Secondary battery, battery assembly, and electronic device

Abstract

To provide a secondary battery in which DCR (direct current resistance) is controlled and optimized to a relatively low value.SOLUTION: A secondary battery of the present invention includes a case, an electrode assembly, and a current collecting member. The electrode assembly is housed in the housing and includes a wound structure in which first and second electrode sheets and a separator are stacked and wound. An end portion of the first electrode sheet includes an uncoated metal thin piece region extending from the separator along a winding axis direction of the electrode assembly, and a part of the region is bent along a radial direction of the electrode assembly to form a bent surface region including a superimposed layer of the region. The current collecting member is welded to the curved surface region to form first and second welding marks. The second welding mark exceeds at least one end of the first welding mark along a radial direction of the electrode assembly. In the axial direction of the electrode assembly, the number of layers of the non-coated metal sheet area connected to the portion of the second welding mark exceeding the first welding mark in the radial direction of the electrode assembly is less than the number of layers of the non-coated metal sheet area connected to the first welding mark.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to the technical field of batteries, and more particularly to secondary batteries, battery assemblies, and electronic devices. [Background technology]

[0002] DCR (direct current resistance) is an important parameter of battery performance, and refers to the internal electrical resistance when direct current flows through the battery. Batteries generate heat during the charging and discharging process, and if the DCR is high, more energy may be lost as heat, which increases the battery temperature and may affect the battery's performance and lifespan. Sustained high temperatures accelerate battery degradation, reduce cycle life, and increase the risk of thermal runaway. A high DCR also reduces the battery's charge and discharge rate.

[0003] Therefore, DCR has a significant impact on the efficiency, lifespan, safety, and cost-effectiveness of a battery, and how to control and optimize DCR to a relatively low value in battery design and manufacturing processes is a technical challenge that needs to be overcome in this field. Summary of the Invention [Problem to be solved by the invention]

[0004] In view of the above-mentioned drawbacks of the prior art, the present invention provides a secondary battery that improves the technical problem that high DCR affects the performance and life of the battery. [Means for solving the problem]

[0005] To achieve the above and other objects, the present invention provides a secondary battery. The secondary battery includes a housing, an electrode assembly, and a current collecting member. The electrode assembly is housed in the housing. The electrode assembly includes a wound structure formed by stacking and winding a first electrode sheet, a second electrode sheet, and a separator. An end of the first electrode sheet includes an uncoated metal flake region extending from the separator along the winding axis direction of the electrode assembly. A portion of the uncoated metal flake region is bent along the radial direction of the electrode assembly to form a curved surface region including an overlapping layer of the uncoated metal flake region. The current collecting member is welded to the bent surface region to form a first weld mark and a second weld mark. The second weld mark extends beyond at least one end of the first weld mark along the radial direction of the electrode assembly. Among these, in the portion of the second weld mark that extends along the axial direction of the electrode assembly beyond the first weld mark along the radial direction of the electrode assembly, the number of layers of the uncoated metal flake area that it connects to is less than the number of layers of the uncoated metal flake area that the first weld mark connects to.

[0006] In the above-mentioned technical solution, when the current collecting member and the curved surface region are welded together, a first weld mark and a second weld mark are formed, and the second weld mark extends beyond at least one end of the first weld mark along the radial direction of the secondary battery, extending the length of the weld mark along the radial direction of the electrode assembly and increasing the number of turns of the curved surface region connected to the current collecting member through the weld mark, thereby achieving the effect of reducing DCR. Furthermore, by controlling the number of layers of the uncoated metal foil region connected by the second weld mark to be less than the number of layers of the uncoated metal foil region connected by the first weld mark, it is possible to reduce the risk of the uncoated metal foil region being burned through by the second weld mark and causing the separator to burn.

[0007] In one example of the secondary battery of the present invention, the uncoated metal flake region is bent toward the winding center, and the bent surface region includes, in order from the outer periphery to the inner periphery of the electrode assembly, a region where the number of layers gradually increases, a region where the number of layers is stable, and a region where the number of layers gradually decreases. The first welding marks are distributed in the stable region of the number of layers, and at least a portion of the second welding marks are distributed in the region where the number of layers gradually increases and / or the region where the number of layers gradually decreases.

[0008] In the above-described technical solution, the uncoated metal flake region is bent toward the winding center, and the number of layers gradually increases from the outer periphery to the inner periphery of the electrode assembly until it stabilizes, and then gradually decreases again, thereby forming a gradually increasing layer number region, a stable layer number region, and a gradually decreasing layer number region. The number of layers in the stable layer number region is the greatest and relatively uniform. The distribution of the first weld mark in the stable layer number region connects with the uncoated metal flake region with a relatively large number of layers and reduces burn-through, thereby reducing DCR and improving conductivity, safety, energy density, and other battery performance benefits. The distribution of at least a portion of the second weld mark in the gradually increasing layer number region and / or the gradually decreasing layer number region can further increase the number of turns of the connecting uncoated metal flake region, further reducing DCR and improving conductivity, safety, energy density, and other battery performance benefits.

[0009] In one example of the secondary battery of the present invention, the current collecting member includes a plurality of sets of weld marks. The sets of weld marks surround the center of the current collecting member at intervals. Each set of weld marks includes a plurality of weld marks, and each set of weld marks includes at least one first weld mark and at least one second weld mark. The distance k between adjacent weld marks along the circumferential direction of the electrode assembly is in the range of 2 mm ≥ k ≥ 0.5 mm.

[0010] In the above-mentioned technical solution, the arrangement of multiple sets of weld marks surrounding the center of the current collecting member at intervals contributes to evenly distributing the current passing through the uncoated metal foil area, further enhancing the performance of the secondary battery and increasing the weld strength. Each set of weld marks includes a first weld mark and a second weld mark, which can increase the number of turns of the uncoated metal foil area connected to each set of weld marks. The provision of multiple sets of weld marks increases the weld area with the uncoated metal foil area, improving the stability of the electrical resistance of the secondary battery. The setting of 2 mm ≥ k ≥ 0.5 mm allows the weld marks in each set of weld marks to be relatively concentrated, leaving space for a pressure relief hole.

[0011] In one example of the secondary battery of the present invention, the number of sets of welding marks is g, where g≧3.

[0012] In the above technical solution, there are three or more sets of welding marks, and the arrangement of the sets of welding marks surrounding the center of the current collecting member at intervals is advantageous for uniform current flow between the electrode assembly and the current collecting member, and can also shorten the path length of the current delivered by the electrode assembly. In addition, the sets of welding marks and the uncoated metal flake regions have a relatively large welding area, which ensures that the secondary battery has good electrical resistance stability.

[0013] In one example of the secondary battery of the present invention, the number of the first welding marks is p, and p≧2×g.

[0014] In the above-mentioned technical solution, the first welding marks are located in a stable layer number region, and the number of layers of the connecting uncoated metal foil region is relatively large. Each welding mark group has two or more first welding marks, which has a significant effect on reducing the DCR of the secondary battery.

[0015] In one example of the secondary battery of the present invention, the number of the second welding marks is q, where q≦p.

[0016] In the above-mentioned technical solution, when at least a portion of the second welding marks are distributed in the region where the number of layers gradually increases and / or the region where the number of layers gradually decreases, the effect of increasing the number of turns in the uncoated metal foil region connected to the current collecting member can be achieved. Therefore, when the number of second welding marks is q and is set within the range of q≦p, the effect of increasing the number of turns in the uncoated metal foil region connected to the current collecting member can be achieved without significantly affecting production efficiency.

[0017] In one example of the secondary battery of the present invention, the sum of the welding areas of the first welding mark and the second welding mark is s, and s≧20 mm 2 is.

[0018] In the above-mentioned technical solution, the welding area refers to the area of ​​the projection of the first welding mark itself and the second welding mark itself along the axial direction of the electrode assembly. When the welding area is within the above range, the secondary battery has favorable electrical resistance stability and is conducive to enhancing the current-carrying capacity.

[0019] In one example of the secondary battery of the present invention, the number of layers in the stable region of the number of layers is greater than 10, the number of layers in the uncoated metal flake region to which the first weld mark is connected ranges from 10 to 18, and the number of layers in the uncoated metal flake region to which the portion of the second weld mark that extends beyond the first weld mark along the radial direction of the electrode assembly is connected ranges from 8 to 12.

[0020] In the above-mentioned technical solution, the number of layers in the uncoated metal flake region connected by the first weld mark along the height direction of the electrode assembly is set to 10 to 18 layers, which can already achieve the effect of reducing DCR and improving the connection stability between the current collecting member and the electrode assembly. Considering that the second weld mark includes a portion located in the region where the number of layers gradually increases and / or decreases, setting the number of layers in the uncoated metal flake region connected by the second weld mark to 8 to 12 layers can reduce the possibility of burn-through in the region where the number of layers gradually increases and / or the region where the number of layers gradually decreases of the second weld mark.

[0021] In one embodiment of the secondary battery of the present invention, the shape of the first welding mark and the shape of the second welding mark are both curved, and the radius of curvature of any one point on the curve is 1 mm or more.

[0022] In the above-mentioned technical solution, the curvature radius of any point on the curve is 1 mm or more, which can ensure that the welding time at any point in the welding process is uniform, increase the uniformity of the number of layers in the uncoated metal flake area where any point on the first weld mark and the second weld mark connect, smooth the transition at the corner of the welding track, and reduce the risk of welding heat concentrating at a certain point, causing the uncoated metal flake area to melt and burn, resulting in separator damage.

[0023] In one example of the secondary battery of the present invention, the curve is formed by connecting a plurality of semicircles.

[0024] In the above-mentioned technical solution, the radius of curvature of each point on the curve of the shape tends to be equal, which further contributes to the uniformity of the number of layers of the uncoated metal flake area where any one point of the first weld mark and the second weld mark connects, and also further reduces the risk of the uncoated metal flake area burning through and causing the separator to burn.

[0025] In one example of the secondary battery of the present invention, along the radial direction of the electrode assembly, the radial length of the second weld mark located in the region where the number of layers gradually increases is longer than the radial length of the second weld mark located in the region where the number of layers gradually decreases.

[0026] In the above-mentioned technical solution, the length of a single circumference in the region where the number of layers gradually increases is longer than the length of a single circumference in the region where the number of layers gradually decreases. Therefore, when the second weld mark increases the number of connecting turns in the region where the number of layers gradually increases and the region where the number of layers gradually decreases, the former has a more significant effect of reducing DCR than the latter. Therefore, when the radial length of the second weld mark located in the region where the number of layers gradually increases is longer than the radial length of the second weld mark located in the region where the number of layers gradually decreases, a better effect of reducing DCR can be achieved.

[0027] In one example of the secondary battery of the present invention, the distance along the radial direction of the electrode assembly from the position of the second weld mark farthest from the winding axis of the electrode assembly to the edge of the curved surface region closest to the outer periphery of the electrode assembly is longer than 1 mm.

[0028] Since the number of layers in the uncoated metal flake area decreases as the electrode assembly approaches the outer periphery, the above-mentioned technical solution configuration can reduce the risk of the second weld mark burning through the uncoated metal flake area at the outer periphery of the electrode assembly, the separator burning, and the active material destruction.

[0029] In one example of the secondary battery of the present invention, the uncoated metal flake region includes a first cut segment close to the winding axis of the electrode assembly, a second cut segment close to the outer periphery of the electrode assembly, and an uncut segment located between the first cut segment and the second cut segment. Along the axial direction of the electrode assembly, the heights of the first cut segment and the second cut segment are both shorter than the uncut segment. In the winding direction of the electrode assembly, the length of the uncut segment is f, the total length of the uncoated metal flake region is a, and the ratio of f to a is in the range of 75%≦f / a≦90%.

[0030] In the above-described technical solution, the provision of the first cut segment can alleviate the problem of interference occurring near the winding axis when the uncoated metal flake region is bent. The provision of the second cut segment can alleviate the problem of protrusions formed toward the outer periphery of the electrode assembly when the uncoated metal flake region is bent, which can affect insertion into the housing. In this technical solution, the uncut segment occupies a relatively large proportion of the total length of the uncoated metal flake region, making the width of the annular region formed in the stack number stabilization region relatively large, which helps increase the allowable length of the first weld mark. This achieves the effect of increasing the number of turns of the connected uncoated metal flake region, thereby reducing DCR and improving battery performance by increasing conductivity, safety, and energy density.

[0031] In one example of the secondary battery of the present invention, the proportion of the number of wound turns in the stack number stable region to the total number of wound turns of the electrode assembly along the radial direction of the electrode assembly is m, and m≧40%.

[0032] In the above-mentioned technical solution, when the value of m is within the above-mentioned range, the width of the annular region formed in the stack number stable region is relatively large when the height of the uncoated metal flake region remains unchanged, which is beneficial for increasing the allowable length of the first weld mark, thereby achieving the effect of increasing the number of turns of the connected uncoated metal flake region, thereby achieving the effect of improving the conductivity, safety, energy density, etc., and improving battery performance.

[0033] In one example of the secondary battery of the present invention, along the radial direction of the electrode assembly, the first cut segment is wound to form a first annular region, and the second cut segment is wound to form a second annular region, and the width of the first annular region is wider than the width of the second annular region.

[0034] In the above-mentioned technical solution, the larger the diameter of the uncoated metal flake region located on the periphery, the longer the periphery and the greater the contribution to reducing electrical resistance. In this configuration, the width of the second annular region is reduced, and the uncoated metal flake region is closer to the periphery, which favorably reduces the effect of reducing electrical resistance.

[0035] In one example of the secondary battery of the present invention, the electrode assembly is wound to form a central wound hole, and the uncoated metal flake region is bent in a direction toward the central wound hole and extends to the central wound hole, and at least a portion of the central wound hole is blocked by the bent surface region.

[0036] In the above technical solution, since the length of the first cut segment is reduced, the uncoated metal flake region bent toward the winding central hole can cover the first annular region, protecting the separator in the first annular region and preventing it from being eroded when electrolyte is injected. Furthermore, although the uncoated metal flake region extends into the winding central hole, at least a portion of the central hole is blocked, the portion extending toward the winding central hole tends to be inclined downward, which can provide a liquid guide function.

[0037] In one example of the secondary battery of the present invention, the secondary battery is a cylindrical battery.

[0038] Among the above technical solutions, the cylindrical battery has the advantages of high energy density, long cycle life, good safety and so on.

[0039] The present invention further provides a battery assembly, which includes any one of the above-described examples of the secondary battery.

[0040] The present invention further provides an electronic device, which includes the battery assembly described above. [Effects of the Invention]

[0041] In the secondary battery of the present invention, a first weld mark and a second weld mark are formed when welding to the curved surface region of the current collecting member, and the second weld mark extends beyond at least one end of the first weld mark along the radial direction of the secondary battery, extending the length of the weld mark along the radial direction of the electrode assembly and increasing the number of turns of the curved surface region connected by welding to the current collecting member, thereby achieving the effect of reducing DCR. Furthermore, the number of layers of the uncoated metal flake region welded by the second weld mark is controlled to be fewer than the number of layers of the uncoated metal flake region welded by the first weld mark, thereby reducing the risk of the uncoated metal flake region being burned through by the second weld mark and causing the separator to burn. [Brief explanation of the drawings]

[0042] In order to more clearly describe the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the accompanying drawings that need to be used in the description of the embodiments or the prior art. The drawings described below are only some embodiments of the present invention, and it is obvious that those skilled in the art can obtain other embodiments based on these drawings without expending creative efforts.

[0043] [Figure 1] 1 is a structural diagram of one embodiment of a secondary battery of the present invention. [Figure 2] 1 is a structural diagram of an electrode assembly in one embodiment of the secondary battery of the present invention. [Figure 3]1 is a cross-sectional view of an electrode assembly in one embodiment of a secondary battery of the present invention. [Figure 4] 2 is a structural diagram of an uncoated metal foil region of an electrode assembly in one embodiment of a secondary battery of the present invention; FIG. [Figure 5] 1 is a structural diagram of an electrode assembly and a current collecting member in one embodiment of a secondary battery of the present invention. [Figure 6] 4 is a structural diagram of an electrode assembly and a current collecting member in another embodiment of the secondary battery of the present invention. FIG. [Figure 7] 4 is a structural diagram of an electrode assembly and a current collecting member in yet another embodiment of the secondary battery of the present invention. FIG. [Figure 8] 1 is a cross-sectional view of an electrode assembly in one embodiment of a secondary battery of the present invention when the electrode assembly is not bent in an uncoated metal flake region. [Figure 9] 1 is a structural diagram of a secondary battery according to an embodiment of the present invention when a first electrode sheet is not wound up. [Figure 10] 2 is a structural diagram of a secondary battery according to an embodiment of the present invention when the second electrode sheet is not wound up. FIG. [Figure 11] 1 is a schematic diagram of one embodiment of a battery assembly of the present invention. [Figure 12] 1 is a schematic diagram of one embodiment of an electronic device of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0044] The following describes how the present invention is implemented through specific embodiments. Those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention may be implemented or applied in other different specific embodiments. Various changes and modifications may be made to the details of this specification based on different perspectives and applications without departing from the spirit of the present invention. The following embodiments and their features may be combined with each other unless inconsistent. It should also be understood that the terms used in the embodiments of the present invention do not limit the scope of protection of the present invention but are intended to describe specific embodiments. Test methods without specifying specific conditions in the following embodiments are usually based on general conditions or conditions recommended by manufacturers.

[0045] When an embodiment provides a numerical range, it should be understood that the two endpoints of each numerical range and any numerical value between the two endpoints can be selected unless otherwise specified in the present invention. Unless otherwise defined, all technical and scientific terms used in the present invention are consistent with the understanding of the prior art by those skilled in the art and the description of the present invention. The present invention can also be achieved by combining any methods, equipment, and materials in the prior art that are similar or equivalent to the methods, equipment, and materials described in the embodiments of the present invention.

[0046] The terms "upper," "lower," "left," "right," "middle," and "one" used in this specification are used for the convenience of explanation and do not limit the scope of the present invention. Changing or adjusting the relative relationships between these terms is also considered to be within the scope of the present invention, provided that the technical content is not substantially changed.

[0047] A secondary battery includes a housing and an electrode assembly. The electrode assembly is housed in the housing. The electrode assembly is the component where the electrochemical reaction in the secondary battery occurs. One or more electrode assemblies may be contained within the housing.

[0048] An electrode assembly is typically formed by winding or stacking a positive electrode sheet and a negative electrode sheet, with a separator typically provided between the positive and negative electrode sheets. The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer. The positive electrode active material layer is coated on the surface of the positive electrode current collector. The positive electrode current collector includes a coated area where the positive electrode active material is coated and an uncoated metal flake area where the positive electrode active material is not coated. The uncoated metal flake area forms the positive electrode tab of the electrode assembly after winding. The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer. The negative electrode active material layer is coated on the surface of the negative electrode current collector. The negative electrode current collector includes a coated area where the negative electrode active material is coated and an uncoated metal flake area where the negative electrode active material is not coated. The uncoated metal flake area forms the negative electrode tab of the electrode assembly after winding. Taking a lithium-ion secondary battery as an example, the positive electrode current collector may be made of aluminum, the positive electrode active material layer may include a positive electrode active material, which may be lithium cobalt oxide, lithium iron phosphate, ternary lithium, or lithium manganese oxide, etc. The negative electrode current collector may be made of copper, and the negative electrode active material layer may include a negative electrode active material, which may be carbon or silicon, etc. The main substrate of the separator may be PP or PE, etc. To provide the cell with protective and insulating functions, the exterior of the cell may be covered with an insulating film, which may be composed of PP, PE, PET, PVC, or other polymer materials.

[0049] In conventional secondary batteries, the uncoated metal flake region bends toward the winding center, and the bent surface region includes, from the outer periphery to the inner periphery of the electrode assembly, a region where the number of layers gradually increases, a region where the number of layers is stable, and a region where the number of layers gradually decreases. The inventors discovered that welding in the region where the number of layers is stable allows for a relatively large number of layers to be welded and reduces burn-through, but the problem of excessively high DCR is commonly present.

[0050] In view of this, the present invention provides a technical solution that extends the length of the weld mark along the radial direction of the electrode assembly in the radial direction of the secondary battery, increases the number of turns of the uncoated metal flake area welded to the current collecting member, and thereby reduces the effect of DCR. Furthermore, by controlling the number of layers of the uncoated metal flake area to be welded by the weld mark, the risk of the uncoated metal flake area being burned through and the separator being burned is reduced.

[0051] 1 to 12, the present invention provides a secondary battery 100. The secondary battery 100 includes a housing 110, an electrode assembly 120, a current collecting member 130, a terminal 150, and a cap plate 160.

[0052] Referring to FIG. 1 , the housing 110 includes 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 may be achieved by various methods, such as integral stamping, integral casting, or split welding, as long as a stable sealing and electrical connection can be formed. The shape of the enclosure by the side wall 112 is not limited and may be cylindrical, prismatic, or any other closed loop shape that matches the end wall. In one embodiment, the outer edge of the end wall 111 is circular, and the side wall 112 is cylindrical and surrounds the outer edge of the end wall 111. A circular opening 113 is formed at one end of the side wall 112 opposite the end wall 111. A cavity is formed within the housing 110, surrounded by the end wall 111 and the side wall 112, to accommodate the electrode assembly 120, electrolyte, and other components required for the battery. Specifically, the diameter size of the housing 110 may be determined based on the specific size of the electrode assembly 120, and may be, for example, 18 mm, 21 mm, 46 mm, etc. The material of the housing 110 may be a variety of materials, such as copper, iron, aluminum, steel, aluminum alloy, etc. To prevent the housing 110 from rusting during long-term use, the surface of the housing 110 may be plated with a layer of an anti-rust material, such as metallic nickel.

[0053] 1 to 3, an electrode assembly 120 is housed in a housing 110. The electrode assembly 120 is a component where an electrochemical reaction occurs in a secondary battery 100. One or more electrode assemblies 120 may be contained within the housing 110. The electrode assembly 120 includes a wound structure formed by stacking and winding a first electrode sheet 122, a second electrode sheet 123, and a separator 125. The long side end of the first electrode sheet 122 includes an uncoated metal flake region 124 extending from the separator 125 along the winding axis direction of the electrode assembly 120. A portion of the uncoated metal flake region 124 is bent along the radial direction of the electrode assembly 120 to form a bent surface region 121 including a superposed layer of the uncoated metal flake regions 124. The polarities of the first electrode sheet 122 and the second electrode sheet 123 are opposite. For example, the first electrode sheet 122 may be a positive electrode sheet, and the second electrode sheet 123 may be a negative electrode sheet. In this embodiment, the first electrode sheet 122 is a negative electrode sheet, and the second electrode sheet 123 is a positive electrode sheet. Specifically, the positive electrode sheet includes a positive electrode current collector 1231 and a positive electrode active material layer. The positive electrode active material layer is coated on the surface of the positive electrode current collector 1231. The positive electrode current collector 1231 includes a second coated region 1231 coated with the active material and an uncoated metal foil region 124 where no active material is coated. The uncoated metal foil region 124 forms the positive electrode tab of the electrode assembly 120 after being wound. The negative electrode sheet includes a negative electrode current collector 1221 and a negative electrode active material layer. The negative electrode active material layer is coated on the surface of the negative electrode current collector 1221. The negative electrode current collector 1221 includes a first coated region coated with the active material and an uncoated metal foil region 124 where no active material is coated. The uncoated metal foil region 124 forms the negative electrode tab of the electrode assembly 120 after being wound.

[0054] Referring to FIG. 1 , the current collecting member 130 includes a first current collecting member 131 electrically connected to the first electrode sheet 122 and a second current collecting member 132 electrically connected to the second electrode sheet 123. The materials of the first current collecting member 131 and the second current collecting member 132 are selected according to the polarity of the electrode sheets to be connected. For example, when the second current collecting member 132 is connected to a positive electrode sheet, aluminum metal may be selected for the second current collecting member 132. In this case, the first current collecting member 131 is connected to a negative electrode sheet, and copper metal may be selected for the material. When the second current collecting member 132 is connected to a negative electrode sheet, copper metal may be selected for the second current collecting member 132. In this case, the first current collecting member 131 is connected to a positive electrode sheet, and aluminum metal may be selected for the material of the first current collecting member 131. There are no limitations on the shape and structure of the second current collecting member 132 and the first current collecting member 131, and any shape and structure that can achieve a stable and reliable electrical connection is suitable.

[0055] 5 to 7 , the current collecting member 130 is welded to the curved surface region 121. The welding method may be, but is not limited to, ultrasonic welding, resistance welding, laser welding, or the like. In this embodiment, laser welding is used, and weld marks are formed during the welding process. The weld marks are formed by heating and subsequent cooling and can symbolically represent the welding path of the current collecting member 130 and the curved surface region 121, the number of layers connected to the uncoated metal foil region 124, and the like. In this embodiment, the welding forms a first weld mark 141 and a second weld mark 142. The second weld mark 142 extends radially through the electrode assembly 120 beyond at least one end of the first weld mark 141. The radial direction here is not limited to the radial direction within a cylinder. For example, in a prism with a polygonal cross section, the direction from the outer periphery of the winding toward the center of the winding axis can also be referred to as the radial direction. The shapes of the first weld mark 141 and the second weld mark 142 are not limited and may be straight lines, curves (wavy lines, arc lines, sinusoidal lines, etc.), polygonal lines, or other irregular shapes. The relative positions of the first weld mark 141 and the second weld mark 142 may take many forms, and are not limited thereto, as long as the second weld mark 142 has a portion that extends beyond one or both ends of the first weld mark 141 along the radial direction of the electrode assembly 120. This configuration extends the length of the weld mark along the radial direction of the electrode assembly 120 and increases the number of turns of the curved surface region 121 to which the current collecting member 130 is connected by welding, thereby achieving the effect of reducing the DCR.

[0056] 5 to 7 , considering that the number of layers of the uncoated metal flake region 124 in the curved surface region 121 where the second weld mark 142 extends beyond the first weld mark 141 is smaller than the number of layers of the uncoated metal flake region 134 in the region where the first weld mark 141 is present, it is preferable that the number of layers of the uncoated metal flake region 142 connected to the portion of the second weld mark 142 extending beyond the first weld mark 141 along the radial direction of the electrode assembly 120 be smaller than the number of layers of the uncoated metal flake region 124 connected to the first weld mark 141 along the axial direction of the electrode assembly 120. This configuration reduces the risk of the uncoated metal flake region 124 being burned through by the second weld mark 142, resulting in separator burnout. In actual operation, the number of layers of the uncoated metal flake region 124 connected to the weld mark may be adjusted by adjusting the magnitude of the welding power. Specifically, the higher the welding power, the greater the number of layers in the uncoated metal flake region 124 connected by the weld mark. The number of layers in the uncoated metal flake region 142 connected by the first weld mark 141 or the second weld mark 142 can be measured by first performing CT on the electrode assembly 120 or by taking a cross section along the axial direction of the electrode assembly 120 to observe the number of layers in the uncoated metal flake region 124 connected by the first weld mark 141 or the second weld mark 142. It should be noted that during welding, there is a gradual increase in the laser power at the start of welding, and the number of layers in the uncoated metal flake region 124 connected by the corresponding weld mark also gradually increases. Similarly, there is a gradual decrease in the laser power at the end of welding, and the number of layers in the uncoated metal flake region 124 connected by the corresponding weld mark also gradually decreases. For this reason, the above-mentioned welding start portion and welding end portion cannot be used to compare the number of layers in the uncoated metal flake area 124 connected to the first welding mark 141 and the number of layers in the uncoated metal flake area 124 connected to the second welding mark 142, but rather the number of layers in the uncoated metal flake area 124 connected to the middle portion of the first welding mark 141 and the middle portion of the second welding mark 142 is compared.

[0057] It should be noted that the above technical solutions can be applied to both the positive and negative electrode sheets to achieve a uniform DCR reduction effect, regardless of whether the first electrode sheet 122 is a positive electrode sheet or a negative electrode sheet. In another embodiment, the above technical solutions can be applied to both the positive electrode sheet and the negative electrode sheet to achieve a more preferable DCR reduction effect.

[0058] 1 and 2 , the terminal 150 penetrates the end wall 111 and is insulated from the end wall 111. The structure of the terminal 150 may be any suitable type capable of penetrating the end wall 111 and electrically connecting with the first electrode sheet 122 or the second electrode sheet 123. For example, the cross section may be circular, square, prismatic, or have a specially shaped profile capable of achieving stable electrical conduction. One end of the terminal 150 facing the electrode assembly 120 penetrates the end wall 111 and is electrically connected directly or indirectly to the uncoated metal foil region 124. For example, the terminal 150 may be electrically connected indirectly to the first electrode sheet 122 via the first current collecting member 131 or to the second electrode sheet 123 via the second current collecting member 132. The other end of the terminal 150 opposite the electrode assembly 120 is exposed to the outside of the housing 110 to form a corresponding electrode. The electrical characteristics of the terminal 150 may be positive or negative. For example, in one embodiment, the terminal 150 is electrically connected to the first electrode sheet 122, the polarity of the first electrode sheet 122 being positive, the terminal 150 being a positive electrode, and a corresponding negative electrode being formed in the housing 110. In another embodiment, the polarity of the first electrode sheet 122 being negative, the terminal 150 being a negative electrode, and a corresponding positive electrode being formed in the housing 110. A terminal 150 mounting hole is formed in the end wall 111, and the terminal 150 is mounted through the terminal 150 mounting hole in a sealed and insulated manner. This type of housing 110 structure can improve mounting efficiency and is easier to assemble and seal than a housing 110 with openings 113 on both ends. The terminal 150 is made of a conductive metal material. The material of the terminal 150 may be aluminum. If the material of the terminal 150 is aluminum, riveting can be easily performed. In this embodiment, the terminal 150 is made of aluminum and has a positive polarity. The housing 110, corresponding to the terminal 150, is made of low-carbon steel and forms a negative polarity. The terminal 150 and the housing 110 are electrically insulated. Electrical insulation between the terminal 150 and the end wall of the housing 110 may be achieved in various ways. For example, insulation may be achieved by placing an insulating washer between the terminal 150 and the end wall 111. Alternatively, insulation may be achieved by forming an insulating coating layer on a portion of the terminal 150.Alternatively, several of the above methods may be applied in combination.

[0059] Referring to FIG. 1 , a cap plate 160 is attached to seal the opening 113. The outer edge shape of the cap plate 160 corresponds to the shape of the opening 113 and connects with the sidewall 112 to seal the opening 113. In a specific embodiment, a convex portion protruding into the housing 110 is provided on the periphery of the cap plate 160. A first depression is provided on the side of the convex portion opposite the electrode assembly 120. The orthogonal shape of the first depression is not limited and may be a ring, a square, or other irregular shape. The convex portion includes a first sidewall 112 that coincides with the inner wall of the housing 110. The first sidewall 112 coincides with the sidewall 112 closest to the opening 113. The protrusion is used to guide the assembly of the cap plate 160 with the opening 113 and to align the side wall 112 of the housing 110 with the cap plate 160, allowing for quick positioning along the circumferential direction between the cap plate 160 and the opening 113, thereby improving the efficiency of welding and the radial positioning accuracy of the welding.

[0060] 2 to 4, in one example of a secondary battery 100 of the present invention, the uncoated metal foil region 124 is bent toward the winding center. This structure creates a change in the number of layers from the outer periphery to the inner periphery of the electrode assembly 120, gradually increasing until it stabilizes and then gradually decreasing again. Therefore, the curved surface region 121 includes, from the outer periphery to the inner periphery of the electrode assembly 120, a region 1211 of gradually increasing number of layers, a region 1212 of stable number of layers, and a region 1213 of gradually decreasing number of layers. Specifically, referring to FIG. 4, the region 1211 of gradually increasing number of layers is the region that is covered by the uncoated metal foil region 124 located at the outermost side of the electrode assembly 120 after being bent. The region 1213 of gradually decreasing number of layers is the region that is covered by the uncoated metal foil region 124 closest to the winding center after being bent. The layer number stable region 1212 is a region between the layer number gradually increasing region 1211 and the layer number gradually decreasing region 1213. The first welding mark 141 is distributed in the layer number stable region 1212. Because the number of layers in the layer number stable region 1212 is the largest and relatively uniform, the distribution of the first welding mark 141 in the layer number stable region 1212 achieves connection of the uncoated metal flake region 124 with a relatively large number of layers and reduces burn-through, thereby reducing DCR and improving conductivity, safety, energy density, and other battery performance. At least a portion of the second welding mark 142 is distributed in the layer number gradually increasing region 1211 and / or the layer number gradually decreasing region 1213. In some embodiments, the second welding mark 142 is distributed in the layer number gradually increasing region 1211 and the layer number stable region 1212. In another embodiment, the second welding marks 142 are distributed in the layer count gradually increasing region 1213 and the layer count stable region 1212. In yet another embodiment, the second welding marks 142 are distributed in the layer count gradually increasing region 1211, the layer count stable region 1212, and the layer count gradually decreasing region 1213. In some other embodiments, the second welding marks 142 may be distributed only in the layer count gradually increasing region 1211 or only in the layer count gradually decreasing region 1213. All of the above configurations achieve the effect of further increasing the number of turns in the connecting uncoated metal foil region, further reducing the DCR and improving the conductivity, safety, energy density, etc., thereby improving battery performance.In this embodiment, the second welding marks 142 are distributed in a layer number gradually increasing region 1211, a layer number stable region 1212, and a layer number gradually decreasing region 1213, and a more preferable effect of lowering the DCR can be obtained.

[0061] 5 to 7 , in one example of a secondary battery 100 according to the present invention, the current collecting member 130 includes multiple sets of weld marks 140, such as two, three, four, five, six, or even more sets. The multiple sets of weld marks 140 are spaced apart and surround the center of the current collecting member 130. This arrangement is advantageous for evenly distributing the current passing through the uncoated metal foil regions 142, further enhancing the performance of the secondary battery 100 and increasing the welding strength. Each set of weld marks 140 includes at least one first weld mark 141 and at least one second weld mark 142. Each set of weld marks 140 can evenly increase the number of turns of the connecting uncoated metal foil regions 124 and can also increase the welding area with the uncoated metal foil regions 124, thereby improving the stability of the DCR of the secondary battery 100.

[0062] Furthermore, the distance between adjacent weld marks along the circumferential direction of the electrode assembly 120 is k, and k is in the range of 2 mm≧k≧0.5 mm. It should be noted that the distance between adjacent weld marks is not limited to a single fixed value because the shape and position of the weld marks are affected. The above range may be understood to mean that the distance between adjacent weld marks is not shorter than 0.5 mm, and the furthest distance does not exceed 2 mm. Setting k≦2 mm allows the weld marks in each weld mark set 140 to be relatively concentrated, thereby leaving space for pressure relief holes.

[0063] Referring to FIGS. 5 to 7 , in one example of the secondary battery 100 of the present invention, the number of welding mark sets 140 is g, where g is greater than or equal to 3. g may take values ​​of 3, 4, 5, 6, 8, 9, etc. In one embodiment, the number of welding mark sets 140 is three, as shown in FIG. 7 . In another embodiment, the number of welding mark sets 140 is four, as shown in FIGS. 5 and 6 . The number of welding mark sets 140 is three or more, and in combination with the arrangement of multiple welding mark sets 140 surrounding the center of the current collecting member 130 at intervals, this contributes to uniform current flow between the electrode assembly 120 and the current collecting member 130 and shortens the path length of the current drawn by the electrode assembly 120. Furthermore, by providing a relatively large welding area between the welding mark sets 140 and the uncoated metal flake region 124, the secondary battery 100 achieves favorable electrical resistance stability.

[0064] 5 to 7, in one example of the secondary battery 100 of the present invention, the number of first weld marks 141 is p, where p≧2×g. The first weld marks 141 are located in the stack number stable region 1212, and the number of layers of the uncoated metal flake regions 124 they connect to is relatively large. Having two or more first weld marks 141 in each weld mark set 140 has a significant effect on reducing the DCR of the secondary battery 100. In one embodiment, each weld mark set 140 has two first weld marks 141, as shown in FIGS. 5 and 6. Furthermore, the arrangement of the multiple first weld marks 141 is not limited thereto and may be parallel or may surround the winding axis.

[0065] 5 to 7 , in one example of the secondary battery 100 of the present invention, the number of second weld marks 142 is q, where q≦p. Distributing at least some of the second weld marks 142 in the lamination number increasing region 1211 and / or lamination number decreasing region 1213 can achieve the effect of increasing the number of turns of the uncoated metal foil region 124 connected to the current collecting member 130. Therefore, setting the number of second weld marks 142 to q within the range of q≦p, i.e., setting the number of second weld marks 142 in each weld mark set 140 to be less than or equal to the number of first weld marks 141, can achieve the effect of increasing the number of turns of the uncoated metal foil region 124 connected without significantly affecting production efficiency. In one embodiment, as shown in FIGS. 5 and 7 , the number of first weld marks 141 in each weld mark set 140 is two, and the number of second weld marks 142 is one. In another embodiment, as shown in FIG. 6, the number of first weld marks 141 in each set of weld marks 140 is two, and the number of second weld marks 142 is also two.

[0066] 5 to 7, in one example of the secondary battery 100 of the present invention, the sum of the welding areas of the first welding mark 141 and the second welding mark 142 is s, and s≧20 mm 2 It should be noted that the weld area refers to the area of ​​the first weld mark 141 itself and the second weld mark 142 itself projected along the axial direction of the electrode assembly 120, and when the weld area is within the above range, the secondary battery 100 has favorable electrical resistance stability and is conducive to increased current-carrying capacity.

[0067] 2 and 4 to 7 , in one example of the secondary battery 100 of the present invention, the number of layers in the stack number stable region 1212 is 10 or more, for example, 11, 12, 13, 14, 15, 16, 17, or even more. The number of layers in the uncoated metal foil region 124 connected to the first weld mark 141 is 10 to 18, for example, 10, 11, 12, 13, 14, 15, 16, 17, or 18. The number of layers in the uncoated metal foil region 124 connected to the second weld mark 142 is 8 to 12, for example, 8, 9, 10, 11, 12, 13, 14, or 15. It should be noted that the weld start and end points of the first and second weld marks 141 and 142 are not used to count the number of uncoated metal flake regions 124 where the first and second weld marks 141 and 142 connect. Setting the number of layers of the uncoated metal flake region 124 where the first weld mark 141 connects to 10 to 18 along the height direction of the electrode assembly 120 can reduce the DCR and improve the connection stability between the current collecting member 130 and the electrode assembly 120. Considering that the second weld mark 142 includes portions located in the layer count increasing region 1211 and / or the layer count decreasing region 1213, setting the number of layers of the uncoated metal flake region 124 where the second weld mark 142 connects to 8 to 12 can reduce the possibility of burn-through in the layer count increasing region 1211 and / or the layer count decreasing region 1213 of the second weld mark 142. In actual operation, the number of layers of the uncoated metal flake region 124 connected by the weld marks can be adjusted by adjusting the magnitude of the welding power. For example, in some embodiments, when laser welding is used, the welding power for welding the first weld mark 141 is 290 W, and the welding power for welding the second weld mark 142 is 270 W.

[0068] 5 to 7, in one example of a secondary battery 100 of the present invention, the shape of the first weld mark 141 and the shape of the second weld mark 142 are both curved, and the radius of curvature of any point on the curve is 1 mm or more. This structure can achieve a uniform welding time at any point in the welding process, improve the uniformity of the number of layers of the uncoated metal flake region 124 where any point on the first weld mark 141 and the second weld mark 142 connects, smooth the transition at the corners of the weld track, and reduce the risk of welding heat concentrating at a certain point, melting through the uncoated metal flake region 124 and burning the separator 125.

[0069] 5 and 6, in one example of the secondary battery 100 of the present invention, the curve is formed by connecting multiple semicircles. The radius of curvature at each point on the curve is equal, which further contributes to the uniformity of the number of layers of the uncoated metal flake region 124 where any one point of the first weld mark 141 and the second weld mark 142 connects. This also further reduces the risk of the uncoated metal flake region 124 melting through and burning the separator 125.

[0070] 5 and 6, in one example of the secondary battery 100 of the present invention, the radial length of the second weld mark 142 located in the region 1211 where the number of laminations gradually increases along the radial direction of the electrode assembly 120 is longer than the radial length of the second weld mark 142 located in the region 1213 where the number of laminations gradually decreases. The longer the radial length of the second weld mark 142, the more turns the second weld mark 142 can connect. Since the length of a single circumference in the region 1211 where the number of layers gradually increases is longer than the length of a single circumference in the region 1213 where the number of layers gradually decreases, if the second welding mark 142 increases the number of connection turns in the region 1211 where the number of layers gradually increases and the region 1213 where the number of layers decreases, the former has a more pronounced effect of reducing DCR than the latter. Therefore, if the radial length of the second welding mark 142 located in the region 1211 where the number of layers gradually increases is longer than the radial length of the second welding mark 142 located in the region 1213 where the number of layers gradually decreases, a better effect of reducing DCR can be obtained.

[0071] Referring to Figures 5 to 7, in one example of the secondary battery 100 of the present invention, taking into consideration that the number of layers of the uncoated metal flake region 124 decreases the closer to the outer periphery of the electrode assembly 120 in the radial direction of the electrode assembly 120, in order to reduce the risk of the uncoated metal flake region 124 burning through at the outer periphery of the electrode assembly 120 at the second weld mark 142, the separator burning, and the active material destruction, the distance from the position of the second weld mark 142 farthest from the winding axis of the electrode assembly 120 to the edge of the curved surface region 121 close to the outer periphery of the electrode assembly 120 is longer than 1 mm.

[0072] 4 and 8 to 10, in one example of a secondary battery 100 of the present invention, the uncoated metal foil region 124 includes a first cut segment 1241 near the winding axis of the electrode assembly 120, a second cut segment 1243 near the outer periphery of the electrode assembly 120, and an uncut segment 1242 located between the first cut segment 1241 and the second cut segment 1243. The heights of the first cut segment 1241 and the second cut segment 1243 along the axial direction of the electrode assembly 120 are all lower than the uncut segment 1242. The provision of the first cut segment 1241 can mitigate interference near the winding axis when the uncoated metal foil region 124 is bent. The provision of the second cut segment 1243 can alleviate the problem of protrusions being formed toward the outer periphery of the electrode assembly 120 when the uncoated metal foil region 124 is bent, which can affect insertion into a housing. Furthermore, along the winding direction of the electrode assembly 120, the length of the uncut segment 1242 is f, the total length of the uncoated metal flake region 124 is a, and the ratio of f to a is in the range of 75%≦f / a≦90%, such as 75%, 78%, 80%, 82%, 85%, 88%, or 90%. The uncut segment 1242 accounts for a relatively large proportion of the total length of the uncoated metal flake region 124, which increases the ring width of the annular region formed in the stack number stable region 1212 and helps increase the allowable length of the first weld mark 141. This allows for a larger number of turns of the connected uncoated metal flake region 124, thereby reducing the DCR and improving the conductivity, safety, energy density, and other aspects of battery performance.

[0073] It should be noted that regardless of whether the first electrode sheet 122 is a positive electrode sheet or a negative electrode sheet, the effect of reducing the DCR can be achieved in either case after adopting this technical solution. In another embodiment, the above technical solution can be adopted for both the positive electrode sheet and the negative electrode sheet to achieve a more preferable effect of reducing the DCR.

[0074] 5 to 8 , in one example of the secondary battery 100 of the present invention, the ratio of the number of winding turns in the stack number stable region 1212 to the total number of winding turns in the electrode assembly 120 along the radial direction of the electrode assembly 120 is m, where m is greater than or equal to 40%, such as 40%, 42%, 45%, 50%, 52%, 55%, 58%, or 60%. Similarly, when the height of the uncoated metal flake region 124 remains unchanged, having the value of m within the above-mentioned range increases the ring width of the annular region formed in the stack number stable region 1212, which is beneficial for increasing the allowable length of the first weld mark 141. This increases the number of winding turns in the connected uncoated metal flake region 124, thereby reducing electrical resistance and improving conductivity, safety, energy density, and other aspects of battery performance. 4, the number of turns of the stacking number stable region 1212 may be measured by first performing CT on the electrode assembly 120 or by taking a cross section along the axial direction of the electrode assembly 120 to observe the number of turns of the uncoated metal foil region 124 located within the stacking number stable region 1212. The total number of turns of the electrode assembly 120 corresponds to the number of turns of the uncoated metal foil region 124 in the entire bending surface region 121.

[0075] 4 and 8 to 10, in one example of the secondary battery 100 of the present invention, along the winding direction of the electrode assembly 120, the length of the first cut segment 1241 is b, the total length of the uncoated metal foil region 124 is a, and the ratio of b to a is in the range of 5%≦b / a<15%, such as 6%, 7%, 8%, 10%, 12%, 14%, or 15%, etc. This configuration reduces the length of the first cut segment 1241 and correspondingly increases the number of turns of the weldable uncoated metal foil region 124, thereby reducing electrical resistance and improving conductivity, safety, energy density, and other aspects of battery performance. When the ratio of "b" to "a" is relatively large, it means that the ratio of the uncoated metal flake region 124 of the second cut segment 1243 to the total length of the second cut segment 1243 is relatively small, which increases the outer diameter of the region of gradually increasing lamination count, further lengthens the single circumference, and more significantly reduces internal resistance. When the ratio of "b" to "a" is relatively small, the region of gradually decreasing lamination count 1213 is closer to the winding center, which provides better protection and current guiding functions for the separator 125.

[0076] 2 and 8, in one example of a secondary battery 100 of the present invention, the electrode assembly 120 is wound to form a central wound hole 126. The uncoated metal flake region 124 may be bent toward the central wound hole 126 to cover the first annular region 1244, protecting the separator 125 in the first annular region 1244 and preventing erosion during electrolyte injection. The uncoated metal flake region 124 extends into the central wound hole 126, which is at least partially blocked by the bent surface region 121. Although at least a portion of the central hole is blocked, the portion extending toward the central wound hole 126 tends to slope downward, which can provide a liquid guide.

[0077] Referring to FIGS. 8 to 10, in one example of the secondary battery 100 of the present invention, along the winding direction of the electrode assembly 120, the length of the second cut segment 1243 is c, the total length of the uncoated metal foil region 124 is a, and the range of the ratio of c to a is 0 < c / a < 15%, for example, it may be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 10%, 12%, 13%, 14%, or 15%, etc. The technical solution is to reduce the length of the second cut segment 1243, and similarly, increase the number of turns of the weldable uncoated metal foil region 124, thereby reducing the electrical resistance and achieving the effect of improving the battery performance by enhancing the conductivity, safety, energy density, etc. Also, when the ratio of c to a is relatively small, the outer diameter of the gradually increasing number of layers region range becomes larger, making the single perimeter longer, and the effect of reducing the internal resistance becomes more significant. When the ratio of c to a is relatively large, the gradually decreasing number of layers region is closer to the winding center and has a more preferable protective effect and current guiding effect of the separator 125.

[0078] In one example of the secondary battery 100 of the present invention, along the radial direction of the electrode assembly 120, the first cut segment 1241 is wound to form the first annular region 1244, the second cut segment is wound to form the second annular region 1245, and the width of the first annular region 1244 is wider than the width of the second annular region 1245. The larger the diameter of the uncoated metal foil region 124 located on the outer periphery, the longer the perimeter, and the greater the contribution to reducing the electrical resistance. This configuration preferably reduces the width of the second annular region 1245, bringing the uncoated metal foil region 124 closer to the outer periphery, thereby reducing the electrical resistance.

[0079] In one example of the secondary battery 100 of the present invention, the secondary battery 100 is a cylindrical battery. The cylindrical battery has advantages such as high energy density, long cycle life, and good safety.

[0080] As long as it is consistent with common knowledge in the art, any combination of the above-mentioned preferred conditions can be used to obtain each preferred embodiment of the present invention. Testing the technical solutions of the present invention against comparative examples and some preferred examples was carried out using the welding format shown in Figure 6 as an example, and the corresponding values ​​of each technical feature and the measured DCR values ​​were recorded as shown in Table 1, which were then analyzed in conjunction with Figures 8 to 10.

[0081] Table 1: Corresponding values ​​of each technical feature and measured DCR values

[0082] [Table 1] JPEG2026034383000003.jpg82160

[0083] It should be noted in Table 1 that the lengths of the first weld marks 141 on the first electrode sheet 122 and the first weld marks 141 on the second electrode sheet 123 in Example 4 are both 11 mm. The first weld marks 141 on the first electrode sheet 122 and the first weld marks 141 on the second electrode sheet 123 are both based on Example 3 and obtained by extending them by 1 mm into the layer number gradually decreasing region 1213. The lengths of the first weld marks 141 on the first electrode sheet 122 and the first weld marks 141 on the second electrode sheet 123 in Example 5 are both 11 mm, but the first weld marks 141 on the first electrode sheet 122 and the first weld marks 141 on the second electrode sheet 123 in Example 5 are both based on Example 3 and obtained by extending them by 1 mm into the layer number gradually increasing region 1211.

[0084] The following will describe the present technical solution in detail through comparative examples and some preferred embodiments in combination with Table 1.

[0085] Comparative Example

[0086] The secondary battery 100 is a cylindrical battery. In this cylindrical battery, the first electrode sheet 122 is the negative electrode sheet, and the second electrode sheet 123 is the positive electrode sheet. For ease of distinction, the total length of the first electrode sheet 122 is designated a1, the length of the first cut segment 1241 of the first electrode sheet 122 is designated b1, and the length of the second cut segment 1243 is designated c1. The total length of the second electrode sheet 123 is designated a2, the length of the first cut segment 1241 of the second electrode sheet 123 is designated b2, and the length of the second cut segment 1243 is designated c2. a1 is 5006 mm, b1 is 680 mm, and c1 is 565 mm. a2 is 4870 mm, b2 is 810 mm, and c2 is 565 mm. It should be noted that the tolerance range for the above length dimensions is ±5 mm, and the lengths listed in Table 1 and the tolerance values ​​for the above lengths are not shown. From the calculations, f1 is 3761mm, f1 / a1 is 75.1%, f2 is 3495mm, and f1 / a1 is 69.8%.

[0087] The number of sets 140 of welding marks formed on the first current collecting member 131 welded to the first electrode sheet 122 is g1, where g1 is 4. The number of first welding marks 141 in each set 140 of welding marks is p1, where p1 is 4, and no second welding marks 142 are formed. The welding power for each first welding mark 141 is 360 W, and the radial length of each first welding mark 141 is 10 mm. The number of sets 140 of welding marks formed on the second current collecting member 132 welded to the second electrode sheet 123 is g2, where g2 is 4. The number of first welding marks 141 in each set 140 of welding marks is p2, where p2 is 4, and no second welding marks 142 are formed. The welding power for each first welding mark 141 is 250 W, and the radial length of each first welding mark 141 is 10 mm.

[0088] The DCR value of the cylindrical battery is 2.25 mΩ under the conditions of SOC 50%, temperature 25°C, rest for 3 hours, and DC 10S.

[0089] Example 1

[0090] The difference between this example and the comparative example is that the welding power for the first weld mark 141 on the first current collecting member 131 is 390 W and the welding power for the first weld mark 141 on the second current collecting member 132 is 290 W, resulting in a DCR value of 2.14 mΩ. In this example, increasing the welding power also increases the number of layers of the uncoated metal flake region 124 that are welded, thereby achieving the effect of reducing the DCR.

[0091] Example 2

[0092] The difference between this example and the comparative example is that, among the sets of welding marks 140 formed on the first current collecting member 131 welded to the first electrode sheet 122, the number p1 of first welding marks 141 in each set of welding marks 140 is 5, and the DCR value at this time is 2.22 mΩ. In this example, the number of first welding marks 141 is increased, which increases the welding area and reduces the DCR.

[0093] Example 3

[0094] The difference between this example and Example 1 is that b1 is 400 mm, c1 is 280 mm, b2 is 500 mm, and c2 is 280 mm. It should be noted that the tolerance range for the above length dimensions is ±5 mm, and the lengths and the tolerance values ​​for the above lengths are not shown in Table 1. From calculations, f1 is 4326 mm, f1 / a1 is 86.4%, f2 is 4090 mm, and f1 / a1 is 84.0%, resulting in a DCR value of 2.06 mΩ. In this example, there is no burn damage to the separator 125. The annular region formed by the stack number stability region 1212 has a relatively wide ring width, which is beneficial for increasing the allowable length and effective length of the first weld mark 141. This increases the connection effect with the relatively large number of turns of the uncoated metal flake region 124, thereby reducing the DCR and improving the conductivity, safety, energy density, and other aspects of battery performance.

[0095] Example 4

[0096] The difference between this embodiment and Example 3 is that the radial length of the first weld mark 141 on the first current collecting member 131 welded to the first electrode sheet 121 is 11 mm. Specifically, the first weld mark 141 in Example 3 is extended by 1 mm into the lamination number tapering region 1213, so that the radial length of the first weld mark 141 on the second current collecting member 132 welded to the second electrode sheet 123 is 11 mm, resulting in a DCR value of 1.98 mΩ. This embodiment increases the allowable length of the first weld mark 141, thereby increasing the number of turns of the connected uncoated metal foil region 124, thereby achieving a lower DCR. However, the number of layers of the uncoated metal foil region 124 in the lamination number tapering region 1213 is relatively small, which can result in a situation where the separator 125 is burned.

[0097] Example 5

[0098] The difference between this example and Example 4 is that the first weld mark 141 on the first current collecting member 131 welded to the first electrode sheet 122 is based on the first weld mark 141 of Example 3 and extended 1 mm into the gradually increasing layer number region 1212, and the first weld mark 141 on the second current collecting member 132 welded to the second electrode sheet 123 is based on the first weld mark 141 of Example 3 and extended 1 mm into the gradually increasing layer number region 1212, resulting in a DCR value of 1.94 mΩ. This example verifies that when the same number of connection turns is added to the weld mark in the gradually increasing layer number region 1212 and the gradually decreasing layer number region 1213, the former has a more significant effect of reducing the DCR than the latter. Therefore, extending the length of the weld mark into the gradually increasing layer number region 1212 can achieve a more favorable DCR reduction effect. This example also involves a situation in which the separator 125 burns out.

[0099] Example 6

[0100] The difference between this embodiment and Example 3 is that, among the sets 140 of welding marks formed on the first current collecting member 131 welded to the first electrode sheet 122, the number p1 of first welding marks 141 in each set 140 of welding marks is 2, the number q1 of second welding marks 142 is 2, the radial length of each second welding mark 142 is 12 mm, and the welding power of each second welding mark 142 is 370 W, and the DCR value at this time is 2.01 mΩ. In this embodiment, the number of first welding marks 141 is reduced, second welding marks 142 are added, and the radial length of the second welding marks 142 is increased, thereby increasing the number of turns of the uncoated metal flake area 124 to be welded. At the same time, the welding power of the second welding marks 142 is reduced to 370 W, reducing the number of layers of the uncoated metal flake area 124 connected to the second welding marks 142, thereby achieving the effect of reducing the DCR value and at the same time reducing the situation in which the separator 125 is burned.

[0101] Example 7

[0102] The difference between this example and Example 6 is that the sets of weld marks 140 formed on the second current collecting member 132 welded to the second electrode sheet 123 were modified. Specifically, the number g2 of the sets of weld marks 140 was 4, the number p2 of the first weld marks 141 in each set of weld marks 140 was 2, the number q2 of the second weld marks 142 was 2, the radial length of each second weld mark 142 was 12 mm, the welding power of each second weld mark 142 was 270 W, and the DCR value at this time was 1.97 mΩ. In this example, the separator 125 was not burned. In addition to Example 6, this example adopts the above-mentioned technical solution on the second electrode sheet 123, reducing the number of first welding marks 141, adding second welding marks 142, and increasing the radial length of the second welding marks 142 to increase the number of turns of the uncoated metal foil area 124 to be welded, while reducing the welding power of the second welding marks 142 and reducing the number of layers of the uncoated metal foil area 124 connected by the second welding marks 142, thereby further reducing the DCR value and simultaneously reducing the risk of the separator 125 being burned.

[0103] Example 8

[0104] The difference between this example and Example 7 is that the welding power for the first weld marks 141 formed on the first current collecting member 131 welded to the first electrode sheet 122 is 420 W, and the welding power for the second weld marks 142 is 390 W, resulting in a DCR value of 1.95 mΩ. Compared to Example 7, this example uses higher welding power for the first weld marks 141 and the second weld marks 142, which increases the number of layers of the uncoated metal flake regions 124 that are welded, further reducing the DCR.

[0105] In one example of the secondary battery 100 of the present invention, the method for manufacturing the secondary battery 100 of the present invention includes the following steps.

[0106] Cutting of the uncoated metal foil region 124: After winding, the first cut segment 1241 close to the winding axis of the electrode assembly 120 and the second cut segment 1243 close to the outer periphery of the electrode assembly 120 are cut, and at the same time, an uncut segment 1242 located between the first cut segment 1241 and the second cut segment 1243 is formed.

[0107] The length of the uncut segment 1242 is f, the total length of the uncoated metal flake region 124 is a, and the ratio of f to a is preferably in the range of 75%≦f / a≦90%, such as 75%, 78%, 80%, 82%, 85%, 88%, or 90%. It should be noted that the above-mentioned methods are used to cut the uncoated metal flake region 124 of the first electrode sheet 122 and the uncoated metal flake region 124 of the second electrode sheet 123. Referring to Figures 9 and 10, a1 in Figure 9 and a2 in Figure 10 are different symbols for a in sheets of different polarities, which distinguish the polarities, and a1 and a2 both correspond to the range of 75%≦f / a≦90%. The uncut segment 1242 accounts for a relatively large proportion of the total length of the uncoated metal flake region 124, widening the width of the ring of the annular region formed by the stack number stable region 1212 and increasing the allowable length of the first weld mark 141, thereby increasing the effect of connecting with the relatively large number of turns of the uncoated metal flake region 124, thereby achieving the effect of reducing DCR and achieving the effect of improving battery performance by increasing conductivity, safety, energy density, etc.

[0108] Winding: The wound structure formed by stacking and winding the first electrode sheet 122, the second electrode sheet 123, and the separator 125 includes uncoated metal flake regions 124, where the long edge portions of the first electrode sheet 122 and the second electrode sheet 123 both extend from the separator 125 along the winding axis direction of the electrode assembly 120. A portion of the uncoated metal flake region 124 is folded along the radial direction of the electrode assembly 120 to form a curved surface region 121 including overlapping layers of the uncoated metal flake regions 124. The polarities of the first electrode sheet 122 and the second electrode sheet 123 are opposite. For example, the first electrode sheet 122 may be a positive electrode sheet, and the second electrode sheet 123 may be a negative electrode sheet. In this embodiment, the first electrode sheet 122 is a negative electrode sheet, and the second electrode sheet 123 is a positive electrode sheet.

[0109] Welding the current collecting member 130 to the electrode assembly 120: Specifically, welding the current collecting member 130 to the curved surface region 121. The current collecting member 130 includes a first current collecting member 131 welded to the curved surface region 121 formed on the first electrode sheet 122, and a second current collecting member 132 welded to the curved surface region 121 formed on the second electrode sheet 123.

[0110] The welding between the current collecting member 130 and the curved surface region 121 preferably forms two types of weld marks, including a first weld mark 141 and a second weld mark 142. The second weld mark 142 extends beyond at least one end of the first weld mark 141 along the radial direction of the electrode assembly 120. By using a lower welding power for the second weld mark 142 than for the first weld mark 141, the number of layers of the uncoated metal foil region 124 connected by the portion of the second weld mark 142 extending beyond the first weld mark 141 along the radial direction of the electrode assembly 120 is reduced compared to the number of layers of the uncoated metal foil region 124 connected by the first weld mark 141. Increasing the number of turns of the curved surface region 121 connected by welding to the current collecting member 130 reduces the DCR while also reducing the risk of the uncoated metal foil region 124 melting through the second weld mark 142 and burning the separator 125.

[0111] Insertion into the housing: The electrode assembly 120, which has been welded to the current collecting member 130, is installed into the housing 110 through the opening 113. The method of installing the electrode assembly 120 in this step is not limited, and may be, for example, installed manually or by a mechanical arm.

[0112] Attaching the positive and negative terminals.

[0113] Injection of Electrolyte: The method of injecting the electrolyte is not limited, and it may be through the opening 113, or through an injection hole provided in the end wall 111. In this embodiment, it is preferable to inject the electrolyte through the opening 113, and by eliminating the process of providing an injection hole in the end wall 111 and directly using the existing opening 113 for injection, the process can be simplified and costs can be reduced. The reduced length of the first cut segment 1241 shortens the distance from the gradually decreasing layer count region 1213 to the winding center, which acts as a flow guide for the injection of the electrolyte, improves the efficiency of the injection, and provides a certain level of protection for the separator 125.

[0114] Sealing the opening: The cap plate 160 is mounted over the opening 113 so as to seal it. There are several sealing methods available, and they are not limited to these. In this embodiment, the outer periphery of the housing 110 is first roll-pressed to form a roll groove recessed toward the center of the housing 110, thereby restricting the axial movement of the electrode assembly 120. Then, a mechanical seal technique is used to mount and seal the cap plate 160, thereby sealing the cap plate 160 over the opening 113 of the housing 110. The technology for this step is mature, low cost, and highly efficient.

[0115] Referring to FIG. 11 , the present invention further provides a battery assembly 10. The battery assembly 10 includes a secondary battery 100 according to any one of the above-described embodiments. In one embodiment of the battery assembly 10 of the present invention, the battery assembly 10 includes a case 101, a lid 102, and a plurality of secondary batteries 100. The plurality of secondary batteries 100 are arranged in the case 101 and connected in series or parallel to each other, or a combination of series and parallel. The lid 102 covers the case 101 to protect the plurality of secondary batteries 100. It should be noted that the battery assembly 10 may include, in addition to the secondary battery 100 of the present invention, a thermal management system, a circuit board, and other components of the battery assembly 10. The battery assembly 10 may be a battery module, a battery pack, an energy storage cabinet, or the like, each of which will not be described here.

[0116] Referring to FIG. 12 , the present invention further provides an electronic device 1. The electronic device 1 includes the above-described battery assembly 10 and an operating unit 11. The operating unit 11 is electrically connected to the battery assembly 10 to obtain power support. As an example, the electronic device 1 is a vehicle. The vehicle may be a fuel-powered vehicle, a gas-powered vehicle, or a new energy vehicle. The new energy vehicle may be, but is not limited to, a pure electric vehicle, a hybrid vehicle, or a range-extending vehicle. The operating unit 11 is a vehicle body, and the battery assembly 10 is installed at the bottom of the vehicle body and provides power support for running the vehicle or operating electrical components inside the vehicle. In other embodiments, the electronic device 1 may be a mobile phone, a portable device, a notebook computer, a boat, an airplane, an electric toy, an electric tool, or the like. Aircraft include airplanes, rockets, space shuttles, spacecraft, and the like. The operating unit 11 may be a unit that obtains electrical energy from the battery assembly 10 and performs a corresponding operation, such as a blade rotation unit of an electric fan or a dust collection unit of a vacuum cleaner. The electric toys include stationary or mobile electric toys, such as game consoles, electric toy cars, electric toy boats, electric toy airplanes, etc. The electric tools include metal cutting electric tools, grinding electric tools, assembly electric tools, and railway electric tools, such as electric drills, electric grinders, electric wrenches, electric screwdrivers, electric hammers, impact drills, concrete vibrators, electric planes, etc. The embodiments of the present invention are not particularly limited to the electronic device 1 described above.

[0117] In the secondary battery of the present invention, a first weld and a second weld are formed when the current collecting member is welded to the curved surface region. The second weld extends beyond at least one end of the first weld along the radial direction of the secondary battery, extending the length of the weld along the radial direction of the electrode assembly. This increases the number of turns of the curved surface region connected by welding to the current collecting member, thereby achieving a lower DCR. Furthermore, the number of layers of the uncoated metal foil region welded by the second weld is controlled to be fewer than the number of layers of the uncoated metal foil region welded by the first weld, thereby reducing the risk of the uncoated metal foil region being burned through by the second weld and causing separator burnout. Therefore, the present invention effectively overcomes several practical problems in the prior art, thereby providing high utility and practical significance. The above-described embodiments are illustrative of the principles and advantages of the present invention, and are not intended to limit the present invention. Those skilled in the art may modify or alter the above-described embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent changes or modifications made by those skilled in the art without departing from the spirit and technical idea disclosed in the present invention should still be protected by the claims of the present invention. [Industrial Applicability]

[0118] The secondary battery, battery assembly, and electronic device of the present invention are applicable to the field of battery technology. [Explanation of symbols]

[0119] 1:Electronic equipment 10:Battery assembly 11: Operating unit 101: Box body 102: Lid 100: Secondary battery 110: Cabinet 111: End wall 112: Side wall 113:Aperture 120: Electrode assembly 121: Bent surface area 1211: Area with gradually increasing number of layers 1212: Stable stacking region 1213: Layer count decreasing area 122: First electrode sheet 1221: Negative electrode current collector 1222: 1st application area 123: Second electrode sheet 1231: Positive electrode current collector 1232:Second application area 124: Uncoated metal flake area 1241: First cut segment 1242: Uncut segment 1243: Second cut segment 1244: First annular region 1245: Second annular region 125: Separator 126: Winding center hole 130: Current collecting member 131: First current collecting member 132: Second current collecting member 140: Weld marks 141: First welding mark 142: Second welding mark 150: Terminal 160: Cap plate

Claims

1. The housing and an electrode assembly housed in the housing and including a wound structure formed by stacking and winding a first electrode sheet, a second electrode sheet, and a separator, wherein an end of the first electrode sheet includes an uncoated metal flake region extending from the separator along a winding axis direction of the electrode assembly, and a portion of the uncoated metal flake region is folded along a radial direction of the electrode assembly to include a curved surface region including a superposed layer of the uncoated metal flake region; a current collecting member welded to the bent surface region to form a first weld mark and a second weld mark, the second weld mark extending beyond at least one end of the first weld mark along a radial direction of the electrode assembly; Including, In a portion of the second weld mark that extends beyond the first weld mark in a radial direction of the electrode assembly along the axial direction of the electrode assembly, the number of layers of the uncoated metal foil region that connects to the second weld mark is smaller than the number of layers of the uncoated metal foil region that connects to the first weld mark. characterized in that Secondary battery.

2. The uncoated metal flake region is bent toward the winding center, and the bent surface region includes, in order from the outer periphery to the inner periphery of the electrode assembly, a region where the number of layers gradually increases, a region where the number of layers is stable, and a region where the number of layers gradually decreases, and the first welding marks are distributed in the region where the number of layers is stable, and at least a portion of the second welding marks are distributed in the region where the number of layers gradually increases and / or the region where the number of layers gradually decreases. characterized in that The secondary battery according to claim 1 .

3. The current collecting member includes a plurality of sets of welding marks, the plurality of sets of welding marks surrounding the center of the current collecting member at intervals, each set of welding marks including a plurality of welding marks, and each set of welding marks including at least one of the first welding mark and at least one of the second welding mark, the distance between adjacent welding marks along the circumferential direction of the electrode assembly is k, and k is in the range of 2 mm≧k≧0.5 mm. characterized in that The secondary battery according to claim 2 .

4. The number of sets of the welding marks is g, and g≧3. characterized in that The secondary battery according to claim 3 .

5. The number of the first welding marks is p, and p≧2×g. characterized in that The secondary battery according to claim 4 .

6. The number of the second welding marks is q, and q≦p. characterized in that The secondary battery according to claim 5 .

7. The sum of the welding areas of the first welding mark and the second welding mark is s, and s≧20 mm ２ is characterized in that The secondary battery according to claim 1 .

8. The number of layers in the stable layer number region is greater than 10, the number of layers in the uncoated metal flake region connected to the first welding mark ranges from 10 to 18, and the number of layers in the uncoated metal flake region connected to the portion of the second welding mark that extends beyond the first welding mark along the radial direction of the electrode assembly ranges from 8 to 12. characterized in that The secondary battery according to claim 2 .

9. The shape of the first welding mark and the shape of the second welding mark are both curved, and the radius of curvature of any one point on the curve is 1 mm or more. characterized in that The secondary battery according to claim 8.

10. The curve is formed by connecting a plurality of semicircles. characterized in that The secondary battery according to claim 9.

11. Along the radial direction of the electrode assembly, the radial length of the second weld mark located in the region where the number of laminations gradually increases is longer than the radial length of the second weld mark located in the region where the number of laminations gradually decreases. characterized in that The secondary battery according to claim 2 .

12. a distance from a position of the second weld mark farthest from a winding axis of the electrode assembly to an edge of the curved surface region close to an outer periphery of the electrode assembly in a radial direction of the electrode assembly that is longer than 1 mm; characterized in that The secondary battery according to claim 1 .

13. The uncoated metal foil region includes a first cut segment close to the winding axis of the electrode assembly, a second cut segment close to the outer periphery of the electrode assembly, and an uncut segment located between the first cut segment and the second cut segment, and the heights of the first cut segment and the second cut segment along the axial direction of the electrode assembly are both lower than the uncut segment, the length of the uncut segment in the winding direction of the electrode assembly is f, the total length of the uncoated metal foil region is a, and the range of the ratio of f to a is 75%≦f / a≦90%. characterized in that The secondary battery according to claim 2 .

14. Along the radial direction of the electrode assembly, the ratio of the number of winding turns in the stack number stable region to the total number of winding turns of the electrode assembly is m, and m≧40%. characterized in that The secondary battery according to claim 13.

15. Along a radial direction of the electrode assembly, the first cut segment is wound to form a first annular region, and the second cut segment is wound to form a second annular region, the width of the first annular region being wider than the width of the second annular region. characterized in that The secondary battery according to claim 13.

16. The electrode assembly is wound to form a central hole, and the uncoated metal flake region is bent toward the central hole and extends to the central hole, and at least a portion of the central hole is blocked by the bent surface region. characterized in that The secondary battery according to claim 13.

17. The secondary battery is a cylindrical battery. characterized in that The secondary battery according to claim 1 .

18. The secondary battery according to any one of claims 1 to 17 is included. characterized in that battery assembly.

19. The battery assembly according to claim 18 characterized in that electronic equipment.

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