WO2025130394A1 - Positive electrode sheet and battery - Google Patents

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

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

Background Art

With the advent of the 5G era and the large-scale use of electric vehicles, lithium-ion batteries will be required to have higher energy density, better fast charging performance and longer life in the future. Increasing the thickness of the electrode can increase the energy density of the battery. However, the increase in electrode thickness will lead to problems such as increased lithium ion transmission distance, large lithium ion concentration gradient, and poor electrolyte infiltration, resulting in irreversible lithium deposition, which will lead to poor battery rate performance and long-term cycle performance. Using multi-electrode structure cells or stacked structure cells can increase the charging rate to obtain fast charging performance, but at a higher charging rate, the negative electrode is prone to lithium precipitation reaction, especially the side edge and the ear position of the ear are more prone to lithium precipitation. When lithium precipitation occurs, the electrode polarization increases, the electrolyte consumption increases, and the electrolyte dries up, further worsening the lithium precipitation. In the later stage of the battery cycle, the battery performance will also deteriorate due to insufficient electrolyte, affecting the battery life.

The storage and release of lithium-ion battery capacity is based on the reversible insertion and extraction of Li ⁺ in electrode materials. However, when some phenomena occur, such as insufficient space for lithium insertion in the negative electrode, too much resistance for Li ⁺ to be embedded in the negative electrode, too fast extraction of Li ⁺ from the positive electrode but inability to embed the same amount into the negative electrode, lithium precipitation reaction will occur (lithium ions are deposited on the surface of the electrode and no longer participate in charging and discharging). Since the negative electrode is usually larger than the positive electrode, lithium precipitation is prone to occur in the edge area (overhang area) of the negative electrode. When lithium precipitation occurs, it will cause battery capacity decay, increase electrode polarization, increase electrolyte consumption at the edge, increase impedance, and further deteriorate lithium precipitation, which will seriously affect the performance of the battery cell, causing rapid decay of battery performance and affecting the use and life of the battery.

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

Summary of the invention

The purpose of the present application is to overcome the above problems existing in the prior art and 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.

In order to achieve the above-mentioned object, the first aspect of the present application provides a positive electrode sheet, the positive electrode sheet comprising a positive electrode collector, a positive electrode active material layer and a protective layer; a positive electrode ear is arranged at one end of the positive electrode 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 collector, the protective layer is arranged 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, The protection layer is provided with a second recessed area, and both the first recessed area and the second recessed area have pits.

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.

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

(1) The positive electrode sheet provided in the present application has a recessed area in the protective layer, which can avoid the problem that the recessed area cannot be set at the edge of the positive electrode active material layer due to reasons such as belt feeding deviation, positioning deviation or unstable electrode sheet cutting width, and improve the problem of lithium deposition at the edge of the negative electrode under a high-rate charging system.

(2) The positive electrode sheet provided in the present application has a recessed area in its positive electrode active material layer and a protective layer, and there are pits in the pit 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 pits. 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 enhancing the mass transfer between the positive and negative electrodes, reducing the ionic impedance, and preventing lithium ions from being unable to be embedded in the electrode sheet in time and being deposited on the surface of the electrode sheet to cause lithium precipitation.

(3) The positive electrode sheet provided in the present application has a space filled with electrolyte at the recessed part, 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 small amount of electrolyte at the edge, resulting in some lithium ions being unable to be embedded in the negative electrode sheet in time and causing 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 embedding ability of the negative electrode sheet for lithium ions, thereby significantly reducing the phenomenon that lithium ions cannot be embedded at the edge of the electrode sheet and precipitate.

(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.

(5) The positive electrode sheet provided in the present application can increase the electrolyte infiltration effect and speed, as well as increase the liquid storage space and improve the liquid storage volume, 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.

The endpoints and any values of the range disclosed in this article are not limited to the precise range or value, 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, in the absence of special instructions, data ranges include endpoints.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a first schematic diagram of a positive electrode sheet in an embodiment of the present application.

FIG. 2 is a schematic diagram showing a case in which a tape run deviation causes a hole to not be formed normally at the edge in the prior art.

FIG. 3 shows a second schematic diagram of the positive electrode sheet in the embodiment of the present application.

FIG. 4 shows a third schematic diagram of the positive electrode sheet in the embodiment of the present application.

FIG. 5 shows a fourth schematic diagram of the positive electrode sheet in the embodiment of the present application.

FIG. 6 shows a fifth schematic diagram of the positive electrode sheet in the embodiment of the present application.

FIG7 is a sixth schematic diagram of a positive electrode sheet in an embodiment of the present application;

FIG8 is a seventh schematic diagram of a positive electrode sheet in an embodiment of the present application;

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

FIG. 10 is an electron microscope image of the positive electrode sheet in the embodiment of the present application.

FIG. 11 shows an eighth schematic diagram of the positive electrode sheet in the embodiment of the present application.

FIG. 12 is a diagram showing 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.

FIG. 13 is a diagram showing the element analysis results of the second recessed area in the protective layer of the positive electrode sheet in the embodiment of the present application.

FIG. 14 is a first schematic diagram of a negative electrode plate in an embodiment of the present application.

FIG. 15 is a second schematic diagram of the negative electrode plate in the embodiment of the present application.

FIG. 16 is a third schematic diagram of the negative electrode plate in the embodiment of the present application.

FIG. 17 is a fourth schematic diagram of the negative electrode plate in the embodiment of the present application.

Reference numerals:

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 ear; 4. Negative electrode active material layer; 41. Top edge region; 42. Bottom edge region; 43. Third recessed region.

DETAILED DESCRIPTION

The specific implementation of the present application is described in detail below. It should be understood that the specific implementation described here is only used to illustrate and explain the present application, and is not used to limit the present application.

In the present invention, the "depressed area" may also be referred to as a "depressed portion", and the "depressed area" and the "depressed portion" have the same meaning.

Unless otherwise defined, all scientific and technical terms used in this application have the same meanings as those commonly used by persons skilled in the art in the technical fields to which this application relates. The same meaning as is commonly understood by members of the public.

The present application research 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 running deviation (as shown in Figure 2, which is a schematic diagram of the tape running 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 two side edges in the width direction of the electrode sheet).

In order to achieve normal hole formation at the edge of the positive electrode sheet, the present application proposes the following technical solution:

In a first aspect, the present application provides a positive electrode sheet, the positive electrode sheet comprising a positive electrode current collector, a positive electrode active material layer and a protective layer; with reference to FIG1 , the direction in which the positive electrode current collector is provided with the positive electrode ear is recorded as the first direction, and the extending direction of the current collector perpendicular to the first direction is recorded as the second direction, and the thickness direction of the positive electrode current collector is also recorded as the thickness direction. For example, in a square battery, the first direction and the second direction are the width direction and the length direction of the positive electrode current collector, respectively.

In some embodiments, referring to FIG. 1 , a positive electrode tab 3 is disposed at one end of the positive electrode current collector in the first direction, the positive electrode active material layer 1 is disposed on one side or both sides of the surface of the positive electrode current collector, and the protective layer 2 is disposed on one side or both sides of the surface of the positive electrode current collector and is located between the positive electrode active material layer 1 and the positive electrode tab 3. It can also be said that the protective layer 2 is disposed on the surface of the positive electrode current collector having the positive electrode active material layer 1, and on the side surface, a part of the positive electrode current collector is disposed on the positive electrode active material layer 1, and a part of the positive electrode current collector is disposed 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.

In some embodiments, referring to FIG. 1 and FIG. 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, and both the first recessed area 13 and the second recessed area 21 have pits. It can also be said that at least a portion of the positive electrode active material layer 1 is provided with a first pit 101, and the portion of the region provided with the first pit 101 is recorded as the first recessed area 13; at least a portion of the protective layer 2 is provided with a second pit 201, and the portion of the region provided with the second pit 201 is recorded as the second recessed area 21.

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

The research in this application found that by setting a recessed area with pits on the protective layer, the recessed area can be normally set at the very edge of the active material layer. This can avoid the problem that the recessed area cannot be set at the very edge of the positive electrode active material layer due to the belt deviation. It can effectively alleviate the phenomenon of lithium deposition at the edge of the negative electrode and improve the cycle performance and capacity retention rate of the battery, improve the problem of lithium deposition at the edge under the high-rate charging system, and improve the durability and service life of the battery.

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 the energy density of the battery.

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 storage space and increase the storage amount, 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.

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.

Specifically, the first recessed area 13 is located on one side surface of the positive electrode current collector or 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 the active material layers on both sides may have the first recessed area 13, or only one side of the active material layer may have the first recessed area 13. Similarly, the protective layer on one side surface of the positive electrode current collector may have the second recessed area 21, or the protective layers on both sides of the positive electrode current collector may have the second recessed area 21.

Furthermore, the first recessed area 13 includes at least part of the edge area of the positive electrode active material layer 1 in the first direction. It can also be said that the edge area of the positive electrode active material layer 1 in the first direction is at least partially provided with the first pit 101, such as the edge area on one side of the first direction of the positive electrode current collector, part of the edge area on one side, the edge area on both sides, the edge areas on both sides are each partially provided with the first pit 101, and so on. For example, as shown in Figures 1 and 8, the first pit 101 may be partially provided in the edge area, or the first pit 101 may be arranged in the edge area from one end of the pole piece to the other end of the pole piece in the second direction. Of course, other areas outside the edge area may also be provided with the first pit 101.

In some embodiments, as shown in FIG. 1 and FIG. 3 , 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. Among them, the first recessed area 13 is at least located in 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 FIG. 1 and FIG. 8 , or at least includes a part of the bottom edge area 12. For example, there may be two first recessed areas 13, which are respectively located at the edge areas on both sides of the positive electrode active material layer 1 in the first direction, as shown in FIG. 3 and FIG. 8 . Providing a recessed area only at the edge region can avoid excessive loss of the positive electrode active material layer 1, which is equivalent to only increasing the N/P ratio at the edge, reducing the number of lithium ions at the edge, thereby alleviating edge lithium precipitation. Alternatively, the first recessed area 13 can also satisfy the entire positive electrode active material layer 1, as shown in FIG6, significantly improving the electrolyte infiltration speed and electrolyte capacity, and improving the lithium ion transmission efficiency.

In some embodiments, as shown in FIGS. 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 to the very edge of the top edge region 11, i.e., 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, i.e., 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, i.e., at least at the edge of the protective layer 2 close to the positive electrode active material layer 1. In this way, it can be effectively guaranteed The positive electrode active material layer 1 has a pit at the edge near the positive electrode ear to ensure that there is sufficient electrolyte at the edge and improve the problem of lithium deposition at the edge.

In some embodiments, the second recessed area includes at least a portion of the edge area of the protective layer 2 close to the positive electrode active material layer 1. The second recessed area can be set at the edge of the protective layer close to the positive electrode active material layer, or the second recessed area can be set in the entire area of the protective layer. Preferably, the second recessed area is set only at the edge of the protective layer close to the positive electrode active material layer. As shown in FIG3, the second recessed area 21 does not cover the entire protective layer 2, and can be set only at the edge area of the protective layer 2 close to the positive electrode active material layer 1. Such a setting has two main functions: first, only holes are punched at the edge, which can prevent the loss of too much ceramic material, ensure the insulating effect of the protective layer, and have little effect on the protective effect of the protective layer; second, it can 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 deposition 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 very edge of the positive electrode (or it can be interpreted as avoiding the absence of pits at the very 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 very edge, to effectively improve the problem of lithium deposition at this edge.

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 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 of the second direction of the positive electrode active material layer 1 to the other end, as shown in FIG1 and FIG3. In this way, the entire top edge region 11/bottom edge region 12 has a first pit 101, and when the positive electrode sheet and the negative electrode sheet are wound to form a battery cell, each turning portion of the battery cell has a first depression, which can solve the problem of lithium deposition that may occur at the turning portion of the battery cell.

In some embodiments, at least two first recessed areas 13 are arranged at intervals in the second direction, that is, at least two first recessed areas 13 are arranged at intervals in the top edge area 11/bottom edge area 12, 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 8. In this way, according to the specific situation, a recessed area (such as a turning part) can be set in the edge area where lithium is easily deposited to solve the lithium deposition problem, and at the same time, excessive loss of the positive electrode active material layer can be avoided.

In some embodiments, at least four first recessed areas are provided, which are located at the edge areas at both ends of the positive electrode active material layer in the first direction, namely, the top edge area and the bottom edge area, and the edge areas at both ends of the positive electrode active material layer in the second direction. That is to say, when the positive electrode sheet is square or rectangular, the outer contour of the active material layer 1 is square or rectangular, and has four edges along the circumferential direction, namely The edge regions at both ends in the first direction and the edge regions at both ends in the second direction, and the four edge regions all have first concave regions.

In the present application, “edge” may be interpreted as a region close to one side of the positive electrode active material layer or the protective layer, and the width of the region is not greater than one fifth of the width of the corresponding positive electrode active material layer or the protective layer.

In order to improve the problem of edge lithium deposition, in this application, for the side of the positive electrode sheet away from the positive electrode ear, a certain distance (for example, 1mm to 3mm, which can be punched on the processing platform) can be punched outside the edge of the electrode sheet when setting the recessed area (making holes), so that the edge of the side away from the positive electrode ear is provided with a recessed area. However, the above method cannot be used to punch holes on the edge close to the electrode ear, otherwise it is easy to cause damage to the electrode ear.

In some embodiments, the first recessed area and/or the second recessed area is disposed at the junction of the protection layer and the positive electrode active material layer.

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 configuration, according to the specific situation, a recessed area (such as a turning portion) can be set in the edge area where lithium is easily deposited to solve the lithium deposition problem, and at the same time, excessive loss of the positive electrode active material layer is avoided.

In some embodiments, the second recessed area 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.

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.

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.

In some embodiments, when the protective layer on both sides of the positive electrode current collector is provided with a second recessed area, the second pits in the second recessed areas on both sides of the surface can be arranged in a staggered manner, that is, the projections of the second pits on both sides of the surface in the thickness direction of the positive electrode sheet do not overlap, and are arranged in a staggered manner. In this way, the problem of accidentally piercing the positive electrode current collector when making the pits can be prevented, thereby improving safety, and preventing the thickness of the protective layer from being excessively thinned by making pits at the same position on both sides of the protective layer, thereby improving the safety protection of the protective layer. Similarly, When the first recessed areas are provided on the positive electrode active material layers on both side surfaces of the positive electrode current collector, the first pits in the first recessed areas on both side surfaces can be staggered, that is, the projections of the first pits on the two side surfaces in the thickness direction of the electrode sheet do not overlap, and they are staggered to avoid accidentally piercing the positive electrode current collector and avoiding battery short circuit.

In some embodiments, a first recessed area is provided at an edge of one side of the positive electrode active material layer along the first direction (width direction) (it may be on the side close to the positive electrode ear or on the side away from the positive electrode ear), or first recessed areas are provided at the edges of both sides. In other embodiments, in addition to providing first recessed areas at the edges of both sides of the positive electrode active material layer, first recessed areas may also be provided at other areas of the positive electrode active material layer, for example, the first recessed area may be provided at the middle area of the positive electrode active material layer, or the first recessed area may be provided on the entire surface of the positive electrode active material layer.

In some embodiments, when the positive electrode sheet is suitable for a multi-electrode wound battery cell, each turn of the battery cell has a first depression, which can solve the problem of lithium deposition that may occur at the turn of the battery cell.

In some embodiments, as shown in FIG. 1 and FIG. 7 , a positive electrode sheet includes a positive electrode collector (not shown), the surface of the positive electrode collector is coated with a positive electrode active material layer 1, and a positive electrode ear 3 (multiple electrodes are arranged at intervals) is provided at one end of the positive electrode collector along the width direction of the positive electrode sheet, and the positive electrode ear 3 is connected to the positive electrode collector. The positive electrode active material layer 1 is divided into a top edge region 11 (the edge close to the positive electrode ear) and a bottom edge region 12 (the edge away from the positive electrode ear) along the width direction of the positive electrode sheet, and the surface of the positive electrode collector close to the edge of the positive electrode ear 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 close to 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.

In some embodiments, as shown in FIG3 , the top edge region 11 and the bottom edge region 12 of the positive electrode active material layer 1 are both provided with a first recessed region 13, and the edge of the protective layer 2 away from the positive electrode ear 3 is provided with a second recessed region 21. Wherein, when the first recessed region is provided at the bottom edge of the positive electrode active material layer, more holes may be punched outside the bottom edge of the positive electrode sheet by a certain distance (for example, 1-3 mm beyond the positive electrode sheet), so that the first recessed region can be normally provided at the outermost edge of the bottom of the positive electrode sheet.

For the edge of the positive electrode active material layer close to the positive electrode ear side, ideally, the recessed area is set at the junction of the positive electrode active material layer and the protective layer when making holes, but in the actual hole making process, there are generally deviations and shifts due to technical problems, so there may be areas without holes at the edge of the positive electrode active material layer close to the positive electrode ear side, as shown in Figure 2. In this way, the present application proposes a technical solution of setting a recessed area at the edge of the protective layer close to 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.

In some embodiments, as shown in FIG5 , a first depression 13 and a second depression 21 are provided at the interface between the protective layer 2 and the positive electrode active material layer 1 , and the pores at the interface fall into the second depression 21 of the protective layer 2 and fall into the first depression 21 of the positive electrode active material layer 1. A recessed area 13, that is, a hole is punched at the junction to cover the edge of the protective layer 2 and the positive electrode active material layer 1 at the same time. Among them, the protective layer is provided with a second recessed area near the edge of the positive electrode active material layer, which can ensure that the first recessed area also exists at the edge of the positive electrode active layer, and the recessed area is normally set at the edge of the positive electrode active material layer. The recessed area is set at the junction of the protective layer and the positive electrode active material layer to minimize the damage to the protective layer as much as possible, and to ensure that the recessed area can be set at the edge of the positive electrode.

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 are provided. It can also be said that 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 the outermost edge of the positive electrode active material layer is not provided with a pit due to a large deviation in the tape run or a large deviation in the positioning of the laser drilling when making the pit; it can not only reduce the damage to the protective layer as much as possible, but also effectively ensure that the pit can be provided at the top edge line of the top edge area.

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 the positive electrode active material with a width of L for the positive electrode sheet, the value after L minus the first recessed area 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 of the top and bottom of the positive electrode sheet (both sides in the width direction).

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, 0.5 L; preferably, L1 = 3 mm to 0.2 L.

It should be noted that when the top edge region and the bottom edge region of the positive electrode active material layer 1 are both provided with the first recessed region, 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 scheme will cause too much capacity loss, it is necessary to balance the surface density and ED loss. In the case of an overall increase in the surface density, it is recommended to use this scheme in combination with negative electrode pores or grooves.

When the first recessed area is set on both sides of the positive electrode sheet and the value of the first recessed area is limited to the above range, when the ED is improved, excessive loss of the positive electrode active material layer can be avoided, the CB value at the edge can be increased, the number of lithium ions at the edge can be reduced, and the effect of alleviating edge lithium deposition can be improved.

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

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

When the ratio of W1/(W-W1) is within the above range, it is possible to avoid W1 being 0 or close to 0 (to avoid too few pits). No second concave area is set or the proportion of the second concave area is too small to avoid the situation where there is no concave area at the edge of the positive electrode active layer due to large deviation of the tape run or large deviation of the laser drilling positioning; it can also avoid the width of the second normal area being smaller than the width of the first concave area, and avoid too many pits causing the protective layer to lose its insulation protection function, and fail to effectively solve the problem of burrs piercing the diaphragm. The setting of the protective layer can significantly reduce the burrs generated on the edge when the positive electrode sheet is cut, effectively reduce the risk of burrs piercing the diaphragm and causing battery short circuit, and improve the safety of the battery.

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, 1/2. When the ratio of W1/(W-W1) is preferably within the above range, the protective layer can also play a protective role when a recessed area is set at the edge of the positive electrode active material layer.

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 the above two point values; 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, and after piercing the diaphragm, it will contact the negative electrode and cause 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, the edge (wide side) in the width direction of the positive electrode sheet can be completely filled, 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 function, and if the width is too large, it will affect the capacity of the battery.

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 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 is easily deposited at the edge of the turning portion in the wound battery cell. By setting 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, and at the same time, the loss of more protective layers 2 can 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, and whether it is a laminated battery cell or a wound battery cell, the problem of edge lithium deposition can be effectively and significantly solved.

In some embodiments, at least two second recessed areas 21 are arranged at intervals in the second direction, that is, at least two second recessed areas 21 are arranged at intervals along the second direction in the edge area of the protective layer 2, and each second recessed area 21 is formed by a part of the edge area, as shown in Figure 8. In this way, a recessed area can be set in the edge area where lithium is easily deposited (such as the turning part of the pole piece) according to the specific situation to solve the lithium deposition problem, and at the same time, it also avoids excessive loss of the protective layer 2.

In some embodiments, as shown in FIG. 10 , 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 depressions arranged in a matrix, and the shapes of the first depressions are similar to circular pits, regular polygonal pits, and irregular polygonal pits; the protective layer includes a plurality of second depressions distributed at intervals, or a plurality of second depressions distributed continuously. 10c is the same as the electron microscope image of 10b, and 10c adds data for measuring the lengths of the first depressions and the second depressions. The electron microscope image of 10d is a certain A magnified view of the second depressed area.

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.

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.

In some embodiments, 0＜d1＜N can be interpreted as the depression depth of the first pit is less than the thickness of the positive electrode active material layer, that is, 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 edge lithium deposition.

In some embodiments, 0＜d2≤D+(0.1-0.3)M can be interpreted as the maximum depression 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 forming a hole on part of the current collector. The depth d2 of the second pit may not penetrate the protective layer, or may not penetrate the positive electrode current collector after penetrating the protective layer. By controlling the depth of d2 within the above range, it is possible to avoid the excessive depression depth of the second pit in the protective layer causing perforation of the positive electrode sheet, and to prevent the positive electrode current collector from being pierced when the pit is made, causing a short circuit, affecting the normal use and effective life of the battery, and improving the safety performance of the battery.

In some embodiments, d2=d1+(0-10) mm, that is, the depression depth of the second pit is equal to or greater than the depression depth of the first pit. The difference in depression depth between the active material layer and the protective layer is due to the different components of the coating. Under the same laser pore-forming parameters, the active particles in the active material layer are more difficult to be pore-formed than the ceramic particles in the protective layer, which results in a difference in depression depth during pore-forming.

In some embodiments, the first pit satisfies at least one, at least two, or three of the following characteristics:

(a1) the depression depth d1 is 1 μm-30 μm, preferably 4 μm-15 μm;

(b1) the path length D1 is 10 μm-300 μm, preferably 50 μm-100 μm;

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

In some embodiments, the contour of the first pit is a regular hole shape or an irregular hole shape (ie, quasi-circular).

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.

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. For example, d1 can be 1μm, 2μm, 5μm, 6μm, 8μm, 10μm, 12μm, 15μm, 18μm, 20μm, 25μm, 28μm, 30μm or any point value in the range composed of two points above. When the value of the depression depth d1 is controlled within the above range, it can avoid the problem that the drilling depth is too small to effectively improve the edge lithium deposition, and it can also avoid excessive loss of positive electrode capacity due to excessive drilling depth.

In (b1), the “path length D1” can be interpreted as the distance between the two inner edges of the first pit in the direction parallel to the positive electrode sheet. The maximum straight-line distance between the two points is 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 composed of the above two point values. When the value of the path length D1 is controlled within the above range, the area size of the first pit can be controlled, and the excessive loss of positive electrode capacity caused by the excessively large path length of the hole can be avoided, and the inability to effectively improve the edge lithium precipitation can also be avoided due to the excessively small path length of the hole.

In (c1), "the spacing S1 between two adjacent first pits" can be interpreted as, taking the shape of the first pit as a circular pit as an example, the distance between the centers of the two circular pits in the two adjacent first pits is recorded as S1, as shown in Figure 11. When the first pit is not a regular shape, the distance between the centers of the circumscribed circles of the two 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 point value in the range consisting of the above two point 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.

Furthermore, the first pits 101 are set to be circular holes 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 a small 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.

In some embodiments, the second pit satisfies at least one of the following characteristics:

(a2) the depression depth d2 is 2 μm-30 μm, preferably 8 μm-15 μm;

(b2) the path length D2 is 20 μm-300 μm, preferably 40 μm-150 μm;

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

The second concave pit may be a groove or a hole, and may 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 shape).

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 in the thickness direction of the positive electrode sheet. d2 can be, for example, 2μm, 5μm, 6μm, 8μm, 10μm, 12μm, 15μm, 18μm, 20μm, 30μm or any point value in the range of two points above. When the depression depth d2 is controlled within the above range, it can be avoided that the second depression in the protective layer is too deep to cause the positive electrode sheet to be perforated, affecting the safety performance of the battery.

In (b2), "path length D2" can be interpreted as the maximum straight-line distance between the two inner edges of the second pit in the 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 value in the range formed by any two of the above point values. When the value of the path length D2 is controlled within the above range, the area of the second pit can be controlled, and the protective layer can be prevented from being damaged too much due to the path length of the hole being too large, thereby affecting the protective effect of the protective layer, and the path length of the hole being too small to ensure normal pore formation at the edge of the positive electrode active material can be avoided.

In (c2), "the spacing S2 between two adjacent second pits" can be interpreted as, for example, taking the shape of the second pit as a circular pit, in the two adjacent and closest second pits in the second direction, the distance between the centers of the two circular pits is recorded as S2, as shown in Figure 11; when the second pit is not a regular shape, in the two adjacent and closest second pits in the second direction, the distance between the centers of the circumscribed circles of the two second pits is recorded as S2. S2 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 point value in the range consisting of the above two point values. When the value of the spacing S2 is controlled 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, which can ensure normal pore formation at the outermost edge of the positive electrode active material and reduce damage to the ceramic layer.

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

The second pits are set to be circular holes, arranged at intervals, and the parameters such as 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.

In some embodiments, some of the second pits are connected to each other, and some of the second pits are arranged at intervals, that is, there are intervals between them.

In some embodiments, the first pit contains active material particles and multiple recessed portions separated by the active material particles. Laser hole making technology is usually used when making holes in the positive electrode sheet, and the hardness of the positive electrode active material particles, such as lithium cobalt oxide/ternary lithium, is relatively high, and it will be difficult to make holes when the laser irradiates the surface of the large positive electrode active material particles. Therefore, the laser will break the active material particles, so that multiple recessed portions separated by the broken active material particles appear in the first pit.

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 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.

The specific number of recessed portions N and the Dv50 of the active material particles may have different ranges depending on the parameters of the laser drilling. In some embodiments, as shown in FIG10 , a portion of the first pit contains active material particles and a plurality of recessed portions separated by the active material particles, and the number of recessed portions N satisfies 1≤N≤10, for example, N is 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, or any combination thereof. 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 composed of any two of the above point values. When the number of depressions N and the Dv50 of the active material particles are in the above range, the degree of breakage of the positive electrode active material particles is low, only part of the 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 precipitation at the edge.

In some embodiments, the diameter of the recessed portion is 5μm-80μm. 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.

In some embodiments, when a hole is made in the protective layer using a laser hole making technique, the second pit is usually a regular hole, and there will not be a situation where multiple recessed portions appear.

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.

In some embodiments, the positive electrode current collector is a material having conductivity and not 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.

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

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.

In some embodiments, the inner sidewall of the second concave pit has protruding ceramic particles, which is a rough wall surface. Therefore, the ceramic particles are mixed in the binder, and when the concave pit is made, the sidewall of the concave pit is likely to have protruding ceramic particles, making the wall surface a rough wall surface.

In some embodiments, the outer edge of the second recessed area in the protective layer includes a metal oxide, and the specific type of the metal oxide is related to the metal type of the ceramic particles in the protective layer. For example, when the ceramic particles in the protective layer are aluminum-containing materials, the metal oxide is aluminum oxide formed at high temperature during laser pore formation. The width of the metal oxide is 0 μm-10 μm. The hardness of the metal oxide is high, which can effectively prevent burrs and improve the safety performance of the battery.

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.

In some embodiments, the inner sidewall of the second recessed area in the protective layer is an uneven interface, including protruding ceramic particles, or the inner sidewall forms a metal oxide under high temperature of the laser. There is a layer of mesh 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 prevent burrs, which also proves that the second recessed area is a layer of aluminum oxide (formed by high temperature of the laser) attached to the positive electrode current collector. The second concave area does not pierce the aluminum foil (positive electrode current collector) to form a through hole, which would cause a short circuit or serious self-discharge. In addition, aluminum oxide compounds are more resistant to high temperatures, and have good resistance to temperature and breakdown voltage, which can avoid perforation or damage to the protective layer caused by high laser power, and better improve the safety of the battery.

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

In some embodiments, the second concave region 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 film are within the above range, the protective layer can effectively play a protective role and effectively avoid the problem of burrs piercing the diaphragm.

In some embodiments, the protective layer includes alumina ceramic particles and PVDF binder. After element content analysis and testing, it is known that the second normal area of the protective layer contains elements C, F, Al, and O, wherein the percentage content range of each element is F: C: Al: O = (1% to 3%): (6% to 10%): (34% to 39%): (50% to 55%). After laser pore making, the percentage content range of each element in the second recessed area of the protective layer is F: C: Al: O = (1% to 3%): (7% to 12%): (40% to 45%): (45% to 50%). When the content of the four elements in the second recessed area is within the above range, it can ensure that the protective layer is not completely pierced, which can not only play the protective role of the protective layer and prevent burrs from piercing the diaphragm and causing a short circuit; but also enable the second recessed area to store electrolyte, effectively alleviating the problem of insufficient electrolyte in the late cycle.

From the analysis of the element content of the second depression area and the second normal area (as shown in Figures 12 and 13), the content of F element has basically not changed, the content of C element and Al element has slightly increased, and the content of O element has slightly decreased. The overall content of the four elements is not much different, which shows that the protective layer is not completely destroyed by the laser, that is, there is still a normal area without holes between the micropores in the second depression area. There are two functions of the normal area in the second depression area: 1. The second normal area and the normal area in the second depression area can still play the protective role of the protective layer; 2. The micropores in the second depression area are equivalent to additional liquid storage space, which can store additional electrolyte to avoid electrolyte loss due to large edge polarization and many side reactions. The content of Al element has increased slightly, indicating that the second depression area is punched into aluminum foil, and the content of aluminum element has increased. The content of O element has decreased slightly, indicating that the protective layer in the second depression area has been removed under the high temperature of the laser, and aluminum oxide has been generated.

In some embodiments, the positive electrode active material layer includes positive electrode active material particles, a positive electrode conductor and a positive electrode binder.

There is no particular limitation on the positive electrode active material, and any common positive electrode active material in the art can be used. For example, the positive electrode active material includes lithium cobalt oxide, sodium-containing lithium cobalt oxide, nickel-cobalt-manganese ternary material (chemical formula Li _a Ni _x Co _y Mn _z A _k O ₂ , wherein 0<x<1, 0<y<1, 0<z<1, 0.9≤a≤1.1, 0≤k≤0.1; wherein 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), nickel-cobalt-aluminum ternary material (chemical formula Li _a Ni _x Co _y Al _z A _k O ₂ , 0<x<1.1, 0<y<1, 0<z<1, 0.9≤a≤1, 0≤k≤0.1, 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), at least one of lithium iron phosphate, lithium-rich manganese-based materials, lithium iron manganese phosphate, lithium titanate, lithium nickel manganese oxide, lithium nickel oxide, lithium manganese oxide, and nickel-manganese binary materials.

There is no particular limitation 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.

In some embodiments, the positive electrode tab includes a plurality of tabs, and the plurality of tabs may be cut integrally with the current collector, or may be subsequently welded to the current collector. A multi-tab structure battery cell or a laminate structure battery cell may increase the charging rate to obtain fast charging performance.

In some embodiments, the positive electrode sheet of the present application is suitable for multi-pole wound battery cells and/or multi-pole stacked battery cells.

When the positive electrode sheet is suitable for multi-electrode winding cells, punching holes on the edge of the positive electrode sheet can also solve arc lithium deposition (the type of arc lithium deposition is the type that diffuses inward from both sides). Punching holes on the edge of the positive electrode is equivalent to setting a recessed area in each arc area of the cell, which can alleviate arc lithium deposition. When the positive electrode sheet is suitable for stacked cells, recessed areas (holes) can be set on all four edges of the positive electrode sheet to alleviate the problem of edge lithium deposition.

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 lithium deposition at the edge of the battery cell. The derivation process of this beneficial effect is basically the same as the derivation process of the beneficial effect of the above-mentioned positive electrode sheet, and will not be repeated here.

In some embodiments, the battery is a multi-pole wound battery or a multi-pole stacked battery.

In some embodiments, the battery further includes a negative electrode sheet, the negative electrode sheet including a negative electrode current collector, and a negative electrode active material layer disposed on at least one side surface of the negative electrode current collector; a third recessed area is disposed on the negative electrode active material layer; the third recessed area includes at least one third pit.

In some embodiments, a third recessed area is provided at an edge of one side of the negative electrode active material layer along the width direction (it can be at a side close to the positive electrode ear or at a side away from the positive electrode ear), or the third recessed area is provided at the edges of both sides. In other embodiments, in addition to the third recessed area being provided at the edges of both sides of the negative electrode active material layer, the third recessed area can also be provided at other areas of the negative electrode active material layer, for example, the third recessed area can be provided at the middle area of the negative electrode active material layer, or the third recessed area can be provided on the entire surface of the negative electrode active material layer.

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 precipitation; 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.

In some embodiments, the third recessed area is provided at least on one side of the edge of the negative electrode active material layer along the width direction of the negative electrode sheet. For example, the third recessed area is provided at one side of the edge of the negative electrode active material layer along the width direction, or the third recessed area is provided at both sides of the edge. Providing the third recessed area on the negative electrode sheet can increase the amount of electrolyte, and can also enhance the speed of the electrolyte infiltrating the negative electrode active material layer, improve the embedding efficiency of lithium ions, prevent lithium ions from being deposited on the surface, and improve the lithium precipitation phenomenon.

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.

In some embodiments, as shown in Fig. 14, 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 recessed pits distributed at intervals, and the third recessed pits are holes or grooves.

In some embodiments, as shown in Fig. 15, 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 recessed pits distributed at intervals, and the third recessed pits are linear grooves.

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

In some embodiments, as shown in Fig. 16, 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 recessed pits distributed at intervals, and the third recessed pits are holes or grooves.

In some embodiments, as shown in Fig. 17, 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 recessed pits distributed at intervals, and the third recessed pits are linear grooves.

There is no limitation on some specific parameters of the pore formation of the negative electrode sheet, and reference may be made to the pore formation parameters of the positive electrode sheet, or some specific parameters of the pore formation of the negative electrode sheet in the art.

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 described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

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

The present application is described in detail below in conjunction with specific embodiments, which are used to understand rather than limit the present application.

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

1. Preparation of positive electrode

(1) Lithium cobalt oxide: conductive carbon black: PVDF are 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 is 74%; the viscosity is 7000mPa.s. The positive electrode slurry is coated on both sides of the positive electrode current collector aluminum foil (thickness is 9μm), and the coating thickness on one side is 33.5μm. The positive electrode sheet is dried, rolled, and die-cut to obtain the corresponding positive electrode sheet; to ensure that the test data has a certain comparability, the size of the positive electrode sheets of all embodiments and comparative examples is consistent, wherein the width L of the positive electrode active material layer is 80mm.

(2) Alumina: PVDF is 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 is 40%. The ceramic layer slurry is coated on the edge of the positive electrode current collector aluminum foil close to the positive electrode ear, with a coating thickness of 30 μm. As shown in Figures 1 and 8, the protective layer is located between the positive electrode active material layer and the positive electrode ear, the width of the protective layer is W, and the width of the second recessed area is W1.

Referring to Figure 3, laser drilling is used to drill holes at the bottom and top of the positive electrode sheet, the width of the first concave area at the bottom is L1, and the width of the first concave area at the top is L3. When laser drilling, the bottom edge of the positive electrode sheet is drilled 1mm to 3mm more outward to ensure that the bottom edge is completely provided with a concave area.

2. Preparation of negative electrode sheet

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 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 dried, rolled and die-cut to obtain the negative electrode sheet.

3. Preparation of diaphragm

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

4. Wind the positive electrode sheet, the negative electrode sheet and the separator into 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; then put the obtained roll core into an aluminum-plastic film, inject 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)), vacuum packaging, aging, formation, secondary sealing, capacity sorting and other processes to obtain the corresponding soft-package wound lithium-ion battery.

Table 1

In Table 1, “\” indicates not tested.

Table 2

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

In the third embodiment, the power of the laser was adjusted to change the depth d1, the diameter D1 and the spacing S1 of the first pit, as well as the number of the recessed parts, the average particle size of the active material particles and the diameter length of the recessed parts. In the fourth embodiment, the depth d1, the diameter D1 and the spacing S1 of the first pit were changed by secondary laser hole making.

Example 6 Group

The method is carried out according to Example 1, except that the composition of the protective layer is changed:

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

Example 6-1: Alumina + hexafluoroethylene were dissolved in NMP solvent in a mass ratio of 95%:5%.

Example 8

The method is carried out in accordance with Example 1, except that the negative electrode sheet is also pore-formed. Specifically referring to FIG. 13 , laser pore-formation is used to form pores at the bottom and top of the negative electrode sheet, and the width of the third concave area at the bottom is 5 mm, and the width of the third concave area at the top is 5 mm. In the third concave area, the concave depth of the third concave area is 15 μm, the diameter length is 100 μm, and the spacing is 200 μm.

Example 9

The method is carried out in accordance with Example 1, except that the negative electrode sheet is also pore-formed. Specifically referring to Figure 16, laser pore-formation is used to form lines on the entire surface of the negative electrode sheet. In the third concave area, the concave depth of the third concave area is 15 μm, the diameter is 150 μm, and the spacing is 1 mm.

Comparative Example 1

The same method is used as in Example 1, except that the ceramic layer is not perforated.

Comparative Example 2

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

Comparative Example 3

The process is carried out in accordance with Example 1, except that no pores are formed on the positive electrode sheet.

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

(1) Lithium precipitation

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 left to stand for 5 minutes; 2A-4.5V, 0.05C; left to stand for 10 minutes; 0.7C discharge to a cut-off voltage of 3.0V, left to stand for 10 minutes; and repeated the test conditions of 1000T charging and discharging. The charge and discharge cycle was repeated for 400T and 800T, and the battery was fully charged after the end. The battery was disassembled in a dry environment to observe the lithium deposition on the negative electrode surface. There are four levels of lithium deposition: 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 there is no gray or silver lithium on the surface of the negative electrode; slight lithium deposition at the edge means that line-like lithium deposition appears at the edge of the negative electrode, which is gray; lithium deposition at the edge means that the lithium deposition area of the negative electrode diffuses to the center of the negative electrode on the basis of slight lithium deposition at the edge, which is also gray; severe lithium deposition at the edge means that the negative electrode has diffused to the center of the electrode on the basis of lithium deposition at the edge, and the lithium deposited at the edge is silver.

(2) Capacity retention rate

The test method for the battery capacity retention rate is: the lithium-ion batteries obtained in the examples and comparative examples are subjected to charge and discharge cycle tests on a blue electric test cabinet, the capacity retention rate of the battery after different cycles is examined and the test results are recorded. Among them, the capacity retention rate = capacity after N cycles/initial capacity*100%.

(3) Capacity test

The battery cells obtained in the embodiments and comparative examples were tested for capacity on a blue-electric test cabinet. Within the usable voltage upper and lower limits specified for the battery cells, constant current discharge was first performed at 25°C±2°C, 0.2C was discharged to the lower limit voltage, and the battery was allowed to stand for 5 min; then constant current and constant voltage charging was performed, 0.5C was charged to the upper limit voltage, the voltage was cut off at 0.025C, the battery was allowed to stand for 10 min, and 0.2C was 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.

(4) Element content analysis

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 discharge to a cut-off voltage of 3.0V, allowed to stand for 10 minutes; and repeated the test condition of 1000T charging and discharging. Repeat the charge and discharge cycle process for 400T and 800T, fully charge the battery after the end, and disassemble the battery cell in a dry environment. By scanning the protective layer on the positive electrode sheet through EDS line scanning analysis, a line distribution curve of the change in element content can be obtained. Combined with the comparative analysis of the sample morphology, the distribution of elements in different areas can be intuitively obtained.

Table 3

In the Example 1 group, the punching size of the first concave area in the top edge area and the bottom edge area 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 concave area. The larger the width of the first concave area, the higher the capacity loss. On the other hand, the width of the punching area of the first concave 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, 1mm is relatively speaking, the improvement of capacity retention rate is not very obvious, but relative to 0.5mm, the improvement effect is more obvious.

In Example 2, the hole size of the protective layer has little effect on the capacity loss and edge lithium deposition of the battery, but mainly affects the safety performance of the battery. In Example 2-3, the second depression area is set in the entire protective layer area, and the cycle capacity retention rate is slightly higher than that of Example 1. Therefore, the holes on the protective layer can increase the liquid storage space and slightly improve the cycle performance; however, it is not recommended to punch all the holes in the protective layer, as it is easy to lose the protective effect of the ceramic layer and cause a short circuit.

In Example 3, the laser power is too large and too small (too large, the depression depth d2 and the path length D2 will become larger, the capacity loss is high, And it is easy to punch through the ceramic layer; 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, which may easily cause the problem of belt breaking, 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.

In the Example 4 group, in Example 4-1, the laser power (or secondary laser) is increased to break the positive electrode active particles into pieces, the number of depressions increases significantly, the average particle size of the active material particles and the diameter of the depressions decrease significantly, the edge lithium precipitation problem can be improved and the cycle capacity retention rate can be improved, but the capacity loss is high. In Example 4-2, the laser power (or secondary laser) is further increased, the positive electrode active particles are broken, and the edge lithium precipitation problem can also be improved and the cycle capacity retention rate can be improved, but the capacity loss is high.

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

In Example 5-2, the protective layer and the current collector were penetrated by increasing the laser power (or secondary laser), but the protective layer on the other side was not penetrated; both can improve the edge lithium plating problem and increase the cycle capacity retention rate, and have no effect on capacity loss.

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

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

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.

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

Table 4

As can be seen from Table 4, the element analysis found that, when compared with Example 3, Example 1, Example 3-1, and Example 3-2 are subjected to appropriate power, the ceramic layer is not punctured, and the element content thereof does not change much. The ceramic layer is not punctured, which can not only play the protective role of the protective layer to prevent the burr from piercing the diaphragm and causing a short circuit, but also enable the second recessed area to store electrolyte, effectively alleviating the problem of insufficient electrolyte in the late cycle.

It should be noted that, in this article, the terms "comprise", "include" or any other variant thereof are intended to cover non-exclusive inclusion, so that the process, method, article or device including a series of elements includes not only those elements, but also includes other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise one..." do not exclude the presence of other identical elements in the process, method, article or device including the element. In addition, it should be pointed out 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 reverse 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.

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, and configured in the manner shown in the drawings. As will be appreciated by those skilled in the art, these components and devices can be connected, arranged, and configured in any manner. Words such as "including", "comprising", "having", etc. are open words, meaning "including but not limited to", and can be used interchangeably with them. The words "or" and "and" used here refer to the words "and/or" and can be used interchangeably with them, unless the context clearly indicates otherwise. The word "such as" used here refers to the phrase "such as but not limited to", and can be used interchangeably with it.

It should also be noted that in the device and apparatus of the present application, each component can be decomposed and/or reassembled, and such decomposition and/or reassembly should be regarded as an equivalent solution of the present application.

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 the widest scope consistent with the principles and novel features disclosed herein.

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 explain the technical solutions and cannot be used to limit the scope of protection of the present application.

The above description has been given for the purpose of illustration and description. In addition, this description is not intended to limit the embodiments of the present application to the forms disclosed herein. Although multiple example aspects and embodiments have been discussed above, those skilled in the art will recognize certain variations, modifications, changes, additions and sub-combinations thereof.

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

Claims (16)

A positive electrode sheet, characterized in that it 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. 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. The positive electrode sheet according to claim 1 or 2, characterized in that, on the same side surface of the positive electrode current collector, the 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. The positive electrode sheet according to any one of claims 1 to 3 is characterized in that 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. 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. The positive electrode sheet according to any one of claims 1 to 5, characterized in that the positive electrode active material layer on both sides of the positive electrode current collector is provided with the first recessed area, and the first pits in the first recessed area on both sides are staggered in the second direction; and/or the protective layer on both sides of the positive electrode current collector is provided with the second recessed area, and the second recessed area on both sides is staggered in the second direction. The second pits in the recessed area are arranged in a staggered manner in the second direction. 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. 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. 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. The positive electrode sheet according to any one of claims 5 to 9, characterized in that the first pit satisfies 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 distance S2 between two adjacent second pits is 50 μm-500 μm. 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. 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%). 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. 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. A battery, characterized by comprising the positive electrode sheet according to any one of claims 1 to 14. The battery according to claim 15 is characterized in that the battery also includes a negative electrode sheet, the negative electrode sheet includes a negative electrode collector, and a negative electrode active material layer arranged on at least one side surface of the negative electrode collector; a third recessed area is arranged on the negative electrode active material layer; the third recessed area includes at least one third pit.