Secondary battery and electronic apparatus

Abstract

Disclosed in the present application are a secondary battery and an electronic apparatus. The secondary battery comprises a packaging pouch, an electrode assembly, positive electrode tabs and first bonding members; the packaging pouch comprises encapsulation portions; the electrode assembly comprises positive electrode current collectors and negative electrode current collectors; each positive electrode tab comprises a first section, a second section, a third section and a fourth section which are sequentially connected and integrally arranged, the first section protruding from the packaging pouch in a first direction, the second section being located within an encapsulation portion, the third section being located between the encapsulation portion and a negative electrode current collector, the fourth section being connected to the surface of a positive electrode current collector, the projection of the fourth section in a second direction perpendicular to the first direction being located within the negative electrode current collector, the second section, the third section and the fourth section being located on the same side of the winding central axis of the electrode assembly in the second direction, and each first bonding member being arranged on the surface of the fourth section facing away from the positive electrode current collector and bonding the fourth section and a positive electrode sheet.

Description

Secondary battery and electronic device TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to a secondary battery and an electronic device. BACKGROUND

[0002] With the continuous updating and development of lithium ion battery technology, the application field of lithium ion batteries is also expanding, and the safety problem that follows is increasingly concerned by the public. The safety accidents of lithium ion batteries characterized by external short circuit leading to thermal runaway occur frequently, which brings certain resistance to the development of lithium ion batteries. How to solve the safety problem of the battery cell is a difficult problem that the current lithium ion battery industry cannot avoid. SUMMARY

[0003] The inventor found that in the soft package battery, in order to alleviate the pulling caused by the relative displacement of the tab and the pole piece during the drop, the tab will have a large bending. When external short circuit occurs, the tab heats up quickly, and the increase of the side reaction of the battery cell at high temperature leads to a large amount of gas production. The packaging bag may expand due to gas production and drive the displacement of the tab, causing the tab to contact the separator on the top surface of the electrode assembly and burn the separator, and then causing the tab to contact the pole piece of the other polarity, resulting in secondary short circuit, increasing the risk of thermal runaway. Especially for the positive tab, the positive tab generates a large amount of heat and has a high temperature rise. The negative pole piece will exceed the edge of the positive pole piece in design. When the positive tab is pulled, it is easy to contact the edge of the negative pole piece on the top section of the electrode assembly.

[0004] An object of the present application is to provide a secondary battery and an electronic device which can reduce the risk of short circuit and improve the drop performance.

[0005] The first aspect of the present application provides a secondary battery, comprising a packaging bag, an electrode assembly and a positive tab. The packaging bag comprises a main body portion for accommodating the electrode assembly and a sealing portion connected with the main body portion. The electrode assembly comprises a positive pole piece, a negative pole piece and a separator arranged between the positive pole piece and the negative pole piece, and the positive pole piece, the separator and the negative pole piece are wound to form the electrode assembly. The positive pole piece comprises a positive current collector, and the negative pole piece comprises a negative current collector. The positive tab comprises a first section, a second section, a third section and a fourth section which are sequentially connected and integrally arranged, the first section is provided outside the packaging bag along a first direction, the second section is located in the sealing portion, the third section is located between the sealing portion and the negative current collector, and the fourth section is connected to the surface of the positive current collector. The projection of the fourth section in a second direction perpendicular to the first direction is located in the negative current collector, and the second direction is the thickness direction of the electrode assembly. As viewed along a third direction, the second section, the third section and the fourth section are located on the same side of the winding center axis of the electrode assembly in the second direction. The secondary battery further comprises a first adhesive, which is arranged on the surface of the fourth section away from the positive current collector and adheres the fourth section and the positive pole piece.

[0006] The second section, the third section and the fourth region of the positive electrode tab are located on the same side of the winding center axis of the electrode assembly in the second direction Z according to the application, so that the degree of bending of the third section relative to the electrode assembly can be controlled in a smaller range, which is conducive to increasing the spacing between the third section and the adjacent separator in the second direction, reducing the risk of the positive electrode tab being in contact with and pressing the separator in the second direction due to the expansion of the electrode assembly when an external short circuit occurs, and further reducing the risk of the positive electrode tab scalding the separator to cause the positive electrode tab to be in contact with the negative electrode tab beyond the part of the positive electrode tab. In addition, by configuring the first adhesive, the relative fixation between the positive electrode tab and the positive electrode tab can be increased, and the risk of the positive electrode tab being easily detached from the positive current collector when falling due to the smaller degree of bending of the positive electrode tab relative to the electrode assembly can be reduced.

[0007] According to some embodiments of the application, the third section includes opposite first and second ends, the first end is in contact with the second section, and the second end is in contact with the fourth section. When viewed in the third direction, a straight line connecting the first and second ends is a first line segment, the first line segment intersects the second direction to form an included angle, and the included angle ranges from 50° to 85°. When the included angle is less than 50°, the risk of the positive electrode tab being in contact with the negative current collector beyond the part of the positive electrode tab to cause a short circuit due to the expansion of the electrode assembly pulling the positive electrode tab when an external short circuit occurs is greater. When the included angle is greater than 85°, the relative impact between the positive electrode tab and the positive current collector is too large during the falling process, which causes the positive electrode tab to be easily detached from the positive current collector, thereby reducing the falling performance.

[0008] According to some embodiments of the application, the included angle ranges from 60° to 85°, which is better for reducing the risk of short circuit.

[0009] According to some embodiments of the application, the positive electrode tab further includes a positive active layer arranged on the surface of the positive current collector, the positive active layer is provided with a groove exposing the positive current collector, the fourth section is accommodated in the groove and is in contact with the positive current collector, and the first adhesive covers and adheres the fourth section and the positive active layer.

[0010] According to some embodiments of the application, the first adhesive includes a first part covering the positive active layer, and in the third direction perpendicular to the first and second directions, the width of the first part is W1, the width of the first adhesive is W2, and 20%≤W1 / W2≤60%. When W1 / W2<20%, the force transferred to the positive active layer from the relative impact between the positive electrode tab and the positive current collector during the falling process is too small, which is limited for improving the effect of the positive electrode tab detaching from the positive current collector. When W1 / W2>60%, the space occupied by the first adhesive is larger, which causes the loss of volume energy density to be too large.

[0011] According to some embodiments of the present application, in the first direction, the first adhesive member comprises a first body region and a first extension region, the first body region covers the fourth section, and the first extension region covers the third section.

[0012] According to some embodiments of the present application, the secondary battery further comprises a second adhesive member, the second adhesive member comprises a second body region and a second extension region, the second body region is arranged on the side of the positive current collector away from the fourth section and covers the fourth section, and the second extension region covers the third section and is connected to the first extension region, further improving the relative fixation between the positive tab and the positive current collector and improving the drop performance.

[0013] According to some embodiments of the present application, the first adhesive member comprises a substrate layer and an adhesive layer, the adhesive layer comprises at least one of polypropylene, polybutadiene, polyethylene terephthalate, styrene, butadiene, isoprene, and a copolymer thereof and polybutadiene; and / or, the second adhesive member comprises a substrate layer and an adhesive layer, the adhesive layer comprises at least one of polypropylene, polybutadiene, polyethylene terephthalate, styrene, butadiene, isoprene, and a copolymer thereof and polybutadiene. These polymers have good adhesive properties.

[0014] According to some embodiments of the present application, the secondary battery further comprises a third adhesive member, the third adhesive member covers the second section and adheres the second section and the packaging bag, and the first extension region and the second extension region are further connected to the third adhesive member, further improving the relative fixation between the positive tab and the positive current collector and improving the drop performance.

[0015] According to some embodiments of the present application, the first adhesive member comprises a second part covering the third adhesive member, and in the first direction, the length of the second part is 0.01mm-2mm. When the length of the second part is less than 0.01mm, the effect of improving the relative fixation between the positive tab and the positive current collector is limited; when the length of the second part is greater than 2mm, the first adhesive member is easy to enter the packaging part, affecting the packaging reliability.

[0016] According to some embodiments of the present application, the third adhesive member comprises at least one of polypropylene, polyethylene, polyimide, and polyethylene terephthalate.

[0017] According to some embodiments of the present application, the negative current collector further comprises a second edge opposite to the first edge in the first direction, the main body part is provided with a receiving cavity for receiving the electrode assembly, the receiving cavity comprises a first side wall on one side of the first edge in the first direction and a second side wall on one side of the second edge in the first direction; in the first direction, the maximum distance between the first edge and the first side wall is D1 mm and the maximum distance between the second edge and the second side wall is D2 mm in the third direction, and 0.8≤D1+D2≤1.6. When the sum of D1 and D2 is less than 0.8 mm, the gap between the negative electrode tab and the packaging bag is too small, and the corner position of the main body part is easily pressed by the negative electrode tab during the falling process, causing corrosion; when the sum of D1 and D2 is greater than 1.6 mm, the gap between the electrode assembly and the packaging bag is too large, and the displacement of the electrode assembly in the packaging bag during the falling process is too large, resulting in excessive voltage and reducing the falling performance.

[0018] According to some embodiments of the present application, the thickness of the positive tab is 60 μm-100 μm, and the positive tab is an aluminum tab or a nickel tab, so that the positive tab has appropriate flexibility.

[0019] According to some embodiments of the present application, the secondary battery further comprises a negative tab, the negative tab is electrically connected to the negative electrode tab and extends out of the packaging bag, the thickness of the negative tab is 60 μm-100 μm, and the negative tab is a copper tab or a copper-nickel plated tab.

[0020] According to some embodiments of the present application, the secondary battery further comprises one negative tab, the number of positive tabs is two, and the two positive tabs and the negative tab are connected to the electrode assembly and extend out of the packaging bag along the first direction through the packaging part. By configuring two positive tabs and one negative tab, the temperature rise of the electrode assembly can be reduced through parallel shunt.

[0021] The second aspect of the present application provides an electronic device comprising any of the above secondary batteries. BRIEF DESCRIPTION OF DRAWINGS

[0022] FIG. 1 is a schematic structural view of a secondary battery in a thickness direction according to an embodiment.

[0023] FIG. 2 is a schematic view of the secondary battery shown in FIG. 1 before packaging.

[0024] FIG. 3 is a schematic cross-sectional view of an electrode assembly according to an embodiment.

[0025] FIG. 4 is an enlarged view of A in FIG. 3.

[0026] FIG. 5 is a schematic cross-sectional view of a secondary battery according to an embodiment.

[0027] FIG. 6 is a schematic view of a positive electrode tab after being unfolded according to an embodiment.

[0028] FIG. 7 is a cross-sectional view of a secondary battery in another embodiment.

[0029] FIG. 8 is a cross-sectional view of a separator in an embodiment.

[0030] Main element symbol explanation: Secondary battery 100 Packaging bag 10 Electrode assembly 20 Positive electrode tab 31 Negative electrode tab 32 Main body portion 11 Sealing portion 12 Accommodation cavity 11A First packaging portion 10A Second packaging portion 10B First region 10A1 Second region 10A2 Third region 10B1 Fourth region 10B2 First recess S1 Second recess S2 Positive electrode tab 21 Negative electrode tab 22 Separator 23 Positive electrode current collector 211 Positive electrode active layer 212 Negative electrode current collector 221 Negative electrode active layer 222 First section 311 Second section 312 Third section 313 Fourth section 314 Winding center axis O First end 313A Second end 313B First line segment L1 First edge 221ASecond line segment L2 Angle α Groove 212A, 222A First adhesive 40 Second adhesive 50 First main body area 41 First extension area 42 Second main body area 51 Second extension area 52 Third adhesive 60 Fourth adhesive 70 Second edge 221B Second portion 40B Substrate layer 401 Adhesive layer 402

[0031] The following detailed embodiments will further illustrate the present application in conjunction with the above-mentioned drawings. DETAILED DESCRIPTION

[0032] The following detailed embodiments are illustrative rather than limiting and are intended to provide further examples of the present application. The key or critical elements of the present application are described throughout the present specification, including claim definitions. The various features mentioned in the various embodiments can be combined in any way, provided that the structure does not contradict itself.

[0033] When one component is said to be "on" another component, it can be directly on the other component or intervening components can also be present. When one component is said to be "connected" to another component, it can be directly connected to the other component or intervening components can also be present.

[0034] Unless otherwise defined, the term "plurality" as used herein to describe a number of components means that the components are two or more.

[0035] Some embodiments of the present application will be described below in conjunction with the accompanying drawings. The following embodiments and features of the embodiments can be combined with each other, provided that there is no structural conflict.

[0036] Referring to FIG. 1, an embodiment of the present application provides a secondary battery 100 including a packaging bag 10, an electrode assembly 20, an electrolyte, and a plurality of tabs. The electrode assembly 20 and the electrolyte are accommodated in the packaging bag 10. The tabs are connected to the electrode assembly 20 and extend out of one side of the packaging bag 10 in a first direction X to connect to external elements. In the present application, the first direction X is the length direction of the electrode assembly 20. In the embodiment, the number of tabs is three, and the three tabs are configured as two positive tabs 31 and one negative tab 32, which can reduce the temperature rise of the electrode assembly 20 by parallel shunt. In other embodiments, the number of tabs can also be two or more than three.

[0037] When viewed in a second direction Z perpendicular to the first direction X, the packaging bag 10 includes a main body portion 11 and a sealing portion 12 extending from the edge of the main body portion 11. In the present application, the second direction Z is the thickness direction of the electrode assembly 20. The sealing portion 12 is configured to seal the main body portion 11 to reduce the risk of liquid leakage. The main body portion 11 is provided with an accommodation cavity 11A (see FIG. 5), and the electrode assembly 20 is arranged in the accommodation cavity 11A. The tabs pass through the sealing portion 12 and extend out of the packaging bag 10 in the first direction X.

[0038] Referring to FIGS. 1 and 2, the packaging bag 10 includes a first packaging portion 10A and a second packaging portion 10B arranged integrally, and the packaging bag 10 is sealed by the first packaging portion 10A and the second packaging portion 10B. For example, the first packaging portion 10A and the second packaging portion 10B are formed by folding a packaging film in half. The first packaging portion 10A includes a first region 10A1 and a second region 10A2 connected to each other. Three sides of the second region 10A2 are surrounded by the first region 10A1. The second packaging portion 10B includes a third region 10B1 and a fourth region 10B2 connected to each other. Three sides of the fourth region 10B2 are surrounded by the third region 10B1. The second region 10A2 of the first packaging portion 10A is provided with a first recess S1 for accommodating the electrode assembly 20, and the fourth region 10B2 of the second packaging portion 10B is provided with a second recess S2 for accommodating the electrode assembly 20, and the first recess S1 and the second recess S2 together form an accommodation cavity 11A (see FIG. 5) for receiving the electrode assembly 20. The first region 10A1 is connected to the third region 10B1 to form the sealing portion 12. In another embodiment, the first packaging portion 10A and the second packaging portion 10B are arranged separately.

[0039] In some embodiments, the first packaging portion 10A and the second packaging portion 10B each include a protective layer, a metal layer, and an encapsulation layer stacked in sequence, the encapsulation layer being proximate to the electrode assembly 20, and the protective layer being distal to the electrode assembly 20. The protective layer is made of a high polymer resin, which is used to protect the metal layer from being damaged by external force, and to prevent air from the external environment from penetrating, so as to maintain a water-free and oxygen-free environment inside the secondary battery 100. The metal layer is made of a metal, such as aluminum, steel, etc., which is used to prevent moisture from the external environment from penetrating, and to prevent damage to the secondary battery 100 caused by external force. The encapsulation layer is made of a polymer, such as polypropylene, polyamide, etc., which is used to encapsulate the encapsulation film, prevent the encapsulation film from being dissolved or swelled by the organic solvent in the electrolyte, and prevent the electrolyte in the electrolyte from contacting the metal layer to cause corrosion of the metal layer. The first packaging portion 10A and the second packaging portion 10B can be formed by folding the encapsulation film in half, and then applying a certain temperature and pressure on the surface of the folded encapsulation film by using a heat sealing head to perform heat sealing, so as to melt and connect the encapsulation layers of the encapsulation film to form the packaging bag 10. At this time, the innermost layer of the packaging bag 10 is the encapsulation layer. In this embodiment, the packaging bag 10 is formed by aluminum plastic film encapsulation.

[0040] Referring to FIG. 3, the electrode assembly 20 includes the positive electrode sheet 21, the negative electrode sheet 22, and the separator 23 stacked and wound. The separator 23 is disposed between the negative electrode sheet 22 and the positive electrode sheet 21. Specifically, the electrode assembly 20 is formed by stacking and winding the positive electrode sheet 21, the negative electrode sheet 22, the separator 23, and the like in the second direction Z. The positive electrode sheet 21 includes the positive electrode current collector 211 and the positive electrode active layer 212 disposed on at least one surface of the positive electrode current collector 211. In this embodiment, the positive electrode active layer 212 is disposed on both surfaces of the positive electrode current collector 211. The positive electrode current collector 211 includes at least one of Ni, Ti, Cu, Ag, Au, Pt, Fe, AL, and combinations thereof. The positive electrode active layer 212 includes a positive electrode active material, which can include at least one of lithium cobaltate, lithium manganate, lithium nickelate, lithium nickel cobalt manganate, lithium iron phosphate, lithium manganese iron phosphate, lithium vanadium phosphate, lithium vanadium oxyphosphate, lithium-rich manganese-based material, lithium nickel cobalt aluminum phosphate, and combinations thereof. The negative electrode sheet 22 includes the negative electrode current collector 221 and the negative electrode active layer 222 disposed on at least one surface of the negative electrode current collector 221. In this embodiment, the negative electrode active layer 222 is disposed on both surfaces of the negative electrode current collector 221. The negative electrode current collector 221 includes at least one of Ni, Ti, Cu, Ag, Au, Pt, Fe, AL, and combinations thereof. The negative electrode active layer 222 includes one or more of soft carbon, hard carbon, artificial graphite, natural graphite, silicon, silicon oxide compounds, silicon-carbon composites, lithium titanate, and metals capable of forming alloys with lithium.

[0041] The positive tab 31 has a certain flexibility. When the electrode assembly 20 is deformed by swelling, the positive tab 31 is pulled, causing the positive tab 31 to contact and press the separator 23. In some embodiments, the thickness of the positive tab 31 is 60 μm to 100 μm, for example, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, or a range defined by any two of the numbers, so that the positive tab 31 has a suitable flexibility. In some embodiments, the material of the positive tab 31 includes at least one of Ni, Ti, Cu, Ag, Au, Pt, Fe, AL, and combinations thereof. In this embodiment, the positive tab 31 is an aluminum tab or a nickel tab.

[0042] In some embodiments, the thickness of the negative tab 32 is 60 μm to 100 μm, for example, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, or a range defined by any two of the numbers. In some embodiments, the material of the negative tab 32 includes at least one of Ni, Ti, Cu, Ag, Au, Pt, Fe, AL, and combinations thereof. In this embodiment, the negative tab 32 is a copper tab or a copper-nickel-plated tab.

[0043] Referring to FIG. 5, the positive tab 31 includes a first section 311, a second section 312, a third section 313 and a fourth section 314 which are sequentially connected and integrally arranged. The first section 311 is outwardly provided along the first direction X from the packaging bag 10, the second section 312 is located within the packaging portion 12, the third section 313 is located between the packaging portion 12 and the negative current collector 221, and the fourth section 314 is connected to the surface of the positive current collector 211 and overlaps the negative current collector 221. Specifically, the first section 311 is a part of the positive tab 31 which is away from the packaging portion 12 and at least partially located outside the packaging bag 10; the second section 312 is a part of the positive tab 31 which is connected to the first section 311 and the projection thereof along the second direction Z overlaps the packaging portion 12 located on the same side of the tab along the first direction X; the third section 313 is a part of the positive tab 31 which is connected to the second section 312 and located between the end surface of the packaging portion 12 located on the same side of the tab along the first direction X and the end surface of the negative current collector 221 located on the same side of the tab along the first direction X and distributed along the second direction Z; and the fourth section 314 is a part of the positive tab 31 which is connected to the third section 313 and the projection thereof along the second direction Z is located within the negative current collector 221. The end surface defined by the multiple edges of the negative current collector 221 located on the same side of the tab along the first direction X and distributed along the second direction Z can be a plane or a curved surface, which is not limited in the present application. The two edges of the second section 312 along the first direction X respectively coincide with the two edges of the packaging portion 12 located on the same side of the tab along the first direction X. As viewed along the third direction Y, the second section 312, the third section 313 and the fourth section 314 are located on the same side of the winding central axis O of the electrode assembly 20 along the second direction Z, so that the bending degree of the third section 313 relative to the electrode assembly 20 can be controlled within a smaller range, which is beneficial to increase the distance between the third section 313 and the adjacent separator 23 along the second direction Z, reduce the risk that the positive tab 31 is contacted and pressed to the separator 23 along the second direction Z due to the expansion of the electrode assembly 20 when external short circuit occurs, and further reduce the risk that the positive tab 31 burns the separator 23 to cause the short circuit between the part of the positive tab 31 which exceeds the positive electrode plate 21 and the negative electrode plate 22. In the present application, the third direction Y is the width direction of the electrode assembly 20.

[0044] Referring to FIG. 5, the third section 313 includes a first end 313A opposite to a second end 313B in the first direction X, the first end 313A is in contact with the second section 312, and the second end 313B is in contact with the fourth section 314. In the present application, the first end 313A is a connection point between the second section 312 and the third section 313, and the first end 313A coincides with an edge of the packaging portion 12 on the side of the tab in the first direction X and close to the electrode assembly 20; the second end 313A is a connection point between the third section 313 and the fourth section 314, and the second end 313A coincides with an edge of the negative current collector 221 on the side of the tab in the first direction X. In the third direction Y, a straight line connecting the first end 313A and the second end 313B is a first line segment L1. The first line segment L1 can or can not coincide with the third section 313. In the present embodiment, the first line segment L1 does not coincide with the third section 313. The first line segment L1 intersects the second direction Z. By configuring the first line segment L1 to intersect the second direction Z, a predetermined distance is provided between the electrode assembly 20 and the packaging portion 12, which is beneficial to improve the packaging reliability of the packaging portion 12.

[0045] The first line segment L1 and the second direction Z form an included angle a. In some embodiments, the included angle a is in the range of 50° to 85°. When the included angle a is less than 50°, when an external short circuit occurs in the secondary battery 100, the electrode assembly 20 expands and pulls the positive tab 31 to contact and press the separator from the second direction Z, causing the separator to be scalded, and further causing the positive tab 31 to contact the part of the negative current collector 211 that exceeds the positive electrode tab 22, resulting in a greater risk of secondary short circuit. When the included angle a is greater than 85°, during the drop process of the secondary battery 100, the relative impact between the positive tab 31 and the positive current collector 211 is too large, causing the positive tab 31 to easily fall off the positive current collector 211, thereby causing the voltage drop during the drop process to be too large, reducing the drop performance. Preferably, the included angle a is in the range of 60° to 85°, which is better for reducing the risk of secondary short circuit.

[0046] Referring to FIGS. 3 and 4, the positive active layer 212 is provided with a recess 212A that exposes the positive current collector 211, and the fourth section 314 is accommodated in the recess 212A and welded with the positive current collector 211. The fourth section 314 and the recess 212A can be interference fit to completely cover the positive current collector 211 exposed in the recess 212A, or can be clearance fit to expose part of the positive current collector 211, which is not limited in the present application. In the present embodiment, recesses 212A are provided in both positive active layers 212, the two recesses 212A are aligned in the second direction Z, and the fourth section 314 is accommodated in one recess 212A. In another embodiment, the recess 212A is provided in only one positive active layer 212.

[0047] Referring to FIGS. 4, 5 and 6, the secondary battery 100 further comprises a first adhesive 40. The first adhesive 40 is disposed on a surface of the fourth section 314 facing away from the positive current collector 211 and adheres the fourth section 314 and the positive electrode tab 21. By configuring the first adhesive 40, the relative fixation between the positive electrode tab 31 and the positive electrode tab 21 can be increased, the risk of the positive electrode tab 31 falling off the positive current collector 211 when dropped can be reduced, and the drop performance can be improved. In addition, configuring the second adhesive 40 can also reduce the risk of the positive electrode tab 31 and the negative electrode tab 22 being short-circuited due to the welding burr formed by welding the positive electrode tab 31 and the positive current collector 211 piercing the separator 23.

[0048] The first adhesive 40 covers a groove 212A and adheres a positive active layer 212 and the fourth section 314 located in the groove 212A. The first adhesive 40 comprises a first portion 40A covering the positive active layer 212. In the present embodiment, the first portion 40A is located on both sides of the groove 212A in the third direction Y. The third direction Y is perpendicular to the first direction X and the second direction Z. In another embodiment, the first portion 40A is located on only one side of the groove 212A in the third direction Y. In the third direction Y, the total width of the first portion 40A is W1, and the width of the first adhesive 40 is W2, 20%≤W1 / W2≤60%. When W1 / W2<20%, the relative impact force between the positive electrode tab 31 and the positive current collector 211 is too small when dropped, and the force transferred to the positive active layer 212 has limited effect on improving the positive electrode tab 31 from the positive current collector 211. When W1 / W2>60%, the space occupied by the first adhesive 40 is too large, resulting in a too large loss of volumetric energy density. It should be noted that in FIGS. 3 and 4, the first adhesive 40 is not shown adhered to the positive electrode tab 21 for clarity of the positional relationship between the elements; in FIGS. 4 and 6, the width of the portion of the first adhesive 40 not covering the positive active layer 212 in the third direction Y is W2-W1, which is used to indirectly show the total width W1 of the first portion 40A.

[0049] Referring to FIGS. 3 and 4, the secondary battery 100 further includes a second adhesive 50. The second adhesive 50 covers the other recess 212A and covers the surface of the positive current collector 211 and the other positive active layer 212 exposed in the other recess 212A away from the fourth section 314. A fourth adhesive 70 covers the positive tab 31 and the positive current collector 211 to facilitate reducing the risk of the positive tab 31 piercing the separator 23 to cause the positive tab 21 and the negative tab 22 to be in contact and short-circuited. In some embodiments, the ratio of the width of the portion of the second adhesive 50 covering the positive active layer 212 to the width of the second adhesive 50 in the third direction Y ranges from 20% to 60%. It is noted that the second adhesive 50 is not shown to be adhered to the positive current collector 211 in FIGS. 3 and 4 for clarity of the positional relationship between the elements.

[0050] Referring to FIG. 5, the first adhesive 40 further includes a first body section 41 and a first extension section 42. The first body section 41 covers the fourth section 314, and the first extension section 42 covers the third section 313. The second adhesive 50 includes a second body section 51 and a second extension section 52. The second body section 51 is disposed on the side of the positive current collector 211 away from the fourth section 314 and covers the fourth section 314, and the second extension section 52 covers the surface of the third section 313 away from the first extension section 42. In the present embodiment, the second body section is disposed on the surface of the positive current collector 211 away from the fourth section 314. The first extension section 42 and the second extension section 52 are connected to each other to further improve the relative fixation between the positive tab 31 and the positive current collector 211. It is noted that the first extension section 42 and the second extension section 52 are not shown to be connected to each other in FIG. 5 for clarity of the positional relationship between the elements.

[0051] Referring to FIGS. 3 and 4, the negative active layer 222 is provided with a recess 222A exposing the negative current collector 221. The negative tab 32 is partially accommodated in the recess 222A and is welded to the negative current collector 221. The negative tab 32 and the recess 222A can be in interference fit to completely cover the negative current collector 221 exposed in the recess 222A, or can be in clearance fit to expose part of the negative current collector 221, which is not limited in the present application. In the present embodiment, the recess 222A is provided in each of the two negative active layers 222. The two recesses 222A are aligned in the second direction Z, and the negative tab 32 is partially accommodated in one of the recesses 222A. In another embodiment, the recess 222A is provided in only one of the negative active layers 222.

[0052] Referring to FIGS. 3 and 4, the secondary battery 100 further comprises fourth adhesive 70 adhering to the negative active layer 222 and covering the negative tab 32 to reduce the phenomenon of piercing the separator 23 caused by the welding mark formed on the negative tab 32, and reduce the risk of short circuit between the positive tab 21 and the negative tab 22. In the embodiment, the number of fourth adhesive 70 is two, one of which is on the same side of the negative current collector 221 in the second direction Z as the negative tab 32, and the other is on the opposite side of the negative current collector 221 in the second direction Z as the negative tab 32. In another embodiment, only one fourth adhesive 70 is provided on the same side of the negative current collector 221 in the second direction Z as the negative tab 32. Referring to FIG. 5, the negative current collector 221 further comprises a second edge 221B opposite the first edge 221A in the first direction X. The accommodation cavity 11A comprises a first side wall 11A1 on one side of the first edge 221A in the first direction X and a second side wall 11A2 on one side of the second edge 221B in the first direction X. In the first direction X, the maximum distance between the first edge 221A and the first side wall 11A1 is D1 mm, and the maximum distance between the second edge 221B and the second side wall 11A2 is D2 mm, 0.8≤D1+D2≤1.6. It should be noted that the maximum distance between the second edge 221B and the second side wall 11A2 refers to the maximum value of the distance between the plurality of first edges 221A1 distributed in the second direction Z of the negative current collector 221 and the second side wall 11A2 in the first direction X. When the sum of D1 and D2 is less than 0.8 mm, the gap between the negative tab 22 and the packaging bag 10 is too small, and the corner position of the main body 11 is easily extruded by the negative tab 22 during the drop process, causing corrosion; when the sum of D1 and D2 is greater than 1.6 mm, the gap between the electrode assembly 20 and the packaging bag 10 is too large, and the displacement of the electrode assembly 20 in the packaging bag 10 during the drop process is too large, resulting in an excessively large voltage and reducing the drop performance.

[0053] Referring to FIG. 7, the secondary battery 100 further comprises a third adhesive 60. The third adhesive 60 covers the second section 311 and adheres to the second section 311 of the positive tab 31, the first region 10A1 of the first packaging portion 10A, and the third region 10B1 of the second packaging portion 10B. By configuring the third adhesive 60, the sealing performance of the packaging portion 12 at the position of the positive tab 31 is improved. Both the first extension region 42 and the second extension region 52 are connected to the third adhesive 60 to further improve the relative fixation between the positive tab 31 and the positive current collector 211.

[0054] Referring to FIG. 7, the first adhesive 40 further includes a second portion 40B covering the third adhesive 60. In the first direction X, the length of the second portion 40B is 0.01-2 mm. When the length of the second portion 40B is less than 0.01 mm, the effect of improving the relative fixation between the positive tab 31 and the positive current collector 211 is limited; when the length of the second portion 40B is greater than 2 mm, the first adhesive 40 is easy to enter the packaging portion 12, affecting the packaging reliability. In some embodiments, the length of the portion of the second adhesive 50 covering the third adhesive 60 in the first direction X is also 0.01-2 mm.

[0055] Referring to FIG. 8, in some embodiments, the first adhesive 40 includes a substrate layer 401 and an adhesive layer 402 arranged in layers, and the adhesive layer 402 is adhered to the positive electrode tab. The substrate layer 401 includes at least one of polyethylene terephthalate, polyethylene, polypropylene, phenolic resin, melamine resin, unsaturated polyester resin, epoxy resin, silicone resin, or polyurethane. The adhesive layer 402 includes at least one of polypropylene, polybutadiene, polyethylene terephthalate, styrene, butadiene, isoprene, and copolymers thereof and polybutadiene, which have good adhesive properties.

[0056] In some embodiments, the material of the second adhesive 50 is the same as that of the first adhesive 40, and the second adhesive 50 also includes a substrate layer 401 and an adhesive layer 402. In some embodiments, the material of the fourth adhesive 70 is the same as that of the first adhesive 40, and the fourth adhesive 70 also includes a substrate layer 401 and an adhesive layer 402.

[0057] In some embodiments, the third adhesive 60 includes at least one of polypropylene, polyethylene, polyimide, and polyethylene terephthalate, which have good packaging properties.

[0058] In some embodiments, the separator 23 includes a base layer and a coating layer. The coating layer is arranged on the surface of the base layer facing the positive electrode tab and adhered to the positive active layer. The coating layer is adhered to the positive electrode tab, reducing the risk of delamination and misalignment of the separator 23 and the positive electrode tab. The coating layer can also be arranged on the surface of the base layer facing the negative electrode tab and adhered to the negative active layer, to reduce the risk of delamination and misalignment of the separator 23 and the negative electrode tab. In another embodiment, the separator 23 includes an adhesive, and the separator 23 is adhered to the positive electrode tab and / or the negative electrode tab.

[0059] In some embodiments, the base layer comprises at least one of polyethylene terephthalate, polyethylene, polypropylene, phenol formaldehyde resin, melamine resin, unsaturated polyester resin, epoxy resin, silicone resin, or polyurethane. In some embodiments, the coating layer is polymerized from at least two of the following monomers: butadiene, methyl acrylate, methyl methacrylate, styrene, butyl methacrylate, isobutyl acrylate, isooctyl acrylate, ethylene, propylene, vinylidene fluoride. The adhesion strength of the coating layer is adjusted by selecting the type and / or mass ratio of the materials of the coating layer, thereby adjusting the peel strength between the separator 23 and the positive electrode tab and the peel strength between the separator 23 and the negative electrode tab.

[0060] In some embodiments, the peel strength between the separator 23 and the positive electrode tab is 7-15 N / m, for example, 7 N / m, 8 N / m, 9 N / m, 10 N / m, 11 N / m, 12 N / m, 13 N / m, 14 N / m, 15 N / m, or a range defined by any two of the above values. In some embodiments, the peel strength between the separator 23 and the negative electrode tab is 7-15 N / m, for example, 7 N / m, 8 N / m, 9 N / m, 10 N / m, 11 N / m, 12 N / m, 13 N / m, 14 N / m, 15 N / m, or a range defined by any two of the above values.

[0061] An electronic device according to an embodiment of the present application includes any one of the secondary batteries described above. The electronic device according to the present application can be, but is not limited to, a notebook computer, a pen-input computer, a mobile computer, an electronic book player, a portable telephone, a portable facsimile, a portable copying machine, a portable printer, a headphone, a video recorder, a liquid crystal television, a portable cleaner, a portable CD player, a mini disc, a transceiver, an electronic organizer, a calculator, a memory card, a portable audio player, a radio, a backup power supply, an electric motor, an automobile, a motorcycle, a power-assisted bicycle, a lighting appliance, a toy, a game machine, a clock, an electric tool, a flashlight, a camera, a home-use large storage battery, a lithium-ion capacitor, and the like.

[0062] The performance of the secondary battery according to the present application is described below by way of specific examples and comparative examples.

[0063] Example 1

[0064] Preparation of the positive electrode tab: A positive electrode active material (lithium cobaltate), a conductive agent (conductive carbon black and carbon nanotube), and a binder (polyvinylidene fluoride) were dissolved in N-methylpyrrolidone solution at a weight ratio of 97.5:1:1.5 to form a positive electrode slurry having a solid content of 75%. An aluminum foil was used as a current collector, and the positive electrode slurry was coated on the surface of the positive electrode current collector to obtain a positive electrode active material layer. Subsequently, cold pressing, cutting, and welding of the positive electrode tab were performed to obtain the positive electrode tab.

[0065] Preparation of the negative electrode tab: the negative electrode active material (graphite), the conductive agent (conductive carbon black), the thickening agent (sodium carboxymethyl cellulose), and the binder (butadiene-styrene rubber) were mixed in a mass ratio of 97.5:1:0.5:1, and then deionized water was added as a solvent to obtain a negative electrode slurry with a solid content of 50 wt%. A copper foil was used as the current collector, and the negative electrode slurry was coated on the surface of the negative electrode current collector to obtain a negative electrode active material layer. Subsequently, cold pressing, cutting, and welding of the negative electrode tab were performed to obtain the negative electrode tab.

[0066] Preparation of the separator film: a polyethylene film was selected as the base layer, and a binder was coated on the surface of the base layer to form a coating layer. The peeling strength between the separator film and the positive electrode tab and the negative electrode tab was 10 N / m.

[0067] Preparation of the electrolyte: ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), propyl propionate (PP), and vinylene carbonate (VC) were mixed in a weight ratio of 20:30:20:28:2 to obtain an organic solvent, and then fully dried lithium salt LiPF6 and the organic solvent were mixed in a weight ratio of 8:92 to obtain the electrolyte.

[0068] Preparation of the lithium ion battery: the positive electrode tab, the polyethylene separator film, and the negative electrode tab were sequentially stacked with the separator film between the positive electrode tab and the negative electrode tab to obtain an electrode assembly; the electrode assembly was placed in an aluminum plastic film packaging bag and hot-pressed and bonded at a preset pressure, and then the lithium ion battery was obtained after liquid injection and formation. The structure of the lithium ion battery is shown in FIGS. 3 and 5.

[0069] Examples 2-16

[0070] The difference between the example 1 and the present example is that at least one of the following is different: the included angle a formed after the positive electrode tab is bent relative to the electrode assembly, the ratio W1 / W2 of the width W1 of the first part of the first adhesive member to the width W2 of the first adhesive member, the distance between the edge of the negative electrode current collector and the side wall of the accommodating cavity, and D1+D2.

[0071] Comparative Examples 1-3

[0072] The difference between the example 1 and the present example is that at least one of the following is different: whether the second section, the third section, and the fourth region of the positive electrode tab are located on the same side of the winding central axis in the thickness direction of the electrode assembly, and whether the first adhesive member is used.

[0073] The test methods for the various parameters of the present application are described below.

[0074] (1) Determination method of the included angle a:

[0075] The lithium ion battery is scanned along the width direction by using the computer tomography method, and a cross-sectional view of the positive tab position is taken; the first end is a point corresponding to the bottom of the positive tab and the packaging part, the second end is a point corresponding to the edge of the negative current collector close to the positive tab, and the first line segment is a line connecting the first end and the second end; a straight line passing through the second end and parallel to the thickness direction is drawn on the cross-sectional view, and the included angle between the first line segment and the straight line is α .

[0076] (2) Test method of the distance between the negative current collector and the side wall of the accommodation cavity and D1+D2:

[0077] The lithium ion battery is scanned along the width direction by using the computer tomography method, and a cross-sectional view of the positive tab position is taken; a plurality of edges of the top of the negative current collector in the width direction form an end face, and the vertical distance between the lowest point of the end face and the highest point of the packaging bag in the length direction is D1; another end face is formed by a plurality of edges of the bottom of the negative current collector in the width direction, and the vertical distance between the highest point of the end face and the lowest point of the packaging bag in the length direction is D2.

[0078] (2) Drop test:

[0079] The lithium ion battery is pretreated at 25°C, and after standing for 60 min in a normal temperature environment, the voltage of the lithium ion battery before the drop test is tested; the lithium ion battery is loaded into a clamp, and the drop equipment is used to drop freely from a position 1.5 m away from the ground in the following order: head-tail-head right corner-tail right corner-head left corner-tail left corner (angle: 45±15°), and the process is repeated for 6 rounds. After the drop, stand for 24 h at room temperature, measure and record the voltage of the lithium ion battery, and check the appearance of the lithium ion battery before and after the test and take photos. The pass criteria for the drop test: no smoke, no leakage, and voltage drop <50 mV. Ten lithium ion batteries are tested, and the number of batteries that pass the test is X, and the test pass rate is X / 10.

[0080] (3) Short circuit test:

[0081] At 25°C, stand for 5 min, charge the lithium ion battery to 4.50V at a constant current of 0.2C, then charge to 0.025C at a constant voltage of 4.50V, stand for 60 min, and use a resistance of 60±20 mΩ for positive and negative short circuit test in a test environment of 55±2°C. When one of the following conditions is reached, the test is stopped: 1) when the sample voltage is lower than 0.1V, and the surface temperature drops to the test environment temperature±10°C, stop; 2) if the voltage cannot be lowered to 0.1V, stop when the surface temperature drops to the test environment temperature. The test pass criteria are that the sample does not catch fire, does not explode, and the sample surface temperature does not exceed 150°C. Ten batteries are tested, and the number of batteries that pass the test is X, and the test pass rate is X / 10.

[0082] (4) Width test of the first adhesive:

[0083] The lithium ion battery was disassembled to take out a positive electrode tab. The width W1 and W2 of the first adhesive were measured by using a charge-coupled device (CCD) or a ruler.

[0084] Table 1 lists the parameters and evaluation results of each example and comparative example.

[0085] Table 1

[0086] As can be seen from Table 1, compared with the comparative examples, in each example, the second section, the third section and the fourth section of the positive tab are located on the same side of the winding central axis of the electrode assembly in the thickness direction, so that the third section has a smaller bending degree relative to the electrode assembly, reducing the risk of short circuit caused by the electrode assembly expanding to pull the positive tab to compress the separator; and the fourth section and the positive tab are bonded by the first adhesive, reducing the risk of the positive tab being separated from the positive current collector during the drop, thus balancing the high pass rate of the external short circuit test and the drop test.

[0087] As can be seen from Table 1, compared with examples 1 and 7, examples 2-6 satisfy 50°≤α≤85°, the degree of the electrode assembly expanding to pull the positive tab to compress the separator during external short circuit and the relative impact degree between the positive tab and the positive current collector during the drop are controlled within a suitable range, and have a high pass rate of the external short circuit test and the drop test. In example 1, the included angle α is too small, the degree of the electrode assembly expanding to pull the positive tab to compress the separator during external short circuit is the most serious, resulting in the smallest pass rate of the external short circuit test; in example 7, the included angle α is too large, the relative impact force between the positive tab and the positive current collector during the drop is too large, resulting in the smallest pass rate of the drop. Among them, examples 4-6 satisfy 60°≤α≤85°, and the improvement effect on short circuit and drop performance is better.

[0088] As can be seen from Table 1, compared with examples 8 and 12, examples 9-11 satisfy 0.8≤D1+D2≤1.6, the degree of the edge corner position of the main body part of the packaging bag being extruded by the negative tab during the drop and the displacement of the electrode assembly in the packaging bag are controlled within a suitable range, and have a high pass rate of the external short circuit test and the drop test. In example 8, D1+D2<0.8, the gap is too small, the degree of the edge corner position of the main body part of the packaging bag being extruded by the negative tab during the drop is the most serious, resulting in the smallest pass rate of the external short circuit test; in example 12, D1+D2>1.6, the gap is too large, the displacement of the electrode assembly in the packaging bag during the drop is too large, resulting in the smallest pass rate of the drop.

[0089] As shown in Table 1, compared with Example 13, Examples 14-16 satisfy W1 / W2≥20%, and when falling, the relative impact force between the positive electrode tab and the positive electrode current collector is largely transferred to the positive electrode active layer, greatly improving the falling performance. When W1 / W2>60%, the space occupied by the first adhesive is large, resulting in excessive loss of volumetric energy density.

[0090] Those skilled in the art should understand that the above examples are only used to illustrate the present application, and are not used as a limitation to the present application, and as long as the above examples are appropriately changed and changed within the scope of the spirit of the present application, they fall within the scope of the present application.

Claims

1. A secondary battery, comprising a packaging bag, an electrode assembly, and a positive electrode tab, wherein the packaging bag includes a main body portion for receiving the electrode assembly and an encapsulation portion connected to the main body portion, the electrode assembly includes a positive electrode plate, a negative electrode plate, and a separator disposed between the positive electrode plate and the negative electrode plate, the positive electrode plate, the separator, and the negative electrode plate being wound to form the electrode assembly, characterized in that, The positive electrode includes a positive current collector, the negative electrode includes a negative current collector, and the positive electrode tab includes a first segment, a second segment, a third segment, and a fourth segment that are sequentially connected and integrally formed. The first segment protrudes from the outside of the packaging bag along a first direction, the second segment is located inside the encapsulation part, the third segment is located between the encapsulation part and the negative current collector, and the fourth segment is connected to the surface of the positive current collector. The projection of the fourth segment along a second direction perpendicular to the first direction is located inside the negative current collector, where the second direction is the thickness direction of the electrode assembly. Viewed along a third direction, the second segment, the third segment, and the fourth segment are located on the same side of the winding center axis of the electrode assembly in the second direction, and the third direction is perpendicular to the first direction and the second direction; The secondary battery further includes a first adhesive component, which is disposed on the surface of the fourth section opposite to the positive electrode current collector and adheres to the fourth section and the positive electrode sheet.

2. The secondary battery as described in claim 1, characterized in that, The third segment includes a first end and a second end, which are opposite each other. The first end is in contact with the second segment, and the second end is in contact with the fourth segment. When viewed along the third direction, the straight line connecting the first end and the second end is a first line segment. The first line segment intersects the second direction to form an angle, and the angle ranges from 50° to 85°.

3. The secondary battery as described in claim 2, characterized in that, The included angle ranges from 60° to 85°.

4. The secondary battery as described in claim 1, characterized in that, The positive electrode sheet further includes a positive active layer disposed on the surface of the positive current collector, the positive active layer having a groove that exposes the positive current collector, the fourth segment being accommodated in the groove and in contact with the positive current collector, and the first adhesive covering and bonding the fourth segment and the positive active layer.

5. The secondary battery as described in claim 4, characterized in that, The first adhesive includes a first portion covering the positive electrode active layer. In a third direction perpendicular to the first direction and the second direction, the width of the first portion is W1, and the width of the first adhesive is W2, where 20% ≤ W1 / W2 ≤ 60%.

6. The secondary battery as described in claim 1, characterized in that, In the first direction, the first adhesive includes a first body region and a first extension region that are in contact, the first body region covering the fourth segment and the first extension region covering the third segment.

7. The secondary battery as described in claim 6, characterized in that, The secondary battery further includes a second adhesive component, which includes a second main body region and a second extension region that are in contact with each other. The second main body region is disposed on the side of the positive electrode current collector away from the fourth segment and covers the fourth segment. The second extension region covers the third segment and is in contact with the first extension region.

8. The secondary battery as described in claim 7, characterized in that, The first adhesive component includes a substrate layer and an adhesive layer, the adhesive layer comprising at least one of polypropylene, polypentadiene, polyethylene terephthalate, styrene, butadiene, isoprene and its copolymers, and polybutadiene; and / or, the second adhesive component includes a substrate layer and an adhesive layer, the adhesive layer comprising at least one of polypropylene, polypentadiene, polyethylene terephthalate, styrene, butadiene, isoprene and its copolymers, and polybutadiene.

9. The secondary battery as described in claim 7, characterized in that, The secondary battery also includes a third adhesive component, which covers the second section and adheres to the second section and the packaging bag. The first extension area and the second extension area are also connected to the third adhesive component.

10. The secondary battery as described in claim 9, characterized in that, The first adhesive includes a second portion covering the third adhesive, and the length of the second portion is 0.01 mm to 2 mm in the first direction.

11. The secondary battery as described in claim 9, characterized in that, The third adhesive comprises at least one of polypropylene, polyethylene, polyimide, and polyethylene terephthalate.

12. The secondary battery as described in claim 1, characterized in that, The negative current collector includes a first edge located on the side of the positive electrode tab in the first direction and a second edge opposite to the first edge. The main body is provided with a receiving cavity for accommodating the electrode assembly. The receiving cavity includes a first sidewall located on the side of the first edge in the first direction and a second sidewall located on the side of the second edge. When viewed along the third direction, in the first direction, the maximum distance between the first edge and the first sidewall is D1 mm, and the maximum distance between the second edge and the second sidewall is D2 mm, where 0.8 ≤ D1 + D2 ≤ 1.

6.

13. The secondary battery as described in claim 1, characterized in that, The thickness of the positive electrode tab is 60μm to 100μm, and the positive electrode tab is an aluminum tab or a nickel tab.

14. The secondary battery as described in claim 1, characterized in that, The secondary battery also includes a negative electrode tab, which is electrically connected to the negative electrode sheet and extends outside the packaging bag. The thickness of the negative electrode tab is 60μm to 100μm, and the negative electrode tab is a copper tab or a copper-plated nickel tab.

15. The secondary battery as described in claim 1, characterized in that, The secondary battery also includes a negative electrode tab, and there are two positive electrode tabs. The two positive electrode tabs and the negative electrode tabs are connected to the electrode assembly and extend out of the packaging bag through the encapsulation part in the first direction.

16. An electronic device, characterized in that, Includes the secondary battery as described in any one of claims 1-15.

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