Secondary battery, battery pack, and electronic device

Abstract

The embodiment of the utility model provides a secondary battery, a battery pack and an electronic device, the secondary battery comprises an electrode assembly, the electrode assembly comprises a negative pole piece, a positive pole piece and a diaphragm arranged between the negative pole piece and the positive pole piece, and the maximum perimeter of the electrode assembly is C, the first length of the third negative electrode uncoated region is greater than 0.5 C and less than 4C, or the second length of the third positive electrode uncoated region is greater than C and less than 4C. According to the technical scheme, at least overlarge direct-current resistance can be avoided, and the negative electrode lug on the outermost ring can be prevented from tilting.

Description

Technical Field

[0001] This utility model relates to a secondary battery, a battery pack, and an electronic device. Background Technology

[0002] In the field of new energy power batteries, the application of rechargeable batteries is becoming increasingly widespread. For example, rechargeable batteries (such as lithium-ion batteries) can be used in electronic devices such as vehicles, energy storage, mobile phones, tablets, wearable devices, power banks, digital products, power tools, power units, and energy storage devices. One type of rechargeable battery is the cylindrical battery, which includes a casing and an electrode assembly. The electrode assembly includes a positive electrode, a first separator, a negative electrode, and a second separator, which are stacked sequentially and wound to form the electrode assembly, and then encapsulated in the casing. However, existing rechargeable batteries still require further improvement in some aspects. Utility Model Content

[0003] In view of the problems existing in related technologies, the purpose of this utility model is to provide a secondary battery, a battery pack and an electronic device.

[0004] An embodiment of this application provides a secondary battery, which includes an electrode assembly. The electrode assembly includes a negative electrode, a positive electrode, and a separator disposed between the negative electrode and the positive electrode. The positive electrode includes a positive current collector and a positive active material layer, and the negative electrode includes a negative current collector and a negative active material layer. Along the height direction of the electrode assembly, the positive current collector includes a positive electrode coated area covered by the positive active material layer and a positive electrode uncoated area not covered by the positive active material layer. The negative current collector includes a negative electrode coated area covered by the negative active material layer and a negative electrode uncoated area not covered by the negative active material layer. The direction from the positive electrode coated area to the positive electrode uncoated area is a first direction. Along the winding direction of the electrode assembly, the positive electrode uncoated area sequentially includes a first positive electrode uncoated area, a second positive electrode uncoated area, and a third positive electrode uncoated area. The electrode assembly comprises a first uncoated negative electrode area, a second uncoated negative electrode area, and a third uncoated negative electrode area. Along a first direction, the second uncoated positive electrode area includes a positive electrode tab and a positive electrode connection area connecting the positive electrode tab and the coated positive electrode area. Neither the first nor the third uncoated positive electrode area includes a positive electrode tab. Along a second direction opposite to the first direction, the second uncoated negative electrode area includes a negative electrode tab and a negative electrode connection area connecting the negative electrode tab and the coated negative electrode area. Neither the first nor the third uncoated negative electrode area includes a negative electrode tab. The maximum circumference of the electrode assembly is C. In the winding direction of the electrode assembly, the first length of the third uncoated negative electrode area is greater than 0.5C and less than 4C, or the second length of the third uncoated positive electrode area is greater than C and less than 4C.

[0005] The above technical solution, by setting the range of the first length of the third uncoated negative electrode area of ​​the negative electrode sheet to be greater than 0.5C and less than 4C, can avoid excessive DC resistance and also prevent the outermost negative electrode tab from warping.

[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 of the uncoated area of ​​the first negative electrode in the winding direction of the electrode assembly ranges from 300 mm to 500 mm.

[0010] In some embodiments, the fourth length of the uncoated area of ​​the first positive electrode ranges from 400 mm to 600 mm in the winding direction of the electrode assembly.

[0011] In some embodiments, the secondary battery further includes: a housing for accommodating an electrode assembly, the housing including a peripheral sidewall and an end wall connected to one end of the peripheral sidewall, the other end of the peripheral sidewall having an opening, and an inwardly protruding crimping portion provided on the peripheral sidewall adjacent to the opening, the electrode assembly being located between the end wall and the crimping portion, wherein a negative electrode tab faces the opening and is connected to the housing via a negative electrode current collector, and the welding position of the negative electrode current collector to the peripheral sidewall is located on the side of the crimping portion facing the electrode assembly.

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

[0013] Embodiments of this application also provide a battery pack, which includes any of the above-described secondary batteries.

[0014] Embodiments of this application also provide an electronic device that includes the battery pack described above.

[0015] The beneficial technical effects of this utility model are as follows:

[0016] By setting the first length of the third uncoated negative electrode area at the end of the negative electrode sheet (before the tab extends out) to be greater than 0.5C and less than 4C, or setting the second length of the third uncoated positive electrode area at the end of the positive electrode sheet (before the tab extends out) to be greater than C and less than 4C, excessive DC resistance can be avoided, and the outermost tab can also be prevented from warping. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 A schematic diagram is shown when the electronic device according to an embodiment of this application is a vehicle.

[0019] Figure 2 A perspective view of a secondary battery according to an embodiment of this application is shown.

[0020] Figure 3 A cross-sectional view of a secondary battery according to an embodiment of this application is shown.

[0021] Figure 4 A cross-sectional view of an electrode assembly according to an embodiment of this application is shown.

[0022] Figure 5 A perspective view of an electrode assembly according to an embodiment of this application is shown.

[0023] Figure 6 A planar schematic diagram of the negative electrode sheet in its unfolded state according to an embodiment of this application is shown.

[0024] Figure 7 A planar schematic diagram of the positive electrode sheet in its unfolded state according to an embodiment of this application is shown. Detailed Implementation

[0025] To better understand the spirit of the embodiments of this application, the following description is based on some preferred embodiments of this application.

[0026] Embodiments of this application will be described in detail below. Throughout this specification, identical or similar components and components having identical or similar functions are indicated by similar reference numerals. The embodiments described herein with reference to the accompanying drawings are illustrative and diagrammatic in nature and are intended to provide a basic understanding of this application. The embodiments of this application should not be construed as limiting this application.

[0027] As used herein, the terms “approximately,” “substantially,” “substantially,” and “about” are used to describe and indicate minor variations. When used in conjunction with an event or situation, these terms may refer to examples in which the event or situation occurred precisely or in examples in which the event or situation occurred very approximately.

[0028] In this specification, unless otherwise specified or limited, relative terms such as “central,” “longitudinal,” “lateral,” “front,” “rear,” “right,” “left,” “inner,” “outer,” “lower,” “higher,” “horizontal,” “vertical,” “above,” “below,” “above,” “below,” “top,” “bottom,” and their derivatives (e.g., “horizontally,” “downward,” “upward,” etc.) should be interpreted as referring to the directions described in the discussion or depicted in the accompanying drawings. These relative terms are used for descriptive convenience only and do not require that this application be constructed or operated in a particular orientation.

[0029] For ease of description, the terms "first," "second," "third," etc., are used herein to distinguish different components of a figure or a series of figures. "First," "second," "third," etc., are not intended to describe corresponding components. Furthermore, unless otherwise specified, the embodiments and features described in these embodiments can be combined with each other. This application will now be described in detail with reference to the accompanying drawings and embodiments.

[0030] This application provides an electronic device 1000. For ease of explanation, the following embodiments use a vehicle as an example to illustrate the electronic device 1000. See also... Figure 1 The vehicle has a battery pack 1002 installed inside, which can be located at the bottom, front, or rear of the vehicle body 1001. The battery pack 1002 can be used to power the vehicle; for example, it can serve as the vehicle's operating power source. The working part of the electronic device 1000 is electrically connected to the battery pack 1002 to obtain electrical power. The vehicle can be a gasoline-powered vehicle, a natural gas-powered vehicle, or a new energy vehicle. New energy vehicles can be pure electric vehicles, hybrid electric vehicles, or range-extended electric vehicles, but are not limited thereto. The working part is the vehicle body, and the battery pack 1002 is located at the bottom of the vehicle body, providing electrical power for the vehicle's movement or the operation of its internal electrical components. However, in some other embodiments, the electronic device 1000 can also be a mobile phone, portable device, laptop, ship, spacecraft, electric toy, and power tool, etc. Spacecraft include airplanes, rockets, space shuttles, and spacecraft, etc.; the working part can obtain electrical energy from the battery pack 1002 and perform corresponding functions, such as a fan blade rotation unit or a vacuum cleaner's suction unit. Electric toys include stationary or mobile electric toys, such as game consoles, electric car toys, electric boat toys, and electric airplane toys, etc.; power tools include metal cutting power tools, grinding power tools, assembly power tools, and railway power tools, such as electric drills, electric grinders, electric wrenches, electric screwdrivers, electric hammers, impact drills, concrete vibrators, and electric planers, etc. This application does not impose any special limitations on the aforementioned electronic device 1000.

[0031] Battery pack 1002 may include multiple secondary batteries (such as cylindrical batteries 100). In the following description, cylindrical batteries are used as an example of secondary batteries. Figure 2 A perspective view of a cylindrical battery 100 according to an embodiment of this application is shown. Figure 3 A cross-sectional view of a cylindrical battery 100 according to an embodiment of this application is shown.

[0032] Combination Figures 2 to 3 As shown, the cylindrical battery 100 includes a housing 200, which includes a peripheral sidewall 109 and an end wall 111 connected to one end of the peripheral sidewall 109. An opening 205 is provided at the other end of the peripheral sidewall 109 opposite to the end wall 111, and a cover plate 220 covers the opening 205 of the housing 200. The cover plate 220 can be used to encapsulate the electrode assembly 120 and the electrolyte together with the housing 200. The housing 200 can be made of any of a variety of available materials, such as copper, iron, aluminum, steel, or aluminum alloy. The housing 200 can be cylindrical and define a receiving cavity in which the electrode assembly 120 is disposed. The outer diameter of the housing 200 can be determined according to the specific diameter of the electrode assembly 120; for example, the outer diameter of the housing 200 can be, for example, 18 mm, 21 mm, or 46 mm. In some embodiments, the cylindrical battery 100 may be a 4680 cylindrical battery (outer diameter 46mm, height 80mm), or a 4695 cylindrical battery (outer diameter 46mm, height 95mm), or a 46120 cylindrical battery (outer diameter 46mm, height 120mm).

[0033] Electrode assembly 120 can be mainly formed by sequentially stacking and winding a positive electrode plate, a negative electrode plate, and a separator located between the positive electrode plate and the negative electrode plate (see below). Figure 4 (Detailed description). The wound electrode assembly 120 has a wound center hole 120c.

[0034] An inwardly protruding crimping portion 113 (also referred to as a groove) is formed on the peripheral sidewall of the housing 200 adjacent to the opening 205. An electrode assembly 120 is disposed between the end wall 111 and the crimping portion 113, and the crimping portion 113 restricts the movement of the electrode assembly 120 in the height direction Hd and the opposite direction between the end wall 111 and the crimping portion 113. The end of the peripheral sidewall 109 of the housing 200 on the opening 205 side can be configured as a rolled edge portion 32, which extends radially inward along the housing 200. The rolled edge portion 32 and the crimping portion 113 are spaced apart in the height direction Hd, and the crimping portion 113 and the rolled edge portion 32 can jointly clamp the cover plate 220. The cover plate 220 is electrically insulated from the housing 200.

[0035] The negative electrode tab of the electrode assembly 120 faces the opening 205 and can be electrically connected to the housing 200 via the negative electrode current collector 201 located between the cover plate 220 and the electrode assembly 120, thereby making the housing 200 negatively charged. The negative electrode current collector 201 can be welded to the housing 200 by laser welding. Specifically, the welding position of the negative electrode current collector 201 to the housing 200 can be located on the side of the crimp portion 113 facing the electrode assembly 120.

[0036] The cylindrical battery 100 may further include a terminal post 160 that passes through and is insulated from the end wall 111. The terminal post 160 can be electrically connected to the positive electrode tab of the electrode assembly 120 via a negative current collector 202 located between the end wall 111 and the electrode assembly 120, thereby making the terminal post 160 positively charged. In some embodiments, the terminal post 160 can be welded to the positive current collector 202 by laser penetration welding.

[0037] Figure 4 A cross-sectional view of an electrode assembly 120 according to some embodiments is shown. See also Figure 4 As shown, the electrode assembly 120 is mainly formed by winding a negative electrode 10 and a positive electrode 20, and a separator 122 is provided between the negative electrode 10 and the positive electrode 20. Electrolyte can be filled between the negative electrode 10, the positive electrode 20 and the separator 122.

[0038] The negative electrode 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 region 18a covered by the negative electrode active material layer 16 and a negative electrode uncoated region 18b not covered by the negative electrode active material layer 16. The positive electrode 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 region 28a covered by the positive electrode active material layer 26 and a positive electrode uncoated region 28b not covered by the positive electrode active material layer 26. The uncoated negative electrode region 18b of the negative current collector 18 and the uncoated positive electrode region 28b of the positive current collector 28 are located at opposite ends in the height direction Hd of the electrode assembly 120. The uncoated negative electrode region 18b of the negative current collector 18 can be used to form a negative electrode tab. The uncoated positive electrode region 28b of the positive current collector 28 can be used to form a positive electrode tab. The direction from the coated positive electrode region 28a to the uncoated positive electrode region 28b is the first direction D2, and the opposite direction is the D2 direction.

[0039] Figure 5 This is a perspective view of an electrode assembly according to an embodiment of this application. (Reference) Figure 4 and Figure 5As shown, the uncoated negative electrode region 18b and the uncoated positive electrode region 28b can be bent toward the winding center hole 120c of the electrode assembly 120. The bent uncoated negative electrode region 18b and the uncoated positive electrode region 28b can be stacked on top of each other. The stacked uncoated negative electrode region 18b can be welded to the negative electrode current collector 201 and further electrically connected to the housing 200 (see Figure 120). Figure 3 The stacked uncoated positive electrode regions 28b can be welded to the positive electrode current collector 202 and further electrically connected to the terminal post 160 (see...). Figure 3 Bending the uncoated negative electrode region 18b and the uncoated positive electrode region 28b can reduce the space occupied by the uncoated negative electrode region 18b and the uncoated positive electrode region 28b, thereby increasing the battery energy density.

[0040] Taking a lithium-ion battery as an example, the material of the negative electrode current collector 18 can be, for example, copper, and the negative electrode current collector 18 can be copper foil. The negative electrode active material of the negative electrode active material layer 16 can be carbon or silicon, etc. The material of the positive electrode current collector 28 can be, for example, aluminum. The positive electrode active material of the positive electrode active material layer 26 can be lithium cobalt oxide, lithium iron phosphate, ternary lithium, or lithium manganese oxide, etc. The material of the separator 122 can be PP (polypropylene) or PE (polyethylene), etc.

[0041] To minimize the possibility of contact between the negative electrode 10 and the positive electrode 20, the electrode assembly 120 may further include an insulating layer 40, which covers at least a portion of the uncoated positive electrode area 28b of the positive current collector 28. The insulating layer 40 may be provided on both sides of the positive current collector 28. The insulating layer 40 effectively prevents electrical contact between the negative electrode 10 and the positive electrode 20.

[0042] In some embodiments, the insulating layer 40 is mainly composed of boehmite and PVDF (polyvinylidene fluoride). Boehmite accounts for 80% of the composition, and PVDF accounts for 20%. In some embodiments, the insulating layer is a ceramic material layer. The thickness of the insulating layer 40 is 1.5mm-2.5mm, for example, 1.5mm, 1.7mm, 2mm, 2.1mm, 2.3mm, or 2.5mm. By setting the thickness range of the insulating layer 40, it is avoided that the coating thickness of the insulating layer 40 is too thin, making it difficult to obtain the required electrical insulation and support strength; at the same time, it is avoided that the thickness of the insulating layer 40 is too thick, which may lead to a longer curing time for the coating layer and an increase in the overall structural thickness.

[0043] In some embodiments, the insulating layer 40 includes a color developer to distinguish whether the side coated with the insulating layer 40 is the front or back side of the positive electrode 20 through the color development effect of the color developer, including but not limited to distinguishing the areal density of the front and back sides of the positive electrode 20. The main component of the color developer may be bismuth vanadate, which is yellow in color.

[0044] In one 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:

[0045] Winding: The negative electrode 10, the separator 122, and the positive electrode 20 are stacked and wound together to form a winding structure. The uncoated portion 18b of the negative electrode current collector 18 of the negative electrode 10 and the uncoated portion 28b of the positive electrode current collector 28 of the positive electrode 20 are bent radially along the electrode assembly 120.

[0046] Welding of current collectors to electrode assemblies: The negative current collector 201 and the positive current collector 202 are welded to the surface areas of the bent uncoated negative electrode portion 18b and the uncoated positive electrode portion 28b, respectively.

[0047] Installation into the housing: The electrode assembly 120, which has been welded to the negative current collector 201 and the positive current collector 202, is installed into the housing 200 through the opening 205. The method of installing the electrode assembly 120 in this step is not limited. For example, it can be installed manually or by a robot.

[0048] Install pole 160.

[0049] Electrolyte injection: The method of electrolyte injection is not limited, and injection can be carried out through opening 205. In this embodiment, electrolyte is injected through opening 205, which reduces the step of opening an injection hole in the end wall 111. The existing opening 205 can be used directly for injection, simplifying the process and reducing costs.

[0050] Sealing: The cover plate 220 is sealed and installed on the opening 205. There are various sealing methods, and this is not limited to one. In some embodiments, a pressing portion 113 recessed towards the center of the housing 200 is first formed by rolling the outer periphery of the housing 200 to restrict the movement of the electrode assembly 120 in the height direction Hd. Then, a mechanical sealing process is used to press and seal the cover plate 220 to form a rolled edge portion 32, thereby sealing and installing the cover plate 220 on the opening 205 of the housing 200. This step is a mature process, low in cost, and highly efficient.

[0051] Figure 6 This is a planar schematic diagram of the negative electrode sheet 10 in its unfolded state according to an embodiment of this application. (See reference) Figure 5 and Figure 6As shown, a portion of the uncoated negative electrode region 18b forms a plurality of negative electrode tabs 18b21. The plurality of negative electrode tabs 18b21 are multiple segments divided from a portion of the uncoated negative electrode region 18b. The 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.

[0052] For details, please refer to Figure 6 As shown, along the winding direction Dj, the negative electrode sheet 10 is wound from the beginning of the roll 10b and terminates at the end of the roll 10e. Along the winding direction Dj, the uncoated negative electrode area 18b sequentially includes a first uncoated negative electrode area 18b1, a second uncoated negative electrode area 18b2, and a third uncoated negative electrode area 18b3. Along the second direction D2, the second uncoated negative electrode area 18b2 includes multiple negative electrode tabs 18b21 and a negative electrode connection area 18b22 connecting the negative electrode tabs 18b21 and the coated negative electrode area 18a. Neither the first uncoated negative electrode area 18b1 nor the third uncoated negative electrode area 18b3 includes negative electrode tabs 18b21. The first uncoated negative electrode area 18b1 is connected to the beginning of the roll 10b of the negative electrode sheet 10. The third uncoated negative electrode area 18b3 is connected to the end of the roll 10e of the negative electrode sheet 10. Multiple negative electrode tabs 182 are arranged along the winding direction Dj. Multiple negative electrode tabs 182 can be formed by cutting a portion of the uncoated negative electrode region 18b. The negative electrode connection region 18b22 is the uncut portion of the uncoated negative electrode region 18b.

[0053] The maximum circumference (i.e., outer circumference) of the electrode assembly 120 is C, 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 uncoated area 18b3 of the third negative electrode is greater than 0.5C and less than 4C. That is, the negative electrode sheet 10 does not have a negative electrode tab 18b21 within the first 0.5 to 4 turns of the winding end. If the first length La is too long, the DC resistance (DCR) of the battery will be too high; if the first length La is too small, the negative electrode tab 18b21 of the outermost ring, adjacent to the winding end 10e, may be warped and difficult to process. By setting the range of the first length La to be greater than 0.5C and less than 4C, excessive DCR can be avoided, and warping of the outermost negative electrode tab can also be avoided.

[0054] Typically, when the negative electrode tab 18b21 is bent, the bending area may protrude radially away from the winding center hole 120c. By providing a third uncoated negative electrode area 18b3 with a first length La for the tab, the orthogonal projection of the negative electrode tab 18b21 in the first direction D1 is located within the area defined by the outer peripheral surface of the electrode assembly 120, that is, the negative electrode tab 18b21 will not bend radially and protrude beyond the outer peripheral surface of the electrode assembly 120 and exceed the diameter of the outer peripheral surface.

[0055] In some embodiments, in the winding direction Dj, the third length Lb of the first uncoated negative electrode area 18b1 of the negative electrode sheet 10 is 300mm-500mm. By setting the third length Lb of the first uncoated negative electrode area 18b1 without tabs at the winding start 10b to 300mm-500mm, tabs can be avoided in the inner turns near the winding center hole 120c, thus preventing the tabs from blocking the center hole and affecting battery safety. In some embodiments, the diameter of the winding center hole 120c ranges from 4mm to 7mm.

[0056] Each negative electrode tab 18b21 may include a first side Ea and a second side Eb opposite each other in the winding direction Dj, and a third side Ec connecting the ends of the first side Ea and the second side Eb away from the negative electrode connection area 18b22. 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 the first side Ea and the second side Eb are inclined toward the winding end 10e, so the angle between the second side Eb and the third side Ec is an acute angle. During the winding of the negative electrode sheet 10, since the first side Ea and the second side Eb of each negative electrode tab 18b21 are inclined toward the winding end 10e, it is convenient to bend and smooth the negative electrode tab 18b21 toward the winding center hole 120c when winding the negative electrode sheet 10. This can effectively reduce the force required to bend the negative electrode tab 18b21, thereby avoiding electrode deformation, reducing the material shedding of the negative electrode active material layer 16 of the negative electrode sheet 10, and improving the yield of the electrode assembly 120.

[0057] Figure 7 This is a planar schematic diagram of the positive electrode 20 in its unfolded state according to an embodiment of this application. (In conjunction with...) Figure 4 and Figure 7 As shown, a portion of the uncoated positive electrode region 28b forms a plurality of positive electrode tabs 28b21. The plurality of positive electrode tabs 28b21 are multiple segments divided from a portion of the uncoated positive electrode region 28b. The end of each positive electrode tab 28b21 that is away from the positive electrode active material layer 26 is bent toward the winding center hole 120c of the electrode assembly 120.

[0058] For details, see Figure 7Along the winding direction Dj, the positive electrode 20 begins winding from its winding start end 20b and terminates at its winding end end 20e. Along the winding direction Dj, the uncoated positive electrode region 28b sequentially includes a first uncoated positive electrode region 28b1, a second uncoated positive electrode region 28b2, and a third uncoated positive electrode region 28b3. Along the first direction D1, the second uncoated positive electrode region 28b2 includes multiple positive electrode tabs 28b21 and a positive electrode connection region 28b22 connecting the positive electrode tabs 28b21 and the coated positive electrode region 28a. Neither the first uncoated positive electrode region 28b1 nor the third uncoated positive electrode region 28b3 includes positive electrode tabs 28b21. The first uncoated positive electrode region 28b1 is connected to the winding start end 20b of the positive electrode 20. The third uncoated positive electrode region 28b3 is connected to the winding end 20e of the positive electrode 20.

[0059] In the winding direction Dj, the second length Lc of the third uncoated positive electrode region 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 too large; if the second length Lc is too small, the outermost positive electrode tab 28b21 adjacent to the winding terminal 20e may lift up, making it difficult to process. By setting the range of the second length Lc to be greater than C and less than 4C, the excessive DCR can be avoided, and the lifting of the outermost positive electrode tab can also be prevented.

[0060] Typically, when the positive electrode tab 28b21 is bent, the bending area may protrude radially away from the winding center hole 120c. By providing a third uncoated positive electrode area 28b3 with a tab having a second length Lc, the orthogonal projection of the positive electrode tab 28b21 in the second direction D2 is located within the area defined by the outer peripheral surface of the electrode assembly 120, that is, the positive electrode tab 28b21 will not bend radially and protrude beyond the outer peripheral surface of the electrode assembly 120 and exceed the diameter of the outer peripheral surface.

[0061] In some embodiments, in the winding direction Dj, the fourth length Ld of the first uncoated positive electrode region 28b1 of the positive electrode sheet 20 is 400mm-600mm, so that the tabs do not appear in the inner few turns near the winding center hole, so as to avoid the tabs blocking the center hole and affecting battery safety.

[0062] Combination Figure 6 and Figure 7As shown, in some embodiments, the second length Lc of the third uncoated positive electrode region 28b3 of the positive electrode 20 can be greater than the first length La of the third uncoated negative electrode region 18b3 of the negative electrode 10. For example, for 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. Because the hardness of the positive current collector 28 (e.g., aluminum) is generally greater than that of the negative current collector 18 (e.g., copper), after the positive and negative electrode tabs are formed by the positive and negative current collectors 28 and 18 and bent, the greater hardness of the positive current collector will cause the bending area of ​​the outermost tab of the electrode assembly to exceed the maximum diameter of the outer circumference of the electrode assembly, thereby affecting the overall radial dimension of the electrode assembly and causing poor assembly housing. Therefore, by controlling the second length Lc of the third uncoated positive electrode region 28b3 of the positive electrode 20 to be longer than the first length La of the third uncoated negative electrode region 18b3 of the negative electrode 10, it is possible to avoid the electrode assembly bending area exceeding the maximum diameter of the outer peripheral surface of the electrode assembly, which would result in poor electrode assembly housing.

[0063] 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 an acute angle. During the winding of the positive electrode sheet 20, since the first side Ed and the second side Ee of each positive electrode tab 28b21 are inclined toward the winding end 20e, the force required to bend the positive electrode tab 28b21 can be effectively reduced, thereby avoiding electrode sheet deformation, reducing material shedding of the positive electrode active material layer 26, and improving the yield of the electrode assembly 120.

[0064] In some embodiments, for a 46-series cylindrical battery with an outer diameter of 46 mm, the first length La is greater than 0.8C and less than 4C, and the second length Lc is greater than 1.5C and less than 4C. In this embodiment, C = π × 46 mm. For this 46-series cylindrical battery, the first length La, which is in the range of 0.8C to 4C, and the second length Lc, which is in the range of 1.5C to 4C, can more effectively prevent the 46-series cylindrical battery from having an excessively large DCR and prevent the outermost tabs from warping.

[0065] In some embodiments, for a 21-series cylindrical battery with an outer diameter of 21 mm, the first length La is greater than 0.5C and less than 3C, and the second length Lc is greater than C and less than 3C. In this embodiment, C = π × 21 mm. For this 21-series cylindrical battery, the first length La, which is in the range of 0.5C to 3C, and the second length Lc, which is in the range of C to 3C, can more effectively prevent the 21-series cylindrical battery from having an excessively large DCR and prevent the outermost tabs from warping.

[0066] The above description is merely a preferred embodiment of this utility model and is not intended to limit the utility model. Various modifications and variations can be made to this utility model by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this utility model should be included within the protection scope of this utility model.

Claims

1. A secondary battery, characterized in that, The electrode assembly includes a negative electrode, a positive electrode, and a separator disposed between the negative electrode and the positive electrode. The positive electrode includes a positive current collector and a positive active material layer, and the negative electrode includes a negative current collector and a negative active material layer. Along the height direction of the electrode assembly, the positive current collector includes a positive electrode coated area covered by the positive active material layer and a positive electrode uncoated area not covered by the positive active material layer. The negative current collector includes a negative electrode coated area covered by the negative active material layer and a negative electrode uncoated area not covered by the negative active material layer. The direction from the positive electrode coated area to the positive electrode uncoated area is a first direction. Along the winding direction of the electrode assembly, the uncoated positive electrode area sequentially includes a first uncoated positive electrode area, a second uncoated positive electrode area, and a third uncoated positive electrode area, and the uncoated negative electrode area sequentially includes a first uncoated negative electrode area, a second uncoated negative electrode area, and a third uncoated negative electrode area; Along the first direction, the second uncoated positive electrode region includes a positive electrode tab and a positive electrode connection region connecting the positive electrode tab and the coated positive electrode region, while neither the first uncoated positive electrode region nor the third uncoated positive electrode region includes the positive electrode tab; Along a second direction opposite to the first direction, the second uncoated negative electrode region includes a negative electrode tab and a negative electrode connection region connecting the negative electrode tab and the coated negative electrode region. Neither the first nor the third uncoated negative electrode region includes the negative electrode tab. Wherein, the maximum circumference of the electrode assembly is C, and in the winding direction of the electrode assembly, the first length of the uncoated area of ​​the third negative electrode is greater than 0.5C and less than 4C, or the second length of the uncoated area 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 of the uncoated area of ​​the first negative electrode ranges from 300mm to 500mm.

6. The secondary battery according to claim 1, characterized in that, In the winding direction of the electrode assembly, the fourth length of the first uncoated positive electrode region ranges from 400mm to 600mm.

7. The secondary battery according to claim 1, characterized in that, Also includes: A housing for accommodating the electrode assembly, the housing including a peripheral sidewall and an end wall connected to one end of the peripheral sidewall, the other end of the peripheral sidewall having an opening, and an inwardly protruding crimping portion provided on the peripheral sidewall adjacent to the opening, the electrode assembly being located between the end wall and the crimping portion. The negative electrode tab faces the opening and is connected to the housing via a negative electrode current collector. The welding position of the negative electrode current collector to the peripheral sidewall is located on the side of the crimping portion facing the electrode assembly.

8. The secondary battery according to claim 1, characterized in that, The negative electrode tab is divided into multiple segments by the portion of the uncoated negative electrode area, and the end of each negative electrode tab away from the negative electrode connection area is bent toward the winding center hole of the electrode assembly. The orthogonal projection of the negative electrode tab in the first direction lies within the area defined by the outer peripheral surface of the electrode assembly.

9. A battery pack, characterized in that, Includes the secondary battery as described in any one of claims 1-8.

10. An electronic device, characterized in that, Includes the battery pack as described in claim 9.

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