Battery cell and battery

Abstract

The present disclosure relates to the field of batteries, and specifically relates to a battery cell and a battery comprising the battery cell. The battery cell comprises a positive electrode sheet; in a winding direction, the positive electrode sheet comprises a double-sided coating area and a single-sided coating area; in the winding direction, the positive electrode sheet comprises a first portion, a second portion and a third portion which are successively connected, the first portion and the second portion being located in the double-sided coating area, and at least part of the third portion being located in the single-sided coating area; with a boundary line between the single-sided coating area and the double-sided coating area as a starting point, a first pressure-resistant coating extends at least 3 mm towards a winding head end of the positive electrode sheet, and extends at least 3 mm towards a winding tail end of the positive electrode sheet; and a second pressure-resistant coating extends at least 3 mm towards the winding head end of the positive electrode sheet, and extends at least 3 mm towards the winding tail end of the positive electrode sheet. The battery of the present disclosure can significantly ameliorate the problems of slight cracking during rolling and fracture during cycling of positive electrode current collectors.

Description

Cells and batteries Technical Field

[0001] This disclosure relates to the field of battery technology, and more specifically to a battery cell and a battery including the battery cell.

[0002] Public background

[0003] In recent years, lithium-ion batteries have gained popularity in the market due to their high energy density, long cycle life, and environmental friendliness. However, current lithium-ion batteries face the problem of range anxiety caused by rapid power consumption. To improve the energy density of lithium-ion batteries, researchers often increase the cell thickness during design to increase battery capacity, while simultaneously increasing the compaction density of the positive and negative electrodes to reduce electrode thickness, thereby further improving the battery's energy density. However, this design often leads to slight cracks in the positive electrode of wound batteries during rolling, and problems with current collector breakage during battery charge-discharge cycles.

[0004] Public content

[0005] The purpose of this disclosure is to overcome the aforementioned problems in the prior art and to provide a battery cell and a battery including the battery cell. The battery of this disclosure can significantly improve the problem of slight cracks appearing in the positive electrode current collector of the wound battery cell during rolling and breakage during cycling.

[0006] To address the issue of slight cracks appearing in the positive electrode current collector of wound cells during rolling and subsequent breakage during battery charge-discharge cycles in related technologies, the inventors of this disclosure conducted extensive research and discovered that, due to the structural characteristics of wound lithium-ion batteries, the electrodes have single-sided and double-sided coated areas, as well as a stepped area transitioning from the double-sided to the single-sided coated area. During rolling, the electrodes (especially the positive electrode) may jump in this stepped area, causing overpressure on the positive electrode current collector in this stepped area, resulting in slight cracks. Furthermore, due to the volume expansion of the battery during charge-discharge cycles, the forces on both sides of the boundary between the single-sided and double-sided coated areas are uneven (the positive electrode in the single-sided area only experiences charging and discharging on one side, while the positive electrode in the double-sided area experiences charging and discharging on both sides). With the continued uneven force, the squeezing effect on the positive electrode current collector in the stepped area transitioning from the double-sided to the single-sided coated area will further intensify, ultimately leading to breakage of the positive electrode current collector. Based on the above findings, the inventors of this disclosure have conducted extensive targeted research and, by setting a tough, pressure-resistant coating on the surface of the positive electrode current collector in the stepped area where the double-sided coating area of ​​the positive electrode sheet transitions to the single-sided coating area, can significantly improve the problem of current collector breakage caused by uneven forces on the positive electrode sheet during the rolling process and battery cycle overcharging.

[0007] This disclosure provides a battery cell, including a positive electrode sheet, the positive electrode sheet including a current collector, the current collector having a first surface and a second surface disposed opposite to each other along the thickness direction of the battery cell; the positive electrode sheet includes a double-sided coating region and a single-sided coating region along a winding direction; along the winding direction, the positive electrode sheet includes a first portion, a second portion and a third portion connected in sequence, the first portion and the second portion being located in the double-sided coating region, and at least a portion of the third portion being located in the single-sided coating region; in the first portion, the first surface is provided with a first positive active coating, and the second surface is provided with a second positive active coating; in the second portion, the first surface is provided with a first pressure-resistant coating and the first positive active coating, the first pressure-resistant coating being close to the current collector, and the first positive active coating being away from the current collector; the second surface... The first surface is provided with a second pressure-resistant coating and a second positive electrode active coating, the second pressure-resistant coating being close to the current collector and the second positive electrode active coating being 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, the first pressure-resistant coating being close to the current collector and the first positive electrode active coating being 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 3 mm towards the first end of the positive electrode sheet winding and at least 3 mm towards the last 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 3 mm towards the first end of the positive electrode sheet winding and at least 3 mm towards the last end of the positive electrode sheet winding.

[0008] A second aspect of this disclosure provides a battery comprising the battery cell described in the first aspect of this disclosure.

[0009] Through the above technical solution, this disclosure has at least the following advantages compared with the prior art: the battery of this disclosure can significantly improve the step area of ​​the positive electrode sheet transitioning from the double-sided coating area to the single-sided coating area, and the problem of slight cracks appearing in the positive electrode current collector during rolling and breakage during cycling.

[0010] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein. Attached Figure Description

[0011] Figure 1 shows a schematic diagram of the positive electrode in an example of this disclosure.

[0012] Figure 2 shows a schematic diagram of the distribution of the positive electrode in an example of this disclosure.

[0013] Figure 3 shows a schematic diagram of the battery cell.

[0014] Figure 4 shows a schematic diagram of the positive electrode in an example of this disclosure.

[0015] Figure 5 shows a schematic diagram of the positive electrode in an example of this disclosure.

[0016] Figure 6 shows a schematic diagram of dimensions L1, L2, and L3.

[0017] Figure 7 shows a schematic diagram of dimension L4.

[0018] Figure 8 shows a schematic diagram of dimension L5; wherein, Figure 8(a) shows the case where the first end of the first compressive coating extends beyond the first end of the second compressive coating; and Figure 8(b) shows the case where the first end of the second compressive coating extends beyond the first end of the first compressive coating.

[0019] Figure 9 shows a schematic diagram of dimension L6.

[0020] Figure 10 shows a schematic diagram of dimensions L7 and L8.

[0021] Figure 11 shows a cross-sectional scanning electron microscope (SEM) image of the positive electrode in an example of this disclosure.

[0022] Figure 12 shows a schematic diagram of dimensions L9 and L10.

[0023] Figure 13 shows a schematic diagram of dimension L11.

[0024] Figure 14 shows a schematic diagram of adhesive tape covering the first compressive strength coating and adhesive tape covering the second compressive strength coating.

[0025] Figure 15 shows a schematic diagram of dimension L12.

[0026] Figure 16 shows a schematic diagram of the cross-section of the positive electrode in Example 1.

[0027] Figure 17 shows a schematic diagram of the cross-section of the positive electrode sheet in Example 12 (the adhesive tape is not shown).

[0028] Figure 18 shows a partial SEM image of the positive electrode in Example 1.

[0029] Figure 19 shows a partial SEM image of the positive electrode in Comparative Example 1.

[0030] Explanation of reference numerals in the attached figures: 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; 1000: Double-sided coating area; 2000: Single-sided coating area; 100: First part; 200: Second part; 300: Third part; 400: Fourth part; 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 Implementation

[0031] The following provides a detailed description of specific embodiments of this disclosure. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit this disclosure.

[0032] This disclosure provides a battery cell in a first aspect. The battery cell may include a positive electrode sheet. The positive electrode sheet may include a current collector having a first surface and a second surface disposed 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 coated region and a single-sided coated region. Along the winding direction, the positive electrode sheet may include a first portion, a second portion, and a third portion connected in sequence. The first portion and the second portion may be located in the double-sided coated region, and at least a portion of the third portion may be located in the single-sided coated region. Figure 1 shows a schematic diagram of a positive electrode sheet in an example of this disclosure. As can be seen from the figure, the positive electrode sheet may include a current collector 1 having a first surface and a second surface disposed 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 includes a double-sided coated region 1000 and a single-sided coated region 2000; along the winding direction, the positive electrode sheet includes a first portion 100, a second portion 200, and a third portion 300 connected in sequence. The first portion 100 and the second portion 200 are located in the double-sided coating area 1000, and part of the third portion 300 is located in the single-sided coating area 2000.

[0033] It is understandable that Figure 1 only shows the case where part of the third portion is located in the single-sided coating area; it is also possible that all of the third portion 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), all of the third portion is located in the single-sided coating area (i.e., the case shown in Figure 5).

[0034] In this disclosure, the terms "single-sided coating area" and "double-sided coating area" have their conventional meanings in the art. A single-sided coating area refers to an area where only one surface (the first surface or the second surface) of the current collector has an active material coating; a double-sided coating area refers to an area where both surfaces (the first surface and the second surface) of the current collector have an active material coating.

[0035] In this disclosure, in the first part, a first positive electrode active coating is disposed on the first surface, and a second positive electrode active coating is disposed on the second surface. In the second part, a first pressure-resistant coating and the first positive electrode active coating are stacked on the first surface, with the first pressure-resistant coating close to the current collector and the first positive electrode active coating away from the current collector; a second pressure-resistant coating and the second positive electrode active coating are stacked on the second surface, with the second pressure-resistant coating close to the current collector and the second positive electrode active coating 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, with the first pressure-resistant coating close to the current collector and the first positive electrode active coating away from the current collector; the second surface is disposed with the second pressure-resistant coating. Figure 2 shows a schematic diagram of the positive electrode sheet in an example of this disclosure. As can be seen from the figure, in the first part 100, the first surface of the current collector 1 is disposed with a first positive electrode active coating 2-1, and the second surface of the current collector 1 is disposed with a second positive electrode active coating 2-2. In the second part 200, a first pressure-resistant coating 3-1 and a first positive electrode active coating 2-1 are stacked on the first surface of the current collector 1, 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; a second pressure-resistant coating 3-2 and a second positive electrode active coating 2-2 are stacked on the second surface of the current collector 1, 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, a first pressure-resistant coating 3-1 and a first positive electrode active coating 2-1 are stacked on the first surface of the current collector 1, 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; a second pressure-resistant coating 3-2 is provided on the second surface of the current collector 1.

[0036] In this disclosure, 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 3 mm towards the beginning of the positive electrode winding and at least 3 mm towards the end of the positive electrode 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 3 mm towards the beginning of the positive electrode winding and at least 3 mm towards the end of the positive electrode winding.

[0037] In this disclosure, 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 do not overlap, wherein the first end is the end close to the beginning of the positive electrode winding.

[0038] Because the positive electrode in a wound cell has both single-sided and double-sided coated areas, it is prone to damage to the current collector and microcracks during rolling. The solution disclosed above has significantly improved the current collector breakage problem. Furthermore, the inventors of this disclosure have discovered that, due to the characteristics of the winding structure, the arc area has a greater outward expansion and compression force than the flat area. The area near the outer ring of the wound cell is the single-sided coated area of ​​the positive electrode. Due to the characteristics of the winding structure, the closer to the outer ring of the wound cell, the more uneven the force at the arc, the greater the outward expansion force and the smaller the inward binding force. The stepped area transitioning between the single and double-sided coated areas of the external positive electrode (i.e., near the single and double-sided coated areas) is located at the third arc near the outer ring (along the direction from the tail end to the head end of the positive electrode winding). The combined effects of these two deterioration factors make the electrode more prone to breakage at the arc near the outer ring and the adjacent plane of the wound cell; at the same time, the boundary between the single-sided and double-sided coating areas will also break due to uneven stress. Based on this, the inventors of this disclosure have made further improvements to the above technical solution, placing the pressure-resistant coating at the boundary between the single-sided and double-sided coating areas and at least at the third arc (along the direction from the tail end to the head end of the positive electrode winding), which can further improve the problem of positive electrode current collector breakage caused by uneven stress during cycling.

[0039] In this disclosure, the positive electrode sheet may further include a fourth portion 400. For example, in FIG1, the fourth portion 400 includes the current collector (i.e., the fourth portion 400 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). In FIG2, the fourth portion 400 includes the 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).

[0040] In this disclosure, along the direction from the tail end to the head end of the positive electrode winding, the battery cell has a first flat region, a first arc region, a second flat region, a second arc region, a third flat region, and a third arc region connected in sequence. Figure 3 shows a schematic diagram of the battery cell. It can be understood that the battery cell is formed by sequentially stacking and winding a positive electrode, a separator, a negative electrode, and a separator, resulting in the structure shown in Figure 3 where both ends are arc regions, the middle is a flat region, and the arc regions at both ends are connected to the two ends of the flat region. As can be seen from the figure, along the direction from the tail end to the head end of the winding, the positive electrode is sequentially located in the outermost flat region on the upper side of the battery cell in Figure 3 (i.e., the dashed box 10 in the figure), the outermost arc region on the left side, the outermost flat region on the lower side (i.e., the dashed box 30 in the figure), the outermost arc region on the right side, and the upper flat region adjacent to the outermost region (i.e., the dashed box 50 in the figure), and so on. Further details are omitted here. Meanwhile, in order to distinguish between the flat and arc regions, along the direction from the tail end to the head end of the positive electrode winding, the outermost flat region on the upper side of the cell is defined as the first flat region (i.e., 10 in Figure 3), the outermost arc region on the left side is defined as the first arc region, the outermost flat region on the lower side is defined as the second flat region (i.e., 30 in Figure 3), the outermost arc region on the right side is defined as the second arc region, and the flat region on the upper side adjacent to the outermost region is defined as the third flat region (i.e., 50 in Figure 3), and so on.

[0041] In this disclosure, at least a portion of the fourth portion is located in the first flat region. Figure 4 shows a schematic diagram of the positive electrode in an example of this disclosure. As can be seen from the figure, the fourth portion 400 is located in the first flat region 10 (i.e., all of the fourth portion 400 is located in the first flat region 10). Figure 5 shows a schematic diagram of the positive electrode in an example of this disclosure. As can be seen from the figure, the fourth portion 400 is located in both the first flat region 10 and the first arc region 20 (i.e., a portion of the fourth portion 400 is located in the first flat region 10).

[0042] In this disclosure, at least a portion of the third portion is located within the first arc region, the second straight region, the second arc region, the third straight region, and the third arc region. As shown in Figure 5, the third portion 300 is located within 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. As shown in Figure 4, the third portion is located within the first straight region 10, 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.

[0043] In this disclosure, along the direction from the tail end to the head end of the positive electrode winding, the battery cell has a first flat region, a first arc region, a second flat region, a second arc region, a third flat region, a third arc region, and a fourth flat region connected in sequence. Along the winding direction, the boundary line between the single-sided coating area and the double-sided coating area may extend beyond the boundary line between the fourth flat region and the third arc region, or it may not extend beyond the boundary line between the fourth flat region and the third arc region. When the boundary line between the single-sided coating area and the double-sided coating area does not extend beyond the boundary line between the fourth flat region and the third arc region, the third portion may also be located within the fourth flat region (i.e., a portion of the third portion is located within the fourth flat region).

[0044] In this disclosure, 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 towards the first 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.

[0045] In one example, L1 is 3mm-6mm.

[0046] Figure 6 shows a schematic diagram of dimensions L1, L2, and L3. As can be seen from the figure, starting from the boundary line between the single-sided and double-sided coated areas, the dimension of the first pressure-resistant coating extending towards the beginning of the positive electrode sheet is L1. When L1 is within a specific range, it can prevent excessive length of the first pressure-resistant coating from overlapping with the tab adhesive paper; or prevent excessive length of the first pressure-resistant coating from causing thickness stacking, thereby affecting the cell thickness and thus the battery's energy density.

[0047] In this disclosure, 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 first 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.

[0048] In one example, L2 is 3mm-6mm.

[0049] As shown in Figure 6, taking the boundary between the single-sided and double-sided coated areas as the starting point, the dimension by which the second pressure-resistant coating extends towards the beginning of the positive electrode sheet is L2. Similarly, when L2 is within a specific range, it can reduce the adverse effects on battery energy density while ensuring safety performance.

[0050] In this disclosure, 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 towards the 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.

[0051] In one example, L3 is 3mm-5mm.

[0052] As shown in Figure 6, taking the boundary between the single-sided and double-sided coated areas as the starting point, the dimension by which the second pressure-resistant coating extends towards the end of the positive electrode winding is L3. Similarly, when L3 is within a specific range, it can reduce the adverse effects on battery energy density while ensuring safety performance.

[0053] In this disclosure, along the winding direction, the second end of the second pressure-resistant coating extends beyond the third arc region and into the third straight region. The dimension L4 of the second end of the second pressure-resistant coating extending beyond the boundary line between the third straight region and the third arc region is 1mm-5mm, for example, 1mm, 2mm, 3mm, 4mm or 5mm. The second end is the end near the winding tail end.

[0054] In one example, L4 is 1mm-3mm.

[0055] Figure 7 shows a schematic diagram of dimension L4. As can be seen from the figure, along the winding direction, the second end of the second pressure-resistant coating (the end of the second pressure-resistant coating near the winding tail end) extends beyond the third arc region 60 and into the third straight region 50. The dimension by which the second end extends beyond the boundary line between the third straight region 50 and the third arc region 60 is L4. Under the premise that L3 meets a specific range, simultaneously controlling the position of the second end of the second pressure-resistant coating to extend into the third straight region and beyond the boundary line between the third straight region and the third arc region by a certain dimension can further improve the risk of current collector breakage in the positive electrode sheet. The reason is that when the second end of the second pressure-resistant coating is located in the third arc region, there will be an area that is not protected, which can still cause breakage of the current collector in the positive electrode sheet. Furthermore, when the second end is located at the boundary line between the third arc region and the third straight region, the stress at this location is relatively high, and the pressure-resistant coating is prone to forming steps; therefore, there is also a risk of current collector breakage in this location. When the second end of the second pressure-resistant coating extends beyond the boundary line between the third straight area and the third arc area by a certain dimension, there will be a better transition, making it less prone to stress accumulation and improving the problem of current collector breakage in the positive electrode sheet.

[0056] In this disclosure, the 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 1mm-12mm, for example, 1mm, 2mm, 3mm, 4mm, 5mm, 6mm, 7mm, 8mm, 9mm, 10mm, 11mm or 12mm.

[0057] In one example, L5 is 1mm-3mm.

[0058] Figure 8 shows a schematic diagram of dimension L5; Figure 8(a) shows the case where the first end of the first pressure-resistant coating extends beyond the first end of the second pressure-resistant coating; Figure 8(b) shows the case where the first end of the second pressure-resistant coating extends beyond the first end of the first pressure-resistant coating. As can be seen from the figures, the distance between the projections of the first ends of the first and second pressure-resistant coatings in the thickness direction is L5. By adjusting L5, the first ends of the first and second pressure-resistant coatings are not in the same position, thus avoiding greater extrusion shear force during rolling, which could cause damage to the current collector at that location.

[0059] In one example, the projection of the first end of the first pressure-resistant coating extends 1mm-3mm beyond the projection of the first end of the second pressure-resistant coating in the direction from the tail end to the head end of the winding. When the first end of the first pressure-resistant coating extends beyond the first end of the second pressure-resistant coating, in addition to reducing damage to the current collector, it also reduces the error caused by large fluctuations in the production process due to the shorter length of the second pressure-resistant coating, which could prevent the pressure-resistant coating from effectively providing protection.

[0060] In this disclosure, in the third part, along the direction from the beginning to the end of the winding, 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, for example, 1 mm, 2 mm, 3 mm, 4 mm or 5 mm.

[0061] As shown in Figure 9, a schematic diagram of dimension L6 is provided. It can be seen from the figure that in the third part 300, along the direction from the beginning to the end of the winding, the size of the first positive electrode active coating exceeds the size of the first pressure-resistant coating by L6. By adjusting L6, the problem of the cell being too wide in the width direction can be effectively avoided. At the same time, it can also prevent the first pressure-resistant coating from stacking in the flat area of ​​the cell, thus avoiding an increase in cell thickness and an adverse effect on energy density.

[0062] In this disclosure, in the third part, along the direction from the beginning to the end of the winding, the size of the first pressure-resistant coating exceeds the size L7 of the first positive electrode active coating by 1mm-10mm (e.g., 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 (e.g., 1mm, 2mm, 3mm, 4mm, or 5mm).

[0063] In one example, L8 is 1mm-3mm.

[0064] Figure 10 shows a schematic diagram of dimensions L7 and L8. As can be seen from the figure, in the third part 300, along the direction from the beginning to the end of the winding, the size of the first pressure-resistant coating exceeds the size of the first positive electrode active coating by L7; and the second end of the first pressure-resistant coating exceeds the boundary line between the first straight region 10 and the first arc region 20 by L8. This design avoids increasing the thickness of the straight region of the cell, which is beneficial to the energy density of the battery.

[0065] In this disclosure, in the third part, along the direction from the beginning of the winding to the end of the winding, one possible situation is that the first pressure-resistant coating extends beyond the first positive electrode active coating; another possible situation is that the first positive electrode active coating extends beyond the first pressure-resistant coating; yet another possible situation is that the size of the first pressure-resistant coating is equal to the size of the first positive electrode active coating.

[0066] In this disclosure, in the battery cell, the projection of the second end of the first pressure-resistant coating located in the third portion onto the thickness direction of the battery cell, and the projection of the second end of the second pressure-resistant coating located in the third portion onto the thickness direction of the battery cell, do not coincide. When they do not coincide, there is a relatively gentle transition at this position, which can avoid the two ends from overlapping in thickness on the same horizontal line, and can further avoid damage to the positive electrode sheet caused by compression.

[0067] In this disclosure, the area resistance of the first portion is R1, and the area resistance of the second portion where the first surface has the first pressure-resistant coating and the second surface has the second pressure-resistant coating is R2. R1 and R2 satisfy the following condition: R2 / R1 is 1.05-1.2, for example, 1.05, 1.1, 1.15, or 1.2. The area resistance of the third portion 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 the following condition: R3 / R1 is 0.5-0.8, for example, 0.5, 0.6, 0.7, or 0.8. R1 can be 100mΩ-1500mΩ, for example, 100mΩ, 200mΩ, 300mΩ, 400mΩ, 500mΩ, 600mΩ, 700mΩ, 800mΩ, 900mΩ, 1000mΩ, 1100mΩ, 1200mΩ, 1300mΩ, 1400mΩ or 1500mΩ.

[0068] By further adjusting the relationship between R1 and R2, as well as between R1 and R3, it is possible to effectively avoid the increase in impedance in this region caused by the setting of the pressure-resistant coating (first pressure-resistant coating and second pressure-resistant coating), which would lead to increased polarization at this location and cause problems such as lithium plating and decreased charging speed.

[0069] In this disclosure, R1, R2, and R3 can be tested using methods conventional in the art, such as using a two-probe resistor.

[0070] In this disclosure, the first and second anti-compression coatings each independently comprise anti-compression particles, a conductive agent, and a binder. The anti-compression particles include at least one of inorganic particles, organic particles, conductive metal particles, ternary nanoparticles, lithium cobalt oxide nanoparticles, and lithium iron phosphate nanoparticles. The ternary nanoparticles are oxides containing at least three of the metal elements nickel, cobalt, manganese, aluminum, and magnesium, for example, including lithium nickel cobalt manganese oxide nanoparticles and / or lithium nickel cobalt aluminum oxide nanoparticles. The inorganic particles include, for example, at least one of magnesium oxide, aluminum oxide, tungsten oxide, titanium oxide, silicon dioxide, boehmite, conductive alumina, and conductive magnesium oxide. The organic particles include, for example, epoxy resin. The binder includes, for example, at least one of polyvinylidene fluoride (PVDF), acrylic acid-modified PVDF, carboxylic acid-modified PVDF, styrene-butadiene rubber, acrylic acid-modified styrene-butadiene rubber, polymethyl methacrylate (PMMA), and polyimide (PI). The conductive agent includes, for example, at least one of conductive carbon black, graphene, single-walled carbon nanotubes, and multi-walled carbon nanotubes.

[0071] In this disclosure, based on the total mass of the first anti-compression coating, the content of the anti-compression particles is 50%-80% (e.g., 50%, 60%, 70% or 80%), the content of the conductive agent is 5%-20% (e.g., 5%, 10%, 15% or 20%), and the content of the binder is 10%-30% (e.g., 10%, 20% or 30%).

[0072] In this disclosure, based on the total mass of the second anti-compression coating, the content of the anti-compression particles is 50%-80% (e.g., 50%, 60%, 70% or 80%), the content of the conductive agent is 5%-20% (e.g., 5%, 10%, 15% or 20%), and the content of the binder is 10%-30% (e.g., 10%, 20% or 30%).

[0073] In this disclosure, the average particle size d of the compressive strength 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.

[0074] In one example, the average particle size d of the compressive particles is 0.05 μm to 0.5 μm.

[0075] By adjusting the average particle size d of the pressure-resistant particles and the content of each substance in the first and second pressure-resistant coatings, it is beneficial to improve the protection of the current collector.

[0076] In this disclosure, the average particle size d of the pressure-resistant particles can be obtained by conventional methods in the art, such as using a scanning electron microscope (SEM), taking a cross-section of the positive electrode, measuring the particle size of at least 100 pressure-resistant particles in a range of 20 μm × 20 μm, and taking the average value.

[0077] In this disclosure, 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 the following: H1 / Dv90 is 1-5 (e.g., 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 the following: H2 / Dv90 is 1-5 (e.g., 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 detrimental to the coating process; at the same time, the problem of positive electrode active material particles embedding into the current collector during rolling is more likely to occur, thereby aggravating the problem of current collector breakage. When H1 / Dv90 and H2 / Dv90 are greater than 5, the positive electrode thickness will be too large, which is not conducive to the transport of lithium ions.

[0078] In one example, H1 / Dv90 is 1.4-2.5. H2 / Dv90 is 1.4-2.5.

[0079] In this disclosure, the average particle size d of the pressure-resistant particles and the particle size Dv90 of the positive electrode active material satisfy the following: 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 adjusting the relationship between the average particle size d of the pressure-resistant particles and the particle size Dv90 of the positive electrode active material, the positive electrode active material is less likely to puncture the pressure-resistant coating (including the first and second pressure-resistant coatings) during rolling, thereby improving the protective effect of the pressure-resistant coating on the current collector.

[0080] In one instance, Dv90 / d is 50-700.

[0081] In one instance, Dv90 / d is 70-500.

[0082] In this disclosure, the particle size Dv90 of the positive electrode active material is 25μm-35μm, for example, 25μm, 26μm, 27μm, 28μm, 29μm, 30μm, 31μm, 32μm, 33μm, 34μm or 35μm. The particle size Dv90 of the positive electrode active material can be tested by conventional methods in the art, such as 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 20mm×20mm range, approximating them as spherical, calculating the volume, distinguishing Dv10, Dv50 and Dv90, and obtaining the Dv90 of the positive electrode active material.

[0083] In this disclosure, the thickness of the first anti-compression coating and the thickness of the second anti-compression coating are each independently 1μm-15μm, for example, 1μm, 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm or 15μm.

[0084] In one example, the thickness of the first compressive coating and the thickness of the second compressive coating are each independently 4 μm-15 μm.

[0085] In this disclosure, the thickness of the first pressure-resistant coating and the thickness of the second pressure-resistant coating can be obtained by conventional methods in the art, 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 thickness of the second pressure-resistant coating.

[0086] In this disclosure, the depth to which the positive electrode active material is embedded in the first pressure-resistant coating is 1 μm-3 μm, for example, 1 μm, 2 μm, or 3 μm. The depth to which the positive electrode active material is embedded in the second pressure-resistant coating is 1 μm-3 μm, for example, 1 μm, 2 μm, or 3 μm.

[0087] Figure 11 shows a cross-sectional SEM image of the positive electrode sheet in an example of this disclosure. The image shows that the depth to which the positive electrode active material is embedded in the pressure-resistant coating (including the first and second pressure-resistant coatings) is 1 μm-3 μm. Since the pressure-resistant coating (including the first and second pressure-resistant coatings) allows the sharp edges of the positive electrode active material particles to be embedded within it during rolling, by adjusting the embedding depth of the positive electrode active material in the pressure-resistant coating (which can be adjusted by regulating the rolling pressure), damage to the current collector caused by the sharp edges of the positive electrode active material particles in this area being squeezed by the current collector during rolling can be avoided.

[0088] In this disclosure, 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 obtained by conventional methods in the art, such as using SEM. Under a 2mm×2mm cross-sectional electron microscope image, the vertical distance from the bottom of at least 10 positive electrode active material particles to the current collector is measured, the average value is taken, and then the thickness of the first pressure-resistant coating or the thickness of the second pressure-resistant coating is subtracted from the 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.

[0089] In this disclosure, the thickness of the current collector in the region formed by extending 4 mm from the boundary line between the double-sided coating area and the single-sided coating area towards the beginning and end of the winding respectively is H3, and the thickness of the current collector in the fourth part is H4. H3 and H4 satisfy: H3 / H4 is 0.8-1, for example, 0.8, 0.85, 0.9, 0.95 or 1.

[0090] In one instance, H3 / H4 is 0.9-1.

[0091] When H3 / H4 is within a specific range, it indicates that near the junction of the single and double-sided coating areas, the positive electrode active material does not directly contact the current collector. 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.

[0092] In this disclosure, the positive electrode sheet may also include adhesive paper.

[0093] In one example, the adhesive tape covers the first positive electrode active coating located at the winding tail end. In the winding direction, the size L9 of the adhesive tape covering the first positive electrode active coating is 3mm-10mm, for example, 3mm, 4mm, 5mm, 6mm, 7mm, 8mm, 9mm, or 10mm. Figure 12 shows a schematic diagram of sizes L9 and L10. As can be seen from the figure, the positive electrode sheet also includes adhesive tape 4. In the winding direction, the adhesive tape 4 covers the first positive electrode active coating located at the winding tail end, and the size of the adhesive tape 4 covering the first positive electrode active coating is L9.

[0094] In one example, the adhesive tape covers the second positive electrode active coating located at the end of the winding. 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. As can be seen from Figure 12, in the winding direction, the adhesive tape 4 covers the second positive electrode active coating located at the end of the winding, and the size of the adhesive tape 4 covering the second positive electrode active coating is L10.

[0095] Covering the first and second positive electrode active coatings at the winding tail with adhesive tape aims to cover the burrs generated at the ends of the positive electrode active coatings (including the first and second positive electrode active coatings) to prevent burrs from piercing the separator and causing a short circuit. When L9 and L10 are within a specific range, the adverse effects 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 separator is low.

[0096] 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, the size L11 of the adhesive paper covering the current collector in the winding direction is 5mm-15mm, for example, 5mm, 6mm, 7mm, 8mm, 9mm, 10mm, 11mm, 12mm, 13mm, 14mm, or 15mm. Figure 13 shows a schematic diagram of the size L11. As can be seen from the figure, in the third part, when the size of the first positive electrode active coating exceeds the size of the first pressure-resistant coating, the size of the adhesive paper covering the current collector in the winding direction is L11.

[0097] When L11 is within a specific range, it allows the adhesive tape to cross the arc area and adhere to the flat area on the adjacent side. This avoids the problem of the adhesive tape folding or falling off due to the end of the tape being located in the arc area or at the junction of the arc area and the flat area.

[0098] In one example, the adhesive tape partially or completely covers the first compression-resistant coating. The adhesive tape also partially or completely covers the second compression-resistant coating. Figure 14 shows a schematic diagram of adhesive tape covering the first and second compression-resistant coatings. As can be seen from the figure, the adhesive tape completely covers the first compression-resistant coating, and partially covers the second compression-resistant coating. It is understood that Figure 14 only shows the cases where the adhesive tape completely covers the first compression-resistant coating and partially covers the second compression-resistant coating. The adhesive tape can also partially cover the first compression-resistant coating. The adhesive tape can also completely cover the second compression-resistant coating.

[0099] The area covered by the adhesive tape of the positive electrode active coating does not undergo charging and discharging, so there is no expansion force in this area. However, the positive electrode sheet near and / or on the opposite side of this area will still undergo charging and discharging, and there will be an expansion force. This results in different expansion forces inside and outside this area. In addition, the current collector damage caused by the roller jumping during rolling makes the current collector of the positive electrode sheet more likely to break in this area.

[0100] In one example, the adhesive tape completely covers the first pressure-resistant coating and extends to the current collector. The adhesive tape also completely covers the second pressure-resistant coating and extends to the current collector. In the winding direction, the dimension L12 of the adhesive tape located on the current collector is 1mm-5mm, for example, 1mm, 2mm, 3mm, 4mm, or 5mm. Figure 15 shows a schematic diagram of dimension L12. As can be seen from the figure, 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 dimension of the adhesive tape located on the current collector is L12.

[0101] The adhesive tape completely covers the pressure-resistant coating (including the first and second pressure-resistant coatings), which can effectively prevent the pressure-resistant coating surface from coming into contact with the electrolyte and causing side reactions, thus avoiding the risk of the battery cell bulging; at the same time, the adhesive tape extends to the current collector, which can improve the structural stability of the battery cell.

[0102] In this disclosure, the battery cell may further include a negative electrode and a separator, both of which can be conventional choices in the art.

[0103] A second aspect of this disclosure provides a battery comprising the battery cell described in the first aspect of this disclosure.

[0104] It should be noted that the numerical designations such as "first" and "second" in this disclosure are only used to distinguish different substances or methods of use, and do not represent a difference in order.

[0105] The present disclosure will be described in detail below through embodiments. The embodiments described in this disclosure are only some embodiments of this disclosure, and not all embodiments. Based on the embodiments in this disclosure, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this disclosure.

[0106] In the following examples, unless otherwise specified, all materials used are commercially available analytical grade.

[0107] The following examples illustrate the battery of this disclosure.

[0108] Example 1

[0109] The battery is prepared according to the following method:

[0110] (1) Preparation of positive electrode sheet

[0111] Nano-conductive alumina (average particle size d = 0.3 μm), conductive carbon black, and polyvinylidene fluoride (PVDF) were mixed uniformly at a mass ratio of 80:8:12, and N-methylpyrrolidone (NMP) was added to prepare a pressure-resistant coating slurry. The pressure-resistant coating slurry was uniformly coated on the surface of aluminum foil as shown in Figure 16 and dried (forming a first and a second pressure-resistant coating). Lithium cobalt oxide (Dv90 = 29 μm), conductive carbon black, and PVDF were mixed uniformly at a mass ratio of 97.5:1:1.5, and NMP was added to prepare a positive electrode active coating slurry. The positive electrode active coating slurry was uniformly coated on the surface of the dried aluminum foil coated with the pressure-resistant coating as shown in Figure 16, dried, and compacted with a roller press (forming a first and a second positive electrode active coating), and then adhesive tape was attached (as shown in Figure 16) to obtain the positive electrode sheet.

[0112] Among them, Dv90 / d is approximately 96.7;

[0113] The thickness of the first anti-compression coating is 8 μm, and the thickness of the second anti-compression coating is 8 μm; the thickness H1 of the first positive electrode active coating is 45 μm, and H1 / Dv90 is approximately 1.55; the thickness H2 of the second positive electrode active coating is 45 μm, and H2 / Dv90 is approximately 1.55.

[0114] L1 is 4mm, L2 is 3mm, L3 is 4mm, L4 is 3mm, L5 is 1mm, and L6 is 3mm;

[0115] L9 is 6mm, L10 is 6mm, L11 is 10mm, and L12 is 5mm.

[0116] (2) Preparation of negative electrode sheet

[0117] Artificial graphite, silicon carbide, styrene-butadiene rubber, and conductive carbon black are mixed evenly in a mass ratio of 85:10:3:2. 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. After drying and compaction by a roller press, a negative electrode sheet is obtained.

[0118] (3) Preparation of electrolyte

[0119] In an argon-filled glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), ethylene carbonate, dimethyl carbonate, and 1,2-propylene glycol carbonate were mixed evenly in a volume ratio of 1:1:1. 1M lithium hexafluorophosphate was added, and the mixture was stirred evenly. After passing the tests for moisture and free acid, the electrolyte was obtained.

[0120] (4) Battery fabrication

[0121] The positive electrode sheet and separator (boehmite ceramic layer and polyvinylidene fluoride adhesive layer on both sides of the polyethylene film) prepared in step (1) and the negative electrode sheet prepared in step (2) are wound together to form a core. After hot pressing, aluminum tabs and copper-plated nickel tabs are welded together. After liquid injection, the battery is formed, sorted and tested by OCV to obtain the battery.

[0122] In this figure, the projection of the second end of the first pressure-resistant coating in the third part onto the cell thickness direction does not coincide with the projection of the second end of the second pressure-resistant coating in the third part onto the cell thickness direction. Figure 18 is a partial SEM image of the positive electrode sheet in Example 1. The prepared battery is disassembled, and the positive electrode sheet is removed. It can be seen that the current collector of the positive electrode sheet with the first and second pressure-resistant coatings is basically undamaged during the rolling process.

[0123] Example 2

[0124] The procedure is the same as in Example 1, except that step (1) involves preparing the positive electrode sheet, as follows:

[0125] Boehmite (average particle size d = 0.5 μm), graphene, and polyvinylidene fluoride were mixed uniformly at a mass ratio of 65:20:15, and NMP was added to prepare a pressure-resistant coating slurry. The pressure-resistant coating slurry was uniformly coated on the surface of aluminum foil as shown in Figure 16 and dried. Lithium cobalt oxide (Dv90 = 35 μm), conductive carbon black, and polyvinylidene fluoride were mixed uniformly at a mass ratio of 97.5:1:1.5, and NMP was added to prepare a positive electrode active coating slurry. The positive electrode active coating slurry was uniformly coated on the surface of the dried aluminum foil coated with the pressure-resistant coating as shown in Figure 16, dried, compacted with a roller press, and then adhesive tape was attached (as shown in Figure 16) to obtain the positive electrode sheet.

[0126] Among them, Dv90 / d is approximately 70;

[0127] The thickness of the first anti-compression coating is 4 μm, and the thickness of the second anti-compression coating is 4 μm; the thickness H1 of the first positive electrode active coating is 50 μm, and H1 / Dv90 is approximately 1.43; the thickness H2 of the second positive electrode active coating is 50 μm, and H2 / Dv90 is approximately 1.43.

[0128] L1 is 5mm, L2 is 4mm, L3 is 3mm, L4 is 2mm, L5 is 1mm, and L6 is 1mm.

[0129] L9 is 3mm, L10 is 3mm, L11 is 15mm, and L12 is 3mm.

[0130] Example 3

[0131] The procedure is the same as in Example 1, except that step (1) involves preparing the positive electrode sheet, as follows:

[0132] Nano-nickel-cobalt-manganese ternary NCM811 (average particle size d of 0.05 μm), single-walled carbon nanotubes, and polymethyl methacrylate were mixed uniformly at a mass ratio of 50:20:30. NMP was added to prepare a pressure-resistant coating slurry. The pressure-resistant coating slurry was uniformly coated on the surface of aluminum foil as shown in Figure 16 and dried. Lithium cobalt oxide (Dv90 of 25 μm), conductive carbon black, and polyvinylidene fluoride were mixed uniformly at a mass ratio of 97.5:1:1.5. NMP was added to prepare a positive electrode active coating slurry. The positive electrode active coating slurry was uniformly coated on the surface of the dried aluminum foil coated with the pressure-resistant coating as shown in Figure 16. The foil was dried, compacted with a roller press, and then adhesive tape was attached (as shown in Figure 16) to obtain the positive electrode sheet.

[0133] Among them, Dv90 / d is approximately 500;

[0134] The thickness of the first anti-compression coating is 15 μm, the thickness of the second anti-compression coating is 15 μm; the thickness H1 of the first positive electrode active coating is 60 μm, H1 / Dv90 is approximately 2.4, the thickness H2 of the second positive electrode active coating is 60 μm, and H2 / Dv90 is approximately 2.4.

[0135] L1 is 6mm, L2 is 3mm, L3 is 5mm, L4 is 1mm, L5 is 3mm, and L6 is 5mm;

[0136] L9 is 10mm, L10 is 3mm, L11 is 5mm, and L12 is 1mm.

[0137] Example 4

[0138] Used to verify the impact of changes to "H1 / Dv90 and H2 / Dv90".

[0139] The procedure 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:

[0140] The thickness H1 of the first positive electrode active coating is 30 μm, and H1 / Dv90 is approximately 1.03. The thickness H2 of the second positive electrode active coating is 30 μm, and H2 / Dv90 is approximately 1.03.

[0141] Example 5 group

[0142] This set of examples is used to verify the impact of the change in "Dv90 / d".

[0143] This set of embodiments refers to Embodiments 2 and 3, the difference being that Dv90 / d is adjusted by changing the average particle size d of the compressive strength particles, as detailed below:

[0144] Example 5a was carried out with reference to Example 2, except that the compressive particles were replaced with the same mass of nano-nickel-cobalt-manganese ternary NCM811 (average particle size d is 0.05 μm), wherein Dv90 / d is 700;

[0145] Example 5b was carried out with reference to Example 3, except that the compressive particles were replaced with the same mass of boehmite (average particle size d of 0.5 μm), wherein Dv90 / d was 50.

[0146] Example 6 group

[0147] This set of embodiments is used to verify the impact of changes in "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".

[0148] This set of embodiments refers to Embodiment 1, except that 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 are controlled by changing the pressure of the roller press, as follows:

[0149] In Example 6a, the positive electrode active material is embedded to a depth of less than 1 μm in the first pressure-resistant coating, and the positive electrode active material is embedded to a depth of less than 1 μm in the second pressure-resistant coating.

[0150] In Example 6b, the positive electrode active material is embedded to a depth greater than 3 μm in the first pressure-resistant coating, and the positive electrode active material is embedded to a depth greater than 3 μm in the second pressure-resistant coating.

[0151] Example 7

[0152] This is used to verify the impact of the change that "the projection of the first end of the first compressive coating exceeds the projection of the first end of the second compressive coating".

[0153] The process is carried out in accordance with Example 1, except that when applying the first and second compressive coating slurries, the projection of the first end of the second compressive coating exceeds the projection of the first end of the first compressive coating by 1 mm. Specifically, L1 is 3 mm and L2 is 4 mm.

[0154] Example 8 group

[0155] This set of examples is used to verify the impact of changes to "L1 and / or L2".

[0156] This set of embodiments is based on Embodiment 1, except that L1 and / or L2 are changed, as follows:

[0157] Example 8a, L1 is 15mm, L2 is 3mm, and L5 is 12mm;

[0158] In Example 8b, L1 is 3mm, L2 is 15mm, and L5 is 12mm.

[0159] Example 9

[0160] Used to verify the impact of changes to "L3".

[0161] The procedure was carried out in accordance with Example 1, except that L3 was changed; specifically, L3 was 15 mm.

[0162] Example 10

[0163] Used to verify the impact of changes to "L4".

[0164] The procedure was carried out in accordance with Example 1, except that L4 was changed; specifically, L4 was 5 mm.

[0165] Example 11

[0166] The effect of the change used to verify whether the projection of the second end of the first compressive coating in the third part in the cell thickness direction coincides with the projection of the second end of the second compressive coating in the third part in the cell thickness direction is valid.

[0167] The same procedure is followed as in Example 1, except that by adjusting L2, the projection of the second end of the first pressure-resistant coating in the third part in the cell thickness direction coincides with the projection of the second end of the second pressure-resistant coating in the third part in the cell thickness direction.

[0168] Example 12 group

[0169] This set of embodiments is based on Embodiment 1, except that the anti-compression coating slurry and the positive electrode active coating slurry are applied in the manner shown in Figure 17, as detailed below:

[0170] Example 12a: L1 is 4mm, L2 is 3mm, L3 is 4mm, L4 is 3mm, L5 is 1mm, L7 is 6mm, and L8 is 2mm;

[0171] Example 12b: L1 is 4mm, L2 is 3mm, L3 is 4mm, L4 is 3mm, L5 is 1mm, L7 is 2mm, and L8 is 1mm.

[0172] In Example 12c, L1 is 4mm, L2 is 3mm, L3 is 4mm, L4 is 3mm, L5 is 1mm, L7 is 10mm, and L8 is 3mm.

[0173] Example 13

[0174] The same procedure is followed as in Example 1, except that L2 is changed so that in the second part, the projections of the first end of the first anti-compression coating and the first end of the second anti-compression coating in the thickness direction overlap, wherein L1 is 4 mm and L2 is 4 mm.

[0175] Examples 1-5 and Examples 7-13 all satisfy the following: the depth of the positive electrode active material embedded in the first pressure-resistant coating is 1μm-3μm, and the depth of the positive electrode active material embedded in the second pressure-resistant coating is 1μm-3μm.

[0176] Comparative Example 1

[0177] The process was carried out in accordance with Example 1, except that the first and second pressure-resistant coatings were not provided (i.e., no pressure-resistant coating slurry was applied during the preparation of the positive electrode). Figure 19 is a partial SEM image of the positive electrode in Comparative Example 1. The prepared battery was disassembled and the positive electrode was removed. It can be seen that the current collector of the positive electrode without the first and second pressure-resistant coatings was significantly damaged during the rolling process.

[0178] Comparative Example 2

[0179] The same procedure is followed as in Example 1, except that the size and position of the first and second anti-compression coatings are changed. Specifically, the anti-compression coating slurry is applied only in the direction extending from the boundary between the single-sided coating area and the double-sided coating area toward the beginning of the winding (i.e., there is no first or second anti-compression coating in the direction from the boundary between the single-sided coating area and the double-sided coating area toward the end of the winding).

[0180] Comparative Example 3

[0181] The same procedure is followed as in Example 1, except that the size and position of the first and second anti-compression coatings are changed. Specifically, the anti-compression coating slurry is applied only in the direction extending from the boundary line between the single-sided coating area and the double-sided coating area toward the winding tail end (i.e., there is no first or second anti-compression coating in the direction from the boundary line between the single-sided coating area and the double-sided coating area toward the winding head end).

[0182] Comparative Example 4

[0183] The procedure was carried out in accordance with Example 1, except that L1 was changed to 1 mm.

[0184] Comparative Example 5

[0185] The same procedure was followed as in Example 1, except that L1 and L2 were changed simultaneously, with L1 being 1 mm and L2 being 1 mm.

[0186] Test Case I

[0187] (1) Current collector thickness test

[0188] 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.

[0189] (2) Zone resistance test

[0190] The batteries prepared in the examples and comparative examples were disassembled, the positive electrode was removed, and the regional resistances R1, R2 and R3 were tested respectively. The results were rounded and recorded in Table 1.

[0191] Table 1

[0192] Test Case II

[0193] (1) Energy density test

[0194] The energy density of the batteries prepared in the examples and comparative examples was tested using the following specific methods:

[0195] Charge the battery at 0.7C to the upper limit voltage (4.3V), cut off the current at 0.025C, and discharge it at 0.5C to the lower limit voltage (2.5V). Output the discharge capacity and operating voltage. Use measuring instruments to measure the length, width and thickness of the battery. Calculate the energy density using the formula: Energy density = Discharge capacity × Operating voltage / (Length × Width × Thickness). Record the results in Table 2.

[0196] (2) Cyclic test and short-circuit test

[0197] 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:

[0198] The battery was subjected to charge-discharge cycle testing at a 1.5C charge rate, a 0.7C discharge rate, and a voltage window of 3.0V-4.5V (using Blue Electric testing equipment), for 800 cycles. The capacity retention rate was calculated using the first discharge capacity C1 and the 800th discharge capacity C800: C800 / C1 × 100%. The battery thickness T1 at 3.9V during the first charge (i.e., initial charge) (tested using PPG testing equipment) and the battery thickness T1 at 4V after 800 cycles were also considered. For a 0.5V battery with thickness T2, calculate the thickness expansion rate (T2 / T1-1)×100%. Record the capacity retention rate and thickness expansion rate in Table 2. During cycling, monitor for short circuits (testing 100,000 batteries), and record the short circuit rate in Table 2. After cycling, disassemble the battery and observe whether the current collector (from the boundary between the single-sided and double-sided coated areas to the winding tail end) is damaged or broken. The severity is listed from least to most severe as: no damage, slight damage, damage, and breakage. Generally, if the current collector is not broken but is damaged, the resulting crack will extend along the width direction of the current collector on the positive electrode sheet (i.e., the extension direction of the positive electrode tab). Therefore, the following definitions apply: No damage is defined as the portion from the boundary between the single-sided and double-sided coated areas to the winding tail end where no cracks are generated; if the longest crack generated in the above portion has a length / width of the current collector less than or equal to 10%, it is considered minor damage; if the longest crack generated in the above portion has a length / width of the current collector greater than 10% and less than or equal to 50%, it is considered damage; if the current collector breaks, it is considered a breakage. The results are recorded in Table 2.

[0199] Table 2

[0200] As can be seen from Table 2, compared with the comparative example, the battery of this disclosure can significantly improve the problems of current collector damage caused during battery manufacturing and current collector breakage during cycling. Furthermore, because the current collector in the comparative example battery breaks during cycling, the burrs generated by the current collector breakage can pierce the separator, leading to a short circuit. Therefore, the short circuit rate of the battery of this disclosure is significantly lower than that of the comparative example battery.

[0201] The preferred embodiments of this disclosure have been described in detail above; however, this disclosure is not limited thereto. Within the scope of the technical concept of this disclosure, various simple modifications can be made to the technical solutions of this disclosure, including combining the various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in this disclosure and are all within the protection scope of this disclosure.

Claims

1. An electric cell, characterized by, The positive electrode includes a current collector, the current collector having a first surface and a second surface disposed opposite to each other along the thickness direction of the battery cell; 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 part, a second part, and a third part connected in sequence, wherein 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 active coating, and the second surface is provided with a second positive active coating; In the second part, the first surface is provided with a first pressure-resistant coating and a first positive electrode active coating, the first pressure-resistant coating being close to the current collector and the first positive electrode active coating being away from the current collector; the second surface is provided with a second pressure-resistant coating and a second positive electrode active coating, the second pressure-resistant coating being close to the current collector and the second positive electrode active coating being 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, 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; Starting from the boundary line between the single-sided coating area and the double-sided coating area, the first pressure-resistant coating extends at least 3 mm towards the first end of the positive electrode sheet winding and at least 3 mm towards the last end of the positive electrode sheet winding. Starting from the boundary line between the single-sided coating area and the double-sided coating area, the second pressure-resistant coating extends at least 3 mm towards the first end of the positive electrode sheet winding and at least 3 mm towards the last end of the positive electrode sheet winding.

2. The electric cell of claim 1, wherein, 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 do not overlap, and the first end is the end close to the beginning of the positive electrode winding.

3. The cell of claim 1 or 2, wherein, The positive electrode sheet also includes a fourth part; along the direction from the tail end to the head end of the winding of the positive electrode sheet, the battery cell has a first straight region, a first arc region, a second straight region, a second arc region, a third straight region and a third arc region connected in sequence; At least part of the fourth portion is located in the first flat 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.

4. The electric cell of any one of claims 1-3, 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 pressure-resistant coating extending towards the first end of the positive electrode sheet is 3mm-15mm, preferably 3mm-6mm; And / or, 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 first end of the positive electrode sheet is 3mm-15mm, preferably 3mm-6mm; And / or, 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 towards the end of the positive electrode sheet is 3mm-15mm, preferably 3mm-5mm.

5. The cell of claim 3 or 4, wherein, Along the winding direction, the second end of the second pressure-resistant coating extends beyond the third arc region and into the third straight region. The dimension L4 of the second end of the second pressure-resistant coating extending beyond the boundary line between the third straight region and the third arc region is 1mm-5mm, preferably 1mm-3mm. The second end is the end near the winding tail end.

6. The electric cell of any one of claims 1-5, wherein, The 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 cell thickness direction is 1mm-12mm. Preferably, the projection of the first end of the first pressure-resistant coating extends 1mm-3mm beyond the projection of the first end of the second pressure-resistant coating in the direction from the tail end to the head end of the winding.

7. The electric cell of claim 3, wherein, In the third part, along the direction from the beginning of the winding to the end of the winding, the size of the first positive electrode active coating exceeds the size L6 of the first compressive coating by 1mm-5mm; And / or, in the third part, along the direction from the beginning to the end of the winding, 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 boundary line of the first straight area and the first arc area by 1mm-5mm, preferably 1mm-3mm; the second end is the end near the end of the winding.

8. The cell of any of claims 1-7, wherein, The projection of the second end of the first pressure-resistant coating in the third part onto the thickness direction of the battery cell, and the projection of the second end of the second pressure-resistant coating in the third part onto the thickness direction of the battery cell, wherein the second end is the end near the winding tail end.

9. The cell of any of claims 1-8, wherein, The area resistance of the first part is R1; the area 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; the area 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 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.

10. The cell of any of claims 1-9, wherein, The first and second anti-compression coatings each independently comprise anti-compression particles, a conductive agent, and a binder. The anti-compression 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 average particle size d of the anti-compression particles is 0.02 μm-1 μm, preferably 0.05 μm-0.5 μm.

11. The cell of any of claims 1-10, 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 the following: 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 the following: H2 / Dv90 is 1-5. And / or, the first pressure-resistant coating and the second pressure-resistant coating each independently comprise pressure-resistant particles, wherein the average particle size d of the pressure-resistant particles satisfies the following condition with respect to the particle size Dv90 of the positive electrode active material: Dv90 / d is 30-1700, preferably 70-500.

12. The cell of any of claims 1-11, wherein, The thickness of the first anti-compression coating and the thickness of the second anti-compression coating are each independently 1μm-15μm; And / or, the first positive electrode active coating includes a positive electrode active material, and the positive electrode active material is embedded in the first pressure-resistant coating to a depth of 1μm-3μm; And / or, the second positive electrode active coating includes a positive electrode active material, wherein the positive electrode active material is embedded in the second pressure-resistant coating to a depth of 1μm-3μm.

13. The electric cell of claim 3, wherein, The thickness of the current collector in the region formed by extending 4mm from the boundary line between the double-sided coating area and the single-sided coating area towards the beginning and end of the winding respectively is H3, and the thickness of the current collector in the fourth part is H4. H3 and H4 satisfy: H3 / H4 is 0.8-1, preferably 0.9-1.

14. The cell of any of claims 1-13, wherein, The positive electrode sheet also includes adhesive paper; Preferably, the adhesive tape covers the first positive electrode active coating located at the winding tail end, and in the winding direction, the size L9 of the adhesive tape covering the first positive electrode active coating is 3mm-10mm; Preferably, the adhesive tape covers the second positive electrode active coating located at the winding tail end, and in the winding direction, the size L10 of the adhesive tape covering the second positive electrode active coating is 3mm-10mm; Preferably, in the third part, when the size of the first positive electrode active coating exceeds the size of the first pressure-resistant coating, the size L11 of the adhesive paper covering the current collector is 5mm-15mm in the winding direction; Preferably, the adhesive tape partially or completely covers the first pressure-resistant coating; Preferably, the adhesive tape partially or completely covers the second pressure-resistant coating; Preferably, the adhesive tape completely covers the first pressure-resistant coating and extends to the current collector, and in the winding direction, the size L12 of the adhesive tape located on the current collector is 1mm-5mm; Preferably, the adhesive tape completely covers the second pressure-resistant coating and extends to the current collector, and in the winding direction, the size L12 of the adhesive tape located on the current collector is 1mm-5mm.

15. A battery, characterized by The battery comprises the cell according to any one of claims 1-14.

Images