Composite current collector, electrode tab, secondary battery, and electrochemical device

Abstract

The application relates to a composite current collector, an electrode sheet, a secondary battery and an electrochemical device, the composite current collector comprising an electrically conductive layer and a support layer; wherein the first surface of the electrically conductive layer has at least one recess; the support layer is arranged on the first surface of the electrically conductive layer, and the support layer is at least partially filled in the recess. By applying the composite current collector, the adhesion between the electrically conductive layer and the support layer can be improved, so that the stability and the cycle performance of the battery are improved; in addition, the composite current collector also has the advantages of excellent electrical conductivity and the help in reducing the probability of thermal runaway.

Description

Technical Field

[0001] This application relates to the field of electrochemical device technology, specifically to a composite current collector, electrode plates, secondary battery, and electrochemical device. Background Technology

[0002] Electrochemical devices, represented by lithium-ion secondary batteries, have advantages such as high energy density and high operating voltage, and are widely used in portable electronic devices (mobile phones, computers, cameras), power tools, electric bicycles, electric motorcycles, electric cars, military equipment, aerospace and many other fields.

[0003] Current collectors are an important component of electrochemical devices, providing support for the active material layer and collecting the current generated by the active material layer for output. With technological advancements, composite current collectors, consisting of a polymer film layer and a metal layer, have emerged. However, because the bonding force between the polymer film layer and the metal layer is usually weak, the metal layer is prone to peeling off during use, affecting the normal operation of the composite current collector. Summary of the Invention

[0004] The purpose of this application is to provide a composite current collector, electrode sheet, secondary battery and electrochemical device. The composite current collector has good adhesion, which can avoid peeling during processing and use, and helps to reduce the probability of thermal runaway.

[0005] To this end, a first aspect of this application provides a composite current collector comprising a conductive layer and a support layer; a first surface of the conductive layer having at least one recess; the support layer being disposed on the first surface of the conductive layer, and the support layer at least partially filling the recess.

[0006] Recesses are formed on the surface of the conductive layer near the support layer, increasing the contact area between the conductive and support layers and enhancing their adhesion. This helps prevent the conductive layer from detaching during processing and use, improving stability. Furthermore, in areas with recesses, the conductive layer is relatively thin, allowing it to disconnect promptly in case of overheating, cutting off the cell circuit and reducing the probability of thermal runaway. In areas without recesses, the conductive layer is relatively thick, compensating for the reduced conductivity caused by the thinner conductive layer, thus maintaining the overall conductivity of the composite current collector at a good level.

[0007] In any embodiment, the area of ​​the recess accounts for 0.5% to 50% of the area of ​​the first surface.

[0008] Therefore, when the area of ​​the recess reaches the above-mentioned proportion in the first surface, it can not only improve the adhesion between the conductive layer and the support layer, but also prevent the overall mechanical strength and conductivity of the composite current collector from being significantly adversely affected by the large area of ​​the recess.

[0009] In any embodiment, the recess includes a groove; the depth of the groove is 10% to 90% of the thickness of the conductive layer.

[0010] Therefore, when the groove depth is within the above range, it exhibits superior performance in enhancing the adhesion between the conductive layer and the support layer, and in timely breaking and cutting off the cell circuit when overheating.

[0011] In any embodiment, the recess includes at least two grooves, with a spacing of 10 to 80 mm between adjacent grooves.

[0012] When the grooves are spaced as described above, in the event of overheating, a fracture of the conductive layer at one groove can easily cause adjacent grooves to fracture simultaneously, resulting in a larger area of ​​fracture and completely severing the conductive circuit. This helps to further reduce the probability of thermal runaway.

[0013] In any embodiment, the side length or diameter of the groove along the cross section of the first surface is 3 to 50 mm.

[0014] This allows the groove size to be within a reasonable range, resulting in superior performance in the following aspects: improved adhesion between the conductive layer and the support layer, timely fracture in case of overheating, and good overall mechanical strength and conductivity of the composite current collector.

[0015] In any embodiment, the groove has a cross-section along the first surface with a shape selected from one or more of the following groups: circle, triangle, square, rectangle, parallelogram, rhombus, trapezoid, polygon, stripe, cross stripe, and irregular shape.

[0016] The cross-sectional shape of the groove can be varied and can be selected according to the actual processing requirements.

[0017] In any embodiment, the recess includes a first groove and a second groove; the depth of the first groove is greater than that of the second groove.

[0018] Since the conductivity, mechanical strength, and ability to cut off the circuit in time when overheating of the composite current collector are strongly correlated with the depth and size of the groove, the cooperation of grooves with different depths can help to further improve the above-mentioned properties of the composite current collector.

[0019] In any embodiment, the depth of the first groove accounts for 50% to 90% of the thickness of the conductive layer.

[0020] In any embodiment, the depth of the second groove is 10% to 50% of the thickness of the conductive layer.

[0021] In any embodiment, along the first surface, the area of ​​the first groove is 10% to 25% of the area of ​​the recess; the area of ​​the second groove is 75% to 90% of the area of ​​the recess.

[0022] In any embodiment, the side length or diameter of the first groove along the cross section of the first surface is 5 to 25 mm.

[0023] In any embodiment, the number of the first grooves is two or more, and at least one second groove is provided between any two first grooves.

[0024] In any embodiment, the first groove and the second groove are alternately arranged.

[0025] Therefore, by alternately setting grooves of different depths, the layout is made more reasonable, avoiding the phenomenon of local unevenness in conductivity or strength of the conductive layer.

[0026] In any embodiment, the recess includes a microgroove with a depth of less than or equal to 100 nm.

[0027] By incorporating microgrooves, the contact and interlocking between the conductive layer and the support layer are further enhanced, which helps to improve the adhesion between them. Furthermore, due to the small depth of the microgrooves, they have almost no impact on the overall conductivity of the composite current collector.

[0028] In any embodiment, the microgroove is disposed on the first surface and / or the inner surface of the groove.

[0029] Microgrooves can be disposed on the first surface or on the inner surface of the groove, both of which help improve the adhesion between the conductive layer and the support layer. Furthermore, by placing the microgrooves on the inner surface of the groove, the conductive layer at the groove is more easily pulled by the support layer in the event of overheating, thus causing breakage.

[0030] In any embodiment, the number of microgrooves is multiple, and the spacing between adjacent microgrooves is 2 to 20 mm.

[0031] In any embodiment, the diameter of the cross-section of the microgroove along the first surface is 50 μm to 2 mm.

[0032] In any embodiment, the thickness of the conductive layer is 1 to 3 μm.

[0033] When the conductive layer is within the above-mentioned thickness range, it exhibits relatively balanced and excellent performance in terms of conductivity and timely breakage under overheating.

[0034] In any embodiment, the thickness of the support layer is 0.3 to 30 μm.

[0035] When the support layer is within the above-mentioned thickness range, it exhibits relatively balanced and excellent performance in terms of energy density and timely fracture under overheating conditions.

[0036] In any implementation, the support layer is a single-layer structure.

[0037] When the support layer is a single-layer structure, it can have a relatively thin thickness, such as 0.3 to 5 μm, which is beneficial to improving the energy density of the battery cell.

[0038] In any embodiment, the support layer has a multi-layer structure, and the support layer includes a base film layer and a connecting layer located between the base film layer and the conductive layer.

[0039] The base film layer can be, for example, a film prepared by biaxial stretching. By applying the base film layer in the support layer, the mechanical strength of the composite current collector can be improved.

[0040] In any embodiment, the elastic modulus of the support layer is 0.5 to 13 GPa.

[0041] The mechanical strength of the composite current collector can be improved by setting the support layer to a multi-layer structure or modifying the support layer material to give the support layer a better elastic modulus, such as 0.5 to 13 GPa.

[0042] In any embodiment, the material of the support layer comprises one or more of the following groups: polyamide, polyimide, polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polycarbonate, polyethylene, carboxylic acids and their derivatives grafted with polyethylene, polypropylene, carboxylic acids and their derivatives grafted with polypropylene, polypropylene, acrylonitrile-butadiene-styrene copolymer, polyvinyl alcohol, polystyrene, polyvinyl chloride, polyvinylidene fluoride, polytetrafluoroethylene, sodium polystyrene sulfonate, polyacetylene, silicone rubber, polyoxymethylene, polyphenylene ether, polyphenylene sulfide, polymethyl methacrylate, polyethylene glycol, polysulfide, polyphenylene, polypyrrole, polyaniline, polythiophene, polypyridine, cellulose, starch, protein, epoxy resin, polypyrrole, polythiophene, polyaniline, and phenolic resin.

[0043] In any embodiment, the support layer further comprises one or more of metal particles, inorganic particles, and nano-strength enhancers.

[0044] Therefore, by incorporating the aforementioned materials into the support layer, the strength and conductivity of the composite current collector can be further improved.

[0045] In any embodiment, the nano-strength enhancer includes one or both of carbon nanotubes and graphene.

[0046] In any embodiment, the composite current collector includes two conductive layers, a support layer disposed between the two conductive layers, a first surface of each conductive layer facing the support layer, and the support layer at least partially filling the recess.

[0047] A second aspect of this application provides a method for preparing the composite current collector described in the first aspect of this application, comprising: forming the recess on a first surface of the conductive layer; disposing the support layer on the first surface, and causing the recess to be at least partially filled by the support layer.

[0048] In any embodiment, the recess is formed by etching; the etching includes at least one of plasma etching, chemical etching, and laser etching.

[0049] In any embodiment, the support layer is disposed on the first surface by coating or hot pressing, and the recess is at least partially filled by the support layer.

[0050] A third aspect of this application provides an electrode sheet comprising an active material layer and a composite current collector as described in the first aspect of this application or a composite current collector prepared according to the method described in the second aspect of this application; the active material layer is disposed on the surface of the conductive layer of the composite current collector opposite to the support layer.

[0051] A fourth aspect of this application provides a secondary battery comprising the electrode plates described in the third aspect of this application.

[0052] In any implementation, the secondary battery may specifically be a battery cell, a battery module, or a battery pack.

[0053] A fifth aspect of this application provides an electrical device comprising the secondary battery described in the fourth aspect of this application.

[0054] Compared with the prior art, the technical solution of this application has the following beneficial effects:

[0055] The composite current collector provided in this application significantly enhances the adhesion between the conductive layer and the support layer by providing at least one recess on the surface of the conductive layer near the support layer, allowing the support layer to be disposed on the surface and at least partially filled in the recess. This prevents the conductive layer from detaching during processing and use, thus improving the cycle life of the battery. Furthermore, the composite current collector provided in this application also helps to disconnect the conductive layer in a timely manner during overheating, thereby reducing the probability of thermal runaway. Attached Figure Description

[0056] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of the embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the scope of this application. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0057] Figure 1 This is a schematic diagram of the structure of a composite current collector according to an embodiment of this application;

[0058] Figure 2 This is a schematic diagram of the structure of a composite current collector according to an embodiment of this application. The recess in the figure includes a first groove and a second groove.

[0059] Figure 3 This is a schematic diagram of the structure of a composite current collector according to an embodiment of this application, in which a support layer is disposed between two conductive layers;

[0060] Figure 4 This is a schematic diagram of the structure of a composite current collector according to an embodiment of this application. In the figure, the support layer is disposed between two conductive layers, and the recesses of the two conductive layers each include a first groove and a second groove.

[0061] Figure 5 This is a schematic diagram of the structure of a composite current collector according to an embodiment of this application. In the figure, a support layer is disposed between two conductive layers, and the recess of one of the conductive layers includes a first groove and a second groove.

[0062] Figure 6 This is a schematic diagram of the structure of a composite current collector according to an embodiment of this application, wherein the support layer has a multi-layer composite structure;

[0063] Figure 7 This is a schematic diagram of the structure of a composite current collector according to an embodiment of this application. In the figure, the support layer is disposed between two conductive layers, and the support layer has a multi-layer composite structure.

[0064] Figure 8This is a schematic diagram of the structure of a composite current collector according to an embodiment of this application. In the figure, the support layer is disposed between two conductive layers, and the support layer has a multi-layer composite structure. The recess of each conductive layer includes a first groove and a second groove.

[0065] Figure 9 This is a schematic diagram of the structure of a composite current collector according to an embodiment of this application, wherein the recess includes a groove and a microgroove;

[0066] Figures 10 to 17 This is a schematic diagram of the shape of the recessed portion of the conductive layer in several embodiments of this application. The shapes of the recesses in the figure include square, triangle, circle, parallelogram, trapezoid, stripe, intersecting stripe and irregular shape.

[0067] Figure 18 This is a schematic diagram of a secondary battery according to one embodiment of this application;

[0068] Figure 19 yes Figure 18 An exploded view of a secondary battery according to an embodiment of this application is shown.

[0069] Figure 20 This is a schematic diagram of a battery module according to one embodiment of this application;

[0070] Figure 21 This is a schematic diagram of a battery pack according to one embodiment of this application;

[0071] Figure 22 yes Figure 21 An exploded view of a battery pack according to one embodiment of this application is shown;

[0072] Figure 23 This is a schematic diagram of an electrical device that uses a secondary battery as a power source according to one embodiment of this application;

[0073] Explanation of reference numerals in the attached figures:

[0074] 1 Conductive layer; 11 First surface; 12 Groove; 121 First groove; 122 Second groove; 13 Microgroove; 2 Support layer; 21 Connecting layer; 22 Base film layer; 3 Battery pack; 4 Upper housing; 5 Lower housing; 6 Battery module; 7 Secondary battery; 71 Housing; 72 Electrode assembly; 73 Top cover assembly. Detailed Implementation

[0075] Exemplary embodiments of this application will now be described in more detail. It should be understood that this application may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided to enable a more thorough understanding of this application and to fully convey the scope of this application to those skilled in the art.

[0076] The "range" disclosed in this application is 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 the 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 included. Furthermore, if minimum range values ​​1 and 2 are listed, and 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 "a–b" 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" indicates that all real numbers between "0~5" have been listed in this article; "0~5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥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.

[0077] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0078] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0079] Unless otherwise specified, all steps of this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates 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.

[0080] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0081] Composite current collectors are typically composed of a polymer film layer and a metal layer. However, because the bonding force between the polymer film layer and the metal layer is usually weak, the metal layer is prone to peeling off during use, affecting the normal operation of the composite current collector.

[0082] This application significantly enhances the adhesion between the conductive layer and the support layer by providing at least one recess on the surface of the conductive layer near the support layer, so that the support layer is disposed on the surface and at least partially filled in the recess, thereby preventing the conductive layer from detaching during the processing and use of the composite current collector. Furthermore, the composite current collector provided by this application can also disconnect the conductive layer in a timely manner when overheated, thereby reducing the probability of thermal runaway.

[0083] The technical solutions described in the embodiments of this application are applicable to composite current collectors, and also to methods for preparing composite current collectors, electrode sheets containing composite current collectors, secondary batteries using electrode sheets, battery modules using secondary batteries, battery packs using secondary batteries or battery modules, and electrical devices using at least one of secondary batteries, battery modules, and battery packs.

[0084] Composite current collector

[0085] refer to Figures 1-9 The first aspect of this application provides a composite current collector, which includes a conductive layer 1 and a support layer 2; the first surface 11 of the conductive layer 1 has at least one recess; the support layer 2 is disposed on the first surface 11 of the conductive layer 1 and at least partially fills the recess.

[0086] On the one hand, at least one recess is provided on the surface of the conductive layer 1 near the support layer 2, which increases the contact area between the conductive layer 1 and the support layer 2, enhances their adhesion, helps to prevent the conductive layer from detaching during the current collector's processing and use, and improves stability.

[0087] On the other hand, in the area with the recess, the conductive layer 1 is relatively thin. The thin area of ​​the conductive layer 1 can disconnect in time when overheated, cutting off the cell circuit, thereby helping to reduce the probability of thermal runaway. In the area without the recess, the conductive layer 1 is relatively thick. The thick area of ​​the conductive layer 1 helps to compensate for the problem of reduced conductivity caused by the thin area, so that the overall conductivity of the composite current collector can still be maintained at a good level.

[0088] In some embodiments, the area of ​​the recess accounts for 0.5% to 50% of the area of ​​the first surface 11; for example, about 0.5%, 1%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, etc.

[0089] When the area of ​​the recess reaches the aforementioned proportion in the area of ​​the first surface 11, it can significantly improve the adhesion between the conductive layer 1 and the support layer 2, without causing significant adverse effects on the overall mechanical strength and conductivity of the composite current collector due to an excessively large recess area. If the area proportion of the recess is too low, for example, below 0.5%, the improvement effect on adhesion may be insignificant; if the area proportion of the recess is too high, for example, above 50%, it may adversely affect the overall strength of the composite current collector and may reduce its conductivity, thereby deteriorating the rate performance of the battery cell. The recess can be formed on the first surface 11 of the conductive layer 1 by means of etching or other methods, and the recess does not penetrate the conductive layer 1.

[0090] In some embodiments, the recess includes a groove 12; the depth of the groove 12 is 10% to 90% of the thickness of the conductive layer 1; for example, about 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, etc.

[0091] When the depth of the groove 12 is within the aforementioned range, it exhibits superior performance in enhancing the adhesion between the conductive layer 1 and the support layer 2, and in promptly breaking and cutting off the cell circuit during overheating. If the depth of the groove 12 is too shallow, for example, less than 10% of the thickness of the conductive layer 1, the effect on improving the adhesion is limited because the contact area and longitudinal contact depth between the support layer 2 and the conductive layer 1 are not significantly increased; furthermore, in the event of overheating, the relatively thick conductive layer 1 at the groove 12 makes it difficult to break, thus having no significant effect on reducing the probability of thermal runaway. If the depth of the groove 12 is too deep, for example, greater than 90% of the thickness of the conductive layer 1, it can easily have an adverse effect on the conductivity of the composite current collector and may also reduce the mechanical strength of the composite current collector.

[0092] In some embodiments, the recess includes at least two grooves 12, and the interval between adjacent grooves 12 is 10 to 80 mm; for example, about 10 mm, 15 mm, 20 mm, 25 mm, 30 mm, 35 mm, 40 mm, 45 mm, 50 mm, 60 mm, 65 mm, 70 mm, 75 mm, 80 mm, etc.

[0093] When the spacing of the grooves 12 is within a suitable range, it is beneficial to improve the adhesion, maintain good conductivity, and withstand fracture under overheating conditions. If the spacing of the grooves 12 is less than 10 mm, the grooves 12 are too dense, resulting in too many thin areas of the conductive layer 1, which affects conductivity. If the spacing of the grooves 12 is greater than 80 mm, when the conductive layer 1 at a certain groove 12 fractures under overheating conditions, it is difficult to induce a coordinated fracture in the surrounding grooves 12, thus making it difficult to form a large-area fracture, which is not conducive to completely cutting off the conductive circuit under overheating conditions.

[0094] In some embodiments, the side length or diameter of the groove 12 along the cross section of the first surface 11 is 3 to 50 mm; for example, about 3 mm, 5 mm, 10 mm, 15 mm, 20 mm, 25 mm, 30 mm, 35 mm, 40 mm, 45 mm, 50 mm, etc.

[0095] When the size of the groove 12 is within a suitable range, it is beneficial for improving adhesion, maintaining good conductivity, and preventing breakage under overheating conditions. If the side length or diameter of the groove 12 is less than 5mm, the improvement in adhesion is not significant, and under overheating conditions, the conductive layer 1 may only break to form a very small fracture, making it difficult to effectively achieve a large-area coordinated fracture effect, and thus failing to promptly cut off the circuit in case of large-area thermal runaway. If the side length or diameter of the groove 12 is greater than 50mm, in actual use, the groove 12 may easily reduce the overall strength of the composite current collector, and may even deteriorate the conductivity of the composite current collector, thereby worsening the rate performance of the battery cell. In addition, setting an excessively large groove 12 does not significantly improve adhesion.

[0096] refer to Figures 10 to 17 In some embodiments, the groove 12 has a cross-section along the first surface 11 with a shape selected from one or more of the following groups: square, circle, triangle, rectangle, parallelogram, rhombus, trapezoid, polygon, stripe, cross stripe and irregular shape.

[0097] The cross-sectional shape of the groove 12 can be varied and can be selected according to the actual processing conditions. For example, when the cross-sectional shape of the groove is circular or near-circular (elliptical, irregular shape similar to a circle), the diameter of the groove along the first surface is 3 to 5 mm; when the cross-sectional shape of the groove is triangular, rectangular, parallelogram, rhombus, trapezoid, polygon, stripe, etc., the side length of the groove along the first surface is 3 to 5 mm.

[0098] refer to Figure 2 , 4 5. In some embodiments, the recess includes a first groove 121 and a second groove 122; the depth of the first groove 121 is greater than the depth of the second groove 122.

[0099] Since the conductivity, mechanical strength, and ability to cut off the circuit in time when overheating of the composite current collector are strongly related to the depth and size of the groove 12, the cooperation between the first groove 121 and the second groove 122 with different depths is beneficial to further improve the above-mentioned performance of the composite current collector.

[0100] In some embodiments, the depth of the first groove 121 accounts for 50% to 90% of the thickness of the conductive layer 1; for example, it can be about 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, etc.

[0101] In some embodiments, the depth of the second groove 122 is 10% to 50% of the thickness of the conductive layer 1; for example, it can be about 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, etc.

[0102] In some embodiments, along the first surface 11, the area of ​​the first groove 121 is 10% to 25% of the total area of ​​the recess, for example, it can be about 10%, 15%, 20%, 25%, etc.; the area of ​​the second groove 122 is 75% to 90% of the total area of ​​the recess, for example, it can be about 75%, 80%, 85%, 90%, etc.

[0103] By using first grooves 121 and second grooves 122 of different depths in combination according to the aforementioned depths and proportions, superior technical effects can be achieved in improving the performance of the composite current collector. When the depth of the first groove 121 accounts for 50% to 90% of the thickness of the conductive layer 1, the support layer 2 is deeply bonded to the conductive layer 1 through the position of the first groove 121, and the conductive layer 1 at the first groove 121 is relatively thin. Therefore, when overheating occurs, the support layer 2 undergoes thermal deformation, and during its thermal contraction, it can easily cause the conductive layer 1 at the first groove 121 to break, thereby promptly cutting off the circuit and reducing the probability of thermal runaway. Therefore, setting the first groove 121 to an appropriate depth has a significant effect on improving adhesion and enhancing fracture performance under overheating conditions.

[0104] Meanwhile, to simultaneously achieve good conductivity and mechanical properties, the area ratio of the first groove 121 and the second groove 122 needs to be within a suitable range. When the area ratio of the first groove 121 is between 10% and 25% and the area ratio of the second groove 122 is between 75% and 90%, it has beneficial effects on adhesion, fracture performance under overheating conditions, conductivity, and mechanical properties. When the area ratio of the first groove 121 is less than 10%, the improvement effect on adhesion and fracture performance under overheating conditions will be worse; when the area ratio of the first groove 121 exceeds 25%, the conductivity of the composite current collector will be negatively affected, thereby increasing the DC impedance and reducing the rate performance of the cell; it will also lead to a significant decrease in the mechanical properties of the composite current collector, increasing the risk of strip breakage during processing.

[0105] In some embodiments, the side length or diameter of the first groove 121 along the cross section of the first surface 11 is 5 to 25 mm; for example, it can be about 5 mm, 10 mm, 15 mm, 20 mm, 25 mm, etc.

[0106] The dimensions of the cross-section of the first groove 121 along the first surface 11 also have a significant impact on the bonding force and the fracture performance under overheating conditions. When its cross-sectional diameter is greater than 25 mm, it will have a negative effect on the conductivity. When its cross-sectional diameter is less than 5 mm, the fracture effect of the conductive layer 1 at the first groove 121 under overheating conditions is not very significant, so its improvement effect on reducing the probability of thermal runaway is relatively limited.

[0107] In some embodiments, there are two or more first grooves 121, and at least one second groove 122 is provided between any two first grooves 121.

[0108] If the first groove 121 is concentrated in a certain area, the overall thickness of the conductive layer 1 in that area will be too thin, which will easily have an adverse effect on the conductivity and mechanical strength of that area, and may even deteriorate the rate performance of the cell.

[0109] In some embodiments, the first groove 121 and the second groove 122 are alternately arranged.

[0110] Therefore, by alternately setting the first groove 121 and the second groove 122 with different depths, the layout is more reasonable, avoiding the phenomenon of local imbalance in conductivity or strength of conductive layer 1; and when the conductive layer 1 at the first groove 121 breaks under overheating conditions, it is easy to cause the conductive layer 1 at the adjacent second groove 122 to break in tandem, thereby generating a large-area break, cutting off the circuit in time, and reducing the probability of thermal runaway.

[0111] refer to Figure 9In some embodiments, the recess includes a microgroove 13, the depth of which is less than or equal to 100 nm; for example, it can be about 5 nm, 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, etc.

[0112] By setting the microgrooves 13, the contact and interlocking between the conductive layer 1 and the support layer 3 are further enhanced, which is beneficial to improving the adhesion between the two. Furthermore, since the depth of the microgrooves 13 is small, it has almost no impact on the overall conductivity of the composite current collector.

[0113] In some embodiments, microgrooves 13 are provided on the inner surfaces of the first surface 11 and / or the groove 12.

[0114] The microgrooves 13 can be disposed on the first surface 11 or on the inner surface of the groove 12, both of which help to improve the adhesion between the conductive layer 1 and the support layer 2. Furthermore, by disposing of the microgrooves 13 on the inner surface of the groove 12, the conductive layer 1 at the groove 12 is more easily driven by the support layer 2 when overheating occurs, thereby causing it to break.

[0115] In some embodiments, there are multiple microgrooves 13, and the spacing between adjacent microgrooves 13 is 2 to 20 mm; for example, it can be about 2 mm, 5 mm, 10 mm, 12 mm, 15 mm, 17 mm, 20 mm, etc.

[0116] In some embodiments, the diameter of the cross section of the microgroove 13 along the first surface 11 is 50 μm to 2 mm; for example, it can be about 50 μm, 100 μm, 200 μm, 300 μm, 500 μm, 700 μm, 800 μm, 1000 μm, 1200 μm, 1400 μm, 1500 μm, 1600 μm, 1900 μm, 2000 μm, etc.

[0117] In some embodiments, the thickness of the conductive layer 1 is 1 to 3 μm; for example, it is about 1 μm, 1.2 μm, 1.5 μm, 1.8 μm, 2 μm, 2.1 μm, 2.2 μm, 2.5 μm, 2.6 μm, 2.8 μm, 3 μm, etc.

[0118] When the conductive layer 1 is within the above-mentioned thickness range, it exhibits relatively balanced and excellent performance in terms of conductivity and timely breakage under overheating.

[0119] In some embodiments, the thickness of the support layer 2 is 0.3 to 30 μm; for example, about 0.3 μm, 0.5 μm, 0.8 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, etc.

[0120] When the support layer 2 is within the above-mentioned thickness range, it exhibits relatively balanced and excellent performance in terms of energy density and timely fracture under overheating conditions.

[0121] In some implementations, the support layer 2 is a single-layer structure.

[0122] When the support layer 2 is a single-layer structure, it can have a relatively thin thickness, such as 0.3 to 5 μm, which is beneficial to improving the energy density of the battery cell.

[0123] In some embodiments, the support layer 2 has a multilayer structure, including a base film layer 22 and a connecting layer 21 located between the base film layer 22 and the conductive layer 1; the room temperature Young's modulus E of the base film layer 22 satisfies: 2GPa≤E≤12GPa.

[0124] The base film layer 22 has the aforementioned room-temperature Young's modulus E, and the base film layer 22 can be, for example, a film prepared by biaxial stretching. By applying the base film layer 22 to the support layer 2, the mechanical strength of the composite current collector can be improved.

[0125] In some embodiments, the material of the support layer 2 includes one or more combinations of the following groups: polyamide, polyimide, polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polycarbonate, polyethylene, carboxylic acids and their derivatives grafted polyethylene, polypropylene, carboxylic acids and their derivatives grafted polypropylene, polypropylene, acrylonitrile-butadiene-styrene copolymer, polyvinyl alcohol, polystyrene, polyvinyl chloride, polyvinylidene fluoride, polytetrafluoroethylene, sodium polystyrene sulfonate, polyacetylene, silicone rubber, polyoxymethylene, polyphenylene ether, polyphenylene sulfide, polymethyl methacrylate, polyethylene glycol, polysulfide, polyphenylene, polypyrrole, polyaniline, polythiophene, polypyridine, cellulose, starch, protein, epoxy resin, polypyrrole, polythiophene, polyaniline, and phenolic resin.

[0126] In some embodiments, the constituent materials of the connecting layer 21 and the base film layer 22 are each independently selected from the aforementioned materials; the constituent materials of the connecting layer 21 and the base film layer 22 may be the same or different. For example, a film obtained by biaxial stretching can be used for the base film layer 22, and the connecting layer 21 can be formed on the surface of the base film layer 22 by coating, so that even if the same material is used, the connecting layer 21 and the base film layer 22 can have a clearly defined layer structure.

[0127] In some embodiments, the support layer 2 further comprises one or more of metal particles, inorganic particles, and nano-strength enhancers. Therefore, by incorporating the above-mentioned materials into the support layer 2, the strength, conductivity, etc., of the composite current collector can be further improved. In some embodiments, the nano-strength enhancer includes one or two of carbon nanotubes and graphene.

[0128] refer to Figures 3-5 7-8, In some embodiments, the composite current collector includes two conductive layers 1, and a support layer 2 is disposed between the two conductive layers 1. The first surface 11 of each conductive layer 1 faces the support layer 2, and the support layer 2 at least partially fills the recess of each conductive layer 1. The shape, depth, position, etc. of the recesses of the two conductive layers 1 may be the same or different.

[0129] In some embodiments, the material of the conductive layer 1 includes one or more combinations of the following: aluminum, copper, nickel, iron, titanium, silver, gold, cobalt, chromium, molybdenum, and tungsten.

[0130] Preparation method of composite current collector

[0131] A second aspect of this application provides a method for preparing a composite current collector according to any embodiment of the first aspect of this application, comprising: forming a recess on a first surface 11 of a conductive layer 1; disposing a support layer 2 on the first surface 11, and causing the recess to be at least partially filled by the support layer 2.

[0132] In some embodiments, a recess is formed on the first surface 11 of the conductive layer 1 by etching. In some embodiments, the etching includes at least one of plasma etching, chemical etching, and laser etching.

[0133] In some embodiments, the support layer 2 is disposed on the first surface 11 and at least partially fills the recess by coating or hot pressing.

[0134] In some implementations, the steps for preparing the composite current collector are as follows:

[0135] S1. A recess is provided on the first surface 11 of the conductive layer 1:

[0136] In some embodiments, a polymer paste layer is coated onto the first surface 11 of the conductive layer 1 (e.g., aluminum foil) using a patterned transfer roller (e.g., forward gravure printing), and dried to serve as a patterned protective layer; then, chemical etching (e.g., alkaline etching) is performed to form grooves 12, and the polymer paste layer is removed; wherein, the polymer paste includes polyvinylidene fluoride, polypropylene, polyethylene, sodium carboxymethyl cellulose, polymethyl methacrylate, etc.

[0137] In some embodiments, grooves 12 of different depths can be provided; for example, a second groove 122 is first formed on the first surface 11 of the conductive layer 1 through the above steps, and then a layer of polymer paste is coated on the first surface 11 of the conductive layer 1, and chemical etching is performed to form a deeper first groove 121; then the polymer layer is removed.

[0138] In some embodiments, microgrooves 13 may also be provided. For example, a laser may be used to perform secondary etching on the first surface 11 of the conductive layer 1 and the interior of the groove 12 to form microgrooves 13. The laser power may be, for example, 30%.

[0139] S2. The support layer 2 is disposed on the first surface 11 and at least partially fills the recess:

[0140] In some embodiments, the support layer 2 includes a base film layer 22 and a connecting layer 21. The following steps are taken: a slurry for forming the connecting layer 21 is coated on the first surface 11 of the conductive layer 1. After drying, the connecting layer 21 and one surface of the base film layer 22 (e.g., a PET film obtained by biaxial stretching) are placed opposite each other. The support layer 2 is disposed on the first surface 11 by hot pressing (the hot pressing temperature needs to exceed the melting point of the connecting layer, for example, ~180°C), and at least partially fills the recess of the first surface 11. Thus, a composite current collector with a "conductive layer-support layer (connecting layer-base film layer)" structure is prepared. In some embodiments, if there are two conductive layers 1, the following steps are performed: a slurry for forming a connecting layer 21 is coated on the first surface 11 of the other conductive layer 1. After drying, the connecting layer 21 is placed opposite to the surface of the base film layer 22 where the connecting layer 21 is not located, and hot-pressed (the hot-pressing temperature must exceed the melting point of the connecting layer, for example, ~180°C). This prepares a composite current collector with a structure of "conductive layer-support layer (connecting layer-base film layer-connecting layer)-conductive layer". Optionally, the conductive layer 1 of the composite current collector is chemically thinned.

[0141] In some embodiments, the support layer 2 is a single-layer structure, which is equivalent to having only a connecting layer 21. The following steps are then performed: a slurry for forming the connecting layer 21 is coated onto the first surface 11 of the conductive layer 1, and at least partially fills the recesses of the first surface 11; then it is dried to obtain a composite current collector with a "conductive layer-support layer (connecting layer)" structure. In some embodiments, there are two conductive layers 1. The following steps are then performed: the first surface 11 of another conductive layer 1 is positioned opposite the connecting layer 21, and then hot-pressed (the hot-pressing temperature must exceed the melting point of the adhesive layer, for example, ~180°C) to obtain a composite current collector with a "conductive layer-support layer (connecting layer)-conductive layer" structure.

[0142] In some embodiments, the support layer 2 is a single-layer structure, which is equivalent to having only the connecting layer 21. The following steps are then performed: material for forming the connecting layer 21 is directly extruded onto the first surface 11 of the conductive layer 1 using a casting extruder, and also at least partially fills the recesses of the first surface 11; then cooled to form a film, thus obtaining a composite current collector with a "conductive layer-support layer (connecting layer)" structure. In some embodiments, there are two conductive layers 1. The following steps are then performed: the first surface 11 of another conductive layer 1 is positioned opposite the connecting layer 21, and then hot-pressed (the hot-pressing temperature must exceed the melting point of the adhesive layer, for example, ~180°C), thus obtaining a composite current collector with a "conductive layer-support layer (connecting layer)-conductive layer" structure.

[0143] S3. Optionally, in some embodiments, a curing step is also included, such as curing at 75°C for 48 hours.

[0144] Electrode plates

[0145] A third aspect of this application provides an electrode sheet comprising an active material layer and a composite current collector according to any embodiment of the first aspect of this application or a composite current collector prepared according to any embodiment of the second aspect of this application; the active material layer is disposed on the surface of the conductive layer 1 of the composite current collector away from the support layer 2.

[0146] In some embodiments, the composite current collector has a conductive layer 1, and the electrode sheet includes the composite current collector and an active material layer disposed on the surface of the conductive layer 1 opposite to the support layer 2.

[0147] In some embodiments, the composite current collector includes two conductive layers 1, a support layer 2 disposed between the two conductive layers 1, a first surface 11 of each conductive layer 1 facing the support layer 2, and the recesses of each conductive layer 1 are at least partially filled by the support layer 2; the surface of each conductive layer 1 facing away from the support layer 2 is a second surface; then the positive electrode includes the composite current collector and an active material layer disposed on at least one second surface.

[0148] In some embodiments, the electrode sheet is a positive electrode sheet. The positive electrode sheet includes a composite current collector according to any embodiment of the first aspect of this application, and a positive active material layer disposed on the surface of the conductive layer 1 of the composite current collector facing away from the support layer 2; the positive active material layer includes a positive active material.

[0149] In some embodiments, when the positive electrode sheet is used in a lithium-ion battery, the positive electrode active material can be a positive electrode active material known in the art for lithium-ion batteries. As an example, the positive electrode active material may include at least one of the following materials: lithium phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as battery positive electrode active materials may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides 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 / 3Mn 1 / 3 O2 (also known as NCM) 333 LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM) 523 LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM) 211 LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM) 622 LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM) 811 ), lithium nickel cobalt aluminum oxide (such as LiNi) 0.85 Co 0.15 Al 0.05 At least one of O2 and its modified compounds. Examples of lithium phosphates with an olivine structure include, but are not limited to, lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites.

[0150] In some embodiments, when the positive electrode is used in a sodium-ion battery, the positive electrode active material can be a known positive electrode active material for sodium-ion batteries. As an example, the positive electrode active material can be a single material or a combination of two or more. The positive electrode active material can be selected from sodium-iron composite oxide (NaFeO2), sodium-cobalt composite oxide (NaCoO2), sodium-chromium composite oxide (NaCrO2), sodium-manganese composite oxide (NaMnO2), sodium-nickel composite oxide (NaNiO2), and sodium-nickel-titanium composite oxide (NaNiO2). 1 / 2 Ti 1 / 2 O2), sodium nickel manganese composite oxide (NaNi) 1 / 2 Mn 1 / 2 O2), sodium iron manganese composite oxide (Na) 2 / 3 Fe 1 / 3 Mn 2 / 3 O2), sodium nickel cobalt manganese composite oxide (NaNi) 1 / 3 Co 1 / 3 Mn 1 / 3 O2), sodium iron phosphate (NaFePO4), sodium manganese phosphate (NaMn) P The present application may use materials such as O4, sodium cobalt phosphate (NaCoPO4), Prussian blue materials, and polyanionic materials (phosphates, fluorophosphates, pyrophosphates, sulfates), but this application is not limited to these materials. Other conventionally known materials that can be used as positive electrode active materials for sodium-ion batteries may also be used.

[0151] In some embodiments, the positive electrode active material layer may optionally include a binder. For example, the binder may include one or more combinations selected from the group consisting of: polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0152] In some embodiments, the positive electrode active material layer may optionally include a conductive agent. For example, the conductive agent may include one or more combinations selected from the group consisting of: Super P, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0153] In some embodiments, the positive electrode sheet can be prepared by dispersing the components used to prepare the positive electrode active material layer, such as the positive electrode active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto a composite current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0154] In some embodiments, the electrode sheet is a negative electrode sheet. The negative electrode sheet includes a composite current collector according to any embodiment of the first aspect of this application, and a negative electrode active material layer disposed on the surface of the conductive layer 1 of the composite current collector facing away from the support layer 2; the negative electrode active material layer includes a negative electrode active material.

[0155] In some embodiments, the negative electrode active material may be a negative electrode active material known in the art for use in batteries. For example, the negative electrode active material includes one or more combinations selected from the group consisting of: natural graphite, artificial graphite, mesophase microcarbon spheres (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composites, Li-Sn alloys, Li-Sn-O alloys, Sn, SnO, SnO2, TiO2-Li4Ti5O 12 Li-Al alloys are used. However, this application is not limited to these materials; other conventional materials that can be used as negative electrode active materials for lithium-ion batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0156] In some embodiments, the negative electrode active material layer may optionally include a binder. For example, the binder may include one or more combinations selected from the group consisting of: styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0157] In some embodiments, the negative electrode active material layer may optionally include a conductive agent. For example, the conductive agent may include one or more combinations selected from the group consisting of: Super P, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0158] In some embodiments, the negative electrode active material layer may also optionally include other additives. For example, other additives may be thickeners (such as sodium carboxymethyl cellulose (CMC-Na)).

[0159] In some embodiments, the negative electrode sheet can be prepared by dispersing the above-mentioned raw materials for preparing the negative electrode active material layer, such as negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto a composite current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0160] Secondary batteries

[0161] The fourth aspect of this application provides a secondary battery, Figures 18-19The secondary battery 7 is used as an example, which includes the electrode plates of any embodiment of the third aspect of this application.

[0162] Typically, a secondary battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and releasing. The electrolyte acts as a conductor of ions between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing ions to pass through.

[0163] In some implementations, the secondary battery is a lithium-ion battery or a sodium-ion battery.

[0164] In some embodiments, at least one of the positive and negative electrodes of the secondary battery adopts the electrode sheet of any embodiment of the third invention of this application.

[0165] [Electrolytes]

[0166] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not specifically limit the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be selected from at least one of solid electrolytes and liquid electrolytes (i.e., electrolyte solutions).

[0167] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0168] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0169] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0170] In some embodiments, the electrolyte may optionally include additives. For example, additives may include 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 or low-temperature performance, etc.

[0171] [Septum]

[0172] The separator is positioned between the positive and negative electrode plates to provide isolation. This application does not impose any particular restriction on the type of separator; any known porous separator with good chemical and mechanical stability can be selected. The separator material can be selected from one or more combinations of the following: glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular restriction. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular restriction.

[0173] [Preparation of Secondary Batteries]

[0174] A secondary battery can be prepared by using a winding process or a stacking process to form an electrode assembly consisting of a positive electrode, a negative electrode, and a separator. After being packaged and encapsulated, an electrolyte is injected.

[0175] The outer packaging can be a hard shell, such as a hard plastic shell, aluminum shell, or steel shell. It can also be a flexible package, such as a pouch. The material of the flexible package can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0176] Battery modules, battery packs

[0177] In some implementations, the secondary batteries can be assembled into a battery module, and the number of secondary batteries contained in the battery module can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery module.

[0178] Figure 20 This is battery module 6 as an example. (See reference...) Figure 20 In battery module 6, multiple secondary batteries 7 can be arranged sequentially along the length of battery module 6. Of course, they can also be arranged in any other manner. Furthermore, these multiple secondary batteries 7 can be fixed in place using fasteners.

[0179] Optionally, the battery module 6 may also include a housing with a receiving space in which a plurality of secondary batteries 7 are received.

[0180] In some implementations, the secondary batteries can also be assembled into a battery pack.

[0181] In some embodiments, the battery module 6 can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0182] Figure 21 and Figure 22This is battery pack 1 as an example. (See reference...) Figure 21 and Figure 22 The battery pack 3 may include a battery box and multiple battery modules 6 disposed within the battery box. The battery box includes an upper body 4 and a lower body 5, with the upper body 4 covering the lower body 5 to form a closed space for accommodating the battery modules 6. The multiple battery modules 6 can be arranged in any manner within the battery box.

[0183] Electrical appliances

[0184] This application also provides an electrical device, which includes the secondary battery provided in this application. In some embodiments, the electrical device includes at least one of the battery module or battery pack provided 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 may include mobile 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., but is not limited thereto.

[0185] As the electrical device, a secondary battery, battery module, or battery pack can be selected according to its usage requirements.

[0186] Figure 23 This is an example of an electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the secondary battery for this device, a battery pack or battery module can be used.

[0187] 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.

[0188] Example 1

[0189] The composite current collector was prepared according to the specific parameters in Table 1 and following the steps below. Its structural schematic diagram is shown below. Figures 8-10 As shown, and a lithium-ion battery cell including the composite current collector:

[0190] I. Composite current collector:

[0191] (1) A polymer paste layer with a pattern is coated on the first surface of the aluminum foil by forward gravure printing and dried as a pattern protective layer; then, chemical etching is performed using alkaline solution to form multiple second grooves on the first surface; then the polymer paste layer is removed.

[0192] (2) A layer of polymer paste is coated on the first surface of the aluminum foil and dried to serve as a pattern protection layer; then, an alkaline solution is used for chemical etching to form multiple first grooves; then the polymer paste layer is removed.

[0193] (3) Use a laser to perform secondary etching on the first surface and the interior of the first and second grooves to form microgrooves. The laser power is 30%. Then, cut the aluminum foil into appropriate sizes to obtain two aluminum foils, which are used as the first conductive layer and the second conductive layer in the following steps, respectively.

[0194] (4) Maleic anhydride-grafted polypropylene is coated on the first surface of the first conductive layer to form the connecting layer. After drying, the connecting layer and the PET film (which is biaxially stretched and has a room temperature Young's modulus E of 4.8 GPa) are placed opposite each other and composite hot-pressed. The hot-pressing temperature is 180°C. The wound single-sided composite aluminum foil is cured at 75°C for 48 hours.

[0195] (5) Maleic anhydride-grafted polypropylene is coated on the first surface of the second conductive layer to form a connecting layer. After drying, the connecting layer is placed opposite to the PET film of the single-sided composite aluminum foil prepared in step (4) and composite hot pressing is performed. The hot pressing temperature is 180℃. The wound double-sided composite aluminum foil is cured at 75℃ for 48h.

[0196] (6) The double-sided composite aluminum foil is rolled up and passed through an alkaline etching tank to reduce the thickness of the first and second conductive layers. After being sprayed with water and dried, it is rolled up to obtain a composite current collector, which is used for the subsequent preparation of lithium-ion battery cells.

[0197] II. Lithium-ion battery cells

[0198] (1) Preparation of positive electrode sheet

[0199] LiNi 0.8 Co 0.1 Mn 0.1 O2 and LiNi 0.5 Co 0.2 Mn 0.3 O2 is mixed in a ratio of 17:3 to serve as the positive electrode active material. The positive electrode active material, superconducting carbon black SP as a conductive agent, and polyvinylidene fluoride (PVDF) as a binder are dispersed in N-methylpyrrolidone (NMP) as a solvent at a mass ratio of 95:3:2 and mixed evenly to obtain a positive electrode slurry. The positive electrode slurry is uniformly coated on a composite current collector, and after drying, cold pressing, edge welding, die cutting, and slitting, a positive electrode sheet is obtained.

[0200] (2) Preparation of negative electrode sheet

[0201] The negative electrode active material graphite, superconducting carbon black SP as a conductive agent, SBR as a binder, and CMC-Na as a thickener are dispersed in deionized water as a solvent at a mass ratio of 96:1:1:2 and mixed evenly to obtain a negative electrode slurry. The negative electrode slurry is then uniformly coated onto a negative electrode current collector copper foil. After drying, cold pressing, and slitting, a negative electrode sheet is obtained.

[0202] (3) Diaphragm

[0203] Polyethylene film is used as the diaphragm.

[0204] (4) Preparation of electrolyte

[0205] Ethyl carbonate (EC), dimethyl carbonate (DMC), and diethyl carbonate (DEC) were mixed uniformly in a volume ratio of 1:1:1 to obtain an organic solvent. Then, fully dried lithium salt LiPF6 was dissolved in the mixed organic solvent to prepare an electrolyte with a concentration of 1 mol / L.

[0206] (6) Preparation of battery cells

[0207] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator acting as a separator between the positive and negative electrode. The cells are then wound to obtain a bare cell, tabs are welded on, and the bare cell is placed in an outer package. Electrolyte is injected into the dried cell, and the cells are then packaged, left to stand, formed, and shaped to obtain a lithium-ion battery cell I-1.

[0208] Examples 2-14

[0209] According to the specific parameters in Table 1, the corresponding composite current collectors and lithium-ion battery cells were prepared by referring to the steps in Example 1.

[0210] The structural schematic diagrams of the composite current collectors prepared in Examples 2-3 and 9-13 are shown below. Figures 8-10 As shown; a schematic diagram of the composite current collector prepared in Example 4 is shown. Figure 8 , 10 As shown; a schematic diagram of the composite current collector prepared in Example 5 is shown. Figures 8-9 As shown in Figures 1 and 12; a schematic diagram of the composite current collector prepared in Example 6 is shown in Figure 12. Figures 8-9 As shown in Figure 11; the structural schematic diagram of the composite current collector prepared in Example 7 is shown in Figure 11. Figures 8-9 As shown in Figures 1 and 13, the structural schematic diagrams of the composite current collectors prepared in Examples 8 and 14 are as follows. Figure 4 , 9 As shown in Figures 1-10; schematic diagrams of the composite current collectors prepared in Examples 15-17 are shown in Figures 1-17. Figure 7 , 9 As shown in ~10.

[0211] In Example 4, no microgrooves are provided.

[0212] In Example 8, the maleic anhydride-grafted polypropylene used to form the connecting layer also contains Al2O3 particles and carbon nanotubes; wherein the mass percentage of alumina particles is 40% and the mass percentage of carbon nanotubes is 10%; and Example 8 does not include a base film layer. The above-mentioned slurry for forming the connecting layer is coated on the first surface of the first conductive layer, dried, and then the connecting layer and the first surface of the second conductive layer are placed opposite each other for composite hot pressing; the hot pressing temperature is 180°C; thus, a composite current collector is prepared.

[0213] In Example 14, excluding the base film layer, a slurry (excluding fillers such as alumina and carbon nanotubes) for forming a connecting layer is coated on the first surface of the first conductive layer. After drying, the connecting layer and the first surface of the second conductive layer are placed opposite each other and composite hot-pressed; the hot-pressing temperature is 180°C; thus, a composite current collector is prepared.

[0214] In Example 15, no second groove is provided.

[0215] In Example 16, the first groove is not provided.

[0216] In Example 17, no second groove is provided.

[0217] Comparative Example 1

[0218] Except for the following differences, the composite current collector and lithium-ion battery are prepared according to the steps in Example 1:

[0219] Instead of creating the first groove, second groove, or micro-groove on the surface of the aluminum foil, the aluminum foil is used directly as the conductive layer.

[0220] Table 1

[0221]

[0222]

[0223] Test case

[0224] I. Adhesion

[0225] Peel tests were performed on the composite current collectors obtained in Examples 1-17 and Comparative Example 1 to obtain the adhesion force data of each composite current collector. The test results are shown in Table 2.

[0226] II. Cycle capability of individual battery cells

[0227] The lithium-ion battery cells obtained in Examples 1-17 and Comparative Example 1 were tested for cycle capability. Fresh battery cells were cycled at 60°C using a 1C rate charge and discharge cycle until the capacity decreased to 80% of the initial capacity. The number of cycles at this point was recorded. The cycle count data for each battery cell was obtained. The test results are shown in Table 2.

[0228] III. DC Resistance (DCR) of a Single Battery Cell

[0229] The lithium-ion battery cells obtained in Examples 1-17 and Comparative Example 1 were subjected to DCR testing. The battery cells were adjusted to 50% SOC and discharged at a 4C rate (corresponding to a discharge current of I) for 30 seconds. The voltage difference ΔV before and after the 30-second discharge was recorded. The DCR corresponding to 50% SOC was calculated using the following formula: DCR = ΔV / I, yielding the DCR data for each battery cell. The test results are shown in Table 2.

[0230] IV. Acupuncture Test

[0231] The lithium-ion battery cells obtained in Examples 1-17 and Comparative Example 1 were subjected to a nail penetration test. After the cells were fully charged, they were fixed on a fixture, and a 3mm diameter high-temperature resistant steel needle was inserted into the cells at a speed of 80mm / s. If smoke, fire, or the explosion-proof valve was forced open after the needle was inserted, the test was considered failed. If no smoke, fire, or explosion-proof valve was forced open after the needle was inserted, the test was considered passed. The nail penetration test results for each battery cell were obtained. The test results are shown in Table 2.

[0232] Table 2 Test Results

[0233]

[0234] manual

[0235]

[0236] According to the test results, compared with Comparative Example 1, the embodiments of this application significantly improve the adhesion of the composite current collector by providing at least one recess on the surface of the conductive layer near the support layer. By improving the adhesion, conductive layer peeling can be prevented during processing and long-term use, thereby effectively improving the long-term performance of the battery. Compared with Comparative Example 1, Examples 1-14 show significant improvements in at least one of the following aspects: battery safety performance and cycle life at 60°C. Furthermore, as demonstrated by Examples 5-7, recesses of different shapes all exhibit relatively good performance.

[0237] It is generally believed that thinning the conductive layer may degrade the conductivity of the current collector. Test results from Examples 1-8 show that when the dimensions, adjacent spacing, and area ratio of the first and second grooves are appropriate, the conductive layer at the second groove and the ungrooved location can still provide a complete conductive network. Therefore, the presence of the first groove does not worsen the conductivity, and the DCR of Examples 1-8 remains close to that of Comparative Example 1. Furthermore, when the cell overheats due to a needle-puncture short circuit, and its temperature approaches the softening point of the connecting layer and the base film, the connecting layer and the base film will deform. Because the surface area where the connecting layer and conductive layer are bonded at the groove is large, and the conductive layer at the groove is thinner, it is the first to fracture under the influence of the connecting layer. Further, this crack will extend to the surrounding area. The fracture at the first groove will cause the surrounding area and the second groove to fracture together, effectively cutting off the short-circuit loop and preventing the spread of thermal runaway, allowing the cell to pass the needle-puncture safety test.

[0238] The test results of Examples 1-3 show that when the interval between adjacent grooves is 10-80mm, the needle penetration test can be passed and the cell performance remains good. Example 9 also shows some improvement in adhesion and cycle count; however, due to its large groove spacing (150mm), the breakage of the conductive layer at the groove cannot form a synergistic effect to cause large-area breakage, thus failing the needle penetration test. Example 10 successfully passed the needle penetration test; however, due to its small groove spacing (7mm) and the high proportion of grooves in the composite current collector (~51%), it is not conducive to maintaining good conductivity, resulting in less improvement in cycle performance compared to Comparative Example 1.

[0239] The proportions of the first and second grooves with different depths also have a significant impact on battery performance. Comparing Examples 11 and 2, it is evident that when the area proportion of the first groove is increased from 20% to 50%, the conductive network of the composite current collector is affected due to the higher proportion of the first groove, resulting in a smaller improvement in cell cycle life (number of revolutions) compared to Comparative Example 1. Comparing Examples 12 and 2, it is evident that when the area proportion of the first groove is reduced from 20% to 5%, the proportion of the first groove is too small. During short-circuit overheating, the breakage of the conductive layer at the first groove cannot effectively drive the surrounding second groove and non-groove areas to form a large-area synergistic breakage, thus making it difficult to completely cut off the short-circuit circuit, resulting in failure to pass the needle penetration test.

[0240] By comparing Example 13 and Example 2, it can be seen that when the side length of the first groove changes from 15mm to 40mm, the thin conductive layer at the first groove becomes too large, and its influence on the conductivity of the current collector becomes prominent. Moreover, the total area of ​​the groove accounts for more than 50%, so the improvement of the cell cycle life (number of revolutions) of Example 13 is relatively small compared with Comparative Example 1.

[0241] A comparison of Example 4 and Example 2 shows that microgrooves can further enhance adhesion, thereby improving the cycle life of the battery.

[0242] Comparing Example 14 with Example 2, it is evident that, compared to the absence of a base film layer, the overall strength of the composite current collector can be further improved by incorporating a base film layer. This reduces the likelihood of deformation during processing and cell cycling, thereby improving interface performance and resulting in good cycle life and DCR value. Further comparison with Example 8 shows that by adding inorganic particles and nano-reinforcing materials to the connecting layer, the overall mechanical strength can be effectively improved even in the absence of a base film layer, thus enhancing cell performance.

[0243] Example 15 only has a first groove, the depth of which accounts for 90% of the conductive layer thickness. Due to the presence of the groove and microgrooves, the adhesion and cycling performance are significantly improved compared to Comparative Example 1. However, since the grooves are relatively deep and the groove area accounts for 0.5% of the conductive layer surface area, effective conductive layer fracture cannot be formed under overheating conditions, and therefore it failed the needle penetration test.

[0244] Example 16 only has a second groove, the depth of which accounts for 10% of the conductive layer thickness. Due to the presence of the groove and microgrooves, and the high area of ​​the groove relative to the conductive layer (50%), the adhesion and cycling performance are significantly improved compared to Comparative Example 1. However, due to the absence of a deep groove, there is a lack of trigger points for conductive network breakage under overheating conditions, thus failing the pinhole test.

[0245] Example 17 only has a first groove, the depth of which accounts for 60% of the conductive layer thickness, and the groove area accounts for 14% of the conductive layer surface area. Due to the presence of the first groove, the adhesion and cycling performance are significantly improved compared to Comparative Example 1. Furthermore, because its area accounts for 14% of the conductive layer surface area, effective conductive layer fracture can be formed under overheating conditions, passing the needle penetration test. However, since all grooves are deep, there is some damage to the conductive network, resulting in a slight deterioration in its DCR compared to Comparative Example 1.

[0246] The above description is merely a preferred embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A composite current collector, characterized by, The composite current collector comprises a conductive layer and a support layer; a first surface of the conductive layer has at least one recess; the support layer is arranged on the first surface of the conductive layer, and the support layer at least partially fills the recess; the recess comprises a groove, and the number of the grooves is at least two, and the interval between adjacent grooves is 10-80 mm.

2. The composite current collector of claim 1, wherein The area of the recess accounts for 0.5%-50% of the area of the first surface.

3. The composite current collector of claim 1, wherein The depth of the groove accounts for 10%-90% of the thickness of the conductive layer.

4. The composite current collector of claim 1, wherein The length of the side or the diameter of the cross section of the groove along the first surface is 3-50 mm.

5. The composite current collector of claim 1, wherein The cross section of the groove along the first surface has a shape selected from one or a combination of two or more of the following group: a circle, a triangle, a square, a parallelogram.

6. The composite current collector of any one of claims 1 to 5, wherein, The groove comprises a first groove and a second groove; the depth of the first groove is greater than that of the second groove.

7. The composite current collector of claim 6, wherein The depth of the first groove accounts for 50%-90% of the thickness of the conductive layer.

8. The composite current collector of claim 6, wherein The length of the side or the diameter of the cross section of the first groove along the first surface is 5-25 mm.

9. The composite current collector of claim 6, wherein, The depth of the second groove accounts for 10%-50% of the thickness of the conductive layer.

10. The composite current collector of claim 6, wherein Along the first surface, the area of the first groove accounts for 10%-25% of the area of the recess; and the area of the second groove accounts for 75%-90% of the area of the recess.

11. The composite current collector of claim 6, wherein The number of the first grooves is two or more, and at least one second groove is arranged between any two first grooves.

12. The composite current collector of claim 1, wherein The recess further comprises a micro-groove, and the depth of the micro-groove is less than or equal to 100 nm.

13. The composite current collector of claim 12, wherein The number of the micro-grooves is multiple, and the interval between adjacent micro-grooves is 2-20 mm.

14. The composite current collector of claim 12, wherein The length of the side or the diameter of the cross section of the micro-groove along the first surface is 50 μm-2 mm.

15. The composite current collector of claim 1, wherein The support layer has a single-layer structure; or The support layer has a multi-layer structure, and the support layer comprises a base film layer and a connecting layer between the base film layer and the conductive layer.

16. The composite current collector of claim 1, wherein The elastic modulus of the support layer is 0.5-13 GPa.

17. The composite current collector of claim 1, wherein The material of the support layer comprises one or a combination of two or more of the following group: polyamide, polyimide, polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polycarbonate, polyethylene, carboxylic acid and its derivative grafted polyethylene, polypropylene, carboxylic acid and its derivative grafted polypropylene, polypropylene, acrylonitrile-butadiene-styrene copolymer, polyvinyl alcohol, polystyrene, polyvinyl chloride, polyvinylidene fluoride, polytetrafluoroethylene, polystyrene sulfonate sodium, polyacetylene, silicone rubber, polyformaldehyde, polyphenylene ether, polyphenylene sulfide, polymethyl methacrylate, polyethylene glycol, polyazothiophene, polystyrene, polypyrrole, polyaniline, polythiophene, polypyridine, cellulose, starch, protein, epoxy resin, phenolic resin.

18. The composite current collector of claim 17, wherein The support layer further contains one or a combination of two or more of the following group: metal particles, inorganic particles, nano-strength reinforcing agents.

19. The composite current collector of claim 1, wherein The composite current collector comprises two conductive layers, and the support layer is arranged between the two conductive layers; the first surface of each conductive layer faces the support layer, and the recess of each conductive layer is at least partially filled by the support layer.

20. A method of making a composite current collector according to any one of claims 1 to 19, characterized in that, forming the recess on a first surface of the electrically conductive layer; disposing the support layer on the first surface, and causing the recess to be at least partially filled by the support layer.

21. An electrode, characterized by a secondary battery comprising the electrode tab of claim 21.

22. A secondary battery characterized by comprising: a secondary battery comprising the electrode tab of claim 21.

23. An electrical device, comprising: a secondary battery comprising the electrode tab of claim 21.

Images