Secondary battery, battery pack, and electronic device

Abstract

The utility model provides a secondary battery, a battery pack and an electronic device, the secondary battery comprises: a housing, which comprises a shell and a cover plate, one end of the shell forms an opening, and the cover plate covers the opening; the electrode assembly is accommodated in the shell, the electrode assembly comprises a first pole piece, a diaphragm and a second pole piece which are sequentially stacked and wound, the first pole piece is provided with a first tab facing the cover plate, and a part of the first tab exceeds the end part, facing the cover plate, of the diaphragm in the height direction of the secondary battery; the collector plate is arranged between the cover plate and the electrode assembly, the collector plate comprises a body welded with the first tab and a welding block welded with the cover plate, the welding direction of the welding block and the cover plate is from the outer surface of the cover plate to the electrode assembly, the heat conductivity coefficient of the welding block is W1, the heat conductivity coefficient of the body is W2, and W2 is larger than W1.

Description

TECHNICAL FIELD

[0001] The utility model relates to a kind of secondary battery, battery pack and electronic device. BACKGROUND

[0002] In the field of new energy power battery, secondary battery generally includes electrode assembly, shell, current collector plate and the like. Electrode assembly includes positive pole sheet, negative pole sheet and diaphragm between positive pole sheet and negative pole sheet. These positive pole sheet, negative pole sheet and diaphragm are stacked and then wound into electrode assembly, and then packaged in shell. Secondary battery usually sets current collector plate at the position close to the opening of shell, so that one end of current collector plate is welded to shell or end cover, and the other end is electrically connected with the tab of electrode assembly, thereby realizing the electrical connection between shell and electrode assembly. SUMMARY

[0003] In view of the problems in the related art, the utility model aims to provide a secondary battery, battery pack and electronic device to avoid the problem of damage to diaphragm caused by high-temperature welding of cover plate and current collector plate.

[0004] To achieve the above-mentioned purpose, the utility model provides a kind of secondary battery, comprising: shell, including shell and cover plate, one end of shell forms opening, and cover plate covers opening;Electrode assembly is contained in shell, and electrode assembly includes first pole sheet, diaphragm and second pole sheet which are stacked and wound in sequence, first pole sheet has first tab facing cover plate, part of first tab exceeds diaphragm end facing cover plate along the height direction of secondary battery;Current collector plate is arranged between cover plate and electrode assembly, and current collector plate includes body welded with first tab and welding block welded with cover plate, the welding direction of welding block and cover plate is from the outer surface of cover plate to electrode assembly, the thermal conductivity of welding block is W1, and the thermal conductivity of body is W2, wherein W2 is greater than W1.

[0005] In some embodiments, W2-W1 is greater than or equal to 300 W / (m·K).

[0006] In some embodiments, welding block is stacked on the side of body away from electrode assembly, and the welding mark formed by welding cover plate and welding block does not exceed the bottom surface of welding block facing body.

[0007] In some embodiments, the track of welding mark extends along the circumference of cover plate, and the minimum width in the radial direction of secondary battery is greater than or equal to 0.5 mm, and the maximum width is less than 1 mm.

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

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

[0010] In some embodiments, in the region where the first electrode tab is welded to the current collector, the number of stacked layers of the first electrode tab in the height direction for each turn is at least 3.

[0011] In some embodiments, in the height direction, the first electrode tab sequentially includes a dense region welded to the body, a loose region connected to the dense region, and a straight region connected to the loose region. The first electrode tab in the straight region extends along the height direction, and the electrode tab stacking density in the loose region is less than the electrode tab stacking density in the dense region.

[0012] In some embodiments, in the height direction, the end of the straight section facing the body extends beyond the end of the diaphragm, and the distance between the end of the straight section and the end of the diaphragm is greater than 0.1 mm.

[0013] In some embodiments, the height of the first electrode tab along the height direction is greater than or equal to 2 mm, the height of the loose region accounts for 45% to 55% of the height of the first electrode tab, and the height of the dense region accounts for 10% to 15% of the height of the first electrode tab.

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

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

[0016] In some embodiments, the width of the heat-insulating adhesive layer in the radial direction of the secondary battery is Da-1mm to Da+1mm, where Da represents the width of the welding block in the radial direction.

[0017] In some embodiments, the housing includes a sidewall surrounding the electrode assembly, one end of which is open, and a cover plate includes a recessed groove facing the manifold, the groove being located within the opening, and the outer wall of the groove facing and fitting against the sidewall of the housing, wherein a welding block is welded between the groove and the body.

[0018] In some embodiments, the welding block is an annular ring extending along the edge of the manifold, and the minimum outer diameter of the welding block is the inner diameter of the sidewall of the housing - 2 × the thickness of the cover plate, and the inner diameter of the welding block / the outer diameter of the electrode assembly > 0.75.

[0019] Embodiments of this application also provide a battery pack, including any of the above-described secondary batteries.

[0020] Embodiments of this application also provide an electronic device including the battery pack described above.

[0021] The beneficial technical effects of this utility model are as follows:

[0022] The technical solution of the present application configures the thermal conductivity of the welding block to be lower than that of the body, so that the welding block with low thermal conductivity can be used to block heat conduction, reduce the heat conduction to the diaphragm in the welding process, reduce the heat reaching the diaphragm, and reduce the temperature at the diaphragm in the welding process, thereby avoiding the risk of diaphragm burn in the welding process, and further avoiding battery short circuit. BRIEF DESCRIPTION OF DRAWINGS

[0023] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or prior art description will be briefly introduced below. Obviously, the drawings in the following description are some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0024] Figure 1 A perspective view of a secondary battery according to an embodiment of the present application is shown.

[0025] Figure 2 A front view of a secondary battery according to an embodiment of the present application is shown.

[0026] Figure 3A And Figure 3B A partial cross-sectional view of a secondary battery according to an embodiment of the present application is shown, corresponding to line X1-X1 in Figure 2

[0027] Figure 4A A top view of a current collecting plate according to an embodiment of the present application is shown.

[0028] Figure 4B A cross-sectional view of a current collecting plate according to an embodiment of the present application is shown.

[0029] Figure 4C A cross-sectional view of a cover plate according to an embodiment of the present application is shown.

[0030] Figure 5 A partial enlarged view of a connection structure of a current collecting plate, a cover plate and a side wall of a shell according to an embodiment of the present application is shown.

[0031] Figure 6 A partial enlarged view of a first tab, a current collecting plate and a welding part of a cover plate of a secondary battery according to some embodiments of the present application is shown.

[0032] Figure 7A A schematic view of an electrode assembly with a crimped tab structure is shown.

[0033] Figure 7B A cross-sectional view of a single ring of first tabs is shown.

[0034] ​Figure 8 A partial enlarged view of a first tab, a current collector, and a cover plate welding portion of a secondary battery according to another embodiment of the present application is shown.

[0035] Figure 9 A connection structure of an electrode assembly and a cover plate according to another embodiment of the present application is shown in FIG.

[0036] Figure 10A A top view of a current collecting disc according to another embodiment of the present application is shown.

[0037] Figure 10B A cross-sectional view of a current collecting disc according to another embodiment of the present application is shown.

[0038] Figure 10C A cross-sectional view of a cover plate according to another embodiment of the present application is shown.

[0039] Figure 11 A schematic view of an electronic device according to an embodiment of the present application is shown. DETAILED DESCRIPTION

[0040] In order to better understand the spirit of the embodiments of the present application, the following further describes the embodiments of the present application in connection with some preferred embodiments of the present application.

[0041] Embodiments of the present application will be described in detail below. Throughout the specification, the same or similar components and components having the same or similar functions are denoted by like reference numerals. The embodiments described herein with reference to the accompanying drawings are illustrative in nature, diagrammatic in nature, and serve to provide a basic understanding of the present application. The embodiments of the present application should not be construed as limiting the present application.

[0042] As used herein, the terms "approximately," "generally," "substantially," and "about" are used to describe and account for small variations. When utilized in connection with an event or circumstance, such terms can refer to instances in which the event or circumstance occurs exactly, as well as instances in which the event or circumstance occurs with a minor approximation.

[0043] In this specification, unless specifically designated or limited, relative terms such as "central," "longitudinal," "lateral," "forward," "rearward," "rightward," "leftward," "internal," "external," "lower," "higher," "horizontal," "vertical," "above," "below," "top," "bottom," and derivatives thereof (e.g., "horizontally," "downwardly," "upwardly," etc.) should be construed to refer to the orientation as described in the discussion or depicted in the figures. These relative terms are used only to describe the orientation for convenience, and do not require the application to be constructed or operated in a particular orientation.

[0044] For ease of description, "first," "second," "third," and the like can be used herein to distinguish between different components of one figure or series of figures. "First," "second," "third," and the like are not intended to describe corresponding components.

[0045] A cylindrical battery is a kind of secondary battery, which has a high energy density, therefore, the cylindrical battery is widely used in the lithium battery industry. The cylindrical battery structure includes a pole, a shell, a current collector plate (including a positive current collector plate and a negative current collector plate), and an electrode assembly. Usually, the current collector plate is first welded to the electrode assembly, and then the current collector plate is welded to the pole and the shell respectively to form the final electrical conduction effect.

[0046] After the current collector plate (for example, the negative current collector plate) is welded to the electrode assembly, it needs to be connected to the shell. There are two existing connection methods. One is that the current collector plate is directly connected to the shell for electrical conduction. The other is that the current collector plate is welded to a cover plate, and then the cover plate is electrically connected to the shell. In the existing latter method, the current collector plate is usually welded to the cover plate by laser penetration welding, that is, the cover plate is welded to the current collector plate below by laser penetration. This kind of welding has high heat input, which often easily causes the lower diaphragm to be damaged and burned. The damaged diaphragm will cause the positive and negative electrode sheets to contact, resulting in a short circuit of the battery.

[0047] Figure 1 A perspective view of a secondary battery 100 according to an embodiment of the present application is shown. Figure 2 A front view of a secondary battery 100 according to an embodiment of the present application is shown. Figure 3A and Figure 3B A partial cross-sectional view of a secondary battery 100 according to an embodiment of the present application is shown, corresponding to line X1-X1 in Figure 2 Figure 3A The connection structure of the electrode assembly 130 and the cover plate 140 is shown in Figure 3B The connection structure of the current collector plate 150 and the cover plate 140 and the side wall 112 of the shell is shown in

[0048] In the present embodiment, a secondary battery 100 is shown as an example of a cylindrical battery. In some embodiments, the secondary battery 100 can be a 4680 cylindrical battery (diameter 46 mm, height 80 mm), or can be a 4695 cylindrical battery (diameter 46 mm, height 95 mm), or can be a 46120 cylindrical battery (diameter 46 mm, height 120 mm). The diameter here refers to the outer diameter dimension of the shell.

[0049] For reference, Figures 1-3B ​The secondary battery 100 includes a housing including a shell 110 and a cover plate 140. The shell 110 can 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 in various ways, such as one-piece stamping, one-piece casting, or separate welding, as long as a stable sealing and electrical connection relationship can be formed. The side wall 112 can surround in a cylindrical shape or any other closed loop profile that can be matched with the end wall 111. In the present 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 an end of the side wall 112 opposite to the end wall 111, and the cover plate 140 covers the opening 113. The electrode assembly 130 is accommodated in an accommodation space defined by the shell 110 and the cover plate 140, which is used to accommodate the electrode assembly 130, electrolyte, and other necessary components of the battery.

[0050] The pole 120 can pass through the end wall 111 and be insulated from the end wall 111. In some embodiments, the pole 120 can be made of a metal material having electrical conductivity. For example, the material of the pole 120 can be aluminum (Al). In some embodiments, the pole 120 is a positive terminal of the secondary battery 100. The electrical insulation between the pole 120 and the end wall 111 of the shell 110 can be achieved in various ways. For example, an insulating gasket assembly can be placed between the pole 120 and the end wall 111 to achieve insulation.

[0051] Specifically, the outer diameter of the shell 110 can be determined according to the specific size of the electrode assembly 130, such as 18 mm, 21 mm, 46 mm, etc. The material of the shell 110 can be various, such as copper, iron, aluminum, steel, aluminum alloy, etc. In order to prevent rusting of the shell 110 during long-term use, a layer of anti-rust material such as metal nickel can also be plated on the surface of the shell 110 and the cover plate 140.

[0052] The electrode assembly 130 can be mainly formed by winding the first and second electrode tabs, and a separator is provided between the first and second electrode tabs. The electrode assembly 130 formed by winding can have a central through hole 133. The first electrode tab can be one of a positive electrode tab and a negative electrode tab, and the second electrode tab can be the other of the positive electrode tab and the negative electrode tab. The positive electrode tab can include a positive electrode current collector and a positive electrode active material coated on a surface of the positive electrode current collector; the positive electrode current collector can include a coated region coated with the active material and an uncoated region not coated with the active material, and the uncoated region forms a positive electrode tab of the electrode assembly 130 after winding. The negative electrode tab includes a negative electrode current collector and a negative electrode active material coated on a surface of the negative electrode current collector; the negative electrode current collector includes a coated region coated with the active material and an uncoated region not coated with the active material, and the uncoated region forms a 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, the positive electrode active material layer includes a positive electrode active material, and the positive electrode active material can be lithium cobaltate, lithium iron phosphate, ternary lithium, or lithium manganate, etc. The material of the negative electrode current collector can be copper, the negative electrode active material layer includes a negative electrode active material, and the negative electrode active material can be carbon or silicon, etc. The material of the separator can be PP (polypropylene), PE (polyethylene), or the like. In order to protect and insulate the electrode assembly 130, an insulating film can also be wrapped outside the electrode assembly 130, and the insulating film can be synthesized by PP, PE, PET (polyethylene terephthalate), PVC (polyvinyl chloride), or other high polymer materials.

[0053] The electrode assembly 130 can include a first tab 300 facing the opening 113. In some embodiments, the first tab 300 is a negative electrode tab of the electrode assembly 130. A current collector disc 150 is disposed between the cover plate 140 and the electrode assembly 130, and the first tab 300 is connected to the sidewall 112 of the shell 110 through the current collector disc 150. In some embodiments, the current collector disc 150 is a negative current collector disc. The electrode assembly 130 can also include a second tab (e.g., a positive electrode tab, not shown) facing the end wall 111, and the second tab can be connected to the pole 120 through another current collector disc (e.g., a positive current collector disc, not shown). The material of the current collector disc 150 can be, for example, copper, or can also be plated with nickel on the surface of copper. The material of the cover plate 140 can be steel, for example, stainless steel or nickel-plated steel.

[0054] In the present embodiment, the first tab 300 is welded to the current collector disc 150, the current collector disc 150 is welded to the cover plate 140, and the cover plate 140 can be welded to the sidewall 112 at the end of the sidewall 112 of the shell 110. Specifically, the current collector disc 150 includes a body 152 welded to the first tab 300, and a welding block 154 located on the side of the body 152 facing the cover plate 140.

[0055] Figure 4A A top view of the current collecting plate 150 according to an embodiment of the present application is shown. Figure 4B A cross-sectional view of the current collecting plate 150 according to an embodiment of the present application is shown. Referring to Figures 3A-4B In this embodiment, the current collecting plate 150 is circular. The welding block 154 can be an annular shape extending along the edge of the current collecting plate 150.

[0056] The current collecting plate 150 can have a central hole 156, which can be coaxially arranged with the central through hole 133 of the electrode assembly 130. A plurality of through grooves 158 can be arranged around the central hole 156. The through grooves 158 penetrate the current collecting plate 150 in the thickness direction of the current collecting plate 150. Each through groove 158 can extend longitudinally in the radial direction of the current collecting plate 150. Figure 4A The shape of the through groove 158 shown in the middle is only an example, and the through groove 158 can have any suitable shape, which is not limited in the present application. The central hole 156 and the through groove 158 can be used as an exhaust path inside the secondary battery, and can be beneficial for the current collecting plate 150 to open when the battery is depressurized.

[0057] Figure 4C A cross-sectional view of the cover plate 140 according to an embodiment of the present application is shown. Referring to Figures 3A-4C As shown, the cover plate 140 includes a recess 145 recessed towards the current collecting plate 150. The welding block 154 is welded between the bottom surface of the recess 145 and the body 152 of the current collecting plate 150. The recess 145 can be a hollow structure formed by stamping.

[0058] Figure 5 A partial enlarged view of the connection structure of the current collecting plate 150, the cover plate 140 and the side wall 112 of the shell according to an embodiment of the present application is shown. Figure 6 A partial enlarged view of the first tab, the current collecting plate and the cover plate welding part of the secondary battery according to some embodiments of the present application is shown. Further referring to Figure 5 and Figure 6As shown, the current collecting plate 150 includes a body 152 welded with the first tab 300, and a welding block 154 welded with the cover plate 140. In some embodiments, the cover plate 140 is welded with the welding block 154, for example, by laser penetration welding. The welding direction of the welding block 154 and the cover plate 140 is from the outer surface 140a of the cover plate 140 facing away from the electrode assembly 130 towards the electrode assembly 130. The welding between the cover plate 140 and the welding block 154 forms a welding bead 220. The trace of the welding bead 220 can extend along the circumference of the cover plate 140. Specifically, the trace of the welding bead 220 can extend along the circumference 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 towards the electrode assembly 130, the width of the welding bead 220 gradually decreases in the direction from the outer surface 140a towards the electrode assembly 130. In addition, as shown, the end portion 132a of the separator 132 of the electrode assembly 130 is disposed between the first tabs 300, and the end portion 132a of the separator 132 faces the cover plate 140, and a portion of the first tab 300 protrudes beyond the end portion 132a of the separator 132 in the height direction Z of the secondary battery. Figure 6 As shown, the separator 132 of the electrode assembly 130 is disposed between the first tabs 300, and the end portion 132a of the separator 132 faces the cover plate 140, and a portion of the first tab 300 protrudes beyond the end portion 132a of the separator 132 in the height direction Z of the secondary battery.

[0059] In some embodiments, the thermal conductivity of the welding block 154 is W1, and the thermal conductivity of the body 152 is W2, and W2 > W1. In some embodiments, the material of the welding block 154 is steel, and the material of the body 152 is copper. In other embodiments, the materials of the welding block 154 and the body 152 can also be other existing materials that satisfy the above thermal conductivity relationship.

[0060] Since the welding direction of the welding block 154 and the cover plate 140 is from the outer surface 140a towards the electrode assembly 130, and the welding heat input is high, a higher welding heat is transmitted towards the electrode assembly 130, which causes the separator to be easily damaged and burned. Considering that the thermal conductivity parameter has a great influence on heat dissipation, the thermal conductivity W1 of the welding block 154 is configured to be less than the thermal conductivity W2 of the body 152, so that the welding block 154 with low thermal conductivity can be used to block heat conduction, reduce the heat conduction to the separator 132 in the welding process, reduce the heat reaching the separator 132, and reduce the temperature at the separator 132 in the welding process, thereby avoiding the risk of separator burning in the welding process, and further avoiding the risk of battery short circuit

[0061] In some embodiments, W2-W1≥300W / (m·K), i.e., the thermal conductivity of the welding block 154 is at least 300 W / (m·K) lower than the thermal conductivity of the body 152. For example, in some embodiments, the material of the welding block 154 is steel, and the material of the body 152 is copper. In other embodiments, the materials of the welding block 154 and the body 152 can also be other existing materials that satisfy the above thermal conductivity relationship, respectively. Configuring the thermal conductivity of the welding block 154 to be at least 300 W / (m·K) lower than the thermal conductivity of the body 152 can effectively reduce the heat conducted to the diaphragm 132 in the welding process, reduce the heat reaching the diaphragm 132, and avoid the risk of diaphragm burn in the welding process.

[0062] Specifically, in some embodiments, the welding block 154 can be stacked on the side of the 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 body 152. The weld print 220 extends from the outer surface 140a of the cover plate 140 toward the body 152, and the weld print 220 does not exceed the bottom surface 154b of the welding block 154 toward the body 152. The body 152, the welding block 154, and the cover plate 140 are arranged in a stacked manner on the electrode assembly 130, so that the body 152 and the welding block 154 are collectively located between the electrode assembly 130 and the cover plate 140, which can further reduce the heat conducted to the diaphragm 132 in the welding process, reduce the temperature at the diaphragm 132 in the welding process, and avoid the risk of diaphragm burn.

[0063] In the present embodiment, the cover plate 140 and the welding block 154, and the welding block 154 and the body 152 are welded by two welding processes, respectively. Therefore, in addition to the welding between the cover plate 140 and the welding block 154 forming the weld print 220, the welding block 154 is also welded with the body 152 and forms a weld print 223. The welding block 154 and the body 152 can be welded, for example, by a laser welding process. The welding direction of the welding block 154 and the body 152 is that the outer surface of the welding block 154 away from the body 152 faces the body 152, and the weld print 223 gradually decreases in width in the direction of the welding block 154 facing the body 152.

[0064] In addition, in the present embodiment, the groove 145 of the cover plate 140 is located in 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 shell and is in abutment with the side wall 112. This interference fit of the cover plate 140 and the shell is more conducive to assembling and compressing the cover plate 140 and the current collector plate 150.

[0065] The thickness of the cover plate 140 along the height direction Z is A. The thickness of the welding block 154 along the height direction Z is B, and the thickness of the body 152 along the height direction Z is C. In some embodiments, the thickness A of the cover plate 140 can range from 0.4 mm to 0.8 mm, and the thickness C of the body 152 can range from 0.1 mm to 0.2 mm, according to design and assembly requirements. 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 plus the thickness C of the body 152, i.e., A≤B+C. Thus, the manufacturability requirement of thin-thick penetration welding can be met.

[0066] As described with respect to Figure 4A The welding block 154 can be annular extending along the edge of the current collector plate 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 the tabs in the radial direction. If the body 152 cannot be welded to all the first tabs 300 in the radial direction, the DCIR (Direct Current Internal Resistance) will be high. In addition, 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 shell 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 A can range from 0.4 mm to 0.8 mm. The above minimum value of the outer diameter D2 of the welding block 154 is such that the outer edge of the welding block 154 can be located below the outer wall 145s of the groove 145. If the outer diameter D2 is less than the above minimum value, the laser penetration welding can be welded outside the welding block 154.

[0067] Referring to Figure 6 According to embodiments of the present application, the first tab 300 adopts a rubbing tab structure. That is, after winding the first electrode sheet, the separator, and the second electrode sheet, the first tab is rubbed and shaped (without cutting the first tab). Figure 7A A schematic view of an electrode assembly showing a rubbing tab structure is shown. For the rubbing structure of the first tab 300, the number of stacked layers of the first tab 300 is more, so that a single circle of tabs can be stacked in the height direction Z by at least 3 layers, so that after stacking multiple circles of tabs, the number of stacked layers of the first tab 300 in the height direction Z is more than 10 layers.

[0068] Figure 7B A cross-sectional schematic view of a single circle of first tabs is shown. Referring to Figure 7B As shown, the number of stacked layers of a single circle of first tabs 300 in the height direction Z is at least 3 layers. Therefore, referring again to Figure 6In the area where the first tab 300 is welded to the body 152 of the current collector 150, the number of stacked layers of the first tab 130 in the height direction Z of each circle is at least 3. Compared to a cut-and-stack tab (after winding, the tab is cut and reshaped), for the same length of the uncoated area of the first current collector, the height in the height direction Z of the tab is greater due to the greater number of stacked layers of the tab, the end portion 132a of the separator 132 is farther from the welding surface of the first tab 300 and the body 152, and thus the heat experienced by the separator 132 is reduced, avoiding burning of the separator.

[0069] Specifically, in the height direction Z, the first tab 300 includes, in sequence, a dense area 302 welded to the body 152, a sparse area 304 connected to the dense area 302, and a flat area 306 connected to the sparse area 304. The first tab 300 in the flat area 306 extends vertically in the height direction Z. The first tab 300 in the dense area 302 and the sparse area 304 is bent multiple times to form multiple layers of stacking in the height direction Z. The dense area 302 contacts the flattening roller during the flattening process, so the current collector foil is attached most tightly and has a large density. Therefore, in the height direction Z, the number of stacked layers of the first tab 300 in the sparse area 304 is less than the number of stacked layers of the first tab 300 in the dense area 302, i.e., the tab stacking density of the sparse area 304 is less than the tab stacking density of the dense area 302. It should be understood that a smaller tab stacking density means that there are more gaps between the tabs in the sparse area 304, and a larger tab stacking density means that the tabs are stacked more densely and have fewer gaps in the dense area 302. By using the flattened tab structure, the tab stacking density of the dense area 302 welded to the body 152 is greater, which is beneficial for welding. On the other hand, because the tab stacking density is smaller in the sparse area 304, there are more gaps between the tabs, and the gaps can act as a heat shield, so the more gaps in the sparse area 304 can further block the transfer of heat to the separator 132, preventing the separator from burning.

[0070] In some embodiments, the end portion 132a of the separator 132 is located below the sparse area 304 of the first tab 300, and the end portion of the flat area 306 toward the body 152 exceeds the end portion 132a of the separator 132 by a distance G1. In some embodiments, the distance G1 is greater than 0.1 mm. That is, the distance between the end portion 132a of the separator 132 and the sparse area 304 is greater than 0.1 mm, and because the spacing between the tabs in the area corresponding to G1 also acts as a heat shield, a distance greater than 0.1 mm is formed between the end portion 132a of the separator 132 and the sparse area 304 to provide further heat shielding, further preventing the separator from burning.

[0071] In some embodiments, the first tab 300 in the dense area 302 has a stack number of 15 to 45 layers. The first tab 300 in the sparse area 304 has a stack number of 15 to 30 layers. It should be understood that the stack number in the dense area 302 and the sparse area 304 herein refers to the total number of layers of the multi-turn tab stack. The above-mentioned larger stack number of the dense area 302 makes the dense area 302 have a higher density of tab stacks, which is more conducive to welding.

[0072] In some embodiments, the total height of the first tab 300 in the height direction Z is H. H is greater than or equal to 2 mm. The height of the sparse area 304 in the height direction Z is H1, and the height of the dense area 302 in the height direction Z is H2. In some embodiments, the range of H1 / H can be 45% to 55%, and the range of H2 / H can be 10% to 15%. That is, the height of the sparse area 304 accounts for 45% to 55% of the total height of the first tab, and the height of the dense area 302 accounts for 10% to 15% of the total height of the first tab. In an example, the range of H1 can be 0.5 mm to 1 mm, and the range of H2 can be 0.1 mm to 0.3 mm. The total height H of the first tab 300 greater than or equal to 2 mm can provide a larger height space for heat insulation, and in combination with the above-mentioned height range configuration in the dense area 302 and the sparse area 304, the dense area 302 with a smaller height ratio can have a higher density that is more conducive to welding, while the sparse area 304 with a larger height ratio has a sufficient interval to provide an effective heat insulation effect.

[0073] In some embodiments, a high-speed multi-time welding method can be used for welding. In order to meet the overcurrent requirement, the width of the weld 220 is usually required to have a certain requirement. If the width requirement is achieved by single welding, the welding heat is large, which can easily cause excessive welding heat to be transmitted downward to the diaphragm, which can easily cause the diaphragm to be burned. The present application uses a high-speed multi-time welding method to achieve the required width of the weld 220, so the heat during each welding is low, which can avoid burning the diaphragm. In some embodiments, the minimum width of the weld 220 formed by the high-speed multi-time welding method in the radial direction is greater than or equal to 0.5 mm to meet the overcurrent requirement and strength requirement. The maximum width of the weld 220 can be less than 1 mm. If the maximum width of the weld 220 is greater than 1 mm, the welding time will be longer, the heat input will be large, and the welding efficiency will be low.

[0074] Specifically, in the high-speed multi-pass welding mode, in terms of the welding equipment selection, a fiber laser with a core diameter of 14 microns can be selected. The fiber is thin and has a high power density, so it is easier to form a deep weld mark and reduce heat transfer. In terms of trajectory selection, an independent line design can be selected, and each line increases a jump time of ≥50 ms to reduce continuous heat input. In terms of welding parameter selection, the welding speed can be selected to be ≥500 mm / s to reduce heat input time. And select 0 focal point to form a maximum power density spot, which is beneficial to form a deep weld mark.

[0075] In some embodiments, the minimum value of the weld mark depth of the weld mark 220 in the height direction Z should be greater than or equal to 50 microns. And the maximum value of the weld mark depth should be less than or equal to 2 / 3 (2 / 3B) of the thickness B of the welding block 154. If the weld mark depth is greater than 2 / 3B, it will cause excessive welding heat to be transferred downward to the diaphragm, which is easy to cause the diaphragm to be burned.

[0076] Figure 8 A partial enlarged schematic view of a first tab, a current collector, and a cover plate welding portion of a secondary battery according to another embodiment of the present application is shown. Figure 8 The difference of the shown embodiment is that a heat insulation adhesive layer 250 can be arranged between the body 152 of the current collector disc 150 and the first tab 300. And the heat 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 heat insulation adhesive layer 250. In some embodiments, the material of the heat insulation adhesive layer 250 can be PI (polyimide) material. The thickness range of the heat insulation adhesive layer 250 can be, for example, greater than or equal to 67 microns. In some embodiments, the thermal conductivity of the heat insulation adhesive layer 250 is less than 0.05 W / (m·K). By arranging such a low thermal conductivity heat insulation adhesive layer 250 between the body 152 and the first tab 300, the welding heat can be further blocked from spreading to the diaphragm 132.

[0077] In some embodiments, the width of the heat insulation adhesive layer 250 in the radial direction is Da-1mm to Da+1mm, where Da represents the width of the welding block 154 in the radial direction. Da can be equal to (D2-D1) / 2 (for example, see Figure 4B ). This width range of the heat insulation adhesive layer 250 can make the heat insulation adhesive layer 250 cover a large enough area below the welding block 154 to block the welding heat when the welding block 154 and the cover plate 140 are welded from conducting to the diaphragm.

[0078] Figure 9 The connection structure of the electrode assembly 130 and the cover plate 140' according to another embodiment of the present application is shown in the middle. Figure 10A A top view schematic diagram of a current collector disc 150' according to another embodiment of the present application is shown. Figure 10BA cross-sectional view of the current collector plate 150' according to another embodiment of the present application. Figure 10C A cross-sectional view of the cover plate 140' according to another embodiment of the present application is shown.

[0079] Reference is made to Figures 9-10C In the embodiment shown, the welding block 154' of the current collector plate 150' is connected between the central region of the cover plate 140' and the body 152. The central region of the cover plate 140' has a recess 147 recessed on one side of the hyperbolic electrode assembly 130, and the welding block 154' can be welded below the bottom surface of the recess 147. The welding block 154' is annular to expose the central hole 156 on the body 152 of the current collector plate 150'. In the embodiment shown, the welding block 154' is welded to the body 152 of the current collector plate 150' and the first lug of the electrode assembly 130 in the same manner as described above with reference to Figures 9-10C Figures 5-6 The description of the welding manner between the body 152 of the current collector plate 150' and the first lug of the electrode assembly 130 in the embodiment shown is the same as described above with reference to

[0080] Reference is made to Figure 11 The utility model provides a kind of electronic device 1000, the following embodiment is for the convenience of explanation, and electronic device 1000 is taken as vehicle to be explained.For example, the inside of vehicle is provided with battery pack 1002, battery pack 1002 can be arranged at the bottom or head or tail of vehicle body 1001.Battery pack 1002 can be used for the power supply of vehicle, for example, battery pack 1002 can be used as the operating power supply of vehicle.Working part of electronic device 1000 is electrically connected with battery pack 1002, to obtain electrical energy support.Vehicle can be fuel automobile, gas automobile or new energy automobile, and new energy automobile can be pure electric vehicle, hybrid electric vehicle or extended range vehicle, but not limited thereto.Working part is vehicle body, and battery pack 1002 is arranged at the bottom of vehicle body, and provides electrical energy support for the running of vehicle or the operation of electrical element in vehicle.However, in some other embodiments, electronic device 1000 can also be mobile phone, portable device, notebook computer, ship, spacecraft, electric toy and electric tool and so on.Spacecraft includes airplane, rocket, space shuttle and spaceship and so on;Working part can obtain the electrical energy of battery pack 1002, and makes corresponding working unit part, for example, fan blade rotating unit of fan, dust collection working unit of dust collector and so on.Electric toy includes fixed or mobile electric toy, for example, game machine, electric car toy, electric ship toy and electric plane toy and so on;Electric tool includes metal cutting electric tool, grinding electric tool, assembly electric tool and railway electric tool, for example, electric drill, electric grinder, electric wrench, electric screwdriver, electric hammer, impact drill, concrete vibrator and electric planer and so on.The above-mentioned electronic device 1000 is not specially limited in the embodiments of the present application.

[0081] ​The above merely describes preferred embodiments of the present application and is not intended to limit the present application. For those skilled in the art, the present application can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A secondary battery, characterized in that, include: An outer casing includes a housing and a cover plate, wherein one end of the housing forms an opening and the cover plate closes to the opening; An electrode assembly is housed within the housing. The electrode assembly includes a first electrode, a separator, and a second electrode that are sequentially stacked and wound. The first electrode has a first tab facing the cover plate, and a portion of the first tab extends beyond the end of the separator facing the cover plate along the height direction of the secondary battery. A current collector is disposed between the cover plate and the electrode assembly. The current collector includes a body welded to the first electrode tab and a welding block welded to the cover plate. The welding direction of 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 body is W2, wherein W2 is greater than W1.

2. The secondary battery according to claim 1, characterized in that, W2-W1 is greater than or equal to 300W / (m·K).

3. The secondary battery according to claim 1, characterized in that, The welding blocks are stacked on the side of the body away from the electrode assembly, and the weld mark formed by welding the cover plate to the welding blocks does not exceed the bottom surface of the welding blocks facing the body.

4. The secondary battery according to claim 3, characterized in that, The trace of the solder mark extends circumferentially along the cover plate, and the minimum width in the radial direction of the secondary battery is greater than or equal to 0.5 mm, and the maximum width is less than 1 mm.

5. The secondary battery according to claim 3, characterized in that, The thickness of the cover plate is less than or equal to the thickness of the welded block along the height direction plus the thickness of the body.

6. The secondary battery according to claim 1, characterized in that, The welding block is made of steel, and the body is made of copper.

7. The secondary battery according to claim 1, characterized in that, In the area where the first electrode tab is welded to the collector plate, the number of stacked layers of the first electrode tab in each ring in the height direction is at least 3.

8. The secondary battery according to claim 1, characterized in that, In the height direction, the first electrode tab sequentially includes a dense region welded to the body, a loose region connected to the dense region, and a straight region connected to the loose region. The first electrode tab in the straight region extends along the height direction, and the electrode tab stacking density in the loose region is less than the electrode tab stacking density in the dense region.

9. The secondary battery according to claim 8, characterized in that, In the height direction, the end of the straight region facing the body extends beyond the end of the diaphragm by a distance greater than 0.1 mm.

10. The secondary battery according to claim 8, characterized in that, The height of the first electrode tab along the height direction is greater than or equal to 2 mm, the height of the loose region accounts for 45% to 55% of the height of the first electrode tab, and the height of the dense region accounts for 10% to 15% of the height of the first electrode tab.

11. The secondary battery according to claim 8, characterized in that, The number of stacked layers of the first electrode in the dense region is 15 to 45.

12. The secondary battery according to claim 1, characterized in that, Also includes: A heat-insulating adhesive layer is disposed between the body of the manifold and the first electrode tab, and the projection of the welding block along the height direction is located on the heat-insulating adhesive layer, the thermal conductivity of the heat-insulating adhesive layer being less than 0.05 W / (m·K).

13. The secondary battery according to claim 12, characterized in that, The width of the heat-insulating adhesive layer in the radial direction of the secondary battery is Da-1mm to Da+1mm, where Da represents the width of the welding block in the radial direction.

14. The secondary battery according to claim 1, characterized in that, The housing includes a sidewall surrounding the electrode assembly, one end of which forms the opening. The cover includes a recessed groove facing the manifold, the groove being located within the opening, and the outer wall of the groove facing and fitting against the sidewall of the housing. The welding block is welded between the groove and the body.

15. The secondary battery according to claim 14, characterized in that, The welding block is an annular ring extending along the edge of the manifold, and the minimum outer diameter of the welding block is the inner diameter of the side wall of the housing minus 2 × the thickness of the cover plate. The ratio of the inner diameter of the welding block to the outer diameter of the electrode assembly is greater than 0.

75.

16. A battery pack, characterized in that, The secondary battery includes any one of claims 1 to 15.

17. An electronic device, characterized in that, Includes the battery pack as described in claim 16.

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