Cells and Batteries

Abstract

The present invention relates to the field of batteries, and in particular to a battery cell and a battery comprising the battery cell. The battery cell comprises a positive electrode sheet; the positive electrode sheet comprises a double-sided coating area and a single-sided coating area along the winding direction; the positive electrode sheet comprises a first part, a second part and a third part connected in sequence along the winding direction; the first part and the second part are located in the double-sided coating area, and at least part of the third part is located in the single-sided coating area; with the boundary line between the single-sided coating area and the double-sided coating area as the starting point, the first compression coating extends at least 3mm to the winding head end of the positive electrode sheet, and at least 3mm to the winding tail end of the positive electrode sheet; the second compression coating extends at least 3mm to the winding head end of the positive electrode sheet, and at least 3mm to the winding tail end of the positive electrode sheet. The battery of the present invention can significantly improve the problem that the positive electrode current collector has slight cracks during rolling and breaks during the cycle.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to a battery cell and a battery comprising the battery cell. Background Art

[0002] In recent years, lithium-ion batteries have been highly favored in the market due to their excellent characteristics such as high energy density, long cycle life, and environmental friendliness. However, current lithium-ion batteries are facing the problem of battery life anxiety caused by rapid power consumption. In order to improve the energy density of lithium-ion batteries, researchers often increase the thickness of the battery cell when designing lithium-ion batteries to increase the capacity of the battery, and increase the compaction density of the positive and negative electrodes to reduce the thickness of the electrodes, thereby further improving the energy density of the battery. However, such a design often causes slight cracks in the positive electrode of the wound battery during rolling, and the problem of current collector breakage occurs during the battery charge and discharge cycle. Summary of the invention

[0003] The purpose of the present invention is to overcome the above problems existing in the prior art and provide a battery cell and a battery comprising the battery cell. The battery of the present invention can significantly improve the problem that the positive electrode current collector of the wound battery cell has slight cracks during rolling and breaks during the cycle.

[0004] In order to solve the problem in the related art that the positive electrode collector of the wound battery cell has slight cracks during rolling and the collector breaks during the battery charge and discharge cycle, the inventors of the present invention have conducted a lot of research and found that due to the structural characteristics of the wound lithium-ion battery, the pole piece has a single-sided coating area and a double-sided coating area, as well as a step area transitioning from the double-sided coating area to the single-sided coating area. When the pole piece (especially the positive electrode piece) is rolled, there will be a jump in the step area, which will cause the positive electrode collector in the step area to be over-pressured, thereby causing slight cracks in the positive electrode collector; and because the battery has volume expansion during the charge and discharge cycle, the force on both sides of the boundary between the single-sided coating area and the double-sided coating area is uneven (only one side of the positive electrode sheet in the single-sided area is charged and discharged, while both sides of the positive electrode sheet in the double-sided area are charged and discharged). With the continuous uneven force, the squeezing effect on the positive electrode collector in the step area where the double-sided coating area transitions to the single-sided coating area will be further aggravated, eventually causing the positive electrode collector to break. Based on the above findings, the inventors of the present invention have conducted a large number of targeted studies. By arranging a tough, compressive-resistant coating on the surface of the positive electrode collector in the step area where the double-sided coating area of ​​the positive electrode sheet transitions to the single-sided coating area, the problem of current collector breakage caused by uneven forces applied to the positive electrode sheet during the rolling process and battery overcharging can be significantly improved.

[0005] According to a first aspect of the present invention, there is provided a battery cell, comprising a positive electrode sheet, the positive electrode sheet comprising a current collector, the current collector having a first surface and a second surface arranged opposite to each other along the thickness direction of the battery cell; the positive electrode sheet comprises a double-sided coating area and a single-sided coating area along the winding direction; along the winding direction, the positive electrode sheet comprises a first part, a second part and a third part connected in sequence, the first part and the second part are located in the double-sided coating area, and at least part of the third part is located in the single-sided coating area; in the first part, the first surface is provided with a first positive electrode active coating, and the second surface is provided with a second positive electrode active coating; in the second part, the first surface is provided with a first pressure-resistant coating and the first positive electrode active coating in a stacked manner, the first pressure-resistant coating is close to the current collector, and the first positive electrode active coating is away from the current collector; the second surface The first surface is stacked with a second pressure-resistant coating and a second positive electrode active coating, the second pressure-resistant coating is close to the current collector, and the second positive electrode active coating is away from the current collector; in the third part, the first surface is stacked with the first pressure-resistant coating and the first positive electrode active coating, the first pressure-resistant coating is close to the current collector, and the first positive electrode active coating is away from the current collector; the second surface is provided with the second pressure-resistant coating; taking the boundary line between the single-sided coating area and the double-sided coating area as the starting point, the first pressure-resistant coating extends at least 3mm to the first end of the positive electrode sheet winding, and at least 3mm to the tail end of the positive electrode sheet winding; taking the boundary line between the single-sided coating area and the double-sided coating area as the starting point, the second pressure-resistant coating extends at least 3mm to the first end of the positive electrode sheet winding, and at least 3mm to the tail end of the positive electrode sheet winding.

[0006] A second aspect of the present invention provides a battery, comprising the battery cell described in the first aspect of the present invention.

[0007] Through the above technical scheme, the present invention has at least the following advantages compared with the prior art: the battery of the present invention can significantly improve the step area where the positive electrode sheet transitions from the double-sided coating area to the single-sided coating area, and the positive electrode current collector has slight cracks during rolling and breaks during the cycle.

[0008] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 Shown is a schematic diagram of a positive electrode sheet in an example of the present invention.

[0010] Figure 2 FIG. 1 is a partial schematic diagram of a positive electrode sheet in an example of the present invention.

[0011] Figure 3 Shown is a schematic diagram of a battery cell.

[0012] Figure 4 Shown is a schematic diagram of a positive electrode sheet in an example of the present invention.

[0013] Figure 5 Shown is a schematic diagram of a positive electrode sheet in an example of the present invention.

[0014] Figure 6 Shown is a schematic representation of dimensions L1, L2 and L3.

[0015] Figure 7 Shown is a schematic diagram of dimension L4.

[0016] Figure 8 The diagram shows the dimension L5; wherein, Figure 8 (a) is a situation where the first end of the first pressure-resistant coating exceeds the first end of the second pressure-resistant coating; Figure 8 (b) is a case where the first end of the second pressure resistant coating exceeds the first end of the first pressure resistant coating.

[0017] Fig. 9 Shown is a schematic diagram of dimension L6.

[0018] Fig.10 Shown is a schematic diagram of dimensions L7 and L8.

[0019] Fig.11 Shown is a cross-sectional scanning electron microscope (SEM) image of a positive electrode sheet in an example of the present invention.

[0020] Fig.12 Shown is a schematic representation of dimensions L9 and L10.

[0021] Fig.13 Shown is a schematic diagram of dimension L11.

[0022] Fig.14 Shown is a schematic diagram of adhesive tape covering the first pressure-resistant coating layer and adhesive tape covering the second pressure-resistant coating layer.

[0023] Fig.15 Shown is a schematic diagram of dimension L12.

[0024] Fig.16 Shown is a schematic cross-sectional view of the positive electrode sheet in Example 1.

[0025] Fig.17 Shown is a schematic cross-sectional view of the positive electrode sheet in Example 12 (the adhesive tape is not drawn).

[0026] Fig.18 Shown is a local SEM image of the positive electrode sheet in Example 1.

[0027] Fig.19 Shown is a local SEM image of the positive electrode sheet in Comparative Example 1.

[0028] Description of Reference Numerals

[0029] 1: current collector, 2-1: first positive electrode active coating, 2-2: second positive electrode active coating, 3-1: first pressure-resistant coating, 3-2: second pressure-resistant coating, 4: adhesive tape;

[0030] 1000: double-sided coating area, 2000: single-sided coating area;

[0031] 100: first part, 200: second part, 300: third part, 400: fourth part;

[0032] 10: first straight area, 20: first arc area, 30: second straight area, 40: second arc area, 50: third straight area, 60: third arc area. DETAILED DESCRIPTION

[0033] The specific embodiments of the present invention are described in detail below. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0034] According to a first aspect of the present invention, there is provided a battery cell. The battery cell may include a positive electrode sheet. The positive electrode sheet may include a current collector, and the current collector has a first surface and a second surface arranged opposite to each other along the thickness direction of the battery cell. Along the winding direction of the positive electrode sheet, the positive electrode sheet may include a double-sided coating area and a single-sided coating area. Along the winding direction, the positive electrode sheet may include a first part, a second part and a third part connected in sequence. The first part and the second part may be located in the double-sided coating area, and at least part of the third part may be located in the single-sided coating area. Figure 1 The diagram shows a schematic diagram of a positive electrode sheet in an example of the present invention. It can be seen from the figure that the positive electrode sheet may include a current collector 1, and the current collector 1 has a first surface and a second surface arranged oppositely along the thickness direction of the battery cell; along the winding direction of the positive electrode sheet, the positive electrode sheet includes a double-sided coating area 1000 and a single-sided coating area 2000; along the winding direction, the positive electrode sheet includes a first part 100, a second part 200 and a third part 300 connected in sequence. The first part 100 and the second part 200 are located in the double-sided coating area 1000, and part of the third part 300 is located in the single-sided coating area 2000.

[0035] Understandably, Figure 1 The case where only part of the third part is located in the single-sided coating area is shown; there may also be a case where the entire third part is located in the single-sided coating area. For example, in the winding direction, when the size of the active material coating (i.e., the first positive electrode active coating) located at the winding tail end of the first surface is equal to or exceeds the size of the pressure-resistant coating (i.e., the first pressure-resistant coating), the entire third part is located in the single-sided coating area (i.e., Figure 5 situation shown).

[0036] In the present invention, the single-sided coating area and the double-sided coating area have the conventional meanings in the art. The single-sided coating area means that only one side surface (first surface or second surface) of the current collector has an active material coating in this area; the double-sided coating area means that both sides (first surface and second surface) of the current collector have an active material coating in this area.

[0037] In the present invention, in the first part, the first surface is provided with a first positive electrode active coating, and the second surface is provided with a second positive electrode active coating. In the second part, the first surface is provided with a first pressure-resistant coating and the first positive electrode active coating in a stacked manner, the first pressure-resistant coating is close to the current collector, and the first positive electrode active coating is away from the current collector; the second surface is provided with a second pressure-resistant coating and the second positive electrode active coating in a stacked manner, the second pressure-resistant coating is close to the current collector, and the second positive electrode active coating is away from the current collector. In the third part, the first surface is provided with the first pressure-resistant coating and the first positive electrode active coating in a stacked manner, the first pressure-resistant coating is close to the current collector, and the first positive electrode active coating is away from the current collector; the second surface is provided with the second pressure-resistant coating. Figure 2The figure shows a schematic diagram of a positive electrode sheet in an example of the present invention. It can be seen from the figure that in the first part 100, the first surface of the current collector 1 is provided with a first positive electrode active coating 2-1, and the second surface of the current collector 1 is provided with a second positive electrode active coating 2-2. In the second part 200, the first surface of the current collector 1 is provided with a first pressure-resistant coating 3-1 and the first positive electrode active coating 2-1 in a stacked manner, wherein the first pressure-resistant coating 3-1 is close to the current collector 1, and the first positive electrode active coating 2-1 is away from the current collector 1; the second surface of the current collector 1 is provided with a second pressure-resistant coating 3-2 and the second positive electrode active coating 2-2 in a stacked manner, wherein the second pressure-resistant coating 3-2 is close to the current collector 1, and the second positive electrode active coating 2-2 is away from the current collector 1. In the third part 300, the first surface of the current collector 1 is stacked with a first pressure-resistant coating 3-1 and a first positive electrode active coating 2-1, the first pressure-resistant coating 3-1 is close to the current collector 1, and the first positive electrode active coating 2-1 is away from the current collector 1; the second surface of the current collector 1 is provided with a second pressure-resistant coating 3-2.

[0038] In the present invention, starting from the boundary line between the single-sided coating area and the double-sided coating area, the first compression-resistant coating extends at least 3 mm to the winding head end of the positive electrode sheet, and at least 3 mm to the winding tail end of the positive electrode sheet. Starting from the boundary line between the single-sided coating area and the double-sided coating area, the second compression-resistant coating extends at least 3 mm to the winding head end of the positive electrode sheet, and at least 3 mm to the winding tail end of the positive electrode sheet.

[0039] In the present invention, in the second portion, the projections of the first end of the first pressure-resistant coating and the first end of the second pressure-resistant coating in the thickness direction do not overlap, wherein the first end is the end close to the first end of the positive electrode sheet winding.

[0040] Since there are single-sided coating areas and double-sided coating areas on the positive electrode sheet in the wound battery cell, it is easy to cause damage to the current collector and microcracks when rolling. The above-mentioned scheme of the present invention has been able to significantly improve the problem of current collector fracture. Furthermore, the inventor of the present invention found that due to the characteristics of the winding structure, the arc area has a greater outward expansion and extrusion force than the straight area. The area close to the outer ring of the wound battery cell is the single-sided coating area of ​​the positive electrode sheet, and due to the characteristics of the winding structure, the closer to the outer ring of the wound battery cell, the more uneven the force at the arc, the greater the expansion force from the inside to the outside, and the smaller the restraint force from the outside to the inside. The step area of ​​the transition between the single-sided and double-sided coating areas of the external positive electrode sheet (i.e., near the single-sided and double-sided coating areas) is just at the third arc near the outer ring (in the direction from the winding tail end to the winding head end of the positive electrode sheet). The above two aspects of degradation are superimposed, which will make the wound battery cell more prone to pole piece fracture at the arc near the outer ring and the adjacent plane; at the same time, the junction of the single-sided and double-sided coating areas will also break due to uneven internal and external forces. Based on this, the inventor of the present invention has made further improvements on the basis of the above technical solution, so that the compression coating is located at the junction of the single-sided coating area and the double-sided coating area and at least at the third arc (along the direction from the winding tail end to the winding head end of the positive electrode sheet), which can further improve the problem of positive electrode sheet current collector fracture caused by uneven force during the cycle.

[0041] In the present invention, the positive electrode sheet may further include a fourth part. Figure 1 In the embodiment, the fourth portion 400 includes the current collector (ie, the fourth portion does not include the first pressure-resistant coating, the second pressure-resistant coating, the first positive electrode active coating, and the second positive electrode active coating). Figure 2 In the embodiment, the fourth portion 400 includes a current collector (the fourth portion 400 does not include the first positive electrode active coating 2-1, the second positive electrode active coating 2-2, the first pressure-resistant coating 3-1, and the second pressure-resistant coating 3-2).

[0042] In the present invention, along the direction from the winding tail end to the winding head end of the positive electrode sheet, the battery cell has a first straight area, a first arc area, a second straight area, a second arc area, a third straight area and a third arc area connected in sequence. Figure 3 The schematic diagram of the battery cell is shown. It can be understood that the battery cell is obtained by stacking the positive electrode sheet, the separator, the negative electrode sheet and the separator in sequence and winding them to form a Figure 3 The two ends of the winding are arc areas, the middle is a straight area, and the arc areas at both ends are connected to the two ends of the straight area. As can be seen from the figure, from the winding end to the winding beginning, the positive electrode sheets are located in sequence Figure 3The outermost straight area on the upper side of the middle cell (i.e., the dotted line frame 10 in the figure), the outermost arc area on the left side, the outermost straight area on the lower side (i.e., the dotted line frame 30 in the figure), the outermost arc area on the right side, the straight area adjacent to the outermost side on the upper side (i.e., the dotted line frame 50 in the figure), and so on, are not repeated here. At the same time, in order to distinguish the straight areas and arc areas, along the direction from the winding end to the winding beginning of the positive electrode sheet, the outermost straight area on the upper side of the middle cell is defined as the first straight area (i.e., Figure 3 10), the outermost arc area on the left is defined as the first arc area, and the outermost straight area on the lower side is defined as the second straight area (i.e. Figure 3 30 in the figure), the outermost arc area on the right is defined as the second arc area, and the straight area adjacent to the outermost area on the upper side is defined as the third straight area (i.e. Figure 3 50 in ), and so on.

[0043] In the present invention, at least part of the fourth portion is located in the first straight region. Figure 4 FIG. 4 is a schematic diagram of a positive electrode sheet in an embodiment of the present invention. It can be seen from the figure that the fourth portion 400 is located in the first straight region 10 (that is, the entire fourth portion 400 is located in the first straight region 10). Figure 5 It is a schematic diagram of a positive electrode sheet in an example of the present invention. It can be seen from the figure that the fourth portion 400 is located in the first straight area 10 and the first arc area 20 (that is, part of the fourth portion 400 is located in the first straight area 10).

[0044] In the present invention, at least part of the third portion is located in the first arc region, the second straight region, the second arc region, the third straight region and the third arc region. Figure 5 It can be seen from the figure that the third portion 300 is located in the first arc region 20, the second straight region 30, the second arc region 40, the third straight region 50 and the third arc region 60. Figure 4 It can be seen that the third portion is located in the first straight area 10 , the first arc area 20 , the second straight area 30 , the second arc area 40 , the third straight area 50 and the third arc area 60 .

[0045] In the present invention, along the direction from the winding tail end to the winding head end of the positive electrode sheet, the battery cell has a first straight area, a first arc area, a second straight area, a second arc area, a third straight area, a third arc area and a fourth straight area connected in sequence. Along the winding direction, the boundary line between the single-sided coating area and the double-sided coating area may exceed the boundary line between the fourth straight area and the third arc area, or may not exceed the boundary line between the fourth straight area and the third arc area. When the boundary line between the single-sided coating area and the double-sided coating area does not exceed the boundary line between the fourth straight area and the third arc area, the third part may also be located in the fourth straight area (that is, part of the third part is located in the fourth straight area).

[0046] In the present invention, taking the boundary line between the single-sided coating area and the double-sided coating area as the starting point, the dimension L1 of the first pressure-resistant coating extending toward the winding head of the positive electrode sheet is 3mm-15mm, for example, 3mm, 4mm, 5mm, 6mm, 7mm, 8mm, 9mm, 10mm, 11mm, 12mm, 13mm, 14mm or 15mm.

[0047] In one example, L1 is 3 mm-6 mm.

[0048] like Figure 6 The diagram shows the dimensions L1, L2 and L3. It can be seen from the figure that the dimension of the first compression-resistant coating extending from the boundary line between the single-sided coating area and the double-sided coating area to the winding head end of the positive electrode sheet is L1. When L1 is within a specific range, it can avoid the excessive length of the first compression-resistant coating overlapping with the tab tape; or avoid the excessive length of the first compression-resistant coating causing thickness stacking, thereby affecting the thickness of the battery cell, and further affecting the energy density of the battery.

[0049] In the present invention, taking the boundary line between the single-sided coating area and the double-sided coating area as the starting point, the dimension L2 of the second pressure-resistant coating extending toward the winding head of the positive electrode sheet is 3mm-15mm, for example, 3mm, 4mm, 5mm, 6mm, 7mm, 8mm, 9mm, 10mm, 11mm, 12mm, 13mm, 14mm or 15mm.

[0050] In one example, L2 is 3 mm-6 mm.

[0051] from Figure 6 It can be seen that, starting from the boundary line between the single-sided coating area and the double-sided coating area, the dimension of the second compression coating extending to the winding head of the positive electrode sheet is L2. Similarly, when L2 is within a specific range, the adverse effect on the battery energy density can be reduced while ensuring safety performance.

[0052] In the present invention, taking the boundary line between the single-sided coating area and the double-sided coating area as the starting point, the dimension L3 of the second pressure-resistant coating extending toward the winding tail end of the positive electrode sheet is 3mm-15mm, for example, 3mm, 4mm, 5mm, 6mm, 7mm, 8mm, 9mm, 10mm, 11mm, 12mm, 13mm, 14mm or 15mm.

[0053] In one example, L3 is 3 mm-5 mm.

[0054] from Figure 6 It can be seen that, starting from the boundary line between the single-sided coating area and the double-sided coating area, the dimension of the second compression coating extending to the winding tail of the positive electrode sheet is L3. Similarly, when L3 is within a specific range, the adverse effect on the battery energy density can be reduced while ensuring safety performance.

[0055] In the present invention, along the winding direction, the second end of the second pressure-resistant coating exceeds the third arc area and extends to the third straight area. The dimension L4 of the second end of the second pressure-resistant coating exceeding the boundary line between the third straight area and the third arc area is 1mm-5mm, for example, 1mm, 2mm, 3mm, 4mm or 5mm; the second end is the end close to the tail end of the winding.

[0056] In one example, L4 is 1 mm-3 mm.

[0057] like Figure 7 The schematic diagram of dimension L4 is shown. It can be seen from the figure that along the winding direction, the second end of the second pressure-resistant coating (the end of the second pressure-resistant coating close to the winding tail end) exceeds the third arc area 60 and extends to the third straight area 50. The dimension of the second end exceeding the intersection of the third straight area 50 and the third arc area 60 is L4. On the premise that L3 meets a specific range, the position of the second end of the second pressure-resistant coating is controlled at the same time, so that it extends to the third straight area and exceeds a certain dimension of the intersection of the third straight area and the third arc area, which can further improve the risk of positive electrode sheet current collector fracture. The reason is that when the second end of the second pressure-resistant coating is located in the third arc area, there will be an unprotected area, which will still cause the positive electrode sheet current collector to fracture. When the second end is at the intersection of the third arc area and the third straight area, due to the large stress at this position and the pressure-resistant coating is prone to form steps, there is also a risk of positive electrode sheet current collector fracture here. When the second end of the second compression-resistant coating exceeds the boundary line of the third straight area and the third arc area by a certain size, there will be a better transition, stress accumulation will not easily occur, and the problem of positive electrode current collector fracture will be improved.

[0058] In the present invention, a distance L5 between the projections of the first end of the first pressure-resistant coating and the first end of the second pressure-resistant coating in the thickness direction of the battery cell is 1 mm-12 mm, for example, 1 mm, 2 mm, 3 mm, 4 mm, 5 mm, 6 mm, 7 mm, 8 mm, 9 mm, 10 mm, 11 mm or 12 mm.

[0059] In one example, L5 is 1 mm-3 mm.

[0060] like Figure 8 The diagram shows the dimension L5; wherein, Figure 8 (a) is a situation where the first end of the first pressure-resistant coating exceeds the first end of the second pressure-resistant coating; Figure 8 (b) is the case where the first end of the second pressure-resistant coating exceeds the first end of the first pressure-resistant coating. As can be seen from the figure, the distance between the projections of the first end of the first pressure-resistant coating and the first end of the second pressure-resistant coating in the thickness direction is L5. By regulating L5, the first ends of the first pressure-resistant coating and the second pressure-resistant coating are not in the same position to avoid greater extrusion shear force during rolling, which may cause extrusion damage to the current collector at this position.

[0061] In one example, the projection of the first end of the first pressure-resistant coating exceeds the projection of the first end of the second pressure-resistant coating by 1 mm to 3 mm in the direction from the winding tail end to the winding head end. When the first end of the first pressure-resistant coating exceeds the first end of the second pressure-resistant coating, in addition to reducing the damage to the current collector, it can also reduce the error caused by large fluctuations in the production process due to the short length of the second pressure-resistant coating, which leads to the pressure-resistant coating being unable to effectively play a protective role.

[0062] In the present invention, in the third part, along the direction from the winding head end to the winding tail end, the size of the first positive electrode active coating exceeds the size L6 of the first compression-resistant coating by 1mm-5mm, for example, 1mm, 2mm, 3mm, 4mm or 5mm.

[0063] like Fig. 9 The schematic diagram of the dimension L6 is shown. It can be seen from the figure that in the third part 300, along the direction from the winding head end to the winding tail end, the dimension of the first positive electrode active coating exceeds the dimension of the first pressure-resistant coating by L6. By regulating L6, the problem of the battery cell being too wide in the width direction can be effectively avoided, and the thickness stacking of the first pressure-resistant coating in the straight area of ​​the battery cell can also be avoided, thereby increasing the thickness of the battery cell and causing an adverse effect on the energy density.

[0064] In the present invention, in the third part, along the direction from the winding head end to the winding tail end, the size of the first pressure-resistant coating exceeds the size L7 of the first positive electrode active coating by 1mm-10mm (for example, 1mm, 2mm, 3mm, 4mm, 5mm, 6mm, 7mm, 8mm, 9mm or 10mm); and the second end of the first pressure-resistant coating exceeds the boundary line of the second straight area and the first arc area by 1mm-5mm (for example, 1mm, 2mm, 3mm, 4mm or 5mm).

[0065] In one example, L8 is 1 mm-3 mm.

[0066] like Fig.10 The schematic diagram of the dimensions L7 and L8 is shown. It can be seen from the figure that in the third part 300, along the winding head end to the winding tail end, the dimension of the first compression coating exceeds the dimension of the first positive electrode active coating by L7; and the dimension of the second end of the first compression coating exceeding the boundary line of the first straight area 10 and the first arc area 20 by L8. This can avoid the thickness of the straight area of ​​the battery cell from increasing, which is beneficial to the energy density of the battery.

[0067] In the present invention, in the third part, along the direction from the winding head end to the winding tail end, a situation may exist that: the first pressure-resistant coating exceeds the first positive electrode active coating; another situation may exist that: the first positive electrode active coating exceeds the first pressure-resistant coating; another situation may exist that the size of the first pressure-resistant coating is equal to the size of the first positive electrode active coating.

[0068] In the present invention, in the battery cell, the projection of the second end of the first pressure-resistant coating in the third portion in the thickness direction of the battery cell and the projection of the second end of the second pressure-resistant coating in the third portion in the thickness direction of the battery cell do not overlap. When the two do not overlap, there is a relatively gentle transition at this position, which can avoid the overlap of thickness of the two ends on the same horizontal line, and further avoid the damage of the positive electrode sheet caused by extrusion.

[0069] In the present invention, the regional resistance of the first part is R1, the regional resistance of the second part where the first surface has the first pressure-resistant coating and the second surface has the second pressure-resistant coating is R2, and R1 and R2 satisfy: R2 / R1 is 1.05-1.2, for example, 1.05, 1.1, 1.15 or 1.2. The regional resistance of the third part where the first surface has the first pressure-resistant coating and the first positive electrode active coating and the second surface does not have the second pressure-resistant coating is R3; R1 and R3 satisfy: R3 / R1 is 0.5-0.8, for example, 0.5, 0.6, 0.7 or 0.8. R1 may be 100 mΩ-1500 mΩ, for example, 100 mΩ, 200 mΩ, 300 mΩ, 400 mΩ, 500 mΩ, 600 mΩ, 700 mΩ, 800 mΩ, 900 mΩ, 1000 mΩ, 1100 mΩ, 1200 mΩ, 1300 mΩ, 1400 mΩ or 1500 mΩ.

[0070] By further regulating the relationship between R1 and R2 as well as R1 and R3, it is possible to effectively avoid the increase in impedance in the region caused by the setting of the pressure-resistant coating (the first pressure-resistant coating and the second pressure-resistant coating), thereby causing the increase in polarization at this position, leading to analysis and a decrease in charging speed.

[0071] In the present invention, R1, R2 and R3 can be measured by conventional methods in the art, such as using a two-probe resistance meter.

[0072] In the present invention, the first pressure-resistant coating and the second pressure-resistant coating each independently include pressure-resistant particles, a conductive agent and a binder. The pressure-resistant particles include at least one of inorganic particles, organic particles, conductive metal particles, nano ternary particles, nano lithium cobalt oxide particles and nano lithium iron phosphate particles. The nano ternary particles are oxides containing at least three elements of the metal elements nickel, cobalt, manganese, aluminum and magnesium, for example, nano nickel cobalt manganese oxide particles and / or nano nickel cobalt aluminum oxide particles. The inorganic particles include at least one of magnesium oxide, aluminum oxide, tungsten oxide, titanium oxide, silicon dioxide, boehmite, conductive aluminum oxide and conductive magnesium oxide. The organic particles include epoxy resin, for example. The binder includes at least one of polyvinylidene fluoride (PVDF), acrylic modified PVDF, carboxylic acid modified PVDF, styrene butadiene rubber, acrylic modified styrene butadiene rubber, polymethyl methacrylate (PMMA) and polyimide (PI). The conductive agent includes at least one of conductive carbon black, graphene, single-walled carbon nanotubes and multi-walled carbon nanotubes.

[0073] In the present invention, based on the total mass of the first pressure-resistant coating, the content of the pressure-resistant particles is 50%-80% (for example, 50%, 60%, 70% or 80%), the content of the conductive agent is 5%-20% (for example, 5%, 10%, 15% or 20%), and the content of the binder is 10%-30% (for example, 10%, 20% or 30%).

[0074] In the present invention, based on the total mass of the second pressure-resistant coating, the content of the pressure-resistant particles is 50%-80% (for example, 50%, 60%, 70% or 80%), the content of the conductive agent is 5%-20% (for example, 5%, 10%, 15% or 20%), and the content of the binder is 10%-30% (for example, 10%, 20% or 30%).

[0075] In the present invention, the average particle size d of the compression-resistant particles is 0.02 μm-1 μm, for example, 0.02 μm, 0.05 μm, 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm or 1 μm.

[0076] In one example, the average particle size d of the compression-resistant particles is 0.05 μm-0.5 μm.

[0077] By regulating the average particle size d of the pressure-resistant particles and the content of each substance in the first pressure-resistant coating and the second pressure-resistant coating, it is beneficial to enhance the protective effect on the current collector.

[0078] In the present invention, the average particle size d of the compression-resistant particles can be obtained by testing by conventional methods in the art, such as using a scanning electron microscope (SEM), taking a cross section of the positive electrode sheet, measuring the particle sizes of at least 100 compression-resistant particles within a range of 20 μm×20 μm, and taking the average value.

[0079] In the present invention, the first positive electrode active coating and the second positive electrode active coating each independently include a positive electrode active material, and the particle size Dv90 of the positive electrode active material and the thickness H1 of the first positive electrode active coating satisfy: H1 / Dv90 is 1-5 (for example, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5 or 5), and the particle size Dv90 of the positive electrode active material and the thickness H2 of the second positive electrode active coating satisfy: H2 / Dv90 is 1-5 (for example, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5 or 5). When H1 / Dv90 and H2 / Dv90 are less than 1, coating blockage is likely to occur, which is not conducive to the coating process; at the same time, it is more likely to cause the problem of positive electrode active material particles being embedded in the current collector during rolling, thereby worsening the problem of current collector fracture. When H1 / Dv90 and H2 / Dv90 are greater than 5, the thickness of the positive electrode sheet will be too large, which is not conducive to the transmission of lithium ions.

[0080] In one embodiment, H1 / Dv90 is 1.4-2.5. H2 / Dv90 is 1.4-2.5.

[0081] In the present invention, the average particle size d of the compression-resistant particles and the particle size Dv90 of the positive electrode active material satisfy: Dv90 / d is 30-1700, for example, 30, 40, 50, 60, 70, 80, 90, 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 1100, 1200, 1300, 1400, 1500, 1600 or 1700. By regulating the relationship between the average particle size d of the compression-resistant particles and the particle size Dv90 of the positive electrode active material, the positive electrode active material can be prevented from piercing the compression-resistant coating (including the first compression-resistant coating and the second compression-resistant coating) during rolling, thereby improving the protective effect of the compression-resistant coating on the current collector.

[0082] In one example, Dv90 / d is 50-700.

[0083] In one example, Dv90 / d is 70-500.

[0084] In the present invention, the particle size Dv90 of the positive electrode active material is 25 μm-35 μm, for example, 25 μm, 26 μm, 27 μm, 28 μm, 29 μm, 30 μm, 31 μm, 32 μm, 33 μm, 34 μm or 35 μm. The particle size Dv90 of the positive electrode active material can be obtained by testing by conventional methods in the art, for example, using SEM, taking a cross section of the positive electrode sheet, measuring the particle size of at least 100 positive electrode active material particles within a range of 20 mm×20 mm, approximating them to a sphere, calculating the volume size, distinguishing Dv10, Dv50 and Dv90, and obtaining the Dv90 of the positive electrode active material.

[0085] In the present invention, the thickness of the first pressure-resistant coating and the thickness of the second pressure-resistant coating are independently 1 μm-15 μm, for example, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm or 15 μm.

[0086] In one example, the thickness of the first pressure-resistant coating layer and the thickness of the second pressure-resistant coating layer are each independently 4 μm-15 μm.

[0087] In the present invention, the thickness of the first pressure-resistant coating and the thickness of the second pressure-resistant coating can be tested by conventional methods in the field, such as using SEM, taking a cross-section of the positive electrode sheet along the thickness direction, randomly selecting at least 10 sites on the first pressure-resistant coating or the second pressure-resistant coating, measuring the thickness of the first pressure-resistant coating or the second pressure-resistant coating at each site, and taking the average value to obtain the thickness of the first pressure-resistant coating or the second pressure-resistant coating.

[0088] In the present invention, the positive electrode active material is embedded in the first compression coating to a depth of 1 μm-3 μm, such as 1 μm, 2 μm or 3 μm. The positive electrode active material is embedded in the second compression coating to a depth of 1 μm-3 μm, such as 1 μm, 2 μm or 3 μm.

[0089] like Fig.11 The cross-sectional SEM image of the positive electrode sheet in one example of the present invention is shown. It can be seen from the figure that the depth of the positive electrode active material embedded in the pressure-resistant coating (including the first pressure-resistant coating and the second pressure-resistant coating) is 1μm-3μm. Since the pressure-resistant coating (including the first pressure-resistant coating and the second pressure-resistant coating) can make the corners of the positive electrode active material particles embedded therein during rolling, therefore, by adjusting the depth of the positive electrode active material embedded in the pressure-resistant coating (the depth of the positive electrode active material embedded in the pressure-resistant coating can be adjusted by adjusting the rolling pressure), it is possible to avoid the positive electrode active material particles with corners in this area being squeezed with the current collector during rolling, causing damage to the current collector.

[0090] In the present invention, the depth of the positive electrode active material embedded in the first pressure-resistant coating and the depth of the positive electrode active material embedded in the second pressure-resistant coating can be tested by conventional methods in the field, for example, using SEM, measuring the vertical distance from the bottom of at least 10 positive electrode active material particles to the current collector under a 2mm×2mm cross-sectional electron microscope image, taking the average value, and then using the thickness of the first pressure-resistant coating or the thickness of the second pressure-resistant coating minus the above average value to obtain the depth of the positive electrode active material embedded in the first pressure-resistant coating and the depth of the positive electrode active material embedded in the second pressure-resistant coating.

[0091] In the present invention, the thickness of the current collector in the area formed by extending 4 mm in the direction of the winding head end and the winding tail end respectively with the boundary line of the double-sided coating area and the single-sided coating area as the starting point is H3, and the thickness of the current collector located in the fourth part is H4, and H3 and H4 satisfy: H3 / H4 is 0.8-1, for example, 0.8, 0.85, 0.9, 0.95 or 1.

[0092] In one example, H3 / H4 is 0.9-1.

[0093] When H3 / H4 is within a specific range, it indicates that the positive electrode active material is not in direct contact with the current collector near the junction of the single-sided and double-sided coating areas. At this time, the pressure-resistant coating (the first pressure-resistant coating and the second pressure-resistant coating) can protect the current collector from damage.

[0094] In the present invention, the positive electrode sheet may further include adhesive tape.

[0095] In one example, the adhesive tape covers the first positive electrode active coating at the winding end. In the winding direction, the size L9 of the adhesive tape covering the first positive electrode active coating is 3 mm-10 mm, for example, 3 mm, 4 mm, 5 mm, 6 mm, 7 mm, 8 mm, 9 mm or 10 mm. Fig.12 The schematic diagram of dimensions L9 and L10 is shown, from which it can be seen that the positive electrode sheet also includes adhesive tape 4. In the winding direction, the adhesive tape 4 covers the first positive electrode active coating at the winding tail end, and the dimension of the adhesive tape 4 covering the first positive electrode active coating is L9.

[0096] In one example, the adhesive tape covers the second positive electrode active coating at the winding end. In the winding direction, the size L10 of the adhesive tape covering the second positive electrode active coating is 3mm-10mm, for example, 3mm, 4mm, 5mm, 6mm, 7mm, 8mm, 9mm or 10mm. Fig.12 It can be seen that in the winding direction, the adhesive tape 4 covers the second positive electrode active coating at the winding tail end, and the size of the adhesive tape 4 covering the second positive electrode active coating is L10.

[0097] The purpose of covering the first positive electrode active coating at the end of the winding and the second positive electrode active coating at the end of the winding with adhesive tape is to cover the burrs generated at the end of the positive electrode active coating (including the first positive electrode active coating and the second positive electrode active coating) to prevent the burrs from piercing the diaphragm and causing a short circuit. When L9 and L10 are within a specific range, the adverse effect of the adhesive tape on the battery energy density can be reduced while ensuring that the risk of short circuit caused by burrs piercing the diaphragm is small.

[0098] In one example, in the third part, when the size of the first positive electrode active coating exceeds the size of the first pressure-resistant coating, in the winding direction, the size L11 of the adhesive paper covering the current collector is 5 mm-15 mm, for example, 5 mm, 6 mm, 7 mm, 8 mm, 9 mm, 10 mm, 11 mm, 12 mm, 13 mm, 14 mm or 15 mm. Fig.13 It is a schematic diagram of the size L11. It can be seen from the figure that in the third part, when the size of the first positive electrode active coating exceeds the size of the first compression-resistant coating, the size of the tape covering the current collector in the winding direction is L11.

[0099] When L11 is within a specific range, the adhesive tape can cross the arc area and adhere to the straight area on the adjacent side, thus avoiding the problem of the adhesive tape folding or falling off caused by the end of the adhesive tape being located in the arc area or at the junction of the arc area and the straight area.

[0100] In one example, the adhesive tape partially covers or completely covers the first pressure-resistant coating. The adhesive tape partially covers or completely covers the second pressure-resistant coating. Fig.14 The figure shows a schematic diagram of adhesive tape covering the first pressure-resistant coating layer and adhesive tape covering the second pressure-resistant coating layer. It can be seen from the figure that the adhesive tape completely covers the first pressure-resistant coating layer and the adhesive tape partially covers the second pressure-resistant coating layer. It can be understood that Fig.14 Only the case where the adhesive tape completely covers the first pressure-resistant coating layer and the case where the adhesive tape partially covers the second pressure-resistant coating layer are shown. The adhesive tape can also partially cover the first pressure-resistant coating layer. The adhesive tape can also completely cover the second pressure-resistant coating layer.

[0101] The area of ​​the positive electrode active coating covered by the adhesive tape is not charged and discharged, so there is no expansion force in this area. However, the positive electrode sheet near and / or on the opposite side of this area is still charged and discharged, and there is an expansion force, which makes the expansion force inside and outside the area different. In addition, the current collector is damaged due to the jumping of the roller during rolling, making it more likely for the current collector of the positive electrode sheet to break in this area.

[0102] In one example, the adhesive tape completely covers the first pressure-resistant coating and extends to the current collector. The adhesive tape completely covers the second pressure-resistant coating and extends to the current collector. In the winding direction, the size L12 of the adhesive tape on the current collector is 1 mm-5 mm, for example, 1 mm, 2 mm, 3 mm, 4 mm or 5 mm. Fig.15 Shown is a schematic diagram of size L12. It can be seen from the figure that the adhesive tape completely covers the first pressure-resistant coating and extends to the current collector, and the adhesive tape completely covers the second pressure-resistant coating and extends to the current collector. In the winding direction, the size of the adhesive tape located on the current collector is L12.

[0103] The adhesive tape completely covers the pressure-resistant coating (including the first pressure-resistant coating and the second pressure-resistant coating), which can effectively prevent the surface of the pressure-resistant coating from coming into contact with the electrolyte and causing side reactions, thereby preventing the risk of battery cell inflation. At the same time, the adhesive tape extends to the current collector, which can improve the structural stability of the battery cell.

[0104] In the present invention, the battery cell may further include a negative electrode sheet and a separator, and both the negative electrode sheet and the separator may be conventionally selected in the art.

[0105] A second aspect of the present invention provides a battery, comprising the battery cell described in the first aspect of the present invention.

[0106] It should be noted that the numerical expressions such as "first" and "second" in the present invention are only used to distinguish different substances or usages, and do not represent the difference in order.

[0107] The present invention will be described in detail below by way of examples. The examples described in the present invention are only a part of the examples of the present invention, rather than all of the examples. Based on the examples in the present invention, all other examples obtained by ordinary technicians in the field without creative work are within the scope of protection of the present invention.

[0108] In the following examples, unless otherwise specified, all materials used were commercially available analytical grade.

[0109] The following examples are provided to illustrate the batteries of the present invention.

[0110] Example 1

[0111] Prepare the battery as follows:

[0112] (1) Preparation of positive electrode

[0113] Nano-conductive alumina (average particle size d is 0.3 μm), conductive carbon black and polyvinylidene fluoride are uniformly mixed in a mass ratio of 80:8:12, and N-methylpyrrolidone (NMP) is added to prepare a compression coating slurry; the compression coating slurry is mixed in a mass ratio of 80:8:12, and N-methylpyrrolidone (NMP) is added to prepare a compression coating slurry; Fig.16 As shown, the positive electrode active coating slurry is uniformly coated on the surface of the aluminum foil and dried (forming a first pressure-resistant coating and a second pressure-resistant coating); lithium cobalt oxide (Dv90 is 29 μm), conductive carbon black and polyvinylidene fluoride are uniformly mixed in a mass ratio of 97.5:1:1.5, and NMP is added to prepare a positive electrode active coating slurry; the positive electrode active coating slurry is Fig.16 As shown, the aluminum foil coated with the compression-resistant coating after drying is evenly coated on the surface, dried, and compacted by a roller press (forming a first positive electrode active coating and a second positive electrode active coating), and adhesive tape (such as Fig.16 As shown), a positive electrode sheet is obtained;

[0114] Among them, Dv90 / d is about 96.7;

[0115] The thickness of the first pressure-resistant coating is 8 μm, and the thickness of the second pressure-resistant coating is 8 μm; the thickness H1 of the first positive electrode active coating is 45 μm, and H1 / Dv90 is about 1.55; the thickness H2 of the second positive electrode active coating is 45 μm, and H2 / Dv90 is about 1.55;

[0116] L1 is 4mm, L2 is 3mm, L3 is 4mm, L4 is 3mm, L5 is 1mm, and L6 is 3mm;

[0117] L9 is 6mm, L10 is 6mm, L11 is 10mm, and L12 is 5mm.

[0118] (2) Preparation of negative electrode sheet

[0119] Artificial graphite, silicon-carbon material, styrene-butadiene rubber and conductive carbon black are mixed evenly in a mass ratio of 85:10:3:2, and deionized water is added to prepare a negative electrode active coating slurry. The negative electrode active coating slurry is evenly coated on both sides of a copper foil, and after drying and roller pressing, a negative electrode sheet is obtained.

[0120] (3) Preparation of electrolyte

[0121] In a glove box filled with argon (H2O < 0.1 ppm, O2 < 0.1 ppm), ethylene carbonate, dimethyl carbonate and 1,2-propylene carbonate were mixed in a volume ratio of 1:1:1, 1 M lithium hexafluorophosphate was added, stirred evenly, and the electrolyte was obtained after passing the moisture and free acid tests.

[0122] (4) Preparation of batteries

[0123] The positive electrode sheet prepared in step (1), the separator (the two sides of the polyethylene base film are respectively a boehmite ceramic layer and a polyvinylidene fluoride adhesive layer) and the negative electrode sheet prepared in step (2) are wound to form a winding core, and the aluminum pole ear and the copper-plated nickel pole ear are welded after hot pressing; after liquid injection, the battery is formed, sorted, and OCV tested to obtain a battery.

[0124] The projection of the second end of the first pressure-resistant coating in the third portion in the thickness direction of the battery cell and the projection of the second end of the second pressure-resistant coating in the third portion in the thickness direction of the battery cell do not overlap. Fig.18 This is a partial SEM image of the positive electrode sheet in Example 1. The prepared battery is disassembled and the positive electrode sheet is taken out. It can be seen that the current collector of the positive electrode sheet provided with the first compression-resistant coating and the second compression-resistant coating is basically not damaged during the rolling process.

[0125] Example 2

[0126] The same method as in Example 1 is used, except that the positive electrode sheet is prepared in step (1), specifically as follows:

[0127] Boehmite (average particle size d is 0.5 μm), graphene and polyvinylidene fluoride are uniformly mixed in a mass ratio of 65:20:25, and NMP is added to prepare a compression coating slurry; the compression coating slurry is prepared according to Fig.16 As shown, the positive electrode active coating slurry is uniformly coated on the surface of the aluminum foil and dried; lithium cobalt oxide (Dv90 is 35 μm), conductive carbon black and polyvinylidene fluoride are uniformly mixed according to a mass ratio of 97.5:1:1.5, and NMP is added to prepare a positive electrode active coating slurry; the positive electrode active coating slurry is Fig.16 As shown, the aluminum foil coated with the pressure-resistant coating is evenly coated on the surface of the aluminum foil after drying, dried, compacted by a roller press, and attached with adhesive tape (such as Fig.16 As shown), a positive electrode sheet is obtained;

[0128] Among them, Dv90 / d is about 70;

[0129] The thickness of the first pressure-resistant coating is 4 μm, and the thickness of the second pressure-resistant coating is 4 μm; the thickness H1 of the first positive electrode active coating is 50 μm, and H1 / Dv90 is about 1.43; the thickness H2 of the second positive electrode active coating is 50 μm, and H2 / Dv90 is about 1.43;

[0130] L1 is 5mm, L2 is 4mm, L3 is 3mm, L4 is 2mm, L5 is 1mm, and L6 is 1mm;

[0131] L9 is 3mm, L10 is 3mm, L11 is 15mm, and L12 is 3mm.

[0132] Example 3

[0133] The same method as in Example 1 is used, except that the positive electrode sheet is prepared in step (1), specifically as follows:

[0134] Nano nickel-cobalt-manganese ternary NCM811 (average particle size d is 0.05 μm), single-walled carbon nanotubes and polymethyl methacrylate are mixed evenly in a mass ratio of 50:20:30, and NMP is added to prepare a compression coating slurry. The compression coating slurry is Fig.16 As shown, the positive electrode active coating slurry is uniformly coated on the surface of the aluminum foil and dried; lithium cobalt oxide (Dv90 is 25 μm), conductive carbon black and polyvinylidene fluoride are uniformly mixed according to a mass ratio of 97.5:1:1.5, and NMP is added to prepare a positive electrode active coating slurry; the positive electrode active coating slurry is Fig.16 As shown, the aluminum foil coated with the pressure-resistant coating is evenly coated on the surface of the aluminum foil after drying, dried, compacted by a roller press, and attached with adhesive tape (such as Fig.16 As shown), a positive electrode sheet is obtained;

[0135] Among them, Dv90 / d is about 500;

[0136] The thickness of the first pressure-resistant coating is 15 μm, and the thickness of the second pressure-resistant coating is 15 μm; the thickness H1 of the first positive electrode active coating is 60 μm, and H1 / Dv90 is about 2.4; the thickness H2 of the second positive electrode active coating is 60 μm, and H2 / Dv90 is about 2.4;

[0137] L1 is 6mm, L2 is 3mm, L3 is 5mm, L4 is 1mm, L5 is 3mm, L6 is 5mm;

[0138] L9 is 10mm, L10 is 3mm, L11 is 5mm, and L12 is 1mm.

[0139] Example 4

[0140] Used to verify the impact of changes to "H1 / Dv90 and H2 / Dv90".

[0141] The method is carried out in accordance with Example 1, except that H1 / Dv90 and H2 / Dv90 are adjusted by changing the thickness H1 of the first positive electrode active coating and the thickness H2 of the second positive electrode active coating. Specifically:

[0142] The thickness H1 of the first positive electrode active coating layer is 30 μm, and H1 / Dv90 is approximately 1.03. The thickness H2 of the second positive electrode active coating layer is 30 μm, and H2 / Dv90 is approximately 1.03.

[0143] Example 5 Group

[0144] This group of embodiments is used to verify the impact of the change of "Dv90 / d".

[0145] This group of examples is carried out with reference to Example 2 and Example 3, except that Dv90 / d is regulated by changing the average particle size d of the compression-resistant particles, as follows:

[0146] Example 5a is carried out in accordance with Example 2, except that the compression-resistant particles are replaced with nano nickel-cobalt-manganese ternary NCM811 (average particle size d is 0.05 μm) of the same mass, wherein Dv90 / d is 700;

[0147] Example 5b is carried out with reference to Example 3, except that the compression-resistant particles are replaced with boehmite of the same mass (average particle size d is 0.5 μm), wherein Dv90 / d is 50.

[0148] Example 6 Group

[0149] This group of embodiments is used to verify the influence of changes in “the depth of the positive electrode active material embedded in the first pressure-resistant coating layer and the depth of the positive electrode active material embedded in the second pressure-resistant coating layer”.

[0150] This group of examples is carried out with reference to Example 1, except that the depth of the positive electrode active material embedded in the first compression-resistant coating and the depth of the positive electrode active material embedded in the second compression-resistant coating are regulated by changing the roller press pressure, as follows:

[0151] In Example 6a, the depth of embedding the positive electrode active material into the first compression-resistant coating is less than 1 μm, and the depth of embedding the positive electrode active material into the second compression-resistant coating is less than 1 μm;

[0152] In Example 6b, the depth to which the positive electrode active material is embedded in the first compression-resistant coating is greater than 3 μm, and the depth to which the positive electrode active material is embedded in the second compression-resistant coating is greater than 3 μm.

[0153] Example 7

[0154] Used to verify the impact of the change of "the projection of the first end of the first pressure resistant coating exceeds the projection of the first end of the second pressure resistant coating".

[0155] Refer to Example 1, except that when applying the first pressure-resistant coating slurry and the second pressure-resistant coating slurry, the projection of the first end of the second pressure-resistant coating is made to exceed the projection of the first end of the first pressure-resistant coating by 1 mm, specifically: L1 is 3 mm, and L2 is 4 mm.

[0156] Example 8 Group

[0157] This group of embodiments is used to verify the impact of changes in "L1 and / or L2".

[0158] This group of examples is carried out with reference to Example 1, except that L1 and / or L2 are changed, as follows:

[0159] Example 8a, L1 is 15 mm, L2 is 3 mm, and L5 is 12 mm;

[0160] In Example 8b, L1 is 3 mm, L2 is 15 mm, and L5 is 12 mm.

[0161] Example 9

[0162] Used to verify the impact of changes to "L3".

[0163] Refer to Example 1, except that L3 is changed, specifically: L3 is 15 mm.

[0164] Example 10

[0165] Used to verify the impact of changes to “L4”.

[0166] Refer to Example 1, except that L4 is changed, specifically: L4 is 5 mm.

[0167] Embodiment 11

[0168] Used to verify the impact of the change in "whether the projection of the second end of the first pressure-resistant coating located in the third part in the direction of the thickness of the battery cell and the projection of the second end of the second pressure-resistant coating located in the third part in the direction of the thickness of the battery cell coincide with each other".

[0169] Refer to Example 1, except that by adjusting L2, the projection of the second end of the first pressure-resistant coating located in the third part in the direction of the thickness of the battery cell and the projection of the second end of the second pressure-resistant coating located in the third part in the direction of the thickness of the battery cell are overlapped.

[0170] Example 12 Group

[0171] This group of examples is carried out with reference to Example 1, except that Fig.17 The compression coating slurry and the positive electrode active coating slurry are coated in the manner shown, as follows:

[0172] In embodiment 12a, L1 is 4 mm, L2 is 3 mm, L3 is 4 mm, L4 is 3 mm, L5 is 1 mm, L7 is 6 mm, and L8 is 2 mm;

[0173] In embodiment 12b, L1 is 4 mm, L2 is 3 mm, L3 is 4 mm, L4 is 3 mm, L5 is 1 mm, L7 is 2 mm, and L8 is 1 mm;

[0174] In embodiment 12c, L1 is 4 mm, L2 is 3 mm, L3 is 4 mm, L4 is 3 mm, L5 is 1 mm, L7 is 10 mm, and L8 is 3 mm.

[0175] Embodiment 13

[0176] The process is carried out with reference to Example 1, except that L2 is changed so that in the second part, the projections of the first end of the first pressure resistant coating and the first end of the second pressure resistant coating in the thickness direction overlap, wherein L1 is 4 mm and L2 is 4 mm.

[0177] The embodiment 1-5 group and the embodiment 7-13 all satisfy: the positive electrode active material is embedded in the first compression-resistant coating to a depth of 1 μm-3 μm, and the positive electrode active material is embedded in the second compression-resistant coating to a depth of 1 μm-3 μm.

[0178] Comparative Example 1

[0179] The method is carried out in accordance with Example 1, except that the first pressure-resistant coating layer and the second pressure-resistant coating layer are not provided (ie, the pressure-resistant coating slurry is not applied during the preparation of the positive electrode sheet). Fig.19 This is a local SEM image of the positive electrode sheet in Example 1. The prepared battery is disassembled and the positive electrode sheet is taken out. It can be seen that the positive electrode sheet without the first compression coating and the second compression coating has a significant damage to its current collector during the rolling process.

[0180] Comparative Example 2

[0181] Refer to Example 1, except that the size and position of the first pressure-resistant coating and the second pressure-resistant coating are changed. Specifically, the pressure-resistant coating slurry is only coated in the extension direction of the boundary line between the single-sided coating area and the double-sided coating area toward the winding head end (that is, there is no first pressure-resistant coating and the second pressure-resistant coating along the direction of the boundary line between the single-sided coating area and the double-sided coating area toward the winding tail end).

[0182] Comparative Example 3

[0183] Refer to Example 1, except that the size and position of the first pressure-resistant coating and the second pressure-resistant coating are changed. Specifically, the pressure-resistant coating slurry is only coated in the extension direction of the boundary line between the single-sided coating area and the double-sided coating area toward the winding tail end (that is, there is no first pressure-resistant coating and the second pressure-resistant coating along the direction of the boundary line between the single-sided coating area and the double-sided coating area toward the winding head end).

[0184] Comparative Example 4

[0185] The same is carried out with reference to Example 1, except that L1 is changed, wherein L1 is 1 mm.

[0186] Comparative Example 5

[0187] The same procedure is carried out with reference to Example 1, except that L1 and L2 are changed at the same time, wherein L1 is 1 mm and L2 is 1 mm.

[0188] Test Case I

[0189] (1) Current collector thickness test

[0190] The batteries prepared in the examples and comparative examples were disassembled, and the thicknesses H3 and H4 were measured respectively. The results are recorded in Table 1.

[0191] (2) Regional resistance test

[0192] The batteries prepared in the examples and comparative examples were disassembled, the positive electrode sheets were taken out, and the regional resistances R1, R2 and R3 were tested respectively. The results were rounded and recorded in Table 1.

[0193] Table 1

[0194]

[0195]

[0196] Test Case II

[0197] (1) Energy density test

[0198] The batteries prepared in the examples and comparative examples were subjected to energy density tests, and the specific test methods are as follows:

[0199] The battery was charged at 0.7C to the upper voltage limit (4.3V), the cut-off current was 0.025C, and discharged at 0.5C to the lower voltage limit (2.5V). The discharge capacity and operating voltage were output. The length, width and thickness of the battery were measured using a measuring instrument. The energy density was calculated using the formula: Energy density = discharge capacity × operating voltage / (length × width × thickness). The results are recorded in Table 2.

[0200] (2) Cycle test and short circuit rate test

[0201] The batteries prepared in the examples and comparative examples were subjected to cycle tests and short circuit rate tests. The specific test methods are as follows:

[0202] The battery was subjected to charge and discharge cycle test at 1.5C charge rate, 0.7C discharge rate, 3.0V-4.5V voltage window (using blue electric test equipment) for 800 cycles. The capacity retention rate was calculated using the first discharge capacity C1 and the 800th cycle discharge capacity C800: C800 / C1×100%. The thickness T1 of the battery charged to 3.9V for the first time (tested using PPG test equipment) and the thickness T2 of the battery charged to 4.5V when the battery was cycled for 800 cycles were used to calculate the thickness expansion rate (T2 / T1-1)×100%. The capacity retention rate and thickness expansion rate are recorded in Table 2. During the cycle, the battery was monitored for short circuit (100,000 batteries were tested), and the short circuit rate was recorded in Table 2. After the cycle was completed, the battery was disassembled to observe whether the current collector (from the boundary between the single-sided coating area and the double-sided coating area to the end of the winding) was damaged or broken. The severity was from light to heavy: no damage, slight damage, damage, and breakage. Generally speaking, if the current collector is not broken but damaged, the cracks will extend in the width direction of the current collector of the positive electrode sheet (that is, the extension direction of the positive electrode tab). Therefore, the definition is: if there is no crack from the boundary line of the single-sided coating area and the double-sided coating area to the winding tail end, it is considered undamaged; if the longest crack generated in the above part has a length / width of the current collector of less than or equal to 10%, it is considered slightly damaged; if the longest crack generated in the above part has a length / width of the current collector of greater than 10% and less than or equal to 50%, it is considered damaged; if the current collector breaks, it is considered broken, and the results are recorded in Table 2.

[0203] Table 2

[0204]

[0205] It can be seen from Table 2 that the battery of the present invention can significantly improve the current collector damage caused during the preparation process of the battery and the current collector breakage problem during the cycle process compared with the comparative example. In addition, since the current collector of the battery of the comparative example breaks during the cycle process, the burrs generated by the current collector breakage will pierce the diaphragm, thereby causing the battery to short-circuit. Therefore, the short-circuit rate of the battery of the present invention is significantly lower than that of the battery of the comparative example.

[0206] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A battery cell, characterized in that: A positive electrode sheet is included, wherein the positive electrode sheet includes a current collector, and the current collector has a first surface and a second surface which are arranged opposite to each other along the thickness direction of the battery core; The positive electrode sheet includes a double-sided coating area and a single-sided coating area along the winding direction; Along the winding direction, the positive electrode sheet includes a first portion, a second portion and a third portion which are connected in sequence, the first portion and the second portion are located in the double-sided coating area, and at least part of the third portion is located in the single-sided coating area; In the first part, the first surface is provided with a first positive electrode active coating, and the second surface is provided with a second positive electrode active coating; In the second part, the first surface is provided with a first compression-resistant coating and the first positive electrode active coating in a stacked manner, the first compression-resistant coating is close to the current collector, and the first positive electrode active coating is away from the current collector; the second surface is provided with a second compression-resistant coating and the second positive electrode active coating in a stacked manner, the second compression-resistant coating is close to the current collector, and the second positive electrode active coating is away from the current collector; In the third part, the first surface is provided with the first pressure-resistant coating and the first positive electrode active coating in a stacked manner, the first pressure-resistant coating is close to the current collector, and the first positive electrode active coating is away from the current collector; The second surface is provided with the second pressure-resistant coating; Taking the boundary line between the single-sided coating area and the double-sided coating area as the starting point, the first compression-resistant coating extends at least 3 mm toward the winding head end of the positive electrode sheet, and at least 3 mm toward the winding tail end of the positive electrode sheet; Taking the boundary line between the single-sided coating area and the double-sided coating area as the starting point, the second compression-resistant coating extends at least 3 mm toward the winding head end of the positive electrode sheet, and at least 3 mm toward the winding tail end of the positive electrode sheet; The first pressure-resistant coating and the second pressure-resistant coating each independently include pressure-resistant particles, a conductive agent and a binder, wherein the pressure-resistant particles include at least one of magnesium oxide, aluminum oxide, tungsten oxide, titanium oxide, silicon dioxide, boehmite, conductive aluminum oxide, conductive magnesium oxide, epoxy resin, conductive metal particles, nano ternary particles, nano lithium cobalt oxide particles and nano lithium iron phosphate particles; In the second portion, projections of the first end of the first pressure-resistant coating layer and the first end of the second pressure-resistant coating layer in the thickness direction do not overlap, and the first end is an end close to the first end of the positive electrode sheet winding.

2. The battery cell according to claim 1, wherein: The positive electrode sheet further includes a fourth portion, the fourth portion does not include the first pressure-resistant coating, the second pressure-resistant coating, the first positive electrode active coating, and the second positive electrode active coating; along the direction from the winding tail end to the winding head end of the positive electrode sheet, the battery cell has a first straight area, a first arc area, a second straight area, a second arc area, a third straight area, and a third arc area connected in sequence; At least part of the fourth portion is located in the first straight region; At least part of the third portion is located in the first arc region, the second straight region, the second arc region, the third straight region and the third arc region.

3. The battery cell according to claim 1 or 2, wherein: Taking the boundary line between the single-sided coating area and the double-sided coating area as the starting point, the dimension L1 of the first compression-resistant coating extending toward the winding head end of the positive electrode sheet is 3 mm to 15 mm; And / or, starting from the boundary line between the single-sided coating area and the double-sided coating area, a dimension L2 of the second compression-resistant coating extending toward the winding head end of the positive electrode sheet is 3 mm to 15 mm; And / or, starting from the boundary line between the single-sided coating area and the double-sided coating area, a dimension L3 of the second pressure-resistant coating extending toward the winding tail end of the positive electrode sheet is 3 mm-15 mm.

4. The battery cell according to claim 3, wherein: L1 is 3mm-6mm; and / or, L2 is 3 mm to 6 mm; And / or, L3 is 3mm-5mm.

5. The battery cell according to claim 2, wherein: Along the winding direction, the second end of the second pressure-resistant coating exceeds the third arc area and extends to the third straight area. The dimension L4 of the second end of the second pressure-resistant coating exceeding the boundary line between the third straight area and the third arc area is 1mm-5mm; the second end is the end close to the winding tail end.

6. The battery cell according to claim 5, wherein: L4 is 1mm-3mm.

7. The battery cell according to claim 1 or 2, wherein: A distance L5 between projections of the first end of the first pressure-resistant coating and the first end of the second pressure-resistant coating in a thickness direction of the battery core is 1 mm-12 mm.

8. The battery cell according to claim 7, wherein: The projection of the first end of the first pressure-resistant coating exceeds the projection of the first end of the second pressure-resistant coating by 1 mm to 3 mm in the direction from the winding tail end to the winding head end.

9. The battery cell according to claim 2, wherein: In the third part, along the direction from the winding head end to the winding tail end, the size of the first positive electrode active coating exceeds the size L6 of the first pressure-resistant coating by 1 mm to 5 mm; And / or, in the third part, along the direction from the winding head end to the winding tail end, the size of the first pressure-resistant coating exceeds the size L7 of the first positive electrode active coating by 1mm-10mm; and the second end of the first pressure-resistant coating exceeds the size L8 of the boundary line between the first straight area and the first arc area by 1mm-5mm; the second end is the end close to the winding tail end.

10. The battery cell according to claim 9, wherein: L8 is 1mm-3mm.

11. The battery cell according to claim 1 or 2, wherein: The projection of the second end of the first pressure-resistant coating located in the third part in the direction of the thickness of the battery cell and the projection of the second end of the second pressure-resistant coating located in the third part in the direction of the thickness of the battery cell do not overlap, and the second end is the end close to the tail end of the winding.

12. The battery cell according to claim 1 or 2, wherein: The regional resistance of the first part is R1, the regional resistance of the area where the first surface has the first pressure-resistant coating and the second surface has the second pressure-resistant coating in the second part is R2, and the regional resistance of the area where the first surface has the first pressure-resistant coating and the first positive electrode active coating and the second surface does not have the second pressure-resistant coating in the third part is R3; R1 and R2 satisfy: R2 / R1 is 1.05-1.2; And / or, R1 and R3 satisfy: R3 / R1 is 0.5-0.8; And / or, R1 is 100mΩ-1500mΩ.

13. The battery cell according to claim 1 or 2, wherein: The average particle size d of the compression-resistant particles is 0.02 μm-1 μm.

14. The battery cell according to claim 13, wherein: d is 0.05μm-0.5μm.

15. The battery cell according to claim 1 or 2, wherein: The first positive electrode active coating and the second positive electrode active coating each independently include a positive electrode active material, the particle size Dv90 of the positive electrode active material and the thickness H1 of the first positive electrode active coating satisfy: H1 / Dv90 is 1-5; and the particle size Dv90 of the positive electrode active material and the thickness H2 of the second positive electrode active coating satisfy: H2 / Dv90 is 1-5; And / or, the first pressure-resistant coating layer and the second pressure-resistant coating layer each independently include pressure-resistant particles, and the average particle size d of the pressure-resistant particles and the particle size Dv90 of the positive electrode active material satisfy: Dv90 / d is 30-1700.

16. The battery cell according to claim 15, wherein: Dv90 / d is 70-500.

17. The battery cell according to claim 1 or 2, wherein: The thickness of the first pressure-resistant coating layer and the thickness of the second pressure-resistant coating layer are each independently 1 μm-15 μm; And / or, the first positive electrode active coating comprises a positive electrode active material, and the positive electrode active material is embedded in the first compression-resistant coating to a depth of 1 μm-3 μm; And / or, the second positive electrode active coating layer comprises a positive electrode active material, and the positive electrode active material is embedded in the second pressure-resistant coating layer to a depth of 1 μm-3 μm.

18. The battery cell according to claim 2, wherein: The thickness of the current collector in the area formed by extending 4 mm in the direction of the winding head end and the winding tail end respectively with the boundary line between the double-sided coating area and the single-sided coating area as the starting point is H3, and the thickness of the current collector located in the fourth part is H4, and H3 and H4 satisfy: H3 / H4 is 0.8-1.

19. The battery cell according to claim 18, wherein: H3 / H4 is 0.9-1.

20. The battery cell according to claim 1 or 2, wherein: The positive electrode sheet also includes adhesive paper; The adhesive tape covers the first positive electrode active coating layer at the winding tail end; And / or, the adhesive tape covers the second positive electrode active coating layer at the winding tail end; and / or, in the third part, when the size of the first positive electrode active coating exceeds the size of the first pressure-resistant coating, in the winding direction, the size L11 of the adhesive paper covering the current collector is 5 mm-15 mm; And / or, the adhesive tape partially covers or completely covers the first pressure-resistant coating layer; And / or, the adhesive tape partially covers or completely covers the second pressure-resistant coating; And / or, the adhesive tape completely covers the first pressure-resistant coating layer and extends to the current collector; And / or, the adhesive tape completely covers the second pressure-resistant coating layer and extends to the current collector.

21. The battery cell according to claim 20, wherein: In the winding direction, the size L9 of the adhesive paper covering the first positive electrode active coating is 3 mm-10 mm; and / or, in the winding direction, a size L10 of the adhesive paper covering the second positive electrode active coating is 3 mm to 10 mm; And / or, in the winding direction, a size L12 of the adhesive tape on the current collector is 1 mm-5 mm.

22. A battery, characterized in that: The battery comprises the battery cell according to any one of claims 1 to 21.

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