing to meet the electrolyte supply requirements at the corners, leading to lithium plating. When the number of intersection points is large (greater than 1.5), the number of first grooves 21 becomes excessive, resulting in an overly dense arrangement. This is a redundant design with no additional benefit, and it reduces the energy density of the electrode 100. By limiting the value to 0.5 ≤ 1 / (W²×tanθ) ≤ 1.5, the risk of lithium plating can be reduced, and the energy density of the electrode 100 can be improved.

[0100] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any changes or substitutions within the technical scope disclosed in this application should be covered within the scope of this application.

Claims

1. An electrode sheet, characterized in that, The electrode includes: A current collector, wherein the thickness direction of the current collector is a first direction, the length direction of the current collector is a second direction, and the width direction of the current collector is a third direction; A first active material layer is disposed on one side of the current collector in the first direction. The surface of the first active material layer facing away from the current collector is provided with a plurality of first grooves arranged at equal intervals along the second direction. When viewed along the first direction, each first groove extends from one side of the first active material layer in the third direction to the other side of the first active material layer in the third direction. The extension direction of each first groove is inclined relative to the second direction, and the extension directions of the plurality of first grooves are parallel to each other. The angle between the extending direction of the first groove and the second direction is θ, where 0 < θ < 90°; The distance between two adjacent grooves in the second direction is W2, and θ and W2 satisfy the following relationship: 0.5≤1 / (W2×tanθ)≤1.

5.

2. The electrode sheet as described in claim 1, characterized in that, 1 / 2 < 1 / (sinθ×2) <K / 2,1<K<2。 3. The electrode sheet as described in claim 2, characterized in that, 30≤(W1×W2×tanθ) / (sinθ×2)≤100, where W1 is the width of the current collector in the third direction and W2 is the spacing between two adjacent first grooves in the second direction.

4. The electrode sheet as described in claim 3, characterized in that, Along the first direction, the thickness h1 of the first active material layer and the depth h2 of the first groove satisfy the following relationship: 1 / 6 ≤ h2 / h1 ≤ 3 / 4.

5. The electrode sheet as described in claim 4, characterized in that, Viewed along the extension direction of the first groove, the first groove includes a bottom wall and two side walls connected to both sides of the bottom wall. Each side wall is inclined relative to the bottom wall, and an opening is formed at the end of the two side walls away from the bottom wall. Along the first direction, the projection of the bottom wall is located within the projection of the opening.

6. The electrode sheet according to any one of claims 1 to 5, characterized in that, The electrode includes two layers of the first active material, which are respectively disposed on both sides of the current collector along the first direction.

7. The electrode sheet as described in claim 6, characterized in that, Along the first direction, the projection of the first groove in one of the first active material layers is parallel to the projection of the first groove in another of the first active material layers.

8. The electrode sheet as described in claim 6, characterized in that, Along the first direction, the projection of the first groove of one layer of the first active material intersects with the projection of the first groove of another layer of the first active material.

9. The electrode sheet according to any one of claims 1 to 8, characterized in that, Along the first direction, the thickness H1 of the current collector satisfies: 3μm≤H1≤15μm.

10. A battery cell, characterized in that, The battery cell includes an electrode assembly, which includes a positive electrode sheet, a separator, and a negative electrode sheet wound together, wherein the positive electrode sheet or the negative electrode sheet is an electrode sheet as described in any one of claims 1 to 9; The electrode assembly includes a first straight section, a first bent section, a second straight section, and a second bent section connected in sequence. The first straight section and the second straight section are arranged opposite to each other along the thickness direction of the battery cell, and the first bent section and the second bent section are arranged opposite to each other along the width direction of the battery cell. The electrode sheet has multiple first grooves at the locations of the first bending section and / or the second bending section.

11. A terminal device, characterized in that, The terminal device includes the battery cell as described in claim 10.

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