Secondary batteries, battery packs, and electronic devices

Abstract

The present invention provides a secondary battery, battery pack, and electronic device that avoids internal short circuits caused by damage to the separator due to high welding temperatures between the cover plate and the current collector panel. [Solution] The secondary battery comprises a housing including a casing and a cover plate, with an opening formed at one end of the casing and the cover plate covering the opening; an electrode assembly housed within the housing and sequentially stacked and wound, the first electrode piece having a first tab facing the cover plate, a portion of which extends beyond the end of the separator facing the cover plate along the height direction of the secondary battery; a main body installed between the cover plate and the electrode assembly and welded to the first tab, and a welding block welded to the cover plate, the welding direction between the welding block and the cover plate toward the electrode assembly from the outer surface of the cover plate, the thermal conductivity coefficient of the welding block being W1, and the thermal conductivity coefficient of the main body being W2, of which W2 is greater than W1; and a current collector panel.

Description

Technical Field

[0001] The present invention relates to a secondary battery, a battery pack, and an electronic device.

Background Art

[0002] In the field of new energy power batteries, a secondary battery generally includes an electrode assembly, a casing, a current collector plate, etc. The electrode assembly includes a positive electrode plate, a negative electrode plate, and a separator located between the positive electrode plate and the negative electrode plate. After these positive electrode plates, negative electrode plates, and separators are stacked on each other, they are wound to form an electrode assembly, and then packaged in a casing. The secondary battery usually installs a current collector plate at a position close to the opening of the casing, welds one end of the current collector plate to the casing or the end cover, and electrically connects the other end to the tab of the electrode assembly to realize the electrical connection between the casing and the electrode assembly.

Summary of the Invention

Problems to be Solved by the Invention

[0003] In view of the problems existing in the related art, an object of the present invention is to provide a secondary battery, a battery pack, and an electronic device that avoid the problem that the high welding temperature of the cover plate and the current collector plate damages the separator and causes an internal short circuit.

Means for Solving the Problems

[0004] To achieve the aforementioned objectives, the present invention provides a secondary battery comprising: a housing including a casing and a cover plate, wherein an opening is formed at one end of the casing and the cover plate is placed over the opening; an electrode assembly housed within the housing and comprising a first electrode piece, a separator and a second electrode piece sequentially stacked and wound, wherein the first electrode piece has a first tab facing the cover plate, and a portion of the first tab extends along the height direction of the secondary battery beyond the end of the separator facing the cover plate; and a current collector panel installed between the cover plate and the electrode assembly and welded to the first tab, and a welding block welded to the cover plate, wherein the welding direction between the welding block and the cover plate is from the outer surface of the cover plate toward the electrode assembly, the thermal conductivity coefficient of the welding block is W1, and the thermal conductivity coefficient of the body is W2, of which W2 is greater than W1.

[0005] In some embodiments, W2-W1 ≥ 300W / (m·K).

[0006] In some embodiments, the welding block is stacked on the side of the main body away from the electrode assembly, and the weld marks formed by welding the cover plate and the welding block do not extend beyond the bottom surface of the welding block facing the main body.

[0007] In some embodiments, the weld marks extend along the circumferential direction of the cover plate, and the minimum width in the radial direction of the secondary battery is 0.5 mm or more, while the maximum width is less than 1 mm.

[0008] In some embodiments, the thickness of the cover plate is less than or equal to the thickness of the welding block along its height plus the thickness of the main body.

[0009] In some embodiments, the material of the weld block is steel, and the material of the main body is copper.

[0010] In some embodiments, within the region where the first tab and the current collector are welded, the number of laminated layers in the height direction of the first tab of each coil is at least three.

[0011] In some embodiments, in the height direction, the first tab sequentially includes a dense region welded to the main body, a dispersed region connected to the dense region, and a linear region connected to the dispersed region, the first tab in the linear region extending along the height direction, and the tab stacking density in the dispersed region is smaller than the tab stacking density in the dense region.

[0012] In some embodiments, in the height direction, the end of the straight region facing the main body extends beyond the end of the separator, and the distance by which the end of the straight region extends beyond the end of the separator is greater than 0.1 mm.

[0013] In some embodiments, the height along the height direction of the first tab is 2 mm or more, the ratio of the height of the dispersed area to the height of the first tab is 45% to 55%, and the ratio of the height of the densely packed area to the height of the first tab is 10% to 15%.

[0014] In some embodiments, the number of stacked layers of the first tab in the dense region ranges from 15 to 45 layers.

[0015] In some embodiments, the secondary battery further includes an insulating adhesive layer, which is installed between the main body of the current collector and the first tab, and the projection along the height direction of the weld block is located on the insulating adhesive layer, and the thermal conductivity of the insulating adhesive layer is less than 0.05 W / (m·K).

[0016] In some embodiments, the radial width of the thermal insulation adhesive layer of the secondary cell is from Da-1 mm to Da+1 mm, where Da represents the radial width of the weld block.

[0017] In some embodiments, the casing includes a side wall surrounding the electrode assembly, one end of which is an opening, and the cover plate includes a recessed groove toward the current collector, the groove is located within the opening, and the outer wall of the groove faces and is in close contact with the side wall of the casing, where a welding block is welded between the groove and the body.

[0018] In some embodiments, the weld block is ring-shaped and extends along the edge of the current collector panel, the minimum outer diameter of the weld block is the inner diameter of the casing side wall - 2 × the thickness of the cover plate, and the inner diameter of the weld block / outer diameter of the electrode assembly > 0.75.

[0019] An embodiment of the present invention further provides a battery pack including a secondary battery as described in any one of the above-described embodiments.

[0020] Embodiments of the present invention further provide an electronic device including the aforementioned battery pack. [Effects of the Invention]

[0021] The beneficial technical effects of the present invention are as follows: The technical solution of the present invention sets the thermal conductivity coefficient of the welding block lower than that of the main body. Therefore, the welding block with a low thermal conductivity coefficient can be used to block heat conduction, reducing the amount of heat conducted to the separator during the welding process, lowering the amount of heat reaching the separator, and lowering the temperature of the separator area during the welding process. This avoids the risk of separator burnout during the welding process and also prevents battery short circuits.

[0022] To more clearly illustrate the embodiments of the present invention or the prior art, the accompanying drawings that may be used in the description of the embodiments or prior art are briefly introduced below. It is clear that the accompanying drawings in the following description represent only a few embodiments of the present invention, and those skilled in the art can obtain other embodiments based on these accompanying drawings without any creative effort. [Brief explanation of the drawing]

[0023] [Figure 1] A three-dimensional diagram of a secondary battery according to an embodiment of the present invention is shown. [Figure 2] This shows a front view of a secondary battery according to an embodiment of the present invention. [Figure 3A] Figure 2 shows a partial cross-sectional view of a secondary battery according to an embodiment of the present invention, corresponding to the line X1-X1. [Figure 3B]A partial cross-sectional view corresponding to line X1-X1 in FIG. 2 of the secondary battery according to an embodiment of the present invention is shown. [Figure 4A] A schematic top view of a current collector according to an embodiment of the present invention is shown. [Figure 4B] A schematic cross-sectional view of a current collector according to an embodiment of the present invention. [Figure 4C] A schematic cross-sectional view of a cover plate according to an embodiment of the present invention is shown. [Figure 5] A partially enlarged schematic view of a connection structure of a current collector, a cover plate, and a side wall of a casing according to an embodiment of the present invention is shown. [Figure 6] A partially enlarged schematic view of a welded portion of a first tab, a current collector, and a cover plate of a secondary battery according to some embodiments of the present invention is shown. [Figure 7A] A schematic view of an electrode assembly having a planarized tab structure is shown. [Figure 7B] A schematic cross-sectional view of a single one-turn first tab is shown. [Figure 8] A partially enlarged schematic view of a welded portion of a first tab, a current collector, and a cover plate of a secondary battery according to another embodiment of the present invention is shown. [Figure 9] A connection structure between an electrode assembly and a cover plate according to another embodiment of the present invention is shown. [Figure 10A] A schematic top view of a current collector according to another embodiment of the present invention is shown. [Figure 10B] A schematic cross-sectional view of a current collector according to another embodiment of the present invention. [Figure 10C] A schematic cross-sectional view of a cover plate according to another embodiment of the present invention is shown. [Figure 11] A schematic view when the electronic device of an embodiment of the present invention is a vehicle is shown.

Embodiments for Carrying Out the Invention

[0024] In order to better understand the spirit of the embodiments of the present invention, it will be further described below in combination with some preferred embodiments of the present invention.

[0025] Embodiments of the present invention are described in detail below. Throughout the entirety of this specification, identical or similar components and components having identical or similar functions are represented by similar reference numerals. The embodiments relating to the drawings described herein are explanatory and illustrative in nature and are used to provide a basic understanding of the present invention. Embodiments of the present invention should not be construed as limitations of the present invention.

[0026] As used in this text, the terms “approximately,” “generally,” “substantially,” and “about” are used to describe and explain small changes. When used in conjunction with events or situations, these terms may refer to examples in which the event or situation occurs exactly, as well as examples in which the event or situation occurs very approximately.

[0027] In this specification, unless otherwise specified or limited, relative terms such as “center,” “longitudinal,” “lateral,” “front,” “rear,” “right,” “left,” “internal,” “external,” “lower,” “higher,” “horizontal,” “vertical,” “higher,” “lower,” “upward,” “downward,” “top,” “bottom,” and their derived terms (e.g., “horizontally,” “downward,” “upward,” etc.) should be interpreted as referring to the direction described in the discussion or depicted in the drawings. These relative terms are used solely for descriptive convenience and do not require the invention to be constructed or operated in any particular direction.

[0028] For convenience of description, terms such as "First," "Second," "Third," etc., may be used in the text to distinguish different components of a single figure or a series of figures. These terms are not intended to describe corresponding components.

[0029] Cylindrical batteries are a type of rechargeable battery with a relatively high energy density, and therefore have a wide range of applications in the lithium battery industry. The cylindrical battery structure includes electrode columns, casing, current collectors (including positive and negative electrode current collectors), and electrode assemblies. Typically, the current collectors are first welded to the electrode assemblies, and then the current collectors are welded to the electrode columns and casings, respectively, to form the final electrical conductivity.

[0030] After welding the current collector panel (e.g., the negative electrode current collector panel) to the electrode assembly, connection to the casing is required, and currently there are two connection methods. One is a method in which the current collector panel is directly connected to the casing for conductivity, and the other is a method in which the current collector panel and cover plate are welded together, and then the cover plate and casing are electrically connected. In the current latter method, the welding of the current collector panel and cover plate usually employs laser penetration welding, that is, a laser penetrates the cover plate and welds onto the current collector panel below. This type of welding has a high heat input and often easily causes damage due to burning of the separator below the weld, and damage to the separator can further cause contact between the positive and negative electrode pieces, resulting in a battery short circuit.

[0031] Figure 1 shows a three-dimensional view of a secondary battery 100 according to an embodiment of the present invention. Figure 2 shows a front view of the secondary battery 100 according to an embodiment of the present invention. Figures 3A and 3B show partial cross-sectional views of the secondary battery 100 according to an embodiment of the present invention corresponding to the line X1-X1 in Figure 2. Figure 3A shows the connection structure between the electrode assembly 130 and the cover plate 140, and Figure 3B shows the connection structure between the current collector panel 150, the cover plate 140 and the side wall 112 of the casing.

[0032] In this embodiment, an example is shown where the secondary battery 100 is a cylindrical battery. In some embodiments, the secondary battery 100 can be a 4680 cylindrical battery (diameter 46 mm, height 80 mm), a 4695 cylindrical battery (diameter 46 mm, height 95 mm), or a 46120 cylindrical battery (diameter 46 mm, height 120 mm). Here, diameter refers to the outer diameter dimension of the casing.

[0033] Referring to Figures 1 to 3B, the secondary battery 100 includes a housing, which includes a casing 110 and a cover plate 140. The casing 110 may specifically include an end wall 111 and a side wall 112 surrounding the end wall 111. The connection between the end wall 111 and the side wall 112 can be achieved through various methods, such as integral press molding, integral casting, or split welding, as long as a stable sealing and electrical connection relationship can be formed. The side wall 112 may surround in a cylindrical shape or along any other arbitrary closed ring contour that can match the end wall 111. In this embodiment, the outer edge of the end wall 111 is circular, and the side wall 112 surrounds the outer edge of the end wall 111 in a cylindrical shape. An opening 113 is formed at one end of the side wall 112 opposite the end wall 111, and the cover plate 140 covers the opening 113. The electrode assembly 130 is housed within a containment space defined by the casing 110 and the cover plate 140, and this containment space is used to house the electrode assembly 130, the electrolyte, and other components necessary for the battery.

[0034] The electrode column 120 can penetrate the end wall 111 and is insulated from the end wall 111. In some embodiments, the electrode column 120 can be made of a conductive metallic material. For example, the material of the electrode column 120 can be aluminum (Al). In some embodiments, the electrode column 120 is the positive electrode terminal of the secondary battery 100. Electrical insulation between the electrode column 120 and the end wall 111 of the casing 110 can be achieved in various ways. For example, insulation can be achieved by placing an insulating washer assembly between the electrode column 120 and the end wall 111.

[0035] Specifically, the outer diameter size of the casing 110 can be determined according to the specific dimensions of the electrode assembly 130, for example, 18 mm, 21 mm, 46 mm, etc. The material of the casing 110 can be various, for example, copper, iron, aluminum, steel, aluminum alloy, etc. In order to prevent rusting of the casing 110 during long-term use, a layer of rust-preventive material such as metallic nickel can be plated onto the surfaces of the casing 110 and the cover plate 140.

[0036] The electrode assembly 130 can be formed mainly by winding a first electrode piece and a second electrode piece, with a separator placed between the first and second electrode pieces. The wound electrode assembly 130 may have a center through hole 133. The first electrode piece may be one of a positive electrode piece and a negative electrode piece, and the second electrode piece may be the other of a positive electrode piece and a negative electrode piece. The positive electrode piece may include a positive electrode current collector and a positive electrode active material, the positive electrode active material being coated on the surface of the positive electrode current collector. The positive electrode current collector may include a coated area with the active material and an uncoated area without the active material, the uncoated area forming the positive electrode tab of the electrode assembly 130 after winding. The negative electrode piece may include a negative electrode current collector and a negative electrode active material, the negative electrode active material being coated on the surface of the negative electrode current collector. The negative electrode current collector may include a coated area with the active material and an uncoated area without the active material, the uncoated area forming the negative electrode tab of the electrode assembly 130 after winding. Taking a lithium-ion secondary battery as an example, the material of the positive electrode current collector can be aluminum, and the positive electrode active material layer contains a positive electrode active material, which can be lithium cobalt oxide, lithium iron phosphate, ternary lithium, or lithium manganese oxide, etc. The material of the negative electrode current collector can be copper, and the negative electrode active material layer contains a negative electrode active material, which can be carbon or silicon, etc. The material of the separator can be PP (polypropylene) or PE (polyethylene), etc. To provide protection and insulation to the electrode assembly 130, an insulating film can be coated on the outside of the electrode assembly 130, and the insulating film can be synthesized from PP, PE, PET (polyethylene terephthalate), PVC (polyvinyl chloride), or other polymer materials.

[0037] The electrode assembly 130 may include a first tab 300 facing the opening 113. In some embodiments, the first tab 300 is the negative electrode tab of the electrode assembly 130. A current collector 150 is installed between the cover plate 140 and the electrode assembly 130, and the first tab 300 is connected to the side wall 112 of the casing 110 through the current collector 150. In some embodiments, the current collector 150 is the negative electrode current collector. The electrode assembly 130 may further include a second tab (e.g., a positive electrode tab, not shown) facing the end wall 111, and the second tab may be connected to the electrode column 120 through another current collector (e.g., a positive electrode current collector, not shown). The material of the current collector 150 may be, for example, copper, or the surface of the copper may be nickel-plated. The material of the cover plate 140 may be steel, for example, stainless steel or nickel-plated steel.

[0038] In this embodiment, the first tab 300 is welded to the current collector panel 150, the current collector panel 150 is welded to the cover plate 140, and the cover plate 140 can be welded to the side wall 112 of the casing 110 at its end portion. Specifically, the current collector panel 150 includes a body 152 that is welded to the first tab 300, and a welding block 154 located on the side of the body 152 facing the cover plate 140.

[0039] Figure 4A shows a schematic top view of the current collector panel 150 according to an embodiment of the present invention. Figure 4B shows a schematic cross-sectional view of the current collector panel 150 according to an embodiment of the present invention. Referring to Figures 3A to 4B, in this embodiment, the current collector panel 150 is circular. The welding block 154 can be annular, extending along the edge of the current collector panel 150.

[0040] The current collector panel 150 may have a center hole 156, which may be coaxially positioned with the center through hole 133 of the electrode assembly 130. Multiple through grooves 158 may be arranged around the center hole 156. The through grooves 158 penetrate the current collector panel 150 in the thickness direction. Each through groove 158 may extend longitudinally in the radial direction of the current collector panel 150. The shape of the through groove 158 shown in Figure 4A is merely an example, and the through groove 158 may have any applicable shape, and the present invention is not limited thereto. The center hole 156 and the through grooves 158 can be used as exhaust paths inside the secondary battery, which is advantageous as it allows the current collector panel 150 to open when the battery pressure is released.

[0041] Figure 4C shows a schematic cross-sectional view of a cover plate 140 according to an embodiment of the present invention. Combining the components shown in Figures 3A to 4C, the cover plate 140 includes a recessed groove 145 that faces the current collector panel 150. The welding block 154 is welded between the bottom surface of the groove 145 and the body 152 of the current collector panel 150. The groove 145 can be a press-formed hollow structure.

[0042] Figure 5 shows a partially enlarged schematic diagram of the connection structure between the current collector panel 150, the cover plate 140, and the side wall 112 of the casing according to one embodiment of the present invention. Figure 6 shows a partially enlarged schematic diagram of the first tab, current collector panel, and cover plate welding portion of a secondary battery according to several embodiments of the present invention. Combining what is shown in Figures 5 and 6, the current collector panel 150 includes a body 152 welded to the first tab 300, and a welding block 154 welded to the cover plate 140. In some embodiments, the cover plate 140 and the welding block 154 are welded, for example, by laser through welding. The welding direction between the welding block 154 and the cover plate 140 is from the outer surface 140a of the cover plate 140, which is backward from the electrode assembly 130, toward the electrode assembly 130. The weld between the cover plate 140 and the welding block 154 forms a weld mark 220. The trajectory of the weld mark 220 can extend along the circumferential direction of the cover plate 140. Specifically, it can be extended along the circumferential direction of the cover plate 140 within the groove 145. Since the welding direction of the welding block 154 and the cover plate 140 is from the outer surface 140a toward the electrode assembly 130, the width of the weld mark 220 gradually decreases in the direction from the outer surface 140a toward the electrode assembly 130. Furthermore, as shown in Figure 6, the separator 132 of the electrode assembly 130 is positioned between the first tabs 300, with the end 132a of the separator 132 facing the cover plate 140, and a portion of the first tab 300 extending beyond the end 132a of the separator 132 along the height direction Z of the secondary battery.

[0043] In some embodiments, the thermal conductivity of the welding block 154 is W1, and the thermal conductivity of the main body 152 is W2, where W2 > W1. In some embodiments, the material of the welding block 154 is steel, and the material of the main body 152 is copper. In other embodiments, the materials of the welding block 154 and the main body 152 can each be other existing materials that satisfy the aforementioned thermal conductivity relationship.

[0044] Because the welding direction of the welding block 154 and the cover plate 140 is from the outer surface 140a toward the electrode assembly 130, and the welding heat input is very high, a higher amount of welding heat is transferred toward the electrode assembly 130, making the separator more susceptible to damage due to burnout. Considering that the thermal conductivity coefficient parameter has a large influence on heat dissipation, the present invention sets the thermal conductivity coefficient W1 of the welding block 154 to less than the thermal conductivity coefficient W2 of the main body 152. As a result, the welding block 154 with a low thermal conductivity coefficient can be used to block heat conduction, reducing the amount of heat conducted to the separator 132 during the welding process, lowering the amount of heat reaching the separator 132, and lowering the temperature at the separator 132 during the welding process. This avoids the risk of separator burnout during the welding process and also avoids battery short circuits.

[0045] In some embodiments, W2-W1≧300W / (m·K), meaning that the thermal conductivity coefficient W1 of the welding block 154 is at least 300W / (m·K) lower than the thermal conductivity coefficient W2 of the main body 152. For example, in some embodiments, the material of the welding block 154 is steel, and the material of the main body 152 is copper. In other embodiments, the materials of the welding block 154 and the main body 152 can each be other existing materials that satisfy the aforementioned thermal conductivity coefficient relationship. By setting the thermal conductivity coefficient W1 of the welding block 154 at least 300W / (m·K) lower than that of the main body 152, the amount of heat conducted to the separator 132 during the welding process is effectively reduced, the amount of heat reaching the separator 132 is decreased, and the risk of separator burnout during the welding process can be avoided.

[0046] Specifically, in some embodiments, the welding block 154 can be stacked on the side of the main body 152 away from the electrode assembly 130. The cover plate 140 can be located on the side of the welding block 154 away from the main body 152. The weld marks 220 extend from the outer surface 140a of the cover plate 140 toward the main body 152, and the weld marks 220 do not extend beyond the bottom surface 154b of the welding block 154 facing the main body 152. Since the main body 152, welding block 154, and cover plate 140 are stacked on top of the electrode assembly 130, the positioning of both the main body 152 and the welding block 154 between the electrode assembly 130 and the cover plate 140 further reduces the amount of heat conducted to the separator 132 during the welding process, lowers the temperature at the separator 132 during the welding process, and avoids the risk of separator burnout.

[0047] In this embodiment, the cover plate 140 and the welding block 154, and the welding block 154 and the main body 152 are welded in two separate welding processes. Therefore, in addition to the formation of a weld mark 220 by welding between the cover plate 140 and the welding block 154, the welding block 154 is further welded to the main body 152, forming a weld mark 223. The welding block 154 and the main body 152 can be welded, for example, by a laser welding process. The welding direction between the welding block 154 and the main body 152 is from the outer surface of the welding block 154 facing away from the main body 152 toward the main body 152, and the width of the weld mark 223 gradually decreases in the direction from the welding block 154 toward the main body 152.

[0048] Furthermore, in this embodiment, the groove 145 of the cover plate 140 is located within the opening 113 at one end of the side wall 112. The outer wall 145s of the groove 145 faces the side wall 112 of the casing and is in close contact with the side wall 112. This interlocking fit between the cover plate 140 and the casing is advantageous for a tighter assembly of the cover plate 140 and the current collector panel 150.

[0049] Let A be the thickness of the cover plate 140 along the height direction Z. Let B be the thickness of the welding block 154 along the height direction Z, and let C be the thickness of the main body 152 along the height direction Z. In some embodiments, depending on the design and assembly requirements, the thickness A of the cover plate 140 can range from 0.4 mm to 0.8 mm, and the thickness C of the main body 152 can range from 0.1 mm to 0.2 mm. In some embodiments, the thickness A of the cover plate 140 is less than or equal to the thickness B of the welding block 154 + the thickness C of the main body 152, i.e., A ≤ B + C. This allows for the meeting of manufacturability requirements for through-welding from thin to thick.

[0050] As described in Figure 4A, the welding block 154 can be annular, extending along the edge of the current collector panel 150. In such embodiments, the inner diameter of the welding block 154 is D1, the outer diameter is D2, and D3 represents the outer diameter of the electrode assembly 130. In some embodiments, the inner diameter D1 of the welding block 154 satisfies D1 / D3 > 0.75. This is to ensure that the welding of the body 152 to the first tab 300 can weld all tabs radially. If the body 152 cannot weld all first tabs 300 radially, the DCIR (Direct Current Internal Resistance) will be high. Furthermore, the minimum value of the outer diameter D2 of the welding block 154 is D4 - 2 × A, where D4 represents the inner diameter of the side wall 112 of the casing 110 and A is the thickness of the cover plate 140. In some embodiments, for a 46 series cylindrical battery, D4 is 46 mm and the range of A can be 0.4 mm to 0.8 mm. The above minimum value of the outer diameter D2 of the welding block 154 allows the outer edge of the welding block 154 to be positioned below the outer wall 145s of the groove 145. If the outer diameter D2 is less than the above minimum value, laser through welding may occur on the outer surface of the welding block 154.

[0051] Referring to Figure 6, according to an embodiment of the present invention, the first tab 300 employs a flattened tab structure. That is, after winding the first electrode piece, separator, and second electrode piece, the first tab is flattened (the first tab is not cut). Figure 7A shows a schematic diagram of an electrode assembly with a flattened tab structure. With respect to the flattened first tab 300, since the number of stacked layers of the first tab 300 is greater, a single single-turn tab may be stacked at least 3 layers in the height direction Z, and therefore, after multiple turns of tabs are stacked, the number of stacked layers of the first tab 300 along the height direction Z exceeds 10 layers.

[0052] Figure 7B shows a schematic cross-sectional view of a single-turn first tab. As shown in Figure 7B, the number of laminated layers in the height direction Z of a single-turn first tab 300 is at least 3. Therefore, referring again to Figure 6, within the area where the first tab 300 and the body 152 of the current collector 150 are welded, the number of laminated layers in the height direction Z of each turn of first tab 130 is at least 3. Compared to cut and stacked tabs (where the tab is cut and reshaped after winding), the number of laminated layers of the flattened tab is greater for the same length of uncoated area of ​​the first current collector, resulting in a greater height along the height direction Z. This allows the end 132a of the separator 132 to be located further away from the weld surface of the first tab 300 and the body 152, thereby reducing the amount of heat received by the separator 132 and preventing the separator from burning out.

[0053] Specifically, in the height direction Z, the first tab 300 sequentially includes a dense region 302 welded to the main body 152, a dispersed region 304 connected to the dense region 302, and a linear region 306 connected to the dispersed region 304. The first tab 300 in the linear region 306 extends vertically along the height direction Z. Both the first tab 300 in the dense region 302 and the dispersed region 304 are bent many times, forming a multilayer lamination along the height direction Z. The dense region 302 comes into contact with the flattening roller during the flattening process, resulting in the current collector foil material being most tightly attached and having the highest density. Therefore, along the height direction Z, the number of laminated layers of the first tab 300 in the dispersed region 304 is less than the number of laminated layers of the first tab 300 in the dense region 302; that is, the tab lamination density of the dispersed region 304 is less than the tab lamination density of the dense region 302. It should be understood that a low tab stacking density means there are more gaps between tabs in the dispersed region 304, while a high tab stacking density means the tabs are stacked more densely in the dense region 302 with fewer gaps. By adopting a flattened tab structure, the tab stacking density in the dense region 302 that is welded to the main body 152 becomes higher, which is advantageous for welding. On the other hand, because the tab stacking density in the dispersed region 304 is lower, there are more gaps between tabs, and these gaps can provide thermal insulation. Therefore, more gaps in the dispersed region 304 further prevent heat transfer to the separator 132, thus preventing burnout of the separator.

[0054] In some embodiments, the end 132a of the separator 132 is located below the dispersion region 304 of the first tab 300, and the end of the linear region 306 facing the body 152 extends beyond the end 132a of the separator 132 by a distance G1. In some embodiments, the distance G1 > 0.1 mm. That is, the distance between the end 132a of the separator 132 and the dispersion region 304 is greater than 0.1 mm, and the spacing between tabs in the region corresponding to G1 can also provide thermal insulation, thus creating a gap of more than 0.1 mm between the end 132a of the separator 132 and the dispersion region 304 to provide further thermal insulation and further prevent burnout of the separator.

[0055] In some embodiments, the number of layers of the first tab 300 in the dense region 302 ranges from 15 to 45. In the dispersed region 304, the number of layers of the first tab 300 ranges from 15 to 30. Here, it should be understood that the number of layers in the dense region 302 and the dispersed region 304 refers to the total number of layers of multiple rolled tabs. Due to the aforementioned higher number of layers in the dense region 302, the dense region 302 has a tab lamination density that is more advantageous for welding.

[0056] In some embodiments, the total height of the flattened first tab 300 along the height direction Z is H, where H is 2 mm or more. The height of the dispersed region 304 along the height direction Z is H1, and the height of the dense region 302 along the height direction Z is H2. In some embodiments, the range of H1 / H is 45% to 55%, and the range of H2 / H is 10% to 15%. That is, the height of the dispersed region 304 accounts for 45% to 55% of the total height of the first tab, and the height of the dense region 302 accounts for 10% to 15% of the total height of the first tab. In one example, the range of H1 is 0.5 mm to 1 mm, and the range of H2 is 0.1 mm to 0.3 mm. The total height H of the first tab 300, which is 2 mm or more, can provide a larger height space for insulation, and when combined with the aforementioned height range configuration in the dense region 302 and the dispersed region 304, it allows the dense region 302, which has a relatively small height occupancy, to have a density that is advantageous for welding, while at the same time the spacing in the dispersed region 304, which has a relatively large height occupancy, is sufficient to provide an effective insulation effect.

[0057] In some embodiments, welding can be performed using a high-speed, multi-pass welding method. To meet overcurrent requirements, there is usually a requirement for the width of the weld mark 220. If this width requirement is achieved by single-pass welding, the welding heat is large, and excessive welding heat is transferred downwards towards the separator, easily causing separator burnout. The present invention achieves the desired width of the weld mark 220 by employing a high-speed, multi-pass welding method, resulting in lower heat output during each welding pass and avoiding separator burnout. In some embodiments, the minimum radial width of the weld mark 220 formed by the high-speed, multi-pass welding method is 0.5 mm or more, satisfying both overcurrent requirements and strength demands. The maximum width of the weld mark 220 can be less than 1 mm. If the maximum width of the weld mark 220 exceeds 1 mm, the welding time becomes relatively long, the heat input is large, and the welding efficiency is low.

[0058] Specifically, in high-speed, multi-pass welding methods, in terms of welding equipment selection, a 14-micrometer core diameter optical fiber laser can be selected. Because the optical fiber is thin and has high power density, it more easily forms deep welds and reduces heat transfer. In trajectory selection, an independent rifle design can be chosen, increasing the jump time between each rifle to ≥50 ms and reducing sustained heat input. In terms of welding parameter selection, the welding speed can be set to ≥500 mm / s to reduce heat input time. Furthermore, selecting a zero focus creates a maximum power density spot, which is advantageous for forming deep welds.

[0059] In some embodiments, the minimum depth of the weld mark 220 in the height direction Z should be 50 micrometers or more. The maximum depth of the weld mark should be 2 / 3 (2 / 3B) or less of the thickness B of the weld block 154. If the depth of the weld mark exceeds 2 / 3B, excessive welding heat is transferred downward towards the separator, which is likely to cause burnout of the separator.

[0060] Figure 8 shows a partially enlarged schematic diagram of the welded portion of the first tab, current collector panel, and cover plate of a secondary battery according to another embodiment of the present invention. The difference in the embodiment shown in Figure 8 is that a thermal insulation adhesive layer 250 can be installed between the main body 152 of the current collector panel 150 and the first tab 300. The thermal insulation adhesive layer 250 is located below the welding block 154, and the projection of the welding block 154 along the height direction Z is located on the thermal insulation adhesive layer 250. In some embodiments, the material of the thermal insulation adhesive layer 250 can be PI (polyimide). The thickness range of the thermal insulation adhesive layer 250 can be, for example, 67 micrometers or more. In some embodiments, the thermal conductivity coefficient of the thermal insulation adhesive layer 250 is less than 0.05 W / (m·K). By installing such a low thermal conductivity thermal insulation adhesive layer 250 between the main body 152 and the first tab 300, the diffusion of welding heat into the separator 132 can be further prevented.

[0061] In some embodiments, the radial width of the thermal insulation adhesive layer 250 is Da-1 mm to Da+1 mm, where Da represents the radial width of the weld block 154. Da can be equal to (D2-D1) / 2 (see, for example, Figure 4B). This width range of the thermal insulation adhesive layer 250 allows it to cover a sufficiently large area below the weld block 154, preventing heat transfer of welding heat to the separator during welding of the weld block 154 and the cover plate 140.

[0062] Figure 9 shows the connection structure between the electrode assembly 130 and the cover plate 140' according to another embodiment of the present invention. Figure 10A shows a schematic top view of the current collector panel 150' according to another embodiment of the present invention. Figure 10B is a schematic cross-sectional view of the current collector panel 150' according to another embodiment of the present invention. Figure 10C shows a schematic cross-sectional view of the cover plate 140' according to another embodiment of the present invention.

[0063] Referring to Figures 9 to 10C, in this embodiment, the welding block 154' of the current collector panel 150' is connected between the central region of the cover plate 140' and the main body 152. The central region of the cover plate 140' has a recess 147 on the side facing the electrode assembly 130, and the welding block 154' can be welded below the bottom surface of the recess 147. The welding block 154' is ring-shaped and exposes the center hole 156 on the main body 152 of the current collector panel 150'. In the embodiment shown in Figures 9 to 10C, the welding method between the main body 152 of the current collector panel 150' and the first tab of the electrode assembly 130 is the same as described above with reference to Figures 5 to 6, and will not be described again here.

[0064] Referring to Figure 11, the present invention provides an electronic device 1000, and in the following embodiments, for convenience of explanation, the electronic device 1000 is described as a vehicle. A battery pack 1002 is installed inside the vehicle, and the battery pack 1002 can be installed at the bottom, top, or tail of the vehicle body 1001. The battery pack 1002 can be used to supply power to the vehicle, for example, it can be used as the operating power source for the vehicle. The working part of the electronic device 1000 is electrically connected to the battery pack 1002 to obtain power support. The vehicle may be a gasoline vehicle, a gas vehicle, or a new energy vehicle, and the new energy vehicle may be, but is not limited to, a battery-powered electric vehicle, a hybrid vehicle, or a range-extender vehicle. The working part is the vehicle body, and the battery pack 1002 is installed at the bottom of the vehicle body and provides power support for the vehicle's movement or the operation of the vehicle's electrical components. However, in some other embodiments, the electronic device 1000 may further be a mobile phone, a portable device, a laptop computer, a ship, a spacecraft, an electric toy, and a power tool. Spacecraft include airplanes, rockets, spacecraft, and spaceflights. The working unit may be a unit component that receives power from the battery pack 1002 and performs the corresponding task, such as a fan blade rotation unit or a vacuum cleaner suction unit. Electric toys include stationary or mobile electric toys, such as game consoles, electric car toys, electric boat toys, and electric airplane toys. Power tools include metal cutting power tools, polishing power tools, assembly power tools, and railway power tools, such as electric drills, electric grinders, electric wrenches, electric screwdrivers, electric hammers, impact drills, concrete vibrators, and electric planers. The embodiments of the present invention do not impose any special limitations on the aforementioned electronic device 1000.

[0065] The foregoing describes only preferred embodiments of the present invention and is not intended to limit it. The present invention can have various modifications and changes for those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention. [Industrial applicability]

[0066] The secondary battery, battery pack, and electronic device of the present invention can be applied to the field of battery technology. [Explanation of Symbols]

[0067] 100: Secondary battery 110: Casing 111: End wall 112: Side wall 113:Aperture 120: Polar column 130: Electrode Assembly 132: Separator 132a: End 133: Center through hole 140, 140′: Cover board 140a: External surface 145: Groove 145s: Exterior wall 147: Recess 150, 150': Current collector panel 152: Main unit 154, 154′: Welding block 154b: Bottom 156: Center hole 158: Through groove 220, 223: Weld marks 250: Insulating adhesive layer 300: Tab 1 302: Dense area 304: Distributed area 306: Straight line area 1000:Electronic equipment 1001: Vehicle body 1002: Battery pack D1: Inner diameter D2:Outer diameter Da: width G1: Distance

Claims

1. A housing comprising a casing and a cover plate, wherein an opening is formed at one end of the casing and the cover plate is placed over the opening, The electrode assembly includes a first electrode piece, a separator, and a second electrode piece, which are housed within the housing and sequentially stacked and wound, the first electrode piece having a first tab facing the cover plate, and a portion of the first tab extending along the height direction of the secondary battery beyond the end of the separator facing the cover plate, The current collector includes a main body installed between the cover plate and the electrode assembly and welded to the first tab, and a welding block welded to the cover plate, wherein the welding direction between the welding block and the cover plate is from the outer surface of the cover plate toward the electrode assembly, the thermal conductivity of the welding block is W1, and the thermal conductivity of the main body is W2, of which W2 is greater than W1. A secondary battery characterized by having the following features.

2. The secondary battery according to claim 1, wherein W2 - W1 ≥ 300 W / (m·K).

3. The secondary battery according to claim 1, wherein the welding block is stacked on the side of the main body away from the electrode assembly, and the weld marks formed by welding the cover plate and the welding block do not extend beyond the bottom surface of the welding block facing the main body.

4. The secondary battery according to claim 3, wherein the trajectory of the welding mark extends along the circumferential direction of the cover plate, and the minimum width in the radial direction of the secondary battery is 0.5 mm or more, and the maximum width is less than 1 mm.

5. The secondary battery according to claim 3, wherein A is the thickness of the cover plate, B is the thickness of the welding block along the height direction, and C is the thickness of the main body, and A ≤ B + C.

6. The secondary battery according to claim 1, wherein the material of the welding block is steel and the material of the main body is copper.

7. The secondary battery according to claim 1, wherein the number of stacked layers in the height direction of the first tab of each coil is at least three within the region where the first tab and the current collector are welded together.

8. The secondary battery according to claim 1, wherein, in the height direction, the first tab sequentially includes a dense region welded to the main body, a dispersed region connected to the dense region, and a linear region connected to the dispersed region, the first tab in the linear region extends along the height direction, and the tab stacking density in the dispersed region is smaller than the tab stacking density in the dense region.

9. The secondary battery according to claim 8, wherein in the height direction, the end of the linear region facing the main body exceeds the end of the separator, and the distance by which the end of the linear region exceeds the end of the separator is greater than 0.1 mm.

10. The secondary battery according to claim 8, wherein the height of the first tab along the height direction is 2 mm or more, the ratio of the height of the dispersion region to the height of the first tab is 45% to 55%, and the ratio of the height of the dense region to the height of the first tab is 10% to 15%.

11. The secondary battery according to claim 8, wherein the number of stacked layers of the first tab in the densely packed region is 15 to 45 layers.

12. The secondary battery according to claim 1, further comprising a heat insulating adhesive layer installed between the main body of the current collector panel and the first tab, wherein the projection of the welding block along the height direction is located on the heat insulating adhesive layer, and the thermal conductivity coefficient of the heat insulating adhesive layer is less than 0.05 W / (m·K).

13. The secondary battery according to claim 12, wherein the radial width of the heat insulating adhesive layer of the secondary battery is from Da-1 mm to Da+1 mm, where Da represents the radial width of the welded block, and the unit of Da is millimeters.

14. The secondary battery according to claim 1, wherein the casing includes a side wall surrounding the electrode assembly, one end of the side wall being the opening, the cover plate includes a recessed groove toward the current collector, the groove is located within the opening, and the outer wall of the groove faces and is in close contact with the side wall of the casing, and the welding block is welded between the groove and the main body.

15. The secondary battery according to claim 14, wherein the welding block is ring-shaped and extends along the edge of the current collector panel, and when the thickness of the cover plate is A and the inner diameter of the side wall of the casing is D4, the minimum value of the outer diameter of the welding block = D4 - 2 × A, and when the inner diameter of the welding block is D1 and the outer diameter of the electrode assembly is D3, D1 / D3 > 0.

75.

16. A battery pack comprising a secondary battery according to any one of claims 1 to 15.

17. An electronic device including the battery pack described in claim 16.

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