Positive electrode sheet and battery cell

Abstract

Provided in the present invention are a positive electrode sheet and a battery cell. The positive electrode sheet comprises: a positive electrode current collector; and a positive electrode active layer applied to a surface of the positive electrode current collector, wherein the positive electrode active layer is provided with a plurality of pit structures spaced apart from each other; the positive electrode active layer comprises a first part located between two adjacent pit structures; at least partial regions of the first parts form crack regions; and crack structures are formed in the crack regions. In the positive electrode sheet of the present invention, the pit structures are arranged on the positive electrode active layer, thereby increasing the storage space for an electrolyte and being beneficial to improving the wetting effect of the electrolyte on the positive electrode sheet; and the crack regions are formed on the positive electrode sheet, and the crack structures form gas discharge paths, such that when gas is generated in a battery, the gas can be discharged through the crack structures in the crack regions, thereby promptly releasing the pressure inside the battery and being beneficial to improving the cycling performance of the battery and prolonging the service life of the battery.

Description

Positive electrode plate and battery cell

[0001] This application claims priority to Chinese Patent Application No. 202411732193.X, filed on November 29, 2024, entitled "Positive Electrode Sheet and Battery Cell", the entire contents of which are incorporated herein by reference. Technical Field

[0002] This invention relates to the field of battery technology, and more particularly to a positive electrode sheet and a battery cell. Background Technology

[0003] Lithium-ion batteries (LIBs) currently dominate the portable electronic device battery market due to their high specific energy density, wide temperature range, and long cycle life; lithium iron phosphate and ternary materials are widely used in the market due to their respective characteristics.

[0004] Then, during the long-term use of the above materials, the electrochemical performance deteriorates significantly, the power performance is not satisfactory, and the capacity retention rate becomes increasingly worse. One reason is that the interlayer compression of the cell is relatively severe, resulting in poor electrolyte wetting. Another reason is that under the environment of high-temperature formation or high-temperature cycling test, the battery may produce gas (such as hydrogen). If these gases cannot be discharged in time, they will cause the internal pressure of the battery to increase, which may lead to poor interfacial adhesion between the electrode and the separator. Poor interfacial adhesion will increase the local current density, resulting in uneven deposition of lithium metal, thereby promoting the formation of lithium dendrites and affecting the performance of the battery. Summary of the Invention

[0005] In view of the above problems, the present invention provides a positive electrode sheet and a battery cell, which can increase the storage space of electrolyte in the battery, improve the wetting effect of electrolyte on the positive electrode sheet, and can timely discharge gas, thereby improving the cycle performance and capacity retention of the battery.

[0006] In a first aspect, embodiments of the present invention provide a positive electrode sheet, comprising: a positive electrode current collector; and a positive electrode active layer coated on the surface of the positive electrode current collector, the positive electrode active layer having a plurality of spaced-apart pit structures, the positive electrode active layer including a first portion located between two adjacent pit structures, at least a portion of the first portion constituting a crack region, the crack region having a crack structure; the positive electrode active material of the positive electrode active layer includes lithium iron phosphate, lithium manganese iron phosphate, lithium manganese phosphate, and Li. a1 Co x1 M1 k1 O2, Li a2 Ni x2 Co y2 D z2 M2 k2At least one of O2, wherein 0.85≤a1≤1.1, 0.85≤a2≤1.1, 0.85≤x1≤1.05, 0.3≤x2≤0.98, 0≤y2≤0.5, 0≤z2≤0.5, 0≤k1≤0.15, 0≤k2≤0.15; D includes at least one of Mn and Al, M1 includes at least one of Al, Mg, Ti, Zr, Y, La, W, B, Nb and Mn, and M2 includes at least one of Al, Mg, Ti, Zr, Y, La, W, B, Nb and Mn.

[0007] The positive electrode sheet of the present invention has multiple pit structures arranged at intervals on the positive electrode active layer, which increases the surface area of ​​the positive electrode active layer, increases the contact area between the electrolyte and the positive electrode active layer, and the pit structure increases the storage space of the electrolyte, which can accommodate more electrolyte, which is beneficial to improving the wetting effect of the electrolyte on the positive electrode sheet, and also helps to improve the capacity retention rate of the battery.

[0008] Furthermore, due to lithium iron phosphate, lithium manganese iron phosphate, lithium manganese phosphate, and Li... a1 Co x1 M1 k1 O2, Li a2 Ni x2 Co y2 D z2 M2 k2 Active materials such as O2 are prone to generating gases through side reactions with the electrolyte during high-temperature formation or high-temperature cycling. The electrolyte may also generate gases (such as hydrogen) through hydrolysis. In this embodiment, a cracked region is formed on the positive electrode. The crack structure in the cracked region constitutes a gas exhaust path, allowing the gas to be discharged from the crack structure within the cracked region. This timely releases the internal pressure of the battery and maintains good interfacial contact between the positive electrode and the separator. During cycling, this promotes a more uniform current density distribution on the positive electrode and the separator, avoiding uneven lithium metal deposition and the resulting formation of lithium dendrites.

[0009] Moreover, the timely discharge of gas through the crack structure can also play a role in heat dissipation to a certain extent, which helps maintain the temperature of the positive electrode during the cycle. This ensures that the heat inside the cell is evenly distributed, thereby creating a stable reaction environment inside the cell, preventing further side reactions, improving the cycle performance of the battery, and extending the battery's lifespan.

[0010] According to some embodiments of the present invention, the crack region includes a first crack region extending circumferentially along the pit structure, the crack structure includes a first crack structure located within the first crack region, and the length C1 of the first crack structure in the circumferential direction of the pit structure is less than the perimeter C of the pit structure.

[0011] According to some embodiments of the present invention, at least a portion of the first crack region is located in the chamfered region between the sidewall of the pit structure and the first portion.

[0012] According to some embodiments of the present invention, C1 and C satisfy: 0.3 ≤ C1 / C ≤ 1.

[0013] And / or, the area S11 of the projection of the pit structure onto the reference plane and the area S12 of the crack structure in the first crack region outside the pit structure satisfy: 0.1 ≤ S12 / S11 ≤ 0.5, and the reference plane is parallel to the positive electrode current collector; and / or,

[0014] The distance between the first crack region and the pit structure is 0-100μm.

[0015] According to some embodiments of the present invention, the crack region further includes a second crack region located between two adjacent pit structures, and the crack structure includes a second crack structure located within the second crack region.

[0016] According to some embodiments of the present invention, the second crack structure extends linearly, and the two ends of the second crack structure are respectively oriented toward two adjacent pit structures.

[0017] According to some embodiments of the present invention, the number of the second crack structures is 0-5; and / or,

[0018] The length of the second crack structure is L3, and the distance between two adjacent pit structures is L2. The L3 and L2 satisfy: 0.05≤L3 / L2≤0.95.

[0019] According to some embodiments of the present invention, the width of the crack structure is in the range of 0.1 μm to 10 μm; and / or, the depth of the crack structure is less than the depth of the pit structure.

[0020] According to some embodiments of the present invention, the positive electrode includes a pit region, and a plurality of pit structures are located in the pit region. The ratio of the area S1 of the pit region to the area S of the positive electrode is: 0.05 ≤ S1 / S ≤ 0.6; and / or,

[0021] The ratio of the sum of the areas S2 of the projections of the pit structures in the pit region onto the reference plane to the area S3 of the non-pit structures in the pit region is: 0.2≤S2 / S3≤1.4.

[0022] According to some embodiments of the present invention, the recess structure includes a bottom wall.

[0023] The width D1 of the top surface of the recessed structure near the positive electrode active layer and the width D2 of the bottom wall satisfy the following condition: D1≥D2.

[0024] According to some embodiments of the present invention, D1 and D2 satisfy: 1 ​​≤ D1 / D2 ≤ 1.5; and / or,

[0025] The value range of D1 is: 80μm≤D1≤2000μm; and / or,

[0026] The value range of D2 is: 50μm≤D2≤1500μm; and / or,

[0027] The perimeter C2 of the bottom wall and the perimeter C of the recess structure satisfy: 1≤C2 / C≤1.5.

[0028] According to some embodiments of the present invention, the spacing between two adjacent recess structures is L1, and the length of the first portion between two adjacent recess structures is L2.

[0029] The L1 and L2 satisfy the condition: 1.2≤L1 / L2≤2.5.

[0030] According to some embodiments of the present invention, the recess structure further includes a sidewall, and the included angle α1 between the sidewall and the bottom wall is in the range of 90° < α1 < 160°.

[0031] According to some embodiments of the present invention, the positive electrode active coating is disposed on one side surface of the positive electrode current collector.

[0032] The depth h1 of the pit structure and the sum h of the thickness of the positive electrode current collector and the positive electrode active layer located on one side of the positive electrode current collector satisfy: 1 / 20 ≤ h1 / h ≤ 1 / 2; and / or,

[0033] The depth h1 of the pit structure is in the range of 1μm≤h1≤40μm.

[0034] Secondly, embodiments of the present invention also provide a battery cell, comprising: a negative electrode sheet; a separator;

[0035] The aforementioned positive electrode, the separator, and the negative electrode are stacked and wound together to form the battery cell;

[0036] The positive electrode includes a first region and a second region, wherein the first region corresponds to the straight portion of the battery cell, the second region corresponds to the bent portion of the battery cell, and the pit structure is provided on at least one of the first region and the second region.

[0037] The battery cell of this invention, using the aforementioned positive electrode sheet, features a concave structure that facilitates the containment of more electrolyte while improving electrolyte wetting. The concave structure is formed during processing, creating a crack structure. When gas is generated inside the battery during high-temperature cycling, the gas can escape through the cracks in the positive electrode sheet, promptly releasing internal battery pressure and ensuring sufficient adhesion at the interface between the positive electrode sheet and the separator. This improves the stability of the electrode interface and prevents lithium plating on the negative electrode. Simultaneously, it maintains the temperature of the positive electrode sheet during cycling, creating a stable reaction environment within the cell, preventing further adverse side reactions, and ultimately improving battery cycle performance and extending battery life.

[0038] In some embodiments, the first region is provided with a first recessed structure, and the second region is provided with a second recessed structure. The depth of the first recessed structure is h11, and the depth of the second recessed structure is h12. The h11 and the h12 satisfy: 1≤h12 / h11≤1.5.

[0039] According to some embodiments of the present invention,

[0040] The positive electrode includes a pit region located in the second region.

[0041] The length L1 of the pit region satisfies the formula: 0.5π(Rmin+H)≤L1≤π(Rmax+H), where Rmin is the curvature of the innermost circle of the second region, Rmax is the curvature of the outermost circle of the second region, and H is the thickness of the positive electrode sheet.

[0042] According to some embodiments of the present invention, the positive electrode includes a pit region, and a plurality of the pit structures are located in the pit region.

[0043] The positive electrode further includes: a first clearance region and a second clearance region located on opposite sides of the pit region along the length of the positive electrode, wherein the first clearance region corresponds to the winding start end of the positive electrode and the second clearance region corresponds to the winding end of the positive electrode.

[0044] The dimension K1 of the first clearance zone along the length of the positive electrode sheet is: 10mm ≤ K1 ≤ 300mm; and / or,

[0045] The dimension K2 of the second clearance zone along the length of the positive electrode sheet is: 10mm≤K2≤100mm.

[0046] According to some embodiments of the present invention, the positive electrode sheet includes a plurality of coils formed by winding, wherein the first void area constitutes at least the innermost coil among the plurality of coils.

[0047] According to some embodiments of the present invention, the positive current collector has a tab connection area on one side edge along the width direction of the positive electrode sheet, and the tab connection area has a plurality of tabs spaced apart along the length direction of the positive electrode sheet;

[0048] The positive electrode includes a ceramic layer located on one side of the positive electrode in the width direction;

[0049] The positive electrode includes a third clearance zone located between the ceramic layer and the pit structure;

[0050] The dimension M1 of the third clearance zone along the width direction of the positive electrode sheet is: 5mm≤M1≤30mm.

[0051] According to some embodiments of the present invention, the pit region includes a plurality of sub-pit regions spaced apart along the length direction of the positive electrode sheet, the positive current collector is provided with a tab connection region on one side edge along the width direction of the positive electrode sheet, the tab connection region is located between two adjacent sub-pit regions, the tab connection region is provided with at least one tab, and the distance between the tab and any one of the sub-pit regions on both sides is 5mm-30mm.

[0052] According to some embodiments of the present invention, the pit region includes a plurality of sub-pit regions spaced apart along the length direction of the positive electrode sheet, and the positive current collector is provided with an adhesive tape connection area on one side edge along the width direction of the positive electrode sheet. The adhesive tape connection area is located between two adjacent sub-pit regions, and the distance between the adhesive tape connection area and any one of the sub-pit regions on both sides is 5mm-30mm. Attached Figure Description

[0053] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0054] Figure 1 is a schematic diagram of the microstructure of the positive electrode active layer in an embodiment of the present invention;

[0055] Figure 2 is a magnified microstructure of the pit structure according to an embodiment of the present invention;

[0056] Figure 3 is a schematic diagram of the structure of the positive current collector having a positive active layer on one side in an embodiment of the present invention;

[0057] Figure 4 is a schematic diagram of the pit structure according to an embodiment of the present invention;

[0058] Figure 5 is a schematic diagram of the structure of the positive electrode sheet in some embodiments of the present invention;

[0059] Figure 6 is a second schematic diagram of the structure of the positive electrode sheet in some embodiments of the present invention.

[0060] Explanation of reference numerals in the attached drawings: 100-Positive electrode sheet; 1-Positive electrode current collector; 11-Adhesive paper connection area; 2-Positive electrode active layer; 21-Pit structure; 212-Bottom wall; 213-Side wall; 22-First part; 23-Crack area; 231-First crack area; 232-Second crack area; 24-Crack structure; 241-First crack structure; 242-Second crack structure; 25-Pit area; 251-Sub-pit area; 110-First clearance area; 120-Second clearance area; 130-Third clearance area; 140-Fourth clearance area; 150-Taper connection area; 151-Taper. Detailed Implementation

[0061] To make the above-mentioned objectives, features, and advantages of the embodiments of this application more apparent and understandable, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0062] In existing lithium-ion batteries, lithium iron phosphate and ternary materials experience severe degradation in electrochemical performance during cycling, resulting in unsatisfactory power performance and increasingly poor capacity retention. This is partly due to severe interlayer compression within the cell, leading to poor electrolyte wetting. Another reason is that under high-temperature chemical environments, lithium iron phosphate and ternary materials are prone to a series of side reactions with the electrolyte. The electrolyte may also generate gases (such as hydrogen) through hydrolysis. If these gases are not promptly released, they can cause increased pressure inside the battery, potentially leading to poor interfacial adhesion between the electrodes and the separator. Poor interfacial adhesion increases local current density, resulting in uneven lithium metal deposition and promoting lithium dendrite formation. Furthermore, gas accumulation can raise the electrode surface temperature, which in turn promotes rapid lithium metal deposition and uneven lithium dendrite growth.

[0063] In view of this, the present invention provides a positive electrode sheet and a battery cell that can increase the storage space of electrolyte in the battery, improve the wetting effect of electrolyte on the positive electrode sheet, and timely discharge gas during cycling, thereby improving the cycle performance and capacity retention of the battery.

[0064] Referring to Figures 1 to 6, in a first aspect, embodiments of the present invention provide a positive electrode 100, which may include: a positive current collector 1 and a positive active layer 2.

[0065] The positive current collector 1 has good conductivity to ensure that electrons are effectively transferred from the positive electrode to the external circuit. Aluminum foil is usually used as the positive current collector 1 because it has good conductivity and low cost. The positive current collector 1 provides physical support and adhesion surface for the positive active layer 2.

[0066] The positive electrode active layer 2 is coated on the surface of the positive electrode current collector 1. The positive electrode active layer 2 has a plurality of recessed structures 21 arranged at intervals. When the positive electrode sheet 100 is used in a battery, the electrolyte can fill the recessed structures 21. At the same time, due to the presence of the recessed structures 21, the surface area of ​​the positive electrode active layer 2 is larger, thereby improving the wetting effect of the electrolyte on the active material of the positive electrode active layer 2 of the positive electrode sheet 100 and improving battery performance.

[0067] The positive electrode active layer 2 includes a first portion 22 located between two adjacent pit structures 21, wherein the first portion 22 can be a straight section between the two pit structures 21. At least a portion of the first portion 22 constitutes a crack region 23, wherein either a portion of the first portion 22 constitutes the crack region 23, or the entire first portion 22 constitutes the crack region 23. Crack structures 24 are formed in the crack region 23, wherein the crack structures 24 can be formed around the pit structures 21 or between the pit structures 21.

[0068] It should be emphasized that the crack structure 24 in this embodiment is a small microcrack. It can be understood that the crack structure specifically refers to the cracking of the positive electrode active layer, rather than the fragmentation of the positive electrode active particles. The partial cracking of the positive electrode active layer can allow the electrolyte to flow better into the bottom surface of the positive electrode active layer. At the same time, it reduces the detour of lithium ions and improves the lithium ion transport rate. The size (such as width, length and depth) of the crack structure 24 does not affect the overall stability of the positive electrode active layer 2 or the adhesion between the positive electrode active layer 2 and the positive electrode current collector 1.

[0069] The crack structure 24 allows gas to escape from the electrode, preventing pressure increase between electrode layers. In addition, the electrolyte can also wet the positive electrode active layer 2 through the crack structure 24, which helps to further improve the electrolyte wetting efficiency.

[0070] Understandably, the crack structure 24 in this embodiment can be formed together with the pit structure 21 by adjusting the pressure of the processing equipment during the process of the processing equipment applying pressure to the positive electrode sheet 100 to process the pit structure 21.

[0071] The positive electrode active layer 2 may include lithium iron phosphate, lithium manganese iron phosphate, lithium manganese phosphate, or Li. a1 Co x1 M1 k1 O2, Li a2 Ni x2 Co y2 D z2 M2 k2 At least one of O2, wherein 0.85≤a1≤1.1, 0.85≤a2≤1.1, 0.85≤x1≤1.05, 0.3≤x2≤0.98, 0≤y2≤0.5, 0≤z2≤0.5, 0≤k1≤0.15, 0≤k2≤0.15; D includes at least one of Mn and Al, M1 includes at least one of Al, Mg, Ti, Zr, Y, La, W, B, Nb and Mn, and M2 includes at least one of Al, Mg, Ti, Zr, Y, La, W, B, Nb and Mn; preferably, it may include lithium iron phosphate, lithium manganese iron phosphate, lithium manganese phosphate or ternary materials.

[0072] For example, the positive electrode active layer 2 may include lithium iron phosphate, lithium manganese iron phosphate, lithium manganese phosphate, or Li. a1 Co x1 M1 k1 O2, Li a2 Ni x2 Co y2 D z2 M2 k2 One of the O2 materials, or the positive electrode active layer 2 may include a combination of the above-mentioned materials.

[0073] Among them, the chemical formula is Li a1 Co x1 M1 k1 The positive electrode material for O2 is a material in which the relative contents of each component can vary, wherein 0.85≤a1≤1.1, where a1 can be 0.85, 0.9, 1, or 1.1; 0.85≤x1≤1.05, where x1 can be 0.85, 0.9, 1, or 1.05; 0≤k1≤0.15, where k1 can be 0, 0.05, 0.1, or 0.15; and M1 can include at least one of Al, Mg, Ti, Zr, Y, La, W, B, Nb, and Mn, i.e., a material with the chemical formula Li. a1 Co x1 M1 k1 The positive electrode material for O2 can be Li 0.85 Co 0.3 AL 0.1 O2, Li 0.9 Co 0.4 AL 0.15 O2 or Li1Co 0.4 AL0.15 O2, of course, depending on a1, x1, k1, and M1, Li a1 Co x1 M1 k1 O2 also has other chemical expressions, which are not limited in this embodiment. Thus, by adjusting the values ​​of a1, x1, and k1 in the formulation, and by selecting a suitable dopant element M1, the energy density, power characteristics, cycle stability, and safety of the positive electrode active layer 2 can be improved.

[0074] The chemical formula is Li a2 Ni x2 Co y2 D z2 M2 k2 The positive electrode material for O2 is another material whose component contents can vary relatively. Specifically, 0.85 ≤ a2 ≤ 1.1, where a2 can be 0.85, 0.9, 1, or 1.1; 0.3 ≤ x2 ≤ 0.98, where x2 can be 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, or 0.9, 0.98; 0 ≤ y2 ≤ 0.5, where y2 can be 0, 0.1, 0.2, 0.3, 0.4, or 0.5; 0 ≤ z2 ≤ 0.5, where z2 can be 0, 0.1, 0.2, 0.3, 0.4, or 0.5; 0 ≤ k2 ≤ 0.15, where k2 can be 0, 0.05, 0.1, or 0.15; D can include at least one of Mn and Al; M2 can include at least one of Al, Mg, Ti, Zr, Y, La, W, B, Nb, and Mn, i.e., the chemical formula is Li. a2 Ni x2 Co y2 D z2 M2 k2 The positive electrode material for O2 can be Li 0.85 Ni 0.3 Co 0.1 Mn 0.1 Mg 0.1 O2, Li 0.85 Ni 0.4 Co 0.15 Mn 0.1 Mg 0.1 O2 or Li 0.9 Ni 0.3 Co 0.1 Mn 0.1 Mg 0.1 O2, of course, depending on the differences in a2, x2, y2, z2, k2, and M2, Li a2 Ni x2 Co y2 D z2 M2 k2O2 also has other chemical expressions, which are not limited in this embodiment. Thus, by adjusting the values ​​of a2, x2, y2, z2 and k2 in the formulation, and by selecting a suitable dopant element M2, the energy density, power characteristics, cycle stability and safety of the positive electrode active layer 2 can be improved.

[0075] According to the positive electrode 100 of the present invention, a plurality of pit structures 21 are arranged at intervals on the positive electrode active layer 2, which increases the surface area of ​​the positive electrode active layer 2, increases the contact area between the electrolyte and the positive electrode active layer 2, and increases the storage space of the electrolyte, which can accommodate more electrolyte, which is beneficial to improving the wetting effect of the electrolyte on the positive electrode 100, and also helps to improve the capacity retention rate of the battery.

[0076] Furthermore, due to lithium iron phosphate, lithium manganese iron phosphate, lithium manganese phosphate, and Li... a1 Co x1 M1 k1 O 2、 Li a2 Ni x2 Co y2 D z2 M2 k2 Active materials such as O2 are prone to generating gas through side reactions with the electrolyte during high-temperature formation or high-temperature cycling. The electrolyte may also generate gas (such as hydrogen) due to hydrolysis. In this embodiment, a crack region 23 is provided on the positive electrode 100. The crack structure 24 in the crack region 23 constitutes a gas exhaust path, allowing gas to be discharged from the crack structure 24. This timely releases the internal pressure of the cell and helps maintain good interfacial contact between the positive electrode 100 and the separator. During cycling, this helps to make the current density distribution on the positive electrode 100 and the separator more uniform, avoiding uneven deposition of lithium metal and the resulting formation of lithium dendrites.

[0077] Moreover, the timely discharge of gas through the crack structure 24 can also play a role in heat dissipation to a certain extent, which helps to maintain the temperature of the positive electrode 100 during the cycle process, so that the heat inside the cell is evenly distributed, thereby creating a stable reaction environment inside the cell, preventing the further occurrence of side reactions, improving the cycle performance of the battery, and extending the battery's service life.

[0078] Referring to Figures 1 and 2, in some embodiments, the crack region 23 includes a first crack region 231 extending circumferentially along the pit structure 21, and the crack structure 24 includes a first crack structure 241 located within the first crack region 231. The length C1 of the first crack structure in the first crack region 231 in the circumferential direction of the pit structure 21 is less than the perimeter C of the pit structure 21. It should be noted that the crack region 23 in this embodiment can be formed during the manufacturing of the pit structure 21 because the positive electrode active layer 2 is composed of lithium iron phosphate, lithium manganese iron phosphate, lithium manganese phosphate, and Li...a1 Co x1 M1 k1 O 2、 Li a2 Ni x2 Co y2 D z2 M2 k2 O2 particles have relatively high hardness. During the processing to form the pit structure 21, under a certain rolling force, the ternary, lithium iron phosphate, and lithium manganese phosphate materials have relatively high hardness and are not easily crushed. Correspondingly, under the action of the pressing force, the ternary, lithium iron phosphate, and lithium manganese phosphate materials slip, thus a part of the positive electrode active layer 2 is subjected to force to form the pit structure 21. At the same time, the active material forming the pit structure 21 extends circumferentially and is squeezed and misaligned with the active material of the positive electrode active layer 2 around the pit structure 21, forming the first crack structure 241. The presence of the pit structure 21 and the crack structure 24 of a certain area can improve the wetting of the electrolyte and the discharge of gas during high-temperature cycling. However, if there are too many crack structures 24 or the crack structures 24 are too long, that is, the crack structures around the pit structure 21 are too long, it will affect the structural stability of the pit structure 21 on the positive electrode current collector 1. It is easy for the positive electrode active layer in the pit structure to fall off due to insufficient support force, which will affect the battery cycle performance and safety performance. Therefore, the length C1 of the first crack structure in the first crack region 231 in the circumferential direction of the pit structure 21 is less than the circumference C of the pit structure 21, so as to avoid the crack structure being too long and affecting the structural stability of the pit structure 21 on the positive current collector 1, and thus easily causing the positive active layer in the pit structure to fall off due to insufficient support.

[0079] Furthermore, the area within the pit structure 21 contains a relatively large amount of electrolyte and has a relatively large contact area between the electrolyte and the positive electrode. Therefore, the gas inside the pit structure 21 may be more concentrated than in other areas. Thus, the first crack structure 241 is provided around the pit structure 21 to facilitate the rapid discharge of gas (such as hydrogen gas generated by possible hydrolysis reactions during electrolyte formation and gas generated by chemical reactions of the positive electrode active material) from the pit structure 21 through the first crack structure 241, thereby improving the interfacial adhesion yield between the positive electrode 100 and the separator.

[0080] In some embodiments, at least a portion of the first crack region 231 is located in the chamfered region between the sidewall of the pit structure 21 and the first portion. For example, only a portion of the first crack region 231 may be located in the chamfered region, or the entire first crack region 231 may be located in the chamfered region. Since the chamfered region can smoothly transition between the sidewall of the pit structure 21 and the first portion with a certain arc or slope, the gas in the pit structure 21 can more easily transfer along the outside of the first crack structure 241 in the chamfered region, thereby better venting the gas.

[0081] According to some embodiments of the present invention, C1 and C satisfy: 0.3 ≤ C1 / C ≤ 1. For example, the value of C1 / C can be 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 or 1. Preferably, the value of C1 / C can be 0.4-0.8. Of course, the value of C1 / C can also be other values, and this embodiment does not limit this. In this way, the length C1 of the first crack region 231 in the circumferential direction of the pit structure 21 is further limited to less than the perimeter C of the pit structure 21, so as to avoid the crack structure 24 occupying too large an area around the pit structure 21, which would affect the structural stability of the pit structure 21 on the positive electrode current collector 1, and thus easily lead to the problem of the positive electrode active layer in the pit structure falling off due to insufficient support force, thereby further improving the structural reliability of the positive electrode sheet 100.

[0082] According to some embodiments of the present invention, the area S11 of the projection of the pit structure 21 onto the reference plane and the area S12 of the crack structure in the first crack region 231 outside the pit structure satisfy the following condition: 0.1 ≤ S12 / S11 ≤ 0.5. For example, the value of S12 / S11 can be 0.1, 0.2, 0.3, 0.4, or 0.5. Of course, the value of S12 / S11 can also be other values, and this embodiment does not limit this. The reference plane is parallel to the positive current collector 1.

[0083] By limiting the ratio of the area of ​​the projected pit structure 21 in the reference plane to the area of ​​the projected crack structure in the first crack region 231 outside the pit structure in the reference plane, the distribution of the first crack region 231 is further limited. When S12 / S11 exceeds 0.5, the area occupied by the crack structure 24 in the first crack region 231 is too large, indicating that the depth of the pit structure 21 is too deep or the distribution of the pit structure 21 is too dense, which may exceed the extension range that the positive electrode sheet 100 can withstand. In other words, when the pit structure 21 and crack structure 24 are formed, or when the positive electrode sheet is subjected to expansion stress during the charging and discharging process, it may cause the positive electrode sheet to crack, resulting in lithium plating or short circuit, affecting the safety performance of the battery. Moreover, the increased distribution density of crack structure 24 will also lead to the deterioration of battery cycle performance. When S12 / S11 is less than 0.1, the gas channels formed by the crack structure 24 on the positive electrode active layer 2 are too small and cannot play a role in venting.

[0084] The distance between the first crack region 231 and the pit structure 21 is 0-100μm. For example, the distance between the first crack region 231 and the pit structure 21 can be 0μm, 10μm, 20μm, 30μm, 40μm, 50μm, 60μm, 70μm, 80μm, 90μm, or 100μm. Of course, the distance between the first crack region 231 and the pit structure 21 can also be other values, and this embodiment does not limit this.

[0085] By limiting the distance between the first crack region 231 and the edge of the pit structure 21, the distribution area of ​​the first crack structure 241 is further limited, so as to avoid the first crack structure 241 being distributed too far (the distance between the first crack region 231 and the edge of the pit structure 21 exceeds 100μm), which would affect the venting effect of the first crack structure 241.

[0086] Referring to FIG2, in some embodiments, the crack region 23 further includes a second crack region 232 located between two adjacent pit structures 21, and the crack structure 24 includes a second crack structure 242 located within the second crack region 232. In some embodiments, the second crack structure 242 extends linearly, with its two ends facing the two adjacent pit structures 21 respectively; in other words, the second crack structure 242 may extend from one pit structure 21 to the other pit structure 21.

[0087] In one embodiment, the second crack structure 242 can form an exhaust channel between two adjacent pit structures 21. In this way, the second crack structure 242 between two adjacent pit structures 21 can connect the first crack structures 241 distributed around the two pit structures 21, thereby making most of the first crack structures 241 and the second crack structures 242 on the positive electrode 100 interconnected to form a channel that can continuously exhaust gas. This allows the gas generated inside the cell (especially the part near the inner ring of the wound cell) to be discharged more smoothly through this channel, thereby avoiding poor interface adhesion between the positive electrode and the separator caused by gas accumulation inside the cell, which could lead to lithium plating.

[0088] According to some embodiments of the present invention, the number of second crack structures 242 is 0-5. For example, the number of second crack structures 242 can be 0, in which case the gas escapes through the first crack structure 241; it can also be 1, 2, 3, 4 or 5. Preferably, the number of second cracks can be 1-3. In this way, the second crack structures 242 are reasonably distributed between the two pit structures 21, which improves the exhaust performance while avoiding the distribution of too many second crack structures 242 (such as more than 5) which would lead to insufficient support for the pit structure 21, and thus cause the positive electrode active layer 2 inside the pit structure 21 to shed powder or fall off.

[0089] The length of the second crack structure 242 is L3, and the distance between two adjacent pit structures 21 is L2. L3 and L2 satisfy: 0.05 ≤ L3 / L2 ≤ 0.95. For example, the value of L3 / L2 can be 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, or 0.95. Preferably, the value of L3 / L2 can be between 0.2 and 0.6. Of course, the value of L3 / L2 can also be other values, and this embodiment does not limit this.

[0090] Limiting the length of the second crack structure 242 serves two purposes. First, it prevents the second crack structure 242 from being too long (L3 / L2 exceeding 0.95), which would affect the structural stability of the adjacent pit structure 21 and make the positive electrode active layer 2 near the pit structure 21 prone to detachment. Second, it prevents the second crack structure 242 from being too short (L3 / L2 less than 0.2), which would reduce its role in dissipating escaping gas.

[0091] Referring to Figures 5 and 6, according to some embodiments of the present invention, the width of the crack structure 24 ranges from 0.1 μm to 10 μm; for example, the width of the crack structure 24 can be 0.1 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, or 10 μm. Preferably, the width of the crack structure 24 can range from 1 to 5 μm. Of course, the width of the crack structure 24 can also be other values, and this embodiment does not limit this. On the one hand, it avoids the crack structure 24 being too wide, which would affect the structural stability of the adjacent pit structure 21, thereby making the positive electrode active layer 2 near the pit structure 21 prone to detachment and affecting the cycle performance of the cell. On the other hand, it avoids the crack structure 24 being too narrow, which would result in insufficient venting effect.

[0092] The depth of the crack structure 24 is less than the depth of the pit structure 21. This avoids the crack structure being too deep, which would affect the structural stability of the pit structure, resulting in insufficient support for the pit structure 21, making the positive electrode active layer 2 near the pit structure 21 prone to detachment, or even causing the electrode sheet to break due to excessive depth.

[0093] According to some embodiments of the present invention, the positive electrode 100 includes a pit region 25, and a plurality of pit structures 21 are all located in the pit region 25. The ratio of the area S1 of the pit region 25 to the area S of the positive electrode 100 is: 0.05 ≤ S1 / S ≤ 0.6; for example, the value of S1 / S can be 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, or 0.6. Preferably, the value of S1 / S can be 0.2-0.4. Of course, the value of S1 / S can also be other values, and this embodiment does not limit this.

[0094] It should be noted that the pit region 25 specifically refers to the distance between the pit structure 21 closest to the inner winding and the pit structure 21 closest to the outer winding along the length of the positive electrode sheet 100; and the distance between the pit structure 21 closest to one edge and the pit structure 21 closest to the other edge along the width of the positive electrode sheet 100. The area of ​​the pit region 25 is the product of the length and width mentioned above.

[0095] Thus, limiting the distribution density of the pit structure 21 on the positive electrode 100 is crucial. If the distribution density is too small (S1 / S less than 0.05), the electrolyte storage capacity is weak, making it difficult to improve the problem of poor electrolyte wetting, and the effect on improving the cycle performance of the cell is minimal. If the distribution density is too large (S1 / S exceeds 0.6), that is, the area of ​​the pits is too large and the pits are too dense, the electrode must withstand a great rolling force when forming such dense pits. Excessive stretching of the electrode can easily lead to defects such as electrode breakage, affecting the cycle performance and safety performance of the cell.

[0096] The ratio of the sum of the areas S2 of the projections of the pit structures 21 within the pit region 25 onto the reference plane to the area S3 of the non-pit structures within the pit region is: 0.2 ≤ S2 / S3 ≤ 1.4. For example, the value of S2 / S3 can be 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3, or 1.4. Preferably, the value of S2 / S3 can be between 0.4 and 1. Of course, the value of S2 / S3 can also be other values, and this embodiment does not limit this.

[0097] Thus, the distribution density of the pit structure 21 within the pit region 25 is further limited. If the distribution density is too small (S2 / S3 less than 0.2), the electrolyte storage capacity is weak, making it difficult to improve the problem of poor electrolyte wetting, and the effect on improving the cycle performance of the cell is small. If the distribution density is too large (S2 / S3 exceeds 1.4), the area of ​​the pits is too large and the pits are too dense. When forming such dense pits, the electrode sheet has to withstand a great rolling force, and the stretching of the positive electrode sheet 100 is too great, which can easily cause the positive electrode sheet 100 to break or other defects, affecting the cycle performance and safety performance of the cell.

[0098] Referring to Figures 3 and 4, according to some embodiments of the present invention, the recessed structure 21 includes a bottom wall 212, and the width D1 of the recessed structure 21 near the top surface of the positive electrode active layer satisfies the condition that D1 ≥ D2 with respect to the width D2 of the bottom wall 212. Thus, in this embodiment, the positive electrode active layer 2 uses ternary lithium material or lithium iron phosphate material. These materials have poor toughness and tend to exhibit low plasticity and brittleness, making the positive electrode sheet prone to breakage or cracking during rolling. Under this premise, the width of the recessed structure 21 exceeds the width of the bottom wall 212, resulting in a cross-section of the recessed structure 21 along the thickness direction of the positive electrode sheet 100 that is wider at the top and narrower at the bottom. This prevents the bottom wall 212 from being too wide and damaging the electrode sheet, and avoids localized breakage of the positive electrode sheet 100 during the processing of the recessed structure 21.

[0099] Referring to Figure 3, according to some embodiments of the present invention, D1 and D2 satisfy: 1 ​​≤ D1 / D2 ≤ 1.5. For example, the value of D1 / D2 can be 1, 1.1, 1.2, 1.3, 1.4, or 1.5. Preferably, the value of D1 / D2 can be 1.05-1.2. Of course, the value of D1 / D2 can also be other values, and this embodiment does not limit this.

[0100] By limiting the ratio of D1 to D2, it is possible to prevent the bottom wall 212 from being too wide, which could damage the electrode and cause localized breakage of the positive electrode 100 during the processing of the pit structure 21. Conversely, if the bottom wall is too narrow, its sharper shape could lead to excessive pressure on the positive electrode active layer during pit formation, potentially causing powder shedding from the active layer. Furthermore, limiting the ratio of D1 to D2 can also control the number of cracks in the first crack region. This is mainly achieved by limiting the stress area during pit formation, thus ensuring the number of cracks is controlled and facilitating timely air venting and heat dissipation.

[0101] The value range of D1 is: 80μm ≤ D1 ≤ 2000μm; for example, D1 can be 80μm, 100μm, 200μm, 300μm, 400μm, 500μm, 600μm, 700μm, 800μm, 900μm, 1000μm, 1100μm, 1200μm, 1300μm, 1400μm, 1500μm, 1600μm, 1700μm, 1800μm, 1900μm, or 2000μm. Preferably, D1 can be 100μm-800μm. Of course, the value of D1 can also be other values, and this embodiment does not limit this.

[0102] The value range of D2 is 50μm ≤ D2 ≤ 1500μm. For example, D2 can be 50μm, 100μm, 200μm, 300μm, 400μm, 500μm, 600μm, 700μm, 800μm, 900μm, 1000μm, 1100μm, 1200μm, 1300μm, 1400μm, or 1500μm. Preferably, D2 can be 80μm-500μm. Of course, the value of D2 can also be other values, and this embodiment does not limit this.

[0103] The perimeter C2 of the bottom wall 212 and the perimeter C of the recess structure 21 satisfy the condition: 1 ≤ C2 / C ≤ 1.5. For example, the value of C2 / C can be 1, 1.1, 1.2, 1.3, 1.4, or 1.5. Preferably, C2 / C can be between 1.05 and 1.2. Of course, the value of C2 / C can also be other values, and this embodiment does not limit this.

[0104] By controlling the ratio of the perimeter C2 of the bottom wall 212 to the perimeter C of the pit structure 21, on the one hand, the perimeter of the pit structure 21 can be avoided from being too large, thus avoiding an excessively large stress surface on the positive electrode sheet 100 during the processing of the pit structure 21, which could easily lead to local breakage and other damage. On the other hand, the width of the bottom wall can also be avoided from being too small, resulting in a sharper shape, which could easily cause excessive pressure to be applied to the positive electrode active layer of the positive electrode sheet when forming the pit structure, thus easily causing the positive electrode active layer to shed powder.

[0105] Referring to Figure 3, according to some embodiments of the present invention, the distance between two adjacent recess structures 21 is L1, and the length of the first portion 22 between two adjacent recess structures 21 is L2. L1 and L2 satisfy: 1.2 ≤ L1 / L2 ≤ 2.5. For example, L1 / L2 can be 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, 2.1, 2.2, 2.3, 2.4, or 2.5. Of course, the value of L1 / L2 can also be other values, and this embodiment does not limit this.

[0106] It is important to understand that the spacing between two adjacent pit structures 21 refers to the distance between the middle of the two adjacent pit structures.

[0107] Preferably, L1 / L2 can be 1.4-2. By limiting the ratio of the spacing between the recessed structures 21 to the length of the first part 22, the density of the recessed structures 21 is limited. At the same time, by combining the ratio of the projected area of ​​the recessed structures 21 to the projected area of ​​the first part 22, the distribution density of the recessed structures 21 is further limited.

[0108] Understandably, when the distribution density of the pit structure 21 is less than a certain value, the improvement effect on battery performance is not obvious. When the distribution density of the pit structure 21 is greater than a certain value, the pits are too dense. When such dense pits are formed, the electrode sheet has to withstand a great rolling force. Excessive stretching of the electrode sheet can easily cause the positive electrode sheet 100 to break or other defects, affecting the cycle performance and safety performance of the cell.

[0109] Referring to Figure 4, according to some embodiments of the present invention, the recess structure 21 may further include a sidewall 213, and the included angle α1 between the sidewall 213 and the bottom wall 212 is in the range of 90° < a1 < 160°. For example, a1 can be 91°, 95°, 100°, 105°, 110°, 120°, 125°, 130°, 135°, 140°, 145°, 150°, 155°, or 159°. Preferably, a1 = 100°-135°. Of course, the degree value of a1 can also be other values, and this embodiment does not limit this.

[0110] On the one hand, if the angle of a1 is too small (e.g., less than 90°), the bottom wall 212 of the recessed structure 21 will be subjected to greater stress during the processing of the recessed structure 21, resulting in insufficient support stability of the recessed structure 21. This can easily lead to powder shedding from the positive electrode active layer 2 during processing, affecting the cycle performance and safety performance of the battery. On the other hand, if the angle of a1 is too large (e.g., exceeding 160°), the dimensional difference between the recessed structure 21 and the bottom wall 212 will be small, resulting in a large rolling area on the positive electrode active layer 2. This makes processing to the designed depth more difficult, and if the designed depth is to be achieved, there is a risk of excessive stress on the electrode sheet leading to local breakage.

[0111] According to some embodiments of the present invention, a positive electrode active coating is disposed on one side surface of the positive electrode current collector 1. The depth h1 of the pit structure 21 and the sum h of the thickness of the positive electrode current collector 1 and the thickness of the positive electrode active layer 2 located on one side of the positive electrode current collector 1 satisfy: 1 / 20 ≤ h1 / h ≤ 1 / 2. For example, the value of h1 / h can be 1 / 20, 1 / 15, 1 / 10, 1 / 5, 1 / 3 or 1 / 2. Preferably, h1 / h can be 1 / 10-1 / 3. Of course, the value of h1 / h can also be other values, and this embodiment does not limit this.

[0112] By limiting the ratio of the depth of the pit structure 21 to the sum of the thicknesses of the positive electrode current collector 1 and the positive electrode active layer 2 located on one side of the positive electrode current collector 1, on the one hand, the depth of the pit structure 21 is avoided from being too small (h1 / h is less than 1 / 20), which would have little effect on improving battery performance. On the other hand, the depth of the pit structure 21 is avoided from being too large (h1 / h exceeds 1 / 2), which would prevent excessive damage to the positive electrode active layer 2 during the formation of the pit structure, causing the positive electrode active layer 2 to detach from the positive electrode current collector 1.

[0113] The depth h1 of the pit structure 21 ranges from 1μm to 40μm. For example, the depth h1 of the pit structure 21 can be 1μm, 5μm, 10μm, 15μm, 20μm, 25μm, 30μm, 35μm, or 40μm. Preferably, the depth h1 of the pit structure 21 can be 5μm-30μm. Of course, the depth h1 of the pit structure 21 can also be other values, and this embodiment does not limit this.

[0114] By limiting the depth of the pit structure 21, the stretching force experienced by the positive electrode active layer 2 during the formation of the pit structure 21 can be controlled, thereby controlling the distribution of the crack structure 24 and ensuring the air venting and heat dissipation effects of the crack structure. If the depth of the pit structure 21 is too small, the improvement effect on battery performance will be poor. If the depth of the pit structure 21 is too large, it may cause the positive electrode sheet 100 to be subjected to excessive stretching force during the formation of the pit structure 21, leading to excessive stretching of the positive electrode sheet 100 and subsequent cracking.

[0115] Secondly, embodiments of the present invention also provide a battery cell, which may include: a negative electrode sheet, a separator, and the aforementioned positive electrode sheet 100, wherein the positive electrode sheet 100, the separator, and the negative electrode sheet are stacked and wound to form a battery cell.

[0116] The positive electrode 100 may include a first region and a second region, wherein the first region corresponds to the straight portion and the second region corresponds to the bent portion of the battery cell. In other words, when the positive electrode 100 is in an unfolded state, the first region and the second region on the positive electrode 100 are arranged alternately.

[0117] The recessed structure 21 is provided on at least one of the first region and the second region. For example, the recessed structure 21 may be provided in the first region, or the recessed structure 21 may also be provided in the second region, or both the first region and the second region may have the recessed structure 21.

[0118] The battery cell of the present invention, due to the use of the aforementioned positive electrode 100, has a pit structure 21 in the positive electrode 100 that facilitates the containment of more electrolyte while improving the wetting effect of the electrolyte. A crack structure 24 is formed during the processing of the pit structure 21. When gas is generated inside the battery during high-temperature cycling, the gas can be discharged from the crack structure 24 within the crack region 23 of the positive electrode 100, timely releasing the internal pressure of the battery and ensuring sufficient adhesion at the interface formed between the positive electrode 100 and the separator, thus preventing lithium dendrite formation on the negative electrode. Simultaneously, it can maintain the temperature of the positive electrode 100 during cycling, providing a stable reaction environment within the battery cell, which is beneficial for improving the battery's cycle performance and extending its lifespan.

[0119] In some embodiments, a first recess structure 21 is provided in a first region, and a second recess structure 21 is provided in a second region. The depth of the first recess structure 21 is h11, and the depth of the second recess structure 21 is h12. h11 and h12 satisfy: 1 ​​≤ h12 / h11 ≤ 1.5. For example, h12 / h11 can be 1, 1.1, 1.2, 1.3, 1.4, or 1.5. Of course, the value of h12 / h11 can also be other values, and this embodiment does not limit this.

[0120] Thus, it is understandable that during the winding process to form a battery cell, the compressive force on the bent portion of the electrode is much greater than that on the straight portion. Because the depth of the second recess structure 21 in the second region of the bent portion exceeds the depth of the first recess structure 21 in the first region, the second recess structure 21 can effectively support the separator and the negative electrode, increasing the gap between the electrodes in the bent portion. This helps alleviate the stress on the positive electrode 100 during bending and prevents excessive stress on the bent portion of the electrode, which could lead to localized breakage. Simultaneously, it avoids the depth of the second recess structure 21 exceeding the depth of the first recess structure 21 by too much (h12 / h11 exceeding 1.5), which would reduce the flatness of the battery cell, increase the overall width of the cell, and affect the battery's energy density.

[0121] In some embodiments, the positive electrode 100 includes a pit region 25 located in the second region, that is, the pit region 25 can be a part of the structure of the second region, or the second region can constitute the pit region 25.

[0122] The length L1 of the pit region 25 satisfies the formula: (0.5π(Rmin+H)≤L1≤π(Rmax+H), where Rmin is the curvature of the innermost layer of the bent portion (second region), Rmax is the curvature of the outermost layer of the bent portion (second region), and H is the thickness of the positive electrode 100. This allows the pit region 25 to be located as close as possible to the bent second region, thereby increasing the gap between the positive electrode 100 and the separator during bending, which helps to release the concentrated stress on the electrode at the corner during bending.

[0123] Referring to Figures 5 and 6, in some embodiments, the positive electrode 100 includes a pit region 25, and a plurality of pit structures 21 are located in the pit region 25. The positive electrode 100 may further include: a first clearance region 110 and a second clearance region 120 located on opposite sides of the pit region 25 along the length direction of the positive electrode 100. The first clearance region 110 corresponds to the winding start end of the positive electrode 100, and the second clearance region 120 corresponds to the winding end of the positive electrode 100. In other words, the first clearance region 110 and the second clearance region 120 are respectively provided at the winding start end and the winding end when winding to form a battery cell, and no pit structures 21 are provided in either the first clearance region 110 or the second clearance region 120.

[0124] The dimension K1 of the first clearance zone 110 along the length of the positive electrode 100 is: 10mm ≤ K1 ≤ 300mm; for example, K1 can be 10mm, 50mm, 100mm, 150mm, 200mm, 250mm, or 300mm. Of course, K1 can also be other values, and this embodiment does not limit this. In this way, the first clearance zone 110 is set at the winding start end of the positive electrode 100, which provides a buffer for the winding operation and avoids folding and powder shedding at the winding start end.

[0125] The dimension K2 of the second clearance zone 120 along the length of the positive electrode 100 is: 10mm ≤ K2 ≤ 100mm. For example, K1 can be 10mm, 20mm, 30mm, 40mm, 50mm, 60mm, 70mm, 80mm, 90mm, or 100mm. Of course, K2 can also be other values, and this embodiment does not limit this. Thus, by setting the second clearance zone 120 at the winding end of the positive electrode 100, the structural stability of the positive electrode 100 during winding is further improved, avoiding the phenomenon of unstable winding and easy folding at the winding end.

[0126] According to some embodiments of the present invention, the positive electrode 100 includes multiple layers formed by winding, and the first clearance region 110 constitutes at least the innermost layer among the multiple layers. In other words, the structure of the innermost layer of the positive electrode 100 before the first bend or between the first and second bends constitutes the first clearance region 110. This further improves the structural stability of the positive electrode 100 during winding and avoids folding and powder shedding at the starting end of winding.

[0127] Referring to Figures 5 and 6, according to some embodiments of the present invention, the positive current collector 1 has a tab connection region 150 on one side edge along the width direction of the positive electrode sheet 100, and the tab connection region 150 has a plurality of tabs 151 spaced apart along the length direction of the positive electrode sheet 100. The positive electrode sheet 100 includes a ceramic layer located on one side along the width direction of the positive electrode sheet; the positive electrode sheet 100 includes a third clearance region 130 located between the ceramic layer and the recess structure 21, and the dimension M1 of the third clearance region along the width direction of the positive electrode sheet is: 5mm ≤ M1 ≤ 30mm, for example, M1 can be 5mm, 10mm, 15mm, 20mm, 25mm or 30mm. Preferably, M1 can be 5mm-20mm. Of course, M1 can also be other values, and this embodiment does not limit this.

[0128] This avoids the occurrence of edge powder shedding during the winding process of the positive electrode 100, and improves the structural stability of the positive electrode 100 during the winding process.

[0129] Understandably, when the positive electrode 100 does not have a ceramic region that matches the plurality of tabs 151 along the width direction, M1 is the distance between the edge of the pit region 25 and the edge of the corresponding side of the width of the positive electrode 100. When the positive electrode 100 has a ceramic region that matches the plurality of tabs 151 along the width direction, M1 is the distance between the edge of the pit region 25 and the ceramic region.

[0130] The positive electrode 100 includes a fourth clearance region 140 located on the other side of the pit region 25 along the width direction of the positive electrode 100. The dimension M2 of the fourth clearance region 140 along the width direction of the positive electrode 100 is: 5mm ≤ M2 ≤ 30mm. For example, M2 can be 5mm, 10mm, 15mm, 20mm, 25mm, or 30mm. Preferably, M2 can be 5mm-20mm. Of course, M2 can also be other values, and this embodiment does not limit this.

[0131] This further avoids edge powder shedding during the winding process of the positive electrode 100, improving the structural stability of the positive electrode 100 during winding. Furthermore, since the pit region 25 has M1 and M2 on both sides along its width direction, the pit region 25 is located near the center of the positive electrode 100, preventing powder shedding from the edges of the positive electrode 100 during the formation of the pit structure 21.

[0132] Referring to Figure 6, according to some embodiments of the present invention, the positive current collector 1 has a tab connection region 150 on one side edge along the width direction of the positive electrode plate 100. The tab connection region 150 has a plurality of tabs 151 spaced apart along the length direction of the positive electrode plate 100. The tab connection region 150 and the tabs 151 can be arranged in the following ways: a plurality of tab connection regions 150 are provided on the positive electrode plate 100, and each tab connection region 150 has one or more tabs 151. Alternatively, a tab connection region 150 is provided on one side along the width direction of the positive electrode plate 100, and the tab connection region 150 extends along the length direction of the positive electrode plate 100, with a plurality of tabs 151 spaced apart within the tab connection region 150 along the length direction of the positive electrode plate 100.

[0133] The tab connection region 150 does not have a positive electrode active layer 2, and the tab connection region 150 is located between the third clearance region 130 and the pit region 25. In this way, the tab 151 can be directly connected to the positive electrode current collector 1, improving the current conduction efficiency and thus improving the performance of the battery.

[0134] Referring to FIG6, according to some embodiments of the present invention, the recessed region 25 may include a plurality of sub-recessed regions 251 spaced apart along the length direction of the positive electrode sheet 100. The positive current collector 1 has a tab connection region 150 on one side edge along the width direction of the positive electrode sheet 100. The tab connection region 150 is located between two adjacent sub-recessed regions 251, and the tab connection region 150 has at least one tab 151. The distance between the tab 151 and any one of the sub-recessed regions 251 on both sides is 5mm-30mm. For example, the distance between the tab 151 and any one of the sub-recessed regions 251 can be 5mm, 10mm, 15mm, 20mm, 25mm or 30mm. Of course, the distance between the tab 151 and any one of the sub-recessed regions 251 can also be other values, and this embodiment does not limit this.

[0135] In this way, the recessed structure 21 can be staggered from the tab 151 during processing, avoiding damage to the tab 151 and affecting the cycle performance of the battery.

[0136] According to some embodiments of the present invention, the pit region 25 includes a plurality of sub-pit regions 251 spaced apart along the length direction of the positive electrode sheet 100. The positive electrode current collector 1 has an adhesive tape connection region 11 on one side edge along the width direction of the positive electrode sheet 100. The adhesive tape connection region 11 is located between two adjacent sub-pit regions 251, and the distance between the adhesive tape connection region 11 and any one of the sub-pit regions 251 on both sides is 5mm-30mm. For example, the distance between the adhesive tape connection region 11 and any one of the sub-pit regions 251 can be 5mm, 10mm, 15mm, 20mm, 25mm or 30mm. Of course, the distance between the adhesive tape connection region 11 and any one of the sub-pit regions 251 can also be other values, and this embodiment does not limit this.

[0137] In this way, the recessed structure can be staggered from the adhesive tape connection area 11 during processing, avoiding damage to the adhesive tape of the protective tab 151 and affecting the cycle performance of the battery.

[0138] The present invention will be further described below through specific embodiments:

[0139] Example 1

[0140] 1. Preparation of positive electrode sheet

[0141] NCM811, conductive agent (a mixture of conductive carbon black and carbon nanotubes), and PVDF were placed in NMP at a mass ratio of 97.60:1.35:1.05 and stirred evenly to prepare a positive electrode active layer slurry. The positive electrode active layer slurry was uniformly coated on both sides of the positive electrode current collector, with a coating density of 0.01704 g / cm2.

[0142] After drying and rolling, a positive electrode sheet with a double-sided positive active layer thickness of 90 μm is obtained. The positive electrode sheet is then slit, and a pit structure is processed on the slit positive electrode sheet using a rolling press with protrusions. The height of the protrusions is 6 μm, the angle between one side of the protrusion and the main body of the roller is 125°, and the width at the junction of the protrusion and the main body of the roller is 320 μm.

[0143] The obtained positive electrode parameters are detailed in Table 1.

[0144] 2. Preparation of negative electrode sheet

[0145] Artificial graphite, conductive carbon black, styrene-butadiene rubber, and sodium carboxymethyl cellulose were placed in deionized water at a mass ratio of 97.2:0.5:1.3:1. The above slurry was stirred evenly to obtain a negative electrode active layer slurry. The negative electrode active layer slurry was then uniformly coated onto the negative electrode current collector.

[0146] After drying, rolling, and slitting, the slitting negative electrode sheet is laser-grooved, with grooves set on the entire surface of the negative electrode sheet. Here, the grooves are matrix grooves, with the spacing between adjacent grooves set to 1.2mm and the groove depth to ~18μm. After laser treatment, the electrode sheet is cleaned and then prepared to obtain the negative electrode sheet.

[0147] 3. Battery manufacturing

[0148] This application uses a 9μm thick substrate + ceramic + adhesive-coated separator. The electrolyte includes lithium salt LiPF6 and solvent, the solvent including ethylene carbonate (EC), diethyl carbonate (DEC), and methyl ethyl carbonate (EMC), wherein the molar ratio of the three is DEC:EC:EMC = 1:1:1. After the above-mentioned diced positive electrode sheet 100, separator, and negative electrode sheet are sequentially stacked, they are wound into a wound cell structure. After the cell is encapsulated, injected with electrolyte, formed, and resealed, a lithium-ion battery is obtained.

[0149] Understandably, the performance parameters of the pit and crack structures formed on the positive electrode are mainly related to the parameters of the protrusions on the rolling equipment. By changing the height of the protrusions, the spacing between the protrusions, and the rolling force on the rolling equipment, positive electrode sheets of multiple different embodiments are obtained and performance tests are conducted.

[0150] In Example 2, compared with Example 1, the ratio of the length of the first crack zone to the perimeter of the pit structure, C1 / C, increases to 0.97, and the ratio of the area of ​​the first crack zone to the area of ​​the pit structure, S12 / S11, becomes 0.44.

[0151] In Example 3, compared with Example 1, the ratio of the length of the first crack zone to the perimeter of the pit structure, C1 / C, is 0.68, and the ratio of the area of ​​the first crack zone to the area of ​​the pit structure, S12 / S11, becomes 0.31.

[0152] In Example 4, compared with Example 1, the ratio of the length of the first crack region to the perimeter of the pit structure, C1 / C, is 0.68. At this time, the ratio of the area of ​​the first crack region to the area of ​​the pit structure, S12 / S11, becomes 0.31, and the ratio of the area of ​​the pit region to the area of ​​the positive electrode, S1 / S, changes to 0.08.

[0153] In Example 5, compared with Example 1, the ratio of the length of the first crack region to the perimeter of the pit structure, C1 / C, is 0.68. At this time, the ratio of the area of ​​the first crack region to the area of ​​the pit structure, S12 / S11, becomes 0.31, and the ratio of the area of ​​the pit region to the area of ​​the positive electrode, S1 / S, changes to 0.57.

[0154] In Example 6, compared with Example 1, the ratio of the length of the first crack zone to the perimeter of the pit structure, C1 / C, is 0.68. At this time, the ratio of the area of ​​the first crack zone to the area of ​​the pit structure, S12 / S11, becomes 0.31, and the width of the pit structure, D1, changes to 100.

[0155] In Example 7, compared with Example 1, the ratio of the length of the first crack zone to the perimeter of the pit structure, C1 / C, is 0.68. At this time, the ratio of the area of ​​the first crack zone to the area of ​​the pit structure, S12 / S11, becomes 0.31, and the width D1 of the pit structure changes to 1422.

[0156] In Example 8, compared with Example 1, the ratio of the length of the first crack zone to the perimeter of the pit structure, C1 / C, is 0.87. At this time, the ratio of the area of ​​the first crack zone to the area of ​​the pit structure, S12 / S11, becomes 0.41, and the angle α1 between the sidewall and bottom wall of the pit structure changes to 93°.

[0157] In Example 9, compared with Example 1, the ratio of the length of the first crack zone to the perimeter of the pit structure, C1 / C, is 0.84. At this time, the ratio of the area of ​​the first crack zone to the area of ​​the pit structure, S12 / S11, becomes 0.42, and the angle α1 between the sidewall and bottom wall of the pit structure changes to 158°.

[0158] In Example 10, compared with Example 1, the depth h1 of the pit structure was changed to 15 μm.

[0159] In Example 11, compared with Example 1, the ratio of the length of the first crack zone to the perimeter of the pit structure, C1 / C, is increased to 0.91. At this time, the ratio of the area of ​​the first crack zone to the area of ​​the pit structure, S12 / S11, becomes 0.43, and the depth h1 of the pit structure changes to 38 μm.

[0160] In Example 12, compared with Example 1, the ratio of the length of the first crack region to the perimeter of the pit structure, C1 / C, is 0.68. At this time, the ratio of the area of ​​the first crack region to the area of ​​the pit structure, S12 / S11, becomes 0.31. The ratio of the area of ​​the pit region to the area of ​​the positive electrode, S1 / S, changes to 0.14. The ratio of the sum of the projected areas of all pit structures to the area of ​​the first part within the pit region, S2 / S3, changes to 0.21.

[0161] In Example 13, compared with Example 1, the ratio of the length of the first crack zone to the perimeter of the pit structure, C1 / C, is 0.68. At this time, the ratio of the area of ​​the first crack zone to the area of ​​the pit structure, S12 / S11, becomes 0.31, and the ratio of the sum of the projected areas of all pit structures to the area of ​​the first part within the pit zone, S2 / S3, changes to 1.38.

[0162] Example 14, compared with Example 1, uses lithium iron phosphate as the positive electrode active material.

[0163] Example 15, compared with Example 1, uses lithium manganese phosphate as the positive electrode active material.

[0164] Example 16, compared with Example 1, uses lithium cobalt oxide as the positive electrode active material.

[0165] In Comparative Example 1, compared with Example 1, the ratio of the length of the first crack region to the perimeter of the pit structure, C1 / C, is 0.13. At this time, the ratio of the area of ​​the first crack region to the area of ​​the pit structure, S12 / S11, becomes 0.04, and the depth h1 of the pit structure changes to 2 μm.

[0166] In Comparative Example 2, compared with Example 1, the ratio of the length of the first crack zone to the perimeter of the pit structure, C1 / C, is 1.54. At this time, the ratio of the area of ​​the first crack zone to the area of ​​the pit structure, S12 / S11, becomes 0.78, and the depth h1 of the pit structure changes to 45 μm.

[0167] In Comparative Example 3, compared with Example 1, the ratio of the length of the first crack region to the perimeter of the pit structure, C1 / C, is 0.68, while the ratio of the area of ​​the first crack region to the area of ​​the pit structure, S12 / S11, becomes 0.31, the ratio of the area of ​​the pit region to the area of ​​the positive electrode, S1 / S, is 0.01, and the depth h1 of the pit structure is changed to 25 μm.

[0168] In Comparative Example 4, compared with Example 1, the ratio of the length of the first crack region to the perimeter of the pit structure, C1 / C, is 0.68, while the ratio of the area of ​​the first crack region to the area of ​​the pit structure, S12 / S11, becomes 0.31, the ratio of the area of ​​the pit region to the area of ​​the positive electrode, S1 / S, is 0.78, and the depth h1 of the pit structure is changed to 25 μm.

[0169] In Comparative Example 5, compared with Example 1, the ratio of the length of the first crack region to the perimeter of the pit structure, C1 / C, is 0.68, while the ratio of the area of ​​the first crack region to the area of ​​the pit structure, S12 / S11, becomes 0.31, the depth h1 of the pit structure changes to 25 μm, and the width D1 of the pit structure changes to 54 μm.

[0170] In Comparative Example 6, compared with Example 1, the ratio of the length of the first crack region to the perimeter of the pit structure, C1 / C, is 0.68, while the ratio of the area of ​​the first crack region to the area of ​​the pit structure, S12 / S11, becomes 0.31, the depth h1 of the pit structure changes to 25 μm, and the width D1 of the pit structure changes to 2438 μm.

[0171] In Comparative Example 7, compared with Example 1, the ratio of the length of the first crack zone to the perimeter of the pit structure, C1 / C, is 0.68, while the ratio of the area of ​​the first crack zone to the area of ​​the pit structure, S12 / S11, becomes 0.31, the depth h1 of the pit structure changes to 25 μm, and the angle a1 between the sidewall and bottom wall of the pit structure is 168°.

[0172] In Comparative Example 8, compared with Example 1, no crack structure was provided and the depth of the pit structure was set to 0.5 μm.

[0173] In Comparative Example 9, compared with Example 1, the ratio of the length of the first crack zone to the perimeter of the pit structure, C1 / C, increased to 0.96, and the ratio of the area of ​​the first crack zone to the area of ​​the pit structure, S12 / S11, became 0.48.

[0174] Comparative Example 10 does not include crack or pit structures.

[0175] Table 1. Parameter table of positive electrode sheets for each embodiment and comparative example.

[0176] Understandably, the pit structure on the positive electrode sheet of the present invention is formed by rolling with processing equipment. Therefore, when adjusting the parameters of the processing equipment, the quantitative values ​​in each set of data will fluctuate. Specifically, if the difference in the width of the pit structure does not exceed 10 μm, it is considered that the pit structure widths of the two sets of data are the same. Similarly, if the difference in the width of the crack structure is within 0.2 μm, the width of the crack structure is considered to be the same. If the fluctuation of the angle between the sidewall and the bottom wall of the pit structure is within 10°, it is considered that the angle remains unchanged.

[0177] The following tests were performed on the above embodiments and comparative examples:

[0178] Liquid retention test: Each battery is injected with a certain amount of electrolyte, for example, the amount of electrolyte injected into each battery n1 is 8.5g ± 0.1g. After injection, the battery is aged. After aging, the battery is sorted and then sealed twice. The second sealing is to remove the excess electrolyte. The remaining amount of electrolyte is the liquid retention n2. Then n2 = (weight after second sealing m2 - weight before injection m1).

[0179] Appearance test of the positive electrode sheet after the pit structure is manufactured: Use a 3D microscope to observe the positive electrode sheet after the pit structure is manufactured, and observe whether there is any damage on the positive electrode sheet and the size of the damaged area.

[0180] Cycle retention and expansion rate tests: Cycle test: The lithium-ion battery was cycle-tested on a Blue Battery test cabinet under the following conditions: 25℃±2℃, 3.2C charge to 4.37V, 2.8C charge to 4.37V, 2C charge to 4.53V, 1.5C charge to 4.58V, cutoff at 0.05C; 0.7C discharge to 3V. Specific method: At 25℃±2℃, allow to stand for 5 minutes, then discharge at 0.2C to the lower limit voltage; allow to stand for 5 minutes, then charge at 0.7C to the upper limit voltage, cutoff at 0.025C; allow to stand for 5 minutes, then discharge at 0.2C to the lower limit voltage (for initial capacity testing); allow to stand for 5 minutes, then charge at 3.2C to 4.37V, 2.8C charge to 4.37V, 2C charge to 4.53V, 1.5C charge to 4.58V, cutoff at 0.05C. Measure and record the data under full charge, including voltage and thickness. The battery was left to stand for 5 minutes at 25℃±2℃, then discharged at 0.7C to 3V, left to stand for 5 minutes, charged at 3.2C to 4.37V, charged at 2.8C to 4.37V, charged at 2C to 4.53V, charged at 1.5C to 4.58V, cut off at 0.05C, left to stand for 5 minutes, discharged at 0.7C to 3V, left to stand for 5 minutes, and so on. This process was repeated 8–91200 times, with 3–4 steps repeated every 100 cycles at 25℃ for capacity testing. For the first 200T: the fully charged cell voltage and thickness were measured every 50T; after 200T: the fully charged cell voltage and thickness were measured every 100T. Then, the capacity retention rate and expansion rate of the lithium-ion battery were tested at 200T and 400T. The battery expansion rate = (full-charge thickness after N cycles - battery sample thickness) / battery sample thickness * 100%).

[0181] Table 2. Test performance of the positive electrode sheets in each embodiment and comparative example.

[0182] By combining the comparative examples and Examples 1-13, setting pit structures and crack structures can reduce the occurrence of lithium plating in the battery.

[0183] Referring to Examples 1 and 2, a ratio C1 / C that is too large or too small for the length of the first crack region to the perimeter of the pit structure may result in lithium plating in the battery. Combining Examples 3-7, with a suitable ratio C1 / C for the length of the first crack region to the perimeter of the pit structure, the battery exhibits good cycle performance and does not experience lithium plating.

[0184] In conjunction with Examples 1 and 2 and Comparative Examples 1 and 2, increasing the ratio of the length of the first crack region to the perimeter of the pit structure C1 / C and the depth dimension of the pit structure is beneficial to improving the liquid retention of the battery and to a certain extent increases the battery capacity retention rate. However, it increases the battery expansion rate and correspondingly reduces the battery cycle retention rate.

[0185] In conjunction with Examples 3-5 and Comparative Examples 3-4, the ratio of the area of ​​the pit region to the area of ​​the positive electrode sheet, S1 / S, has a significant impact on the battery's capacity retention rate. If the ratio of the area of ​​the pit region to the area of ​​the positive electrode sheet, S1 / S, is too large or too small, the battery's capacity retention rate will decrease.

[0186] In conjunction with Examples 3, 6, and 7 and Comparative Examples 5 and 6, the width of the pit structure has a significant impact on the lithium plating situation of the battery. When the width of the pit structure is too large or too small, lithium plating will occur in the battery.

[0187] In conjunction with Examples 8 and 9 and Comparative Example 7, when the angle α1 between the sidewall and bottom wall of the pit is within a suitable range, lithium plating will not occur in the battery. However, if the angle α1 between the sidewall and bottom wall of the pit is too large, it will not be possible to reduce the occurrence of lithium plating in the battery.

[0188] In conjunction with Examples 1, 2, 10, 11 and Comparative Example 8, the presence of a cracked structure can reduce lithium plating in the battery. The depth of the pit structure has a greater impact on lithium plating than the ratio of the length of the first crack region to the perimeter of the pit structure, C1 / C.

[0189] In conjunction with Examples 3, 12, and 13, the ratio S2 / S3 of the sum of the projected areas of all pit structures to the area of ​​the first part within the pit region is relatively large. This indicates that when the distribution density of the pit structures is high, the battery can exhibit higher capacity retention and cycle retention rates. However, further in conjunction with Comparative Example 9, if the ratio S2 / S3 of the sum of the projected areas of all pit structures to the area of ​​the first part within the pit region is excessively large, lithium plating will occur in the battery.

[0190] Further, referring to Examples 1 and 14-16, the selection of the positive electrode active material also affects battery performance. When NCM811 (ternary lithium) and lithium cobalt oxide are used as the positive electrode active material, lithium plating is prone to occur. When lithium iron phosphate or lithium manganese phosphate are used as the positive electrode active material, lithium plating does not occur. Moreover, the cycle retention rate of the battery is higher when lithium iron phosphate or lithium manganese phosphate is used as the positive electrode active material. Therefore, using lithium iron phosphate or lithium manganese phosphate as the positive electrode active material is beneficial to improving the overall performance of the battery.

[0191] It should be noted that the embodiments referred to in the specification, such as "one embodiment," "embodiment," "exemplary embodiment," and "some embodiments," may include specific features, structures, or characteristics, but not every embodiment necessarily includes that specific feature, structure, or characteristic. Furthermore, such phrases do not necessarily refer to the same embodiment. Moreover, when a specific feature, structure, or characteristic is described in connection with an embodiment, implementing such a feature, structure, or characteristic in conjunction with other embodiments, whether explicitly described or not, is within the knowledge scope of those skilled in the art.

[0192] Generally speaking, terms should be understood at least in part by their use in context. For example, at least in part by context, the term "one or more" as used in the text can be used to describe any feature, structure, or characteristic of the singular meaning, or a combination of features, structures, or characteristics of the plural meaning. Similarly, at least in part by context, terms such as "a" or "the" can also be understood to convey either singular or plural usage.

[0193] It should be readily understood that the terms “on,” “above,” and “on top of” in this disclosure should be interpreted in the broadest possible sense, such that “on” means not only “directly on something” but also “on something” with an intermediate feature or layer therebetween, and that “above” or “on top of” means not only “on top of something” but also “on top of something” without an intermediate feature or layer therebetween (i.e., directly on something).

[0194] Furthermore, for ease of explanation, spatially relative terms such as "below," "below," "under," "above," and "above" may be used to describe the relationship of one element or feature relative to other elements or features as shown in the figures. Spatially relative terms are intended to encompass different orientations of the device in use or operation other than those shown in the figures. The device may have other orientations (rotated 90 degrees or in other orientations), and the spatially relative descriptive terms used herein may be interpreted accordingly.

[0195] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A positive electrode plate, characterized in that, include: Positive current collector; A positive electrode active layer is coated on the surface of the positive electrode current collector. The positive electrode active layer has a plurality of pit structures arranged at intervals. The positive electrode active layer includes a first part located between two adjacent pit structures. At least a portion of the first part constitutes a crack region, and the crack region has a crack structure. The positive electrode active material of the positive electrode active layer includes lithium iron phosphate, lithium manganese iron phosphate, lithium manganese phosphate, and Li. a1 Co x1 M1 k1 O2, Li a2 Ni x2 Co y2 D z2 M2 k2 At least one of O2, Wherein, 0.85≤a1≤1.1, 0.85≤a2≤1.1, 0.85≤x1≤1.05, 0.3≤x2≤0.98, 0≤y2≤0.5, 0≤z2≤0.5, 0≤k1≤0.15, 0≤k2≤0.15; D includes at least one of Mn and Al. M1 includes at least one of Al, Mg, Ti, Zr, Y, La, W, B, Nb, and Mn. M2 includes at least one of Al, Mg, Ti, Zr, Y, La, W, B, Nb, and Mn; The crack region includes a first crack region extending circumferentially along the pit structure, and the crack structure includes a first crack structure located within the first crack region. The length C1 of the first crack structure in the first crack region in the circumferential direction of the pit structure is less than the perimeter C of the pit structure.

2. The positive electrode sheet according to claim 1, characterized in that, At least a portion of the first crack region is located in the chamfered area between the sidewall of the pit structure and the first portion.

3. The positive electrode sheet according to claim 1, characterized in that, The C1 and the C satisfy: 0.3 ≤ C1 / C < 1; And / or, the area S11 of the projection of the pit structure onto the reference plane and the area S12 of the crack structure in the first crack region outside the pit structure satisfy: 0.1 ≤ S12 / S11 ≤ 0.5, and the reference plane is parallel to the positive electrode current collector; and / or, The distance between the first crack region and the pit structure is 0-100μm.

4. The positive electrode sheet according to claim 1, characterized in that, The cracked region also includes a second cracked region located between two adjacent pit structures, and the cracked structure includes a second cracked structure located within the second cracked region.

5. The positive electrode sheet according to claim 4, characterized in that, The second crack structure extends linearly, with its two ends facing the two adjacent pit structures respectively.

6. The positive electrode sheet according to claim 4, characterized in that, The number of the second crack structure is 0-5; and / or, The length of the second crack structure is L3, and the distance between two adjacent pit structures is L2. The L3 and L2 satisfy: 0.05≤L3 / L2≤0.

95.

7. The positive electrode sheet according to any one of claims 1-6, characterized in that, The width of the crack structure ranges from 0.1 μm to 10 μm; and / or, the depth of the crack structure is less than the depth of the pit structure.

8. The positive electrode sheet according to any one of claims 1-6, characterized in that, The positive electrode includes a pit region, and multiple pit structures are located within the pit region. The ratio of the area S1 of the pit region to the area S of the positive electrode is: 0.05 ≤ S1 / S ≤ 0.6; and / or, The ratio of the sum of the areas S2 of the projections of the pit structures in the pit region onto the reference plane to the area S3 of the non-pit structures in the pit region is: 0.2≤S2 / S3≤1.

4.

9. The positive electrode sheet according to any one of claims 1-6, characterized in that, The recessed structure includes a bottom wall. The width D1 of the top surface of the recessed structure near the positive electrode active layer and the width D2 of the bottom wall satisfy the following condition: D1≥D2.

10. The positive electrode sheet according to claim 9, characterized in that, The conditions D1 and D2 satisfy: 1 ​​≤ D1 / D2 ≤ 1.5; and / or, The value range of D1 is: 80μm≤D1≤2000μm; and / or, The value range of D2 is: 50μm≤D2≤1500μm; and / or, The perimeter C2 of the bottom wall and the perimeter C of the recess structure satisfy: 1≤C2 / C≤1.

5.

11. The positive electrode sheet according to claim 9, characterized in that, The distance between two adjacent recessed structures is L1, and the length of the first portion between two adjacent recessed structures is L2. The L1 and L2 satisfy the condition: 1.2≤L1 / L2≤2.

5.

12. The positive electrode sheet according to claim 9, characterized in that, The recessed structure also includes a sidewall, and the included angle α1 between the sidewall and the bottom wall ranges from 90° to 160°.

13. The positive electrode sheet according to any one of claims 1-6, characterized in that, The positive electrode active layer is disposed on one side surface of the positive electrode current collector. The depth h1 of the pit structure and the sum h of the thickness of the positive electrode current collector and the positive electrode active layer located on one side of the positive electrode current collector satisfy: 1 / 20 ≤ h1 / h ≤ 1 / 2; and / or, The depth h1 of the pit structure is in the range of 1μm≤h1≤40μm.

14. A battery cell, characterized in that, include: Negative electrode plate; Diaphragm; The positive electrode sheet according to any one of claims 1-13, wherein the positive electrode sheet, the separator, and the negative electrode sheet are stacked and wound to form the battery cell; The positive electrode includes a first region and a second region, wherein the first region corresponds to the straight portion of the battery cell, and the second region corresponds to the bent portion of the battery cell. The recessed structure is provided on at least one of the first region and the second region.

15. The battery cell according to claim 14, characterized in that, The first region has a first recessed structure, and the second region has a second recessed structure. The depth of the first recessed structure is h11, and the depth of the second recessed structure is h12. The h11 and h12 satisfy: 1≤h12 / h11≤1.

5.

16. The battery cell according to claim 14, characterized in that, The positive electrode includes a pit region located in the second region. The length L1 of the pit region satisfies the formula: 0.5π(Rmin+H)≤L1≤π(Rmax+H), where Rmin is the curvature of the innermost circle of the second region, Rmax is the curvature of the outermost circle of the second region, and H is the thickness of the positive electrode sheet.

17. The battery cell according to claim 14, characterized in that, The positive electrode includes a pit region, and multiple pit structures are located within the pit region. The positive electrode further includes: a first clearance region and a second clearance region located on opposite sides of the pit region along the length of the positive electrode, wherein the first clearance region corresponds to the winding start end of the positive electrode and the second clearance region corresponds to the winding end of the positive electrode. The dimension K1 of the first clearance zone along the length of the positive electrode sheet is: 10mm ≤ K1 ≤ 300mm; and / or, The dimension K2 of the second clearance zone along the length of the positive electrode sheet is: 10mm≤K2≤100mm.

18. The battery cell according to claim 17, characterized in that, The positive electrode sheet comprises multiple layers formed by winding, and the first void area constitutes at least the innermost layer among the multiple layers.

19. The battery cell according to claim 18, characterized in that, The positive current collector has a tab connection area on one side edge along the width direction of the positive electrode sheet, and the tab connection area has a plurality of tabs spaced apart along the length direction of the positive electrode sheet; The positive electrode includes a ceramic layer located on one side of the positive electrode in the width direction; The positive electrode includes a third clearance zone located between the ceramic layer and the pit structure; The dimension M1 of the third clearance zone along the width direction of the positive electrode sheet is: 5mm≤M1≤30mm.

20. The battery cell according to claim 17, characterized in that, The pit area includes a plurality of sub-pit areas spaced apart along the length of the positive electrode sheet. The positive current collector has a tab connection area on one side edge along the width of the positive electrode sheet. The tab connection area is located between two adjacent sub-pit areas. The tab connection area has at least one tab. The distance between the tab and any one of the sub-pit areas on both sides is 5mm-30mm.

21. The battery cell according to claim 17, characterized in that, The pit region includes a plurality of sub-pit regions spaced apart along the length of the positive electrode sheet. The positive current collector has an adhesive tape connection area on one side edge along the width of the positive electrode sheet. The adhesive tape connection area is located between two adjacent sub-pit regions. The distance between the adhesive tape connection area and any one of the sub-pit regions on both sides is 5mm-30mm.

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