Secondary batteries, battery packs, and electronic devices

Abstract

The present invention provides a secondary battery, battery pack, and electronic device that can avoid excessive DC resistance and also prevent warping of the outermost negative electrode tab. [Solution] The secondary battery of the present invention includes an electrode assembly, the electrode assembly includes a negative electrode sheet, a positive electrode sheet, and a separator placed between the negative electrode sheet and the positive electrode sheet, the maximum circumference of the electrode assembly is C, and in the winding direction of the electrode assembly, the first length of the uncoated portion of the third negative electrode is greater than 0.5C and less than 4C, or the second length of the uncoated portion of the third positive electrode is greater than C and less than 4C.

Description

Technical Field

[0001] The present invention relates to secondary batteries, battery packs, and electronic devices.

Background Art

[0002] In the field of new energy power batteries, the application of secondary batteries has become increasingly widespread. For example, secondary batteries (such as lithium-ion batteries) can be applied to electronic devices such as vehicles, power storage, mobile phones, tablet computers, wearable devices, mobile power supplies, digital products, power tools, power devices, and power storage devices. One type of secondary battery is a cylindrical battery, which includes an outer shell and an electrode assembly. The electrode assembly includes a positive electrode sheet, a first separator, a negative electrode sheet, and a second separator. After being sequentially laminated with each other, they are wound to form an electrode assembly, and then encapsulated in the outer shell. However, existing secondary batteries still need further improvement in some aspects.

Summary of the Invention

Problems to be Solved by the Invention

[0003] In view of the problems existing in the related art, an object of the present invention is to provide secondary batteries, battery packs, and electronic devices.

Means for Solving the Problems

[0004] Embodiments of the present invention provide a secondary battery comprising an electrode assembly including a negative electrode sheet, a positive electrode sheet, and a separator placed between the negative electrode sheet and the positive electrode sheet, wherein the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer, along the height direction of the electrode assembly, the positive electrode current collector includes a positive electrode coated portion covered by the positive electrode active material layer and a positive electrode uncoated portion not covered by the positive electrode active material layer, the negative electrode current collector includes a negative electrode coated portion covered by the negative electrode active material layer and a negative electrode uncoated portion not covered by the negative electrode active material layer, the direction from the positive electrode coated portion to the positive electrode uncoated portion is the first direction, and along the winding direction of the electrode assembly, the positive electrode uncoated portion sequentially includes a first positive electrode uncoated portion, a second positive electrode uncoated portion, and a third positive electrode uncoated portion. The uncoated negative electrode portion sequentially includes a first uncoated negative electrode portion, a second uncoated negative electrode portion, and a third uncoated negative electrode portion. Along the first direction, the second uncoated positive electrode portion includes a positive electrode tab and a positive electrode connector connected between the positive electrode tab and the coated positive electrode portion, while neither the first uncoated positive electrode portion nor the third uncoated positive electrode portion includes a positive electrode tab. Along the second direction opposite to the first direction, the second uncoated negative electrode portion includes a negative electrode tab and a negative electrode connector connected between the negative electrode tab and the coated negative electrode portion, while neither the first uncoated negative electrode portion nor the third uncoated negative electrode portion includes a negative electrode tab. In this configuration, if the maximum circumference of the electrode assembly is C, then in the winding direction of the electrode assembly, the first length of the third uncoated negative electrode portion is greater than 0.5C and less than 4C, or the second length of the third uncoated positive electrode portion is greater than C and less than 4C.

[0005] In the above-described technical means, by making the first length range of the third uncoated negative electrode portion of the negative electrode sheet greater than 0.5C and less than 4C, it is possible to avoid excessive DC resistance and also to avoid warping of the outermost negative electrode tab.

[0006] In some embodiments, the second length is greater than the first length.

[0007] In some embodiments, the first length is greater than 0.8C and less than 4C, and the second length is greater than 1.5C and less than 4C.

[0008] In some embodiments, the first length is greater than 0.5C and less than 3C, and the second length is greater than C and less than 3C.

[0009] In some embodiments, the third length range of the uncoated portion of the first negative electrode in the winding direction of the electrode assembly is 300 mm to 500 mm.

[0010] In some embodiments, the fourth length range of the uncoated portion of the first positive electrode in the winding direction of the electrode assembly is 400 mm to 600 mm.

[0011] In some embodiments, the secondary battery further comprises a case used to house the electrode assembly. The case includes a circumferential side wall and an end wall connected to one end of the circumferential side wall, the other end of which has an opening, and a crimped portion projecting inward is provided on the circumferential side wall adjacent to the opening, the electrode assembly being located between the end wall and the crimped portion, in which the negative electrode tab faces the opening and is connected to the case via a negative electrode current collector plate, and the welding position between the negative electrode current collector plate and the circumferential side wall is located on the side of the crimped portion facing the electrode assembly.

[0012] In some embodiments, the negative electrode tab is a plurality of segments from which a portion of the uncoated negative electrode area is divided, and one end of each negative electrode tab away from the negative electrode connection is bent toward the winding center hole of the electrode assembly, and the orthogonal projection of the negative electrode tab in the first direction is located within a region limited by the outer circumferential surface of the electrode assembly.

[0013] Embodiments of the present invention further provide a battery pack including any of the secondary batteries described above.

[0014] Embodiments of the present invention further provide an electronic device including the battery pack described above. [Effects of the Invention]

[0015] The advantageous technical effects of the present invention are as follows: By making the first length range of the third uncoated negative electrode portion where no tab protrudes at the winding end of the negative electrode sheet greater than 0.5C and less than 4C, or by making the second length range of the third uncoated positive electrode portion where no tab protrudes at the winding end of the positive electrode sheet greater than C and less than 4C, it is possible to avoid excessive DC resistance and also to avoid warping of the outermost tab. [Brief explanation of the drawing]

[0016] To more clearly illustrate embodiments of the present invention or technical means in the prior art, the accompanying drawings that may be used in the description of embodiments or the prior art are briefly introduced below. Clearly, the accompanying drawings in the following description are some embodiments of the present invention, and a person of the ordinary skill in the art may obtain other accompanying drawings based on these without any creative effort.

[0017] [Figure 1] This is a schematic diagram showing an example of the present invention where the electronic device is in a vehicle. [Figure 2] This is a three-dimensional diagram of a secondary battery according to an embodiment of the present invention. [Figure 3] This is a cross-sectional view of a secondary battery according to an embodiment of the present invention. [Figure 4] This is a cross-sectional view of an electrode assembly according to an embodiment of the present invention. [Figure 5] This is a schematic three-dimensional view of an electrode assembly according to an embodiment of the present invention. [Figure 6] This is a schematic plan view of the unfolded state of the negative electrode sheet according to an embodiment of the present invention. [Figure 7] This is a schematic plan view of the positive electrode sheet in its unfolded state according to an embodiment of the present invention. [Modes for carrying out the invention]

[0018] To better understand the spirit of the embodiments of the present invention, some preferred embodiments of the present invention will be described below.

[0019] Embodiments of the present invention will be described in detail below. Throughout the specification of the present invention, components having the same or similar configurations and components having the same or similar functions are represented by similar reference numerals. The embodiments regarding the drawings described herein are of an illustrative nature and are used to provide a basic understanding of the present invention. The embodiments of the present invention should not be construed as limitations of the present invention.

[0020] As used herein, the terms "substantially", "essentially", "substantively" and "about" are used to describe and account for minor variations. When used in conjunction with an event or situation, these terms may refer to instances where the event or situation occurs exactly and instances where the event or situation occurs very approximately.

[0021] In this specification, unless specifically specified or limited otherwise, relative terms such as "central", "vertical", "lateral", "front", "rear", "right", "left", "inner", "outer", "lower", "higher", "horizontal", "vertical", "higher", "lower", "upper", "lower", "top", "bottom" and their derivative terms (such as "horizontally", "downwardly", "upwardly", etc.) should be construed as referring to the directions described in the discussion or shown in the drawings. These relative terms are used only for convenience of description and do not require the present invention to be constructed or operated in a specific direction.

[0022] For convenience of description, "first", "second", "third", etc. may be used in the text to distinguish different components of one figure or a series of figures. "First", "second", "third", etc. are not intended to describe corresponding components. Also, where there is no contradiction, the embodiments and features in the embodiments of the present invention can be combined with each other. Hereinafter, the present invention will be described in detail with reference to the drawings and in combination with the embodiments.

[0023] The present invention provides an electronic device 1000, and for convenience of explanation, the following embodiments will be described using a vehicle as an example of the electronic device 1000. Referring to Figure 1, a battery pack 1002 is installed inside the vehicle, and the battery pack 1002 may be installed at the bottom, front, or rear of the vehicle body 1001. The battery pack 1002 may be used to power the vehicle, for example, the battery pack 1002 may be used as the operating power source for the vehicle. The operating part of the electronic device 1000 is electrically connected to the battery pack 1002 to receive power support. The vehicle may be a fuel-powered vehicle, a gas vehicle, or a new energy vehicle, and the new energy vehicle may be, but is not limited to, a pure electric vehicle, a hybrid vehicle, or a range extender vehicle. The operating part is the vehicle body, and the battery pack 1002 is installed at the bottom of the vehicle body and provides power support for the vehicle's movement or the operation of in-vehicle electrical components. However, in some other embodiments, the electronic device 1000 may be a mobile phone, a portable device, a laptop computer, a ship, a spacecraft, an electric toy, or a power tool. Spacecraft include airplanes, rockets, space shuttles, and other spacecraft. The operating part may be a unit component that obtains power from the battery pack 1002 and performs the corresponding task, such as a fan blade rotation unit or a vacuum cleaner suction unit. Electric toys include stationary or mobile electric toys, such as game consoles, electric car toys, electric boat toys, and electric airplane toys. Power tools include metal cutting power tools, polishing power tools, assembly power tools, and railway power tools, such as electric drills, electric grinders, electric wrenches, electric screwdrivers, electric hammers, impact electric drills, concrete vibrators, and electric planers. The embodiments of the present invention do not impose any special limitations on the electronic device 1000 described above.

[0024] The battery pack 1002 may include multiple secondary batteries (such as cylindrical batteries 100). In the following description, the secondary batteries will be described using cylindrical batteries as an example. Figure 2 shows a three-dimensional view of cylindrical battery 100 according to an embodiment of the present invention, and Figure 3 shows a cross-sectional view of cylindrical battery 100 according to an embodiment of the present invention.

[0025] As shown in Figures 2 and 3, the cylindrical battery 100 includes a case 200, which includes a circumferential side wall 109 and an end wall 111 connected to one end of the circumferential side wall 109. An opening 205 is provided at the other end of the circumferential side wall 109 opposite the end wall 111, and a cover plate 220 is fitted over the opening 205 of the case 200. The cover plate 220 may be used together with the case 200 to seal the electrode assembly 120 and the electrolyte. The material of the case 200 may be any of the many usable materials, such as copper, iron, aluminum, steel, or aluminum alloy. The case 200 may be cylindrical, defining the housing cavity, and the electrode assembly 120 is housed within the housing cavity. The outer diameter of the case 200 may be determined by the specific diameter of the electrode assembly 120; for example, the outer diameter of the case 200 may be 18 mm, 21 mm, 46 mm, etc. In some embodiments, the cylindrical battery 100 may be a 4680 cylindrical battery (outer diameter 46 mm, height 80 mm), or a 4695 cylindrical battery (outer diameter 46 mm, height 95 mm), or a 46120 cylindrical battery (outer diameter 46 mm, height 120 mm).

[0026] The electrode assembly 120 may be formed by sequentially stacking and winding a positive electrode sheet, a negative electrode sheet, and a separator placed between the positive electrode sheet and the negative electrode sheet (see Figure 4 for further details). The wound electrode assembly 120 has a winding center hole 120c.

[0027] A crimped portion 113 (also called a rolling groove) protruding inward is formed on the circumferential side wall of the case 200 adjacent to the opening 205. The electrode assembly 120 is installed between the end wall 111 and the crimped portion 113, and the crimped portion 113 may restrict the movement of the electrode assembly 120 in the height direction Hd and the opposite direction between the end wall 111 and the crimped portion 113. The end of the circumferential side wall 109 of the case 200 on the opening 205 side may be configured as a crimped portion 32, which extends inward along the radial direction of the case 200. The crimped portion 32 and the crimped portion 113 are spaced apart in the height direction Hd, and both the crimped portion 113 and the crimped portion 32 may clamp the cover plate 220. The cover plate 220 is electrically insulated from the case 200.

[0028] The negative electrode tab of the electrode assembly 120 faces the opening 205 and is electrically connected to the case 200 via a negative electrode current collector plate 201 located between the cover plate 220 and the electrode assembly 120, which may cause the case 200 to be negatively charged. The negative electrode current collector plate 201 may be welded to the case 200 by laser welding. Specifically, the welding position between the negative electrode current collector plate 201 and the case 200 may be located on the side of the crimped portion 113 facing the electrode assembly 120.

[0029] The cylindrical battery 100 may further include a terminal 160 that penetrates the end wall 111 and is insulated from the end wall 111. The terminal 160 may be electrically connected to the positive electrode tab of the electrode assembly 120 through a positive electrode current collector plate 202 located between the end wall 111 and the electrode assembly 120, thereby positively charging the terminal 160. In some embodiments, the terminal 160 may be welded to the positive electrode current collector plate 202 by laser through welding.

[0030] Figure 4 shows cross-sectional views of electrode assemblies 120 according to several embodiments. As shown in Figure 4, the electrode assembly 120 is mainly formed by winding a negative electrode sheet 10 and a positive electrode sheet 20, with a separator 122 provided between the negative electrode sheet 10 and the positive electrode sheet 20. The electrolyte may be filled between the negative electrode sheet 10, the positive electrode sheet 20, and the separator 122.

[0031] The negative electrode sheet 10 may include a negative electrode current collector 18 and a negative electrode active material layer 16, wherein a portion of the opposing surfaces of the negative electrode current collector 18 along its thickness direction is covered by the negative electrode active material layer 16. In the height direction Hd, the negative electrode current collector 18 includes a negative electrode coated portion 18a covered by the negative electrode active material layer 16 and a negative electrode uncoated portion 18b not covered by the negative electrode active material layer 16. The positive electrode sheet 20 includes a positive electrode current collector 28 and a positive electrode active material layer 26, wherein at least a portion of the opposing surfaces of the positive electrode current collector 28 along its thickness direction is covered by the positive electrode active material layer 26. In the height direction Hd, the positive electrode current collector 28 includes a positive electrode coated portion 28a covered by the positive electrode active material layer 26 and a positive electrode uncoated portion 28b not covered by the positive electrode active material layer 26. The uncoated negative electrode portion 18b of the negative electrode current collector 18 and the uncoated positive electrode portion 28b of the positive electrode current collector 28 are located at opposite ends in the height direction Hd of the electrode assembly 120. The uncoated negative electrode portion 18b of the negative electrode current collector 18 may be used to form a negative electrode tab. The uncoated positive electrode portion 28b of the positive electrode current collector 28 may be used to form a positive electrode tab. The direction from the coated positive electrode portion 28a to the uncoated positive electrode portion 28b is the first direction D1, and the opposite direction is the D2 direction.

[0032] Figure 5 is a schematic three-dimensional diagram of an electrode assembly according to an embodiment of the present invention. As shown in Figures 4 and 5, the uncoated negative electrode portion 18b and the uncoated positive electrode portion 28b may be bent toward the winding center hole 120c of the electrode assembly 120. The bent uncoated negative electrode portion 18b and the uncoated positive electrode portion 28b may be stacked on top of each other. The stacked uncoated negative electrode portion 18b may be welded to the negative electrode current collector plate 201 and further electrically connected to the case 200 (see Figure 3). The stacked uncoated positive electrode portion 28b may be welded to the positive electrode current collector plate 202 and further electrically connected to the terminal 160 (see Figure 3). By bending the uncoated negative electrode portion 18b and the uncoated positive electrode portion 28b, the space occupied by the uncoated negative electrode portion 18b and the uncoated positive electrode portion 28b can be reduced, thereby improving the energy density of the battery.

[0033] Taking a lithium-ion battery as an example, the material of the negative electrode current collector 18 may be copper, for example, and the negative electrode current collector 18 is copper foil. The negative electrode active material of the negative electrode active material layer 16 may be carbon or silicon, etc. The material of the positive electrode current collector 28 may be aluminum, for example. The positive electrode active material of the positive electrode active material layer 26 may be lithium cobalt oxide, lithium iron phosphate, ternary lithium, or lithium manganese oxide, etc. The material of the separator 122 may be PP (polypropylene) or PE (polyethylene), etc.

[0034] To minimize the possibility of contact between the negative electrode sheet 10 and the positive electrode sheet 20, the electrode assembly 120 may further include an insulating layer 40, which covers at least a portion of the uncoated positive electrode portion 28b of the positive electrode current collector 28. The insulating layer 40 may also be provided on both side surfaces of the positive electrode current collector 28. The insulating layer 40 can effectively prevent electrical contact between the negative electrode sheet 10 and the positive electrode sheet 20.

[0035] In some embodiments, the main composition of the insulating layer 40 is boehmite and PVDF (polyvinylidene difluoride). Boehmite accounts for 80% and PVDF accounts for 20%. In some embodiments, the insulating layer is a ceramic material layer. The thickness of the insulating layer 40 is 1.5 mm to 2.5 mm, and may be, for example, 1.5 mm, 1.7 mm, 2 mm, 2.1 mm, 2.3 mm, or 2.5 mm. By setting a thickness range for the insulating layer 40, it is possible to avoid the insulating layer 40 being too thin, thus preventing difficulty in obtaining the required electrical insulation and support strength. At the same time, it is possible to avoid the insulating layer 40 being too thick, thus preventing the curing time of the coated layer from becoming longer and the overall structure thickness from increasing.

[0036] In some embodiments, the insulating layer 40 includes a coloring agent, and the coloring action of the coloring agent allows for distinction between the front and back surfaces of the positive electrode sheet 20, and distinguishes between the surface density and other conditions of the front and back surfaces of the positive electrode sheet 20. However, the embodiment is not limited to this. The main component of the coloring agent may be bismuth vanadate, which exhibits a yellow color.

[0037] In an example of the cylindrical battery 100 of the present invention, the method for manufacturing the cylindrical battery 100 of the present invention includes the following steps. Winding: This is a winding structure formed by stacking and winding a negative electrode sheet 10, a separator 122, and a positive electrode sheet 20. The uncoated negative electrode portion 18b of the negative electrode current collector 18 of the negative electrode sheet 10 and the uncoated positive electrode portion 28b of the positive electrode current collector 28 of the positive electrode sheet 20 are bent in the radial direction of the electrode assembly 120. Welding of current collector plates and electrode assemblies: The negative electrode current collector plate 201 and the positive electrode current collector plate 202 are welded to the surface areas of the bent negative electrode uncoated portion 18b and the positive electrode uncoated portion 28b, respectively. Case insertion: The electrode assembly 120, with the negative electrode current collector plate 201 and the positive electrode current collector plate 202 welded together, is installed into the case 200 through the opening 205. The method of installing the electrode assembly 120 in this step is not limited and may be done by manual installation or by machine installation. Install terminal 160. Electrolyte injection: The method of electrolyte injection is not limited, and injection may be performed through the opening 205. In this embodiment, the electrolyte is injected through the opening 205, eliminating the step of creating an injection hole in the end wall 111, and allowing injection to be performed directly using the existing opening 205, thereby simplifying the process and reducing costs. Sealing: The lid plate 220 is sealed and mounted on the opening 205. There are various sealing methods, and this is not limited to them. In some embodiments, first, the outer circumference of the case 200 is rolled to form a crimped portion 113 that is recessed toward the center of the case 200, thereby restricting the movement of the electrode assembly 120 in the height direction Hd. Then, a mechanical sealing process is employed to crimp and seal the lid plate 220 to form a crimped portion 32, thereby sealing the lid plate 220 on the opening 205 of the case 200. This step is a mature process, low-cost, and highly efficient.

[0038] Figure 6 is a schematic plan view of the unfolded state of the negative electrode sheet 10 according to an embodiment of the present invention. As shown in Figures 5 and 6, a portion of the uncoated negative electrode portion 18b forms a plurality of negative electrode tabs 18b21, and the plurality of negative electrode tabs 18b21 are a plurality of sections obtained by dividing a portion of the uncoated negative electrode portion 18b, and one end of each negative electrode tab 18b21 away from the negative electrode active material layer 16 is bent toward the winding center hole 120c of the electrode assembly 120.

[0039] Specifically, as shown in Figure 6, along the winding direction Dj, the negative electrode sheet 10 starts winding from the winding start end 10b and ends at the winding end 10e. Along the winding direction Dj, the uncoated negative electrode portion 18b sequentially includes a first uncoated negative electrode portion 18b1, a second uncoated negative electrode portion 18b2, and a third uncoated negative electrode portion 18b3. Along the second direction D2, the second uncoated negative electrode portion 18b2 includes a plurality of negative electrode tabs 18b21 and a negative electrode connection portion 18b22 connected between the negative electrode tabs 18b21 and the negative electrode coated portion 18a. Neither the first uncoated negative electrode portion 18b1 nor the third uncoated negative electrode portion 18b3 includes negative electrode tabs 18b21. The first uncoated negative electrode portion 18b1 is connected to the winding start end 10b of the negative electrode sheet 10. The third uncoated negative electrode portion 18b3 is connected to the winding end end 10e of the negative electrode sheet 10. Multiple negative electrode tabs 18b21 are arranged along the winding direction Dj. Multiple negative electrode tabs 18b21 may be formed by cutting a portion of the uncoated negative electrode portion 18b. The negative electrode connection portion 18b22 is the uncut portion of the uncoated negative electrode portion 18b.

[0040] Let C be the maximum circumference (i.e., outer circumference) of the electrode assembly 120, where C = πd, and d is the outer diameter of the electrode assembly 120. In some embodiments, in the winding direction Dj of the electrode assembly 120, the first length La of the third negative electrode uncoated portion 18b3 is greater than 0.5C and less than 4C. That is, the negative electrode sheet 10 does not have a negative electrode tab 18b21 in the range from 0.5 turns to 4 turns from the end of the winding. If the first length La is too long, the DCR (DC resistance) of the battery will be excessive, and if the first length La is too short, warping may occur in the negative electrode tab 18b21 adjacent to the outermost winding end 10e, making processing difficult. By setting the range of the first length La to be greater than 0.5C and less than 4C, it is possible to avoid excessive DCR and also avoid warping in the outermost negative electrode tab.

[0041] Normally, when the negative electrode tab 18b21 bends, the bent portion may protrude radially away from the winding center hole 120c. By providing a tabless third negative electrode uncoated portion 18b3 having a first length La, the orthogonal projection of the negative electrode tab 18b21 in a first direction D1 is positioned within a region limited by the outer circumferential surface of the electrode assembly 120, that is, the negative electrode tab 18b21 does not bend and protrude radially beyond the outer circumferential surface of the electrode assembly 120 and exceed the diameter of the outer circumferential surface.

[0042] In some embodiments, in the winding direction Dj, the third length Lb of the first uncoated negative electrode portion 18b1 of the negative electrode sheet 10 is 300 mm to 500 mm. By setting the third length Lb of the first uncoated negative electrode portion 18b1, where no tab is installed at the winding start end 10b, to 300 mm to 500 mm, it is possible to prevent tabs from appearing in the internal turns close to the winding center hole 120c, thereby avoiding the tabs blocking the center hole and affecting battery safety. In some embodiments, the range of the diameter value of the winding center hole 120c is 4 mm to 7 mm.

[0043] Each negative electrode tab 18b21 may include a first side Ea and a second side Eb that are opposite each other in the winding direction Dj, as well as a third side Ec at the end away from the negative electrode connection portion 18b22 that connects the first side Ea and the second side Eb. The first side Ea and the second side Eb may be parallel to each other. The second side Eb is closer to the winding end 10e than the first side Ea, and since the first side Ea and the second side Eb are inclined toward the winding end 10e, the angle between the second side Eb and the third side Ec is acute. During the winding process of the negative electrode sheet 10, the first side Ea and the second side Eb of each negative electrode tab 18b21 are inclined toward the winding end 10e. This makes it easier to bend and flatten the negative electrode tab 18b21 toward the winding center hole 120c when winding the negative electrode sheet 10, effectively reducing the force required to bend the negative electrode tab 18b21. This prevents deformation of the electrode plate, reduces material shedding of the negative electrode active material layer 16 of the negative electrode sheet 10, and improves the yield rate of the electrode assembly 120.

[0044] Figure 7 is a schematic plan view of the unfolded state of the positive electrode sheet 20 according to an embodiment of the present invention. As shown in Figures 4 and 7, a portion of the uncoated positive electrode portion 28b forms a plurality of positive electrode tabs 28b21, and the plurality of positive electrode tabs 28b21 are a plurality of sections that divide a portion of the uncoated positive electrode portion 28b, and one end of each positive electrode tab 28b21 away from the positive electrode active material layer 26 is bent toward the winding center hole 120c of the electrode assembly 120.

[0045] Specifically, referring to Figure 7, along the winding direction Dj, the positive electrode sheet 20 begins winding from its winding start end 20b and ends at its winding end 20e. Along the winding direction Dj, the uncoated positive electrode portion 28b sequentially includes a first uncoated positive electrode portion 28b1, a second uncoated positive electrode portion 28b2, and a third uncoated positive electrode portion 28b3. Along the first direction D1, the second uncoated positive electrode portion 28b2 includes a plurality of positive electrode tabs 28b21 and a positive electrode connection portion 28b22 connected between the positive electrode tabs 28b21 and the positive electrode coated portion 28a. Neither the first uncoated positive electrode portion 28b1 nor the third uncoated positive electrode portion 28b3 includes any positive electrode tabs 28b21. The first uncoated positive electrode portion 28b1 is connected to the winding start end 20b of the positive electrode sheet 20. The third positive electrode uncoated portion 28b3 is connected to the winding end 20e of the positive electrode sheet 20.

[0046] In the winding direction Dj, the second length Lc of the third positive electrode uncoated portion 28b3 of the positive electrode sheet 20 is greater than C and less than 4C. If the second length Lc is too long, the DCR of the battery will be excessive, and if the second length Lc is too short, warping may occur in the positive electrode tab 28b21 adjacent to the outermost winding end 20e, making it difficult to process. By setting the range of the second length Lc to be greater than C and less than 4C, it is possible to avoid excessive DCR and also avoid warping in the outermost positive electrode tab.

[0047] Normally, when the positive electrode tab 28b21 bends, the bent portion may protrude radially away from the winding center hole 120c. By providing a tabless third positive electrode uncoated portion 28b3 having a second length Lc, the orthogonal projection of the positive electrode tab 28b21 in the second direction D2 is positioned within a region limited by the outer circumferential surface of the electrode assembly 120, that is, the positive electrode tab 28b21 does not bend and protrude radially beyond the outer circumferential surface of the electrode assembly 120 and exceed the diameter of the outer circumferential surface.

[0048] In some embodiments, in the winding direction Dj, the fourth length Ld of the first uncoated positive electrode portion 28b1 of the positive electrode sheet 20 is 400 mm to 600 mm, so that tabs do not protrude in the internal few turns near the winding center hole, thereby avoiding tabs blocking the center hole and affecting the safety of the battery.

[0049] As shown in Figures 6 and 7, in some embodiments, the second length Lc of the third uncoated positive electrode portion 28b3 of the positive electrode sheet 20 may be greater than the first length La of the third uncoated negative electrode portion 18b3 of the negative electrode sheet 10. For example, in a 46 series cylindrical battery with an outer diameter of 46 mm, the first length La is, for example, 140 mm and the second length Lc is, for example, 280 mm. Since the hardness of the positive electrode current collector 28 (e.g., aluminum) is usually greater than that of the negative electrode current collector 18 (e.g., copper), the positive electrode tab and negative electrode tab are formed by the positive electrode current collector 28 and the negative electrode current collector 18 and after bending, the greater hardness of the positive electrode current collector causes the outermost tab bending portion of the electrode assembly to exceed the maximum diameter of the outer surface of the electrode assembly, affecting the overall radial dimension of the electrode assembly and causing a case insertion failure of the electrode assembly. Therefore, by controlling the second length Lc of the tabless third positive electrode uncoated portion 28b3 of the positive electrode sheet 20 to be longer than the first length La of the third negative electrode uncoated portion 18b3 of the negative electrode sheet 10, it is possible to avoid the tab bending portion exceeding the maximum diameter of the outer surface of the electrode assembly, thereby preventing the electrode assembly from being inserted into the case.

[0050] In this embodiment, similar to the negative electrode tab, the first side Ed and the second side Ee of the positive electrode tab 28b21 are inclined toward the winding end 20e, and the angle between the second side Ee and the third side Ef of the positive electrode tab 28b21 is acute. During the winding process of the positive electrode sheet 20, the inclination of the first side Ed and the second side Ee of each positive electrode tab 28b21 toward the winding end 20e effectively reduces the force required to bend the positive electrode tab 28b21, thereby avoiding deformation of the electrode plate, reducing material shedding of the positive electrode active material layer 26, and improving the yield rate of the electrode assembly 120.

[0051] In some embodiments, for a 46 series cylindrical battery with an outer diameter of 46 mm, the first length La is greater than 0.8 C and less than 4 C, and the second length Lc is greater than 1.5 C and less than 4 C. In these embodiments, C = π × 46 mm. For the 46 series cylindrical battery, a first length La in the range of 0.8 C to 4 C and a second length Lc in the range of 1.5 C to 4 C can more effectively prevent the DCR of the 46 series cylindrical battery from becoming excessive, and prevent warping of the outermost tab.

[0052] In some embodiments, for a 21 series cylindrical battery with an outer diameter of 21 mm, the first length La is greater than 0.5 C and less than 3 C, and the second length Lc is greater than C and less than 3 C. In these embodiments, C = π × 21 mm. For the 21 series cylindrical battery, a first length La in the range of 0.5 C to 3 C and a second length Lc in the range of C to 3 C can more effectively prevent the DCR of the 21 series cylindrical battery from becoming excessive and prevent warping of the outermost tab.

[0053] The foregoing describes only preferred embodiments of the present invention and is not intended to limit it. The present invention may have various modifications and changes for those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection. [Industrial applicability]

[0054] This invention relates to a secondary battery, a battery pack, and an electronic device. [Explanation of Symbols]

[0055] 10 Negative electrode sheets 10b Starting end of winding 10e End of winding 16 Negative electrode active material layer 18 Negative electrode current collector 18a Negative electrode coating area 18b Negative electrode uncoated area 18b1 Uncoated area of ​​the first negative electrode 18b2 Uncoated area of ​​the second negative electrode 18b3 Third negative electrode uncoated area 18b21 Negative Electrode Tab 18b22 Negative electrode connection 20 Positive electrode sheets 20b Starting end of winding 20e End of winding 26 Cathode active material layer 28 Positive electrode current collector 28a Positive electrode coating area 28b Positive electrode uncoated area 28b1 Uncoated portion of the first positive electrode 28b2 Uncoated area of ​​the second positive electrode 28b3 Third positive electrode uncoated area 28b21 Positive Tab 28b22 Positive electrode connection 32 Crimping section 40 Insulating layer 100 cylindrical batteries 109 Peripheral wall 111 End wall 113 Crimping section 120 Electrode Assembly 120c winding center hole 122 Separator 160 terminals 200 cases 201 Negative electrode current collector plate 202 Positive electrode current collector plate 205 Aperture 220 Lid plate 1000 electronic devices 1001 Car body 1002 Battery Pack C Maximum circumference D1 1st direction D2 2nd direction Dj winding direction Ea, first side Eb, second side Ec, third side First side Ee, second side Ef, third side Hd Height direction La 1st length Lb Third length Lc 2nd length Ld 4th length

Claims

1. The electrode assembly includes a negative electrode sheet, a positive electrode sheet, and a separator placed between the negative electrode sheet and the positive electrode sheet. The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer, and along the height direction of the electrode assembly, the positive electrode current collector includes a positive electrode coated portion covered by the positive electrode active material layer and a positive electrode uncoated portion not covered by the positive electrode active material layer, the negative electrode current collector includes a negative electrode coated portion covered by the negative electrode active material layer and a negative electrode uncoated portion not covered by the negative electrode active material layer, and the direction from the positive electrode coated portion to the positive electrode uncoated portion is the first direction. Along the winding direction of the electrode assembly, the uncoated portion of the positive electrode sequentially includes a first uncoated portion of the positive electrode, a second uncoated portion of the positive electrode, and a third uncoated portion of the positive electrode, and the uncoated portion of the negative electrode sequentially includes a first uncoated portion of the negative electrode, a second uncoated portion of the negative electrode, and a third uncoated portion of the negative electrode. Along the first direction, the second uncoated positive electrode portion includes a positive electrode tab and a positive electrode connection portion connected between the positive electrode tab and the positive electrode coated portion, while neither the first uncoated positive electrode portion nor the third uncoated positive electrode portion includes the positive electrode tab. Along the second direction opposite to the first direction, the second uncoated negative electrode portion includes a negative electrode tab and a negative electrode connection portion connected between the negative electrode tab and the negative electrode coated portion, while neither the first uncoated negative electrode portion nor the third uncoated negative electrode portion includes the negative electrode tab. A secondary battery characterized in that, with C being the maximum circumference of the electrode assembly, the first length of the uncoated portion of the third negative electrode in the winding direction of the electrode assembly is greater than 0.5C and less than 4C, or the second length of the uncoated portion of the third positive electrode is greater than C and less than 4C.

2. The secondary battery according to claim 1, characterized in that the second length is greater than the first length.

3. The secondary battery according to claim 1, characterized in that the first length is greater than 0.8C and less than 4C, and the second length is greater than 1.5C and less than 4C.

4. The secondary battery according to claim 1, characterized in that the first length is greater than 0.5C and less than 3C, and the second length is greater than C and less than 3C.

5. The secondary battery according to claim 1, characterized in that, in the winding direction of the electrode assembly, the third length range of the uncoated portion of the first negative electrode is 300 mm to 500 mm.

6. The secondary battery according to claim 1, characterized in that, in the winding direction of the electrode assembly, the fourth length range of the uncoated portion of the first positive electrode is 400 mm to 600 mm.

7. The case further comprises a case used to house the electrode assembly, The case includes a circumferential wall and an end wall connected to one end of the circumferential wall, the other end of the circumferential wall having an opening, a crimped portion protruding inward is provided on the circumferential wall adjacent to the opening, and the electrode assembly is located between the end wall and the crimped portion. The secondary battery according to claim 1, characterized in that the negative electrode tab faces the opening and is connected to the case via a negative electrode current collector plate, and the welding position between the negative electrode current collector plate and the peripheral side wall is located on the side of the crimped portion facing the electrode assembly.

8. The negative electrode tab is a plurality of sections from which a portion of the uncoated portion of the negative electrode is divided, and one end of each negative electrode tab, away from the negative electrode connection portion, is bent toward the winding center hole of the electrode assembly. The secondary battery according to claim 1, characterized in that the orthographic projection of the negative electrode tab in the first direction is located within a region limited by the outer circumferential surface of the electrode assembly.

9. A battery pack characterized by including a secondary battery according to any one of claims 1 to 8.

10. An electronic device characterized by including the battery pack described in claim 9.

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