Positive electrode and battery cell

Abstract

The present invention provides a positive electrode sheet and a battery cell, the positive electrode sheet comprising: a positive electrode current collector; a positive electrode active layer, coated on the surface of the positive electrode current collector, the positive electrode active layer is provided with a plurality of pit structures arranged at intervals, the positive electrode active layer comprises a first part located between two adjacent pit structures, at least a part of the first part constitutes a crack zone, and the crack zone forms a crack structure. The positive electrode sheet of the present invention is provided with a pit structure on the positive electrode active layer, which increases the storage space of the electrolyte, and is conducive to improving the infiltration effect of the electrolyte on the positive electrode sheet, and a crack zone is formed on the positive electrode sheet, and the crack structure forms a gas discharge path, when gas is generated in the battery, the gas can be discharged from the crack structure in the crack zone, and the internal pressure of the battery is released in time, which is conducive to improving the cycle performance of the battery and extending the service life of the battery.

Description

Technical Field

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

[0002] 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 materials and ternary materials are widely used in the market due to their respective characteristics.

[0003] Then, during the long-term use of the above materials, the electrochemical performance is severely attenuated, the power performance cannot be met, and the capacity retention rate is getting worse and worse; on the one hand, the reason is that the interlayer extrusion of the battery cell is relatively serious, resulting in poor electrolyte infiltration; on the other hand, in the environment of high-temperature formation or high-temperature cycle testing, the battery may produce gas (such as hydrogen). If these gases cannot be discharged in time, it will cause pressure increase inside the battery and may cause poor interface bonding between the electrode and the diaphragm. Poor interface bonding will increase local current density and lead to uneven deposition of lithium metal, thereby promoting the formation of lithium dendrites and affecting battery performance. Summary of the invention

[0004] 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 the electrolyte in the battery, improve the infiltration effect of the electrolyte on the positive electrode sheet, and discharge the gas in time, thereby improving the cycle performance and capacity retention rate of the battery.

[0005] In a first aspect, an embodiment of the present invention provides a positive electrode sheet, comprising: a positive electrode current collector; a positive electrode active layer, coated on the surface of the positive electrode current collector, the positive electrode active layer is provided with a plurality of pit structures arranged at intervals, the positive electrode active layer comprises a first portion located between two adjacent pit structures, at least a portion of the first portion constitutes a crack zone, and the crack zone forms a crack structure; the positive electrode active material of the positive electrode active layer comprises lithium iron phosphate, lithium manganese iron phosphate, lithium manganese phosphate, Li a1 Co x1 M1 k1 O 2、 Li a2 Ni x2 Co y2 D z2 M2 k2O2, 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.

[0006] The positive electrode sheet of the present invention has a plurality of 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, 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.

[0007] Furthermore, due to lithium iron phosphate, lithium manganese iron phosphate, lithium manganese phosphate, 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 produce gas due to side reactions with the electrolyte during the high-temperature formation process or high-temperature cycle, and the electrolyte may also produce gas (such as hydrogen) due to hydrolysis. In this embodiment, a crack zone is formed on the positive electrode sheet, and the crack structure of the crack zone constitutes a gas discharge path, so that the gas can be discharged from the crack structure in the crack zone, and the internal pressure of the battery is released in time, so that a good interface contact is maintained between the positive electrode sheet and the diaphragm. During the cycle process, it is beneficial to make the current density distribution on the positive electrode sheet and the diaphragm more uniform, avoiding uneven deposition of lithium metal and the resulting formation of lithium dendrites.

[0008] Moreover, timely discharge of gas through the crack structure can also play a heat dissipation role to a certain extent, which is beneficial to maintaining the temperature of the positive electrode during the cycle, so that the heat inside the battery cell is evenly dispersed, thereby creating a stable reaction environment inside the battery cell and preventing further occurrence of side reactions, thereby improving the cycle performance of the battery and extending the battery life.

[0009] According to some embodiments of the present invention, the crack zone includes a first crack zone extending along the circumference of the pit structure, the crack structure includes a first crack structure located in the first crack zone, and the length C1 of the first crack structure in the circumference of the pit structure is less than the circumference C of the pit structure.

[0010] According to some embodiments of the present invention, at least a portion of the first crack zone is located in a chamfered area between a sidewall of the pit structure and the first portion.

[0011] According to some embodiments of the present invention, C1 and C satisfy: 0.3≤C1 / C≤1,

[0012] and / or, the projection area S11 of the pit structure in 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,

[0013] The distance between the first crack zone and the pit structure is 0-100 μm.

[0014] According to some embodiments of the present invention, the crack zone further includes a second crack zone located between two adjacent pit structures, and the crack structure includes a second crack structure located within the second crack zone.

[0015] According to some embodiments of the present invention, the second crack structure extends linearly, and two ends of the second crack structure are respectively oriented toward two adjacent pit structures.

[0016] According to some embodiments of the present invention, the number of the second crack structures is 0-5; and / or,

[0017] The length of the second crack structure is L3, the distance between two adjacent pit structures is L2, and L3 and L2 satisfy: 0.05≤L3 / L2≤0.95.

[0018] According to some embodiments of the present invention, 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.

[0019] According to some embodiments of the present invention, the positive electrode sheet includes a pit area, the plurality of pit structures are all located in the pit area, and the ratio of the area S1 of the pit area to the area S of the positive electrode sheet is: 0.05≤S1 / S≤0.6; and / or,

[0020] The ratio of the sum of the areas S2 of the projections of the pit structures in the pit area on the reference plane to the area S3 of the non-pit structures in the pit area is: 0.2≤S2 / S3≤1.4.

[0021] According to some embodiments of the present invention, the pit structure comprises a bottom wall,

[0022] A width D1 of a top surface of the pit structure close to the positive electrode active layer and a width D2 of the bottom wall satisfy: D1 ≥ D2.

[0023] According to some embodiments of the present invention, D1 and D2 satisfy: 1≤D1 / D2≤1.5; and / or,

[0024] The value range of D1 is: 80 μm ≤ D1 ≤ 2000 μm; and / or,

[0025] The value range of D2 is: 50 μm ≤ D2 ≤ 1500 μm; and / or,

[0026] The circumference C2 of the bottom wall and the circumference C of the pit structure satisfy: 1≤C2 / C≤1.5.

[0027] According to some embodiments of the present invention, the distance between two adjacent pit structures is L1, the length of the first portion between two adjacent pit structures is L2,

[0028] The L1 and the L2 satisfy: 1.2≤L1 / L2≤2.5.

[0029] According to some embodiments of the present invention, the pit structure further includes a side wall, and a value range of an angle a1 between the side wall and the bottom wall is: 90°<a1<160°.

[0030] 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.

[0031] The depth h1 of the pit structure and the sum of the thickness h 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,

[0032] The depth h1 of the pit structure has a value range of 1 μm≤h1≤40 μm.

[0033] In a second aspect, an embodiment of the present invention further provides a battery cell, comprising: a negative electrode sheet; a separator;

[0034] The positive electrode sheet mentioned above, the positive electrode sheet, the separator and the negative electrode sheet are stacked and wound to form the battery cell;

[0035] The positive electrode sheet includes a first area and a second area, wherein the first area corresponds to a straight portion of the battery cell, the second area corresponds to a bent portion of the battery cell, and the pit structure is provided on at least one of the first area and the second area.

[0036] The battery cell of the present invention uses the above-mentioned positive electrode sheet, and the pit structure of the positive electrode sheet is conducive to accommodating more electrolyte while improving the infiltration effect of the electrolyte. When the pit structure is processed, a crack structure is formed. When gas is generated in the battery during the high-temperature cycle, the gas can be discharged from the crack structure in the crack area of ​​the positive electrode sheet, and the internal pressure of the battery is released in time, ensuring that the interface formed between the positive electrode sheet and the diaphragm has sufficient adhesion, improving the stability of the interface of the electrode sheet, thereby avoiding the situation of lithium precipitation of the negative electrode sheet. At the same time, the temperature of the positive electrode sheet during the cycle can also be maintained, so that the battery cell has a stable reaction environment, preventing the further occurrence of adverse side reactions, which is conducive to improving the cycle performance of the battery and extending the service life of the battery.

[0037] In some embodiments, the first region is provided with a first pit structure, the second region is provided with a second pit structure, the depth of the first pit structure is h11, the depth of the second pit structure is h12, and h11 and h12 satisfy: 1≤h12 / h11≤1.5.

[0038] According to some embodiments of the present invention,

[0039] The positive electrode sheet includes a concave region located in the second region,

[0040] The length L1 of the pit area satisfies the formula: (0.5π(Rmin+H)≤L1≤π(Rmax+H), where Rmin is the arc curvature of the innermost circle layer of the second area, Rmax is the curvature of the outermost circle layer of the second area, and H is the thickness of the positive electrode sheet.

[0041] According to some embodiments of the present invention, the positive electrode sheet includes a pit area, and the plurality of pit structures are all located in the pit area.

[0042] The positive electrode sheet further includes: a first avoidance area and a second avoidance area located on opposite sides of the pit area along the length direction of the positive electrode sheet, wherein the first avoidance area corresponds to the winding start end of the positive electrode sheet, and the second avoidance area corresponds to the winding end end of the positive electrode sheet.

[0043] The dimension K1 of the first air-avoiding area along the length direction of the positive electrode sheet is: 10 mm ≤ K1 ≤ 300 mm; and / or,

[0044] The dimension K2 of the second air-avoiding area along the length direction of the positive electrode sheet is: 10 mm ≤ K2 ≤ 100 mm.

[0045] According to some embodiments of the present invention, the positive electrode sheet includes a plurality of winding layers, and the first air-avoiding area constitutes at least an innermost layer among the plurality of winding layers.

[0046] According to some embodiments of the present invention, the positive electrode current collector is provided with a tab connection area at one side edge along the width direction of the positive electrode sheet, and the tab connection area is provided with a plurality of tabs spaced apart and distributed along the length direction of the positive electrode sheet;

[0047] The positive electrode sheet includes a ceramic layer located on one side of the positive electrode sheet in a width direction;

[0048] The positive electrode sheet includes a third space-avoiding area between the ceramic layer and the pit structure;

[0049] A dimension M1 of the third air-avoiding area along the width direction of the positive electrode sheet is: 5 mm ≤ M1 ≤ 30 mm.

[0050] According to some embodiments of the present invention, the pit area includes a plurality of sub-pit areas spaced apart along the length direction of the positive electrode sheet, and a pole lug connection area is provided on one side edge of the positive electrode collector along the width direction of the positive electrode sheet, and the pole lug connection area is located between two adjacent sub-pit areas. The pole lug connection area is provided with at least one pole lug, and the spacing between the pole lug and any one of the sub-pit areas on both sides is 5mm-30mm.

[0051] According to some embodiments of the present invention, the pit area includes a plurality of sub-pit areas spaced apart along the length direction of the positive electrode sheet, and a tape connection area is provided on one side edge of the positive electrode collector along the width direction of the positive electrode sheet, and the tape connection area is located between two adjacent sub-pit areas, and the spacing between the tape connection area and any one of the sub-pit areas on both sides is 5mm-30mm. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, a brief introduction will be given below to the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0053] Figure 1 A schematic diagram of the microstructure of the positive electrode active layer of an embodiment of the present invention;

[0054] Figure 2 This is an enlarged view of the microstructure of the pit structure of an embodiment of the present invention;

[0055] Figure 3 This is a schematic structural diagram of a positive electrode current collector in an embodiment of the present invention provided with a positive electrode active layer on one side;

[0056] Figure 4 A schematic structural diagram of a pit structure according to an embodiment of the present invention;

[0057] Figure 5 This is one of the structural schematic diagrams of the positive electrode sheet of some embodiments of the present invention;

[0058] Figure 6 This is the second structural schematic diagram of the positive electrode sheet of some embodiments of the present invention.

[0059] Description of reference numerals:

[0060] 100- positive electrode;

[0061] 1-positive electrode current collector; 11-tape connection area;

[0062] 2-positive electrode active layer; 21-pit structure; 212-bottom wall; 213-side wall;

[0063] 22-first part; 23-crack zone; 231-first crack zone; 232-second crack zone; 24-crack structure; 241-first crack structure; 242-second crack structure; 25-pit zone; 251-sub-pit zone;

[0064] 110-First air refuge zone;

[0065] 120-Second air refuge area;

[0066] 130-the third air-avoidance zone;

[0067] 140-the fourth air-avoidance zone;

[0068] 150-ear connection area; 151-ear. DETAILED DESCRIPTION

[0069] In order to make the above-mentioned purposes, features and advantages of the embodiments of the present application more obvious and understandable, the technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work belong to the scope of protection of this application.

[0070] The lithium iron phosphate materials and ternary materials in the existing lithium-ion batteries are accompanied by serious attenuation of electrochemical performance during the cycle use process, the power performance cannot be satisfied, and the capacity retention rate is getting worse and worse. On the one hand, the reason is that the interlayer extrusion of the battery cell is relatively serious, resulting in poor electrolyte infiltration. On the other hand, in a high-temperature chemical environment, lithium iron phosphate materials and ternary materials are prone to a series of side reactions with the electrolyte, and the electrolyte may also produce gases (such as hydrogen) due to hydrolysis. If these gases are not discharged in time, it will cause pressure increase inside the battery and may cause poor interface bonding between the electrode and the diaphragm. Poor interface bonding will increase local current density, leading to uneven deposition of lithium metal, thereby promoting the formation of lithium dendrites. In addition, the accumulation of gas may cause the electrode surface temperature to increase, and higher temperatures are conducive to the rapid deposition of lithium metal and uneven growth of lithium dendrites.

[0071] In view of this, the present invention provides a positive electrode sheet and a battery cell, which can increase the storage space of the electrolyte in the battery, improve the infiltration effect of the electrolyte on the positive electrode sheet, and discharge the gas in time during the cycle process, thereby improving the cycle performance and capacity retention rate of the battery.

[0072] refer to Figures 1 to 6 In a first aspect, an embodiment of the present invention provides a positive electrode sheet 100 , which may include: a positive electrode current collector 1 and a positive electrode active layer 2 .

[0073] The positive electrode 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 electrode current collector 1, which has good conductivity and low cost. The positive electrode current collector 1 provides physical support and attachment surface for the positive electrode active layer 2.

[0074] The positive electrode active layer 2 is coated on the surface of the positive electrode current collector 1, and the positive electrode active layer 2 is provided with a plurality of pit structures 21 arranged at intervals. When the positive electrode sheet 100 is used in a battery, the electrolyte can be filled in the pit structure 21. At the same time, due to the provision of the pit structure 21, the surface area of ​​the positive electrode active layer 2 is larger, thereby improving the infiltration effect of the electrolyte on the active material of the positive electrode active layer 2 of the positive electrode sheet 100, and improving the battery performance.

[0075] The positive electrode active layer 2 includes a first portion 22 located between two adjacent pit structures 21, wherein the first portion 22 may be a straight portion between the two pit structures 21. At least a portion of the first portion 22 constitutes a crack zone 23, wherein a portion of the first portion 22 may constitute the crack zone 23, or the first portion 22 as a whole may constitute the crack zone 23. The crack zone 23 is formed with a crack structure 24, wherein the crack structure 24 may be formed around the pit structure 21 or between the pit structures 21.

[0076] It should be emphasized that the crack structure 24 of the present embodiment is a micro-crack of smaller size. 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 cracking of a part of the positive electrode active layer can make the electrolyte flow into the bottom surface of the positive electrode active layer better, and at the same time, reduce the tortuosity of lithium ions and improve the transmission rate of lithium ions. The size of the crack structure 24 (such as width, length, depth) does not affect the stability of the overall structure of the positive electrode active layer 2 and the adhesion between the positive electrode active layer 2 and the positive electrode current collector 1.

[0077] The gas in the electrode can be discharged through the crack structure 24 to avoid the pressure increase between the electrode layers. In addition, the electrolyte can also infiltrate the positive electrode active layer 2 from the crack structure 24, which helps to further improve the electrolyte infiltration efficiency.

[0078] It can be understood that the crack structure 24 of the present embodiment can be formed together with the pit structure 21 by adjusting the pressure of the processing equipment when the processing equipment applies pressure to the positive electrode sheet 100 to process the pit structure 21.

[0079] The positive electrode active layer 2 may include lithium iron phosphate, lithium manganese iron phosphate, lithium manganese phosphate, Li a1 Co x1 M1 k1 O 2、 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 can include lithium iron phosphate, lithium manganese iron phosphate, lithium manganese phosphate or a ternary material.

[0080] For example, the positive electrode active layer 2 may include lithium iron phosphate, lithium manganese iron phosphate, lithium manganese phosphate, Li a1 Co x1 M1 k1 O 2、 Li a2 Ni x2 Co y2 D z2 M2 k2O2, or the positive electrode active layer 2 may also include a combination of the above-mentioned multiple materials.

[0081] The chemical formula is Li a1 Co x1 M1 k1 The positive electrode material of O2 is a material in which the contents of each component can be relatively changed, wherein 0.85≤a1≤1.1, a1 can be 0.85, 0.9, 1 or 1.1, 0.85≤x1≤1.05, x1 can be 0.85, 0.9, 1, 1.05, 0≤k1≤0.15, k1 can be 0, 0.05, 0.1 or 0.15, M1 can include at least one of Al, Mg, Ti, Zr, Y, La, W, B, Nb and Mn, that is, the positive electrode material of the chemical formula Lia1Cox1M1k1O2 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 AL 0.15 O2, of course, depending on a1, x1, k1 and M1, Li a1 Co x1 M1 k1 O2 may also have other chemical expressions, which are not limited in this embodiment. Thus, by adjusting the values ​​of a1, x1 and k1 in the formula and selecting a suitable doping element M1, the energy density, power characteristics, cycle stability and safety of the positive electrode active layer 2 can be improved.

[0082] The chemical formula is Li a2 Ni x2 Co y2 D z2 M2 k2 The positive electrode material of O2 is another material in which the contents of each component can be relatively changed, wherein 0.85≤a2≤1.1, a2 can be 0.85, 0.9, 1 or 1.1, 0.3≤x2≤0.98, x2 can be 0.3, 0.4, 0.5, 0.6, 0.7, 0.8 or 0.9, 0.98, 0≤y2≤0.5, y2 can be 0, 0.1, 0.2, 0.3, 0.4 or 0.5, 0≤z2≤0.5, z2 can be 0, 0.1, 0.2, 0.3, 0.4 or 0.5, 0≤k2≤0.15, 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, that is, the chemical formula is Li a2 Nix2 Co y2 D z2 M2 k2 The positive electrode material of 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 a2, x2, y2, z2, k2 and M2, Li a2 Ni x2 Co y2 D z2 M2 k2 O2 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 formula and selecting a suitable doping element M2, the energy density, power characteristics, cycle stability and safety of the positive electrode active layer 2 can be improved.

[0083] According to the positive electrode sheet 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 the pit structure 21 increases the storage space of the electrolyte, which can accommodate more electrolyte, is beneficial to improving the wetting effect of the electrolyte on the positive electrode sheet 100, and also helps to improve the capacity retention rate of the battery.

[0084] Furthermore, due to lithium iron phosphate, lithium manganese iron phosphate, lithium manganese phosphate, Li a1 Co x1 M1 k1 O 2、 Li a2 Ni x2 Co y2 D z2 M2 k2Active materials such as O2 are prone to produce gas due to side reactions with the electrolyte during high-temperature formation or high-temperature circulation, and the electrolyte may also produce gas (such as hydrogen) due to hydrolysis. In this embodiment, a crack zone 23 is set on the positive electrode sheet 100, and the crack structure 24 in the crack zone 23 constitutes a gas discharge path, so that the gas can be discharged from the crack structure 24, and the internal pressure of the battery cell is released in time, which is beneficial to maintaining a good interface contact between the positive electrode sheet 100 and the diaphragm. During the cycle process, it is beneficial to make the current density distribution on the positive electrode sheet 100 and the diaphragm more uniform, avoiding uneven deposition of lithium metal and the resulting formation of lithium dendrites.

[0085] Moreover, timely discharge of gas through the crack structure 24 can also play a heat dissipation role to a certain extent, which is beneficial to maintaining the temperature of the positive electrode sheet 100 during the cycle process, so that the heat inside the battery cell is evenly dispersed, thereby providing a stable reaction environment inside the battery cell and preventing further occurrence of side reactions, thereby improving the cycle performance of the battery and extending the battery life.

[0086] refer to Figure 1 and Figure 2 In some embodiments, the crack zone 23 includes a first crack zone 231 extending along the circumference of the pit structure 21, and the crack structure 24 includes a first crack structure 241 located in the first crack zone 231. The length C1 of the first crack structure of the first crack zone 231 in the circumference of the pit structure 21 is less than the circumference C of the pit structure 21. It should be noted that the crack zone 23 of this embodiment can be formed when the pit structure 21 is manufactured, because the lithium iron phosphate, lithium manganese iron phosphate, lithium manganese phosphate, Li a1 Co x1 M1 k1 O 2、 Li a2 Ni x2 Co y2 D z2 M2 k2The particle hardness of O2 is relatively large. When the pit structure 21 is formed by processing, under the action of a certain rolling force, the hardness of materials such as ternary, lithium iron phosphate, and lithium manganese phosphate is relatively large and not easy to be crushed. Under the action of the pressing force, the materials such as ternary, lithium iron phosphate, and lithium manganese phosphate slip accordingly, so that 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 material forming the pit structure 21 extends circumferentially, and is squeezed and dislocated with the active material of the positive electrode active layer 2 around the pit structure 21 to form a first crack structure 241. The presence of the pit structure 21 and the crack structure 24 of a certain area can improve the infiltration of the electrolyte and the discharge of gas during high-temperature cycling. However, if there are too many crack structures 24 or the crack structure 24 is too long, that is, the crack structure around the pit structure 21 is too long, it will affect the structural stability of the pit structure 21 on the positive electrode collector 1, and it is easy to cause the positive electrode active layer in the pit structure to fall off due to insufficient support force, affecting the battery cycle performance and safety performance. Therefore, the length C1 of the first crack structure of the first crack zone 231 in the circumferential direction of the pit structure 21 is smaller than the circumference C of the pit structure 21, thereby avoiding the problem that the crack structure is too long and affects the structural stability of the pit structure 21 on the positive electrode current collector 1, and then easily causes the positive electrode active layer in the pit structure to fall off due to insufficient supporting force.

[0087] In addition, the pit structure 21 is an area with a relatively large amount of electrolyte storage and a relatively large contact area between the electrolyte and the positive electrode sheet. Therefore, the gas inside the pit structure 21 may be more concentrated than that in other areas. Therefore, a first crack structure 241 is provided around the pit structure 21, which is beneficial for the gas in the pit structure 21 (for example, gas (such as hydrogen) generated by possible hydrolysis reaction of the electrolyte during the formation process, gas generated by chemical reaction of the positive electrode active material) to be quickly discharged from the pit structure 21 through the first crack structure 241, so as to improve the interface bonding yield between the positive electrode sheet 100 and the diaphragm.

[0088] In some embodiments, at least part of the first crack zone 231 is in the chamfered area between the sidewall of the pit structure 21 and the first portion. For example, only part of the first crack zone 231 may be in the chamfered area, or the entire first crack zone 231 may be in the chamfered area. Since the chamfered area can smoothly transition the sidewall of the pit structure 21 and the first portion with a certain arc or slope, the gas in the pit structure 21 is more easily transferred along the first crack structure 241 in the chamfered area to the outside of the pit structure 21, thereby better exhausting the gas.

[0089] According to some embodiments of the present invention, C1 and C satisfy: 0.3≤C1 / C≤1. For example, the value of C1 / C may be 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 or 1. Preferably, the value of C1 / C may be 0.4-0.8. Of course, the value of C1 / C may also be other values, which are not limited in the present embodiment. In this way, it is further limited that the length C1 of the first crack zone 231 in the circumferential direction of the pit structure 21 is less than the circumference C of the pit structure 21, thereby avoiding that the crack structure 24 occupies too large an area around the pit structure 21, affecting the structural stability of the pit structure 21 on the positive electrode current collector 1, and thus easily causing the positive electrode active layer in the pit structure to fall off due to insufficient support force, thereby further improving the structural reliability of the positive electrode sheet 100.

[0090] According to some embodiments of the present invention, the area S11 of the projection of the pit structure 21 in the reference plane and the area S12 of the crack structure in the first crack zone 231 outside the pit structure satisfy: 0.1≤S12 / S11≤0.5, for example, the value of S12 / S11 may be 0.1, 0.2, 0.3, 0.4 or 0.5. Of course, the value of S12 / S11 may also be other values, which are not limited in this embodiment. The reference plane is parallel to the positive electrode current collector 1.

[0091] The distribution of the first crack zone 231 is further limited by limiting the area ratio of the projection of the pit structure 21 in the reference plane to the projection of the crack structure in the first crack zone 231 outside the pit structure in the reference plane. When S12 / S11 exceeds 0.5, the area occupied by the crack structure 24 of the first crack zone 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 easily exceeds the extension range that the positive electrode sheet 100 can withstand. That is to say, when the pit structure 21 and the crack structure 24 are formed, or when the positive electrode sheet is subjected to expansion stress during the charge and discharge process of the electrode sheet, the positive electrode sheet may be broken, thereby causing lithium precipitation or short circuit, affecting the safety performance of the battery. Moreover, the increase in the distribution density of the crack structure 24 will also lead to the deterioration of the battery cycle performance. When S12 / S11 is less than 0.1, the gas channel formed by the crack structure 24 on the positive active layer 2 is too small to play a role in exhaust.

[0092] The spacing between the first crack zone 231 and the pit structure 21 is 0-100 μm. For example, the spacing between the first crack zone 231 and the pit structure 21 can be 0 μm, 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm or 100 μm. Of course, the spacing between the first crack zone 231 and the pit structure 21 can also be other values, which is not limited in this embodiment.

[0093] By limiting the distance between the first crack zone 231 and the edge of the pit structure 21 , the distribution area of ​​the first crack structure 241 is further limited to avoid the first crack structure 241 being distributed too far (the distance between the first crack zone 231 and the edge of the pit structure 21 exceeds 100 μm), which affects the exhaust effect of the first crack structure 241 .

[0094] refer to Figure 2 In some embodiments, the crack zone 23 further includes a second crack zone 232 located between two adjacent pit structures 21, and the crack structure 24 includes a second crack structure 242 located in the second crack zone 232. In some embodiments, the second crack structure 242 extends linearly, and both ends of the second crack structure 242 face the two adjacent pit structures 21 respectively. In other words, the second crack structure 242 may extend from one pit structure 21 to another pit structure 21.

[0095] In one embodiment, the second crack structure 242 can constitute an exhaust channel between two adjacent pit structures 21, so that 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, so that most of the first crack structures 241 and the second crack structures 242 on the positive electrode sheet 100 are interconnected to form a channel that can continuously exhaust gas to the outside, so that the gas generated inside the battery cell (especially the part close to the inner circle of the wound battery cell) can be discharged more smoothly through the channel, thereby avoiding poor interface bonding between the positive electrode sheet and the diaphragm due to gas accumulation inside the battery cell, resulting in lithium precipitation.

[0096] According to some embodiments of the present invention, the number of the second crack structures 242 is 0-5, for example, the number of the 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 the second cracks can be 1-3. In this way, the second crack structures 242 are reasonably distributed between the two pit structures 21, improving the exhaust performance while avoiding the insufficient support force of the pit structure 21 caused by too many second crack structures 242 (such as more than 5), which further causes the positive electrode active layer 2 in the pit structure 21 to fall off.

[0097] The length of the second crack structure 242 is L3, and the spacing 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 0.2-0.6. Of course, the value of L3 / L2 can also be other values, which are not limited in this embodiment.

[0098] The length of the second crack structure 242 is limited. On the one hand, the second crack structure 242 is prevented from being too long (L3 / L2 exceeds 0.95), which affects the structural stability of the adjacent pit structure 21, thereby making the positive electrode active layer 2 near the pit structure 21 easy to fall off. On the other hand, the second crack structure 242 is prevented from being too short (L3 / L2 is less than 0.2), because the second crack structure 242 has a small effect on the escape of gas.

[0099] refer to Figure 5 and Figure 6 According to some embodiments of the present invention, the width of the crack structure 24 ranges from 0.1μm to 10μm; for example, the width of the crack structure 24 may be 0.1μm, 1μm, 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm or 10μm. Preferably, the width of the crack structure 24 ranges from 1 to 5μm. Of course, the width of the crack structure 24 may also be other values, which are not limited in this embodiment. On the one hand, it is necessary to avoid the width of the crack structure 24 being too large, which may affect the structural stability of the adjacent pit structure 21, thereby making the positive electrode active layer 2 near the pit structure 21 easy to fall off, affecting the cycle performance of the battery cell. On the other hand, it is necessary to avoid the width of the crack structure 24 being too small, which may have a small exhaust effect.

[0100] The depth of the crack structure 24 is less than the depth of the pit structure 21. In this way, it is avoided that the crack structure depth is too large, which will affect the structural stability of the pit structure, resulting in too little support for the pit structure 21, causing the positive electrode active layer 2 near the pit structure 21 to easily fall off, or even too large a depth, causing the electrode sheet to easily break.

[0101] According to some embodiments of the present invention, the positive electrode sheet 100 includes a pit area 25, and the plurality of pit structures 21 are all located in the pit area 25. The ratio of the area S1 of the pit area 25 to the area S of the positive electrode sheet 100 is: 0.05≤S1 / S≤0.6; for example, the value of S1 / S may be 0.05, 0.1, 0.2, 0.3, 0.4, 0.5 or 0.6. Preferably, the value of S1 / S may be 0.2-0.4. Of course, the value of S1 / S may also be other values, which are not limited in this embodiment.

[0102] It should be noted that the pit area 25 specifically refers to the distance between the pit structure 21 closest to the inner side of the winding and the pit structure 21 closest to the outer circle of the winding in the length direction of the positive electrode sheet 100, which is the length of the pit area 25; in the width direction of the positive electrode sheet 100, the distance between the pit structure 21 closest to one side edge of the positive electrode sheet 100 and the pit structure 21 closest to the other side edge of the positive electrode sheet 100 is the width of the pit area 25. The area of ​​the pit area 25 is the product of the above length and width.

[0103] In this way, the distribution density of the pit structure 21 on the positive electrode sheet 100 is limited. If the distribution density is too small (S1 / S is less than 0.05), the ability to store electrolyte is weak, it is difficult to improve the problem of poor electrolyte infiltration, and the effect of improving the cycle performance of the battery cell is small. If the distribution density is too large (S1 / S exceeds 0.6), that is, the area of ​​the concave portion is too large, and the concave portions are too dense. When such dense concave portions are formed, the electrode sheet has to withstand a great rolling force, and the stretching of the electrode sheet is too large, which can easily cause the electrode sheet to break and other undesirable conditions, affecting the cycle performance and safety performance of the battery cell.

[0104] The ratio of the sum of the projected areas S2 of the pit structures 21 in the pit area 25 on the reference surface to the area S3 of the non-pit structures in the pit area is: 0.2≤S2 / S3≤1.4. For example, the value of S2 / S3 may 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 may be 0.4-1. Of course, the value of S2 / S3 may also be other values, which are not limited in this embodiment.

[0105] In this way, the distribution density of the pit structure 21 in the pit area 25 is further limited. If the distribution density is too small (S2 / S3 is less than 0.2), the ability to store electrolyte is weak, it is difficult to improve the problem of poor electrolyte infiltration, and the effect of improving the cycle performance of the battery cell is small. If the distribution density is too large (S2 / S3 exceeds 1.4), the area of ​​the concave part is too large, and the concave parts are too dense. When such dense concave parts are formed, the pole piece has to withstand a great rolling force, and the stretching of the positive electrode sheet 100 is too large, which can easily cause the positive electrode sheet 100 to break and other undesirable conditions, affecting the cycle performance and safety performance of the battery cell.

[0106] refer to Figure 3 and Figure 4According to some embodiments of the present invention, the pit structure 21 includes a bottom wall 212, and the width D1 of the top surface of the pit structure 21 close to the positive electrode active layer and the width D2 of the bottom wall 212 satisfy: D1 ≥ D2. In this way, the positive electrode active layer 2 of this embodiment uses ternary lithium material or lithium iron phosphate material, which has poor toughness and is prone to low plasticity and brittleness, making the positive electrode sheet easy to break or crack during rolling; under this premise, the width of the pit structure 21 exceeds the width of the bottom wall 212, so that the cross-section of the pit structure 21 along the thickness direction of the positive electrode sheet 100 presents a structure that is wide at the top and narrow at the bottom, preventing the excessive width of the bottom wall 212 from damaging the electrode sheet, and avoiding local fracture of the positive electrode sheet 100 during the processing of the pit structure 21.

[0107] refer 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 may be 1, 1.1, 1.2, 1.3, 1.4 or 1.5. Preferably, the value of D1 / D2 may be 1.05-1.2. Of course, the value of D1 / D2 may also be other values, which are not limited in this embodiment.

[0108] By limiting the ratio of D1 and D2, it is possible to prevent the width of the bottom wall 212 from being too large to damage the electrode sheet, and to avoid local fracture of the positive electrode sheet 100 during the processing of the pit structure 21, and to prevent the width of the bottom wall from being too small, which makes the morphology more sharp, and it is easy to apply too much pressure to the positive active layer of the positive electrode sheet when forming the pit structure, which is easy to cause the positive active layer to fall off. On the other hand, limiting the ratio of D1 and D2 can also control the number of cracks in the first crack zone to a certain extent, mainly by limiting the ratio of D1 and D2 to limit the force area when forming the pit structure, thereby ensuring the number of cracks and ensuring the timely exhaust and heat dissipation of the cracks.

[0109] 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, which is not limited in this embodiment.

[0110] 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, which is not limited in this embodiment.

[0111] The circumference C2 of the bottom wall 212 and the circumference C of the pit structure 21 satisfy: 1≤C2 / C≤1.5. For example, the value of C2 / C may be 1, 1.1, 1.2, 1.3, 1.4 or 1.5. Preferably, C2 / C may be 1.05-1.2. Of course, the value of C2 / C may also be other values, which are not limited in this embodiment.

[0112] By controlling the ratio of the circumference C2 of the bottom wall 212 to the circumference C of the pit structure 21, on the one hand, it is possible to avoid the circumference of the pit structure 21 being too large, and to avoid the positive electrode sheet 100 being subjected to excessive force during the processing of the pit structure 21, which may easily lead to damage such as local fractures. On the other hand, it is also possible to avoid the bottom wall being too small, which may result in a sharper morphology and may easily cause excessive pressure on the positive electrode active layer of the positive electrode sheet when the pit structure is formed, thus causing the positive electrode active layer to lose powder.

[0113] refer to Figure 3 According to some embodiments of the present invention, the spacing between two adjacent pit structures 21 is L1, the length of the first portion 22 between two adjacent pit 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, which are not limited in this embodiment.

[0114] It should be understood that the spacing between two adjacent pit structures 21 refers to the distance between the middles of the two adjacent pit structures.

[0115] Preferably, L1 / L2 may be 1.4-2. By limiting the ratio of the spacing between the pit structures 21 and the length of the first portion 22, it is equivalent to limiting the density of the pit structures 21, and by limiting the ratio of the projection area of ​​the pit structures 21 to the projection area of ​​the first portion 22, the distribution density of the pit structures 21 is further limited.

[0116] It can be understood that when the distribution density of the pit structure 21 is less than a certain value, the improvement effect on the performance of the battery is not obvious. When the distribution density of the pit structure 21 is greater than a certain value, the recesses are too dense. When such dense recesses are formed, the pole piece has to withstand a huge rolling force, and the pole piece is stretched too much, which can easily cause the positive electrode sheet 100 to break and other adverse conditions, affecting the cycle performance and safety performance of the battery cell.

[0117] refer to Figure 4 According to some embodiments of the present invention, the pit structure 21 may further include a side wall 213, and the angle a1 between the side wall 213 and the bottom wall 212 may be in the range of 90°<a1<160°. For example, a1 may be 91°, 95°, 100°, 105°, 110°, 120°, 125°, 130°, 135°, 140°, 145°, 150°, 155° or 159°. Preferably, a1=100°-135°. Of course, the degree of a1 may also be other values, which is not limited in this embodiment.

[0118] On the one hand, if the angle of a1 is too small (such as less than 90°), the bottom wall 212 of the pit structure 21 is subjected to a large force during the processing of the pit structure 21, resulting in insufficient support stability of the pit structure 21, and the positive electrode active layer 2 is prone to powdering during the processing, affecting the cycle performance and safety performance of the battery. On the other hand, if the angle of a1 is too large (such as more than 160°), the size difference between the pit structure 21 and the bottom wall 212 is small, the rolling action area on the positive electrode active layer 2 is large, and the processing to the designed depth is difficult. If it is to be processed to the designed depth, there is a risk of excessive force on the pole piece and local fracture.

[0119] According to some embodiments of the present invention, the positive electrode active coating is disposed on one side of the positive electrode current collector 1, and the depth h1 of the pit structure 21 and the sum of the thickness h 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 satisfy: 1 / 20≤h1 / h≤1 / 2, for example, the value of h1 / h may be 1 / 20, 1 / 15, 1 / 10, 1 / 5, 1 / 3 or 1 / 2, preferably, h1 / h may be 1 / 10-1 / 3. Of course, the value of h1 / h may also be other values, which are not limited in this embodiment.

[0120] By limiting the ratio of the depth of the pit structure 21 to the sum of the thickness 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 prevented from being too small (h1 / h is less than 1 / 20), which has little effect on improving the performance of the battery. On the other hand, the depth of the pit structure 21 is prevented from being too large (h1 / h exceeds 1 / 2), which prevents excessive damage to the positive electrode active layer 2 when the pit structure is formed, causing the positive electrode active layer 2 to fall off from the positive electrode current collector 1.

[0121] The depth h1 of the pit structure 21 has a value range of 1 μm ≤ h1 ≤ 40 μm. For example, the depth h1 of the pit structure 21 may be 1 μm, 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm or 40 μm. Preferably, the depth h1 of the pit structure 21 may be 5 μm-30 μm. Of course, the depth h1 of the pit structure 21 may also be other values, which is not limited in this embodiment.

[0122] By limiting the depth of the pit structure 21, the extension force to which the positive electrode active layer 2 is subjected when the pit structure 21 is formed can be controlled, and the distribution of the crack structure 24 can be controlled, thereby ensuring the exhaust effect and heat dissipation effect of the crack structure. If the depth of the pit structure 21 is too small, the improvement effect on the battery performance is not good. If the depth of the pit structure 21 is too large, the positive electrode sheet 100 may be subjected to excessive extension force when the pit structure 21 is formed, resulting in excessive stretching of the positive electrode sheet 100 and rupture.

[0123] In a second aspect, an embodiment of the present invention further provides a battery cell, which may include: a negative electrode sheet, a separator and the above-mentioned positive electrode sheet 100 , wherein the positive electrode sheet 100 , the separator and the negative electrode sheet are stacked and wound to form the battery cell.

[0124] The positive electrode sheet 100 may include a first region and a second region, wherein the first region corresponds to a straight portion and the second region corresponds to a bent portion of the battery cell. In other words, when the positive electrode sheet 100 is in an unfolded state, the first region and the second region on the positive electrode sheet 100 are spaced apart.

[0125] The pit structure 21 is provided in at least one of the first region and the second region. For example, the pit structure 21 can be provided in the first region, or the pit structure 21 can also be provided in the second region, or both the first region and the second region can be provided with the pit structure 21.

[0126] The battery cell of the present invention uses the above-mentioned positive electrode sheet 100, and the pit structure 21 of the positive electrode sheet 100 is conducive to accommodating more electrolyte while improving the infiltration effect of the electrolyte. A crack structure 24 is formed when the pit structure 21 is processed. When gas is generated in the battery during high-temperature cycling, the gas can be discharged from the crack structure 24 in the crack area 23 of the positive electrode sheet 100, and the internal pressure of the battery is released in time to ensure that there is sufficient adhesion on the interface formed between the positive electrode sheet 100 and the diaphragm, thereby avoiding the occurrence of lithium dendrites on the negative electrode sheet. At the same time, the temperature of the positive electrode sheet 100 during the cycle can also be maintained, so that the battery cell has a stable reaction environment, which is conducive to improving the cycle performance of the battery and extending the service life of the battery.

[0127] In some embodiments, the first region is provided with a first concave structure 21, the second region is provided with a second concave structure 21, the depth of the first concave structure 21 is h11, the depth of the second concave 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, which are not limited in this embodiment.

[0128] In this way, it can be understood that when winding to form a battery cell, the extrusion force on the bent portion of the electrode sheet is much greater than the extrusion force on the straight portion of the electrode sheet; the depth of the second pit structure 21 in the second area of ​​the bent portion exceeds the depth of the first pit structure 21 in the first area, and the second pit structure 21 can effectively support the diaphragm and the negative electrode sheet, increase the gap between the pole sheets in the bent portion, and help to relieve the stress on the positive electrode sheet 100 when bending, and prevent the pole sheet in the bent portion from being subjected to excessive force and local fracture. At the same time, avoid the depth of the second pit structure 21 exceeding the depth of the first pit structure 21 by too much (h12 / h11 exceeds 1.5), which reduces the flatness of the battery cell, increases the overall width of the battery cell, and affects the energy density of the battery.

[0129] In some embodiments, the positive electrode sheet 100 includes a pit area 25 located in the second region, that is, the pit area 25 may be a partial structure of the second region, or the pit area 25 may also be constituted by the second region.

[0130] The length L1 of the pit area 25 satisfies the formula: (0.5π(Rmin+H)≤L1≤π(Rmax+H), where Rmin is the arc curvature of the innermost circle of the bent portion (second region), Rmax is the curvature of the outermost circle of the bent portion (second region), and H is the thickness of the positive electrode sheet 100. In this way, the pit area 25 can be located as much as possible within the bent second region, thereby increasing the gap formed between the positive electrode sheet 100 and the diaphragm when bent, which is conducive to releasing the concentrated stress on the electrode sheet at the corner when bent.

[0131] refer to Figure 5 and Figure 6In some embodiments, the positive electrode sheet 100 includes a pit area 25, and the plurality of pit structures 21 are all located in the pit area 25. The positive electrode sheet 100 may further include: a first space avoidance area 110 and a second space avoidance area 120 located on opposite sides of the pit area 25 along the length direction of the positive electrode sheet 100, the first space avoidance area 110 corresponds to the winding start end of the positive electrode sheet 100, and the second space avoidance area 120 corresponds to the winding end of the positive electrode sheet 100. In other words, the first space avoidance area 110 and the second space avoidance area 120 are respectively arranged at the winding start end and the winding end when the battery cell is wound, and the pit structure 21 is not arranged in the first space avoidance area 110 and the second space avoidance area 120.

[0132] The dimension K1 of the first air avoidance area 110 along the length direction of the positive electrode sheet 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, which are not limited in this embodiment. In this way, the first air avoidance area 110 is set at the starting end of the winding of the positive electrode sheet 100, which provides a buffering effect for the winding operation and avoids folding and powder loss at the starting end of the winding.

[0133] The dimension K2 of the second air avoidance area 120 along the length direction of the positive electrode sheet 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, which are not limited in this embodiment. In this way, the second air avoidance area 120 is provided at the winding end of the positive electrode sheet 100, which further improves the structural stability of the positive electrode sheet 100 during winding, and avoids the phenomenon that the winding is unstable and easy to fold at the winding end.

[0134] According to some embodiments of the present invention, the positive electrode sheet 100 includes a plurality of coils formed by winding, and the first air-avoiding area 110 constitutes at least the innermost coil of the plurality of coils. In other words, the structure of the coil formed by the first bending and the second bending of the innermost coil of the positive electrode sheet 100 of the battery cell before the first bending constitutes the first air-avoiding area 110, thus further improving the structural stability of the positive electrode sheet 100 during winding, and avoiding the situation of folding and powder falling at the starting end of winding.

[0135] refer to Figure 5 and Figure 6According to some embodiments of the present invention, the positive electrode current collector 1 is provided with a tab connection area 150 at one side edge along the width direction of the positive electrode sheet 100, and the tab connection area 150 is provided with 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 in the width direction of the positive electrode sheet 100; the positive electrode sheet 100 includes a third air-avoiding area 130 located between the ceramic layer and the pit structure 21, and the dimension M1 of the third air-avoiding area along the width direction of the positive electrode sheet is: 5mm≤M1≤30mm, for example, M1 may be 5mm, 10mm, 15mm, 20mm, 25mm or 30mm. Preferably, M1 may be 5mm-20mm. Of course, M1 may also be other values, which are not limited in this embodiment.

[0136] In this way, the edge powder loss of the positive electrode sheet 100 during the winding process is avoided, and the structural stability of the positive electrode sheet 100 during the winding process is improved.

[0137] It can be understood that when the positive electrode sheet 100 does not have a ceramic area that matches the multiple pole ears 151 along the width direction, M1 is the distance between the edge of the pit area 25 and the edge of the corresponding side of the width of the positive electrode sheet 100. When the positive electrode sheet 100 has a ceramic area that matches the multiple pole ears 151 along the width direction, M1 is the distance between the edge of the pit area 25 and the ceramic area.

[0138] The positive electrode sheet 100 includes a fourth space-avoiding area 140 located on the other side of the pit area 25 along the width direction of the positive electrode sheet 100. The size M2 of the fourth space-avoiding area 140 along the width direction of the positive electrode sheet 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, which are not limited in this embodiment.

[0139] In this way, the powder loss at the edge of the positive electrode sheet 100 during the winding process is further avoided, and the structural stability of the positive electrode sheet 100 during the winding process is improved. In addition, since the two sides of the pit area 25 along the width direction have M1 and M2 respectively, the pit area 25 is located near the middle of the positive electrode sheet 100, which avoids the powder loss at the edge of the positive electrode sheet 100 when the pit structure 21 is formed.

[0140] refer to Figure 6According to some embodiments of the present invention, a tab connection area 150 is provided at one side edge of the positive electrode sheet 100 in the width direction, and the tab connection area 150 is provided with a plurality of tabs 151 spaced apart along the length direction of the positive electrode sheet 100, wherein the tab connection area 150 and the tabs 151 may be arranged in such a manner that a plurality of tab connection areas 150 are provided on the positive electrode sheet 100, and each tab connection area 150 is respectively provided with one or more tabs 151. Alternatively, a tab connection area 150 is provided at one side of the positive electrode sheet 100 in the width direction, and the tab connection area 150 extends along the length direction of the positive electrode sheet 100, and a plurality of tabs 151 are spaced apart and arranged in the tab connection area 150 along the length direction of the positive electrode sheet 100.

[0141] The tab connection area 150 is not provided with the positive electrode active layer 2, and the tab connection area 150 is located between the third air-avoiding area 130 and the pit area 25. In this way, the tab 151 can be directly connected to the positive electrode current collector 1, thereby improving the current conduction efficiency and thus improving the performance of the battery.

[0142] refer to Figure 6 According to some embodiments of the present invention, the pit area 25 may include a plurality of sub-pit areas 251 spaced apart along the length direction of the positive electrode sheet 100, and a pole ear connection area 150 is provided at one side edge of the positive electrode current collector 1 along the width direction of the positive electrode sheet 100, and the pole ear connection area 150 is located between two adjacent sub-pit areas 251, and the pole ear connection area 150 is provided with at least one pole ear 151, and the spacing between the pole ear 151 and any sub-pit area 251 on both sides is 5mm-30mm, for example, the spacing between the pole ear 151 and any sub-pit area 251 may be 5mm, 10mm, 15mm, 20mm, 25mm or 30mm. Of course, the spacing between the pole ear 151 and any sub-pit area 251 may also be other values, which is not limited in this embodiment.

[0143] In this way, when processing the pit structure 21 , it can be staggered with the pole tab 151 to avoid damaging the pole tab 151 and affecting the cycle performance of the battery.

[0144] According to some embodiments of the present invention, the pit area 25 includes a plurality of sub-pit areas 251 spaced apart along the length direction of the positive electrode sheet 100, and a tape connection area 11 is provided on one side edge of the positive electrode current collector 1 along the width direction of the positive electrode sheet 100, and the tape connection area 11 is located between two adjacent sub-pit areas 251, and the spacing between the tape connection area 11 and any one of the sub-pit areas 251 on both sides is 5mm-30mm. For example, the spacing between the tape connection area 11 and any one of the sub-pit areas 251 can be 5mm, 10mm, 15mm, 20mm, 25mm or 30mm. Of course, the spacing between the tape connection area 11 and any one of the sub-pit areas 251 can also be other values, which is not limited in this embodiment.

[0145] In this way, when processing the concave-convex structure, it can be staggered with the adhesive tape connecting area 11 to avoid damaging the adhesive tape protecting the tab 151 and affecting the cycle performance of the battery.

[0146] The present invention is further described below by specific embodiments:

[0147] Example 1

[0148] 1. Preparation of positive electrode

[0149] NCM811, a conductive agent (a mixture of conductive carbon black and carbon nanotubes), and PVDF are placed in NMP in a mass ratio of 97.60:1.35:1.05, stirred evenly, and a positive electrode active layer slurry is prepared; the positive electrode active layer slurry is evenly coated on the front and back surfaces of the positive electrode current collector, and the coating surface density is 0.01704 g / cm2.

[0150] After drying and rolling treatment in sequence, a positive electrode sheet with a double-sided positive electrode active layer thickness of 90μm was obtained; the positive electrode sheet was cut, and a concave-convex structure was processed on the cut positive electrode sheet using a rolling equipment containing a convex portion, the height of the convex portion was 6μm, the angle between one side of the convex portion and the roller body was 125°, and the width of the junction between the convex portion and the roller body was 320μm.

[0151] The obtained positive electrode parameters are shown in Table 1.

[0152] 2. Preparation of negative electrode sheet

[0153] Artificial graphite, conductive carbon black, styrene-butadiene rubber and sodium carboxymethyl cellulose are placed in deionized water at a mass ratio of 97.2:0.5:1.3:1; the above slurry is stirred evenly to obtain a negative electrode active layer slurry; and the negative electrode active layer slurry is evenly coated on the negative electrode current collector.

[0154] After drying, rolling and slitting in sequence, the slit negative electrode sheet is grooved by laser, and grooves are set on the entire surface of the negative electrode sheet. The grooves here are matrix grooves, the spacing between adjacent grooves is set to 1.2mm, and the groove depth is ~18μm; after the electrode sheet is laser treated, it is cleaned and sheeted to obtain the negative electrode sheet;

[0155] 3. Preparation of batteries

[0156] The separator of the present application adopts a 9μm thick substrate + ceramic + coated separator. The electrolyte includes lithium salt LiPF6 and a solvent, and the solvent includes ethylene carbonate (EC), diethyl carbonate (DEC) and ethyl methyl carbonate (EMC), wherein the molar ratio of the three is DEC:EC:EMC=1:1:1. The above-mentioned cut positive electrode sheet 100, separator, and negative electrode sheet are stacked in sequence and wound into a wound structure battery cell. The battery cell is packaged, injected, formed, and sealed twice to obtain a lithium-ion battery.

[0157] It can be understood that the performance parameters of the pit structure and crack structure formed on the positive electrode sheet are mainly related to the parameters of the protrusions on the rolling equipment. By changing the height of the protrusions on the rolling equipment, the spacing between the protrusions and the rolling force, positive electrode sheets of multiple different embodiments are obtained and performance testing experiments are carried out.

[0158] 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.

[0159] 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.

[0160] In Example 4, 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 area of ​​the pit zone to the area of ​​the positive electrode sheet S1 / S changes to 0.08.

[0161] In Example 5, 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 area of ​​the pit zone to the area of ​​the positive electrode sheet S1 / S changes to 0.57.

[0162] 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 D1 of the pit structure is changed to 100.

[0163] 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.

[0164] 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, and 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 a1 between the side wall and the bottom wall of the pit structure changes to 93°.

[0165] 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, and 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 a1 between the side wall and the bottom wall of the pit structure changes to 158°.

[0166] In Example 10, compared with Example 1, the depth h1 of the pit structure is changed to 15 μm.

[0167] 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 increases 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 38μm.

[0168] In Example 12, 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, the ratio of the area of ​​the pit zone to the area of ​​the positive electrode sheet S1 / S changes to 0.14, and the ratio of the sum of the projected areas of all the pit structures to the area of ​​the first part of the pit zone S2 / S3 changes to 0.21.

[0169] 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, and 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 of the pit zone S2 / S3 changes to 1.38.

[0170] In Example 14, compared with Example 1, the positive electrode active material is lithium iron phosphate.

[0171] In Example 15, compared with Example 1, the positive electrode active material is lithium manganese phosphate.

[0172] In Example 16, compared with Example 1, the positive electrode active material adopts lithium cobalt oxide.

[0173] In Comparative Example 1, compared with Example 1, the ratio of the length of the first crack zone to the perimeter of the pit structure C1 / C is 0.13, at this time, the ratio of the area of ​​the first crack zone to the area of ​​the pit structure S12 / S11 becomes 0.04, and the depth h1 of the pit structure is changed to 2μm.

[0174] 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 1.53, 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 is changed to 45μm.

[0175] In Comparative Example 3, compared with Example 1, the ratio of the length of the first crack zone to the circumference 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 ratio of the area of ​​the pit zone to the area of ​​the positive electrode sheet S1 / S is 0.01, and the depth h1 of the pit structure is changed to 25 μm.

[0176] In Comparative Example 4, compared with Example 1, the ratio of the length of the first crack zone to the circumference 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 ratio of the area of ​​the pit zone to the area of ​​the positive electrode sheet S1 / S is 0.01, and the depth h1 of the pit structure is changed to 25 μm.

[0177] In Comparative Example 5, compared with Example 1, the ratio of the length of the first crack zone to the circumference 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, the ratio of the area of ​​the pit zone to the area of ​​the positive electrode sheet S1 / S is 0.01, the depth h1 of the pit structure is changed to 25μm, and the width D1 of the pit structure is changed to 54μm.

[0178] In Comparative Example 6, compared with Example 1, the ratio of the length of the first crack zone to the circumference 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, the ratio of the area of ​​the pit zone to the area of ​​the positive electrode sheet S1 / S is 0.01, the depth h1 of the pit structure is changed to 25μm, and the width D1 of the pit structure is changed to 2438μm.

[0179] 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, and the ratio of the area of ​​the first crack zone to the area of ​​the pit structure S12 / S11 becomes 0.31, the ratio of the area of ​​the pit zone to the area of ​​the positive electrode sheet S1 / S is 0.01, the depth h1 of the pit structure is changed to 25μm, and the angle a1 between the side wall and the bottom wall of the pit structure is 168°.

[0180] In Comparative Example 8, compared with Example 1, no crack structure is provided and the depth of the pit structure is set to 0.5 μm.

[0181] 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 increases to 0.96, and the ratio of the area of ​​the first crack zone to the area of ​​the pit structure S12 / S11 becomes 0.48.

[0182] In Comparative Example 10, no crack structure and no pit structure are provided.

[0183] Table 1. Parameters of positive electrode sheets of various embodiments and comparative examples

[0184]

[0185] It can be understood that the pit structure on the positive electrode sheet of the present invention is formed by rolling of the processing equipment. Therefore, when the parameters of the processing equipment are adjusted, the quantitative data in each group of data will fluctuate. Among them, the difference in the width of the pit structure does not exceed 10μm, and the pit structure widths of the two groups of data are regarded as the same. Similarly, the difference between the widths of the crack structure is within 0.2μm, and the widths of the crack structure are regarded as the same; the angle between the side wall and the bottom wall of the pit structure fluctuates within 10°, and the angle is regarded as unchanged.

[0186] The above embodiments and comparative examples were tested as follows:

[0187] Liquid retention test: Each battery is filled with a certain amount of liquid, for example, the liquid filling amount of each battery n1 is 8.5g±0.1g, and then aged. After aging, the battery is formed into a second seal after sorting. The second seal is to extract excess electrolyte, and the remaining electrolyte volume is the liquid retention volume n2; then n2=(weight after second sealing m2-weight before filling m1).

[0188] Appearance test of the positive electrode sheet after manufacturing the pit structure: Use a 3D microscope to observe the positive electrode sheet after processing the pit structure to observe whether there is any damage on the positive electrode sheet and the size of the damaged area.

[0189] Cycle retention rate and expansion change rate test, cycle test: the lithium-ion battery is charged and cycled on the blue electric test cabinet, the test conditions are 25℃±2℃, 3.2C charge 4.37V, 2.8C charge 4.37V, 2C charge 4.53V, 1.5C charge 4.58V, cut off 0.05C; 0.7C discharge 3V. The specific method is: stand at 25℃±2℃ for 5 minutes, 0.2C discharge to the lower limit voltage; stand for 5 minutes, 0.7C charge to the upper limit voltage, cut off 0.025C, stand for 5 minutes, 0.2C discharge to the lower limit voltage; (do initial capacity test), stand for 5 minutes, 3.2C charge 4.37V, 2.8C charge 4.37V, 2C charge 4.53V, 1.5C charge 4.58V, cut off 0.05C. Measure and record the data of the fully charged state, including voltage and thickness. Stand for 5min at 25℃±2℃, discharge 3V at 0.7C, stand for 5min, charge 4.37V at 3.2C, charge 4.37V at 2.8C, charge 4.53V at 2C, charge 4.58V at 1.5C, cut off at 0.05C, stand for 5min, discharge 3V at 0.7C, stand for 5min, 8~91200 times, repeat 3~4 steps at 25℃ for capacity test every 100 times, first 200T: measure the voltage and thickness of the fully charged cell every 50T, after 200T: measure the voltage and thickness of the fully charged cell every 100T. Then test the capacity retention rate and expansion change rate of lithium-ion batteries at 200T and 400T. Battery expansion rate = (full-charge thickness of battery cycle N times - battery sample thickness) / battery sample thickness * 100%).

[0190] Table 2. Test performance of positive electrode sheets of various embodiments and comparative examples

[0191]

[0192] In combination with the comparative example and embodiments 1-13, the provision of a pit structure and a crack structure can reduce the occurrence of lithium plating in the battery.

[0193] Referring to Example 1 and Example 2, a larger or smaller ratio C1 / C of the length of the first crack zone to the perimeter of the pit structure may result in lithium deposition in the battery. In combination with Examples 3-7, under the condition of a suitable ratio C1 / C of the length of the first crack zone to the perimeter of the pit structure, the battery has good cycle performance and lithium deposition will not occur.

[0194] In combination with Examples 1 and 2 and Comparative Examples 1 and 2, increasing the ratio of the length of the first crack zone to the circumference of the pit structure C1 / C and the depth of the pit structure is beneficial to improving the liquid retention of the battery and increasing the capacity retention rate of the battery to a certain extent. However, it increases the expansion change rate of the battery and correspondingly reduces the cycle retention rate of the battery.

[0195] In combination with Examples 3-5 and Comparative Examples 3-4, the ratio S1 / S of the area of ​​the pit area to the area of ​​the positive electrode sheet has an important influence on the capacity retention rate of the battery. If the ratio S1 / S of the area of ​​the pit area to the area of ​​the positive electrode sheet is too large or too small, the capacity retention rate of the battery will decrease.

[0196] In combination with Examples 3, 6, 7 and Comparative Examples 5 and 6, the width of the pit structure has an important influence on the lithium deposition of the battery. When the width of the pit structure is too large or too small, it will cause lithium deposition in the battery.

[0197] In combination with Examples 8 and 9 and Comparative Example 7, when the angle a1 between the side wall and the bottom wall of the pit is within an appropriate range, lithium deposition will not occur in the battery. However, if the angle a1 between the side wall and the bottom wall of the pit is too large, lithium deposition in the battery will not be reduced.

[0198] In combination with Examples 1, 2, 10, 11 and Comparative Example 8, the crack structure can reduce the occurrence of lithium deposition in the battery, and the depth of the pit structure has a greater impact on the lithium deposition than the ratio of the length of the first crack zone to the circumference of the pit structure C1 / C.

[0199] In combination with Examples 3, 12, and 13, the ratio S2 / S3 of the sum of the projected areas of all the pit structures to the area of ​​the first part in the pit area is larger, that is, when the distribution density of the pit structures is larger, the battery can have a higher capacity retention rate and cycle retention rate. However, further combined with Comparative Example 9, when the ratio S2 / S3 of the sum of the projected areas of all the pit structures to the area of ​​the first part in the pit area is too large, lithium deposition will occur in the battery.

[0200] Further combined with Examples 1, 14-16, the selection of positive electrode active materials will also affect the performance of the battery. When the positive electrode active material uses NCM811 (ternary lithium) and lithium cobalt oxide, the battery is prone to lithium precipitation. When the positive electrode active material uses lithium iron phosphate or lithium manganese phosphate, the battery does not produce lithium precipitation. In addition, when the positive electrode active material uses lithium iron phosphate or lithium manganese phosphate, the battery cycle retention rate is higher. Therefore, the positive electrode active material can use lithium iron phosphate or lithium manganese phosphate, which is beneficial to improve the overall performance of the battery.

[0201] It should be noted that the embodiments represented by "one embodiment", "an embodiment", "an exemplary embodiment", "some embodiments", etc. mentioned in the specification may include specific features, structures or characteristics, but not every embodiment may include the specific features, structures or characteristics. In addition, such phrases do not necessarily refer to the same embodiment. In addition, when describing specific features, structures or characteristics in conjunction with an embodiment, it is within the knowledge of those skilled in the art to implement such features, structures or characteristics in conjunction with other embodiments that are explicitly or not explicitly described.

[0202] In general, terms should be understood, at least in part, by the context in which they are used. For example, the term "one or more" as used herein may be used to describe any feature, structure, or characteristic in a singular sense, or may be used to describe a combination of features, structures, or characteristics in a plural sense, depending, at least in part, on the context. Similarly, terms such as "a," "an," or "the" may also be understood to convey singular usage or to convey plural usage, depending, at least in part, on the context.

[0203] It should be easily understood that “on,” “above,” and “over” in the present disclosure should be interpreted in the broadest manner, so that “on” not only means “directly on something,” but also includes the meaning of “on something” with intervening features or layers therebetween, and “above” or “over” not only includes the meaning of “above” or “over,” but also may include the meaning of “above” or “over something” with no intervening features or layers therebetween (i.e., directly on something).

[0204] In addition, spatially relative terms, such as "below," "below," "beneath," "above," "above," etc., may be used herein for ease of description 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 in addition to the orientation shown in the figures. The device may have other orientations (rotated 90 degrees or at other orientations), and the spatially relative descriptors used herein may likewise be interpreted accordingly.

[0205] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit it. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A positive electrode sheet, characterized in that: include: Positive electrode current collector; A positive electrode active layer is coated on the surface of the positive electrode current collector, the positive electrode active layer is provided with a plurality of pit structures arranged at intervals, the positive electrode active layer includes a first portion located between two adjacent pit structures, at least a portion of the first portion constitutes a crack zone, and the crack zone forms 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, 、 At least one of Among them, 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 zone includes a first crack zone extending along the circumference of the pit structure, and the crack structure includes a first crack structure located in the first crack zone. The length C1 of the first crack structure in the circumference of the pit structure is smaller than the circumference 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 zone is located in a chamfered area between a 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 projection area S11 of the pit structure in 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 zone and the pit structure is 0-100 μm.

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

5. The positive electrode sheet according to claim 4, characterized in that: The second crack structure extends linearly, and two ends of the second crack structure are respectively directed toward two adjacent pit structures.

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

95.

7. The positive electrode sheet according to any one of claims 1 to 6, characterized in that: 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 smaller than the depth of the pit structure.

8. The positive electrode sheet according to any one of claims 1 to 6, characterized in that: The positive electrode sheet includes a pit area, the plurality of pit structures are all located in the pit area, and the ratio of the area S1 of the pit area to the area S of the positive electrode sheet 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 area on the reference surface to the area S3 of the non-pit structures in the pit area is: 0.2≤S2 / S3≤1.

4.

9. The positive electrode sheet according to any one of claims 1 to 6, characterized in that: The pit structure comprises a bottom wall, A width D1 of a top surface of the pit structure close to the positive electrode active layer and a width D2 of the bottom wall satisfy: D1 ≥ D2.

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

5.

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

5.

12. The positive electrode sheet according to claim 9, characterized in that: The pit structure further includes a side wall, and the value range of the angle a1 between the side wall and the bottom wall is: 90°<a1<160°.

13. The positive electrode sheet according to any one of claims 1 to 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 of the thickness h 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 has a value range of 1 μm≤h1≤40 μm.

14. A battery cell, characterized in that: include: Negative electrode; Diaphragm; The positive electrode sheet according to any one of claims 1 to 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 sheet includes a first area and a second area, wherein the first area corresponds to a straight portion of the battery cell, and the second area corresponds to a bent portion of the battery cell. The pit structure is disposed 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 is provided with a first pit structure, and the second region is provided with a second pit structure. The depth of the first pit structure is h11, and the depth of the second pit 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 sheet includes a concave region located in the second region, The length L1 of the pit area satisfies the formula: 0.5π(Rmin+H)≤L1≤π(Rmax+H), wherein Rmin is the arc curvature of the innermost circle layer of the second area, Rmax is the curvature of the outermost circle layer of the second area, and H is the thickness of the positive electrode sheet.

17. The battery cell according to claim 14, characterized in that: The positive electrode sheet includes a pit area, and the plurality of pit structures are all located in the pit area. The positive electrode sheet further includes: a first avoidance area and a second avoidance area located on opposite sides of the pit area along the length direction of the positive electrode sheet, wherein the first avoidance area corresponds to the winding start end of the positive electrode sheet, and the second avoidance area corresponds to the winding end end of the positive electrode sheet. The dimension K1 of the first air-avoiding area along the length direction of the positive electrode sheet is: 10 mm ≤ K1 ≤ 300 mm; and / or, The dimension K2 of the second air-avoiding area along the length direction of the positive electrode sheet is: 10 mm ≤ K2 ≤ 100 mm.

18. The battery cell according to claim 17, characterized in that: The positive electrode sheet includes a plurality of winding layers, and the first air-avoiding area at least constitutes the innermost layer among the plurality of winding layers.

19. The battery cell according to claim 18, characterized in that: The positive electrode current collector is provided with a tab connection area at one side edge along the width direction of the positive electrode sheet, and the tab connection area is provided with a plurality of tabs distributed at intervals along the length direction of the positive electrode sheet; The positive electrode sheet includes a ceramic layer located on one side of the positive electrode sheet in a width direction; The positive electrode sheet includes a third space-avoiding area between the ceramic layer and the pit structure; A dimension M1 of the third air-avoiding area along the width direction of the positive electrode sheet is: 5 mm ≤ M1 ≤ 30 mm.

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 direction of the positive electrode sheet. A pole lug connection area is provided on one side edge of the positive electrode collector along the width direction of the positive electrode sheet. The pole lug connection area is located between two adjacent sub-pit areas. The pole lug connection area is provided with at least one pole lug, and the spacing between the pole lug and any one of the sub-pit areas on both sides is 5 mm-30 mm.

21. 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 direction of the positive electrode sheet. A tape connection area is provided on one side edge of the positive electrode collector along the width direction of the positive electrode sheet. The tape connection area is located between two adjacent sub-pit areas. The spacing between the tape connection area and any one of the sub-pit areas on both sides is 5mm-30mm.

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