CN110190319B - Electrode assembly and secondary battery - Google Patents

Electrode assembly and secondary battery Download PDF

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Publication number
CN110190319B
CN110190319B CN201910445888.2A CN201910445888A CN110190319B CN 110190319 B CN110190319 B CN 110190319B CN 201910445888 A CN201910445888 A CN 201910445888A CN 110190319 B CN110190319 B CN 110190319B
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China
Prior art keywords
separator
electrode
flat
electrode assembly
flat portion
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Active
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CN201910445888.2A
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Chinese (zh)
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CN110190319A (en
Inventor
魏曦晨
朱宝健
徐守江
陈雷
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Contemporary Amperex Technology Co Ltd
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Contemporary Amperex Technology Co Ltd
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Priority to CN201910445888.2A priority Critical patent/CN110190319B/en
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/04—Construction or manufacture in general
    • H01M10/0431—Cells with wound or folded electrodes
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/058—Construction or manufacture
    • H01M10/0583—Construction or manufacture of accumulators with folded construction elements except wound ones, i.e. folded positive or negative electrodes or separators, e.g. with "Z"-shaped electrodes or separators
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/10—Primary casings; Jackets or wrappings
    • H01M50/116—Primary casings; Jackets or wrappings characterised by the material
    • H01M50/124—Primary casings; Jackets or wrappings characterised by the material having a layered structure
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/463—Separators, membranes or diaphragms characterised by their shape
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
    • Y02P70/50—Manufacturing or production processes characterised by the final manufactured product

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  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • General Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Manufacturing & Machinery (AREA)
  • Sealing Battery Cases Or Jackets (AREA)
  • Cell Separators (AREA)

Abstract

The invention provides an electrode assembly and a secondary battery. The electrode assembly includes an electrode unit and a first separator wound around an outer side of the electrode unit. The electrode unit includes a plurality of electrode sheets and a second separator, the second separator is folded into a multi-layer structure and includes a plurality of flat portions, and the plurality of electrode sheets and the plurality of flat portions are alternately laminated in a thickness direction. The plurality of flat parts comprise a first flat part and a second flat part, the first flat part and the second flat part are respectively positioned at two ends of the second diaphragm along the thickness direction, and the second flat part is positioned between two adjacent pole pieces. The first separator extends from one end of the second flat portion in the width direction and sequentially bypasses the pole piece on the side of the second flat portion close to the first flat portion and the pole piece on the side of the second flat portion away from the first flat portion.

Description

Electrode assembly and secondary battery
Technical Field
The present invention relates to the field of batteries, and more particularly, to an electrode assembly and a secondary battery.
Background
The electrode assembly of the secondary battery is a core component for performing a charge and discharge function, and generally includes a positive electrode tab, a negative electrode tab, and a separator separating the positive electrode tab and the negative electrode tab. For the laminated electrode assembly, when the secondary battery vibrates in the working process, the electrode plate is easy to misplace, and the service life and the safety performance of the electrode assembly are affected.
Disclosure of Invention
In view of the problems in the background art, it is an object of the present invention to provide an electrode assembly and a secondary battery that can reduce misalignment between electrode tabs and improve the life span and safety performance of the electrode assembly.
In order to accomplish the above object, the present invention provides an electrode assembly and a secondary battery.
The electrode assembly includes an electrode unit and a first separator wound around an outer side of the electrode unit. The electrode unit includes a plurality of electrode sheets and a second separator, the second separator is folded into a multi-layer structure and includes a plurality of flat portions, and the plurality of electrode sheets and the plurality of flat portions are alternately laminated in a thickness direction. The plurality of flat parts comprise a first flat part and a second flat part, the first flat part and the second flat part are respectively positioned at two ends of the second diaphragm along the thickness direction, and the second flat part is positioned between two adjacent pole pieces. The first separator extends from one end of the second flat portion in the width direction and sequentially bypasses the pole piece on the side of the second flat portion close to the first flat portion and the pole piece on the side of the second flat portion away from the first flat portion.
The first diaphragm and the second diaphragm are integrally formed.
The first separator is provided in 2-4 layers on both sides of the electrode unit in the width direction.
The free end of the first separator is located on the side of the electrode unit in the thickness direction close to the second flat portion.
The free ends of the first separator and the first flat portions are opposite in direction of width, and all the pole pieces are located on one side of the first flat portion in the thickness direction close to the second flat portion.
The secondary battery includes the electrode assembly.
The secondary battery further includes a pouch and an electrode lead. The electrode assembly is accommodated in a packing bag, the edge of the packing bag is provided with a sealing part, and an electrode lead is connected to the electrode assembly and passes through the sealing part. The region of the first separator located outside the electrode unit in the width direction is connected to the sealing portion.
The sealing part comprises a first sealing area and a second sealing area, the second sealing area is positioned on one side of the first sealing area far away from the first diaphragm, and the thickness of the first sealing area is larger than that of the second sealing area. The first diaphragm is connected to the first seal area.
In the regions of the first separator located on both sides of the electrode unit in the width direction, respectively, regions farther from the free ends of the first separator are connected to the sealing portion.
The packaging bag comprises two layers of packaging films, the electrode assembly is positioned between the two layers of packaging films, and the two layers of packaging films are connected at the edges and form a sealing part. Each packaging film comprises a protective layer, a metal layer and a first connecting layer, wherein the first connecting layer is arranged on the surface of the metal layer, facing the electrode assembly, and the protective layer is arranged on the surface, far away from the electrode assembly, of the metal layer. The first connecting layers of the two layers of packaging films are welded into a whole. The first separator includes a second connection layer connected to the first connection layer, and an absolute difference between a melting point of the second connection layer and a melting point of the first connection layer is less than or equal to 40 degrees.
The beneficial effects of the application are as follows: in the application, the first diaphragm can fix the pole pieces from the outer side of the electrode unit, when the secondary battery vibrates in the working process, the first diaphragm can reduce the movement of the pole pieces, reduce the dislocation between the pole pieces and improve the service life and the safety performance of the electrode assembly. In addition, the winding direction of the first separator may improve the stability of the electrode assembly as a whole, and reduce the risk of the electrode assembly scattering when the secondary battery vibrates.
Drawings
Fig. 1 is a schematic view of a secondary battery according to the present invention.
Fig. 2 is a cross-sectional view of the secondary battery of fig. 1.
Fig. 3 is an enlarged view of fig. 2 at block a.
Fig. 4 is a schematic view of a packaging film of a packaging bag of a secondary battery of the present invention.
Fig. 5 is a cross-sectional view of the packaging film of fig. 4.
Fig. 6 is a schematic view of an embodiment of an electrode assembly of a secondary battery according to the present invention.
Fig. 7 is another cross-sectional view of the secondary battery of fig. 1.
Fig. 8 is an enlarged view of fig. 7 at block B.
Fig. 9 is a cross-sectional view of a first separator of an electrode assembly of a secondary battery according to the present invention.
Fig. 10 is a schematic view of another embodiment of an electrode assembly of a secondary battery of the present invention.
Wherein reference numerals are as follows:
1. electrode assembly
11. Electrode unit
111. Positive electrode plate
112. Negative pole piece
113. Second diaphragm
113A first flat portion
113B second flat portion
113C bending part
12. First diaphragm
121. Second connecting layer
122. Base layer
13. Adhesive tape
2. Packaging bag (GY)
21. Sealing part
211. First seal area
212. Second seal area
22. Packaging film
221. Protective layer
222. Metal layer
223. First connecting layer
3. Electrode lead
4. Insulating member
In the X length direction
Y width direction
Z thickness direction
Detailed Description
The present application will be described in further detail with reference to the drawings and examples, in order to make the objects, technical solutions and advantages of the present application more apparent. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the application.
In the description of the present application, the terms "first," "second," and the like, are used for descriptive purposes only and are not to be construed as indicating or implying relative importance unless explicitly specified or limited otherwise; the term "plurality" refers to more than two (including two); the term "coupled" is used in a broad sense, unless specified or indicated otherwise, and may be, for example, either permanently or detachably, or integrally, or electrically, or signally; "coupled" may be directly coupled or indirectly coupled through intermediaries. The specific meaning of the above terms in the present application can be understood by those of ordinary skill in the art according to the specific circumstances.
In the description of the present specification, it should be understood that the terms "upper", "lower", and the like used in the embodiments of the present application are described in terms of the angles shown in the drawings, and should not be construed as limiting the embodiments of the present application. The application will now be described in further detail with reference to specific examples thereof in connection with the accompanying drawings.
Referring to fig. 1 to 3, the secondary battery of the present application includes an electrode assembly 1, a pouch 2, an electrode lead 3, and an insulating member 4. The electrode assembly 1 is a core member for a secondary battery to realize a charge and discharge function.
The packaging bag 2 includes two layers of packaging films 22, the two layers of packaging films 22 being disposed up and down in the thickness direction Z. Referring to fig. 4, at least one packaging film 22 is punched to form a cavity, and the electrode assembly 1 is positioned between two packaging films 22 and received in the cavity.
Referring to fig. 5, each packaging film 22 includes a protective layer 221, a metal layer 222, and a first connection layer 223, and the protective layer 221 and the first connection layer 223 are disposed on both sides of the metal layer 222, respectively. Specifically, the protective layer 221 may be fixed to a surface of the metal layer 222 remote from the electrode assembly 1 by an adhesive, and the first connection layer 223 may be fixed to a surface of the metal layer 222 close to the electrode assembly 1 by an adhesive.
The material of the protective layer 221 may be nylon or polyethylene terephthalate, the material of the metal layer 222 may be aluminum foil or steel foil, and the material of the first connection layer 223 may be polypropylene.
The two packaging films 22 are joined at the edges and form a seal 21. Specifically, the first joining layers 223 of the two packaging films 22 are directly or indirectly welded together by heat pressing, thereby forming the sealed packaging bag 2.
The electrode lead 3 is connected to the electrode assembly 1, passes through the sealing part 21, and extends to the outside of the packing bag 2. The number of the electrode leads 3 may be two, and the two electrode leads 3 connect the electrode assembly 1 with other members outside the packing bag 2, thereby achieving charge and discharge of the electrode assembly 1. The electrode lead 3 may be nickel-plated with aluminum, nickel or copper. The two electrode leads 3 may protrude from the same end of the package 2 in the length direction X, or may protrude from both ends of the package 2 in the length direction X, respectively.
The number of the insulating members 4 may be two. The two insulators 4 separate the two electrode leads 3 from the sealing part 21, respectively. Each insulating member 4 surrounds the outside of a corresponding one of the electrode leads 3. A portion of the insulating member 4 is sandwiched between the two layers of the wrapping film 22 so as to separate the electrode lead 3 from the wrapping film 22, reducing the risk of the electrode lead 3 coming into contact with the metal layer 222. The material of the insulating member 4 may be polypropylene.
Referring to fig. 6, the electrode assembly 1 includes an electrode unit 11 and a first separator 12, and the first separator 12 is wound around the outside of the electrode unit 11.
The electrode unit 11 includes a plurality of electrode sheets including a positive electrode sheet 111 and a negative electrode sheet 112, the positive electrode sheet 111 and the negative electrode sheet 112 being alternately laminated in the thickness direction Z. The pole pieces are generally thin sheets perpendicular to the thickness direction Z.
The positive electrode sheet 111 includes a positive electrode current collector, which may be aluminum foil, and a positive electrode active material layer coated on the surface of the positive electrode current collector, which includes ternary material, lithium manganate or lithium iron phosphate. The negative electrode tab 112 includes a negative electrode current collector, which may be a copper foil, and a negative electrode active material layer coated on a surface of the negative electrode current collector, which includes graphite or silicon.
The positive electrode tab 111 may be electrically connected to one electrode lead 3, and the negative electrode tab 112 may be electrically connected to the other electrode lead 3.
In order to avoid contact between the positive electrode tab 111 and the negative electrode tab 112 and to prevent short circuits, the electrode unit 11 of the present application further includes a second separator 113, the second separator 113 separating the positive electrode tab 111 and the negative electrode tab 112.
During operation of the secondary battery, lithium ions of the positive electrode tab 111 need to pass through the second separator 113 and be inserted into the negative electrode tab 112; in order to enable lithium ions to be inserted into the negative electrode tab 112 as much as possible, the risk of lithium precipitation is reduced, and the dimensions of the negative electrode tab 112 in the length direction X and in the width direction Y are both larger than those of the positive electrode tab 111.
The second diaphragm 113 is folded into a multi-layered structure and includes a plurality of flat portions and a plurality of folded portions. Two flat portions adjacent in the thickness direction Z may be connected via one bent portion. The flat part is generally parallel to the pole piece, and the bending part is generally positioned on the outer side of the pole piece along the width direction Y.
The plurality of electrode sheets and the plurality of flat portions are alternately laminated in the thickness direction Z, the flat portions separating adjacent electrode sheets, i.e., the flat portions separating the positive electrode sheet 111 and the negative electrode sheet 112.
The plurality of flat portions includes a first flat portion 113a and a second flat portion 113b, the first flat portion 113a and the second flat portion 113b being located at both ends of the second diaphragm 113 in the thickness direction Z, respectively. In other words, in the thickness direction Z, the other flat portions are located between the first flat portion 113a and the second flat portion 113 b.
The second flat portion 113b is located between two adjacent pole pieces. Since the second flat portion 113b is located at one end of the second separator 113 in the thickness direction Z, the second separator 113 is necessarily located at one side of one pole piece in the thickness direction Z, that is, the second separator 113 cannot cover the one pole piece from both sides. Preferably, the one pole piece is a negative pole piece 112.
The first separator 12 extends from one end of the second flat portion 113b in the width direction Y, and sequentially bypasses the pole piece located on the side of the second flat portion 113b near the first flat portion 113a and the pole piece located on the side of the second flat portion 113b far from the first flat portion 113a. In the orientation shown in fig. 6, the first separator 12 extends from the right end of the second flat portion 113b in the width direction Y, and is wound around the outside of the electrode unit 11 in the clockwise direction.
In the application, the first diaphragm 12 can fix the pole pieces from the outer side of the electrode unit 11, when the secondary battery vibrates in the working process, the first diaphragm 12 can reduce the movement of the pole pieces, reduce the dislocation between the pole pieces, and improve the service life and the safety performance of the electrode assembly 1. Meanwhile, the first diaphragm 12 can cover the pole pieces from the outer side, so that the second diaphragm 113 does not need to cover all the pole pieces from two sides, and the length of the second diaphragm 113 can be reduced, and materials are saved. In addition, the winding direction of the first separator 12 may improve the stability of the electrode assembly 1 as a whole, reducing the risk of the electrode assembly 1 scattering when the secondary battery vibrates.
During the charge and discharge process, the active material layer in the pole piece expands; in order to increase the capacity of the electrode assembly 1, the number of pole pieces is generally increased; while the expansion of the plurality of pole pieces will gradually overlap. If the electrode unit 11 is not bound from the outside, the electrode unit 11 may undergo a large degree of swelling deformation, affecting the appearance and performance of the secondary battery. In the present application, the first separator 12 can bind the electrode unit 11 from the outside, reduce the expansion of the electrode unit 11, reduce the deformation of the electrode assembly 1, and improve the appearance and performance of the secondary battery.
The end of the first separator 12 wound is a free end, and in order to fix the first separator 12 to prevent the first separator 12 from being scattered, the electrode assembly 1 of the present application further includes an adhesive tape 13, the adhesive tape 13 being adhered to the free end of the first separator 12.
The surface areas of the electrode units 11 facing each other in the thickness direction Z are large, and therefore, it is preferable that the free ends of the first separator 12 are located at one side of the electrode units 11 in the thickness direction Z. This allows the adhesive tape 13 to be adhered to a substantially flat surface, and ensures the adhesive strength of the adhesive tape 13.
The first separator 12 and the second separator 113 are integrally formed, so that the connection process of the first separator 12 and the second separator 113 can be saved, thereby simplifying the molding process of the electrode assembly 1.
The more the number of layers the first separator 12 is wound, the better the fixing effect of the first separator 12 to the electrode unit 11; however, in the secondary battery, the electrolyte needs to pass through the first separator 12 into the electrode unit 11, and if the number of layers of the first separator 12 is excessive, the difficulty of the electrolyte entering the electrode unit 11 increases, wettability decreases, and a lithium precipitation risk is induced. Thus, the number of layers of the first separator 12 is preferably 2 to 4.
All the pole pieces are located on one side of the first flat portion 113a near the second flat portion 113b in the thickness direction Z. That is, the first flat portion 113 is located at the outermost end of the electrode unit 11 in the thickness direction Z, and only one side of the first flat portion 113a is provided with a pole piece. The purpose of the first flat portion 113a is to protect the pole piece when the lamination process is started. One end of the first flat portion 113a in the width direction Y is a free end.
If the electrode assembly 1 is connected to the packing bag 2 only through the electrode lead 3, the electrode assembly 1 is relatively displaced with the packing bag 2 when the secondary battery vibrates, which easily causes risks of damage to the sealing part 21 of the packing bag 2, breakage of the electrode lead 3, and the like.
Therefore, preferably, referring to fig. 8, a region of the first separator 12 located outside the electrode unit 11 in the width direction Y is connected to the sealing portion 21. Since the first separator 12 is connected to the sealing part 21, the first separator 12 can effectively fix the electrode assembly 1 when the secondary battery vibrates, reduce the relative displacement between the electrode assembly 1 and the packing bag 2, reduce the risk of breakage of the sealing part 21 and breakage of the electrode leads 3, and improve the safety performance of the secondary battery.
The sealing portion 21 includes a first sealing region 211 and a second sealing region 212, the second sealing region 212 is located at a side of the first sealing region 211 away from the first diaphragm 12, and the thickness of the first sealing region 211 is greater than the thickness of the second sealing region 212. The first diaphragm 12 is connected to the first seal area 211. Because the first sealing region 211 is closer to the first film 12 than the second sealing region 212 and the first sealing region 211 has a greater thickness, a portion of the first film 12 may be more conveniently embedded in the first sealing region 211, thereby achieving the connection of the first film 12 to the package 2.
In the present application, the two-layer packaging film 22 may be hot-pressed using a packaging apparatus to form the sealing portion 21. In this embodiment, a partial area of the packaging film 22 is subjected to the heat pressing action of the packaging device and generates the gel, which flows inward. The area of the packaging film 22 directly subjected to the heat and pressure of the packaging device is the second seal area 212. The inwardly flowing glue bonds the two layers of packaging film 22 together, thereby forming a first seal area 211. During the hot pressing process, the second sealing region 212 is thinned, so the thickness of the first sealing region 211 is greater than the thickness of the second sealing region 212. In addition, the inwardly flowing glue will contact the first membrane 12, and after the glue is cured, the first membrane 12 is fixedly connected to the first seal area 211.
The first separator 12 may have a single-layer structure or a multi-layer structure. For example, in one embodiment, the first separator 12 is a single-layer structure and includes a second connection layer 121, and the second connection layer 121 is connected to the first connection layer 223; the material of the second connection layer 121 may be polyethylene or polypropylene. In another embodiment, referring to fig. 9, the first separator 12 is a multi-layered structure and includes a base layer 122 and a second connection layer 121, the second connection layer 121 being disposed at both sides of the base layer 122 and connected to the first connection layer 223; the material of the base layer 122 may be polyethylene, and the material of the second connection layer 121 may be polypropylene. Of course, the material of the second diaphragm 113 is the same as that of the first diaphragm 12.
In the present application, the second connection layer 121 is welded to the first connection layer 223. The smaller the difference between the melting point of the first connection layer 223 and the melting point of the second connection layer 121 is, the easier the two are to be connected together during the hot pressing, and the higher the connection strength between the two is. Thus, the method is applicable to a variety of applications. Preferably, the absolute difference between the melting point of the second connection layer 121 and the melting point of the first connection layer 223 is less than or equal to 40 degrees.
Further preferably, the first connection layer 223 and the second connection layer 121 are made of the same material, so that the welding difficulty between the two layers can be reduced, and the connection strength between the two layers can be improved.
Of the regions of the first separator 12 respectively located on both sides of the electrode unit 11 in the width direction Y, regions farther from the free end of the first separator 12 are connected to the sealing portion 21. The adhesive tape 13 is required to be adhered to the free end of the first separator 12, and thus, a region closer to the free end of the first separator 12 is affected by the adhesive tape 13; if the regions of the first separator 12, which are respectively located at both sides of the electrode unit 11 in the width direction Y, are connected to the sealing portion 21, it is easy to cause the adhesive tape 13 to be welded to the sealing portion 21 during the hot pressing, affecting the adhesive strength of the adhesive tape 13 and the sealing performance of the packing bag 2. In addition, when the sealing portion 21 applies a pulling force to the first diaphragm 12 during the hot pressing, if a region closer to the free end of the first diaphragm 12 is connected to the sealing portion 21, the free end of the first diaphragm 12 is subjected to a large pulling force, which tends to cause the adhesive tape 13 to fail and the first diaphragm 12 to be scattered. Therefore, it is preferable that only the region farther from the free end of the first diaphragm 12 is connected to the sealing portion 21.
A second embodiment of the secondary battery of the present application will be described below. For simplicity of description, only the differences between the second embodiment and the first embodiment will be mainly described below, and the undescribed portions can be understood with reference to the first embodiment.
The first separator 12 is opposite to the end of the pole piece in the width direction Y, which may generate burrs during the molding process. However, when the secondary battery vibrates, the first diaphragm 12 can limit the deflection of the pole piece, and correspondingly, burrs of the pole piece also easily stab the first diaphragm 12. Therefore, in the second embodiment, referring to fig. 10, the first separator 12 is provided in 2-4 layers on both sides of the electrode unit 11 in the width direction Y, that is, 2, 3 or 4 layers may be provided, so that the risk of burrs penetrating the first separator 12 can be effectively reduced, the pole piece is spaced from the package bag 2, and safety performance is improved.
Referring to fig. 10, at both ends of the electrode unit 1 in the thickness direction Z, only one end is a flat portion, i.e., a first flat portion 113a. For the two pole pieces located at both ends in the thickness direction Z, the number of layers of the separator located outside the pole piece near the first flat portion 113a is larger, and the number of layers of the separator located outside the pole piece near the second flat portion 113b is smaller. In order to avoid an excessive number of separator layers, which affects wettability, it is preferable that the free end of the first separator 12 is located on the side of the electrode unit 11 close to the second flat portion 113b in the thickness direction Z.
In the width direction Y, the free ends of the first separator 12 and the first flat portions 113a are opposite in orientation. When the secondary battery vibrates, the free end of the first diaphragm 12 and the free end of the first flat portion 113a are subjected to force, and when the directions of the free end of the first diaphragm 12 and the free end of the first flat portion 113a are opposite, the force applied to the free end of the first flat portion 113a can be reduced, and the risk of loosening the second diaphragm 113 can be reduced.

Claims (10)

1. An electrode assembly characterized by comprising an electrode unit (11) and a first separator (12), the first separator (12) being wound on the outside of the electrode unit (11);
the electrode unit (11) comprises a plurality of electrode plates and a plurality of second diaphragms (113), wherein the electrode plates are arranged in a plurality, the second diaphragms (113) are bent into a multi-layer structure and comprise a plurality of flat parts and a plurality of bending parts, the plurality of electrode plates and the plurality of flat parts are alternately laminated along the thickness direction (Z), and two adjacent flat parts are connected through one bending part;
the plurality of flat parts comprise a first flat part (113 a) and a second flat part (113 b), the first flat part (113 a) and the second flat part (113 b) are respectively positioned at two ends of the second diaphragm (113) along the thickness direction (Z), and the second flat part (113 b) is positioned between two adjacent pole pieces;
the first separator (12) extends from one end of the second flat portion (113 b) in the width direction (Y), and sequentially bypasses the plurality of pole pieces located on the side of the second flat portion (113 b) close to the first flat portion (113 a) and the pole pieces located on the side of the second flat portion (113 b) away from the first flat portion (113 a).
2. The electrode assembly according to claim 1, wherein the first separator (12) and the second separator (113) are integrally formed.
3. The electrode assembly according to claim 1, wherein the first separator (12) is provided in 2-4 layers on both sides of the electrode unit (11) in the width direction (Y).
4. The electrode assembly according to claim 1, wherein the free end of the first separator (12) is located on the side of the electrode unit (11) in the thickness direction (Z) close to the second flat portion (113 b).
5. The electrode assembly according to claim 4, wherein the free ends of the first separator (12) and the first flat portion (113 a) are opposite in orientation in the width direction (Y), and all the pole pieces are located on one side of the first flat portion (113 a) in the thickness direction (Z) close to the second flat portion (113 b).
6. A secondary battery, characterized by comprising an electrode assembly (1) according to any one of claims 1-5.
7. The secondary battery according to claim 6, further comprising a packaging bag (2) and an electrode lead (3);
The electrode assembly (1) is accommodated in the packaging bag (2), the edge of the packaging bag (2) is provided with a sealing part (21), and the electrode lead (3) is connected to the electrode assembly (1) and penetrates through the sealing part (21);
A region of the first separator (12) located outside the electrode unit (11) in the width direction (Y) is connected to the sealing portion (21).
8. The secondary battery according to claim 7, wherein the sealing portion (21) includes a first sealing region (211) and a second sealing region (212), the second sealing region (212) is located on a side of the first sealing region (211) away from the first separator (12), and a thickness of the first sealing region (211) is greater than a thickness of the second sealing region (212);
the first membrane (12) is connected to the first seal area (211).
9. The secondary battery according to claim 7, wherein, in the regions of the first separator (12) respectively located on both sides of the electrode unit (11) in the width direction (Y), a region farther from the free end of the first separator (12) is connected to the sealing portion (21).
10. The secondary battery according to claim 7, wherein the packaging bag (2) includes two packaging films (22), the electrode assembly (1) is located between the two packaging films (22), and the two packaging films (22) are connected at edges and form the sealing portion (21);
Each packaging film (22) comprises a protective layer (221), a metal layer (222) and a first connecting layer (223), wherein the first connecting layer (223) is arranged on the surface of the metal layer (222) facing the electrode assembly (1), and the protective layer (221) is arranged on the surface of the metal layer (222) far away from the electrode assembly (1);
the first connecting layers (223) of the two layers of packaging films (22) are welded into a whole;
the first separator (12) includes a second connection layer (121), the second connection layer (121) is connected to the first connection layer (223), and an absolute difference between a melting point of the second connection layer (121) and a melting point of the first connection layer (223) is less than or equal to 40 degrees.
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