Electrochemical device, preparation method thereof and electronic device

Abstract

The invention discloses an electrochemical device, a preparation method thereof and an electronic device. An electrochemical device includes an electrode assembly and a first tab. The electrode assembly comprises a first pole piece, the first pole piece comprises a first current collector and a first active material layer arranged on the first current collector, the first tab comprises a first connection area, and the first connection area is in welded connection with the first current collector. Along the thickness direction of the first connection region, the surface, deviating from the first current collector, of the first connection region is a first surface, the first surface is provided with a first welding mark, the arithmetic mean roughness of the first surface is Ra [mu] m, and Ra is greater than or equal to 0.3 and less than or equal to 1.5. The short circuit risk caused by the fact that welding mark burrs pierce the isolating membrane can be reduced.

Description

Technical Field

[0001] The present application relates to the field of energy storage technology, and in particular to an electrochemical device, a method for preparing the electrochemical device, and an electronic device having the electrochemical device. Background Art

[0002] With the popularity of consumer electronic products such as laptops, mobile phones, handheld game consoles, tablets, mobile power supplies and drones, people are placing increasingly stringent requirements on electrochemical devices (such as secondary batteries).

[0003] The electrochemical device includes an electrode assembly and a tab electrically connected to the electrode assembly. In the related art, the tab is electrically connected to the electrode sheet of the electrode assembly by welding. The weld burrs formed by welding may pierce the isolation membrane and cause a short circuit risk, thereby reducing the safety and service life of the electrochemical device. Summary of the invention

[0004] In view of this, it is necessary to provide an electrochemical device that can solve at least one of the above problems. In addition, it is also necessary to provide a method for preparing the electrochemical device and an electronic device having the electrochemical device.

[0005] The first aspect of the present application provides an electrochemical device, comprising an electrode assembly and a first pole ear. The electrode assembly comprises a first pole piece, the first pole piece comprises a first current collector and a first active material layer disposed on the first current collector, and the first pole ear comprises a first connection area, and the first connection area is welded to the first current collector. Along the thickness direction of the first connection area, the surface of the first connection area away from the first current collector is the first surface, and the first surface is provided with a first weld mark. The arithmetic mean roughness of the first surface is Ra μm, 0.3≤Ra≤1.5.

[0006] In the present application, the arithmetic mean roughness of the first surface is low, so the flatness of the first surface including the first weld mark is improved, which is beneficial to reduce the risk of short circuit that may be caused after the first weld mark pierces the isolation membrane, thereby improving the safety and service life of the electrochemical device.

[0007] Based on the first aspect, in some possible implementations, 0.6≤Ra≤1.2. Therefore, while further improving the flatness of the first surface and reducing the risk of short circuit that may be caused by the first weld mark piercing the isolation film, it is also possible to reduce the impact of the mechanical properties (such as weld mark shear strength) and microstructure (such as grain size) of the first pole ear when the arithmetic mean roughness of the first surface is small (for example, when the laser power is large or the irradiation time is long when the first weld mark is treated by laser irradiation), thereby further improving the safety and service life of the electrochemical device.

[0008] Based on the first aspect, in some possible implementations, 0.6≤Ra≤1.0, thereby further reducing the risk of short circuit that may be caused by the first weld mark piercing the isolation membrane, thereby improving the safety and service life of the electrochemical device.

[0009] Based on the first aspect, in some possible implementations, the first active material layer is provided with a first groove, and the first connection area is provided in the first groove. The electrochemical device also includes a first adhesive, which is bonded to the first surface and covers the first weld print. The first active material layer includes a first active material area surrounding the first groove. The first adhesive also bonds the first active material area. The thickness of the first adhesive along the thickness direction is T, 5 μm≤T≤12 μm. The first adhesive can not only isolate the first weld print to further reduce the risk of short circuit caused by the first weld print piercing the isolation film, but also play a good fixing role on the first pole ear, reducing the risk of the first weld print breaking or the first pole ear separating from the first current collector during mechanical abuse such as falling and collision. Moreover, since the arithmetic mean roughness of the first surface is low, it is not only conducive to increasing the bonding area between the first adhesive and the first pole piece, reducing the risk of the first adhesive falling off from the first surface, but also the thickness of the first adhesive can be appropriately reduced, which can also play a role in inhibiting the piercing of the first weld print, thereby reducing the influence of the first adhesive on the energy density of the electrochemical device and improving the contact interface.

[0010] Based on the first aspect, in some possible implementations, 5 μm≤T≤10 μm, so that the influence of the provision of the first adhesive on the energy density of the electrochemical device can be further reduced and the contact interface can be improved.

[0011] Based on the first aspect, in some possible implementations, the surface of the first current collector connected to the first connection area is the first surface. In the thickness direction, the maximum height of the first weld mark from the first surface is less than or equal to the thickness of the first active material layer. Therefore, the thickness difference between the first connection area and the first active material layer can be reduced, and the total thickness of the electrode assembly at the first pole ear can be reduced, which is conducive to further reducing the short circuit risk that may be caused by the first weld mark piercing the separator, and can also improve the energy density of the electrochemical device.

[0012] Based on the first aspect, in some possible implementations, the first weld mark is processed by laser irradiation. Laser irradiation can reduce the arithmetic mean roughness of the first surface. Moreover, the laser beam energy used during laser irradiation is concentrated, and the heat-affected zone is small, which can reduce the impact of the laser beam on surrounding materials such as active materials, and the non-contact welding method is also conducive to reducing damage to the first pole ear or other areas. Moreover, the laser beam can be irradiated from the side of the first pole ear away from the first current collector, and the power or pulse frequency of the laser beam can be adjusted more conveniently to process the first weld mark, which is conducive to precise control.

[0013] Based on the first aspect, in some possible implementations, the first surface is irradiated with a laser. Therefore, in the case where the first electrode tab itself is relatively thick or even protrudes from the first active material layer, this can further reduce the thickness difference between the first connection area and the first active material layer, and reduce the total thickness of the electrode assembly at the first electrode tab, thereby further reducing the short circuit risk that may be caused by the first weld piercing the separator, and can also improve the energy density of the electrochemical device.

[0014] Based on the first aspect, in some possible implementations, along the thickness direction, the thickness of the first connection area is less than or equal to the thickness of the first active material layer, thereby further reducing the thickness difference between the first connection area and the first active material layer, reducing the risk of short circuit that may be caused by the first weld piercing the isolation membrane, and also improving the energy density of the electrochemical device.

[0015] Based on the first aspect, in some possible implementations, the first pole piece is a negative pole piece, the first current collector is a copper foil, and the first pole tab is a copper alloy sheet. Even if the weld burr formed by the first pole tab made of copper alloy after welding is relatively hard, the present application can reduce the short circuit risk that may be caused by the first weld burr piercing the isolation membrane, thereby improving the safety and service life of the electrochemical device. The second aspect of the present application provides a method for preparing the above-mentioned electrochemical device, comprising the following steps: providing a first pole piece, the first pole piece comprising a first current collector and a first active material layer disposed on the first current collector; welding and connecting the first connection area of ​​the first pole ear to the first current collector; laser irradiating the first weld mark on the surface of the first connection area away from the first current collector; making the first pole piece into an electrode assembly, and placing the electrode assembly in a housing to obtain an electrochemical device. In the present application, the laser irradiation treatment can reduce the arithmetic mean roughness of the first surface, thereby improving the flatness of the first surface including the first weld mark, which is also conducive to reducing the risk of short circuit that may be caused by the first weld mark piercing the isolation membrane, thereby improving the safety and service life of the electrochemical device.

[0016] Based on the second aspect, in some possible implementations, the first connection area of ​​the first pole piece is ultrasonically welded to the first current collector. Therefore, the first weld has higher welding reliability, improves the connection strength between the first connection area and the first current collector, and reduces the influence of laser irradiation on the welding reliability of the first weld.

[0017] Based on the second aspect, in some possible implementations, the laser irradiation treatment uses a pulsed laser, the laser power is less than or equal to 150W, and the pulse frequency is less than or equal to 50Hz. Among them, the arithmetic mean roughness of the first surface after laser irradiation can be adjusted by adjusting the laser power and the pulse frequency. By controlling the range of laser power and pulse frequency, the influence of the laser beam on the mechanical properties and microstructure of the first pole ear can be further reduced, and the safety and service life of the electrochemical device can be further improved.

[0018] Based on the second aspect, in some possible implementations, the preparation method further includes: performing laser irradiation treatment on the surface of the first connection area away from the first current collector. Therefore, in the case where the first electrode ear itself is relatively thick or even protrudes from the first active material layer, this can reduce the thickness difference between the first connection area and the first active material layer, reduce the total thickness of the electrode assembly at the first electrode ear, thereby reducing the short circuit risk that may be caused by the first weld piercing the separator, and can also improve the energy density of the electrochemical device.

[0019] The third aspect of the present application provides an electronic device, comprising a storage chamber and the electrochemical device. The electrochemical device is disposed in the storage chamber. The electronic device is powered by the electrochemical device, and the arithmetic mean roughness of the first surface is low, which can reduce the risk of short circuit caused by the first weld mark piercing the isolation film, thereby improving the safety and service life of the electrochemical device. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a schematic structural diagram of an electrochemical device provided in one embodiment of the present application when viewed from a first direction.

[0021] Figure 2 for Figure 1 The electrochemical device is shown in a cross-sectional view along the cutting line II-II.

[0022] Figure 3 for Figure 2 A partial enlarged view of the electrochemical device at III is shown.

[0023] Figure 4 for Figure 2 The schematic diagram of the structure of the first electrode sheet of the electrochemical device after unfolding is shown.

[0024] Figure 5 A flow chart of a method for preparing an electrochemical device provided in one embodiment of the present application.

[0025] Figure 6 A schematic diagram of the structure of an electronic device provided in one embodiment of the present application.

[0026] The following specific implementation methods will further illustrate the present application in conjunction with the above-mentioned drawings. DETAILED DESCRIPTION

[0027] The technical scheme in the embodiment of the present application is described clearly and in detail below. Obviously, the described embodiment is only a part of the embodiment of the present application, rather than all the embodiments. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those generally understood by those skilled in the art of the present application. The terms used in the specification of the present application are only for the purpose of describing specific embodiments and are not intended to limit the present application.

[0028] Hereinafter, the embodiments of the present application will be described in detail. However, the present application can be embodied in many different forms and should not be construed as being limited to the exemplary embodiments illustrated herein. Rather, these exemplary embodiments are provided so that the present application is thoroughly and in detail communicated to those skilled in the art.

[0029] In addition, for simplicity and clarity, in the accompanying drawings, the size or thickness of various components, layers may be amplified. Throughout the entire text, the same numerical value refers to the same element. As used herein, the term "and / or", "and / or" includes any and all combinations of one or more related enumerated items. In addition, it should be understood that when element A is referred to as "connecting" element B, element A may be directly connected to element B, or there may be an intermediate element C and element A and element B may be indirectly connected to each other.

[0030] Further, the use of “may” when describing embodiments of the present application means “one or more embodiments of the present application”.

[0031] The technical terms used herein are for the purpose of describing specific embodiments and are not intended to limit the present application. As used herein, the singular form is intended to also include the plural form, unless the context clearly indicates otherwise. It should be further understood that the term "comprising", when used in this specification, refers to the presence of narrated features, values, steps, operations, elements and / or components, but does not exclude the presence or increase of one or more other features, values, steps, operations, elements, components and / or combinations thereof.

[0032] Spatial related terms, such as "on" and the like can be used herein for convenient description, to describe the relationship between an element or feature and another element (multiple elements) or feature (multiple features) as illustrated in the figure. It should be understood that, in addition to the directions described in the figure, spatial related terms are intended to include different directions of equipment or devices in use or operation. For example, if the equipment in the figure is turned over, the elements described as "above" or "on" other elements or features will be oriented "below" or "below" other elements or features. Therefore, the exemplary term "on" may include the direction above and below. It should be understood that although the terms first, second, third, etc. can be used herein to describe various elements, components, regions, layers and / or parts, these elements, components, regions, layers and / or parts should not be limited by these terms. These terms are used to distinguish an element, component, region, layer or part from another element, component, region, layer or part. Therefore, the first element, component, region, layer or part discussed below may be referred to as the second element, component, region, layer or part without departing from the teaching of the exemplary embodiment.

[0033] See also Figure 1 and Figure 2 In one embodiment of the present application, an electrochemical device 100 is provided, comprising a housing 10 , an electrode assembly 20 , an electrolyte (not shown), a first electrode tab 30 , and a second electrode tab 40 . The electrode assembly 20 and the electrolyte are located in the housing 10 .

[0034] like Figure 2As shown, the electrode assembly 20 includes a first pole piece 21, a second pole piece 22 and a separator 23, and the separator 23 is arranged between the first pole piece 21 and the second pole piece 22. The first pole piece 21 includes a first current collector 210 and a first active material layer 211 arranged on the first current collector 210. The first current collector 210 includes a first surface 2101 and a second surface 2102 arranged oppositely, and the first active material layer 211 is arranged on the first surface 2101 and the second surface 2102 respectively. The second pole piece 22 includes a second current collector 220 and a second active material layer 221 arranged on the second current collector 220. The second current collector 220 includes a third surface 2201 and a fourth surface 2202 arranged oppositely, and the second active material layer 221 is arranged on the third surface 2201 and the fourth surface 2202 respectively. This embodiment is illustrated by taking the electrode assembly 20 as a winding structure, that is, the first pole piece 21, the separator 23 and the second pole piece 22 are stacked and wound. At this time, the first surface 2101 of the first current collector 210 and the third surface 2201 of the second current collector 220 are both arranged away from the winding center axis O, and the second surface 2102 of the first current collector 210 and the fourth surface 2202 of the second current collector 220 are both arranged toward the winding center axis O. Among them, a three-dimensional coordinate system is defined by a first direction X, a second direction Y, and a third direction Z that are perpendicular to each other. The first direction X is the thickness direction of the electrode assembly 20, and the second direction Y is the direction in which the first pole tab 30 or the second pole tab 40 protrudes from the electrode assembly 20. When the electrode assembly 20 is a winding structure, the second direction Y is also the width direction of the first pole sheet 21 or the second pole sheet 22.

[0035] The first electrode tab 30 and the second electrode tab 40 are respectively welded to the first current collector 210 and the second current collector 220, and the first electrode tab 30 and the second electrode tab 40 can be connected to external components (not shown). Figure 1 As shown, in some embodiments, the housing 10 may be a packaging bag encapsulated by a packaging film (such as an aluminum-plastic film), and the first pole tab 30 and the second pole tab 40 both extend out of the housing 10 from the inside of the housing 10. In other embodiments, the electrochemical device 100 may also be a steel shell battery, an aluminum shell battery, etc.

[0036] The first electrode sheet 21 may be a negative electrode sheet, and the second electrode sheet 22 may be a positive electrode sheet. Correspondingly, the first current collector 210 is a negative electrode current collector, the first active material layer 211 is a negative electrode active material layer, and the first electrode tab 30 is a negative electrode tab; the second current collector 220 is a positive electrode current collector, the second active material layer 221 is a positive electrode active material layer, and the second electrode tab 40 is a positive electrode tab. In other embodiments, the first electrode sheet 21 may be a positive electrode sheet, and the second electrode sheet 22 may be a negative electrode sheet. Figure 4 As shown, Figure 4 for Figure 2 The structure schematic diagram of the first pole piece 21 after unfolding is shown. Figure 4A three-dimensional coordinate system is established by a fourth direction X′, a second direction Y and a fifth direction Z′, wherein the fourth direction X′ is a thickness direction of the first pole piece 21 , and the fifth direction Z′ is a length direction of the first pole piece 21 .

[0037] Among them, the positive electrode current collector can be made of aluminum foil or nickel foil, and the negative electrode current collector can be made of copper foil, nickel foil or carbon-based current collector. The positive electrode tab can be made of aluminum sheet or aluminum alloy sheet, and the negative electrode tab can be made of copper sheet or copper alloy sheet. Among them, the alloy tab has higher welding performance and mechanical properties, such as the negative electrode tab can be made of copper-plated nickel material.

[0038] The positive electrode active material of the positive electrode active material layer includes a compound (i.e., a lithiated intercalation compound) that can reversibly embed and deintercalate metal ions (such as lithium ions, sodium ions, etc., and lithium ions are used as an example below). In some embodiments, the positive electrode active material may include a lithium transition metal composite oxide. The lithium transition metal composite oxide contains lithium and at least one element selected from cobalt, manganese and nickel. In some embodiments, the positive electrode active material is selected from lithium cobalt oxide (LiCoO 2 ), nickel cobalt manganese oxide ternary material (NCM), nickel cobalt aluminum oxide ternary material (NCA), lithium manganese oxide (LiMn 2 O 4 ), lithium nickel manganese oxide (LiNi 0.5 Mn 1.5 O 4 ) or lithium iron phosphate (LiFePO 4 ) at least one of.

[0039] The negative active material of the negative active material layer can be a negative active material capable of reversibly deintercalating active ions, and can include but is not limited to a combination of one or more of graphite, soft carbon, hard carbon, carbon fiber, mesophase carbon microspheres, silicon-based materials, tin-based materials, lithium titanate or other metals that can form alloys with lithium. Among them, graphite can be selected from a combination of one or more of artificial graphite, natural graphite and modified graphite; silicon-based materials can be selected from a combination of one or more of elemental silicon, silicon oxide compounds, silicon-carbon composites, and silicon alloys; tin-based materials can be selected from a combination of one or more of elemental tin, tin oxide compounds, and tin alloys.

[0040] The isolation film 23 includes at least one of polyethylene, polypropylene, polyvinylidene fluoride, polyethylene terephthalate, polyimide or aramid. For example, the polyethylene includes at least one selected from high-density polyethylene, low-density polyethylene or ultra-high molecular weight polyethylene.

[0041] like Figure 3 and Figure 4As shown, the first pole ear 30 includes a first connection area 31 and a second connection area 32 connected to each other. In the first direction X, the orthographic projection of the first connection area 31 is located within the range of the orthographic projection of the first current collector 210, and the orthographic projection of the second connection area 32 is located outside the range of the orthographic projection of the first current collector 210. When the shell 10 is a packaging bag obtained by packaging film packaging, the second connection area 32 can extend out of the shell 10. The first direction X is also the thickness direction of the first connection area 31. The first connection area 31 is welded to the first current collector 210. For example, the first connection area 31 can be connected to the first surface 2101 of the first current collector 210 by ultrasonic welding, so that the first weld mark 33 has a higher welding reliability, improves the connection strength between the first connection area 31 and the first current collector 210, and reduces the influence of subsequent laser irradiation treatment on the welding reliability of the first weld mark 33. Furthermore, the first connection region 31 includes a first partition 311 and a second partition 312 disposed around an edge of the first partition 311 , and the first connection region 31 may be welded to the first current collector 210 through the first partition 311 .

[0042] In some embodiments, the first active material layer 211 is provided with a first groove 2110, and the first groove 2110 exposes a portion of the first surface 2101 of the first current collector 210. The first connection region 31 is provided in the first groove 2110 and is welded and connected to the exposed first surface 2101. The first groove 2110 can be cleaned out in the first active material layer 211 by laser cleaning, so that a portion of the first surface 2101 of the first current collector 210 is exposed; foam glue can also be attached to the first surface 2101 of the first current collector 210 in advance, and after the active material is applied, the foam glue is heated to make it fall off, so that a portion of the first surface 2101 is exposed; or, a portion of the active material can be directly scraped off with a scraper, so that a portion of the first surface 2101 of the first current collector 210 is exposed.

[0043] like Figure 3 and Figure 4 As shown, along the first direction X, the surface of the first connection area 31 away from the first current collector 210 is the first surface 310. After the first connection area 31 and the first current collector 210 are welded, a first weld mark 33 protrudingly arranged on the first surface 310 is formed. The first weld mark 33 may include a plurality of welding points 330, and the plurality of welding points 330 are arranged in a single matrix or in a plurality of matrices. The first connection area 31 and the first current collector 210 are fixed to each other through the first weld mark 33. The arithmetic mean roughness of the first surface 310 is Ra μm, 0.3≤Ra≤1.5.

[0044] In some embodiments, the arithmetic average roughness of the first surface 310 after welding is relatively high (for example, 2.0-4.0), and the arithmetic average roughness of the first surface 310 can be reduced by laser irradiation. That is, the first weld mark 33 is irradiated with a high-energy laser beam without contacting the first connection area 31, so that at least part of the first weld mark 33 absorbs the energy of the laser beam and vaporizes under heat, thereby reducing the arithmetic average roughness of the first surface 310, so that the flatness of the first surface 310 including the first weld mark 33 is improved. In other embodiments, the arithmetic average roughness of the first surface 310 can also be reduced by mechanical grinding or the like.

[0045] In an embodiment of the present application, the test steps of the arithmetic mean roughness Ra may include: 1) discharging the electrochemical device 100 to 0 SOC% at a test temperature of 25°C, and disassembling to obtain the first pole piece 21; 2) selecting an area including multiple welds 330 of the first weld mark 33 on the first pole piece 21 as a test sample; 3) under a laser confocal microscope, characterizing the surface roughness of the area by the vertical deviation of the surface contour line of the test sample relative to the reference line, i.e., the first surface 310, with reference to standard ISO 25178; 4) selecting three areas in total and measuring them according to the above steps respectively, and taking the average value as the arithmetic mean roughness Ra.

[0046] In the present application, the arithmetic mean roughness of the first surface 310 is low, so the flatness of the first surface 310 including the first weld mark 33 is improved, which is conducive to reducing the risk of short circuit caused by the first weld mark 33 piercing the isolation membrane 23 and contacting the second pole piece 22, thereby improving the safety and service life of the electrochemical device 100. Among them, even if the weld mark burr formed by the first pole ear 30 made of copper alloy after welding is relatively hard, the present application can also reduce the risk of short circuit that may be caused by the first weld mark 33 piercing the isolation membrane.

[0047] In some embodiments, 0.6≤Ra≤1.2, thereby further improving the flatness of the first surface 310 and reducing the risk of short circuit caused by the first weld mark 33 piercing the isolation membrane 23 and contacting the second pole piece 22. At the same time, it can also reduce the impact on the mechanical properties (such as weld mark shear strength) and microstructure (such as grain size) of the first pole ear 30 when the arithmetic mean roughness of the first surface 310 is small (for example, when the laser power is large or the irradiation time is long when the first weld mark is treated by laser irradiation), thereby further improving the safety and service life of the electrochemical device 100. Optionally, 0.6≤Ra≤1.0 can be set to further reduce the risk of short circuit caused by the first weld mark 33 piercing the isolation membrane 23 and contacting the second pole piece 22. As an example, Ra can be 0.6, 0.7, 0.8, 0.9, 1.0 or any value within the range composed of any two of the above values.

[0048] like Figure 3 As shown, in some embodiments, along the first direction X, the maximum height H of the first weld mark 33 from the first surface 2101 is 2 Less than or equal to the thickness of the first active material layer 211. Therefore, the first weld mark 33 does not protrude from the first active material layer 211 along the first direction X, that is, the thickness difference between the first connection area 31 and the first active material layer 211 is zero, thereby further reducing the short circuit risk that may be caused by the first weld mark 33 piercing the isolation film 23, and also improving the energy density of the electrochemical device 100.

[0049] like Figure 3 and Figure 4 As shown, in some embodiments, the electrochemical device 100 further includes a first adhesive 50, which is bonded to the first surface 310 and covers the first weld mark 33. The first active material layer 211 includes a first active material area 2111 surrounding the first groove 2110, and the first adhesive 50 is also bonded to the first active material area 2111. The first adhesive 50 can isolate the first weld mark 33, further reducing the risk of short circuit caused by the first weld mark 33 piercing the isolation film 23, and the first adhesive 50 can also play a certain role in fixing the first electrode 30, reducing the risk of the first weld mark 33 breaking or the first electrode 30 separating from the first current collector 210 during mechanical abuse such as falling and collision. Since the arithmetic mean roughness of the first surface 310 in the present application is low, it is not only conducive to increasing the bonding area between the first adhesive 50 and the first electrode sheet 21, but also reducing the risk of the first adhesive 50 falling off from the first surface 310. Moreover, the thickness of the first adhesive 50 along the first direction X is T, 5 μm≤T≤12 μm. The thickness of the first adhesive 50 along the first direction X can be appropriately reduced, and can also play a role in inhibiting the piercing of the first weld mark 33, thereby reducing the influence of the first adhesive 50 on the energy density of the electrochemical device 100, and improving the contact interface between the first pole piece 21 and the second pole piece 22. In some embodiments, the first adhesive 50 can be a single-sided adhesive or a double-sided adhesive, and the specific material can be selected from at least one of polypropylene, polyethylene, polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polymethyl methacrylate or polyethylene glycol.

[0050] Optionally, 5 μm≤T≤10 μm can be set, so as to further reduce the influence of the first adhesive 50 on the energy density of the electrochemical device 100 and improve the contact interface between the first pole piece 21 and the second pole piece 22. As an example, T can be 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, or any value within the range formed by any two of the above values.

[0051] like Figure 3As shown, the electrochemical device 100 may further include a second adhesive 60. Along the first direction X, the first adhesive 50 is disposed between the second adhesive 60 and the first connection area 31. Along the first direction X, the orthographic projection of the first groove 2110 is located within the range of the orthographic projection of the second adhesive 60. When the first electrode 21 is a negative electrode and the second electrode 22 is a positive electrode, the second adhesive 60 may be used to prevent the active ions (such as lithium ions) released from the part of the second active material layer 221 corresponding to the second adhesive 60 in the first direction X from moving toward the first groove 2110, thereby reducing the risk of lithium plating caused by the lack of the first groove 2110 capable of embedding these lithium ions, thereby further improving the safety and service life of the electrochemical device 100.

[0052] It can be understood that since the arithmetic mean roughness of the first surface 310 in the present application is relatively low, the risk of the first weld mark 33 successively piercing the first adhesive 50 and the second adhesive 60 is also reduced, which is conducive to reducing the risk of failing to prevent the corresponding lithium ions from escaping after the second adhesive 60 is pierced and causing lithium deposition.

[0053] In some embodiments, in addition to laser irradiation treatment of the first weld mark 33, laser irradiation treatment may also be performed on the first surface 310 of the first pole tab 30. For example, when the first weld mark 33 is heated and vaporized under the action of the laser beam until the first weld mark 33 is flush with the first surface 310, if the laser beam irradiation is continued, the area of ​​the first pole tab 30 adjacent to the first surface 310 may be heated and vaporized, so that the thickness of the first pole tab 30 itself is reduced. Therefore, in the case where the first pole tab 30 itself is relatively thick or even protrudes from the first active material layer 211, this can further reduce the thickness difference between the first connection area 31 and the first active material layer 211, and reduce the total thickness of the electrode assembly 20 at the first pole tab 30, thereby further reducing the risk of short circuit that may be caused by the first weld mark 33 piercing the isolation membrane 23, and can also improve the energy density of the electrochemical device 100.

[0054] Further, after the first surface 310 is treated by laser irradiation, the thickness of the first connection area 31 along the first direction X may be less than or equal to the thickness of the first active material layer 211, thereby further reducing the thickness difference between the first connection area 31 and the first active material layer 211. For example, the thickness of the first connection area 31 may be set to be less than the thickness of the first active material layer 211, so that the space formed by the thickness difference between the first connection area 31 and the first active material layer 211 can also accommodate at least part of the first adhesive 50, thereby further reducing the total thickness of the electrode assembly 20 at the first electrode tab 30, thereby improving the energy density of the electrochemical device 100.

[0055] The electrochemical device 100 of the present application may be a lithium secondary battery, including a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery or a lithium ion polymer secondary battery.

[0056] See also Figure 5 In one embodiment of the present application, a method for preparing the electrochemical device 100 is also provided. According to different requirements, the order of the steps of the preparation method can be changed, and some steps can be omitted or combined. The preparation method comprises the following steps: Step S1 : providing a first electrode sheet 21 , wherein the first electrode sheet 21 comprises a first current collector 210 and a first active material layer 211 disposed on the first current collector 210 .

[0057] Step S2 , welding the first connection region 31 of the first electrode tab 30 to the first current collector 210 .

[0058] In some embodiments, a first groove 2110 may be provided in the first active material layer 211 to expose a portion of the first surface 2101 of the first current collector 210, and then the first connection region 31 may be provided in the first groove 2110 and welded to the exposed first surface 2101. The first groove 2110 may be cleaned in the first active material layer 211 by laser cleaning to expose a portion of the first surface 2101 of the first current collector 210; foam glue may be applied to the first surface 2101 of the first current collector 210 in advance, and the foam glue may be heated after the active material is applied to fall off, thereby exposing a portion of the first surface 2101; or a portion of the active material may be directly scraped off with a scraper, thereby exposing a portion of the first surface 2101 of the first current collector 210.

[0059] In some embodiments, the first connection region 31 may be welded to the first surface 2101 of the first current collector 210 by an ultrasonic welding process.

[0060] Step S3 , performing laser irradiation treatment on the first weld mark 33 on the surface of the first connection region 31 facing away from the first current collector 210 (ie, the first surface 310 ).

[0061] Specifically, the first weld mark 33 is irradiated with a high-energy laser beam without contacting the first connection area 31, so that at least part of the first weld mark 33 absorbs the energy of the laser beam and then vaporizes due to heat, thereby reducing the arithmetic mean roughness of the first surface 310 and improving the surface flatness of the first weld mark 33. Among them, the laser beam energy used during laser irradiation is concentrated, and the heat-affected zone is small, which can reduce the impact of the laser beam on surrounding materials such as active materials, and the non-contact welding method is also conducive to reducing damage to the first pole ear 30 or other areas. In addition, the laser beam can be irradiated from the side of the first pole ear 30 away from the first current collector 210, and the power or pulse frequency of the laser beam can be adjusted more conveniently to process the first weld mark 33, which is conducive to achieving precise control.

[0062] In this embodiment, the laser irradiation treatment uses a pulsed laser, the laser power is less than or equal to 150W, and the pulse frequency is less than or equal to 50Hz. The arithmetic mean roughness of the first surface 310 after laser irradiation can be adjusted by adjusting the laser power and the pulse frequency. By controlling the range of the laser power and the pulse frequency, the influence of the laser beam on the mechanical properties (such as weld shear strength) and microstructure (such as grain size) of the first pole tab 30 can be further reduced.

[0063] In some embodiments, the first surface 310 may be further subjected to laser irradiation treatment. Therefore, in the case where the first electrode tab 30 itself is relatively thick or even protrudes from the first active material layer 211, this can reduce the thickness difference between the first connection area 31 and the first active material layer 211, and reduce the total thickness of the electrode assembly 20 at the first electrode tab 30, thereby reducing the short circuit risk that may be caused by the first weld mark 33 piercing the separator 23, and can also improve the energy density of the electrochemical device 100.

[0064] In step S4 , the first electrode sheet 21 is manufactured into an electrode assembly 20 , and the electrode assembly 20 is placed in the housing 10 to obtain the electrochemical device 100 .

[0065] In some embodiments, the first electrode sheet 21 , the isolation film 23 , and the second electrode sheet 22 may be stacked and wound to obtain the electrode assembly 20 .

[0066] See also Figure 6In one embodiment of the present application, an electronic device 1 is provided, which includes a storage chamber 101 and the electrochemical device 100 provided in the storage chamber 101. The electrochemical device 100 of the present application is applicable to electronic devices 1 in various fields. The electronic device 1 supplies power to a load (not shown) through the electrochemical device 100, and the first weld mark 33 can not only improve the energy density of the electrochemical device 100 after laser irradiation treatment, but also reduce the risk of short circuit caused by the weld mark burr piercing the isolation membrane 23, thereby improving the safety and service life of the electrochemical device 100. In one embodiment, the electronic device 1 of the present application can be, but is not limited to, a laptop computer, a pen-input computer, a mobile computer, an e-book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a head-mounted stereo headset, a video recorder, an LCD TV, a portable cleaner, a portable C machine, a mini CD, a transceiver, an electronic notepad, a calculator, a memory card, a portable recorder, a radio, a backup power supply, a motor, a car, a motorcycle, a power-assisted bicycle, a bicycle, a lighting fixture, a toy, a game console, a clock, an electric tool, a flashlight, a camera, a large household battery and a lithium-ion capacitor, etc.

[0067] The present application is described in detail below through specific embodiments and comparative examples. Among them, the present application is described by taking the electrochemical device 100 as a wound lithium-ion secondary battery, the first pole piece 21 as a negative pole piece, and the second pole piece 22 as a positive pole piece as an example and combining the specific preparation process and test method. Those skilled in the art should understand that the preparation method described in the present application is only an example, and any other suitable preparation method is within the scope of the present application.

[0068] Examples 1-9 (1) Preparation of the first electrode sheet, i.e., the negative electrode sheet: the negative electrode active material artificial graphite, silicon carbon material, conductive carbon black (Super P), polyacrylic acid binder (PAA), and lithium difluorophosphate (LDPF) are mixed in a weight ratio of 69:5:6:19:1, deionized water is added as a solvent, and a slurry with a weight percentage of 55wt% is prepared and stirred evenly. Pre-apply foam glue to the surface of the negative electrode current collector, i.e., copper foil, with a thickness of 6μm, and evenly coat the slurry on the first side of the copper foil. Heat the foam glue to make it fall off so that the first side of the copper foil is exposed, and then dry it at 90°C. Repeat the above coating steps on the second side of the copper foil to obtain a double-sided coated negative electrode sheet. The initial negative electrode sheet is rolled to obtain a negative electrode active material layer with a single-sided coating thickness of 64.5 μm. Then, a first pole ear with a thickness of 100 μm is welded to the exposed copper foil by ultrasonic welding. The first pole ear is made of copper-plated nickel, and then the first weld mark is laser irradiated. Then, a first bonding member is bonded onto the first electrode tab.

[0069] (2) Preparation of the second electrode, namely the positive electrode: the positive electrode active material lithium cobalt oxide (LiCoO 2 ), conductive carbon black (Super P), and polyvinylidene fluoride (PVDF) are mixed in a weight ratio of 96.5:1.5:2, and N-methylpyrrolidone (NMP) is added as a solvent to prepare a slurry with a solid content of 75wt%, and stirred evenly. Pre-apply foam glue to the surface of the positive electrode current collector, that is, the aluminum foil with a thickness of 9.5 μm, and evenly coat the slurry on the third side of the aluminum foil, heat it to make the foam glue fall off so that part of the third side of the aluminum foil is exposed, and then dry it at 90°C, repeat the above coating steps on the fourth surface of the aluminum foil to obtain a double-sided coated positive electrode sheet, and cold press the initial positive electrode sheet to obtain a single coating thickness of 52.7 μm positive electrode active material layer, and then cut and other processes to obtain a positive electrode sheet. A second pole ear with a thickness of 100 μm is welded to the exposed aluminum foil by ultrasonic welding, and the second pole ear is made of aluminum alloy.

[0070] (3) Preparation of electrolyte: In a dry argon atmosphere, organic solvents ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) were first mixed at a mass ratio of EC:EMC:DEC = 30:50:20, and then lithium salt lithium hexafluorophosphate (LiPF 6 ) are dissolved and mixed evenly to obtain an electrolyte with a lithium salt concentration of 1.15 mol / L.

[0071] (4) Preparation of isolation film: A polyethylene (PE) film with a thickness of 9 μm was selected.

[0072] (5) Preparation of electrochemical device: The first electrode sheet, the separator and the second electrode sheet are stacked and wound in sequence to obtain Figure 2 The electrode assembly shown in the figure is to place the aluminum-plastic film (thickness of 150 μm) with a pit formed in an assembly fixture, with the pit facing upward, and place the electrode assembly in the pit. Then, an electrolyte is injected into the pit of the aluminum-plastic film, and the first and second pole ears are led out of the aluminum-plastic film and then packaged and formed to obtain a secondary battery. The difference between Examples 1-9 is that the power or pulse frequency of the laser beam is adjusted to adjust the arithmetic mean roughness of the first surface after laser irradiation.

[0073] Examples 10-14 The difference from the fourth embodiment is that the thickness T of the first adhesive member.

[0074] Examples 15-18 The difference from Example 1 is that the weld mark on the second electrode tab is irradiated with laser. The difference from Examples 15 to 18 is that the power or pulse frequency of the laser beam is adjusted to adjust the arithmetic mean roughness of the surface of the second electrode tab away from the second current collector after laser irradiation.

[0075] Comparative Example 1 The difference from the first embodiment is that the step of laser irradiating the first weld mark on the first electrode tab is omitted.

[0076] Comparative Example 2 The difference from Example 15 is that the step of laser irradiating the weld mark on the second electrode tab is omitted.

[0077] Then, 20 secondary batteries of each embodiment and comparative example were taken for needle penetration rate and drop pass rate tests, and the test results are recorded in Table 1.

[0078] The test steps of the needle penetration pass rate include: 1) fully charging the state of charge (SOC) of the secondary battery to 100% at a test temperature of 25°C; 2) using a blunt needle with a semi-circular head and pressing the center position of the pole ear in the second direction at a lift speed of 300N / min±10N / min (wherein, in Examples 1-14 and Comparative Example 1, the blunt needle presses the center position of the first pole ear in the second direction, and in Examples 15-18 and Comparative Example 2, the blunt needle presses the center position of the second pole ear in the second direction), wherein the pressure applied to the secondary battery is gradually increased from 0N to 1300N and then the test is stopped. If the surface temperature of the secondary battery after the needle penetration test is less than 200°C, and there is no smoke, fire, or explosion, the secondary battery is determined to have passed the needle penetration test.

[0079] The test steps of the drop pass rate include: 1) At a test temperature of 25°C, fully charge the secondary battery to 100% SOC, and test the voltage of the secondary battery before the drop test; 2) Place the secondary battery in the fixture compartment, and use an automatic drop device to drop the bottom, side, and top of the secondary battery from a position of 1.8m to a steel plate in a round, for a total of 6 rounds, or 18 times; 3) After the drop, let it stand at room temperature for 24 hours, measure and record the voltage of the secondary battery, and then disassemble the secondary battery to observe whether the welding mark of the pole ear is broken and whether the pole ear is separated from the current collector. If the voltage drop of the secondary battery is greater than 30mV, the welding mark of the pole ear is broken or the pole ear is separated, it is judged that the secondary battery has not passed the drop test. The results are recorded in Table 1.

[0080] Table 1 From the data in Table 1, it can be seen that compared with Comparative Example 1, Example 1-9 can reduce the arithmetic mean roughness of the first surface by laser irradiating the first weld print, so the short circuit risk that may be caused by the first weld print piercing the isolation membrane can be reduced in the needle puncture test, so the needle puncture test pass rate of the secondary battery is relatively high. Among them, Example 4-7 satisfies: 0.6≤Ra≤1.2. Compared with Examples 8-9, the arithmetic mean roughness in Example 4-7 is smaller, so the short circuit risk that may be caused by the first weld print piercing the isolation membrane can be further reduced, so the needle puncture pass rate of the secondary battery is relatively high; and compared with Examples 1-3, the arithmetic mean roughness in Example 4-7 is higher, so the effect of the mechanical strength of the first weld print during laser irradiation can be reduced, so the risk of the first weld print breaking after the secondary battery falls and the first pole ear separating from the first current collector is reduced, and the drop test pass rate is relatively high. Among them, Example 4-6 satisfies 0.6≤Ra≤1.0, so the needle puncture pass rate of the secondary battery is further improved.

[0081] Compared with Example 14, the thickness T of the first adhesive in Examples 4, 10-13 is larger, satisfying 5 μm≤T≤12 μm, and the first adhesive can better isolate the first weld print to further reduce the risk of short circuit caused by the first weld print piercing the isolation film, so the secondary battery has a higher needle puncture pass rate, and the first adhesive can also better fix the first pole ear, reducing the risk of the first weld print breaking or the first pole ear separating from the first current collector after falling, so the secondary battery has a higher drop test pass rate. Compared with Examples 4 and 10, the thickness T of the first adhesive in Examples 11-13 satisfies 5 μm≤T≤10 μm, so while maintaining a high needle puncture pass rate and drop pass rate, the secondary battery can also take into account a higher energy density.

[0082] Compared with Comparative Example 2, Examples 15-18 can also reduce the arithmetic mean roughness of the surface of the second pole ear away from the second current collector by laser irradiation of the weld mark on the second pole ear. Therefore, the risk of short circuit that may be caused by the weld mark of the second pole ear piercing the isolation membrane can be reduced in the needle penetration test. Therefore, the pass rate of the needle penetration test of the secondary battery is relatively high.

[0083] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present application and are not intended to limit it. Although the present application has been described in detail with reference to the preferred embodiments, a person of ordinary skill in the art should understand that the technical solution of the present application may be modified or replaced by equivalents without departing from the spirit and scope of the technical solution of the present application.

Claims

1. An electrochemical device, comprising an electrode assembly and a first electrode tab, wherein: The electrode assembly includes a first pole piece, the first pole piece includes a first current collector and a first active material layer disposed on the first current collector, the first pole tab includes a first connection area, and the first connection area is welded to the first current collector; Along the thickness direction of the first connecting region, the surface of the first connecting region away from the first current collector is a first surface, a first weld mark is provided on the first surface, and an arithmetic mean roughness of the first surface is Ra μm, 0.3≤Ra≤1.

5.

2. The electrochemical device according to claim 1, wherein 0.6≤Ra≤1.

2.

3. The electrochemical device according to claim 2, wherein: 0.6≤Ra≤1.

0.

4. The electrochemical device according to claim 1, wherein The first active material layer is provided with a first groove, and the first connection area is provided in the first groove; The electrochemical device further comprises: A first adhesive member, the first adhesive member is bonded to the first surface and covers the first weld mark, the first active material layer includes a first active material area surrounding the first groove, the first adhesive member is also bonded to the first active material area, and the thickness of the first adhesive member along the thickness direction is T, 5 μm≤T≤12 μm.

5. The electrochemical device according to claim 4, wherein 5 μm≤T≤10 μm.

6. The electrochemical device according to claim 1, wherein The surface of the first current collector connected to the first connection area is a first surface, and along the thickness direction, the maximum height of the first weld mark from the first surface is less than or equal to the thickness of the first active material layer.

7. The electrochemical device according to claim 1, wherein: The first weld mark is processed by laser irradiation.

8. The electrochemical device according to claim 1, wherein The first surface is treated by laser irradiation.

9. The electrochemical device according to claim 8, wherein: Along the thickness direction, the thickness of the first connection region is less than or equal to the thickness of the first active material layer.

10. The electrochemical device according to claim 1, wherein The first pole piece is a negative pole piece, the first current collector is a copper foil, and the first pole tab is a copper alloy sheet.

11. A method for preparing an electrochemical device according to any one of claims 1 to 10, wherein: The steps include: Providing a first pole piece, the first pole piece comprising a first current collector and a first active material layer disposed on the first current collector; Welding the first connection area of ​​the first electrode tab to the first current collector; performing laser irradiation treatment on a first weld mark on a surface of the first connection region facing away from the first current collector; as well as The first pole piece is made into an electrode assembly, and the electrode assembly is placed in a shell to obtain the electrochemical device.

12. The method for preparing an electrochemical device according to claim 11, wherein: The first connection area of ​​the first pole piece is connected to the first current collector by ultrasonic welding.

13. The method for preparing an electrochemical device according to claim 11, wherein: The laser irradiation treatment uses a pulsed laser, the laser power is less than or equal to 150W, and the pulse frequency is less than or equal to 50Hz.

14. The method for preparing an electrochemical device according to claim 11, wherein: Also includes: A surface of the first connection region facing away from the first current collector is subjected to laser irradiation treatment.

15. An electronic device, comprising a storage compartment, wherein: The electronic device further comprises an electrochemical device as claimed in any one of claims 1 to 10, wherein the electrochemical device is disposed in the containing chamber.

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