Secondary battery and battery pack

Abstract

The embodiment of the utility model discloses a secondary battery and a battery pack, the secondary battery comprises an electrode roll formed by winding a first pole piece, a diaphragm and a second pole piece, and the diaphragm is arranged between the first pole piece and the second pole piece; one of the first pole piece and the second pole piece is a positive pole piece, the other one is a negative pole piece, the first pole piece comprises a first active layer, and the second pole piece comprises a second active layer; the electrode roll is provided with a flat part and bent parts located at the two opposite ends of the flat part, at least one of the first active layer and the second active layer is provided with a first groove located in the flat part, at least one of the first active layer and the second active layer is provided with a second groove located in the bent part, and notches of the first groove and the second groove located in the same active layer face the active layer of the adjacent pole piece; in the second direction, the size of the first groove is larger than that of the second groove. By adopting the structural design, the electrolyte infiltration time of the thick-coated pole piece can be shortened, the stress of the pole piece at the bending part can be reduced, and the low-temperature performance, the rate performance and the fast-charge cycle performance of the battery can be improved.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to a secondary battery and a battery pack. Background Art

[0002] With the rapid development of mobile phones, laptops, electric vehicles, power tools, etc., secondary batteries with high energy density, high cycle life and high safety performance have been widely used and developed. There is an urgent need for secondary batteries with larger capacity, better durability and longer battery life. Therefore, how to improve the rate performance and cycle performance of secondary batteries has become an urgent problem to be solved. Utility Model Content

[0003] Embodiments of the present application provide a secondary battery and a battery pack to improve the rate performance and cycle performance of the secondary battery.

[0004] In order to solve the above technical problems, the embodiments of the present application disclose the following technical solutions:

[0005] In one aspect, a secondary battery is provided, comprising:

[0006] An electrode roll, wherein the electrode roll is wound by a first electrode sheet, a diaphragm and a second electrode sheet, wherein the diaphragm is disposed between the first electrode sheet and the second electrode sheet; one of the first electrode sheet and the second electrode sheet is a positive electrode sheet and the other is a negative electrode sheet, wherein the first electrode sheet includes a first active layer and the second electrode sheet includes a second active layer;

[0007] The electrode roll has a flat portion and curved portions at opposite ends of the flat portion; a first groove is formed in a portion of at least one of the first active layer and the second active layer located at the flat portion, and a second groove is formed in a portion located at the curved portion; and the notches of the first groove and the second groove located on the same active layer are both oriented toward the active layer of the adjacent electrode piece;

[0008] The electrode roll is unfolded to a flat state, and has a first direction and a second direction intersecting with each other;

[0009] The same pole piece has a first area and a second area arranged alternately along a first direction; the first groove is arranged in the first area, and the second groove is arranged in the second area;

[0010] In the second direction, the size of the first groove is larger than the size of the second groove.

[0011] In some embodiments, the first electrode sheet is a negative electrode sheet, the first electrode sheet further comprises a negative electrode current collector, and the first active layer is attached to at least one surface of the negative electrode current collector;

[0012] The first groove and the second groove are both opened in the first active layer, and the notches of the first groove and the second groove are both oriented toward the second active layer adjacent to the first active layer.

[0013] In some embodiments, when the electrode roll is unfolded to a flat state, a plurality of first grooves are provided in each first region of the first active layer, each of the first grooves extends along the second direction, and the plurality of first grooves are arranged at intervals along the first direction;

[0014] A plurality of second grooves are provided in each second region of the first active layer, and the plurality of second grooves are arranged in a plurality of rows and columns at intervals in the first direction and the second direction.

[0015] In some embodiments, when the electrode roll is unfolded to a flat state, there are n second regions in the first electrode sheet, and the size of the nth second region in the first direction is L n mm, meet: L n =L1+(n-1)[π(2H1+H2+H3)];

[0016] Wherein, L1 mm is the size of the first second region in the first direction, satisfying: 1≤L1≤5; H1μm is the thickness of the diaphragm; H2μm is the thickness of the second pole piece; H3μm is the thickness of the first pole piece; and n is the number of bending times of the electrode roll.

[0017] In some embodiments, when the electrode roll is unfolded to a flat state, the number of columns of the second grooves in the nth second region of the first electrode sheet is K. n , satisfying: K n =L n / T1;

[0018] Wherein, T1 μm is the distance between two adjacent second grooves in the second region in the first direction.

[0019] In some embodiments, when the electrode roll is unfolded to a flat state, a distance T1 μm between two adjacent second grooves in the same second region in the first direction satisfies: 250≤T1≤1000.

[0020] In some embodiments, the size of each of the first regions in the first direction is W mm, satisfying: 30≤W≤400; and / or,

[0021] When the electrode roll is unfolded to a flat state, a distance between two adjacent first grooves in each first region in the first direction is T2 μm, satisfying: 1000≤T2≤2000.

[0022] In some embodiments, the depth of the first groove is h1 μm, the thickness of the first active layer attached to one side of the negative electrode current collector is h2 μm, and the depth of the second groove is h3 μm, satisfying: 0.1≤h1 / h2≤0.8; and / or, 0.1≤h3 / h2≤0.8.

[0023] In some embodiments, when the electrode roll is unfolded to a flat state, the size of the first groove in the first direction is T3 μm, satisfying: 50≤T3≤150; and / or,

[0024] The size of the second groove in the first direction is T4 μm, satisfying: 50≤T4≤150.

[0025] In some embodiments, the first electrode sheet further includes a negative electrode ear connected to the negative electrode current collector;

[0026] The first active layer has a first edge and a second edge arranged opposite to each other in the second direction, and the first edge is arranged closer to the negative electrode ear relative to the second edge;

[0027] The dimension between one end of the first groove close to the first edge and the first edge is P1 mm, satisfying: 1≤P1≤5; and / or,

[0028] A dimension between one end of the first groove close to the second edge and the second edge is P2 mm, satisfying the condition 0≤P2≤3.

[0029] In some embodiments, the dimension between the second groove closest to the first edge and the first edge is P3 mm, satisfying: 1≤P3≤5; and / or,

[0030] The dimension between the second groove closest to the second edge and the second edge is P4 mm, satisfying; 0≤P4≤3.

[0031] In some embodiments, the electrode roll further has a third direction intersecting the first direction and the second direction in pairs;

[0032] Along the third direction, the orthographic projection of the notch of the second groove on the negative electrode current collector is at least one of a circle, an ellipse or a strip.

[0033] On the other hand, a battery pack is further disclosed. In some embodiments, the battery pack includes a case; and a secondary battery as described in any one of the above items, wherein the secondary battery is accommodated in the case.

[0034] One of the above technical solutions has the following advantages or beneficial effects: the secondary battery of the present application includes a first electrode sheet and a second electrode sheet, and the first electrode sheet includes a first active layer, and the second electrode sheet includes a second active layer. By providing a first groove in a flat portion of at least one of the first active layer and the second active layer and providing a second groove in a curved portion, it is beneficial to shorten the electrolyte infiltration time in the electrolyte infiltration link, increase the diffusion rate of active ions (such as lithium ions) in the thickness direction of the electrode sheet, reduce the maximum first principal stress of the electrode sheet at the curved portion, inhibit electrode crushing caused by expansion during the cyclic charge and discharge process of the electrode sheet, and ultimately improve the low temperature performance, rate performance and fast charge cycle performance of the thick-coated electrode sheet; at the same time, the size of the first groove is controlled to be larger than the size of the second groove, so that the active material located in the second area during the winding process is not easy to fall off, which helps to reduce the capacity loss and electrode defects caused by the easy falling of the active material, thereby effectively maintaining the electrical properties of the electrode sheet. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The technical solution and other beneficial effects of the present application will be made apparent by describing in detail the specific implementation methods of the present application in conjunction with the accompanying drawings.

[0036] Figure 1 is an exploded structural view of a secondary battery provided according to an embodiment of the present application;

[0037] Figure 2 is a structural diagram of an electrode roll in a wound state provided in an embodiment of the present application;

[0038] Figure 3 is a partial cross-sectional view of an electrode roll provided according to an embodiment of the present application;

[0039] Figure 4 is a structural diagram of a first pole piece in an unfolded state provided in an embodiment of the present application;

[0040] Figure 5 is a partial cross-sectional view of a first pole piece in an unfolded state provided in an embodiment of the present application;

[0041] Figure 6 is a structural diagram of a first pole piece in an unfolded state provided according to an embodiment of the present application;

[0042] Figure 7 This is a structural diagram of a first pole piece in an unfolded state provided according to another embodiment of the present application.

[0043] Description of reference numerals:

[0044] 100. Secondary battery;

[0045] 110. Shell;

[0046] 120, electrode roll; 121, second pole piece; 1211, positive electrode current collector; 1212, second active layer; 122, separator; 123, first pole piece; 1231, negative electrode current collector; 1232, first active layer; 12321, first edge; 12322, second edge; 1233, first region; 1234, second region; 1235, first groove; 1236, second groove; 1237, negative electrode ear; 124, flat portion; 125, curved portion;

[0047] 130. Cover plate. DETAILED DESCRIPTION

[0048] In order to make the purpose, technical solution and beneficial effects of this application more clear, the following further describes this application in detail in conjunction with the accompanying drawings and specific implementation methods. It should be understood that the specific implementation methods described in this specification are only for explaining this application, not for limiting this application.

[0049] Secondary batteries such as lithium-ion batteries are the main power supply devices for consumer electronics and electric vehicles. With the rapid development of materials science and engineering, the performance, reliability and safety of lithium-ion batteries have been significantly improved, and the cost has been reduced. In existing secondary batteries, the energy density of secondary batteries can be improved by increasing the thickness of the active material layer on the electrode. However, the increase in electrode thickness will lead to problems such as low actual capacity utilization of secondary batteries, poor rate performance and long electrolyte infiltration. The disadvantages outweigh the advantages.

[0050] To solve the above technical problems, please refer to Figures 1 to 7 The present application provides a secondary battery 100. The secondary battery 100 includes: a housing 110, an electrode roll 120, a cover plate 130 and an electrolyte. The electrode roll 120 is received in the housing 110, the electrolyte is received in the housing 110 and soaks the electrode roll 120, and the cover plate 130 is connected to the housing 110 and seals the housing 110.

[0051] The secondary battery 100 may be a lithium-ion battery, a lithium-sulfur battery, a sodium-ion battery or a magnesium-ion battery, but is not limited thereto.

[0052] The secondary battery 100 may be cylindrical, flat, elongated, or in other shapes.

[0053] Specifically, the electrode roll 120 is formed by winding a first electrode sheet 123, a diaphragm 122 and a second electrode sheet 121. The diaphragm 122 is arranged between the first electrode sheet 123 and the second electrode sheet 121 to isolate the first electrode sheet 123 and the second electrode sheet 121 to prevent the first electrode sheet 123 and the second electrode sheet 121 from contacting each other; one of the first electrode sheet 123 and the second electrode sheet 121 is a positive electrode sheet and the other is a negative electrode sheet. The first electrode sheet 123 includes a first active layer 1232, and the second electrode sheet 121 includes a second active layer 1212.

[0054] The electrode roll 120 has a flat portion 124 and a curved portion 125 located at opposite ends of the flat portion 124. A first groove 1235 is provided at a portion of at least one of the first active layer 1232 and the second active layer 1212 located at the flat portion 124, and a second groove 1236 is provided at a portion of the curved portion 125. The openings of the first groove 1235 and the second groove 1236 located on the same active layer are both oriented toward the active layer of the adjacent electrode sheet. That is, when the first groove 1235 and the second groove 1236 are both arranged in the first active layer 1232, the openings of the first groove 1235 and the second groove 1236 are both oriented toward the second active layer 1212 adjacent to the first active layer 1232; and when the first groove 1235 and the second groove 1236 are both arranged in the second active layer 1212, the openings of the first groove 1235 and the second groove 1236 are both oriented toward the first active layer 1232 adjacent to the second active layer 1212.

[0055] The electrode roll 120 has a winding state and a flat state. When the electrode roll 120 is unfolded to the flat state, it has an intersecting first direction X, a second direction Y and a third direction Z, wherein the first direction X is the length direction of the electrode sheet in the flat state, the second direction Y is the width direction of the electrode sheet in the flat state, and the third direction Z is the thickness direction of the electrode sheet in the flat state. Preferably, the first direction X, the second direction Y and the third direction Z are perpendicular to each other. In this application, "perpendicular" refers to the state where the angle formed by a straight line and a straight line, a straight line and a plane, or a plane and a plane is 89° to 91°.

[0056] When the electrode roll 120 is unfolded to a flat state, the same electrode sheet has first areas 1233 and second areas 1234 arranged alternately along the first direction X; the first groove 1235 is provided in the first area 1233, and the second groove 1236 is provided in the second area 1234; in the second direction Y, the size of the first groove 1235 is larger than the size of the second groove 1236.

[0057] Among them, the first area 1233 corresponds to the flat portion 124, and the second area 1234 corresponds to the curved portion 125, that is, after the pole piece is wound into the electrode roll 120, the portion of the pole piece located in the first area 1233 constitutes the flat portion 124, so that the first groove 1235 is set in the flat portion 124, and the portion of the pole piece located in the second area 1234 constitutes the curved portion 125, so that the second groove 1236 is set in the curved portion 125.

[0058] The size of the first groove 1235 in the second direction Y can be obtained by measuring the distance between two groove walls of the first groove 1235 on the first pole piece 123 that are opposite to each other in the second direction after the secondary battery 100 is disassembled and the electrode roll 120 is unfolded to a flat state, and calculating the average value by using a measuring tool for multiple times; the size of the second groove 1236 in the second direction Y can be obtained by measuring the distance between two groove walls of the second groove 1236 on the first pole piece 123 that are opposite to each other in the second direction after the secondary battery 100 is disassembled and the electrode roll 120 is unfolded to a flat state, and calculating the average value by using a measuring tool for multiple times. The measuring tool can be any one of a ruler, a vernier caliper, or other dimension measuring instruments, but is not limited thereto.

[0059] It is understandable that the energy density of existing secondary batteries can be improved by increasing the thickness of the active material layer on the electrode at the electrode level. However, the increase in electrode thickness will lead to problems such as prolonged electrolyte infiltration of the secondary battery, low actual capacity utilization, and poor rate performance.

[0060] In the present application, at least one of the first active layer 1232 and the second active layer 1212 is provided with a first groove 1235 at the position located on the flat portion 124, and a second groove 1236 is provided at the position located on the curved portion 125, so as to shorten the electrolyte infiltration time in the electrolyte infiltration process, and at the same time increase the diffusion rate of active ions (such as lithium ions or sodium ions) in the thickness direction of the electrode, reduce the maximum first principal stress of the electrode, inhibit the expansion of the electrode during the cyclic charge and discharge process to cause the electrode to be crushed, reduce the risk of lithium precipitation, and ultimately improve the low temperature performance, rate performance and fast charging cycle performance of the thick-coated electrode; at the same time, the size of the first groove 1235 is controlled to be larger than the size of the second groove 1236, so that the active material located in the second area 1234 is not easy to fall off during the winding process, which helps to reduce the capacity loss and electrode defects caused by the easy falling of the active material, so as to effectively maintain the electrical properties of the electrode.

[0061] In one embodiment, the first electrode sheet 123 is a negative electrode sheet, and the first electrode sheet 123 further includes a negative electrode current collector 1231, and the first active layer 1232 is attached to at least one surface of the negative electrode current collector 1231. That is, the first active layer 1232 can be attached to any surface of the negative electrode current collector 1231, or to two opposite surfaces of the negative electrode current collector 1231, which is not specifically limited in the present application and can be specifically selected according to actual circumstances.

[0062] The first groove 1235 and the second groove 1236 are both opened in the first active layer 1232 , and the openings of the first groove 1235 and the second groove 1236 are both oriented toward the second active layer 1212 adjacent to the first active layer 1232 .

[0063] It can be understood that in the present application, by opening the first groove 1235 and the second groove 1236 on the first active layer 1232, the low temperature performance, rate performance and fast charging cycle performance of the thick-coated electrode are improved; at the same time, the active material located in the second area 1234 is not easy to fall off during the winding process, which helps to reduce the capacity loss and electrode defects caused by the easy falling of the active material, so as to effectively maintain the electrical performance of the electrode.

[0064] In one embodiment, the negative electrode current collector 1231 includes metal foil, metal cylinder, metal strip, metal plate, metal film, metal mesh, stamped metal, foamed metal, etc. In one embodiment, the negative electrode current collector 1231 is copper foil or composite copper foil. As used herein, the term "copper foil" includes copper alloy foil.

[0065] The first active layer 1232 may be one or more layers, and each layer of the multiple first active layers 1232 may contain the same or different negative electrode active materials. In the embodiment of the present application, the chargeable capacity of the negative electrode active material is greater than the discharge capacity of the positive electrode active material, that is, the CB (Ce11 Balance) value is greater than 1, so as to prevent lithium metal from being precipitated on the negative electrode sheet during charging.

[0066] The first active layer 1232 includes artificial graphite, natural graphite, soft carbon, hard carbon, amorphous carbon, carbon fiber carbon nanotubes, mesophase carbon microspheres, silicon-based materials, etc. The above negative electrode active materials can be used alone or in any combination.

[0067] The first electrode sheet 123 in the secondary battery 100 of the present application can be prepared by any known method. For example, a conductive agent, a binder, an additive, and a solvent are added to the negative electrode active material to prepare a slurry, which is then coated on the negative electrode current collector 1231 and pressed after drying to form an electrode.

[0068] In one embodiment, please follow Figure 6 and Figure 7, along the third direction Z, the orthographic projection of the notch of the second groove 1236 on the negative electrode current collector 1231 is at least one of a circle, an ellipse or a strip. That is, the area surrounded by the notch of the second groove 1236 can be circular, elliptical, or strip-shaped. Among them, when the notch of the second groove 1236 is elliptical, the major axis of the elliptical structure extends along the second direction Y, and when the notch of the second groove 1236 is strip-shaped, the strip structure extends along the second direction Y, and the strip shape can be a straight line or a curve, such as a wave shape.

[0069] In one embodiment, when the electrode roll 120 is unfolded to a flat state, a plurality of first grooves 1235 are provided in each first region 1233 of the first active layer 1232 , each first groove 1235 extends along the second direction Y, and the plurality of first grooves 1235 are arranged at intervals along the first direction X.

[0070] A plurality of second grooves 1236 are provided in each second region 1234 of the first active layer 1232 , and the plurality of second grooves 1236 are arranged in a plurality of rows and columns in the first direction X and the second direction Y at intervals.

[0071] It can be understood that in the present application, by providing a plurality of first grooves 1235 in the first area 1233 and a plurality of second grooves 1236 in the second area 1234, the electrolyte infiltration time of the electrolyte infiltration process is shortened, and at the same time, the diffusion rate of active ions (such as lithium ions or sodium ions) in the thickness direction of the electrode is further improved, the maximum first principal stress of the electrode is reduced, and the electrode crushing caused by expansion during the cyclic charge and discharge process of the electrode is suppressed, the risk of lithium plating is reduced, and the low temperature performance, rate performance and fast charge cycle performance of the thick-coated electrode are further improved.

[0072] In one embodiment, two adjacent first grooves 1235 in each first region 1233 in the first direction X may be arranged in a staggered manner or not in a staggered manner in the second direction Y. This is not specifically limited in the present application and may be selected according to actual circumstances.

[0073] In one embodiment, when the notch of the second groove 1236 is elliptical or strip-shaped, in the second direction Y, the ratio of the interval between two adjacent second grooves 1236 to the size of the second groove 1236 in the second direction Y is 0.2-5.

[0074] In one embodiment, when the electrode roll 120 is unfolded to a flat state, there are n second regions 1234 in the first electrode sheet 123, and the size of the nth second region 1234 in the first direction X is L. n mm, meet: L n =L1+(n-1)[π(2H1+H2+H3)].

[0075] Wherein, L1 mm is the size of the first second region 1234 in the first direction X; H1 μm is the thickness of the diaphragm 122 ; H2 μm is the thickness of the second pole piece 121 ; H3 μm is the thickness of the first pole piece 123 ; and n is the number of times the electrode roll 120 is bent.

[0076] The size of the second area 1234 in the first direction X can be obtained by measuring the size of the second area 1234 on the first electrode sheet 123 multiple times with a measuring tool after the secondary battery is disassembled, unfolding the electrode roll 120 to a flat state, and calculating the average value. The measuring tool can be any one of a ruler, a vernier caliper, or other size measuring instruments, but is not limited thereto.

[0077] The thickness H1 μm of the diaphragm 122, the thickness H2 μm of the second pole piece 121, and the thickness H3 μm of the first pole piece 123 can be obtained by measuring the thickness of different positions of the diaphragm 122, the second pole piece 121, and the first pole piece 123 by a measuring tool for multiple times and calculating the average value. The measuring tool can be any one of an X / β-ray microspot surface density meter, a laser thickness gauge, or other dimension measuring instruments, but is not limited thereto.

[0078] It can be understood that the size L of the nth second region 1234 in the first direction X is n mm is related to the size of the first second region 1234 in the first direction X, the thickness of the diaphragm 122, the thickness of the second electrode sheet 121, the thickness of the first electrode sheet 123 and the number of bends of the electrode roll 120. In this application, by defining the size L of the nth second region 1234 in the first direction X n mm satisfies:

[0079] L n = L1 + (n-1) [π (2H1 + H2 + H3)], so that the size L of the second region 1234 in the first direction X is designed according to different parameters in the secondary battery. n mm, thereby ensuring that each second area 1234 can have multiple second grooves 1236 to improve the low temperature performance, rate performance and fast charging cycle performance of the thick-coated electrode.

[0080] In one embodiment, when the electrode roll 120 is unfolded to a flat state, the dimension L1 mm of the first second area 1234 in the first direction X satisfies: 1≤L1≤5. That is, the dimension L1 mm of the first second area 1234 in the first direction X can be controlled within the range of 1 to 5 mm. For example, the dimension L1 mm of the first second area 1234 in the first direction X can be 1 mm, 1.5 mm, 2 mm, 2.5 mm, 3 mm, 3.5 mm, 4 mm, 4.5 mm or 5 mm, or a range consisting of any two of them. The present application controls the dimension L1 mm of the first second area 1234 in the first direction X within the range of 1 to 5 mm, so as to reasonably design the dimension L1 mm of the first second area 1234 in the first direction X, thereby ensuring the overall reasonable design of the secondary battery, thereby improving the low temperature performance, rate performance and fast charging cycle performance of the thick-coated electrode.

[0081] In one embodiment, when the electrode roll 120 is unfolded to a flat state, the number of rows of the second grooves 1236 in the nth second region 1234 of the first electrode sheet 123 is K. n , satisfying: K n =L n / T1; i.e. K n =

[0082] {L1+(n-1)[π(2H1+H2+H3)]} / T1, wherein T1 μm is the distance between two adjacent second grooves 1236 in the second region 1234 in the first direction X.

[0083] The distance T1 μm between two adjacent second grooves 1236 in the same second region 1234 in the first direction X can be obtained by disassembling the actual secondary battery, unfolding the electrode roll 120 to a flat state, measuring the distance between two adjacent second grooves 1236 in the second region 1234 on the first pole piece 123 by a measuring tool for multiple times and calculating the average value. The measuring tool can be any one of a ruler, a vernier caliper or other dimension measuring instruments, but is not limited thereto.

[0084] It can be understood that the number of columns K of the second grooves 1236 in the nth second region 1234 of the first pole piece 123 is n The size L of the nth second region 1234 in the first direction X n mm and the spacing between two adjacent second grooves 1236 in the second region 1234 in the first direction X. In the present application, the number of columns K of the second grooves 1236 in the nth second region 1234 in the first pole piece 123 is defined. n Satisfaction: K n =L n / T1, so as to design different numbers of columns K of the second grooves 1236 in the second region 1234 according to different parameters in the secondary battery. n , so as to reasonably design the parameters of the second groove 1236, shorten the electrolyte infiltration time of the electrolyte infiltration link, and further improve the diffusion rate of active ions (such as lithium ions or sodium ions) in the thickness direction of the electrode, reduce the maximum first principal stress of the electrode, inhibit the electrode crushing caused by expansion during the cyclic charge and discharge process of the electrode, reduce the risk of lithium precipitation, and further improve the low temperature performance, rate performance and fast charge cycle performance of the thick-coated electrode.

[0085] Specifically, when π(2H1+H2+H3)<T1, K n The specific value of is rounded upward. When π(2H1+H2+H3)>T1, K n The specific value of is rounded down to an integer.

[0086] In one embodiment, when the electrode roll 120 is unfolded to a flat state, the spacing T1μm between two adjacent second grooves 1236 in the same second region 1234 in the first direction X satisfies: 250≤T1≤1000. That is, the spacing T1μm between two adjacent second grooves 1236 in the same second region 1234 in the first direction X can be controlled within the range of 250 to 1000μm. For example, the spacing T1μm between two adjacent second grooves 1236 in the second region 1234 in the first direction X can be 250μm, 300μm, 400μm, 500μm, 600μm, 700μm, 800μm, 900μm or 1000μm, or a range consisting of any two of them. The present application controls the spacing T1μm between two adjacent second grooves 1236 in the second region 1234 in the first direction X within the range of 250 to 1000μm, and reasonably designs the spacing between two adjacent second grooves 1236, so as to further prevent the active material located in the second region 1234 from falling off during the winding process while maintaining the electrical properties of the electrode sheet, further helping to reduce the capacity loss and electrode sheet defects caused by the easy falling off of the active material, thereby effectively maintaining the electrical properties of the electrode sheet.

[0087] In one embodiment, the size of each first region 1233 in the first direction X is W mm, satisfying: 30≤W≤400. That is, the size W mm of the first region 1233 in the first direction X can be controlled within the range of 30 to 400 mm. For example, the size W mm of the first region 1233 in the first direction X can be 30 mm, 50 mm, 100 mm, 150 mm, 200 mm, 250 mm, 300 mm, 350 mm or 400 mm, or a range consisting of any two of them. The present application controls the size W mm of the first region 1233 in the first direction X within the range of 30 to 400 mm, so as to reasonably design the size W mm of the first region 1233 in the first direction X, thereby ensuring the overall reasonable design of the secondary battery, thereby improving the low temperature performance, rate performance and fast charging cycle performance of the thick-coated electrode.

[0088] The measurement method of the dimension W mm of the first area 1233 in the first direction X is the same as the measurement method of the second area 1234 , which will not be elaborated herein.

[0089] The overall size of the first pole piece 123 in the first direction X is the sum of the size of each first region 1233 in the first direction X and the size of each second region 1234 in the first direction X.

[0090] In one embodiment, when the electrode roll 120 is unfolded to a flat state, the spacing between two adjacent first grooves 1235 in each first region 1233 in the first direction X is T2 μm, satisfying: 1000≤T2≤2000. That is, the spacing T2 μm between two adjacent first grooves 1235 in each first region 1233 can be controlled within the range of 1000 to 2000 μm. For example, the spacing T2 μm between two adjacent first grooves 1235 in each first region 1233 can be 1000 μm, 1100 μm, 1200 μm, 1300 μm, 1400 μm, 1500 μm, 1600 μm, 1700 μm, 1800 μm, 1900 μm or 2000 μm, or a range consisting of any two of them. The present application controls the spacing T2μm between two adjacent first grooves 1235 in each first area 1233 within the range of 1000 to 2000μm, and reasonably designs the spacing between two adjacent first grooves 1235 to shorten the electrolyte infiltration time in the electrolyte infiltration process, further reduce the maximum first principal stress of the electrode, inhibit the electrode crushing caused by expansion during the cyclic charge and discharge process of the electrode, reduce the risk of lithium plating, and further improve the low temperature performance, rate performance and fast charge cycle performance of the thick-coated electrode.

[0091] The method for measuring the distance T2 μm between two adjacent first grooves 1235 in the first region 1233 is the same as the method for measuring the distance between two adjacent second grooves 1236 in the second region 1234 , and will not be described in detail herein.

[0092] In one embodiment, the depth of the first groove 1235 is h1 μm, and the thickness of the first active layer 1232 attached to one side of the negative electrode current collector 1231 is h2 μm, satisfying: 0.1≤h1 / h2≤0.8. That is, the ratio of the depth h1 μm of the first groove 1235 and the thickness h2 μm of the first active layer 1232 attached to one side of the negative electrode current collector 1231 can be controlled within the range of 0.1 to 0.8. For example, h1 / h2 can be one of 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7 or 0.8 or a range consisting of any two of them. This can not only shorten the infiltration time of the electrolyte, but also avoid a significant decrease in the energy density of the secondary battery.

[0093] The depth of the second groove 1236 is h3μm, which satisfies: 0.1≤h3 / h2≤0.8. That is, the ratio of the depth h3μm of the second groove 1236 and the thickness h2μm of the first active layer 1232 attached to one side of the negative electrode current collector 1231 can be controlled within the range of 0.1 to 0.8. For example, h3 / h2 can be in the range of 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7 or 0.8 or any two of them. The second groove 1236 is designed to such a size that the electrolyte infiltration time of the curved portion 125 can be effectively shortened and the stress in the curved portion 125 area can be released.

[0094] The depth h1 μm of the first groove 1235, the thickness h2 μm of the first active layer 1232, and the depth h3 μm of the second groove 1236 can be obtained by measuring multiple times by a measuring tool and calculating the average value. The measuring tool can be any one of an X / β-ray microspot surface density meter, a laser thickness gauge, or other dimension measuring instruments, but is not limited thereto.

[0095] It can be understood that the present application controls the ratio of the depth h1μm of a groove 1235 and the thickness h2μm of the first active layer 1232 attached to one side of the negative electrode current collector 1231 within the range of 0.1 to 0.8, and controls the ratio of the depth h3μm of the second groove 1236 and the thickness h2μm of the first active layer 1232 attached to one side of the negative electrode current collector 1231 within the range of 0.1 to 0.8. This can shorten the electrolyte infiltration time in the electrolyte infiltration link, thereby further reducing the maximum first principal stress of the electrode piece, inhibiting the electrode crushing caused by expansion during the cyclic charge and discharge process of the electrode piece, reducing the risk of lithium plating, and further improving the low temperature performance, rate performance and fast charge cycle performance of the thick-coated electrode piece.

[0096] In one embodiment, when the electrode roll 120 is unfolded to a flat state, the size of the first groove 1235 in the first direction X is T3μm, satisfying: 50≤T3≤150. That is, the size T3μm of the first groove 1235 in the first direction X can be controlled within the range of 50 to 150μm. For example, the size T3μm of the first groove 1235 in the first direction X can be 50μm, 60μm, 70μm, 80μm, 90μm, 100μm, 110μm, 120μm, 130μm, 140μm or 150μm, or a range consisting of any two of them. The present application controls the size T3μm of the first groove 1235 in the first direction X within the range of 50 to 150μm to further shorten the electrolyte infiltration time of the electrolyte infiltration link, reduce the risk of lithium plating, and further improve the low temperature performance, rate performance and fast charge cycle performance of the thick-coated electrode.

[0097] The size of the second groove 1236 in the first direction X is T4μm, satisfying: 50≤T4≤150. That is, the size T4μm of the second groove 1236 in the first direction X can be controlled within the range of 50 to 150μm. For example, the size T4μm of the second groove 1236 in the first direction X can be 50μm, 60μm, 70μm, 80μm, 90μm, 100μm, 110μm, 120μm, 130μm, 140μm or 150μm, or a range consisting of any two of them. The present application controls the size T4μm of the second groove 1236 in the first direction X within the range of 50 to 150μm to further shorten the electrolyte infiltration time of the electrolyte infiltration link, reduce the risk of lithium precipitation, and further improve the low temperature performance, rate performance and fast charging cycle performance of the thick-coated electrode.

[0098] The size of the first groove 1235 in the first direction X is T3 μm, and the size of the second groove 1236 in the first direction X is T4 μm. After the actual secondary battery is disassembled, the electrode roll 120 is unfolded to a flat state, and the size of the corresponding groove on the first active layer 1232 in the first direction X is measured multiple times by a measuring tool and the average value is calculated. The measuring tool can be any one of a ruler, a vernier caliper, or other dimension measuring instruments, but is not limited thereto.

[0099] In one embodiment, the first electrode sheet 123 further includes a negative electrode ear 1237 connected to the negative electrode current collector 1231; the first active layer 1232 has a first edge 12321 and a second edge 12322 arranged opposite to each other in the second direction Y, and the first edge 12321 is arranged close to the negative electrode ear 1237 relative to the second edge 12322. In some embodiments, the negative electrode current collector 1231 and the negative electrode ear 1237 are integrally formed, and the negative electrode ear 1237 is formed at the edge of the negative electrode current collector 1231 by die cutting.

[0100] Specifically, the dimension between the end of the first groove 1235 close to the first edge 12321 and the first edge 12321 is P1 mm, which satisfies; 1≤P1≤5. That is, the dimension P1 mm between the end of the first groove 1235 close to the first edge 12321 and the first edge 12321 can be controlled within the range of 1 to 5 mm. For example, the dimension P1 mm between the end of the first groove 1235 close to the first edge 12321 and the first edge 12321 can be 1 mm, 1.5 mm, 2 mm, 2.5 mm, 3 mm, 3.5 mm, 4 mm, 4.5 mm, or 5 mm, or any two of them.

[0101] The dimension between one end of the first groove 1235 close to the second edge 12322 and the second edge 12322 is P2 mm, which satisfies; 0≤P2≤3. That is, the dimension P2 mm between one end of the first groove 1235 close to the second edge 12322 and the second edge 12322 can be controlled within the range of 0 to 3 mm. For example, the dimension P2 mm between one end of the first groove 1235 close to the second edge 12322 and the second edge 12322 can be 0 mm, 0.5 mm, 1 mm, 1.5 mm, 2 mm, 2.5 mm or 3 mm, or any two of them.

[0102] The dimension P1 mm between one end of the first groove 1235 close to the first edge 12321 and the first edge 12321, and the dimension P2 mm between one end of the first groove 1235 close to the second edge 12322 and the second edge 12322 can be obtained by measuring the distance between the first groove and the corresponding edge on the first active layer 1232 multiple times with a measuring tool and calculating the average value. The measuring tool can be any one of a ruler, a vernier caliper, or other dimension measuring instruments, but is not limited thereto.

[0103] It can be understood that since the edge of the first active layer 1232 has a thinning area, in the present application, the dimension P1 mm between one end of the first groove 1235 close to the first edge 12321 and the first edge 12321 is controlled within the range of 1 to 5 mm, and the dimension P2 mm between one end of the first groove 1235 close to the second edge 12322 and the second edge 12322 is controlled within the range of 0 to 3 mm, so that the first groove 1235 avoids the thinning area of ​​the edge of the first active layer 1232, thereby ensuring the consistency of the overall structural parameters of the first groove 1235, and then ensuring the lithium ion diffusion rate of the electrode in the thickness direction, and ultimately improving the low temperature performance, rate performance and fast charging cycle performance of the thick-coated electrode.

[0104] In one embodiment, the dimension between the second groove 1236 closest to the first edge 12321 and the first edge 12321 is P3 mm, which satisfies; 1≤P3≤5. That is, the dimension P3 mm between the second groove 1236 closest to the first edge 12321 and the first edge 12321 can be controlled within the range of 1 to 5 mm. For example, the dimension P3 mm between the second groove 1236 closest to the first edge 12321 and the first edge 12321 can be 1 mm, 1.5 mm, 2 mm, 2.5 mm, 3 mm, 3.5 mm, 4 mm, 4.5 mm, or 5 mm, or any two of them.

[0105] The dimension between the second groove 1236 closest to the second edge 12322 and the second edge 12322 is P4 mm, which satisfies; 0≤P4≤3. That is, the dimension P4 mm between the second groove 1236 closest to the second edge 12322 and the second edge 12322 can be controlled within the range of 0 to 3 mm. For example, the dimension P4 mm between the second groove 1236 closest to the second edge 12322 and the second edge 12322 can be 0 mm, 0.5 mm, 1 mm, 1.5 mm, 2 mm, 2.5 mm or 3 mm, or any two of them.

[0106] The dimension P3 mm between the second groove 1236 closest to the first edge 12321 and the first edge 12321, and the dimension P4 mm between the second groove 1236 closest to the second edge 12322 and the second edge 12322 can be obtained by measuring the distance between the second groove 1236 on the first active layer 1232 and the corresponding closest edge multiple times using a measuring tool and calculating the average value. The measuring tool can be any one of a ruler, a vernier caliper, or other dimension measuring instruments, but is not limited thereto.

[0107] It can be understood that since the edge of the first active layer 1232 has a thinning area, in the present application, the dimension P3 mm between the second groove 1236 closest to the first edge 12321 and the first edge 12321 is controlled within the range of 1 to 5 mm, and the dimension P4 mm between the second groove 1236 closest to the second edge 12322 and the second edge 12322 is controlled within the range of 0 to 3 mm, so that the second groove 1236 avoids the thinning area of ​​the edge of the first active layer 1232, thereby ensuring the consistency of the overall structural parameters of the second groove 1236, and then ensuring the lithium ion diffusion rate of the electrode in the thickness direction, and ultimately improving the low temperature performance, rate performance and fast charging cycle performance of the thick-coated electrode.

[0108] In one embodiment, the second electrode sheet 121 is a positive electrode sheet, and the second electrode sheet 121 includes a positive electrode current collector 1211 , and the second active layer 1212 is attached to at least one surface of the positive electrode current collector 1211 .

[0109] In one embodiment, the type of the positive electrode current collector 1211 in the present application is not particularly limited, and it can be any known material suitable for use as the positive electrode current collector 1211 as long as it does not impair the effect of the present application.

[0110] Specifically, the positive electrode current collector 1211 may include metal materials such as aluminum, composite aluminum foil, titanium, tantalum, etc. In one embodiment, the positive electrode current collector 1211 is aluminum foil.

[0111] In one embodiment, the second active layer 1212 may be provided with one or more layers, and each layer of the multiple layers of positive polarity materials may contain the same or different positive polarity materials. The positive polarity material is any substance that can reversibly embed and extract metal ions such as lithium ions. The second active layer 1212 includes positive electrode active materials, positive electrode binders, and positive electrode conductors. The positive electrode active materials include lithium cobalt oxide, lithium manganese oxide, lithium iron phosphate, nickel cobalt manganese oxide, or nickel cobalt aluminum oxide. The above-mentioned positive electrode active materials may be used alone or in any combination.

[0112] The positive electrode active material may further include doping elements. The doping elements may include aluminum, magnesium, titanium, zirconium, strontium and the like, as long as the structure of the positive electrode active material can be made more stable.

[0113] The positive electrode active material may further include coating elements, and the coating elements may include aluminum, magnesium, titanium, zirconium, fluorine, boron and the like, as long as the structure of the positive electrode active material can be made more stable.

[0114] The positive electrode binder includes polyvinylidene fluoride or polytetrafluoroethylene, and the above positive electrode binders can be used alone or in any combination.

[0115] The positive electrode conductive agent includes carbon black, conductive graphite, carbon fiber or carbon nanotube, and the above positive electrode conductive agents can be used alone or in any combination.

[0116] The second pole piece 121 in the secondary battery 100 of the present application can be prepared by any known method. For example, a conductive agent, a binder, and a solvent are added to the positive electrode active material to prepare a slurry, and the slurry is coated on the positive electrode substrate, and the electrode is formed by pressing after drying. The positive electrode active material can also be roll-formed into a sheet electrode, or compressed into a granular electrode.

[0117] In one embodiment, the electrolyte used in the secondary battery 100 of the present application includes an electrolyte and a solvent for dissolving the electrolyte.

[0118] There is no particular limitation on the electrolyte in the present application, and it is usually a lithium salt. In some embodiments, the electrolyte includes LiPF6.

[0119] Meanwhile, there is no particular limitation on the electrolyte content in the present application, as long as the effect of the present application is not impaired, for example, it can be 0.8 mol / L to 2.2 mol / L.

[0120] There is no particular limitation on the solvent in the present application, and the solvent may include ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), butylene carbonate (BC) and methylethylene carbonate (MEC). The above solvents may be used alone or in any combination.

[0121] In one embodiment, in order to prevent short circuit, a separator 122 is usually provided between the positive electrode and the negative electrode. In this case, the electrolyte of the present application is usually infiltrated into the separator 122 for use.

[0122] In the present application, there is no particular limitation on the material, shape, thickness, porosity and average pore size of the diaphragm 122 as long as the effects of the present application are not impaired.

[0123] On the other hand, the present application further provides a battery pack, comprising a housing box and a secondary battery as described in any one of the above items, wherein the secondary battery is accommodated in the housing box.

[0124] On the other hand, the present application also provides an electric device, including the secondary battery or battery pack as described above, the secondary battery or battery pack serving as a power supply for the electric device. The electric device may be, but is not limited to, a mobile device (such as a mobile phone, a laptop computer, etc.), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship and a satellite, an energy storage system, etc.

[0125] In order to better understand the technical solution of the present application, a lithium-ion battery is taken as an example for further explanation below.

[0126] Example 1

[0127] This embodiment provides a method for preparing a lithium ion battery, and the specific process is as follows:

[0128] 1. Preparation of positive electrode

[0129] The positive electrode active material is lithium iron phosphate, the conductive agent is conductive carbon black SP, and the binder is PVDF, which are mixed in a mass ratio of 96:2:2, and then NMP is added as a solvent for mixing, and stirred under vacuum until the system becomes uniform to obtain a positive electrode slurry; the positive electrode slurry is evenly coated on both sides of the positive electrode current collector aluminum foil, and then transferred to a 120°C oven for drying, and then rolled, slit, and cut into pieces to obtain a positive electrode sheet.

[0130] 2. Preparation of negative electrode sheet

[0131] The negative electrode active material graphite, the conductive agent conductive carbon black SP, the thickener CMC, and the binder SBR are mixed in a mass ratio of 96.2:1.2:1.2:1.4, and then deionized water is added as a solvent for mixing, and stirred under vacuum until the system becomes uniform to obtain a negative electrode slurry; the negative electrode slurry is evenly coated on both sides of the negative electrode collector copper foil, and then transferred to a 110°C oven for drying, and then rolled, slit, and cut to obtain a negative electrode sheet.

[0132] 3. Preparation of electrolyte

[0133] Ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) are mixed in a ratio of 30%:40%:30% to obtain an organic solvent, 1 mol / L of LiPF6 is added and mixed evenly, and then vinylene carbonate, vinyl sulfate and lithium difluorophosphate are added to prepare an electrolyte.

[0134] 4. Preparation of diaphragm

[0135] PP film is used as the separator.

[0136] 5. Preparation of lithium-ion batteries

[0137] After drying, the negative electrode sheet and the positive electrode sheet prepared by the above steps are used together with the separator to prepare a wound electrode roll by a winding machine, the positive electrode ear and the negative electrode ear are welded to the top cover, and the welded electrode assembly with the top cover is placed in an aluminum shell for packaging; after filling the electrolyte and forming a constant capacity, a lithium-ion battery is obtained, and a batch of lithium-ion batteries are manufactured.

[0138] Among them, in this batch of lithium-ion batteries, a plurality of first grooves 1235 are opened in the first area 1233 of the first active layer 1232 of the negative electrode sheet, and the area surrounded by the orthographic projection of the notch of the first groove 1235 on the surface of the negative electrode current collector is linear, and a plurality of second grooves 1236 are opened in the second area 1234, and the area surrounded by the orthographic projection of the notch of the second groove 1236 on the surface of the negative electrode current collector is circular. In the second direction Y, the size of the first groove 1235 is larger than the size of the second groove 1236, the size W mm of the first area 1233 in the first direction X is 150 mm, the ratio h1 / h2 of the depth of the first groove 1235 h1 μm and the thickness of the first active layer 1232 attached to one side of the negative electrode current collector 1231 h2 μm is 0.5, h2 is 123 μm, and the size of the first groove 1235 in the first direction X is T3 mm is 100 μm, the spacing T2 μm between two adjacent first grooves 1235 in each first region 1233 is 2000 μm, the dimension P1 mm between one end of the first groove 1235 close to the first edge 12321 and the first edge 12321 is 3 mm, the dimension P2 mm between one end of the first groove 1235 close to the second edge 12322 and the second edge 12322 is 3 mm, the ratio h3 / h2 of the depth of the second groove 1236 h3 μm and the thickness of the first active layer 1232 attached to one side of the negative electrode current collector 1231 h2 μm is 0.5, the spacing T1 μm between two adjacent second grooves 1236 in the first direction X in the second region 1234 is 1000 μm, the dimension T4 μm of the second groove 1236 in the first direction X is 100 μm, and the dimension P3 between the second groove 1236 closest to the first edge 12321 and the first edge 12321 is 0. mm is 3 mm, the dimension P4 mm between the second groove 1236 closest to the second edge 12322 and the second edge 12322 is 3 mm, the dimension L1 mm of the first second region 1234 in the first direction X is 3 mm, the thickness H1 μm of the diaphragm 122 is 7 μm, the thickness H2 μm of the second pole piece 121 is 261 μm, the thickness H3 μm of the first pole piece 123 is 195 μm, and the number of bending times n of the electrode roll 120 is 20 times, then L n It can be 3000μm, 4477μm, 5953μm, 7430μm, 8906μm, 10383μm, 11859μm, 13336μm, 14812μm, 16289μm, 1 7765μm, 19242μm, 20719μm, 22195μm, 23672μm, 25148μm, 26625μm, 28101μm, 29578μm, 31054μm, K nThey are 3, 4, 5, 7, 8, 10, 11, 13, 14, 16, 17, 19, 20, 22, 23, 25, 26, 28, 29, and 31, respectively. The overall size of the negative electrode sheet in the first direction X is 3373575 μm.

[0139] Example 2

[0140] A lithium ion battery was prepared according to the method of Example 1, except that:

[0141] A plurality of second grooves 1236 are provided in the second region 1234 , and the area enclosed by the orthographic projection of the notches of the second grooves 1236 on the surface of the negative electrode current collector is in the shape of an elongated strip. In the second direction Y, the size of the first groove 1235 is larger than that of the second groove 1236 .

[0142] Example 3

[0143] A lithium ion battery was prepared according to the method of Example 1, except that:

[0144] A dimension W of the first area 1233 in the first direction X is 30 mm.

[0145] Example 4

[0146] A lithium ion battery was prepared according to the method of Example 1, except that:

[0147] A dimension W of the first area 1233 in the first direction X is 400 mm.

[0148] Example 5

[0149] A lithium ion battery was prepared according to the method of Example 1, except that:

[0150] The interval T2 between two adjacent first grooves 1235 in each first region 1233 is 1500 μm.

[0151] Example 6

[0152] A lithium ion battery was prepared according to the method of Example 1, except that:

[0153] The interval T2 between two adjacent first grooves 1235 in each first region 1233 is 1000 μm.

[0154] Example 7

[0155] A lithium ion battery was prepared according to the method of Example 1, except that:

[0156] The ratio h1 / h2 of the depth h1 of the first groove 1235 to the thickness h2 of the first active layer 1232 attached to one side of the negative electrode current collector 1231 is 0.1.

[0157] Example 8

[0158] A lithium ion battery was prepared according to the method of Example 1, except that:

[0159] The ratio h1 / h2 of the depth h1 of the first groove 1235 to the thickness h2 of the first active layer 1232 attached to one side of the negative electrode current collector 1231 is 0.8.

[0160] Example 9

[0161] A lithium ion battery was prepared according to the method of Example 1, except that:

[0162] The dimension T3 of the first groove 1235 in the first direction X is 50 μm.

[0163] Example 10

[0164] A lithium ion battery was prepared according to the method of Example 1, except that:

[0165] The dimension T3 of the first groove 1235 in the first direction X is 150 μm.

[0166] Embodiment 11

[0167] A lithium ion battery was prepared according to the method of Example 1, except that:

[0168] A dimension P1 between one end of the first groove 1235 close to the first edge 12321 and the first edge 12321 is 1 mm.

[0169] Example 12

[0170] A lithium ion battery was prepared according to the method of Example 1, except that:

[0171] A dimension P1 between one end of the first groove 1235 close to the first edge 12321 and the first edge 12321 is 5 mm.

[0172] Example 13

[0173] A lithium ion battery was prepared according to the method of Example 1, except that:

[0174] A dimension P2 between one end of the first groove 1235 close to the second edge 12322 and the second edge 12322 is 1.5 mm.

[0175] Embodiment 14

[0176] A lithium ion battery was prepared according to the method of Example 1, except that:

[0177] A dimension P2 between one end of the first groove 1235 close to the second edge 12322 and the second edge 12322 is 0 mm.

[0178] Embodiment 15

[0179] A lithium ion battery was prepared according to the method of Example 1, except that:

[0180] The thickness H2 of the second pole piece 121 is 175 μm, and the thickness H3 of the first pole piece 123 is 125 μm.

[0181] Example 16

[0182] A lithium ion battery was prepared according to the method of Example 1, except that:

[0183] The dimension W of the first region 1233 in the first direction X is 20 mm, the ratio h1 / h2 of the depth h1 of the first groove 1235 and the thickness h2 of the first active layer 1232 attached to one side of the negative electrode current collector 1231 is 0.05, the dimension T3 of the first groove 1235 in the first direction X is 20 μm, the spacing T2 between two adjacent first grooves 1235 in each first region 1233 is 500 μm, the dimension P1 between one end of the first groove 1235 close to the first edge 12321 and the first edge 12321 is 0 mm, and the dimension P2 between one end of the first groove 1235 close to the second edge 12322 and the second edge 12322 is 0 mm.

[0184] Embodiment 17

[0185] A lithium ion battery was prepared according to the method of Example 1, except that:

[0186] The dimension W of the first region 1233 in the first direction X is 500 mm, the ratio h1 / h2 of the depth h1 of the first groove 1235 and the thickness h2 of the first active layer 1232 attached to one side of the negative electrode current collector 1231 is 0.9, the dimension T3 of the first groove 1235 in the first direction X is 200 μm, the spacing T2 between two adjacent first grooves 1235 in each first region 1233 is 2500 μm, the dimension P1 between one end of the first groove 1235 close to the first edge 12321 and the first edge 12321 is 6 mm, and the dimension P2 between one end of the first groove 1235 close to the second edge 12322 and the second edge 12322 is 4 mm.

[0187] Embodiment 18

[0188] A lithium ion battery was prepared according to the method of Example 1, except that:

[0189] A dimension L1 of the first second region 1234 in the first direction X is 1 mm.

[0190] Embodiment 19

[0191] A lithium ion battery was prepared according to the method of Example 1, except that:

[0192] The dimension L1 of the first second region 1234 in the first direction X is 5 mm.

[0193] Embodiment 20

[0194] A lithium ion battery was prepared according to the method of Example 1, except that:

[0195] A distance T1 between two adjacent second grooves 1236 in the second region 1234 in the first direction X is 500 μm.

[0196] Embodiment 21

[0197] A lithium ion battery was prepared according to the method of Example 1, except that:

[0198] A distance T1 between two adjacent second grooves 1236 in the second region 1234 in the first direction X is 250 μm.

[0199] Embodiment 22

[0200] A lithium ion battery was prepared according to the method of Example 1, except that:

[0201] The ratio h3 / h2 of the depth h3 of the second groove 1236 to the thickness h2 of the first active layer 1232 attached to one side of the negative electrode current collector 1231 is 0.8.

[0202] Embodiment 23

[0203] A lithium ion battery was prepared according to the method of Example 1, except that:

[0204] The ratio h3 / h2 of the depth h3 of the second groove 1236 to the thickness h2 of the first active layer 1232 attached to one side of the negative electrode current collector 1231 is 0.1.

[0205] Embodiment 24

[0206] A lithium ion battery was prepared according to the method of Example 1, except that:

[0207] A dimension T4 of the second groove 1236 in the first direction X is 150 μm.

[0208] Embodiment 25

[0209] A lithium ion battery was prepared according to the method of Example 1, except that:

[0210] The dimension T4 of the second groove 1236 in the first direction X is 50 μm.

[0211] Embodiment 26

[0212] A lithium ion battery was prepared according to the method of Example 1, except that:

[0213] A dimension P3 between the second groove 1236 closest to the first edge 12321 and the first edge 12321 is 1 mm.

[0214] Embodiment 27

[0215] A lithium ion battery was prepared according to the method of Example 1, except that:

[0216] A dimension P3 between the second groove 1236 closest to the first edge 12321 and the first edge 12321 is 5 mm.

[0217] Embodiment 28

[0218] A lithium ion battery was prepared according to the method of Example 1, except that:

[0219] A dimension P4 between the second groove 1236 closest to the second edge 12322 and the second edge 12322 is 1.5 mm.

[0220] Embodiment 29

[0221] A lithium ion battery was prepared according to the method of Example 1, except that:

[0222] A dimension P4 between the second groove 1236 closest to the second edge 12322 and the second edge 12322 is 0 mm.

[0223] Embodiment 30

[0224] A lithium ion battery was prepared according to the method of Example 1, except that:

[0225] The dimension L1 of the first second region 1234 in the first direction X is 0.5 mm, the spacing T1 between two adjacent second grooves 1236 in the second region 1234 in the first direction X is 150 μm, the ratio h3 / h2 of the depth h3 of the second groove 1236 to the thickness h2 of the first active layer 1232 attached to one side of the negative electrode current collector 1231 is 0.05, the dimension T4 of the second groove 1236 in the first direction X is 20 μm, the dimension P3 between the second groove 1236 closest to the first edge 12321 and the first edge 12321 is 0 mm, and the dimension P4 between the second groove 1236 closest to the second edge 12322 and the second edge 12322 is 0 mm.

[0226] Embodiment 31

[0227] A lithium ion battery was prepared according to the method of Example 1, except that:

[0228] The dimension L1 of the first second region 1234 in the first direction X is 6 mm, the spacing T1 between two adjacent second grooves 1236 in the second region 1234 in the first direction X is 1300 μm, the ratio h3 / h2 of the depth h3 of the second groove 1236 to the thickness h2 of the first active layer 1232 attached to one side of the negative electrode current collector 1231 is 0.9, the dimension T4 of the second groove 1236 in the first direction X is 200 μm, the dimension P3 between the second groove 1236 closest to the first edge 12321 and the first edge 12321 is 6 mm, and the dimension P4 between the second groove 1236 closest to the second edge 12322 and the second edge 12322 is 4 mm.

[0229] Comparative Example 1

[0230] A lithium ion battery was prepared according to the method of Example 1, except that:

[0231] Neither the first region 1233 nor the second region 1234 of the first active layer 1232 of the negative electrode sheet is grooved.

[0232] Comparative Example 2

[0233] A lithium ion battery was prepared according to the method of Example 1, except that:

[0234] A first groove 1235 is formed in the first region 1233 of the first active layer 1232 of the negative electrode sheet, while a second groove 1236 is not formed in the second region 1234 .

[0235] Comparative Example 3

[0236] A lithium ion battery was prepared according to the method of Example 1, except that:

[0237] The first region 1233 of the first active layer 1232 of the negative electrode sheet does not have the first groove 1235 , but the second region 1234 has the circular second groove 1236 .

[0238] Comparative Example 4

[0239] A lithium ion battery was prepared according to the method of Example 1, except that:

[0240] A plurality of first grooves 1235 are formed in the second region 1234 of the first active layer 1232 of the negative electrode sheet.

[0241] Comparative Example 5

[0242] A lithium ion battery was prepared according to the method of Example 1, except that:

[0243] A plurality of second grooves 1236 are formed in the first region 1233 of the first active layer 1232 of the negative electrode sheet, and a circular groove is formed in the second region 1234 .

[0244] In the above embodiments and comparative examples, a batch of batteries were manufactured for each embodiment and each comparative example, and then the batteries prepared in the above embodiments and comparative examples were subjected to performance tests. The methods for the specific test items are as follows:

[0245] 1. Test method for powder loss optimization degree of lithium-ion batteries

[0246] At 25°C, the lithium-ion battery was left to stand for 30 minutes, charged to 3.65V at 1C constant current, then charged to 0.05C at constant voltage, left to stand for 30 minutes, and then discharged to 2.5V at 1C constant current. After 500 cycles of charge and discharge, the lithium-ion battery at 50% SOC was disassembled to observe the amount of powder falling off at the corners of the pole pieces with the first groove and the second groove. The amount of powder falling was calculated based on the accumulated area of ​​the falling powder as 0.01cm 2 The integer count of each powder falling corner after the lithium-ion battery is disassembled is counted. Among them, the fewer the number of powder falling corners, the better the powder falling optimization degree of the lithium-ion battery is; the moderate number of powder falling corners, the medium degree of powder falling optimization degree of the lithium-ion battery is; and the more the number of powder falling corners, the worse the powder falling optimization degree of the lithium-ion battery is.

[0247] 2. Test method for electrolyte immersion time of lithium-ion batteries

[0248] Add 0.03wt.% of phosphor to the electrolyte; inject according to the process specifications and stand at 45℃ for 6 hours; disassemble the lithium-ion battery and remove the diaphragm; place the diaphragm in a purple light box to observe the fluorescence position of the diaphragm and take photos to record; analyze the infiltration path and infiltration degree, observe the infiltration of phosphor; compare the corresponding standing time under the same infiltration area. Among them, the longer the standing time, the worse the surface lithium-ion battery wettability, and conversely, the shorter the standing time, the better the surface lithium-ion battery wettability.

[0249] 3. Test method for lithium deposition area rate of disassembled pole pieces of lithium-ion batteries

[0250] At 25°C, the lithium-ion battery was left to stand for 30 minutes, charged to 3.65V at 1C constant current, then charged to 0.05C at constant voltage, left to stand for 30 minutes, then discharged to 2.5V at 1C constant current, and after 2000 cycles of charge and discharge, the lithium-ion battery at 50% SOC was charged to 3.65V at 0.33C constant current, then charged to 0.05C at constant voltage. After the lithium-ion battery was fully charged, the negative electrode was disassembled and the lithium deposition of the negative electrode was observed and photographed to determine the lithium deposition area rate, which is the percentage of the lithium deposition area to the total photographed electrode area. Among them, the lithium deposition area is 0.01cm based on the cumulative area of ​​lithium deposition. 2 The area is calculated as an integer; therefore, the higher the lithium deposition area rate, the more serious the lithium deposition of the lithium-ion battery is. Conversely, the lower the lithium deposition area rate, the better the lithium deposition prevention effect of the lithium-ion battery is.

[0251] 4. Test method of EIS impedance of positive electrode in lithium-ion battery

[0252] After the positive electrode sheets in Example 1, Example 2 and Comparative Examples 1 to 4 are manufactured, part of the positive electrode sheets in each example and comparative example are cut off and assembled into symmetrical batteries, which are kept at a constant temperature of -10°C for 180 minutes; a disturbance voltage of 5mV is used; a frequency range of 100kHz to 10mHz is used; an AC impedance test is performed on the symmetrical battery to obtain an AC impedance Nyquist plot; the impedance R1 at high frequency and the impedance R2 at low frequency in the curve are extracted to obtain R 正 =3×(R1-R2); where R 正 is a characteristic parameter representing the mobility of lithium ions, R 正 The smaller the value, the smaller the lithium ion migration resistance. 正 The larger the value, the greater the lithium ion migration resistance.

[0253] 5. Test method of EIS impedance of negative electrode in lithium-ion battery

[0254] After the negative electrode sheets in Example 1, Example 2 and Comparative Examples 1 to 4 are manufactured, part of the negative electrode sheets in each example and comparative example are cut off and assembled into symmetrical batteries, and left to stand at a constant temperature of -10°C for 180 minutes; an AC impedance test is performed on the assembled symmetrical batteries with a disturbance voltage of 5mV and a frequency range of 100kHz to 10mHz to obtain an AC impedance Nyquist plot; the impedance R1 at high frequency and the impedance R2 at low frequency in the curve are extracted to obtain R 负 =3×(R1-R2); where R 负 is a characteristic parameter representing the mobility of lithium ions, R 负 The smaller the value, the smaller the lithium ion migration resistance. 负 The larger the value, the greater the lithium ion migration resistance.

[0255] 6. Test method for rate performance of lithium-ion batteries

[0256] At 25°C, the lithium-ion battery was allowed to stand for 30 minutes, then charged to 3.65V at a constant current of 1C0, then charged at a constant voltage to a current of 0.05C0, and allowed to stand for 10 minutes; then discharged to 2.5V at a constant current of 0.33C0 to complete a charge and discharge cycle; after charging according to the above charging system, 0.5C0 / 1C0 / 2C0 / 3C0 / 4C0 rate discharges were completed in sequence, and the first discharge capacity (i.e., 0.33C0 discharge capacity) and the discharge capacity at 4C0 rate discharge were recorded respectively, and the 4C capacity retention rate was calculated as follows = discharge capacity at 4C0 rate discharge / first discharge capacity × 100%.

[0257] 7. Test method for fast charge cycle performance of lithium-ion batteries

[0258] At 25°C, the lithium-ion battery was charged to 25% SOC at a constant current of 1.75C0, and then 1.6C0, 1.4C0, 1.3C0, 1.1C0, 0.95C0, 0.8C0, 0.7C0, 0.6C0, 0.5C0, 0.3C0, and 0.1C0 were respectively charged to 35%, 40%, 50%, 65%, 70%, 75%, 80%, 85%, 95%, and 100% SOC. After standing for 30 minutes, the battery was discharged to 2.5V at a constant current of 1C0. According to the above charge and discharge system, after 800 cycles of charge and discharge, the first charge and discharge capacity and the discharge capacity after 800 cycles were recorded respectively, and the fast charge capacity retention rate = 800 cycle discharge capacity / first discharge capacity × 100% was calculated.

[0259] The relevant parameters and test results in the above embodiments and comparative examples are recorded in Tables 1 to 3.

[0260] Table 1 Parameters of Examples 1 to 2 and Parameters and Test Results of Comparative Examples 1 to 5

[0261]

[0262] It can be seen from the data in Table 1 that in Comparative Examples 1 to 5, the first pole piece 123 and the second pole piece 121 are both thick-coated pole pieces, and the lithium-ion battery does not show corresponding performance. In Examples 1 to 2, since a plurality of first grooves 1235 are provided in the first region 1233 of the first pole piece 123, and a plurality of second grooves 1236 are provided in the second region 1234, in the second direction Y, the size of the first groove 1235 is larger than the size of the second groove 1236, the degree of optimization of the powder loss risk of the lithium-ion battery, the electrolyte infiltration time, the area rate of lithium decomposition after disassembly, the EIS impedance of the positive pole piece, and the EIS impedance of the negative pole piece are all improved to a certain extent relative to Comparative Example 1.

[0263] It can be seen that the present application opens a plurality of first grooves 1235 in the first area 1233 of the first electrode 123, and opens a plurality of second grooves 1236 in the second area 1234. In the second direction Y, the size of the first groove 1235 is larger than the size of the second groove 1236, thereby shortening the electrolyte infiltration time of the electrolyte infiltration link, increasing the diffusion rate of active ions (such as lithium ions) in the thickness direction of the electrode, reducing the maximum first principal stress of the electrode, inhibiting the electrode crushing caused by expansion during the cyclic charge and discharge process of the electrode, reducing the risk of lithium precipitation, and ultimately improving the low temperature performance, rate performance and fast charging cycle performance of the thick-coated electrode; at the same time, on the basis of maintaining the electrical properties of the electrode, the active material located in the second area during the winding process is not easy to fall off, which helps to reduce the capacity loss and electrode defects caused by the easy falling of the active material.

[0264] Table 2 Parameters and test results of Example 1 and Examples 3 to 17

[0265]

[0266] It can be seen from the data in Table 2 that: In Example 15, the thickness of the first active material layer 1212 and the second active material layer 1213 is relatively small, and they do not belong to thick-coated pole pieces. The electrolyte is easily infiltrated, and the lithium-ion battery does not show corresponding performance. In Example 16, the first pole piece 123 and the second pole piece 121 belong to thick-coated pole pieces. Since the depth of the first groove 1235 is too shallow, there is no obvious structural improvement effect, and the lithium-ion battery does not show corresponding performance. In Example 17, the first pole piece 123 and the second pole piece 121 belong to thick-coated pole pieces. The depth of the first groove 1235 is too deep, which increases the risk of foil leakage and lithium precipitation, increases the risk of lithium precipitation, and increases lithium consumption, resulting in poor cycle performance. The lithium-ion battery does not show corresponding performance. In Example 1 and Examples 3 to 14, the 4C capacity retention rate and 2C capacity retention rate of the lithium-ion battery are improved to a certain extent compared with Examples 15 to 17.

[0267] The present application defines that the size W of the first region 1233 in the first direction X is controlled within a range of 30 to 400 mm, the spacing T2 between two adjacent first grooves 1235 in each first region 1233 is controlled within a range of 1000 to 2000 μm, the ratio of the depth h1 of the first groove 1235 to the thickness h2 of the first active layer 1232 attached to one side of the negative electrode current collector 1231 is controlled within a range of 0.1 to 0.8, the size T3 of the first groove 1235 in the first direction X is controlled within a range of 50 to 150 μm, the first groove 1235 is close to the first groove 1235, and the first groove 1235 is close to the first groove 1235. The dimension P1 between one end of the edge 12321 and the first edge 12321 is controlled within the range of 1 to 5 mm, and the dimension P2 between one end of the first groove 1235 close to the second edge 12322 and the second edge 12322 is controlled within the range of 0 to 3 mm, thereby shortening the electrolyte infiltration time in the electrolyte infiltration link, increasing the lithium ion diffusion rate of the electrode in the thickness direction, reducing the maximum first principal stress of the electrode, inhibiting electrode crushing caused by expansion during the cyclic charge and discharge process of the electrode, reducing the risk of lithium plating, and ultimately improving the low temperature performance, rate performance and fast charge cycle performance of the thick-coated electrode.

[0268] Table 3 Parameters and test results of Example 1 and Examples 18 to 31

[0269]

[0270] It can be seen from the data in Table 3 that: In Example 15, the thickness of the first active material layer 1212 and the second active material layer 1213 is relatively small, and they do not belong to thick-coated pole pieces. The electrolyte is easily infiltrated, and the lithium-ion battery does not show the corresponding performance. In Example 30, the first pole piece 123 and the second pole piece 121 belong to thick-coated pole pieces. Since the depth of the second groove 1236 is too shallow, there is no obvious structural improvement effect, and the lithium-ion battery does not show the corresponding performance. In Example 31, the first pole piece 123 and the second pole piece 121 belong to thick-coated pole pieces. The depth of the second groove 1236 is too deep, which increases the risk of foil leakage and lithium precipitation, resulting in increased lithium consumption and poor cycle performance. The lithium-ion battery does not show the corresponding performance. In Example 1 and Examples 18 to 29, the 4C capacity retention rate and 2C capacity retention rate of the lithium-ion battery are improved to a certain extent compared with Examples 15 and Examples 30 to 31.

[0271] The present application defines that the size L1 of the first second region 1234 in the first direction X is controlled within a range of 1 to 5 mm, the spacing T1 between two adjacent second grooves 1236 in the second region 1234 in the first direction X is controlled within a range of 250 to 1000 μm, the ratio of the depth h3 of the second groove 1236 to the thickness h2 of the first active layer 1232 attached to one side of the negative electrode current collector 1231 is controlled within a range of 0.1 to 0.8, the size T4 of the second groove 1236 in the first direction X is controlled within a range of 50 to 150 μm, and the distance T1 between the adjacent second grooves 1236 in the second region 1234 in the first direction X is controlled within a range of 250 to 1000 μm. The dimension P3 between the second groove 1236 of 1 and the first edge 12321 is controlled within the range of 1 to 5 mm, and the dimension P4 between the second groove 1236 closest to the second edge 12322 and the second edge 12322 is controlled within the range of 0 to 3 mm, which can effectively shorten the electrolyte infiltration time of the electrolyte infiltration link, increase the lithium ion diffusion rate of the electrode in the thickness direction, reduce the maximum first principal stress of the electrode, inhibit the electrode crushing caused by expansion during the cyclic charge and discharge process of the electrode, reduce the risk of lithium precipitation, and ultimately improve the low temperature performance, rate performance and fast charge cycle performance of the thick-coated electrode.

[0272] The introduction provided in the above steps is only used to help understand the method, structure and core idea of ​​the present application. For ordinary technicians in this technical field, without departing from the principles of the present application, several improvements and modifications can be made to the present application, and these improvements and modifications also fall within the scope of protection of the claims of the present application.

Claims

1. A secondary battery, characterized in that: include: An electrode roll, wherein the electrode roll is wound by a first electrode sheet, a diaphragm and a second electrode sheet, wherein the diaphragm is disposed between the first electrode sheet and the second electrode sheet; one of the first electrode sheet and the second electrode sheet is a positive electrode sheet and the other is a negative electrode sheet, wherein the first electrode sheet includes a first active layer and the second electrode sheet includes a second active layer; The electrode roll has a flat portion and curved portions at opposite ends of the flat portion; a first groove is formed in a portion of at least one of the first active layer and the second active layer located at the flat portion, and a second groove is formed in a portion located at the curved portion; and the notches of the first groove and the second groove located on the same active layer are both oriented toward the active layer of the adjacent electrode piece; The electrode roll is unfolded to a flat state, and has a first direction and a second direction intersecting with each other; The same pole piece has a first area and a second area arranged alternately along the first direction; the first groove is arranged in the first area, and the second groove is arranged in the second area; In the second direction, a size of the first groove is larger than a size of the second groove.

2. The secondary battery according to claim 1, wherein: The first electrode sheet is a negative electrode sheet, and the first electrode sheet further comprises a negative electrode current collector, and the first active layer is attached to at least one surface of the negative electrode current collector; The first groove and the second groove are both opened in the first active layer, and the notches of the first groove and the second groove are both oriented toward the second active layer adjacent to the first active layer.

3. The secondary battery according to claim 2, characterized in that: When the electrode roll is unfolded to be flat, a plurality of the first grooves are provided in each of the first regions of the first active layer, each of the first grooves extends along the second direction, and the plurality of the first grooves are arranged at intervals along the first direction; A plurality of second grooves are provided in each second region of the first active layer, and the plurality of second grooves are arranged in a plurality of rows and columns at intervals in the first direction and the second direction.

4. The secondary battery according to claim 3, characterized in that: When the electrode roll is unfolded to a flat state, there are n second regions in the first electrode sheet, and the size of the nth second region in the first direction is L n mm, meet: L n =L1+(n-1)[π(2H1+H2+H3)]; Wherein, L1 mm is the size of the first second region in the first direction, satisfying: 1≤L1≤5; H1μm is the thickness of the diaphragm, and H2μm is the thickness of the second pole piece; H3μm is the thickness of the first pole piece; n is the number of times the electrode roll is bent.

5. The secondary battery according to claim 4, characterized in that: When the electrode roll is unfolded to a flat state, the number of columns of the second grooves in the nth second region of the first electrode sheet is K n , satisfying: K n =L n / T1; Wherein, T1 μm is the distance between two adjacent second grooves in the second region in the first direction.

6. The secondary battery according to claim 5, characterized in that: When the electrode roll is unfolded to a flat state, a distance T1 μm between two adjacent second grooves in the same second region in the first direction satisfies: 250≤T1≤1000.

7. The secondary battery according to claim 3, characterized in that: The size of each of the first regions in the first direction is W mm, satisfying: 30≤W≤400; and / or, When the electrode roll is unfolded to a flat state, a distance between two adjacent first grooves in each first region in the first direction is T2 μm, satisfying: 1000≤T2≤2000.

8. The secondary battery according to claim 2, wherein: The depth of the first groove is h1 μm, the thickness of the first active layer attached to one side of the negative electrode current collector is h2 μm, the depth of the second groove is h3 μm, and the following conditions are satisfied: 0.1≤h1 / h2≤0.8; and / or, 0.1≤h3 / h2≤0.

8.

9. The secondary battery according to claim 4, characterized in that: When the electrode roll is unfolded and flattened, the size of the first groove in the first direction is T3 μm, satisfying: 50≤T3≤150; and / or, The size of the second groove in the first direction is T4 μm, satisfying: 50≤T4≤150.

10. The secondary battery according to claim 2, wherein: The electrode roll also has a third direction intersecting the first direction and the second direction in pairs; Along the third direction, the orthographic projection of the notch of the second groove on the negative electrode current collector is at least one of a circle, an ellipse or a strip.

11. A battery pack, characterized in that: include: Box; as well as The secondary battery according to any one of claims 1 to 10, wherein the secondary battery is housed in the casing.

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