Positive plate and lithium battery thereof

Abstract

In order to solve the problems of edge lithium precipitation and warping caused by edge lithium precipitation of an existing battery negative plate, the utility model provides a positive plate, a lithium battery and a positive plate, the positive plate comprises a positive coating layer and a positive current collector, the positive coating layer is arranged on at least one side surface of the positive current collector, and in the width direction of the positive coating layer, the width direction of the positive coating layer is larger than the width direction of the positive current collector. The positive electrode coating layer comprises a middle area and at least one thinned area, and one side of the middle area is connected with the thinned area; the thinning area comprises at least two step parts, each step part comprises an inclined area and a buffer area, one side edge of the inclined area is connected with one side edge of the buffer area in every two adjacent step parts, and the inclined areas and the buffer areas are alternately arranged; and the thickness of the coating layer in the step part is gradually reduced from the connecting position of the middle area and the thinning area to the direction far away from the middle area. According to the positive plate provided by the invention, lithium precipitation in the edge area of the negative plate can be reduced, the problem that the edge of the negative plate is warped due to lithium precipitation bulge is effectively solved, and the safety performance of the battery is improved.

Description

Technical Field

[0001] The utility model relates to the technical field of energy storage, in particular to a positive electrode sheet and a lithium battery thereof. Background Art

[0002] As the energy density of lithium batteries increases, battery cell manufacturers use thinner current collectors, higher compaction density and surface density. At the same time, the positive and negative electrode overhang and CB (cell balance) values ​​are designed to be lower and lower. Lithium deposition is prone to occur at the edge of the negative electrode, affecting the battery's cycle life and other electrical performance. As the number of battery cycles increases, the thickness of the edge of the negative electrode increases due to lithium deposition, and the lithium deposition area bulges. The edge of the negative electrode due to the bulge of lithium deposition causes the edge to warp, reducing the safety performance of the battery.

[0003] Existing lithium-ion batteries include a positive electrode, a negative electrode, and a separator. During the charge and discharge process of existing lithium-ion batteries, lithium is easily deposited at the edge of the negative electrode, affecting the electrical performance of the battery. The lithium deposition at the edge of the negative electrode is analyzed as follows.

[0004] like Figure 1 As shown, during the charging process of the lithium-ion battery, the positive electrode 1 releases lithium ions, passes through the diaphragm 3, and migrates to the negative electrode 2. The migration path direction is as shown in Figure 1 As shown in FIG, most lithium ions migrate vertically toward the negative electrode sheet 2 along the shortest migration path a, while a small number of lithium ions migrate from both sides along a path longer than path a (such as Figure 1 The lithium ions migrate in a circuitous manner toward the negative electrode sheet 2, as shown in the curved paths (these schematic paths are used only to explain lithium ion migration in this article). As the distance increases, the amount of lithium ions migrating to the sides gradually decreases. Similarly, as lithium ions are released from different locations on the positive electrode sheet 1, lithium ions located on both sides of the positive electrode sheet migrate along path a toward the edge n region of the negative electrode sheet 2. Lithium ions located near the sides of the positive electrode sheet also migrate toward the edge n region of the negative electrode sheet 2. The amount of lithium ion migration gradually increases, reaching a maximum, with the most lithium being inserted at the n-most edge of the negative electrode sheet 2. When the lithium insertion rate at the n-most edge of the negative electrode sheet 2 approaches its limit, a small amount of lithium ions will escape into the region m of the negative electrode sheet 2 that extends beyond the positive electrode sheet 1, known as the overhang region, but the vast majority of lithium ions remain concentrated in the n-most edge of the negative electrode sheet 2. As the CB value (the excess ratio of the negative electrode to the positive electrode) is designed to become increasingly extreme, the lithium ions accumulated at the edge of the negative electrode sheet 2 cannot effectively insert into the graphite interlayers, and in severe cases, lithium plating will occur.

[0005] like Figure 2As shown, during the discharge process of the lithium-ion battery, the lithium ions received by the negative electrode sheet 2 will return to the positive electrode sheet 1. Similarly, most of the lithium ions return vertically to the positive electrode sheet 1 along the shortest migration path. In this way, the excess lithium ions at the edge n position of the negative electrode sheet 2 cannot all return to the positive electrode sheet 1, and will remain at the edge n position of the negative electrode sheet 2. As the number of cycles increases, the excess lithium ions at the edge n position of the negative electrode sheet 2 will increase, and lithium precipitation will also occur, affecting the cycle performance. Utility Model Content

[0006] The utility model aims to solve the problems of lithium deposition at the edge of the negative electrode sheet of the existing battery and the warping caused by the lithium deposition at the edge, and provides a positive electrode sheet and a lithium battery thereof.

[0007] In one aspect, the present application provides a positive electrode sheet, comprising a positive electrode coating layer and a positive electrode current collector, wherein the positive electrode coating layer is disposed on at least one side of the positive electrode current collector, and in a width direction of the positive electrode coating layer, the positive electrode coating layer comprises a middle region and at least one thinned region, and one side of the middle region is connected to the thinned region;

[0008] The thinning zone includes at least two stepped portions, each of which includes an inclined zone and a buffer zone. In two adjacent stepped portions, one side of the inclined zone is connected to one side of the buffer zone, and the inclined zones and the buffer zones are alternately arranged; from the position where the middle area is connected to the thinning zone toward the direction away from the middle area, the thickness of the coating layer in the stepped portion gradually decreases.

[0009] Preferably, in the first direction, the angle between the inclined area and the first direction is α, 0<α<90°;

[0010] The first direction is parallel to a thickness direction of the positive electrode coating layer.

[0011] Preferably, the thinned area further includes a retention area, one side of the retention area is connected to one side of the inclined area, and the side of the retention area away from the inclined area is connected to the positive electrode current collector;

[0012] From the position where the inclined area is connected to the retention area to the direction away from the inclined area, the thickness of the coating layer in the retention area remains unchanged.

[0013] Preferably, in the first direction, the thickness of the coating layer in the retention area is h1, the thickness of the positive electrode coating layer is h, and h1>0.28h;

[0014] The first direction is parallel to a thickness direction of the positive electrode coating layer.

[0015] Preferably, in the width direction of the coating layer, the width of the retention area is 0-2 mm.

[0016] Preferably, the thinning zone includes three step portions, which are respectively a first step portion, a second step portion and a third step portion, the second step portion is arranged between the first step portion and the third step portion, one side of the inclined zone of the first step portion is connected to the side of the positive electrode coating layer away from the positive electrode current collector, and one side of the inclined zone of the third step portion is connected to the side of the retention zone away from the positive electrode current collector.

[0017] Preferably, the thickness of the positive electrode coating layer is T, and in the first direction, the height of the inclined area of ​​the first step portion is Y1, 0%T<Y1<18%T, the height of the inclined area of ​​the second step portion is Y2, and the height of the inclined area of ​​the third step portion is Y3, Y2=Y3=2Y1; the first direction is parallel to the thickness direction of the positive electrode coating layer.

[0018] Preferably, in the width direction of the positive electrode coating layer, the width of the buffer zone of the first step portion is X1, the width of the buffer zone of the second step portion is X2, the width of the buffer zone of the third step portion is X3, and X1=2X2=3X3.

[0019] Preferably, the width of the thinning zone is 5-8 mm.

[0020] In the second aspect, the present application provides a lithium battery, comprising a positive electrode sheet, a negative electrode sheet and a separator, wherein the positive electrode sheet is the positive electrode sheet described above.

[0021] The positive electrode sheet provided in the present application has a thinning area including at least two stepped portions. The arrangement of the stepped portions gradually reduces the thickness of the positive electrode dressing of the positive electrode sheet in the stepped portions as the distance from the middle area of ​​the positive electrode sheet increases. Positive electrode coating layers with different thicknesses of the positive electrode dressing are formed in the thinning area to avoid a large difference in the dressing thickness and ensure the mechanical properties of the positive electrode sheet. At the same time, the thickness of the positive electrode dressing of the positive electrode sheet in the stepped portions gradually decreases, and the lithium ions migrating to the edge area of ​​the negative electrode during the battery charging and discharging process are reduced, which can reduce lithium plating in the edge area of ​​the negative electrode sheet, effectively solve the problem of edge warping caused by the protrusion of lithium plating at the edge of the negative electrode sheet, and improve the safety performance of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a schematic diagram of the simulated structure of lithium ions escaping from the positive electrode during charging of an existing battery;

[0023] Figure 2 This is a schematic diagram of the simulated structure of lithium ions escaping from the negative electrode during discharge of an existing battery;

[0024] Figure 3 This is a structural schematic diagram of a positive electrode sheet provided in one embodiment of the present utility model.

[0025] 1. Positive electrode sheet; 2. Negative electrode sheet; 3. Separator; 4. Positive electrode current collector; 5. Positive electrode coating layer; 51. Thinning area; 512. Retention area; 511. Step portion; 5112. Inclined area; 5111. Buffer zone. DETAILED DESCRIPTION

[0026] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0027] In order to illustrate the technical solution of the present invention, specific embodiments are provided below for description.

[0028] First, as Figure 3 As shown, one embodiment of the present application provides a positive electrode sheet 1, including a positive electrode coating layer 5 and a positive electrode current collector 4, wherein the positive electrode coating layer 5 is arranged on at least one side surface of the positive electrode current collector 4, that is, the positive electrode coating layer 5 can be arranged on one side surface of the positive electrode current collector 4, or the positive electrode coating layer 5 can be arranged on both the upper and lower surfaces of the positive electrode current collector 4.

[0029] In the width direction of the positive electrode coating layer 5 , the positive electrode coating layer 5 includes a middle region and at least one thinned region 51 , and one side of the middle region is connected to the thinned region 51 .

[0030] Specifically, the positive electrode coating layer 5 includes a middle region and a skived region 51. The thickness of the coating layer in the skived region 51 is less than that in the middle region. The skived region 51 is a region of the positive electrode coating layer 5 with a relatively low thickness. The thickness of the coating layer in the skived region 51 is much less than that in the middle region. Generally, skived regions 51 are present on both sides of the positive electrode sheet 1 in the width direction of the positive electrode coating layer 5.

[0031] The thinning zone 51 includes at least two stepped portions 511, each of the stepped portions 511 includes an inclined zone 5112 and a buffer zone 5111, and one side of the inclined zone 5112 in two adjacent stepped portions 511 is connected to one side of the buffer zone 5111, and the inclined zones 5112 and the buffer zones 5111 are alternately arranged.

[0032] The thinning zone 51 includes at least two steps 511. In two adjacent steps 511, one side of the inclined zone 5112 is connected to one side of the buffer zone 5111. For example, when the thinning zone 51 includes two steps 511, they are the first step and the second step, respectively. The first step includes a first inclined zone and a first buffer zone, and the second step includes a second inclined zone and a second buffer zone. The first buffer zone coincides with the side of the positive electrode coating layer 5 away from the positive electrode current collector 4, one side of the first buffer zone is connected to one side of the first inclined zone, the side of the first inclined zone facing the positive electrode current collector 4 is connected to one side of the second buffer zone, and the side of the second buffer zone away from the first inclined zone is connected to one side of the second inclined zone.

[0033] From the position where the middle region is connected to the thinned region 51 to the direction away from the middle region, the thickness of the coating layer in the stepped portion 511 gradually decreases; Figure 3 As shown, the stepped portion 511 includes an inclined area 5112 and a buffer area 5111. The setting of the inclined area 5112 is capable of reducing the dressing of the coating layer. In the specific preparation, the positive electrode dressing is cleaned in the thickness direction of the positive electrode sheet 1, thereby forming the inclined area 5112; as for the buffer area 5111, the positive electrode dressing is cleaned in the width direction of the positive electrode sheet 1, thereby forming the buffer area 5111; therefore, in the inclined area 5112 of the stepped portion 511, the thickness of the coating layer gradually decreases in the direction away from the middle area of ​​the positive electrode sheet 1.

[0034] The positive electrode sheet 1 provided in the present application has a thinning area 51 including at least two stepped portions 511. The arrangement of the stepped portions 511 gradually reduces the thickness of the positive electrode dressing of the positive electrode sheet 1 in the stepped portions 511 as it moves away from the middle area of ​​the positive electrode sheet 1. A positive electrode coating layer 5 with different positive electrode dressing thicknesses is formed in the thinning area 51 to avoid a large difference in dressing thickness and ensure the mechanical properties of the positive electrode sheet 1. At the same time, the thickness of the positive electrode dressing of the positive electrode sheet 1 in the stepped portions 511 gradually decreases, and the lithium ions migrating to the edge area of ​​the negative electrode during the battery charging and discharging process are reduced, which can reduce lithium deposition in the edge area of ​​the negative electrode sheet 2, effectively solve the problem of edge warping caused by the protrusion of lithium deposition at the edge of the negative electrode sheet 2, and improve the battery safety performance.

[0035] In this embodiment, in the first direction, the angle between the inclined area 5112 and the first direction is α, 0<α<90°;

[0036] The first direction is parallel to the thickness direction of the positive electrode coating layer 5 .

[0037] Specifically, such as Figure 3As shown, the first direction is positioned as the z direction, and the angle between the inclined area 5112 and the z direction is α. When α is within the range of 0<α<90°, it is beneficial to clean the positive electrode dressing in the inclined area 5112 and reduce the thickness of the positive electrode dressing in the step portion 511, thereby forming a structure in which the thickness of the positive electrode dressing gradually decreases in the z direction in the step portion 511. Figure 3 As shown, it includes three stepped portions 511, corresponding to three inclined areas 5112, and the angles between the corresponding inclined areas 5112 and the first direction are defined as α1, α2, and α3, 0<α1<90°, 0<α2<90°, and 0<α3<90°.

[0038] In this embodiment, the thinning area 51 also includes a retention area 512, one side of the retention area 512 is connected to one side of the inclined area 5112, and the side of the retention area 512 away from the inclined area 5112 is connected to the positive electrode collector 4; from the position where the inclined area 5112 is connected to the retention area 512 to the direction away from the inclined area 5112, the thickness of the coating layer in the retention area 512 remains unchanged.

[0039] Specifically, such as Figure 3 As shown, the retention area 512 refers to a portion of the positive electrode dressing in the thinning area 51 close to the positive electrode current collector 4. From the position where the inclined area 5112 is connected to the retention area 512 to the direction away from the inclined area 5112, the thickness of the coating layer in the retention area 512 remains unchanged, that is, in actual operation, the positive electrode dressing in the retention area 512 is not cleaned, so that there is a corresponding positive electrode coating layer 5 near the edge of the negative electrode, which has little effect on the capacity of the battery.

[0040] In this embodiment, in the first direction, the thickness of the coating layer of the retention area 512 is h1, the thickness of the positive electrode coating layer 5 is T, and h1>0.28T;

[0041] The first direction is parallel to the thickness direction of the positive electrode coating layer 5 .

[0042] Specifically, such as Figure 3 As shown, the first direction is the z direction in the figure, the thickness of the retention area 512 is h1, and the thickness of the positive electrode coating layer 5 is T, which refers to the thickness of the middle area of ​​the positive electrode sheet 1; h1 is limited to be greater than 0.28T, so that the retention area 512 has a positive electrode dressing, reducing the impact on the capacity of the battery.

[0043] In this embodiment, the width of the retention area 512 in the width direction of the coating layer is 0-2 mm.

[0044] The width of the retention area 512 is limited to 0~2mm. When the width of the retention area 512 is 0, the retention area 512 is the outermost edge of the electrode in the width direction of the electrode, and can be used for buffering when the positive electrode dressing is actually cleaned. When the width of the retention area 512 is greater than 0 and less than or equal to 2mm, the retention area 512 contains positive electrode dressing in the width direction of the electrode, and has lithium ion deintercalation during the battery charging and discharging process. At the same time, a small amount of positive electrode dressing reduces the lithium ions at the edge of the negative electrode sheet 2, reduces lithium plating in the edge area of ​​the negative electrode sheet 2, and has little effect on the reduction of battery capacity. Specifically, the width of the retention area 512 can be 0, 0.1mm, 0.4mm, 0.5mm, 1.0mm, 1.3mm, 1.5mm, 2.0mm, etc., as long as the width of the retention area 512 is within the range of 0~2mm.

[0045] In this embodiment, the thinning zone 51 includes three stepped portions 511, and the three stepped portions 511 are respectively a first step portion, a second step portion and a third step portion. The second step portion is arranged between the first step portion and the third step portion. The buffer zone 5111 of the first step portion coincides with the side of the positive electrode coating layer 5 away from the positive electrode current collector 4, and one side of the inclined zone 5112 of the third step portion is connected to the side of the retention zone 512 away from the positive electrode current collector 4.

[0046] Specifically, such as Figure 3 As shown, the thinning area 51 of the positive electrode sheet 1 includes three step portions 511 and a retention area 512, the second step portion is arranged between the first step portion and the second step portion, the inclined area 5112 of the third step portion is connected to the retention area 512 on the side facing the positive electrode collector 4, and the buffer zone 5111 of the first step portion coincides with the side of the positive electrode coating layer 5 away from the positive electrode collector 4.

[0047] The first stepped portion includes a first inclined area and a first buffer zone, the second stepped portion includes a second inclined area and a second buffer zone, and the third stepped portion includes a third inclined area and a third buffer zone. The first buffer zone coincides with the side of the positive electrode coating layer 5 away from the positive electrode current collector 4, one side of the first buffer zone is connected to one side of the first inclined area, the side of the first inclined area away from the first buffer zone is connected to one side of the second buffer zone, the side of the second buffer zone away from the first inclined area is connected to one side of the second inclined area, the side of the second inclined area away from the second buffer zone is connected to one side of the third buffer zone, the side of the third buffer zone away from the second inclined area is connected to one side of the third inclined area, and the side of the third inclined area away from the third buffer zone is connected to the side of the retention area 512 away from the positive electrode current collector 4.

[0048] In this embodiment, the thickness of the positive electrode coating layer 5 is T. In the first direction, the height of the inclined area 5112 of the first step portion is Y1, 0%T<Y1<18%T, the height of the inclined area 5112 of the second step portion is Y2, and the height of the inclined area 5112 of the third step portion is Y3, Y2=Y3=2Y1; the first direction is parallel to the thickness direction of the positive electrode coating layer 5.

[0049] Specifically, the height of the inclined zone 5112 of the first step portion is Y1, which is the height of the first inclined zone in the first direction; the height of the inclined zone 5112 of the second step portion is Y2, which is the height of the second inclined zone in the first direction; and the height of the inclined zone 5112 of the third step portion is Y3, which is the height of the third inclined zone in the first direction.

[0050] The relationship between Y1 and T is defined as 0%T<Y1<18%T. At the same time, the relationship between Y1, Y2, and Y3 is defined as Y2=Y3=2Y1. From the position where the middle area is connected to the thinning area 51 to the direction away from the middle area, the thickness of the coating layer in the three step portions 511 gradually decreases. During the battery charging and discharging process, the lithium ions migrating to the edge area of ​​the negative electrode are reduced, which can reduce lithium deposition in the edge area of ​​the negative electrode sheet 2, effectively solve the problem of edge warping caused by lithium deposition on the edge of the negative electrode sheet 2, and improve the battery safety performance.

[0051] In this embodiment, in the width direction of the positive electrode coating layer 5, the width of the inclined area 5112 of the first step portion is X1, the width of the inclined area 5112 of the second step portion is X2, and the width of the inclined area 5112 of the third step portion is X3, where X1=2X2=3X3.

[0052] Specifically, X1=2X2=3X3 is defined, and the width of the inclined area 5112 of the first step is greater than the width of the inclined area 5112 of the second step, and the width of the inclined area 5112 of the second step is greater than the width of the inclined area 5112 of the third step, indicating that as the distance from the middle area of ​​the positive electrode sheet 1 increases, the positive electrode dressing of the positive electrode sheet 1 gradually decreases, and the lithium ions migrating to the edge area of ​​the negative electrode during the battery charging and discharging process decreases, which can reduce lithium deposition in the edge area of ​​the negative electrode sheet 2, effectively solve the problem of edge warping caused by lithium deposition at the edge of the negative electrode sheet 2, and improve the battery safety performance.

[0053] like Figure 1 As shown, in the width direction of the positive electrode coating layer 5 , the width of the second buffer area is X11, the width of the third buffer area is X21, 2X11=X1, X21=X2.

[0054] In this embodiment, the width of the thinned area 51 is 5-8 mm.

[0055] It is understandable that the positive electrode dressing on the stepped portion 511 can be removed by laser cleaning, scraping, or the like.

[0056] In a second aspect, the present application provides a lithium battery, comprising a positive electrode sheet 1, a negative electrode sheet 2 and a separator 3, wherein the positive electrode sheet 1 is the positive electrode sheet 1 described above.

[0057] The lithium battery provided in the present application adopts the above-mentioned positive electrode sheet 1. The setting of the step portion 511 enables the thinned area 51 of the positive electrode sheet 1 to form a positive electrode coating layer 5 with different positive electrode dressing thicknesses, thereby avoiding a large difference in dressing thickness and ensuring the mechanical properties of the positive electrode sheet 1. At the same time, the thickness of the positive electrode dressing of the positive electrode sheet 1 in the step portion 511 gradually decreases, and the lithium ions migrating to the edge area of ​​the negative electrode during the battery charging and discharging process are reduced, which can reduce lithium plating in the edge area of ​​the negative electrode sheet 2 and improve the battery's cycle performance and other electrical properties. At the same time, reducing lithium plating on the negative electrode sheet 2 can also effectively solve the problem of edge warping caused by the protrusion of lithium plating on the edge of the negative electrode sheet 2, thereby improving the battery safety performance.

[0058] The above embodiments are intended only to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art will appreciate that modifications may be made to the technical solutions described in the aforementioned embodiments, or that some of the technical features may be replaced with equivalents. These modifications or replacements do not deviate from the spirit and scope of the technical solutions of the various embodiments of the present invention and are therefore intended to be included within the scope of protection of the present invention.

Claims

1. A positive electrode sheet, characterized in that: The positive electrode coating layer (5) comprises a positive electrode coating layer (5) and a positive electrode current collector (4), wherein the positive electrode coating layer (5) is arranged on at least one side surface of the positive electrode current collector (4), and in the width direction of the positive electrode coating layer (5), the positive electrode coating layer (5) comprises a middle region and at least one thinned region (51), and one side of the middle region is connected to the thinned region (51); The thinning zone (51) includes at least two stepped portions (511), each of the stepped portions (511) includes an inclined zone (5112) and a buffer zone (5111), one side of the inclined zone (5112) in two adjacent stepped portions (511) is connected to one side of the buffer zone (5111), and the inclined zones (5112) and the buffer zones (5111) are alternately arranged; the thickness of the coating layer in the stepped portion (511) gradually decreases from the position where the middle region is connected to the thinning zone (51) in a direction away from the middle region.

2. The positive electrode sheet according to claim 1, characterized in that In the first direction, the angle between the inclined area (5112) and the first direction is α, 0<α<90°; The first direction is parallel to the thickness direction of the positive electrode coating layer (5).

3. The positive electrode sheet according to claim 1, characterized in that The thinned region (51) further comprises a retention region (512), one side of the retention region (512) being connected to one side of the inclined region (5112), and a side of the retention region (512) away from the inclined region (5112) being connected to the positive electrode current collector (4); From the position where the inclined area (5112) is connected to the retention area (512) in a direction away from the inclined area (5112), the thickness of the coating layer in the retention area (512) remains unchanged.

4. The positive electrode sheet according to claim 3, characterized in that In the first direction, the thickness of the coating layer of the retention area (512) is h1, the thickness of the positive electrode coating layer (5) is T, and h1>0.28T; The first direction is parallel to the thickness direction of the positive electrode coating layer (5).

5. The positive electrode sheet according to claim 4, characterized in that: In the width direction of the coating layer, the width of the retention area (512) is 0-2 mm.

6. The positive electrode sheet according to claim 3, characterized in that: The thinning area (51) includes three stepped portions (511), and the three stepped portions (511) are respectively a first stepped portion, a second stepped portion and a third stepped portion, the second stepped portion is arranged between the first stepped portion and the third stepped portion, the buffer zone (5111) of the first stepped portion coincides with a side of the positive electrode coating layer (5) away from the positive electrode current collector (4), and one side of the inclined area (5112) of the third stepped portion is connected to a side of the retention area (512) away from the positive electrode current collector (4).

7. The positive electrode sheet according to claim 6, characterized in that: The thickness of the positive electrode coating layer (5) is T. In the first direction, the height of the inclined area (5112) of the first step portion is Y1, 0%T<Y1<18%T, the height of the inclined area (5112) of the second step portion is Y2, and the height of the inclined area (5112) of the third step portion is Y3, Y2=Y3=2Y1; the first direction is parallel to the thickness direction of the positive electrode coating layer (5).

8. The positive electrode sheet according to claim 6, characterized in that: In the width direction of the positive electrode coating layer (5), the width of the inclined area (5112) of the first step portion is X1, the width of the inclined area (5112) of the second step portion is X2, and the width of the inclined area (5112) of the third step portion is X3, where X1=2X2=3X3.

9. The positive electrode sheet according to claim 1, characterized in that: The width of the thinning area (51) is 5-8 mm.

10. A lithium battery, characterized in that: The invention comprises a positive electrode sheet (1), a negative electrode sheet (2) and a separator (3), wherein the positive electrode sheet (1) is the positive electrode sheet (1) according to any one of claims 1 to 9.

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