Secondary battery, battery module, battery pack, and electric device

Abstract

This application provides a secondary battery comprising a positive electrode, a negative electrode, a separator located between the positive and negative electrodes, and an electrolyte. The positive electrode comprises a positive current collector having two main surfaces, and the negative electrode comprises a negative current collector having two main surfaces. At least one of the positive and negative current collectors comprises at least one recessed structure extending from at least one main surface into the interior of the current collector. The recessed structure has a recess depth h1 and a recess width W, both in micrometers. An electrode active material is disposed on the current collector. The relationship between the particle size D90 of the electrode active material on the current collector and the recess depth h1 and recess width W of the recessed structure on the current collector is: h1 ≤ D90 ≤ W, where the particle size D90, the recess depth h1, and the recess width W are expressed in the same unit.

Description

Technical Field

[0001] This application belongs to the field of secondary batteries, and more specifically relates to a secondary battery having at least one current collector having a recessed structure, a battery module containing the secondary battery, a battery pack containing the battery module, and an electrical device containing the secondary battery, battery module, or battery pack. Background Technology

[0002] A secondary battery, also known as a rechargeable battery or storage battery, is a battery that can be recharged after being discharged to reactivate its active materials and continue to be used. The main types of secondary batteries on the market include nickel-metal hydride batteries, nickel-cadmium batteries, lead-acid (or lead-acid) batteries, lithium-ion batteries, and polymer lithium-ion batteries.

[0003] Lithium-ion batteries have been commercialized for about 30 years, initially primarily used in consumer electronics such as cameras, laptops, and mobile phones. With increasing public concern about environmental issues, the need to replace fossil fuels with clean energy is becoming increasingly urgent. Simultaneously, with advancements in lithium-ion battery technology, they have rapidly entered the electric vehicle sector in recent years.

[0004] The battery cell is the core component of a lithium-ion battery, and its lifespan is a primary consideration for consumers. Therefore, developing long-life battery cells is a common goal. High-power lithium-ion batteries offer significant advantages in vehicle acceleration and energy recovery. However, during long-term charge-discharge cycles, the positive and negative electrode active materials gradually detach from the current collector, severely impacting the cell's lifespan and power performance. Summary of the Invention

[0005] Through extensive and in-depth research, the inventors of this application have invented a novel electrode that not only mitigates or even eliminates the problem of electrode active material shedding during long-cycle operation and prevents damage to the protective film on the current collector surface, but also improves the long-life performance and power performance of the battery cell. Furthermore, the electrode weight is reduced, the battery cell energy density is increased, and the amount of current collector used is reduced, thereby lowering costs.

[0006] According to a first aspect of this application, a secondary battery is provided, comprising a positive electrode, a negative electrode, a separator located between the positive and negative electrodes, and an electrolyte, wherein the positive electrode comprises a positive current collector having two main surfaces, and the negative electrode comprises a negative current collector having two main surfaces, at least one of the positive and negative current collectors comprising at least one recessed structure extending from at least one main surface into the interior of the current collector, the recessed structure having a recess depth h1 in micrometers, and the electrolyte having a conductivity σ in Siemens per meter, wherein σ and h1 numerically satisfy the following relationship: 8tanhh1 + 0.2h1 ≤ σ ≤ 10tanh(h1)2 +2+0.1h1.

[0007] In some embodiments, the relationship between the recess depth h1 of the recessed structure and the thickness h2 of the current collector where the recessed structure is located is as follows: The recess depth h1 and the current collector thickness h2 are expressed in the same units.

[0008] In some embodiments, the recessed structure has a recess width W, and the relationship between the recess width W and the recess depth h1 is: h1≤W≤6h1, wherein the recess width W is the straight-line distance between two points with the maximum straight-line distance on the periphery of the cross-section where the recessed structure intersects with the main surface of the current collector where the recessed structure is located, and wherein the recess width W and the recess depth h1 are expressed in the same unit.

[0009] In some embodiments, an electrode active material is disposed on the current collector, and the relationship between the particle size D90 of the electrode active material on the current collector and the depression depth h1 and depression width W of the depression structure on the current collector is: h1≤D90≤W, wherein the particle size D90, the depression depth h1 and the depression width W are expressed in the same unit.

[0010] In some embodiments, the relationship between the recessed area A1 of the recessed structure and the surface area A2 of the current collector where the recessed structure is located is as follows: The recessed area A1 is the sum of the areas of the cross sections where all the recessed structures on the current collector intersect with the main surface of the current collector, and the recessed area A1 and the surface area A2 of the current collector are expressed in the same unit.

[0011] In some embodiments, the minimum distance d between the area with the recessed structure on the surface of the current collector and the edge of the current collector satisfies 1mm≤d≤10mm.

[0012] In some embodiments, the current collector is selected from aluminum foil and copper foil.

[0013] In some implementations, recessed structures exist on both main surfaces of the current collector, and the recessed structures on the two main surfaces may be staggered.

[0014] In some embodiments, the recess depth h1 is between 0.9 and 9.0 μm, optionally between 1 and 8 μm, or optionally between 2 and 7 μm.

[0015] In some embodiments, the positive current collector includes a recessed structure extending from at least one main surface into the interior of the positive current collector.

[0016] In some embodiments, the positive current collector includes recessed structures extending from two main surfaces into the interior of the positive current collector, wherein the recessed structures on the two main surfaces are optionally staggered.

[0017] In some embodiments, the secondary battery is a lithium-ion battery, and the electrolyte contains a lithium salt and an additive, wherein the lithium salt is selected from at least one of LiFSI, LiPF6, lithium trifluoromethanesulfonate, lithium tetrafluoroborate, and lithium perchlorate, and may be selected from at least one of LiFSI and LiPF6.

[0018] In some embodiments, the additive is selected from at least one of the following groups:

[0019]

[0020] According to a second aspect of this application, a battery module is provided, which includes the aforementioned secondary battery.

[0021] According to a third aspect of this application, a battery pack is provided that includes the aforementioned battery module.

[0022] According to a fourth aspect of this application, an electrical device is provided, which includes at least one of the above-described secondary battery, battery module, and battery pack. Attached Figure Description

[0023] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments of this application will be briefly described below. Obviously, the accompanying drawings in the embodiments of this application described below are merely examples. For those skilled in the art, other drawings can be obtained based on the accompanying drawings without creative effort.

[0024] Figure 1 This is a cross-sectional view of a current collector with a recessed structure according to one embodiment of this application.

[0025] Figure 2 yes Figure 1 The top view of the current collector shown.

[0026] Figure 3 This is a schematic diagram of one embodiment of the secondary battery of this application.

[0027] Figure 4 yes Figure 3 The diagram shows an exploded view of the secondary battery.

[0028] Figure 5 This is a schematic diagram of one embodiment of the battery module of this application.

[0029] Figure 6 This is a schematic diagram of one embodiment of the battery pack of this application.

[0030] Figure 7 yes Figure 6 An exploded view of the battery pack shown.

[0031] Figure 8 This is a schematic diagram of one embodiment of a device that uses the secondary battery of this application as a power source. Detailed Implementation

[0032] The embodiments of this application are described in further detail below. This detailed description is intended to illustrate the principles of this application and should not be construed as limiting the scope of the application; that is, this application is not limited to the described embodiments.

[0033] The ranges disclosed herein are defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also expected. Furthermore, if minimum range values ​​1 and 2 are listed, and if maximum range values ​​3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range “ab” represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range “0-5” means that all real numbers between “0-5” have been listed herein; “0-5” is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is described as an integer greater than or equal to 2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0034] Unless otherwise specified in this application, all embodiments and preferred embodiments mentioned herein can be combined to form new technical solutions.

[0035] Unless otherwise specified, all technical features and preferred features mentioned herein can be combined to form new technical solutions.

[0036] In this application, unless otherwise specified, all steps mentioned herein may be performed sequentially or randomly, but are preferably performed sequentially. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, if the method may also include step (c), it means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0037] In this application, unless otherwise specified, the terms "comprising" and "including" as used herein are open-ended or closed-ended. For example, "comprising" and "including" may mean that other components not listed may also be included, or that only the listed components may be included.

[0038] In this description, it should be noted that, unless otherwise stated, "above" and "below" include the stated number, and "several" in "one or more" means two or more. In this description, the terms "first," "second," "third," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0039] In this description, unless otherwise stated, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0040] Secondary batteries

[0041] During long-term charge-discharge cycles, the active materials of both the positive and negative electrodes gradually detach from the current collector, severely impacting the cell's lifespan and power performance. Furthermore, fresh current collectors (copper foil, aluminum foil) form a protective oxide layer upon contact with air. However, during the cold-pressing process in cell manufacturing, some electrode active material particles are forced into the current collector under pressure (this is particularly significant for the positive electrode), damaging the oxide protective layer on the current collector surface. Under high temperatures and during long cycles, the current collector slowly corrodes, causing electrode breakage. This not only severely affects cell performance but may also lead to safety issues.

[0042] To this end, this application provides a secondary battery comprising a positive electrode, a negative electrode, a separator located between the positive and negative electrodes, and an electrolyte, wherein the positive electrode comprises a positive current collector having two main surfaces, the negative electrode comprises a negative current collector having two main surfaces, and at least one of the positive and negative current collectors comprises at least one recessed structure extending from at least one main surface into the interior of the current collector.

[0043] Unrestricted by any particular theory, the inventors believe that during coating, the bottom of the active material particles is embedded inside the recessed structure. After drying, the particles and the pits of the recessed structure form a certain interlocking force, which can greatly alleviate or avoid the shedding of active particles in the later stages of cycling. In addition, it avoids the active material particles squeezing the current collector during the cold pressing process, thus preventing damage to the passivation film on the surface of the current collector. The combined effect can improve the long life performance of the battery cell.

[0044] As described above, either or both of the positive and negative current collectors may include a recessed structure; specifically, either or both main surfaces of the positive and / or negative current collectors may include a recessed structure. The following describes a current collector with a recessed structure. For ease of description, unless specifically specified herein, "current collector" may refer to both the positive and / or negative current collectors, and the two main surfaces of the current collector may be referred to as the first and second main surfaces. The current collector may be selected from aluminum foil and copper foil, typically aluminum foil is used as the positive current collector and copper foil as the negative current collector. Unless specifically specified, "main surface" may refer to the first and / or second main surfaces. In some embodiments, the first main surface may be substantially parallel to the second main surface. Unless specifically specified, "electrode" may refer to the positive and / or negative electrode. It should be understood that when both "current collector" and "recessed structure" are mentioned in the following description, the recessed structure refers to a recessed structure located on the current collector.

[0045] The shape of the cross-section of the recessed structure extending from the main surface into the current collector is not particularly limited. The cross-section refers to a section parallel to the main surface of the current collector. For example, the cross-section where the recessed structure intersects the main surface of the current collector can be circular, elliptical, semi-circular, triangular, square, rectangular, trapezoidal, star-shaped, polygonal, or irregular in shape. The shape of the longitudinal section of the recessed structure perpendicular to its cross-section is not particularly limited; for example, it can be rectangular, triangular, trapezoidal, arc-shaped, or irregular in shape. In some embodiments, the recessed structure is cylindrical. In some embodiments, the recessed structure is conical. In some embodiments, the recessed structure is prismatic. In some embodiments, the recessed structure is hemispherical.

[0046] In some embodiments, the recessed structure extending from the main surface into the current collector has a recess depth h1, and the relationship between the recess depth h1 and the current collector thickness h2 can be as follows: The recess depth h1 and the current collector thickness h2 are expressed in the same units. For example, This includes, but is not limited to, 0.10, 0.20, 0.30, 0.40, 0.50, and ranges defined by any two of the above values ​​as endpoints. The recess depth refers to the maximum distance from the main surface of the current collector to the bottom of the recessed structure. For example, for a cylindrical recessed structure, the recess depth is the distance between the main surface of the current collector and the bottom surface of the cylinder. For a conical recessed structure, the recess depth is the distance between the apex of the cone and the main surface of the current collector. In some embodiments, the recess depth h1 is in the range of 0.9-9.0 μm, optionally between 1-8 μm, or optionally between 2-7 μm. For example, the depression depth h1 includes, but is not limited to, 0.9 μm, 1.0 μm, 1.2 μm, 1.4 μm, 1.6 μm, 1.8 μm, 2.0 μm, 2.2 μm, 2.4 μm, 2.6 μm, 2.8 μm, 3.0 μm, 3.2 μm, 3.4 μm, 3.6 μm, 3.8 μm, 4.0 μm, 4.2 μm, 4.4 μm, 4.6 μm, 4.8 μm, 5 μm. 0μm, 5.2μm, 5.4μm, 5.6μm, 5.8μm, 6.0μm, 6.2μm, 6.4μm, 6.6μm, 6.8μm, 7.0μm, 7.2μm, 7.4μm, 7.6μm, 7.8μm, 8.0μm, 8.2μm, 8.4μm, 8.6μm, 8.8μm, 9.0μm, and the range formed by any two of the above values ​​as endpoints. In some embodiments, the current collector thickness h2 is in the range of 9.0-18.0 μm, including but not limited to 9.5 μm, 10.0 μm, 10.5 μm, 11.0 μm, 11.5 μm, 12.0 μm, 12.5 μm, 13.0 μm, 13.5 μm, 14.0 μm, 14.5 μm, 15.0 μm, 15.5 μm, 16.0 μm, 16.5 μm, 17.0 μm, 17.5 μm, and the range formed by any two of the above values ​​as endpoints. The indentation depth h1 and the current collector thickness h2 can be measured using methods known in the art, for example, current collector profile analysis can be performed according to JY / T010-1996, and online measurement is possible. The inventors discovered that when the depth h1 of the aforementioned recessed structure and the thickness h2 of the current collector satisfy the above relationship, the adhesion (interlocking force) between the current collector and the active material is maximized, which can effectively suppress the shedding of the active material during long-term cycling.

[0047] In some embodiments, the recessed structure has a recess width W, and the relationship between the recess width W and the recess depth h1 can be: h1≤W≤6h1, where the recess width W is the straight-line distance between two points with the maximum straight-line distance on the periphery of the cross-section where the recessed structure intersects with the main surface of the current collector, and the recess width W and the recess depth h1 are expressed in the same unit. For example, when the cross-section where the recessed structure intersects with the main surface of the current collector is rectangular or square, the recess width W is the length of the diagonal of the rectangle; when the cross-section where the recessed structure intersects with the main surface of the current collector is circular, the recess width W is the diameter of the circle; when the cross-section where the recessed structure intersects with the main surface of the current collector is triangular, the recess width W is the length of the longest side of the triangle. In some embodiments, the recess width W can be selected as h1, 1.5h1, 2.0h1, 2.5h1, 3.0h1, 3.5h1, 4.0h1, 4.5h1, 5.0h1, 5.5h1, 6h1, and a range formed by any two of the above values ​​as endpoints. In some embodiments, the recess width W is in the range of 0.9-54.0 μm, including but not limited to 1.0 μm, 1.5 μm, 2.0 μm, 2.5 μm, 3.0 μm, 3.5 μm, 4.0 μm, 4.5 μm, 5.0 μm, 5.5 μm, 6.0 μm, 6.5 μm, 7.0 μm, 7.5 μm, 8.0 μm, 8.5 μm, 9.0 μm, 9.5 μm, 10.0 μm, 12.0 μm. The depth ranges are 14.0 μm, 16.0 μm, 18.0 μm, 20.0 μm, 22.0 μm, 24.0 μm, 26.0 μm, 28.0 μm, 30.0 μm, 32.0 μm, 34.0 μm, 36.0 μm, 38.0 μm, 40.0 μm, 42.0 μm, 44.0 μm, 46.0 μm, 48.0 μm, 50.0 μm, 52.0 μm, and any two of the above values ​​forming a range. The recess width W can be measured online according to JY / T010-1996 for surface morphology analysis. The inventors have found that when the width and depth of the recess structure satisfy the above relationship, the active material particles and the current collector have good and effective contact, which can quickly conduct electrons, reduce electrode polarization, and improve cell life.

[0048] In some embodiments, the electrode further comprises an electrode active material located on a current collector. The electrode active material is located on a first main surface and / or a second main surface of the current collector. It is understood that the positive electrode active material is disposed on the first main surface and / or the second main surface of the positive electrode current collector, and the negative electrode active material is disposed on the first main surface and / or the second main surface of the negative electrode current collector. In some embodiments, the relationship between the particle size D90 of the electrode active material and the indentation depth h1 and indentation width W can be: h1 ≤ D90 ≤ W, wherein the particle size D90, the indentation depth h1, and the indentation width W are expressed in the same units. D90 refers to the particle size value corresponding to the cumulative percentage of particles from smallest to largest reaching 90% in the particle size distribution, that is, in the electrode active material, the number of particles with a particle size smaller than D90 accounts for 90% of the total number of particles. In some embodiments, the particle size D90 of the electrode active material is in the range of 0.9-54.0 μm, including but not limited to 1.0 μm, 1.5 μm, 2.0 μm, 2.5 μm, 3.0 μm, 3.5 μm, 4.0 μm, 4.5 μm, 5.0 μm, 5.5 μm, 6.0 μm, 6.5 μm, 7.0 μm, 7.5 μm, 8.0 μm, 8.5 μm, 9.0 μm, 9.5 μm, 10.0 μm, and 12. The particle size distribution is 0 μm, 14.0 μm, 16.0 μm, 18.0 μm, 20.0 μm, 22.0 μm, 24.0 μm, 26.0 μm, 28.0 μm, 30.0 μm, 32.0 μm, 34.0 μm, 36.0 μm, 38.0 μm, 40.0 μm, 42.0 μm, 44.0 μm, 46.0 μm, 48.0 μm, 50.0 μm, 52.0 μm, and a range defined by any two of the above values ​​as endpoints. D90 can be measured according to GB / T19077-2016. The inventors discovered that when the particle size D90 of the electrode active material satisfies the above relationship with the recess depth h1 and recess width W, the recess structure and the positive electrode material particles are matched, ensuring that the benefits of the recess structure can be fully utilized.

[0049] In some implementations, the relationship between the recessed area A1 and the current collector surface area A2 can be: The recessed area A1 is the sum of the areas of the cross-sections where all recessed structures intersect with the main surface of the current collector, and the recessed area A1 and the current collector surface area A2 are expressed in the same unit. For example, in some embodiments, the units of the recessed area A1 and the current collector surface area A2 are centimeters. In some embodiments, This includes, but is not limited to, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, and ranges defined by any two of the above values ​​as endpoints. The inventors have discovered that when the area A1 of all the recessed structures on the current collector and the surface area A2 of the current collector satisfy the above relationship, the shedding of active material during long-term cycling can be suppressed as a whole.

[0050] In some embodiments, the minimum distance d between the area with recessed structures on the current collector surface and the edge of the current collector can be in the following range: 1mm ≤ d ≤ 10mm. The minimum distance between the area with recessed structures on the current collector surface and the edge of the current collector can be determined as follows: observe the cross-section where all recessed structures adjacent to the edge of the current collector intersect with the main surface of the current collector, find the point on the periphery of the cross-section closest to the edge of the current collector, and the shortest distance between this point and the edge of the current collector is the aforementioned minimum distance d. d can be measured using methods known in the art, such as with a ruler. In some embodiments, d includes, but is not limited to, 1mm, 2mm, 3mm, 4mm, 5mm, 6mm, 7mm, 8mm, 9mm, 10mm, and ranges formed by any two of the above values ​​as endpoints. For the currently mainstream wound assembly, the axial edge electrodes at both ends of the battery typically break preferentially during winding and subsequent use, affecting the cell lifespan.

[0051] Figure 1 A cross-sectional view of an exemplary current collector according to one embodiment of the present application is shown, illustrating a schematic diagram of the recessed structure of the current collector. Figure 2 A top view of the current collector is shown, illustrating an exemplary shape and distribution of the recessed structure. It should be understood that the recessed structure of the current collector is not limited to the case illustrated.

[0052] In some embodiments, a recessed structure exists on one main surface (the first main surface or the second main surface) of the current collector. In some embodiments, a recessed structure exists on both the first and second main surfaces of the current collector. In embodiments where a recessed structure exists on both the first and second main surfaces of the current collector, the recessed structure on the first main surface and the recessed structure on the second main surface can be staggered. "Staggered" means that if a recessed structure exists at a certain position on the first main surface, there is no recessed structure at the corresponding position on the second main surface; and vice versa. This arrangement effectively avoids the recessed structures on the first and second main surfaces being at the same position on both sides of the current collector, thereby preventing the current collector from becoming too thin or even perforated.

[0053] In some embodiments, the electrode can be either a positive or a negative electrode. Optionally, the electrode is a positive electrode.

[0054] The aforementioned electrodes can be the positive and / or negative electrodes of a secondary battery, such as the positive and / or negative electrodes of a lithium-ion battery. However, it should be understood that the aforementioned electrodes are not limited to electrodes of secondary batteries; all electrodes that make the aforementioned improvements to the current collector according to this application fall within the scope of this application.

[0055] This application also provides a method for preparing the above-mentioned electrode, the method comprising:

[0056] A current collector is provided, the current collector comprising a first main surface and a second main surface;

[0057] At least one of the first and second main surfaces is formed on at least one of the main surfaces, and at least one recessed structure as described above is formed extending into the interior of the current collector.

[0058] In some embodiments, the recessed structure is formed by physical or chemical methods. In some embodiments, the recessed structure is formed by chemical etching. For example, a current collector with a thickness of 10-50 μm can be used, and a DC etching process can be performed on the surface of the current collector with a current of 0.1-1.0 A, an energizing time of 0.05-3.0 s, and at least one energizing cycle.

[0059] The secondary battery according to this application can be a lithium-ion battery, a potassium-ion battery, a sodium-ion battery, a lithium-sulfur battery, etc.

[0060] In some embodiments, the secondary battery is a lithium-ion battery, wherein the electrolyte comprises a lithium salt and an additive, wherein the lithium salt is selected from at least one of LiFSI, LiPF6, lithium trifluoromethanesulfonate, lithium tetrafluoroborate, and lithium perchlorate, and may be selected from at least one of LiFSI and LiPF6; the additive is selected from at least one of the following:

[0061]

[0062] Electrolytes containing the aforementioned lithium salts and additives have high conductivity and preferentially form a highly stable and low-impedance interface film at the anode-cathode interface during the capacity formation process. These characteristics are beneficial for improving the cycle life and power performance of the battery cell.

[0063] According to some embodiments of this application, a secondary battery is provided, comprising a positive electrode, a negative electrode, a separator located between the positive and negative electrodes, and an electrolyte. The positive electrode includes a positive current collector having two main surfaces, and the negative electrode includes a negative current collector having two main surfaces. At least one of the positive and negative current collectors includes at least one recessed structure extending from at least one main surface into the interior of the current collector. The recessed structure has a recess depth h1 in micrometers. The electrolyte has a conductivity σ in Siemens per meter, wherein σ and h1 numerically satisfy the following relationship: 8tanhh1 + 0.2h1 ≤ σ ≤ 10tanh(h1) 2 +2+0.1h1.

[0064] The conductivity of the electrolyte can be measured according to relevant standards, such as HG-T 4067-2015. Unrestricted by any particular theory, the inventors believe that after the active material enters the recessed structure, the lithium-ion transport path is longer compared to the case without the recessed structure, thus requiring a faster lithium-ion transport speed. When the depth of the recessed structure and the conductivity satisfy the above-mentioned relationship, lithium ions can be rapidly conducted into the active material within the recessed structure, avoiding the generation of internal polarization within the particles.

[0065] In the above formula, tanh is the symbol for the hyperbolic tangent function.

[0066] This application also provides a method for preparing the above-mentioned secondary battery, which includes:

[0067] A positive electrode and a negative electrode are provided, the positive electrode comprising a positive current collector having two main surfaces, and the negative electrode comprising a negative current collector having two main surfaces. At least one of the positive and negative current collectors includes at least one recessed structure extending from at least one main surface into the interior of the current collector, the recessed structure having a recess depth h1.

[0068] A separator is placed between the positive and negative electrodes to form a bare cell;

[0069] The bare battery cell is placed in an outer packaging, and an electrolyte with a conductivity σ is injected into the outer packaging.

[0070] The numerical relationship between σ and h1 is as follows: 8tanhh1 + 0.2h1 ≤ σ ≤ 10tanh(h1) 2 +2+0.1h1, where the indentation depth h1 is in micrometers and the electrolyte conductivity σ is in Siemens per meter.

[0071] In the secondary battery of this application, a negative electrode film layer is disposed on the negative electrode current collector. The negative electrode film layer comprises a negative electrode active material, such as one or more of natural graphite, artificial graphite, soft carbon, hard carbon, silicon current collector material, tin current collector material, and lithium titanate. The silicon current collector material may be selected from one or more of elemental silicon, silicon oxide, and silicon-carbon composites. The tin current collector material may be selected from one or more of elemental tin, tin oxide, and tin alloys.

[0072] The negative electrode film layer comprises a negative electrode active material and optional binders, optional conductive agents, and other optional additives, and is typically formed by coating and drying a negative electrode slurry. The negative electrode slurry coating is usually formed by dispersing the negative electrode active material, optional conductive agents, and binders in a solvent and stirring until homogeneous. The solvent can be N-methylpyrrolidone (NMP) or deionized water.

[0073] As an example, conductive agents may include one or more of superconducting carbon, carbon black (e.g., acetylene black, Ketjen black), carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0074] As an example, the binder may include one or more of styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS). Other optional additives include thickeners (such as sodium carboxymethyl cellulose CMC-Na), PTC thermistor materials, etc.

[0075] Furthermore, in the secondary battery of this application, the negative electrode sheet does not exclude other additional functional layers besides the negative electrode film layer. For example, in some embodiments, the negative electrode sheet of this application may also include a conductive undercoat layer (e.g., composed of a conductive agent and a binder) sandwiched between the negative electrode current collector and the negative electrode film layer and disposed on the surface of the negative electrode current collector. In other embodiments, the negative electrode sheet of this application may also include a protective covering layer covering the surface of the negative electrode film layer.

[0076] In the secondary battery of this application, a positive electrode film layer is disposed on the positive electrode current collector, and the positive electrode film layer comprises a positive electrode active material. The positive electrode active material may be selected from LiNi. 0.5-a Mn 1.5 M a O4 (0≤a≤0.1), LiNi x Co y N z M 1-x-y-zO2, where N is selected from Mn and Al, and M is selected from any one of Co, Ni, Mn, Mg, Cu, Zn, Al, Sn, B, Ga, Cr, Sr, V, and Ti, 0≤x<1, 0≤y≤1, 0≤z≤1, and x+y+z≤1. Examples may include, but are not limited to, lithium cobalt oxides (such as LiCoO2), lithium nickel oxides (such as LiNiO2), lithium manganese oxides (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, and lithium nickel cobalt manganese oxides (such as LiNi). 1 / 3 Co 1 / 3 Mn 1 / 3 O2(NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2(NCM523), LiNi 0.5 Co 0.25 Mn 0.25 O2(NCM211), LiNi 0.6 Co 0.2 Mn 0.2 O2(NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2 (NCM811)), lithium nickel cobalt aluminum oxide (such as LiNi) 0.85 Co 0.15 Al 0.05 One or more of O2 and its modified compounds.

[0077] The positive electrode film layer may optionally include a binder. Non-limiting examples of binders that can be used in the positive electrode film layer may include one or more of the following: polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resins. In some embodiments, the positive electrode film layer may optionally include a conductive agent. Examples of conductive agents used in the positive electrode film layer may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. In one embodiment of this application, the positive electrode can be prepared by dispersing the above-mentioned components for preparing the positive electrode, such as the positive electrode active material, conductive agent, binder, and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a uniform positive electrode slurry; coating the positive electrode slurry onto a positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing, and other processes.

[0078] In the secondary battery of this application, a separator separates the anode and cathode sides, providing selective permeability or blocking for substances of different types, sizes, and charges within the system. For example, the separator can insulate against electrons, physically isolate the positive and negative electrode active materials of the secondary battery, prevent internal short circuits, and create an electric field in a certain direction, while allowing ions in the battery to pass through the separator and move between the positive and negative electrodes. In one embodiment of this application, the material used to prepare the separator may include one or more of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multilayer composite film. When the separator is a multilayer composite film, the materials of each layer can be the same or different.

[0079] In the secondary battery of this application, the electrolyte may be selected from at least one of solid electrolytes and liquid electrolytes (i.e., electrolyte solutions). In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent. In some embodiments, the electrolyte salt may be selected from one or more of LiPF6 (lithium hexafluorophosphate), LiBF4 (lithium tetrafluoroborate), LiClO4 (lithium perchlorate), LiAsF6 (lithium hexafluoroarsenate), LiFSI (lithium bis(fluorosulfonyl)imide), LiTFSI (lithium bis(trifluoromethanesulfonyl)imide), LiTFS (lithium trifluoromethanesulfonate), LiDFOB (lithium difluorooxalate borate), LiBOB (lithium dioxalate borate), LiPO2F2 (lithium difluorophosphate), LiDFOP (lithium difluorodioxalate phosphate), and LiTFOP (lithium tetrafluorooxalate phosphate). In one embodiment of this application, the solvent may be selected from one or more of the following: ethylene carbonate (EC), propylene carbonate (PC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butyl carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE). In one embodiment of this application, the solvent content is 60-99% by weight, for example 65-95% by weight, or 70-90% by weight, or 75-89% by weight, or 80-85% by weight, based on the total weight of the electrolyte. In another embodiment of this application, the electrolyte content is 1-40% by weight, for example 5-35% by weight, or 10-30% by weight, or 11-25% by weight, or 15-20% by weight, based on the total weight of the electrolyte.

[0080] In one embodiment of the secondary battery of this application, the electrolyte may optionally contain additives. For example, the additives may include one or more of the following: negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature performance, additives that improve battery low-temperature performance, etc.

[0081] In one embodiment of this application, the above-mentioned positive electrode, negative electrode and separator can be fabricated into electrode assembly / bare cell by winding process or stacking process.

[0082] In one embodiment of this application, the secondary battery may include an outer packaging that can be used to encapsulate the aforementioned electrode components and electrolyte / electrolyte. In some embodiments, the outer packaging of the secondary battery may be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. In other embodiments, the outer packaging of the secondary battery may be a soft pack, such as a pouch. The material of the soft pack may be plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0083] The secondary battery of this application can be cylindrical, square, or any other arbitrary shape. Figure 3 This is an example of a square-structured secondary battery 5. Figure 4 Showing Figure 3 An exploded view of the secondary battery 5 shows that the outer packaging may include a housing 51 and a cover plate 53. The housing 51 may include a bottom plate and side plates connected to the bottom plate, the bottom plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover plate 53 can be placed over the opening to close the receiving cavity. A positive electrode, a negative electrode, and a separator can be formed into an electrode assembly 52 by a winding process or a stacking process. This electrode assembly is encapsulated in the receiving cavity, and the electrolyte is immersed in the electrode assembly 52. ​​The secondary battery 5 may contain one or more electrode assemblies 52.

[0084] Battery modules, battery packs and electrical devices

[0085] In one embodiment of this application, several secondary batteries can be assembled together to form a battery module. The battery module contains two or more secondary batteries as described in this application, the specific number depending on the application of the battery module and the parameters of the individual battery module.

[0086] Figure 5 This is battery module 4, used as an example. (See reference...) Figure 5In battery module 4, multiple secondary batteries 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple secondary batteries 5 can be fixed in place using fasteners.

[0087] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of secondary batteries 5 are received.

[0088] In one embodiment of this application, two or more of the above-described battery modules can be assembled into a battery pack. The number of battery modules contained in the battery pack depends on the application of the battery pack and the parameters of individual battery modules. The battery pack may include a battery box and multiple battery modules disposed within the battery box. The battery box includes an upper box and a lower box, the upper box being able to cover and fit snugly onto the lower box to form a closed space for accommodating the battery modules. Two or more battery modules can be arranged in the battery box in a desired manner.

[0089] Figure 6 and Figure 7 This is battery pack 1 as an example. (See reference...) Figure 6 and Figure 7 The battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3. The upper body 2 covers the lower body 3, forming a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0090] In one embodiment of this application, the electrical device includes at least one of the secondary battery, battery module, or battery pack described in this application. The secondary battery, battery module, or battery pack can be used as a power source for the electrical device or as an energy storage unit for the electrical device. The electrical device includes, but is not limited to, mobile digital devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0091] Figure 8 This is an example device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the device's requirements for high power and high energy density, a battery pack or battery module can be used.

[0092] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a rechargeable battery as their power source.

[0093] Technical effect

[0094] This application unexpectedly improves battery cycle life and battery performance by setting a recessed structure on the electrode current collector and appropriately setting the particle size of the recessed structure and / or the electrode active material set on the current collector, or by appropriately setting the conductivity of the recessed structure and the electrolyte.

[0095] This application includes, but is not limited to, the following beneficial technical effects:

[0096] (1) Improve the interlocking force between the electrode active material particles and the current collector, increase the matching between the electrode active material particles and the recessed structure, avoid the active material particles squeezing the current collector during the cold pressing process and causing damage to the passivation film on the surface of the current collector, effectively inhibit or avoid the shedding of electrode active material particles in the later stage of the cycle, especially inhibiting the shedding of active material in the long-term cycle process as a whole.

[0097] (2) The active material particles have good and effective contact with the current collector, which can quickly conduct electrons, reduce electrode polarization, and improve cell life;

[0098] (3) It effectively compensates for the defect of the lithium-ion transport path length caused by the concave structure, helps electrons to be transported quickly, and improves the power performance of the cell.

[0099] Example

[0100] The present invention will now be described in further detail with reference to embodiments. It should be understood that these embodiments are provided for illustrative purposes only and are not intended to limit the scope of the invention.

[0101] Unless otherwise specified, all reagents, materials and instruments used in the following examples and comparative examples are commercially available or synthesized.

[0102] Examples 1-25 and Comparative Example 1

[0103] 1. Preparation of electrolyte

[0104] In an argon-filled glove box (water content <10ppm, oxygen content <1ppm), ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) were uniformly mixed in a 1:1:1 ratio (mass ratio). Appropriate amounts of lithium salts LiFSI and LiPF6 were slowly added to the resulting non-aqueous organic solvent. After the lithium salts were completely dissolved, 1% by weight of ethylene sulfate (DTD) was added to obtain an electrolyte with a lithium salt concentration of 1 mol / L (0.1M LiFSI + 0.9M LiPF6).

[0105] 2. Preparation of positive and negative current collectors

[0106] Except for the positive electrode current collector aluminum foil in Comparative Example 1, which does not have a recessed structure, a semi-circular cross-section recessed structure is created on both the front and back main surfaces of the positive electrode current collector aluminum foil using electrochemical etching according to the parameters shown in Table 1 below. The thickness (h2) of the aluminum foil used is 18 μm and the width is 80 mm. In Table 1, d represents the minimum distance between the area with the recessed structure on the aluminum foil surface and the edge of the aluminum foil, measured using a ruler; A1 represents the recessed area, A2 represents the aluminum foil surface area; h1 represents the recessed depth, h2 represents the aluminum foil thickness, which are measured online according to the current collector profile analysis in JY / T010-1996; W represents the recessed width, measured online according to the surface morphology analysis in JY / T010-1996; D90 represents the D90 particle size of the electrode active material particles, measured according to GB / T19077-2016; "√" indicates double-sided misaligned etching is used, and "×" indicates that double-sided misaligned etching is not used.

[0107] A copper foil with a thickness of 18μm and a width of 80mm was used as the negative electrode current collector.

[0108] Table 1. Aluminum foil preparation parameters in Examples 1-25 and Comparative Example 1

[0109]

[0110] 3. Preparation of the positive electrode sheet

[0111] LiNi, the positive electrode active material 0.8 Co 0.1 Mn 0.1 A positive electrode slurry is prepared in N-methylpyrrolidone (NMP) using O2, conductive agent Super P carbon black, and binder polyvinylidene fluoride (PVDF). The solid content of the positive electrode slurry is 50 wt%, and the solid component is LiNi. 0.8 Co 0.1 Mn 0.1 The mass ratio of O2, Super P, and PVDF is 8:1:1. The positive electrode slurry is coated onto an aluminum foil current collector and dried at 85°C. Then it is cold-pressed, trimmed, cut into sheets, and slit. Finally, it is dried under vacuum at 85°C for 4 hours to produce the positive electrode sheet.

[0112] 4. Preparation of negative electrode sheet

[0113] Graphite, used as the negative electrode active material, was mixed evenly with Super P carbon black (a conductive agent), carboxymethyl cellulose (CMC) (a thickener), and styrene-butadiene rubber (SBR) (a binder) in deionized water to prepare a negative electrode slurry. The solid content of the negative electrode slurry was 30 wt%, and the mass ratio of graphite, Super P, CMC, and SBR in the solid components was 80:15:3:2. The negative electrode slurry was coated onto a copper foil current collector and dried at 85°C. Then, it was cold-pressed, trimmed, cut into sheets, and slit. Finally, it was dried under vacuum at 120°C for 12 hours to prepare the negative electrode sheet.

[0114] 5. Preparation of lithium-ion batteries

[0115] A 16μm polyethylene film (PE) is used as the separator. The prepared positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to isolate them. The cells are then wound to obtain bare cells, tabs are welded on, and the bare cells are placed in outer packaging. The electrolyte prepared above is injected into the dried cells, followed by encapsulation, settling, formation, shaping, and capacity testing to complete the preparation of the lithium-ion battery (the thickness of the soft-pack lithium-ion battery is 4.0mm, the width is 60mm, and the length is 140mm).

[0116] The testing process for lithium-ion batteries will be explained next.

[0117] 1. Cycle performance of lithium-ion batteries

[0118] At 25℃, the battery was charged at a constant current of 1C to 4.25V, then charged at a constant voltage of 0.05C, and finally discharged at 1C to 2.8V. The initial discharge capacity C1 was recorded. This cycle was repeated, and the discharge capacity on the 200th cycle was Cn. The capacity retention rate was calculated as C1 / Cn*100%.

[0119] 2. Power performance of lithium-ion batteries

[0120] At room temperature, a lithium-ion battery is charged at a constant current of 1C to 4.25V, then charged at a constant voltage to a current of 0.05C. After the battery is fully charged, it is left to stand for 5 minutes, then discharged at 1C for 30 minutes (the cell has a charge of 50% SOC), left to stand for 5 minutes, and the temperature is adjusted to 25℃. After standing for 1 hour, the cell voltage V1 is recorded. Then, the cell is discharged at 0.4C for 15 seconds, and the voltage V2 after the pulse discharge is recorded. The DC impedance DCR of the cell at 50% SOC is calculated as (V1-V2) / I, where I = 0.4C.

[0121] The test results are shown in Table 2.

[0122] Table 2. Battery performance characterization results of Examples 1-25 and Comparative Example 1

[0123] Battery number Battery cycle performance DCR (mΩ) at room temperature Example 1 84.20％ 56 Example 2 98.60％ 18 Example 3 99.30％ 10 Example 4 99.00％ 13 Example 5 91.30％ 41 Example 6 81.30％ 60 Example 7 98.80％ 14 Example 8 99.50％ 8 Example 9 99.10％ 16 Example 10 84.60％ 53 Example 11 85.10％ 50 Example 12 98.00％ 26 Example 13 98.30％ 23 Example 14 86.60％ 46 Example 15 96.90％ 34 Example 16 97.30％ 30 Example 17 97.70％ 28 Example 18 97.10％ 32 Example 19 85.60％ 51 Example 20 98.90％ 15 Example 21 99.50％ 9 Example 22 99.00％ 13 Example 23 90.10％ 38 Example 24 96.40％ 37 Example 25 80.10％ 65 Comparative Example 1 83.10％ 57

[0124] Examples 26-29 and Comparative Example 2

[0125] The electrolyte and the aluminum foil positive electrode current collector with a recessed structure were prepared according to the methods described in "Examples 1-25 and Comparative Example 1" above. The difference is that the conductivity σ of the electrolyte and the depth h1 of the recessed structure are shown in Table 3 below. The preparation methods of the positive electrode, negative electrode, and lithium-ion battery are the same as those described in "Examples 1-25 and Comparative Example 1", and the cycle performance and power performance of the lithium-ion battery were tested in the same way. The results are shown in Table 4. The conductivity of the electrolyte can be determined by adjusting the solvent, the type and content of lithium salt. See Table 5 for details. The conductivity of the electrolyte was measured according to HG-T4067-2015.

[0126] Table 3. Aluminum foil recess structure and electrolyte parameters in Examples 26-29 and Comparative Example 2.

[0127] <![CDATA[Depth h1 (μm) of the recessed structure]]> Electrolyte conductivity σ (mS / cm) Example 26 0.9 7.5 Example 27 2 10 Example 28 4 11 Example 29 9 12 Comparative Example 2 0.9 5

[0128] Table 4. Battery performance characterization results of Examples 26-29 and Comparative Example 2

[0129] Battery cycle performance DCR (mΩ) at room temperature Example 26 98.9％ 21 Example 27 99.3％ 16 Example 28 99.5％ 17 Example 29 98.0％ 27 Comparative Example 2 83.2％ 41

[0130] Table 5. Types and contents of solvents and lithium salts in the electrolytes of Examples 26-29 and Comparative Example 2.

[0131]

[0132]

[0133] In Examples 26-29, the depth h1 of the recessed structure on the aluminum foil and the electrolyte conductivity σ satisfy 8tanhh1+0.2h1≤σ≤10tanh(h1) 2 +2+0.1h1. The results show that when the depth h1 of the recessed structure on the current collector and the electrolyte conductivity σ satisfy the above relationship, the cycle performance and power performance of the lithium-ion battery are significantly improved, thereby increasing the battery cycle life and overall performance. Without being limited to any specific theory, it is believed that when the electrode active material particles are partially embedded in the recessed structure of the current collector, it is not conducive to rapid electrolyte wetting, i.e., it is not conducive to the migration of lithium ions in the solid phase. Adjusting the electrolyte conductivity (adjusting the transport speed of lithium ions in the electrolyte) can help compensate for the problems caused by the aforementioned recessed structure.

[0134] Although this application has been described with reference to embodiments, various modifications can be made thereto and components can be replaced with equivalents without departing from the scope of this application. In particular, the technical features mentioned in the various embodiments can be combined in any manner, provided there is no structural conflict. This application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A secondary battery comprising a positive electrode, a negative electrode, a separator between the positive and negative electrodes, and an electrolyte, wherein the positive electrode comprises a positive current collector having two main surfaces, the negative electrode comprises a negative current collector having two main surfaces, at least one of the positive and negative current collectors comprises at least one recessed structure extending from at least one main surface into the interior of the current collector, the recessed structure having a recess depth h1 in micrometers, and the electrolyte having a conductivity σ in Siemens per meter, wherein σ and h1 numerically satisfy the following relationship: 8tanhh1 + 0.2h1 ≤ σ ≤ 10tanh(h1) 2 +2+0.1h1.

2. The secondary battery as described in claim 1, wherein the relationship between the recess depth h1 of the recessed structure and the thickness h2 of the current collector where the recessed structure is located is: 0.10 ≤ ≤0.50, wherein the recess depth h1 and the current collector thickness h2 are expressed in the same units.

3. The secondary battery as claimed in claim 1, wherein the recessed structure has a recess width W, and the relationship between the recess width W and the recess depth h1 is: h1≤W≤6h1, wherein the recess width W is the straight-line distance between two points with the maximum straight-line distance on the periphery of the cross-section where the recessed structure intersects with the main surface of the current collector where the recessed structure is located, and wherein the recess width W and the recess depth h1 are expressed in the same unit.

4. The secondary battery as claimed in claim 1, wherein an electrode active material is disposed on the current collector, and the relationship between the particle size D90 of the electrode active material on the current collector and the depression depth h1 and depression width W of the depression structure on the current collector is: h1≤D90≤W, wherein the particle size D90, the depression depth h1 and the depression width W are expressed in the same unit.

5. The secondary battery as described in claim 1, wherein the relationship between the recessed area A1 of the recessed structure and the surface area A2 of the current collector where the recessed structure is located is: 0.2 ≤ ≤0.8, wherein the recessed area A1 is the sum of the cross-sectional areas of all recessed structures on the current collector that intersect with the main surface of the current collector, and the recessed area A1 and the surface area A2 of the current collector are expressed in the same unit.

6. The secondary battery as claimed in claim 1, wherein the minimum distance d between the region with the recessed structure distributed on the surface of the current collector and the edge of the current collector satisfies 1mm≤d≤10mm.

7. The secondary battery of claim 1, wherein the current collector is selected from aluminum foil and copper foil.

8. The secondary battery of claim 1, wherein a recessed structure exists on both main surfaces of the current collector.

9. The secondary battery as described in claim 1, wherein, The recessed structures on the two main surfaces are misaligned.

10. The secondary battery of claim 1, wherein the indentation depth h1 is between 0.9 and 9.0 μm.

11. The secondary battery of claim 1, wherein the indentation depth h1 is between 1 and 8 μm.

12. The secondary battery of claim 1, wherein the recess depth h1 is between 2-7 μm.

13. The secondary battery of claim 1, wherein the positive current collector includes a recessed structure extending from at least one of its main surfaces into the interior of the positive current collector.

14. The secondary battery of claim 13, wherein the positive current collector includes a recessed structure extending from its two main surfaces into the interior of the positive current collector.

15. The secondary battery of claim 14, wherein the recessed structures on the two main surfaces are staggered.

16. The secondary battery of claim 1, wherein the secondary battery is a lithium-ion battery, and the electrolyte comprises a lithium salt and an additive, wherein the lithium salt is selected from at least one of LiFSI, LiPF6, lithium trifluoromethanesulfonate, lithium tetrafluoroborate, and lithium perchlorate.

17. The secondary battery of claim 16, wherein the lithium salt is at least one of LiFSI and LiPF6.

18. The secondary battery of claim 16, wherein the additive is selected from at least one of the following: 。 19. A battery module comprising the secondary battery as described in any one of claims 1-18.

20. A battery pack comprising the battery module of claim 19.

21. An electrical device comprising at least one of the secondary battery as described in any one of claims 1-18, the battery module as described in claim 19, and the battery pack as described in claim 20.

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