Positive electrode sheet and battery

Abstract

The present application relates to the technical field of lithium battery electrode sheets, and provides a positive electrode sheet and a battery. The positive electrode sheet comprises a positive electrode current collector, a positive electrode active material layer and a protective layer; a positive electrode lug is arranged at one end of the positive electrode current collector in a first direction; the positive electrode active material layer is arranged on one side surface or two side surfaces of the positive electrode current collector; and the protective layer is arranged on one side surface or two side surfaces of the positive electrode current collector and located between the positive electrode active material layer and the positive electrode lug, wherein the positive electrode active material layer is provided with first recessed areas, the protective layer is provided with a second recessed area, and the first recessed areas and the second recessed area are all provided with pits. According to the positive electrode sheet, by forming the recessed area in the protective layer, the problem of being unable to form a recessed area on the outermost edge of a positive electrode active material layer due to strip running deviation, positioning deviation or unstable electrode sheet slitting width and the like is avoided, the problem of edge lithium precipitation under a high-rate charging system is mitigated, the cycle performance and the capacity retention rate of the battery are improved, the durability of the battery is improved, and the service life of the battery is prolonged.

Description

Positive electrode sheet and battery Technical Field

[0001] The present application relates to the technical field of lithium batteries, and in particular to a positive electrode sheet and a battery. Background Art

[0002] With the advent of the 5G era and the widespread use of electric vehicles, lithium-ion batteries will be required to have higher energy density, better fast-charging performance, and longer lifespans in the future. Increasing electrode thickness can improve battery energy density, but this can lead to problems such as increased lithium ion transmission distance, large lithium ion concentration gradients, and poor electrolyte wetting, resulting in irreversible lithium deposition, which in turn impairs the battery's rate performance and long-term cycling performance. Using multi-tab or laminated cells can increase the charge rate and achieve fast-charging performance, but at higher charge rates, the negative electrode is susceptible to lithium plating, especially at the tab edges and tab locations. When lithium plating occurs, electrode polarization increases, electrolyte consumption intensifies, and electrolyte depletion occurs, further exacerbating lithium plating. In the later stages of the battery cycle, insufficient electrolyte can also lead to deterioration in battery performance, impacting battery life.

[0003] The storage and release of lithium-ion battery capacity is based on Li + Reversible insertion and extraction in electrode materials. However, when some problems occur, such as insufficient lithium insertion space in the negative electrode, Li + The resistance of embedding into the negative electrode is too large, Li + Lithium deposition occurs when lithium ions are rapidly deintercalated from the positive electrode but cannot be equally intercalated into the negative electrode (lithium ions are deposited on the electrode surface and no longer participate in charging and discharging). Since the negative electrode is usually larger than the positive electrode, lithium deposition is more likely to occur at the edge (overhang) of the negative electrode. When lithium deposition occurs, it causes battery capacity decay, increased electrode polarization, increased electrolyte consumption at the edge, and increased impedance, which further worsens lithium deposition, severely affecting the performance of the battery cell, leading to rapid degradation of battery performance and affecting the battery's service life.

[0004] Therefore, it is of great significance to develop an electrode that can effectively improve the problem of edge lithium plating.

[0005] Summary of the Invention

[0006] The purpose of this application is to overcome the above-mentioned problems existing in the prior art and to provide a positive electrode sheet and a battery. The positive electrode sheet can effectively alleviate the problem of lithium deposition at the edge of the negative electrode sheet and improve the capacity retention rate of the battery.

[0007] In order to achieve the above-mentioned objectives, the first aspect of the present application provides a positive electrode sheet, which includes a positive electrode collector, a positive electrode active material layer and a protective layer; a positive electrode ear is provided at one end of the positive electrode collector in the first direction, the positive electrode active material layer is provided on one side or both sides of the surface of the positive electrode collector, and the protective layer is provided on one side or both sides of the surface of the positive electrode collector, and the protective layer is located between the positive electrode active material layer and the positive electrode ear; wherein, the positive electrode active material layer is provided with a first recessed area, and the protective layer is provided with a second recessed area, and both the first recessed area and the second recessed area have pits.

[0008] A second aspect of the present application provides a battery, which includes the positive electrode sheet described in the first aspect of the present application.

[0009] The above technical solution adopted in this application has the following beneficial effects:

[0010] (1) The positive electrode provided in the present application has a recessed area in the protective layer, which can avoid the problem of being unable to set a recessed area at the edge of the positive electrode active material layer due to reasons such as belt deviation, positioning deviation or unstable electrode cutting width, and improve the problem of lithium deposition at the edge of the negative electrode under a high-rate charging system.

[0011] (2) The positive electrode sheet provided in the present application has a recessed area in its positive electrode active material layer and protective layer, and there are pits in the recessed area. Since the protective layer is located between the positive electrode active material layer and the positive electrode ear, that is, located at the edge of the electrode sheet, at least the edge area of ​​the electrode sheet close to the electrode ear is provided with a pit. Such a setting can reduce the pore tortuosity of the active material layer, increase the electrolyte infiltration effect and speed, form a channel for rapid diffusion of lithium ions inside the electrode sheet, accelerate the diffusion speed of lithium ions, and improve the lithium ion diffusion coefficient, which is beneficial to enhance the mass transfer between the positive and negative electrodes, reduce the ion impedance, and prevent lithium ions from not being able to be embedded in the electrode sheet in time and being deposited on the surface of the electrode sheet to cause lithium precipitation.

[0012] (3) The positive electrode sheet provided in the present application has a space filled with electrolyte at the recessed portion, which can increase the electrolyte capacity, and a pit is provided in the protective layer to ensure that the positive electrode sheet has a recessed area at the edge of this side. The recessed area provided at the edge of this side of the positive electrode sheet can ensure that the electrolyte at the edge is increased, ensuring that there is sufficient electrolyte at the edge of this side of the positive electrode sheet, ensuring that the lithium ion transmission and embedding efficiency at the edge is improved, and avoiding the phenomenon that the lithium ion concentration at the edge is too high due to the lack of electrolyte at the edge, resulting in some lithium ions being unable to be embedded in the negative electrode sheet in time and lithium precipitation. In addition, a recessed area is also provided on the positive electrode active material layer, which improves the N / P ratio of the negative electrode sheet and the positive electrode sheet, and improves the negative electrode sheet's ability to embed lithium ions, thereby significantly reducing the phenomenon that lithium ions cannot be embedded and precipitated at the edge of the electrode sheet.

[0013] (4) The positive electrode sheet provided in the present application has a recessed area in the positive electrode active material layer, which is beneficial to enhancing the mass transfer between the positive and negative electrodes, reducing the ionic impedance, shortening the transmission distance of lithium ions, increasing the CB value at the recessed area, alleviating the problem of lithium desorption, and to a certain extent improving the surface density of the electrochemical system and the energy density of the battery.

[0014] (5) The positive electrode provided in this application can increase the electrolyte infiltration effect and speed, as well as increase the liquid storage space and increase the liquid storage volume, effectively solving the problems of poor electrolyte infiltration of thick electrodes and insufficient electrolyte in the late cycle, thereby improving the battery cycle life and capacity retention rate.

[0015] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article. Herein, unless otherwise specified, data ranges include endpoints. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] FIG1 shows a first schematic diagram of a positive electrode sheet in an embodiment of the present application.

[0017] FIG. 2 is a schematic diagram showing a case in which a tape run deviation causes a failure in normal hole formation at the edge in the prior art.

[0018] FIG3 shows a second schematic diagram of the positive electrode sheet in an embodiment of the present application.

[0019] FIG4 shows a third schematic diagram of the positive electrode sheet in the embodiment of the present application.

[0020] FIG5 shows a fourth schematic diagram of the positive electrode sheet in the embodiment of the present application.

[0021] FIG6 shows a fifth schematic diagram of the positive electrode sheet in the embodiment of the present application.

[0022] FIG7 shows a sixth schematic diagram of the positive electrode sheet in the embodiment of the present application;

[0023] FIG8 shows a seventh schematic diagram of the positive electrode sheet in the embodiment of the present application;

[0024] FIG9 is a schematic diagram showing the size markings of different areas in an embodiment of the present application;

[0025] FIG10 is an electron microscope image of the positive electrode sheet in the embodiment of the present application.

[0026] FIG11 shows an eighth schematic diagram of the positive electrode sheet in the embodiment of the present application.

[0027] FIG12 shows the element analysis results of the second normal area in the protective layer of the positive electrode sheet in the embodiment of the present application.

[0028] FIG13 shows the elemental analysis results of the second recessed area in the protective layer of the positive electrode sheet in an embodiment of the present application.

[0029] FIG14 is a first schematic diagram of the negative electrode sheet in an embodiment of the present application.

[0030] FIG15 is a second schematic diagram of the negative electrode sheet in an embodiment of the present application.

[0031] FIG16 is a third schematic diagram of the negative electrode plate in the embodiment of the present application.

[0032] FIG17 is a fourth schematic diagram of the negative electrode plate in the embodiment of the present application.

[0033] Reference numerals:

[0034] 1. Positive electrode active material layer; 11. Top edge region; 12. Bottom edge region; 13. First recessed region; 101. First pit; 2. Protective layer; 21. Second recessed region; 201. Second pit; 3. Positive electrode tab; 4. Negative electrode active material layer; 41. Top edge region; 42. Bottom edge region; 43. Third recessed region. DETAILED DESCRIPTION

[0035] The following is a detailed description of the specific embodiments of the present application. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present application and are not intended to limit the present application.

[0036] In the present invention, the "depressed area" may also be referred to as a "concave portion", and the "depressed area" and the "concave portion" have equivalent meanings.

[0037] Unless otherwise defined, all scientific and technical terms used in this application have the same meanings as commonly understood by one of ordinary skill in the art to which this application relates.

[0038] The research in this application found that when making holes at the edge of the positive electrode sheet, the outermost position of the positive electrode sheet often cannot be properly made due to the tape deviation (as shown in Figure 2, a schematic diagram of the tape deviation or positioning deviation). This results in the inability to effectively improve the lithium deposition situation in the outermost area of ​​the electrode sheet (usually the edges on both sides in the width direction of the electrode sheet).

[0039] In order to achieve normal hole formation at the outermost edge of the positive electrode sheet, this application proposes the following technical solutions:

[0040] In a first aspect, the present application provides a positive electrode sheet comprising a positive electrode current collector, a positive electrode active material layer, and a protective layer. Referring to FIG1 , the direction in which the positive electrode tabs are disposed of the positive electrode current collector is referred to as a first direction, the direction in which the current collector extends perpendicular to the first direction is referred to as a second direction, and the thickness direction of the positive electrode current collector is also referred to as a thickness direction. For example, in a prismatic battery, the first direction and the second direction are the width and length directions of the positive electrode current collector, respectively.

[0041] In some embodiments, referring to FIG1 , a positive electrode tab 3 is provided at one end of the positive electrode current collector in the first direction, the positive electrode active material layer 1 is provided on one or both surfaces of the positive electrode current collector, and the protective layer 2 is provided on one or both surfaces of the positive electrode current collector and is located between the positive electrode active material layer 1 and the positive electrode tab 3. In other words, the protective layer 2 is provided on the surface of the positive electrode current collector having the positive electrode active material layer 1, and on this side surface, a portion of the positive electrode current collector is provided on the positive electrode active material layer 1, and a portion of the portion is provided on the protective layer 2, and the protective layer 2 is located between the positive electrode active material layer 1 and the positive electrode tab 3.

[0042] In some embodiments, referring to Figures 1 and 5 , the positive electrode active material layer 1 is provided with a first recessed area 13, and the protective layer 2 is provided with a second recessed area 21. Both the first recessed area 13 and the second recessed area 21 have pits. Alternatively, at least a portion of the positive electrode active material layer 1 is provided with the first pit 101, and this portion of the area provided with the first pit 101 is referred to as the first recessed area 13; and at least a portion of the protective layer 2 is provided with the second pit 201, and this portion of the area provided with the second pit 201 is referred to as the second recessed area 21.

[0043] In the present application, the pits in the first recessed area and the second recessed area include holes or grooves.

[0044] The research in this application found that by setting a recessed area with pits on the protective layer, it is possible to set a recessed area normally at the outermost edge of the active material layer. This can avoid the problem of not being able to set a recessed area at the outermost edge of the positive electrode active material layer due to belt deviation, and can effectively alleviate the phenomenon of lithium plating at the edge of the negative electrode and improve the cycle performance and capacity retention rate of the battery, improve the problem of lithium plating at the edge under high-rate charging system, and improve the durability and service life of the battery.

[0045] Furthermore, setting a first recessed area in the active material layer is beneficial to enhancing the mass transfer between the positive and negative electrodes, reducing the ionic impedance, shortening the transmission distance of lithium ions, increasing the CB value (the ratio of the negative electrode capacity per unit area to the positive electrode capacity per unit area) at the recessed area, alleviating the lithium decomposition problem, and to a certain extent, improving the surface density of the electrochemical system and improving the energy density of the battery.

[0046] Furthermore, setting a first recessed area in the positive electrode sheet and a second recessed area in the protective layer can also increase the electrolyte infiltration effect and speed, as well as increase the liquid storage space and increase the liquid storage capacity, effectively solving the problems of poor electrolyte infiltration in thick electrodes and insufficient electrolyte in the late cycle, thereby improving the battery cycle life and capacity retention rate.

[0047] In some embodiments, the first recessed area is located on one side of the positive electrode current collector or distributed on both sides of the positive electrode current collector, and / or the second recessed area is located on one side of the positive electrode current collector or distributed on both sides of the positive electrode current collector.

[0048] Specifically, the first recessed region 13 is located on one side of the positive electrode current collector or is distributed on both sides of the positive electrode current collector. That is, the positive electrode current collector may be coated with the positive electrode active material layer 1 on both sides, and both active material layers may have the first recessed region 13, or the active material layer may have the first recessed region 13 on only one side. Similarly, the protective layer on one side of the positive electrode current collector may have the second recessed region 21, or the protective layer on both sides of the positive electrode current collector may have the second recessed region 21.

[0049] Furthermore, the first recessed area 13 includes at least a portion of the edge area of ​​the positive electrode active material layer 1 in the first direction. In other words, the edge area of ​​the positive electrode active material layer 1 in the first direction is at least partially provided with a first pit 101, such as the edge area on one side of the positive electrode current collector in the first direction, a portion of the edge area on one side, the edge areas on both sides, the edge areas on both sides are each partially provided with a first pit 101, and so on. For example, as shown in Figures 1 and 8, the first pit 101 can be partially provided in the edge area, or the first pit 101 can be arranged in the edge area from one end of the electrode sheet to the other end of the electrode sheet in the second direction. Of course, other areas outside the edge area can also be provided with the first pit 101.

[0050] In some embodiments, as shown in FIG1 and FIG3 , on the same side of the positive electrode current collector, that is, on the positive electrode active material layer 1 on the same side, at least one first recessed area 13 is provided, which is at least located at or includes the edge area on one side of the positive electrode active material layer 1 in the first direction. For example, the two end areas of the positive electrode active material layer 1 in the first direction are two edge areas, and the edge area closer to the protective layer 2 in these two edge areas is recorded as the top edge area 11, and the edge area on the other side is recorded as the bottom edge area 12. The first recessed area 13 is at least located at the top edge area 11 and / or the bottom edge area 12. For example, the first recessed area 13 includes at least a part of the top edge area 11, as shown in FIG1 and FIG8 , or includes at least a part of the bottom edge area 12. For example, there may be two first recessed areas 13, which are located at the edge areas on both sides of the positive electrode active material layer 1 in the first direction, as shown in FIG3 and FIG8 . Providing recessed areas only at the edge can prevent excessive loss of the positive electrode active material layer 1, which is equivalent to increasing the N / P ratio only at the edge, reducing the number of lithium ions at the edge, and thus alleviating edge lithium deposition. Alternatively, the first recessed area 13 can also satisfy the entire positive electrode active material layer 1, as shown in Figure 6, significantly improving the electrolyte infiltration speed and electrolyte capacity, and improving lithium ion transmission efficiency.

[0051] In some embodiments, as shown in Figures 3 and 4, a first recessed area 13 is provided in the bottom edge region 12 and / or the top edge of the positive electrode active material layer 1, which can improve the problem of lithium deposition at the bottom edge. In actual production, the first recessed area 13 in the bottom edge region 12 can cover the very edge of the top edge region 11, that is, the bottom edge line. However, due to operational deviations or positional deviations and other reasons, it is difficult to ensure that there is a pit at the very edge of the top edge region 11, that is, the top edge line. Therefore, in the present application, a second recessed area 21 is provided on the protective layer 2, and on the protective layer 2, the second recessed area 21 includes at least part of the edge area of ​​the protective layer 2 on the side close to the positive electrode active material layer 1, that is, at least the edge of the protective layer 2 close to the positive electrode active material layer 1. In this way, it can be effectively ensured that there is a pit at the edge position of the positive electrode active material layer 1 close to the positive electrode ear, ensuring that there is sufficient electrolyte at the edge of the side, and improving the problem of lithium deposition at the edge.

[0052] In some embodiments, the second recessed region includes at least a portion of the edge region of the protective layer 2 near the positive electrode active material layer 1. The second recessed region can be provided at the edge of the protective layer near the positive electrode active material layer, or the second recessed region can be provided across the entire area of ​​the protective layer. Preferably, the second recessed region is provided only at the edge of the protective layer near the positive electrode active material layer. As shown in FIG3 , the second recessed region 21 does not cover the entire protective layer 2 and can be provided only at the edge region of the protective layer 2 near the positive electrode active material layer 1. Such a setting has two main functions: one is to only punch holes at the edge, which can prevent the loss of too much ceramic material, ensure the insulating effect of the protective layer, and have little impact on the protective effect of the protective layer; the other is to ensure that there is a pit at the edge of the top edge area of ​​the positive electrode active material layer closest to the protective layer, which can avoid the phenomenon of lithium plating not being able to be improved due to deviations or technical problems in the hole making process, which makes it impossible to set a recessed area at the edge of the positive electrode (or it can be interpreted as avoiding the lack of pits at the edge due to operational deviations or position deviations when making pits), and ensure that there is sufficient electrolyte at the top edge area of ​​the positive electrode active material layer, especially at the edge, to effectively improve the problem of lithium plating at the edge.

[0053] In some embodiments, the top edge region 11 / bottom edge region 12 of the positive electrode active material layer 1 may be provided with a first recessed region 13 in the second direction, and its size in the second direction may be smaller than the size of the positive electrode active material layer 1 in the second direction, that is, the first recessed region 13 does not completely cover the top edge region 11 in the second direction. Alternatively, the size of the first recessed region 13 in the second direction is equal to the size of the positive electrode active material layer 1 in this direction, that is, the first recessed region 13 extends from one end to the other end of the positive electrode active material layer 1 in the second direction, as shown in Figures 1 and 3. With this arrangement, the entire top edge region 11 / bottom edge region 12 has a first pit 101. When the positive and negative electrode sheets are wound to form a battery cell, each turning portion of the battery cell has a first recess, which can solve the problem of lithium deposition at the turning portion of the battery cell.

[0054] In some embodiments, at least two first recessed areas 13 are provided in the second direction and are arranged at intervals, that is, at least two first recessed areas 13 are provided in the top edge region 11 / bottom edge region 12 and are arranged at intervals along the second direction, and each first recessed area 13 is formed by a portion of the top edge region 11 / bottom edge region 12, as shown in Figure 8. In this manner, recessed areas can be provided in edge regions prone to lithium deposition (such as bends) to solve the problem of lithium deposition, depending on the specific situation, while also avoiding excessive loss of the positive electrode active material layer.

[0055] In some embodiments, at least four first recessed regions are provided, located at the edge regions of the positive electrode active material layer at both ends in the first direction, namely the top edge region and the bottom edge region, and at both ends in the second direction. In other words, when the positive electrode sheet is square or rectangular, the outer contour of the active material layer 1 is square or rectangular, with four edges along the circumference, namely the edge regions at both ends in the first direction and the edge regions at both ends in the second direction, and all four edge regions have first recessed regions.

[0056] In the present application, “edge” can be interpreted as an area close to one side of the positive electrode active material layer or the protective layer, and the width of this area is not greater than one fifth of the width of the corresponding positive electrode active material layer or the protective layer.

[0057] To improve the problem of lithium deposition at the edge, in this application, when setting the recessed area (making holes), a certain distance (for example, 1mm to 3mm, which can be made on the processing platform) can be drilled outside the edge of the positive electrode sheet away from the positive electrode tab to achieve a recessed area at the edge away from the positive electrode tab. However, the above method cannot be used to drill holes on the edge close to the tab, otherwise it will easily damage the tab.

[0058] In some embodiments, the first recessed area and / or the second recessed area is provided at the junction of the protective layer and the positive electrode active material layer.

[0059] In some embodiments, the first recessed area includes at least two first pits arranged along the second direction or includes two or more first pits arranged in a matrix, and the first pits do not penetrate the positive electrode active material layer. In the second direction, the first recessed area 13 is provided with at least two first pits arranged at intervals, that is, in the top edge area 11 and the bottom edge area 12, the first recessed area 13 is provided with at least two and arranged at intervals along the second direction, and each first recessed area 13 is formed by a part of the top edge area 11 / bottom edge area 12, as shown in Figure 3. With such a setting, according to the specific situation, a recessed area (such as a turning portion) can be provided in the edge area where lithium is easily deposited to solve the problem of lithium deposition, while also avoiding excessive loss of the positive electrode active material layer.

[0060] In some embodiments, the second recessed region includes at least two second pits arranged along the second direction, and the second pits do not penetrate the protective layer or the second pits penetrate the protective layer but do not penetrate the positive electrode current collector.

[0061] In some embodiments, the shape of the first recessed area and / or the second recessed area is independently at least one of a circle, a regular polygon, an irregular polygon, a linear shape, and a strip shape.

[0062] In some embodiments, the positive electrode active material layer on both side surfaces of the positive electrode current collector is provided with the first recessed area, and the first pits in the first recessed areas on both side surfaces are staggered in the second direction; and / or, the protective layer on both side surfaces of the positive electrode current collector is provided with the second recessed area, and the second pits in the second recessed areas on both side surfaces are staggered in the second direction.

[0063] In some embodiments, when a second recessed area is provided on the protective layer on both sides of the positive electrode current collector, the second pits in the second recessed areas on both sides can be staggered, that is, the projections of the second pits on both sides in the thickness direction of the positive electrode sheet do not overlap, and are staggered. In this way, the problem of accidentally piercing the positive electrode current collector when making the pits can be prevented, thereby improving safety. It also prevents the thickness of the protective layer from being excessively thinned by making pits in the same position on both sides of the protective layer, thereby improving the safety and protectiveness of the protective layer. Similarly, when a first recessed area is provided on the positive electrode active material layer on both sides of the positive electrode current collector, the first pits in the first recessed areas on both sides can be staggered, that is, the projections of the first pits on both sides in the thickness direction of the electrode sheet do not overlap, and are staggered to avoid accidentally piercing the positive electrode current collector and prevent battery short circuits.

[0064] In some embodiments, a first recessed region is provided on an edge of one side of the positive electrode active material layer along the first direction (width direction) (which may be on the side close to the positive electrode tab or on the side away from the positive electrode tab), or a first recessed region is provided on both edges. In other embodiments, in addition to providing first recessed regions on both edges of the positive electrode active material layer, first recessed regions may also be provided in other areas of the positive electrode active material layer, for example, a first recessed region may be provided in the middle area of ​​the positive electrode active material layer, or a first recessed region may be provided on the entire surface of the positive electrode active material layer.

[0065] In some embodiments, when the positive electrode sheet is suitable for a multi-electrode wound battery cell, each bend of the battery cell has a first recess, which can solve the problem of lithium plating that may occur at the bend of the battery cell.

[0066] In some embodiments, as shown in Figures 1 and 7, a positive electrode sheet includes a positive electrode current collector (not shown), the surface of the positive electrode current collector is coated with a positive electrode active material layer 1, and a positive electrode tab 3 (multiple tabs are arranged at intervals) is provided at one end of the positive electrode current collector along the width direction of the positive electrode sheet, and the positive electrode tab 3 is connected to the positive electrode current collector. The positive electrode active material layer 1 is divided into a top edge region 11 (the edge close to the positive electrode tab) and a bottom edge region 12 (the edge away from the positive electrode tab) along the width direction of the positive electrode sheet. The surface of the positive electrode current collector close to the edge of the positive electrode tab 3 is coated with a protective layer 2. The top edge region 11 of the positive electrode active material layer 1 is provided with a first recessed area 13, and the edge of the protective layer 2 close to the active material layer 1 is provided with a second recessed area 21. Among them, the protective layer is provided with a second recessed area near the edge of the positive electrode active material layer, so that the first recessed area can be normally provided at the top edge of the positive electrode active material layer.

[0067] In some embodiments, as shown in FIG3 , a first recessed area 13 is provided in both the top edge region 11 and the bottom edge region 12 of the positive electrode active material layer 1, and a second recessed area 21 is provided at the edge of the protective layer 2 away from the positive electrode tab 3. When the first recessed area is provided at the bottom edge of the positive electrode active material layer, more holes can be punched a certain distance outside the bottom edge of the positive electrode sheet (for example, 1-3 mm beyond the positive electrode sheet) to ensure that the first recessed area is normally provided at the bottom edge of the positive electrode sheet.

[0068] For the edge of the positive electrode active material layer near the positive electrode ear, ideally, the recessed area is set exactly at the junction of the positive electrode active material layer and the protective layer during pore formation. However, due to technical problems, there are usually deviations and shifts in the actual pore formation process. Therefore, there may be areas without pores at the edge of the positive electrode active material layer near the positive electrode ear, as shown in Figure 2. Therefore, this application proposes a technical solution of setting a recessed area at the edge of the protective layer near the positive electrode active layer, or drilling holes at the junction to cover the edges of the protective layer and the positive electrode active material layer at the same time.

[0069] In some embodiments, as shown in FIG5 , a first recessed area 13 and a second recessed area 21 are provided at the interface between the protective layer 2 and the positive electrode active material layer 1. The holes at the interface that fall into the protective layer 2 are the second recessed area 21, and the holes that fall into the positive electrode active material layer 1 are the first recessed area 13. That is, the holes punched at the interface simultaneously cover the edges of the protective layer 2 and the positive electrode active material layer 1. The second recessed area is provided on the protective layer near the edge of the positive electrode active material layer, which ensures that the first recessed area also exists at the edge of the positive electrode active material layer, thereby achieving a normal recessed area at the very edge of the positive electrode active material layer. The recessed area is provided at the interface between the protective layer and the positive electrode active material layer to minimize damage to the protective layer as much as possible and to ensure that a recessed area can be provided at the very edge of the positive electrode.

[0070] In some embodiments, a pit is provided at the junction of the protective layer 2 and the positive electrode active material layer 1, that is, a first recessed area 13 and / or a second recessed area 21 is provided. In other words, a first pit 101 and / or a second pit 201 is provided at the junction of the protective layer 2 and the positive electrode active material layer 1, and the first pit 101 / the second pit 201 at the junction is partially located in the protective layer 2 and partially located in the positive electrode active material layer 1, as shown in FIG5 . In this way, by providing a pit at the junction, it is possible to avoid the situation where a pit is not provided at the very edge of the positive electrode active material layer due to large deviation in the tape run or large deviation in the laser drilling positioning when making the pit; it can not only minimize damage to the protective layer, but also effectively ensure that a pit can be provided at the top edge line of the top edge area.

[0071] In some embodiments, in the first direction, the size of the positive electrode active material layer is L, and the size of the first recessed area is L1. For a positive electrode active material with a width of L, the value after subtracting the first recessed area from L refers to the width without the first recessed area, which can be recorded as the width of the first normal area. The specific value of the size L1 of the first recessed area is not limited, and the size of L1 can be adjusted according to the lithium deposition situation at the top and bottom of the positive electrode sheet (both sides in the width direction).

[0072] In some embodiments, the relationship between L and L1 satisfies: L1 = 0.5 mm to 0.5 L. For example, L1 can be 0.5 mm, 1 mm, 2 mm, 3 mm, 0.01 L, 0.05 L, 0.1 L, 0.2 L, 0.3 L, 0.4 L, or 0.5 L; preferably, L1 = 3 mm to 0.2 L.

[0073] It should be noted that when the top and bottom edge regions of the positive electrode active material layer 1 are both provided with first recessed regions, when L1 is equal to 0.5L, it is equivalent to providing the first recessed region on the entire surface of the positive electrode active material layer, as shown in Figure 6. Because this implementation will result in a significant capacity loss, it is necessary to balance the areal density and ED loss. When the overall areal density is improved, this solution is recommended in combination with negative electrode pores or grooves.

[0074] When a first recessed area is provided on both sides of the positive electrode sheet and the value of the first recessed area is limited to the above range, while improving ED, it is possible to avoid excessive loss of the positive electrode active material layer, increase the CB value at the edge, reduce the number of lithium ions at the edge, and improve the effect of alleviating edge lithium plating.

[0075] In some embodiments, the size of the protective layer 2 in the first direction is W (as shown in Figure 9, W refers to the vertical distance from one side edge line to the other side edge line of the protective layer in the first direction), and the size of the second recessed area 21 in the first direction is W1 (as shown in Figure 9, W refers to the vertical distance from one side edge line to the other side edge line of the second recessed area in the first direction).

[0076] In some embodiments, W and W1 satisfy the following: 0<W1 / (W-W1)≤1. In the protective layer, W-W1 refers to the width of the region without the second recessed area, which can be referred to as the width of the second normal region. That is, the width of the region with the second recessed area is smaller than the width of the region without the second recessed area (the second normal region).

[0077] When the ratio of W1 / (W-W1) is within the above range, it is possible to avoid the situation where W1 is 0 or close to 0 (to avoid too few pits), the protective layer does not have a second recessed area or the proportion of the second recessed area is too small, and the situation where there is no recessed area at the edge of the positive electrode active layer due to large tape run deviation or large laser drilling positioning deviation can be avoided. It is also possible to avoid the width of the second normal area being less than the width of the first recessed area, and to avoid the protective layer losing its insulating protection function due to too many pits, and being unable to effectively solve the problem of burrs piercing the diaphragm. The provision of the protective layer can significantly reduce the burrs generated at the edge of the positive electrode sheet when cutting, effectively reducing the risk of burrs piercing the diaphragm and causing a battery short circuit, and improving the safety of the battery.

[0078] In some preferred embodiments, 1 / 8 ≤ W1 / (W-W1) ≤ 1 / 2. For example, the ratio of W1 / (W-W1) can be 1 / 8, 1 / 7, 1 / 6, 1 / 5, 1 / 4, 1 / 3, or 1 / 2. Preferably, when the ratio of W1 / (W-W1) is within the above range, the protective layer can still function as a protective layer even when a recessed area is provided at the outermost edge of the positive electrode active material layer.

[0079] In some embodiments, the width W of the protective layer is 0.5 mm to 5 mm, for example, 0.5 mm, 1 mm, 1.5 mm, 2 mm, 2.5 mm, 3 mm, 3.5 mm, 4 mm, 4.5 mm, 5 mm, or any point value in the range of two points above; preferably 1 mm to 3 mm. Since the positive electrode sheet is generally smaller than the negative electrode sheet, the edge of the wide side of the electrode sheet is prone to burrs during cutting, which will pierce the diaphragm and contact the negative electrode, causing a short circuit in the battery. After the protective layer is applied and the width of the protective layer is limited to the above range, it can completely fill the edge (wide side) of the width direction of the positive electrode sheet, so that the surface of the positive electrode sheet after cutting is smooth and free of burrs, thereby improving the safety performance of the battery. If the width of the protective layer is too small, it will affect its protective effect, and if the width is too large, it will affect the capacity of the battery.

[0080] In some embodiments, in the second direction, as shown in FIG9 , the size of the second recessed area 21 may be smaller than the size of the protective layer 2, that is, the second recessed area 21 does not have an edge area fully covered with the protective layer 2 in the second direction. In contrast, the recessed area can be specifically set according to the battery type. For example, lithium deposition is easy at the edge of the turning portion in the wound battery cell. By providing the second recessed area 21 in the area corresponding to the turning portion, the problem of lithium deposition in the wound battery cell can be effectively solved. At the same time, the loss of more protective layers 2 can also be avoided. Alternatively, the size of the second recessed area 21 in the second direction is equal to the size of the protective layer 2 in this direction, that is, the second recessed area 21 extends from one end of the second direction of the protective layer 2 to the other end, as shown in FIG4 . In this way, it can be ensured that there are pits at the edge of the positive active material layer 1 close to the positive ear side. Whether it is a laminated battery cell or a wound battery cell, the problem of edge lithium deposition can be effectively and significantly solved.

[0081] In some embodiments, at least two second recessed regions 21 are provided in the second direction and are arranged at intervals. That is, at least two second recessed regions 21 are provided in the edge region of the protective layer 2 and are arranged at intervals along the second direction. Each second recessed region 21 is formed by a portion of the edge region, as shown in FIG8 . In this manner, recessed regions can be provided in edge regions prone to lithium deposition (such as the electrode turning portion) to solve the lithium deposition problem according to specific circumstances, while also avoiding excessive loss of the protective layer 2.

[0082] In some embodiments, as shown in FIG10 , 10a is an electron microscope image of the positive electrode active material layer and the protective layer (ceramic layer) (before drilling). Among them, the upper part with tiny pores is the active material layer, and the lower part is denser and is the protective layer. In 10b, the active material layer includes a plurality of first recessed areas arranged in a matrix, and the shapes of the first recessed areas are similar to circular pits, regular polygonal pits, and irregular polygonal pits; the protective layer includes a plurality of second recessed areas distributed at intervals, or a plurality of second recessed areas distributed continuously. 10c is the same as the electron microscope image of 10b, and 10c adds data for measuring the diameter lengths of the first recessed areas and the second recessed areas. The electron microscope image of 10d is an enlarged view of a second recessed area.

[0083] In some embodiments, the thickness of the positive electrode current collector is M, the thickness of the positive electrode active material layer is N, the thickness of the protective layer is D, the depression depth of the first pit is d1, and the depression depth of the second pit is d2; wherein, 0<d1<N; 0<d2≤D+(0.1-0.3)M.

[0084] There is no limitation on the specific values ​​of the thickness M of the positive electrode current collector, the thickness N of the positive electrode active material layer, and the thickness D of the protective layer, and they can be freely selected according to the specifications of the positive electrode sheet and the battery.

[0085] In some embodiments, 0<d1<N can be interpreted as meaning that the depth of the first pit is less than the thickness of the positive electrode active material layer, meaning that the first pit does not penetrate the positive electrode active material layer. Controlling the depth of d1 within the above range can avoid excessive loss of positive electrode active material and effectively alleviate the problem of lithium deposition at the edge.

[0086] In some embodiments, 0 < d2 ≤ D + (0.1-0.3) M can be interpreted as meaning that the maximum depth of the second pit is greater than the thickness of the protective layer, and the second pit is formed by penetrating the protective layer and creating a hole in a portion of the current collector. The depth d2 of the second pit may not penetrate the protective layer, or may penetrate the protective layer but not the positive electrode current collector. Controlling the depth of d2 within the above range can avoid excessive depth of the second pit in the protective layer, which may cause perforation of the positive electrode sheet. This prevents the positive electrode current collector from being pierced during pit formation, causing a short circuit, and affecting the normal use and effective life of the battery, thereby improving the safety performance of the battery.

[0087] In some embodiments, d2 = d1 + (0-10) mm, meaning the depth of the second recess is equal to or greater than the depth of the first recess. The difference in recess depth between the active material layer and the protective layer is due to the different coating compositions. Under the same laser pore-forming parameters, the active particles in the active material layer are more difficult to form pores with than the ceramic particles in the protective layer, resulting in a difference in recess depth during pore formation.

[0088] In some embodiments, the first dimple satisfies at least one, at least two, or three of the following characteristics:

[0089] (a1) the depression depth d1 is 1 μm to 30 μm, preferably 4 μm to 15 μm;

[0090] (b1) the path length D1 is 10 μm to 300 μm, preferably 50 μm to 100 μm;

[0091] (c1) The interval S1 between two adjacent first pits is 50 μm-500 μm, preferably 100 μm-200 μm.

[0092] In some embodiments, the first recess has a regular hole shape or an irregular hole shape (ie, quasi-circular).

[0093] In some embodiments, the first recessed region includes a row of at least two first pits arranged along the second direction or includes a plurality of first pits arranged in a matrix, and the first pits do not penetrate the positive electrode active material layer.

[0094] In (a1), "depression depth d1" can be interpreted as the maximum distance between the bottom of the first pit and the outer surface of the positive electrode active material layer in the thickness direction of the positive electrode sheet. d1 can be, for example, 1μm, 2μm, 5μm, 6μm, 8μm, 10μm, 12μm, 15μm, 18μm, 20μm, 25μm, 28μm, 30μm, or any point value in the range consisting of any two of the above points. When the value of the depression depth d1 is controlled within the above range, it is possible to avoid the problem of the drilling depth being too small to effectively improve the edge lithium deposition, and it is also possible to avoid the drilling depth being too large to cause excessive loss of positive electrode capacity.

[0095] In (b1), "path length D1" can be interpreted as the maximum straight-line distance between the two inner edges of the first pit in a direction parallel to the positive electrode sheet, as shown in Figure 11. D1 can be, for example, 10μm, 20μm, 30μm, 40μm, 45μm, 50μm, 55μm, 60μm, 65μm, 70μm, 75μm, 80μm, 85μm, 90μm, 95μm, 100μm, 110μm, 120μm, 130μm, 140μm, 150μm, 200μm, 250μm, 300μm or any point value in the range of two points above. When the value of the path length D1 is controlled within the above range, the area size of the first pit can be controlled, which can avoid excessive loss of positive electrode capacity due to excessively large diameter of the hole, and can also avoid the inability to effectively improve edge lithium plating due to the diameter of the hole being too small.

[0096] In (c1), "the spacing S1 between two adjacent first pits" can be interpreted as, for example, taking the shape of the first pits as circular pits, the distance between the centers of the two circular pits of the two closest adjacent first pits is recorded as S1, as shown in Figure 11. When the first pits are not regular shapes, the distance between the centers of the circumscribed circles of the two closest adjacent first pits is recorded as S1. S1 can be, for example, 50μm, 60μm, 80μm, 100μm, 110μm, 120μm, 130μm, 140μm, 150μm, 160μm, 170μm, 180μm, 190μm, 200μm, 220μm, 250μm, 280μm, 300μm, 350μm, 400μm, 450μm, 500μm, or any value within the range of any two of the above values. When the value of the spacing S1 is controlled within the above range, the arrangement density of the first pits can be controlled, and the number of the first pits can be controlled within a certain perforated area, thereby effectively alleviating edge lithium deposition and reducing capacity loss.

[0097] Furthermore, the first pits 101 are set to be circular hole-shaped and arranged at intervals, and the depression depth d1, diameter D1 and spacing S1 in the first pits are limited in combination and coordinated to improve lithium plating at the edge of the electrode with less capacity loss (avoiding the loss of more positive electrode active materials). Moreover, the first pits are equivalent to additional liquid storage space, which can store additional electrolyte and avoid electrolyte loss due to large edge polarization and many side reactions.

[0098] In some embodiments, the second recess satisfies at least one of the following characteristics:

[0099] (a2) the recess depth d2 is 2 μm-30 μm, preferably 8 μm-15 μm;

[0100] (b2) the path length D2 is 20 μm to 300 μm, preferably 40 μm to 150 μm;

[0101] (c2) The spacing S2 between two adjacent second pits is 50 μm-500 μm, preferably 80 μm-150 μm.

[0102] The second concave pit can be a groove or a hole, and can be preferably a hole. For example, in some embodiments, the contour of the second concave pit is a regular hole shape or an irregular hole shape (ie, a quasi-circular hole shape).

[0103] In (a2), "depression depth d2" can be interpreted as the maximum distance between the bottom of the second depression and the outer surface of the protective layer, along the thickness direction of the positive electrode sheet. For example, d2 can be 2μm, 5μm, 6μm, 8μm, 10μm, 12μm, 15μm, 18μm, 20μm, 30μm, or any value within a range of any two of these values. Controlling the depression depth d2 within this range prevents excessive depth of the second depression in the protective layer from causing perforation of the positive electrode sheet and impacting battery safety.

[0104] In (b2), "path length D2" can be interpreted as the maximum straight-line distance between the two inner edges of the second recess in a direction parallel to the positive electrode sheet, as shown in Figure 11. D2 can be, for example, 20μm, 40μm, 50μm, 60μm, 70μm, 80μm, 90μm, 100μm, 110μm, 120μm, 130μm, 140μm, 150μm, 160μm, 180μm, 190μm, 200μm, 250μm, 280μm, 300μm, or any point in the range formed by any two of the above points. When the value of path length D2 is controlled within the above range, the area of ​​the second recess can be controlled, which can avoid excessive damage to the protective layer caused by the punching path length being too large, thereby affecting the protective effect of the protective layer, and can also avoid excessive damage to the protective layer caused by the punching path length being too small, thereby preventing the positive electrode active material from being properly formed at the outermost edge of the hole.

[0105] In (c2), the "spacing S2 between two adjacent second dimples" can be interpreted as follows: for example, in the case of circular second dimples, the distance between the centers of the two closest second dimples in the second direction is S2, as shown in FIG11 . When the second dimples are not regular shapes, the distance between the centers of the circumscribed circles of the two closest second dimples in the second direction is S2. S2 can be, for example, 50 μm, 60 μm, 80 μm, 100 μm, 110 μm, 120 μm, 130 μm, 140 μm, 150 μm, 160 μm, 170 μm, 180 μm, 190 μm, 200 μm, 220 μm, 250 μm, 280 μm, 300 μm, 350 μm, 400 μm, 450 μm, 500 μm, or any value within a range consisting of any two of the above values. When the value of the control spacing S2 is within the above range, the arrangement density of the second pits can be controlled, and the number of the second pits can be controlled within a certain punching area, thereby ensuring normal pore formation at the outermost edge of the positive electrode active material and reducing damage to the ceramic layer.

[0106] Furthermore, the combination of the depression depth d2, the diameter D2 and the spacing S2 in the second pit can improve the edge lithium deposition without damaging the ceramic layer too much and affecting the protective effect. In addition, the second pit can store additional electrolyte to avoid electrolyte loss due to large edge polarization and multiple side reactions.

[0107] The second pits are set to be circular holes, arranged at intervals, and the parameters such as the hole diameter, spacing, and hole depth are limited. This can improve the problem of lithium deposition at the edge of the electrode without losing too much protective layer.

[0108] In some embodiments, some of the second recesses are connected, and some of the second recesses are arranged at intervals, that is, there are intervals between them.

[0109] In some embodiments, the first recess contains active material particles and a plurality of recesses separated by the active material particles. Laser pore formation is typically used to create pores in the positive electrode sheet. However, the hardness of positive electrode active material particles, such as lithium cobalt oxide / ternary lithium, is relatively high, making pore formation difficult when the laser irradiates the surface of large positive electrode active material particles. Consequently, the laser may break up the active material particles, resulting in a plurality of recesses separated by the broken active material particles in the first recess.

[0110] In some embodiments, the first pit contains active material particles and a plurality of recessed portions separated by the active material particles; the recessed portions or the active material particles meet at least one of the following characteristics:

[0111] (a3) the number N of the recessed portions satisfies 1≤N≤10;

[0112] (b3) the active material particles have a Dv50 of 5 μm to 30 μm;

[0113] (c3) The diameter of the recessed portion is 5 μm to 80 μm.

[0114] The specific number of depressions N and the Dv50 of the active material particles will have different ranges depending on the parameters of the laser drilling. In some embodiments, as shown in Figure 10, some of the first pits contain active material particles and multiple depressions separated by the active material particles, and the number of depressions N satisfies 1≤N≤10, for example, N is 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, or any point value in the range of the above two points. In some embodiments, the Dv50 of the active material particles is 5μm-30μm, for example, d can be 5μm, 6μm, 8μm, 10μm, 12μm, 15μm, 18μm, 20μm, 25μm, 28μm, 30μm, or any point value in the range of the above two points. When the number N of depressions and the Dv50 of the active material particles are within the above range, the degree of breakage of the positive electrode active material particles is low, only partial capacity is lost, and the NP ratio at the edge of the positive electrode sheet can be increased, and the number of lithium ions at the edge of the positive electrode sheet can be reduced, thereby alleviating the problem of lithium plating at the edge.

[0115] In some embodiments, the diameter of the recessed portion is 5 μm-80 μm. Here, "diameter" can be interpreted as the maximum straight-line distance between the two inner edges of each recessed portion in a direction parallel to the positive electrode sheet. The diameter length of the recessed portion is related to the degree of crushing of the active material particles. The higher the degree of crushing of the active material particles, the smaller the diameter length of the recessed portion. When the diameter length of the recessed portion is controlled within the above range, it is possible to avoid the situation where the degree of crushing of the active material particles is too high and the capacity loss is too large.

[0116] In some embodiments, when a laser hole-making technique is used to make holes in the protective layer, the second pit is usually a regular hole, and multiple recessed portions do not appear.

[0117] In some embodiments, as shown in FIG. 10 , some of the first pits are connected, and some of the first pits are arranged at intervals.

[0118] In some embodiments, the positive electrode current collector is a material having electrical conductivity without causing adverse chemical changes in the secondary battery, including but not limited to aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, preferably aluminum, such as aluminum foil.

[0119] In some embodiments, the protective layer includes ceramic particles and a binder.

[0120] In some embodiments, the ceramic particles are selected from at least one of inorganic metal oxides (e.g., aluminum oxide, boehmite, magnesium oxide, calcium oxide, magnesium hydroxide, titanium dioxide, silicon dioxide, and zirconium dioxide), inorganic metal nitrides (e.g., tungsten nitride, silicon carbide, boron nitride, aluminum nitride, titanium nitride, and magnesium nitride), and inorganic metal salts (e.g., barium sulfate, calcium titanate, and barium titanate). The binder may include at least one of polyvinylidene fluoride (PVDF), hexafluoroethylene, polytetrafluoroethylene, methacrylate, and styrene-butadiene rubber.

[0121] In some embodiments, ceramic particles protrude from the inner sidewall of the second recess, resulting in a rough surface. The ceramic particles are mixed into the binder, and when the recess is formed, the sidewall of the recess is likely to have protruding ceramic particles, resulting in a rough surface.

[0122] In some embodiments, the outer edge of the second recessed area in the protective layer comprises a metal oxide. The specific type of the metal oxide is related to the metal type of the ceramic particles in the protective layer. For example, if the ceramic particles in the protective layer are aluminum-containing, the metal oxide is aluminum oxide formed under the high temperature of laser pore formation. The width of the metal oxide is 0 μm-10 μm. The high hardness of the metal oxide can effectively prevent burrs and improve battery safety.

[0123] In some embodiments, the inner bottom wall of the second recess has an aluminum oxide layer formed on the surface of the positive electrode current collector.

[0124] In some embodiments, the inner sidewall of the second recessed area in the protective layer is an uneven interface, including protruding ceramic particles, or metal oxide is formed on the inner sidewall under high temperature of the laser. There is a layer of meshed aluminum oxide (formed by high temperature of the laser) at the bottom of the inner side of the second recessed area attached to the positive electrode current collector. This part of the aluminum oxide material can also play a role in preventing burrs, and also proves that the second recessed area does not penetrate the aluminum foil (positive electrode current collector) to form a through hole. Punching through the aluminum foil will cause a short circuit or serious self-discharge. In addition, the aluminum oxide compound is relatively resistant to high temperatures and has good temperature resistance and breakdown voltage resistance, which avoids perforation caused by high laser power or damage to the protective layer, thereby better improving the safety of the battery.

[0125] In some embodiments, the second recessed region contains at least C element and O element.

[0126] In some embodiments, the second recessed area has a C content of 6% to 10% and an O content of 50% to 55%. When the C and O contents in the protective layer are within the above ranges, the protective layer can effectively ensure that the protective layer plays a protective role and effectively prevent burrs from piercing the diaphragm.

[0127] In some embodiments, the protective layer comprises alumina ceramic particles and a PVDF binder. Through elemental content analysis and testing, it is known that the second normal region of the protective layer contains elements C, F, Al, and O, and the percentage content ranges of each element are F:C:Al:O = (1% - 3%):(6% - 10%):(34% - 39%):(50% - 55%). After laser pore formation, the percentage content ranges of each element in the second concave region of the protective layer are F:C:Al:O = (1% - 3%):(7% - 12%):(40% - 45%):(45% - 50%). When the contents of the four elements in the second concave region are within the above ranges, it can ensure that the protective layer is not completely penetrated. It can not only play the protective role of the protective layer to avoid burrs piercing the diaphragm and causing short circuits, but also enable the second concave region to store the electrolyte, effectively alleviating the problem of insufficient electrolyte in the later stage of cycling.

[0128] From the analysis of the elemental contents of the second concave region and the second normal region (as shown in FIGS. 12 and 13), the content of the F element remains basically unchanged, the contents of the C element and the Al element increase slightly, and the content of the O element decreases slightly. Generally, the differences in the contents of the four elements are not significant, which indicates that the protective layer is not completely damaged by the laser, that is, there are still normal regions without pore formation between the micropores in the second concave region. The presence of the normal region in the second concave region has two functions. 1. The normal regions in the second normal region and the second concave region can still play the protective role of the protective layer. 2. The micropores in the second concave region are equivalent to additional liquid storage spaces, which can store the electrolyte additionally, avoiding electrolyte loss caused by large edge polarization and many side reactions. The slight increase in the content of the Al element indicates that the second concave region is drilled to the aluminum foil, increasing the aluminum element content. The slight decrease in the content of the O element indicates that under the action of laser high temperature, the protective layer at the second concave region is removed, generating aluminum oxide.

[0129] In some embodiments, the positive electrode active material layer comprises positive electrode active material particles, a positive electrode conductive agent, and a positive electrode binder.

[0130] There is no particular limitation on the positive electrode active material, and any commonly used positive electrode active material in the art can be used. For example, the positive electrode active material comprises lithium cobaltate, sodium-containing lithium cobaltate, nickel cobalt manganese ternary material (chemical formula: Li a Ni x Co y Mn z A k O2, where 0 < x < 1, 0 < y < 1, 0 < z < 1, 0.9 ≤ a ≤ 1.1, 0 ≤ k ≤ 0.1; where A is a dopant including the following elements: Co, Cu, Zn, Fe, Al, Mg, Ti, Zr, Y, B, La, Mo, Nb, P, Mn or a combination thereof), nickel cobalt aluminum ternary material (chemical formula: Li aNi x Co y Al z A k O2, where 0 < x < 1.1, 0 < y < 1, 0 < z < 1, 0.9 ≤ a ≤ 1, 0 ≤ k ≤ 0.1, and A is a dopant comprising the following elements: Co, Cu, Zn, Fe, Al, Mg, Ti, Zr, Y, B, La, Mo, Nb, P, Mn, or a combination thereof), lithium iron phosphate, lithium-rich manganese-based material, lithium manganese iron phosphate, lithium titanate, lithium nickel manganate, lithium nickelate, lithium manganate, nickel-manganese binary material, or at least one of them.

[0131] There are no particular restrictions on the positive electrode conductive agent and the positive electrode binder, and any commonly used conductive agent and binder in the art can be used. For example, the conductive agent is selected from at least one of conductive carbon black (SP), acetylene black, Ketjen black, graphene, conductive carbon fiber, 350G, carbon nanotubes (CNTs), metal powder, and carbon fiber.

[0132] In some embodiments, the positive electrode tab includes multiple tabs, and the multiple tabs can be integrally cut from the current collector or can be welded to the current collector subsequently. A multi-tab structure battery cell or a stacked structure battery cell can improve the charging rate to obtain fast charging performance.

[0133] In some embodiments, the positive electrode sheet of the present application is applicable to a multi-tab wound battery cell and / or a multi-tab stacked battery cell.

[0134] When the positive electrode sheet is applicable to a multi-tab wound battery cell, punching holes in the edge of the positive electrode sheet can also solve the problem of arc-shaped lithium deposition (the type of arc-shaped lithium deposition is the type that diffuses inward from both sides). Punching holes in the positive electrode edge is equivalent to setting a depression area in each arc area of the battery cell, which can alleviate arc-shaped lithium deposition. When the positive electrode sheet is applicable to a stacked battery cell, depression areas (punching holes) can be provided on all four edges of the positive electrode sheet to alleviate the problem of edge lithium deposition.

[0135] The second aspect of the present application provides a battery, which includes the positive electrode sheet described in the first aspect of the present application. The battery provided by the present application can improve the problem of edge lithium deposition in the battery cell. The derivation process of this beneficial effect is basically the same as that of the beneficial effect of the above positive electrode sheet, and will not be elaborated here.

[0136] In some embodiments, the battery is a multi-tab wound battery or a multi-tab stacked battery.

[0137] In some embodiments, the battery further includes a negative electrode sheet, the negative electrode sheet includes a negative electrode current collector, and a negative electrode active material layer provided on at least one surface of the negative electrode current collector; a third depression area is provided on the negative electrode active material layer; the third depression area includes at least one third pit.

[0138] In some embodiments, a third recessed region is provided on one edge of the negative electrode active material layer along the width direction (either on the side close to the positive electrode tab or on the side away from the positive electrode tab), or on both edges. In other embodiments, in addition to providing third recessed regions on both edges of the negative electrode active material layer, third recessed regions may also be provided in other areas of the negative electrode active material layer, for example, in the middle area of ​​the negative electrode active material layer, or on the entire surface of the negative electrode active material layer.

[0139] The positive electrode sheet of the first aspect of the present application can be assembled into a battery together with a pore-forming negative electrode sheet. The pores in the negative electrode sheet can improve the negative electrode dynamics and reduce the tortuosity of lithium ion transmission. The pore-forming positive electrode sheet and the pore-forming negative electrode sheet are used together to increase the surface density, enhance the mass transfer between the positive and negative electrodes, increase the lithium ion transmission rate, and alleviate the problem of edge lithium plating; it can also further increase the liquid storage capacity and more effectively solve the problems of poor electrolyte infiltration and insufficient electrolyte in the late cycle.

[0140] In some embodiments, the third recessed region is provided at least on one edge of the negative electrode active material layer along the width direction of the negative electrode sheet. For example, the third recessed region is provided on one edge of the negative electrode active material layer along the width direction, or on both edges. Providing the third recessed region on the negative electrode sheet can increase the amount of electrolyte and enhance the rate at which the electrolyte infiltrates the negative electrode active material layer, thereby improving the efficiency of lithium ion insertion, preventing lithium ion deposition on the surface, and improving lithium precipitation.

[0141] In some embodiments, the shape of the third recessed area is independently at least one of a circle, a regular polygon, an irregular polygon, a linear shape, and a strip shape.

[0142] In some embodiments, as shown in FIG14 , the top edge region 41 and the bottom edge region 42 of the negative electrode active material layer 4 are both provided with a third recessed region 43. The third recessed region 43 includes a plurality of third pits distributed at intervals, and the third pits are holes or grooves.

[0143] In some embodiments, as shown in FIG15 , the top edge region 41 and the bottom edge region 42 of the negative electrode active material layer 4 are both provided with a third recessed region 43. The third recessed region 43 includes a plurality of third pits distributed at intervals, and the third pits are linear grooves.

[0144] In some embodiments, the outline of the third pit is a strip-shaped groove or a regular hole shape or an irregular hole shape.

[0145] In some embodiments, as shown in FIG16 , the entire area of ​​the negative active material layer 4 is provided with a third recessed area 43. The third recessed area 43 includes a plurality of third pits distributed at intervals, and the third pits are holes or grooves.

[0146] In some embodiments, as shown in FIG17 , the entire region of the negative active material layer 4 is provided with a third recessed region 43. The third recessed region 43 includes a plurality of third pits distributed at intervals, and the third pits are linear grooves.

[0147] There is no limitation on the specific parameters for forming pores in the negative electrode sheet, and reference may be made to the pore forming parameters of the positive electrode sheet or to the specific parameters for forming pores in the negative electrode sheet in the art.

[0148] The following will be combined with the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the embodiments described are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments of the present application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0149] Unless otherwise specified, the materials and reagents used in the following examples can be obtained from commercial sources.

[0150] The present application is described in detail below with reference to specific embodiments, which are intended to help understand but not limit the present application.

[0151] The lithium-ion batteries of the following examples and comparative examples were all prepared according to the following method, with the difference being the positive electrode sheets or negative electrode sheets. The specific differences between the positive electrode sheets or negative electrode sheets are shown in Table 1.

[0152] 1. Preparation of positive electrode

[0153] (1) Lithium cobalt oxide: conductive carbon black: PVDF were dissolved in NMP solvent at a mass ratio of 97.6%: 1.35%: 1.05% to obtain a positive electrode slurry. The solid content of the positive electrode slurry was 74% and the viscosity was 7000 mPa.s. The positive electrode slurry was coated on both sides of the positive electrode current collector aluminum foil (thickness of 9 μm) with a coating thickness of 33.5 μm on one side. The positive electrode sheet was dried, rolled, and die-cut to obtain the corresponding positive electrode sheet. To ensure that the test data has a certain degree of comparability, the dimensions of the positive electrode sheets of all embodiments and comparative examples are kept consistent, wherein the width L of the positive electrode active material layer is 80 mm.

[0154] (2) Alumina:PVDF were dissolved in NMP solvent at a mass ratio of 95%:5% to obtain a protective layer slurry (ceramic layer slurry). The solid content of the ceramic layer slurry was 40%. The ceramic layer slurry was coated on the edge of the positive electrode current collector aluminum foil near the positive electrode tab with a coating thickness of 30 μm. As shown in Figures 1 and 8, the protective layer was located between the positive electrode active material layer and the positive electrode tab. The width of the protective layer was W, and the width of the second recessed area was W1.

[0155] Referring to Figure 3, laser drilling is used to create holes at the bottom and top of the positive electrode sheet. The width of the first recessed area at the bottom is L1, and the width of the first recessed area at the top is L3. During laser drilling, the hole is drilled 1mm to 3mm further outward from the bottom edge of the positive electrode sheet to ensure that the bottom edge is completely covered by the recessed area.

[0156] 2. Preparation of negative electrode sheet

[0157] Artificial graphite negative electrode material, conductive carbon black (SP) conductive agent, sodium carboxymethyl cellulose (CMC) binder, and styrene-butadiene rubber (SBR) binder are made into a slurry by a wet process in a mass ratio of 97.2:0.5:1.0:1.3, coated on the surface of the negative electrode current collector copper foil, and then dried, rolled and die-cut to obtain the negative electrode sheet.

[0158] 3. Preparation of diaphragm

[0159] A titanium oxide layer with a thickness of 2 μm is coated on one side of a polyethylene separator with a thickness of 5 μm, and a polyvinylidene fluoride-hexafluoropropylene copolymer mixed composite layer with a thickness of 1 μm is coated on both sides.

[0160] 4. The positive electrode sheet, negative electrode sheet, and separator are wound a certain number of layers to obtain a wound multi-electrode battery, wherein the separator is located between the positive electrode and the negative electrode; the obtained coil core is then placed in an aluminum-plastic film, and an electrolyte (containing 1M lithium hexafluorophosphate, the solvent is a mixed solvent of ethylene carbonate / dimethyl carbonate / 1,2-propylene glycol carbonate-1:1:1 (volume ratio)) is injected, and vacuum packaging, aging, formation, secondary sealing, capacity sorting and other processes are carried out to obtain the corresponding soft-package wound lithium-ion battery.

[0161] Table 1

[0162] In Table 1, “\” indicates not tested.

[0163] Table 2

[0164] In Table 2, “\” indicates that the calculation cannot be performed.

[0165] In Example 3, laser power was adjusted to alter the depth d1, diameter D1, and spacing S1 of the first pits, as well as the number of recesses, the average particle size of the active material particles, and the diameter of the recesses. In Example 4, secondary laser pore formation was used to alter the depth d1, diameter D1, and spacing S1 of the first pits.

[0166] Example 6

[0167] The same procedure was carried out with reference to Example 1, except that the components of the protective layer were changed:

[0168] Example 6-1: Boehmite + PVDF, dissolved in NMP solvent at a mass ratio of 95%:5%;

[0169] Example 6-1: Aluminum oxide + hexafluoroethylene were dissolved in NMP solvent in a mass ratio of 95%:5%.

[0170] Example 8

[0171] The same process as in Example 1 was performed, except that the negative electrode sheet was also pore-formed. Specifically, referring to Figure 13 , laser pore formation was used at the bottom and top of the negative electrode sheet. The width of the third recessed area at the bottom was 5 mm, and the width of the third recessed area at the top was 5 mm. The third recessed area had a depth of 15 μm, a diameter of 100 μm, and a spacing of 200 μm.

[0172] Example 9

[0173] The same procedure as in Example 1 was followed, except that the negative electrode sheet was also pore-formed. Specifically, referring to Figure 16 , laser pore formation was performed across the entire surface of the negative electrode sheet. The third recessed region had a depth of 15 μm, a diameter of 150 μm, and a spacing of 1 mm.

[0174] Comparative Example 1

[0175] The same process was carried out as in Example 1, except that the ceramic layer was not perforated.

[0176] Comparative Example 2

[0177] The process was carried out in accordance with Example 1, except that a hole was made at the top of the positive electrode sheet 2 mm away from the protective layer, and no hole was made at the very edge.

[0178] Comparative Example 3

[0179] The process is carried out in accordance with Example 1, except that the positive electrode sheet is not pore-formed.

[0180] The relevant performance tests of the battery separators and batteries in the above examples and comparative examples are recorded in Tables 3 and 4. The test methods are described as follows:

[0181] (1) Lithium deposition

[0182] The lithium deposition was observed as follows: the lithium-ion batteries obtained in the examples and comparative examples were charged at 7C-4.25V to 6C-4.25V to 4C-4.5V to 3.1C-4.55V (cut-off 0.75C), and then allowed to stand for 5 minutes; 2A-4.5V, 0.05C; allowed to stand for 10 minutes; 0.7C discharged to a cut-off voltage of 3.0V, and allowed to stand for 10 minutes; and the test conditions of 1000T were repeated. The charge and discharge cycle was repeated for 400T and 800T, and after the end, the battery was fully charged, the battery cell was disassembled in a dry environment, and the lithium deposition on the negative electrode surface was observed. The degree of lithium deposition was divided into four levels: no lithium deposition, slight lithium deposition at the edge, lithium deposition at the edge, and severe lithium deposition at the edge. No lithium deposition means that no gray or silver lithium is produced on the surface of the negative electrode sheet; slight lithium deposition on the edge means that line-like lithium deposition appears on the edge of the negative electrode sheet, which appears gray; edge lithium deposition means that the lithium deposition area of ​​the negative electrode sheet diffuses toward the center of the negative electrode sheet on the basis of slight lithium deposition on the edge, and also appears gray; severe lithium deposition on the edge means that the negative electrode sheet has diffused toward the center of the electrode sheet on the basis of lithium deposition on the edge, and the lithium deposited on the edge appears silver.

[0183] (2) Capacity retention rate

[0184] The battery capacity retention rate was tested by subjecting the lithium-ion batteries obtained in the Examples and Comparative Examples to a charge-discharge cycle test in a blue-power test cabinet. The capacity retention rate after different cycles was examined and the test results were recorded. Capacity retention rate = capacity after N cycles / initial capacity * 100%.

[0185] (3) Capacity test

[0186] The battery cells obtained in the examples and comparative examples were capacity tested on a blue electric test cabinet. Within the upper and lower voltage limits specified for the battery cells, at 25°C ± 2°C, constant current discharge was first performed, 0.2C discharged to the lower limit voltage, and allowed to stand for 5 minutes; then constant current and constant voltage charging was performed, 0.5C charged to the upper limit voltage, cut off at 0.025C, allowed to stand for 10 minutes, and 0.2C discharged to the lower limit voltage. Then an initial capacity test was performed, and the capacity obtained at this time was the initial capacity (mAh) of the battery cell.

[0187] (4) Element content analysis

[0188] The lithium-ion batteries obtained in the examples and comparative examples were charged at 7C-4.25V to 6C-4.25V to 4C-4.5V to 3.1C-4.55V (cut-off 0.75C), then allowed to stand for 5 minutes; 2A-4.5V, 0.05C; allowed to stand for 10 minutes; discharged at 0.7C to a cut-off voltage of 3.0V, allowed to stand for 10 minutes; and repeated the test cycle of 1000T. The charge and discharge cycle was repeated for 400T and 800T, and after completion, the battery was fully charged and the cell was disassembled in a dry environment. The protective layer on the positive electrode was scanned by EDS line scanning analysis to obtain a line distribution curve of the change in element content. Combined with the comparative analysis of the sample morphology, the distribution of elements in different areas can be intuitively obtained.

[0189] Table 3

[0190] In Example 1, the punching size of the first recessed area in the top and bottom edge areas of the positive electrode active layer (the width in the width direction of the positive electrode sheet) was changed. From the data in Table 1, it can be seen that the battery capacity is inversely proportional to the width of the punching area of ​​the first recessed area. The wider the width of the first recessed area, the higher the capacity loss. On the other hand, the width of the punching area of ​​the first recessed area needs to be within a certain range. For example, the effect of 40mm is not very obvious compared with 16mm and 8mm, but the capacity loss is higher. For example, the improvement of the capacity retention rate of 1mm is not very obvious, but the improvement is more obvious compared with 0.5mm.

[0191] In Example 2, the size of the holes in the protective layer had little effect on the battery's capacity loss and edge lithium deposition, primarily affecting its safety performance. In Examples 2-3, the entire protective layer was provided with a second recessed area, and the cycle capacity retention was slightly higher than in Example 1. This is because the holes in the protective layer increase the liquid storage space and slightly improve the cycle performance. However, drilling the entire protective layer is not recommended, as this can easily lose the protective effect of the ceramic layer and cause a short circuit.

[0192] In the Example 3 group, the laser power is too large and too small (if it is too large, the depression depth d2 and the path length D2 will become larger, the capacity loss is high, and the ceramic layer is easily penetrated; if it is too small, the improvement effect is not obvious. For example, in Example 3-1, the laser power is small, the depression depth d2 and the path length D2 are small, and the drilling spacing S2 remains consistent, which can improve the edge lithium deposition problem and improve the cycle capacity retention rate. In Example 3-3, the laser power is small, the depression depth d2 and the path length D2 are small. Although the capacity loss can be reduced, the improvement effect on the edge lithium deposition and the cycle capacity retention rate is not obvious. In addition, in Example 3-5, the depression depth d2, the path length D2 and the spacing S2 are too large (the depression depth d2 and the path length D2 are too large may easily cause the problem of broken belts, so the spacing S2 is increased accordingly), the capacity loss is high, and the improvement effect on the edge lithium deposition and the cycle capacity retention rate is not obvious.

[0193] In the Example 4 group, in Example 4-1, increasing the laser power (or secondary laser) to break up the positive electrode active particles, significantly increasing the number of depressions, and significantly reducing the average particle size of the active material particles and the diameter of the depressions, can improve the edge lithium deposition problem and improve the cycle capacity retention rate, but the capacity loss is relatively high. In Example 4-2, further increasing the laser power (or secondary laser) to destroy the positive electrode active particles, can also improve the edge lithium deposition problem and improve the cycle capacity retention rate, but the capacity loss is relatively high.

[0194] In the Example 5 group, in Example 5-1, the laser power (or secondary laser) was increased to penetrate the protective layer and hit part of the current collector;

[0195] In Example 5-2, increasing the laser power (or secondary laser) penetrates both the protective layer and the current collector, but does not hit the protective layer on the other side; both can improve the edge lithium plating problem and increase the cycle capacity retention rate, without affecting the capacity loss.

[0196] In Example 6, changing the components of the protective layer had no obvious effect on improving edge lithium deposition and cycle capacity retention, and had no effect on capacity loss.

[0197] In Example 7, the width of the protective layer is too small, and the improvement effect on edge lithium plating and cycle capacity retention is not obvious. The width of the protective layer is too large, and the capacity loss is high.

[0198] In Examples 8 and 9, pore formation on the positive electrode sheet combined with pore formation on the negative electrode can significantly improve the capacity retention rate and cycle performance, but the capacity loss is larger than that of only pore formation on the positive electrode. The capacity loss can be reduced by balancing the surface density.

[0199] Comparative Examples 1-3 have no obvious effect on improving edge lithium deposition and cycle capacity retention.

[0200] Table 4

[0201] As shown in Table 4, elemental analysis reveals that, compared with Comparative Example 3, the ceramic layer is not penetrated at appropriate power levels, and the elemental content changes little. This non-penetrating ceramic layer not only ensures the protective layer's effectiveness, preventing burrs from piercing the diaphragm and causing a short circuit, but also allows the second recessed area to store electrolyte, effectively alleviating the problem of electrolyte shortage in the later stages of the cycle.

[0202] It should be noted that, in this article, the terms "comprise", "include" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, an element defined by the statement "comprises a ..." does not exclude the presence of other identical elements in the process, method, article or device comprising the element. In addition, it should be noted that the scope of the methods and devices in the embodiments of the present application is not limited to performing functions in the order shown or discussed, and may also include performing functions in a substantially simultaneous manner or in the opposite order according to the functions involved. For example, the described method may be performed in an order different from that described, and various steps may also be added, omitted, or combined. In addition, the features described with reference to certain examples may be combined in other examples.

[0203] The components and devices involved in this application are only illustrative examples and are not intended to require or imply that they must be connected, arranged, or configured in the manner shown in the accompanying drawings. As will be appreciated by those skilled in the art, these components and devices can be connected, arranged, or configured in any manner. Words such as "including," "comprising," "having," and the like are open-ended words that mean "including but not limited to," and can be used interchangeably therewith. The words "or" and "and" used herein refer to the words "and / or" and can be used interchangeably therewith unless the context clearly indicates otherwise. The word "such as" used herein refers to the phrase "such as but not limited to," and can be used interchangeably therewith.

[0204] It should also be noted that in the devices and equipment of the present application, the components can be decomposed and / or reassembled, and such decompositions and / or reassemblies should be regarded as equivalent solutions of the present application.

[0205] The above description of the disclosed aspects is provided to enable any person skilled in the art to make or use the present application. Various modifications to these aspects will be readily apparent to those skilled in the art, and the general principles defined herein may be applied to other aspects without departing from the scope of the present application. Therefore, the present application is not intended to be limited to the aspects shown herein, but rather to be accorded the widest scope consistent with the principles and novel features disclosed herein.

[0206] It should be understood that the qualifiers "first", "second", "third", "fourth", "fifth" and "sixth" used in the description of the embodiments of the present application are only used to more clearly illustrate the technical solutions and cannot be used to limit the scope of protection of the present application.

[0207] The above description has been provided for the purpose of illustration and description. Furthermore, this description is not intended to limit the embodiments of the present application to the forms disclosed herein. Although a number of example aspects and embodiments have been discussed above, those skilled in the art will recognize certain variations, modifications, alterations, additions, and sub-combinations thereof.

[0208] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent replacements, etc. made within the spirit and principles of the present application shall be included in the scope of protection of the present application.

Claims

1. A positive electrode sheet, characterized in that: The invention comprises a positive electrode current collector, a positive electrode active material layer and a protective layer; a positive electrode ear is arranged at one end of the positive electrode current collector in a first direction, the positive electrode active material layer is arranged on one side or both sides of the surface of the positive electrode current collector, the protective layer is arranged on one side or both sides of the surface of the positive electrode current collector, and the protective layer is located between the positive electrode active material layer and the positive electrode ear; The positive electrode active material layer is provided with a first recessed area, the protective layer is provided with a second recessed area, and both the first recessed area and the second recessed area have pits.

2. The positive electrode sheet according to claim 1, characterized in that: The first recessed area is located on one side surface of the positive electrode current collector or distributed on both side surfaces of the positive electrode current collector; And / or, the second recessed area is located on one side surface of the positive electrode current collector or distributed on both side surfaces of the positive electrode current collector.

3. The positive electrode sheet according to claim 1 or 2, characterized in that: On the same side surface of the positive electrode current collector, two ends of the positive electrode active material layer in the first direction are respectively a top edge region and a bottom edge region, wherein the first recessed region is at least located in the top edge region and / or the bottom edge region; And / or, the second recessed area at least includes a portion of the edge area of ​​the protective layer close to the positive electrode active material layer; And / or, at least four first recessed areas are provided, which are respectively located at edge areas at both ends of the positive electrode active material layer in the first direction and at both ends of the positive electrode active material layer in the second direction.

4. The positive electrode sheet according to any one of claims 1 to 3, characterized in that: The first recessed area and / or the second recessed area is arranged at the junction of the protection layer and the positive electrode active material layer.

5. The positive electrode sheet according to any one of claims 1 to 4, characterized in that: The first recessed area includes at least two first pits arranged along the second direction, or includes two or more first pits arranged in a matrix; And / or, the second recessed area includes at least two second pits arranged along the second direction, or includes two or more second pits arranged in a matrix, and the second pits do not penetrate the protective layer or the second pits penetrate the protective layer but do not penetrate the positive electrode current collector.

6. The positive electrode sheet according to any one of claims 1 to 5, characterized in that: The positive electrode active material layer on both side surfaces of the positive electrode current collector is provided with the first recessed area, and the first pits in the first recessed areas on both side surfaces are staggered in the second direction; and / or, the protective layer on both side surfaces of the positive electrode current collector is provided with the second recessed area, and the second pits in the second recessed areas on both side surfaces are staggered in the second direction.

7. The positive electrode sheet according to any one of claims 1 to 6, characterized in that: In the first direction, the size of the positive electrode active material layer is L, and the size of the first recessed area is L1; The relationship between L and L1 satisfies: L1=0.5mm~0.5L; preferably, L1=3mm~0.2L.

8. The positive electrode sheet according to any one of claims 1 to 7, characterized in that: Along the first direction, the size of the protective layer is W, and the size of the second recessed area is W1; The relationship between W and W1 satisfies: 0<W1 / (W-W1)≤1; preferably, 1 / 8≤W1 / (W-W1)≤1 / 2; And / or, 0.5 mm≤W≤5 mm, preferably, 1 mm≤W≤3 mm.

9. The positive electrode sheet according to any one of claims 5 to 8, characterized in that: The thickness of the positive electrode current collector is M, the thickness of the positive electrode active material layer is N, the thickness of the protective layer is D, the depression depth of the first pit is d1, and the depression depth of the second pit is d2; wherein 0<d1<N; and / or, 0<d2≤D+(0.1-0.3)M; And / or, d2=d1+(0-10)mm.

10. The positive electrode sheet according to any one of claims 5 to 9, characterized in that: The first pit meets at least one of the following characteristics: (a1) The depth of the depression d1 is 1 μm-30 μm; (b1) Path length D1 is 10 μm-300 μm; (c1) the spacing S1 between two adjacent first pits is 50 μm-500 μm; (d1) some of the first pits are connected, and some of the first pits are arranged at intervals; And / or, the second pit satisfies at least one of the following characteristics: (a2) The depth of the depression d2 is 2 μm-30 μm; (b2) Path length D2 is 20 μm-300 μm; (c2) The interval S2 between two adjacent second pits is 50 μm-500 μm.

11. The positive electrode sheet according to any one of claims 5 to 10, characterized in that: The first pit contains active material particles and a plurality of recessed portions separated by the active material particles; the recessed portions or the active material particles satisfy at least one of the following characteristics: (a3) the number N of the recessed portions satisfies 1≤N≤10; (b3) the Dv50 of the active material particles is 5 μm-30 μm; (c3) The diameter of the recessed portion is 5 μm-80 μm.

12. The positive electrode sheet according to any one of claims 1 to 11, characterized in that: The second recessed area contains at least C element and O element; Preferably, in the second recessed area, the content of C element is 6% to 10%, and the content of O element is 50% to 55%; Preferably, the second recessed area includes F element, C element, Al element and O element, and the percentage content range of the four elements is F:C:Al:O=(1%~3%):(7%~12%):(40%~45%):(45%~50%).

13. The positive electrode sheet according to any one of claims 1 to 12, characterized in that: The positive electrode active material layer comprises positive electrode active material particles, a positive electrode conductive agent and a positive electrode binder; And / or, the positive electrode active material includes at least one of lithium cobalt oxide, sodium-containing lithium cobalt oxide, nickel-cobalt-manganese ternary material, nickel-cobalt-aluminum ternary material, lithium iron phosphate, lithium-rich manganese-based material, lithium iron manganese phosphate, lithium titanate, lithium nickel manganese oxide, lithium nickel oxide, lithium manganese oxide, and nickel-manganese binary material; preferably lithium cobalt oxide; and / or, the protective layer comprises ceramic particles and a binder; And / or, the positive electrode tab includes at least one electrode tab.

14. The positive electrode sheet according to any one of claims 5 to 13, characterized in that: Ceramic particles protrude from the inner sidewall of the second pit, and the ceramic particles include one of an inorganic metal oxide, an inorganic metal nitride and an inorganic metal salt; And / or, the inner bottom wall of the second pit has an aluminum oxide layer, and the aluminum oxide layer contains aluminum oxide.

15. A battery, characterized in that: A positive electrode sheet comprising any one of claims 1 to 14.

16. The battery according to claim 15, characterized in that The battery also includes a negative electrode sheet, which includes a negative electrode collector and a negative electrode active material layer arranged on at least one side of the negative electrode collector; a third recessed area is arranged on the negative electrode active material layer; and the third recessed area includes at least one third pit.

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