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 formed by laminating and winding a first diaphragm, a positive pole piece, a second diaphragm and a negative pole piece. The first pole piece comprises a first current collector and a first active material layer, a coating region of the first current collector is provided with the first active material layer on at least one of the first surface and the second surface, and an uncoated region is not provided with the first active material layer on the first surface and the second surface; the coating area and the first active material layer are main body parts of the first pole piece, the first pole piece comprises a first area connected with the starting end of the first pole piece, a second area connected with the first area and a third area connected with the second area and the ending end of the first pole piece in the winding direction of the electrode assembly, and the depth of the second concave part is larger than that of each first concave part. According to the technical scheme, the influence of expansion of the electrode assembly on battery performance can be relieved at least.

Description

TECHNICAL FIELD

[0001] The utility model relates to the field of battery, more particularly, a secondary battery, battery pack and electronic device. BACKGROUND

[0002] In the field of new energy power battery, the application of secondary battery is more and more widely, such as the secondary battery (for example, lithium ion battery) can be applied to the car, energy storage, mobile phone, tablet computer, wearable device, mobile power supply, electronic cigarette, digital product, electric tool, power device, energy storage device and other electronic devices. One of the secondary batteries is a cylindrical battery, which includes a shell and an electrode assembly, the electrode assembly includes a positive electrode sheet, a first separator, a negative electrode sheet and a second separator, which are stacked in sequence and then wound into an electrode assembly, and then packaged in the shell. The electrode assembly in the shell of the secondary battery will produce swelling pressure after swelling. SUMMARY

[0003] In view of the problems in the related art, the purpose of the utility model is to provide a secondary battery, battery pack and electronic device to at least alleviate the influence of electrode assembly swelling on battery performance.

[0004] To achieve the above-mentioned purpose, the embodiment of the present application provides a secondary battery, which includes an electrode assembly formed by laminating and winding a first separator, a first electrode sheet, a second separator and a second electrode sheet, the first electrode sheet includes: a first current collector and a first active material layer, the first current collector has opposite first and second surfaces along its thickness direction, the first current collector includes a coated area and an uncoated area connected to each other along the axial direction of the electrode assembly, the uncoated area is not provided with the first active material layer on both the first and second surfaces, the coated area and the first active material layer are the main part of the first electrode sheet, along the winding direction of the electrode assembly, the first electrode sheet includes a first area connecting the starting end of the first electrode sheet, a second area connecting the first area, and a third area connecting the second area and the ending end of the first electrode sheet, the main part has at least one first recess in the first area and at least one second recess in the second area, wherein the depth of the second recess is greater than the depth of each first recess.

[0005] In some embodiments, the depth of the second recess is 1.05-6 times the depth of the first recess, wherein the first recess and the second recess are recesses on the first surface of the first active material layer, the first recess and the second recess respectively have a bottom on the first surface of the recess farthest from the un-recessed first surface along the thickness direction, and the depth of the first recess and the depth of the second recess are respectively the distance between the corresponding bottom and the un-recessed first surface along the thickness direction.

[0006] In some embodiments, the second region is a region having a distance from the starting end of the first tab in a range of 0.3L-0.7L, where L is a length of the first tab in a winding direction.

[0007] In some embodiments, the main body portion has at least one third recess in the third region, and a depth of the second recess is greater than a depth of each third recess.

[0008] In some embodiments, the depth of the second recess is 1-6 μm, the depth of the first recess is 0.5-3 μm, and the depth of the third recess is 0.5-3 μm, wherein the first recess, the second recess, and the third recess are respectively a recess on the first surface of the first active material layer, the first recess, the second recess, and the third recess respectively have a bottom farthest from the un-recessed first surface in a thickness direction on the first surface of the recess, and the depth of the first recess, the depth of the second recess, and the depth of the third recess are respectively distances of the respective bottoms from the un-recessed first surface in the thickness direction.

[0009] In some embodiments, the electrode assembly has a winding center hole, and any one of the first recess, the second recess, and the third recess is formed on a side of the main body portion of the first tab facing away from the winding center hole.

[0010] In some embodiments, the first recess, the second recess, and the third recess are respectively a first protrusion, a second protrusion, and a third protrusion protruding toward the winding center hole on another side of the first tab facing the winding center hole, wherein a height of the second protrusion is greater than a height of the first protrusion and greater than a height of the third protrusion.

[0011] In some embodiments, the first tab is a positive tab, or the secondary battery is a cylindrical battery.

[0012] Embodiments of the present application also provide a battery pack including any one of the secondary batteries described above.

[0013] Embodiments of the present application also provide an electronic device including the battery pack described above.

[0014] The beneficial technical effects of the present application are as follows:

[0015] By providing the second recess with a greater depth in the second zone of the main body portion of the first tab, sufficient buffer space can be provided for the expansion of the electrode assembly during the cycling process, so as to more effectively alleviate the problem of stress concentration of the middle tab. The first recess provided in the first zone can prevent the center hole from collapsing; and the first recess has a smaller depth, which can not only meet the requirements of alleviating the expansion of the inner ring battery and preventing the center hole from collapsing, but also improve the electrolyte infiltration, improve the cycling performance and safety of the battery, and ensure that the diameter of the electrode assembly and the energy density of the battery are controlled. In the embodiment in which the secondary battery is a cylindrical battery, since the expansion force and the group margin of the cylindrical battery are greater, it is more advantageous to configure a deeper recess in the middle ring for the cylindrical battery. BRIEF DESCRIPTION OF DRAWINGS

[0016] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description are some embodiments of the present application, and those skilled in the art can also obtain other drawings according to these drawings without any creative effort.

[0017] Figure 1 A perspective view of a secondary battery according to an embodiment of the present application is shown.

[0018] Figure 2 A cross-sectional view of a secondary battery according to an embodiment of the present application is shown.

[0019] Figure 3 is a cross-sectional view of an electrode assembly of a secondary battery according to an embodiment of the present application in a cross-section perpendicular to the axis.

[0020] Figure 4 is a cross-sectional view of a first tab of an electrode assembly in a thickness direction according to some embodiments.

[0021] Figure 5A A plan view of a main body portion of a first tab in an unfolded state according to some embodiments is shown.

[0022] Figure 5B A cross-sectional view of the main body portion of the first tab in line C1-C1 in Figure 5A is shown.

[0023] Figure 6A A plan view of a main body portion of a first tab in an unfolded state according to some embodiments is shown.

[0024] Figure 6B A cross-sectional view of the main body portion of the first tab in line C2-C2 in Figure 6A is shown.

[0025] Figure 7 A schematic view of an electronic device according to an embodiment of the present application is shown. DETAILED DESCRIPTION

[0026] For better understanding of the spirit of the embodiments of the present application, the following further describes the embodiments of the present application in combination with some preferred embodiments of the present application.

[0027] Embodiments of the present application will be described in detail below. In the entire description of the present application, the same or similar components and components having the same or similar functions are denoted by like reference numerals. The embodiments described herein with reference to the accompanying drawings are illustrative in nature, diagrammatic in nature, and serve to provide a basic understanding of the present application. The embodiments of the present application should not be construed as limiting the present application.

[0028] As used herein, the terms "approximately", "substantially", "essentially", and "about" are used to describe and account for small variations. When used in connection with an event or circumstance, the terms can refer to instances in which the event or circumstance occurs exactly, as well as instances in which the event or circumstance occurs approximately.

[0029] In the present specification, unless specifically designated or limited, relative terms such as "central", "longitudinal", "lateral", "forward", "rearward", "rightward", "leftward", "internal", "external", "lower", "higher", "horizontal", "vertical", "higher than", "lower than", "above", "below", "top", "bottom", and derivatives thereof (e.g., "horizontally", "downwardly", "upwardly", etc.) should be interpreted to refer to the orientation described in the discussion or depicted in the drawings. These relative terms are used only for convenience and do not require the present application to be constructed or operated in a particular orientation.

[0030] For ease of description, "first", "second", "third", and the like can be used herein to distinguish between different components of one figure or series of figures. "First", "second", "third", and the like are not intended to describe corresponding components.

[0031] Embodiments of the present application provide a secondary battery. Figure 1 A perspective view of a secondary battery 100 according to an embodiment of the present application is shown, Figure 2 A cross-sectional view of a secondary battery 100 according to an embodiment of the present application is shown. In the following description, the embodiments of the present application are described taking a cylindrical battery as an example.

[0032] In combination with Figures 1-2As shown, the secondary battery 100 includes a housing including a case 200 and a cover plate 220. Specifically, the case 200 includes a peripheral sidewall 109 and an end wall 111 connected to one end of the peripheral sidewall 109, and the other end of the peripheral sidewall 109 opposite the end wall 111 is provided with an opening 205, and the cover plate 220 covers the opening 205 of the case 200. The cover plate 220 can be used to jointly encapsulate the electrode assembly 120 and the electrolyte with the case 200. The material of the case 200 can be any of a variety of available materials, such as copper, iron, aluminum, steel, aluminum alloy, etc. The case 200 can be cylindrical and define a receiving cavity in which the electrode assembly 120 is disposed. The outer diameter of the case 200 can be determined according to the specific diameter size of the electrode assembly 120, for example, the outer diameter of the case 200 can be, for example, 18 mm, 21 mm, 46 mm, etc. In some embodiments, the secondary battery 100 can be a 4680 cylindrical battery (outer diameter 46 mm, height 80 mm), or the secondary battery 100 can be a 4695 cylindrical battery (outer diameter 46 mm, height 95 mm), or the secondary battery 100 can be a 46120 cylindrical battery (outer diameter 46 mm, height 120 mm).

[0033] The electrode assembly 120 can be formed by sequentially stacking and winding a positive electrode sheet, a negative electrode sheet, and a separator between the positive electrode sheet and the negative electrode sheet. The positive electrode sheet, the negative electrode sheet, and the separator can be wound about an axis Lc. Also, the electrode assembly 120 has a winding center hole 120c, and the axis Lc can be an axis of the winding center hole 120c. The electrode assembly 120 formed by winding can have the winding center hole 120c. In some embodiments, the positive electrode sheet can include a positive electrode current collector and a positive electrode active material layer coated on part of the surface of the positive electrode current collector. An uncoated region of the positive electrode current collector that is not covered by the positive electrode coating region is used to form a positive electrode tab 125. The negative electrode sheet can include a negative electrode current collector and a negative electrode active material layer coated on part of the surface of the negative electrode current collector. An uncoated region of the negative electrode current collector that is not covered by the negative electrode coating region is used to form a negative electrode tab 124.

[0034] A circumferential side wall of the case 200 adjacent to the opening 205 is formed with a roll groove 113 (may also be referred to as a crimping portion) protruding inward. The electrode assembly 120 is disposed between the end wall 111 and the roll groove 113, and the roll groove 113 is capable of restricting movement of the electrode assembly 120 in the direction Z and the reverse direction thereof between the end wall 111 and the roll groove 113. The direction of the opening 205 to the end wall 111 is the axial direction of the electrode assembly 120, and the height direction Z of the secondary battery. The end portion of the circumferential side wall 109 of the case 200 on the opening 205 side can be configured as a curled portion 32 extending into the case along the radial direction of the case 200 perpendicular to the direction Z. The curled portion 32 is arranged apart from the roll groove 113 in the direction Z, and the roll groove 113 and the curled portion 32 can collectively clamp the cover plate 220. The cover plate 220 can be electrically insulated from the case 200.

[0035] The cover plate 220 can be provided with a weak portion, and when the battery experiences thermal runaway, high-temperature and high-pressure discharge inside the battery can be discharged to the outside through the weak portion on the cover plate 220, thereby achieving good discharge of the discharge.

[0036] The negative tab 124 of the electrode assembly 120 faces the opening 205, and can be electrically connected to the case 200 through the negative current collector 201 between the cover plate 220 and the electrode assembly 120, so that the case 200 is negatively charged. The negative current collector 201 can be welded to the case 200 by laser welding. Specifically, the welding position of the negative current collector 201 and the case 200 is located on the side of the roll groove 113 facing the electrode assembly 120.

[0037] The secondary battery 100 can also include a pole 160 that passes through the end wall 111 and is insulated from the end wall 111. The pole 160 can be electrically connected to the positive tab 125 of the electrode assembly 120 through the positive current collector 202 between the pole 160 and the electrode assembly 120, so that the pole 160 is positively charged. In some embodiments, the pole 160 can be welded to the positive current collector 202 by laser penetration welding.

[0038] In an example of the secondary battery 100 of the present application, the method for manufacturing the secondary battery 100 of the present application includes the following steps:

[0039] Winding: The winding structure formed by stacking and winding the negative electrode sheet, the separator, and the positive electrode sheet, and the uncoated portions of the negative current collector of the negative electrode sheet and the positive current collector of the positive electrode sheet are used as the positive tab 125 and the negative tab 124, and the positive tab 125 and the negative tab 124 are bent along the radial direction of the electrode assembly 120.

[0040] Current collector welding: The positive current collector 202 and the negative current collector 201 are respectively welded to the surface area of the bent positive tab 125 and the negative tab 124.

[0041] Shell entry: the electrode assembly 120, which is welded with the negative current collector 201 and the positive current collector 202, is installed into the shell 200 from the opening 205. The installation of the electrode assembly 120 in this step is not limited, for example, it can be installed manually or by a mechanical hand.

[0042] The pole post 160 is installed.

[0043] Injection of electrolyte: the injection of electrolyte is not limited, and can be selected to be injected at the opening 205. In this embodiment, the electrolyte is injected at the opening 205, which reduces the process of opening the injection hole in the end wall 111, can directly use the existing opening 205 for injection, simplifies the process, and reduces the cost.

[0044] Sealing: the cover plate 220 is sealed and installed on the opening 205, and the sealing method is various and is not limited. In some embodiments, the rolling groove 113 is formed on the outer periphery of the shell 200 by rolling the shell 200, so as to limit the movement of the electrode assembly 120 in the direction Z, and then the cover plate 220 is potted to form the curling part 32 by using a mechanical sealing process, so as to seal and install the cover plate 220 on the opening 205 of the shell 200. This step has mature process, low cost and high efficiency.

[0045] Figure 3 is a sectional view of the electrode assembly 120 of the secondary battery according to the embodiment of the present application in a cross section perpendicular to the axis Lc. It should be understood that the electrode assembly 120 of the winding type has a winding center hole 120c, and the axis Lc of the winding center hole 120c extends in the direction Z (see Figure 3 ), Figure 3 The X-Y plane shown in Figure 3 may have a circular shape in the cross section. The projection point P can be the center of the winding center hole 120c.

[0046] Referring to Figure 3 , the electrode assembly 120 can include a first electrode sheet 121, a first separator 141, a second electrode sheet 122, and a second separator 142. In addition, the secondary battery can also include an electrolyte, which can be located between the first electrode sheet 121, the first separator 141, the second electrode sheet 122, and the second separator 142.

[0047] The first tab 121, the first separator 141, the second tab 122 and the second separator 142 are sequentially stacked to form the electrode assembly 120 in the winding direction D. Specifically, the first tab 121 is wound from its starting end 121s to its ending end 121e in the winding direction D, the second tab 122 is wound from its starting end 122s to its ending end 122e, and the first separator 141 and the second separator 142 isolate the first tab 121 from the second tab 122.

[0048] Figure 4 is a schematic cross-sectional view of a first tab of an electrode assembly in a thickness direction according to some embodiments. Referring to Figure 4 As shown, the first tab 121 can include a first current collector 18 and a first active material layer 16. The first current collector 18 has opposite first and second surfaces 18a and 18b in its thickness direction (i.e., the thickness direction of the first tab). In the direction Z, the first current collector 18 includes a coated region 181 and an uncoated region 182 connected to each other. The uncoated region 182 is not provided with the first active material layer 16 on both the first and second surfaces 18a and 18b. In the present embodiment, the first and second surfaces 18a and 18b of the first current collector 18 in the coated region 181 are covered by the first active material layer 16. The coated region 181 and the first active material layer 16 form a main portion 121M of the first tab. The uncoated region 182 can serve as a first tab (e.g., a positive electrode tab).

[0049] In some embodiments, the first tab 121 is a positive electrode tab, and the second tab 122 is a negative electrode tab. The first current collector 18 is a positive electrode current collector, and the first active material layer 16 is a positive electrode active material layer. Taking a lithium-ion battery as an example, the material of the positive electrode current collector can be aluminum, and the positive electrode active material layer can include a positive electrode active material, which can be lithium cobaltate, lithium iron phosphate, ternary lithium, or lithium manganate, etc. For a high-nickel ternary lithium battery, the positive electrode active material can be a ternary material composed of nickel, cobalt, and manganese (or aluminum), in which the content of nickel is usually relatively high, generally more than 60%. Similarly, the negative electrode tab can include a negative electrode current collector and a negative electrode active material layer coated on both sides of the negative electrode current collector. The part of the negative electrode current collector that is not coated with the negative electrode active material layer constitutes a negative electrode tab. The material of the negative electrode current collector can be copper, and the negative electrode active material layer can include a negative electrode active material, which can be carbon or silicon, etc.

[0050] Figure 5A is a schematic plan view of the main portion 121M of the first tab 121 in an unfolded state according to some embodiments. Figure 5B is a schematic cross-sectional view of the main portion 121M of the first tab 121 in line C1-C1 in Figure 5A It should be understood that, Figure 5AThe plane shown is perpendicular to the thickness direction of the first tab 121.

[0051] In combination Figure 5A And Figure 5B As shown, the length of the first tab 121 is L, and the length direction of the first tab 121 can correspond to the winding direction of the electrode assembly 120. The width direction of the first tab 121 can correspond to the axial direction of the electrode assembly 120, i.e., direction Z. In the length direction of the first tab 121, the first tab 121 includes a first region A1 connecting the starting end 121s thereof, a second region A2 connecting the first region A1, and a third region A3 connecting the second region A2 and the ending end 121e of the first tab 121. In the wound electrode assembly 120, the first region A1 connected with the starting end 121s is closer to the winding center hole 120c and can be referred to as the inner circle. The third region A3 is closer to the outer peripheral surface of the electrode assembly 120 and can be referred to as the outer circle. The second region A2 can be referred to as the middle circle.

[0052] The main body portion 121M has at least one first recess 171 in the first region A1 and at least one second recess 172 in the second region A2. The depth of the second recess 172 can be greater than the depth of each first recess 171.

[0053] The electrode assembly 120 of the secondary battery will swell during the cycle process, especially in the second region A2 (middle circle), and the stress caused by the swelling has no place to release, and the stress concentration will cause the middle circle tab to break the bridge and analyze lithium, ultimately affecting the battery performance, and there is a greater safety risk. By providing a second recess 172 with a greater depth in the second region A2 where the stress is more concentrated, sufficient buffer space can be provided for the swelling of the electrode assembly during the cycle process to more effectively alleviate the problem of stress concentration of the middle circle tab. For the first region A1, since it is closer to the winding center hole 120c, providing a first recess 171 in the first region A1 can prevent the tab in the first region A1 from collapsing the center hole. And the depth of the first recess 171 is small, which can not only meet the requirements of relieving the swelling of the inner circle battery and preventing the center hole from collapsing, but also improve the electrolyte infiltration, improve the cycle performance and safety of the battery, and also ensure that the diameter of the electrode assembly and the energy density of the battery are controlled. In the embodiment in which the secondary battery is a cylindrical battery, since the swelling force and the group margin of the cylindrical battery are greater, therefore, configuring a deeper recess in the middle circle is more advantageous for the cylindrical battery.

[0054] In some embodiments, the depth of the second recess 172 is 1.05-6 times the depth of the first recess 172. If the depth of the second recess 172 is more than 6 times the depth of the first recess 172, the gap between the middle circle pole pieces will be too large, which will reduce the energy density of the battery. If the depth of the second recess 172 is less than 1.05 times the depth of the first recess 172, the stress concentration of the middle circle pole pieces cannot be effectively alleviated.

[0055] In addition, in some embodiments, the main body part 121M of the first pole piece 121 has at least one third recess 173 in the third zone A3. The depth of each third recess 173 can be different from the depth of each second recess 172. Since the expansion force in the third zone A3 is different from that in the second zone A2, configuring the second recess 172 and the third recess 173 to have different depths can provide corresponding buffer spaces for the different expansion forces in the second zone A2 and the third zone A3.

[0056] In some embodiments, the depth of each third recess 173 is less than the depth of each second recess 172. Generally, the expansion force in the third zone A3 is smaller than that in the second zone A2, so the third recess 173 can be configured to have a smaller depth. If the third recess 173 has the same depth as the second recess 172, the gap between the pole pieces in the third zone A3 will be too large (but actually not needed to be so large), which will make the path of lithium ion intercalation longer and require more electrolyte to fill, which will reduce the energy density of the battery. In addition, if the third recess 173 has the same depth as the second recess 172, the size of the outer diameter of the electrode assembly will increase under the same pole piece length and the same expansion force, which will result in too large a group margin.

[0057] In embodiments where the secondary battery is a cylindrical battery, since the expansion force and the group margin of the cylindrical battery are larger, and the requirement for energy density is also higher. Therefore, it is more advantageous for the cylindrical battery to configure different depths for the recesses in the inner circle, the middle circle and the outer circle of the pole piece.

[0058] In the present embodiment, the first recess 171, the second recess 172 and the third recess 173 are all recesses on the first surface S1 of the main body part 121M. The first surface S1 is one of the opposite side surfaces of the first active material layer 16 in the thickness direction of the pole piece. Specifically, as shown in FIG. 1, the first surface S1 is the side surface of the first active material layer 16 that is closer to the first surface S1 of the main body part 121M. Figure 5BAs shown in the enlarged local area R1 in FIG. 1, it should be understood that the first surface S1 includes a non-recessed first surface S11 and a recessed first surface S12, and the first recess 171, the second recess 172 and the third recess 173 are respectively formed by the recessed first surface S12. Taking the second recess 172 as an example, the depth of the second recess 172 is T. The depth T is the distance between the bottom 172b of the second recess 172 and the non-recessed first surface S11 along the thickness direction of the pole piece, and the bottom 172b of the second recess 172 is the position farthest from the non-recessed first surface S11 along the thickness direction of the recessed first surface S12. The depths of the first recess 171 and the third recess 173 also have similar meanings as the depth T.

[0059] In some embodiments, the depths of the plurality of first recesses 171 can be the same (within the process error range), the depths of the plurality of second recesses 172 can be the same (within the process error range), and the depths of the plurality of third recesses 173 can be the same (within the process error range). In some embodiments, the depths of the first recesses 171 and the depths of the third recesses 173 can be the same (within the process error range), and less than the depths of the second recesses 172.

[0060] In some embodiments, the depth of the second recess 172 can be in the range of 1 μm to 6 μm. The depth of the first recess 171 can be in the range of 0.5 μm to 3 μm. The depth of the third recess 173 can be in the range of 0.5 μm to 3 μm. Such depth configurations of the first recess 171, the second recess 172 and the third recess 173 can achieve a balance in preventing the center hole from collapsing, relieving the stress concentration of the middle ring pole piece and maintaining the energy density of the battery.

[0061] In some embodiments, the length of the first pole piece is L, and the length of the first area A1 is in the range of 0.2L-0.4L, for example, 0.3L. The length of the second area A2 is in the range of 0.3L to 0.5L, for example, 0.4L. In some embodiments, the length of the third area A3 is in the range of 0.2L-0.4L, for example, 0.3L. Because the expansion force is the largest within the length range of the second area A2, configuring the recess depth according to such a length range can better meet the need of providing a buffer space for the expansion force.

[0062] In some embodiments, the first recess 171, the second recess 172 and the third recess 173 can be formed by applying pressure on the first pole piece 121 by a rolling device. The first recess 171 and the third recess 173 can be formed by applying a smaller pressure (for example, a pressure of 0.12 MPa), and the third recess 173 can be formed by applying a larger pressure (for example, a pressure of 0.16 MPa).

[0063] In some embodiments, the plurality of first recesses 171, second recesses 172 and third recesses 173 are formed on a first surface S1 of the main body portion 121M of the first tab 121 on a side facing away from the winding central hole 120c, that is, the first surface S1 faces towards the housing of the secondary battery. By arranging each recess on the side of the first tab 121 facing away from the winding central hole 120c, it can be more conducive to relieving the expansion force.

[0064] Referring to Figure 5B In some embodiments, as shown in FIG. 1 1, each of the first recess 171, the second recess 172 and the third recess 173 forms a first protrusion 171p, a second protrusion 172p and a third protrusion 173p, respectively, on a second surface S2 opposite to the first surface S1. The second surface S2 is the side of the first tab 121 facing the winding central hole 120c, and the first protrusion 171p, the second protrusion 172p and the third protrusion 173p all protrude towards the winding central hole 120c. The corresponding first protrusion 171p, second protrusion 172p and third protrusion 173p can be formed at the same time as the first recess 171, second recess 172 and third recess 173 are formed by rolling. By arranging the first protrusion 171p, second protrusion 172p and third protrusion 173p, further buffer space can be provided to relieve the expansion force.

[0065] Due to the larger depth of the second recess 172, the height of the second protrusion 172p can be larger accordingly. In some embodiments, the height of the second protrusion 172p can be greater than the height of the first protrusion 171p and greater than the height of the third protrusion 173p, so that more sufficient buffer space can be provided in the second area A2 where the stress is more concentrated.

[0066] In the present embodiment, the plurality of first recesses 171, second recesses 172 and third recesses 173 each have a circular shape in plan view and are arranged in a dot matrix layout. The width (such as the diameter) of the plurality of first recesses 171, second recesses 172 and third recesses 173 in plan view can be any appropriate value less than the length of the corresponding first area A1, second area A2 and third area A3. The spacing between the plurality of first recesses 171, second recesses 172 and third recesses 173 can be equal or can also be unequal.

[0067] Figure 6A A plan view schematic diagram of the main body portion 121M of the first tab 121 in an unfolded state according to further embodiments is shown. Figure 6B A cross-sectional view schematic diagram of the main body portion 121M of the first tab 121 in line C2-C2 is shown in Figure 6A Figure 6A And Figure 6B Aspects of the embodiments shown can be combined with the above reference Figure 5A And​Figure 5B The same is described, and the same reference numerals are adopted for the same structures, and only the differences between the embodiments shown in Figure 6A and Figure 6B the embodiments are described below.

[0068] In Figure 6A and Figure 6B , the plurality of first recesses 171, the plurality of second recesses 172, and the plurality of third recesses 173 each have a strip shape in a plan view, and the strip shape can pass through the entire main body portion 121M along the width direction of the first tab 121. In other embodiments, the plurality of first recesses 171, the plurality of second recesses 172, and the plurality of third recesses 173 can also have other applicable shapes, such as a pattern shape, etc.

[0069] The above describes the embodiments of the present application with the first tab as the positive electrode tab and the second tab as the negative electrode tab, but it should be understood that in other embodiments, the first tab can be the negative electrode tab and the second tab can be the positive electrode tab. In addition, the above describes the embodiments of the present application with the first tab having the first recess to the third recess, but it should be understood that in other embodiments, the second tab can be configured to have the first recess to the third recess described above, or both the first tab and the second tab have the first recess to the third recess described above.

[0070] Referring to Figure 7The application also provides an electronic device 1000. In the following embodiments, the electronic device 1000 is taken as a vehicle for convenience of description. The vehicle is internally provided with a battery pack 1002, which can be arranged at the bottom, head or tail of a vehicle body 1001. The battery pack 1002 can be used for power supply of the vehicle, for example, the battery pack 1002 can be used as an operating power supply of the vehicle. A working part of the electronic device 1000 is electrically connected with the battery pack 1002 to obtain electric energy support. The vehicle can be a fuel automobile, a gas automobile or a new energy automobile, and the new energy automobile can be a pure electric automobile, a hybrid electric automobile or a range extended automobile, but is not limited thereto. The working part is the vehicle body, the battery pack 1002 is arranged at the bottom of the vehicle body, and provides electric energy support for driving of the vehicle or operation of electrical elements in the vehicle. However, in some other embodiments, the electronic device 1000 can also be a mobile phone, a portable device, a notebook computer, a ship, a spacecraft, an electric toy and an electric tool, and the like. The spacecraft includes an airplane, a rocket, a space shuttle and a spacecraft, and the like. The working part can obtain electric energy of the battery pack 1002, and make corresponding working unit parts, for example, a fan blade rotating unit, a dust suction working unit of a dust collector, and the like. The electric toy includes a fixed or mobile electric toy, for example, a game machine, an electric automobile toy, an electric ship toy and an electric airplane toy, and the like. The electric tool includes a metal cutting electric tool, a grinding electric tool, an assembling electric tool and a railway electric tool, for example, an electric drill, an electric grinder, an electric wrench, an electric screwdriver, an electric hammer, an impact electric drill, a concrete vibrator and an electric planer, and the like. The embodiments of the application do not specially limit the above-mentioned electronic device 1000. The battery pack 1002 can include a plurality of above-mentioned secondary batteries, for example, cylindrical batteries.

[0071] The above merely describes preferred embodiments of the present application and is not used to limit the present application. For those skilled in the art, the present application can have various modifications and changes. Any modification, equivalent replacement, improvement and the like within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A secondary battery characterized by comprising: An electrode assembly including a first separator, a first tab, a second separator, and a second tab, which are stacked and wound, a first current collector and a first active material layer, the first current collector having opposite first and second surfaces along a thickness direction thereof, the first current collector including mutually connected coated and uncoated regions along an axial direction of the electrode assembly, the uncoated region being free of the first active material layer on both the first and second surfaces, the coated region being a main portion of the first tab, the first tab including, along a winding direction of the electrode assembly, a first region connecting a start end of the first tab, a second region connected to the first region, and a third region connecting the second region to an end end of the first tab, the main portion having at least one first recess in the first region and at least one second recess in the second region, wherein a depth of the second recess is greater than a depth of each of the first recesses.

2. The secondary battery according to claim 1, wherein the depth of the second recess is 1.05-6 times the depth of the first recess, wherein the first recess and the second recess are respectively a recess on the first surface of the first active material layer, the first recess and the second recess respectively have a bottom on a first surface of the recess that is farthest from an un-recessed first surface along the thickness direction, and the depth of the first recess and the depth of the second recess are respectively distances of the respective bottom from the un-recessed first surface along the thickness direction.

3. The secondary battery according to claim 1, wherein the second region is a region having a distance from the start end of the first tab in a range of 0.3L-0.7L, where L is a length of the first tab along the winding direction.

4. The secondary battery according to claim 1, wherein the main portion has at least one third recess in the third region, and the depth of the second recess is greater than a depth of each of the third recesses.

5. The secondary battery according to claim 4, wherein the depth of the second recess is 1 pm-6 pm, the depth of the first recess is 0.5 pm-3 pm, and the depth of the third recess is 0.5 pm-3 pm, wherein the first recess, the second recess, and the third recess are respectively a recess on the first surface of the first active material layer, the first recess, the second recess, and the third recess respectively have a bottom on a first surface of the recess that is farthest from an un-recessed first surface along the thickness direction, and the depth of the first recess, the depth of the second recess, and the depth of the third recess are respectively distances of the respective bottom from the un-recessed first surface along the thickness direction.

6. The secondary battery according to claim 4, wherein the electrode assembly has a winding center hole, and any one of the first recess, the second recess, and the third recess is formed on a side of the main portion of the first tab that faces away from the winding center hole.

7. The secondary battery according to claim 6, characterized in that the first recess, the second recess, and the third recess are first, second, and third protrusions protruding toward the winding central hole on the other side of the first tab facing the winding central hole, wherein the height of the second protrusion is greater than the height of the first protrusion and greater than the height of the third protrusion.

8. The secondary battery according to claim 1, characterized in that the first tab is a positive tab, or the secondary battery is a cylindrical battery.

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

10. An electronic device, comprising: A battery pack according to claim 9. A battery pack according to claim 9.

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