CN110190319A - electrode assembly and secondary battery - Google Patents

Abstract

The present invention provides an electrode assembly and a secondary battery. The electrode assembly includes an electrode unit and a first separator, and the first separator is wound on the outside of the electrode unit. The electrode unit includes a pole piece and a second diaphragm, the pole pieces are arranged in plurality, the second diaphragm is bent into a multi-layer structure and includes a plurality of flat parts, and the plurality of pole pieces and the plurality of flat parts are alternately stacked along the thickness direction. The plurality of flat parts include a first flat part and a second flat part, the first flat part and the second flat part are respectively located at two ends of the second diaphragm along the thickness direction, and the second flat part is located at two adjacent pole pieces between. The first diaphragm extends from one end of the second flat part in the width direction, and successively bypasses the pole piece located on the side of the second flat part close to the first flat part and a pole piece located on the side of the second flat part far from the first flat part. side pole pieces.

Description

Electrode assemblies and secondary batteries

technical field

The present invention relates to the field of batteries, in particular to an electrode assembly and a secondary battery.

Background technique

The electrode assembly of the secondary battery is the core component of its charging and discharging function, and the electrode assembly usually includes a positive electrode piece, a negative electrode piece, and a separator separating the positive electrode piece and the negative electrode piece. For the laminated electrode assembly, when the secondary battery vibrates during operation, the electrode assembly is prone to dislocation, which affects the service life and safety performance of the electrode assembly.

SUMMARY OF THE INVENTION

In view of the problems in the background art, the purpose of the present invention is to provide an electrode assembly and a secondary battery, which can reduce the dislocation between the pole pieces and improve the service life and safety performance of the electrode assembly.

In order to achieve the above objects, the present invention provides an electrode assembly and a secondary battery.

The electrode assembly includes an electrode unit and a first separator, and the first separator is wound on the outside of the electrode unit. The electrode unit includes a pole piece and a second diaphragm, the pole pieces are arranged in multiples, the second diaphragm is bent into a multi-layer structure and includes a plurality of flat parts, and the plurality of pole pieces and the plurality of flat parts are alternately stacked along the thickness direction. The plurality of flat parts include a first flat part and a second flat part, the first flat part and the second flat part are respectively located at both ends of the second diaphragm along the thickness direction, and the second flat part is located at two adjacent pole pieces between. The first diaphragm extends from one end of the second flat part in the width direction, and bypasses the pole piece located on the side of the second flat part close to the first flat part and a pole piece located on the side of the second flat part away from the first flat part in turn. side pole pieces.

The first diaphragm and the second diaphragm are integrally formed.

The first separator is provided with 2-4 layers on both sides of the electrode unit along the width direction.

The free end of the first separator is located on the side of the electrode unit close to the second flat portion in the thickness direction.

In the width direction, the free end of the first diaphragm and the free end of the first flat portion are oriented oppositely, and all the pole pieces are located on the side of the first flat portion close to the second flat portion in the thickness direction.

A secondary battery includes the electrode assembly.

The secondary battery further includes a packaging bag and electrode leads. The electrode assembly is accommodated in a packaging bag, the edge of the packaging bag has a sealing part, and the electrode leads are connected to the electrode assembly and pass through the sealing part. A region of the first separator located on the outer side of the electrode unit in the width direction is connected to the sealing portion.

The sealing part includes a first sealing area and a second sealing area, the second sealing area is located on a side of the first sealing area away from the first membrane, and the thickness of the first sealing area is greater than that of the second sealing area. The first membrane is connected to the first seal area.

Of the regions of the first separator located on both sides of the electrode unit in the width direction, regions farther from the free end of the first separator are connected to the sealing portion.

The packaging bag includes two layers of packaging films, the electrode assembly is located between the two layers of packaging films, and the two layers of packaging films are connected at the edges and form a sealing portion. Each packaging film includes a protective layer, a metal layer and a first connection layer, the first connection layer is disposed on the surface of the metal layer facing the electrode assembly, and the protective layer is disposed on the surface of the metal layer away from the electrode assembly. The first connection layers of the two-layer packaging films are welded into one. The first separator includes a second connection layer, the second connection layer is connected to the first connection layer, and the absolute difference between the melting point of the second connection layer and the melting point of the first connection layer is less than or equal to 40 degrees.

The beneficial effects of the present invention are as follows: In the present application, the first diaphragm can fix the pole piece from the outside of the electrode unit, and when the secondary battery vibrates during operation, the first diaphragm can reduce the movement of the pole piece and reduce the Dislocation between sheets improves the service life and safety performance of the electrode assembly. In addition, the winding direction of the first separator can improve the overall stability of the electrode assembly and reduce the risk of the electrode assembly falling apart when the secondary battery is shaken.

Description of 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 at block A of FIG. 2 .

FIG. 4 is a schematic view of the packaging film of the packaging bag of the 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 diagram of an embodiment of the electrode assembly of the secondary battery of 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 the first separator of the electrode assembly of the secondary battery of the present invention.

FIG. 10 is a schematic diagram of another example of the electrode assembly of the secondary battery of the present invention.

Among them, the reference numerals are described as follows:

1 Electrode assembly

11 Electrode unit

111 Positive pole piece

112 Negative pole piece

113 Second diaphragm

113a First flat portion

113b Second flat part

113c Bend

12 First diaphragm

121 Second connection layer

122 Grassroots

13 Tape

2 bags

21 Seal

211 First Seal Area

212 Second Sealed Area

22 Packaging film

221 Protective layer

222 metal layers

223 First connection layer

3 Electrode leads

4 insulation

X length direction

Y width direction

Z thickness direction

Detailed ways

In order to make the purpose, technical solutions and advantages of the present application more clearly understood, the present application will be described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application, but not to limit the present application.

In the description of this application, unless otherwise expressly specified and limited, the terms "first" and "second" are only used for the purpose of description, and cannot be understood as indicating or implying relative importance; the term "a plurality" is a Refers to two or more (including two); unless otherwise specified or stated, the term "connection" should be understood in a broad sense, for example, "connection" may be a fixed connection, a detachable connection, or an integral connection, or an electrical connection. Connection, or signal connection; "connection" may be a direct connection or an indirect connection through an intermediate medium. For those of ordinary skill in the art, the specific meanings of the above terms in this application can be understood according to specific situations.

In the description of this specification, it should be understood that the directional words such as "upper" and "lower" described in the embodiments of the present application are described from the perspective shown in the accompanying drawings, and should not be construed as referring to the embodiments of the present application. limited. The present application will be further described in detail below through specific embodiments and in conjunction with the accompanying drawings.

1 to 3 , the secondary battery of the present application includes an electrode assembly 1 , a packaging bag 2 , an electrode lead 3 and an insulating member 4 . The electrode assembly 1 is the core component of the secondary battery to realize the charging and discharging function.

The packaging bag 2 includes two layers of packaging films 22 , and the two layers of packaging films 22 are arranged up and down along the thickness direction Z. Referring to FIG. 4 , at least one layer of packaging film 22 is punched to form a cavity, and the electrode assembly 1 is located between the two layers of packaging film 22 and accommodated in the cavity.

5 , each packaging film 22 includes a protection layer 221 , a metal layer 222 and a first connection layer 223 , and the protection layer 221 and the first connection layer 223 are respectively disposed on both sides of the metal layer 222 . Specifically, the protective layer 221 can be fixed on the surface of the metal layer 222 away from the electrode assembly 1 through an adhesive, and the first connection layer 223 can be fixed on the surface of the metal layer 222 close to the electrode assembly 1 through an adhesive.

The protective layer 221 can be made of nylon or polyethylene terephthalate, the metal layer 222 can be made of aluminum foil or steel foil, and the first connection layer 223 can be made of polypropylene.

The two layers of packaging film 22 are joined at the edges and form the seal 21 . Specifically, through hot pressing, the first connecting layers 223 of the two layers of packaging films 22 are directly or indirectly welded together, thereby forming the sealed packaging bag 2 .

The electrode lead 3 is connected to the electrode assembly 1 , passes through the sealing portion 21 and extends to the outside of the packaging bag 2 . There may be two electrode leads 3 , and the two electrode leads 3 connect the electrode assembly 1 to other components outside the packaging bag 2 , thereby realizing charging and discharging of the electrode assembly 1 . The material of the electrode lead 3 can be aluminum, nickel or copper plated with nickel. The two electrode leads 3 may protrude from the same end of the packaging bag 2 along the length direction X, or may respectively extend from both ends of the packaging bag 2 along the length direction X.

The insulating members 4 may be two. The two insulating members 4 separate the two electrode leads 3 from the sealing portion 21, respectively. Each insulating member 4 surrounds the outer side of a corresponding one of the electrode leads 3 . A part of the insulating member 4 is sandwiched between the two layers of packaging films 22 , thereby separating the electrode leads 3 from the packaging films 22 and reducing the risk of the electrode leads 3 coming into contact with the metal layer 222 . The material of the insulating member 4 can be polypropylene.

6 , the electrode assembly 1 includes an electrode unit 11 and a first separator 12 , and the first separator 12 is wound on the outside of the electrode unit 11 .

The electrode unit 11 includes a plurality of pole pieces including a positive pole piece 111 and a negative pole piece 112 , and the positive pole piece 111 and the negative pole piece 112 are alternately stacked along 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 and a positive electrode active material layer coated on the surface of the positive electrode current collector. The positive electrode current collector can be aluminum foil, and the positive electrode active material layer includes a ternary material, lithium manganate or lithium iron phosphate. The negative electrode sheet 112 includes a negative electrode current collector and a negative electrode active material layer coated on the surface of the negative electrode current collector. The negative electrode current collector can be copper foil, and the negative electrode active material layer includes graphite or silicon.

The positive pole piece 111 can be electrically connected to one electrode lead 3 , and the negative pole piece 112 can be electrically connected to the other electrode lead 3 .

In order to avoid contact between the positive pole piece 111 and the negative pole piece 112 and prevent short circuit, the electrode unit 11 of the present application further includes a second separator 113 that separates the positive pole piece 111 and the negative pole piece 112 .

During the operation of the secondary battery, the lithium ions of the positive pole piece 111 need to pass through the second separator 113 and be embedded in the negative pole piece 112 ; in order to enable the lithium ions to be embedded in the negative pole piece 112 as much as possible, and reduce the risk of lithium precipitation , the size of the negative pole piece 112 along the length direction X and the dimension along the width direction Y are both larger than those of the positive pole piece 111 .

The second diaphragm 113 is bent into a multi-layer structure and includes a plurality of flat portions and a plurality of bent portions. Two flat portions adjacent in the thickness direction Z may be connected via one bent portion. The flat portion is generally parallel to the pole piece, and the bent portion is generally located outside the pole piece along the width direction Y.

A plurality of pole pieces and a plurality of flat parts are alternately stacked along the thickness direction Z, and the flat parts separate adjacent pole pieces, that is, the flat parts separate the positive pole piece 111 and the negative pole piece 112 .

The plurality of flat parts include a first flat part 113a and a second flat part 113b, the first flat part 113a and the second flat part 113b are 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 all located between the first flat portion 113a and the second flat portion 113b.

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 diaphragm 113 along the thickness direction Z, the second diaphragm 113 must be located at one side of a pole piece along the thickness direction Z, that is to say, the second diaphragm 113 cannot cover all sides from both sides. Describe a pole piece. Preferably, the one pole piece is a negative pole piece 112 .

The first diaphragm 12 extends from one end of the second flat portion 113b along the width direction Y, and sequentially bypasses the pole piece located on the side of the second flat portion 113b close to the first flat portion 113a and the pole piece located on the side of the second flat portion 113b away from the second flat portion 113b. A pole piece on one side of 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 113 b along the width direction Y, and is wound around the outside of the electrode unit 11 in a clockwise direction.

In the present application, the first diaphragm 12 can fix the pole pieces from the outside of the electrode unit 11. When the secondary battery vibrates during operation, the first diaphragm 12 can reduce the movement of the pole pieces and reduce the dislocation between the pole pieces , to improve the service life and safety performance of the electrode assembly 1 . Meanwhile, the first diaphragm 12 can cover the pole pieces from the outside, so the second diaphragm 113 does not need to cover all the pole pieces from both sides, which can reduce the length of the second diaphragm 113 and save material. In addition, the winding direction of the first separator 12 can improve the overall stability of the electrode assembly 1 and reduce the risk of the electrode assembly 1 falling apart when the secondary battery is vibrated.

During the charging and discharging process, the active material layer in the pole piece will expand; in order to increase the capacity of the electrode assembly 1, the number of pole pieces is usually increased; and the expansion of multiple pole pieces will gradually overlap. If the electrode unit 11 is not bound from the outside, the electrode unit 11 will be expanded and deformed to a large extent, affecting the appearance and performance of the secondary battery. In the present application, the first separator 12 can restrain 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 wound end of the first diaphragm 12 is a free end. In order to fix the first diaphragm 12 and prevent the first diaphragm 12 from spreading out, the electrode assembly 1 of the present application further includes an adhesive tape 13 , and the adhesive tape 13 is adhered to the free end of the first diaphragm 12 . end.

The surface areas of the electrode units 11 facing each other along the thickness direction Z are relatively large, therefore, preferably, the free end of the first separator 12 is located on one side of the electrode unit 11 along the thickness direction Z. In this way, the adhesive tape 13 can be generally adhered to the plane, and the adhesive strength of the adhesive tape 13 can be ensured.

The first diaphragm 12 and the second diaphragm 113 are integrally formed, so that the connection process of the first diaphragm 12 and the second diaphragm 113 can be saved, thereby simplifying the forming process of the electrode assembly 1 .

The more layers the first separator 12 is wound, the better the fixing effect of the first separator 12 on the electrode unit 11; however, in a secondary battery, the electrolyte needs to pass through the first separator 12 into the electrode unit 11, if If the number of layers of the first separator 12 is too large, it will increase the difficulty of the electrolyte entering the electrode unit 11 , reduce the wettability, and cause the risk of lithium precipitation. Therefore, preferably, the number of layers of the first separator 12 is 2-4 layers.

All the pole pieces are located on the side of the first flat portion 113a close to the second flat portion 113b along the thickness direction Z. That is, the first flat portion 113 is located at the outermost end of the electrode unit 11 along the thickness direction Z, and only one side of the first flat portion 113a is provided with a pole piece. The purpose of disposing the first flat portion 113a is to protect the pole pieces 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 only connected to the packaging bag 2 through the electrode lead 3, when the secondary battery is vibrated, the electrode assembly 1 and the packaging bag 2 will be displaced relative to each other, which is likely to cause damage to the sealing portion 21 of the packaging bag 2 and the electrode lead 3 Risk of breakage, etc.

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 portion 21 , when the secondary battery is vibrated, the first separator 12 can effectively fix the electrode assembly 1 , reduce the relative displacement between the electrode assembly 1 and the packaging bag 2 , and lower the sealing portion 21 . The risk of breakage and breakage of the electrode lead 3 improves the safety performance of the secondary battery.

The sealing portion 21 includes a first sealing area 211 and a second sealing area 212 , the second sealing area 212 is located on the side of the first sealing area 211 away from the first diaphragm 12 , and the thickness of the first sealing area 211 is greater than that of the second sealing area 212 thickness of. The first membrane 12 is connected to the first sealing area 211 . Because the first sealing area 211 is closer to the first membrane 12 than the second sealing area 212, and the thickness of the first sealing area 211 is larger, a part of the first membrane 12 can be embedded in the first sealing area 211 more conveniently, Thus, the connection between the first membrane 12 and the packaging bag 2 is realized.

In the present application, the two-layer packaging film 22 may be hot-pressed using packaging equipment to form the sealing portion 21 . In this embodiment, a partial area of the packaging film 22 is subjected to the action of heat and pressure by the packaging equipment to generate colloid, and the colloid will flow inward. The area of the packaging film 22 that is directly subjected to the heat-pressing action of the packaging equipment is the second sealing area 212 . The inwardly flowing colloid bonds the two layers of packaging films 22 together, thereby forming the first sealing area 211 . During the hot pressing process, the second sealing area 212 is thinned, so the thickness of the first sealing area 211 is greater than the thickness of the second sealing area 212 . In addition, the colloid flowing inward will come into contact with the first membrane 12 , and after the colloid is cured, the first membrane 12 is fixedly connected to the first sealing area 211 .

The first membrane 12 may have a single-layer structure or a multi-layer structure. For example, in one embodiment, the first membrane 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; wherein, the material of the second connection layer 121 may be polyethylene or polypropylene. In another embodiment, referring to FIG. 9 , the first membrane 12 is a multi-layer structure and includes a base layer 122 and a second connection layer 121 . The second connection layer 121 is disposed on both sides of the base layer 122 and is connected to the first connection layer 223 ; Wherein, the material of the base layer 122 may be polyethylene, and the material of the second connecting 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 process, and the higher the connection strength between the two is. therefore. 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, which can reduce the difficulty of welding between the two and improve the connection strength between the two.

Among the regions of the first separator 12 respectively located on both sides of the electrode unit 11 in the width direction Y, the regions farther from the free end of the first separator 12 are connected to the sealing portion 21 . The adhesive tape 13 needs to be attached to the free end of the first diaphragm 12. Therefore, the area closer to the free end of the first diaphragm 12 will be affected by the adhesive tape 13; The areas on both sides of Y are connected to the sealing part 21 , which easily causes the adhesive tape 13 to be welded to the sealing part 21 during the hot pressing process, which affects the adhesive strength of the adhesive tape 13 and the sealing performance of the packaging bag 2 . In addition, during hot pressing, the sealing part 21 will exert a pulling force on the first diaphragm 12 . If the area close to the free end of the first diaphragm 12 is connected to the sealing part 21 , the free end of the first diaphragm 12 will be affected. Under a large pulling force, the adhesive tape 13 is likely to fail, and the first diaphragm 12 is scattered. Therefore, preferably, only the region farther from the free end of the first diaphragm 12 is connected to the sealing portion 21 .

Next, a second embodiment of the secondary battery of the present application will be described. In order to simplify the description, only the differences between the second embodiment and the first embodiment are mainly introduced below, and the undescribed parts can be understood with reference to the first embodiment.

The first diaphragm 12 is opposite to the end of the pole piece along the width direction Y, and the end of the pole piece along the width direction Y may generate burrs during the molding process. However, when the secondary battery is vibrated, the first diaphragm 12 can limit the deflection of the pole piece, and correspondingly, the burr of the pole piece can easily stab the first diaphragm 12 . Therefore, in the second embodiment, referring to FIG. 10 , the first diaphragm 12 is provided with 2-4 layers on both sides of the electrode unit 11 along the width direction Y, that is to say, 2 layers, 3 layers or 4 layers may be provided, This can effectively reduce the risk of burrs piercing the first diaphragm 12, separate the pole piece from the packaging bag 2, and improve safety performance.

Referring to FIG. 10 , at both ends of the electrode unit 1 along the thickness direction Z, only one end is a flat portion, that is, the first flat portion 113a. For the two pole pieces respectively located at both ends of the thickness direction Z, the number of layers of the diaphragm located on the outer side of the pole piece near the first flat portion 113a is larger, and the number of layers of the diaphragm located on the outer side of the pole piece near the second flat portion 113b is relatively high. few. In order to avoid excessive number of separator layers and influence on wettability, preferably, 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 along the thickness direction Z.

In the width direction Y, the free end of the first diaphragm 12 and the free end of the first flat portion 113a are oriented in opposite directions. When the secondary battery is vibrated, both the free end of the first separator 12 and the free end of the first flat portion 113a are subjected to force, and when the free end of the first separator 12 and the free end of the first flat portion 113a are oriented oppositely , the force on the free end of the first flat portion 113a can be reduced, and the risk of loosening of the second diaphragm 113 can be reduced.

Claims (10)

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