CN213042959U - Aluminum-plastic film packaging structure and soft package battery - Google Patents

Abstract

The utility model relates to the technical field of batteries, a plastic-aluminum membrane packaging structure and laminate polymer battery are provided, including plastic-aluminum membrane main part and side banding. The side seal edge comprises a transition section and an encapsulation section. The height from the bent packaging section to the transition section exceeds the boundary of the aluminum plastic film main body wrapping the battery cell in the thickness direction. The utility model provides an aluminum-plastic film packaging structure, including aluminum-plastic film main part and side banding, wherein, the side banding includes changeover portion and encapsulation section again, here, the effective structure section of encapsulation section for the side banding carries out the encapsulation, highly surpassing through buckling the encapsulation section back to the changeover portion in aluminum-plastic film main part parcel electric core the ascending border of thickness side length of defining the encapsulation section, thereby obtain the longer side banding of effective encapsulation length, like this, make the tensile strength of side banding improve.

Description

Aluminum-plastic film packaging structure and soft package battery

Technical Field

The utility model relates to the technical field of batteries, especially, provide an aluminum-plastic film packaging structure and have this aluminum-plastic film packaging structure's laminate polymer battery.

Background

At present, the soft package lithium ion battery utilizes an aluminum plastic film as a shell material of a battery cell. Specifically, after the aluminum plastic film is punched into a bag shape, the polypropylene layer on the inner side of the aluminum plastic film is melted and sealed.

Typically, pouch cells have a three-sided edge seal or a four-sided edge seal. In order to promote volume energy density, can buckle to the side banding to, highly depend on the thickness of battery after buckling, however, to slim laminate polymer battery, the effective width of the hem of its side banding is not enough, leads to the tensile strength of hem to be lower, and then influences laminate polymer battery's life.

SUMMERY OF THE UTILITY MODEL

The utility model aims at providing an aluminum-plastic film packaging structure aims at solving the lower problem of the stretch-proofing intensity of the hem that current aluminum-plastic film packaging structure leads to because of the effective width of the hem of its side banding is not enough.

In order to achieve the above object, the utility model adopts the following technical scheme: the utility model provides an aluminum-plastic film packaging structure, is including the side banding that is used for the aluminum-plastic film main part of parcel electric core and outwards extends the formation by the aluminum-plastic film main part, and the side banding is including connecting in the changeover portion of aluminum-plastic film main part and by the outside encapsulation section that extends of changeover portion, and the encapsulation section highly surpasses in the ascending border of aluminum-plastic film main part parcel electric core in thickness direction after buckling to the changeover portion.

The utility model has the advantages that: the utility model provides an aluminum-plastic film packaging structure, including aluminum-plastic film main part and side banding, wherein, the side banding includes changeover portion and encapsulation section again, here, the effective structure section of encapsulation section for the side banding carries out the encapsulation, and the height H through buckling back with the encapsulation section to the changeover portion surpasses in aluminum-plastic film main part parcel electric core length of defining the encapsulation section in the ascending border of thickness side to obtain the longer side banding of effective encapsulation length, like this, make the tensile strength of side banding improve.

In one embodiment, the height from the bent packaging section to the transition section exceeds the boundary range of the aluminum plastic film main body wrapped on the battery cell in the thickness direction by 0.1 mm-1 mm.

Through adopting above-mentioned technical scheme, utilize the length of quantitative concrete data limit encapsulation section to, in the within range, the side banding can obtain suitable tensile strength, and, can not lead to because of the side banding is overlength after laminate in soft-package battery series-parallel connection and influences each other.

In one embodiment, the encapsulation section is close to the aluminum plastic film main body after being bent at least twice.

Through adopting above-mentioned technical scheme, utilize the mode of buckling to accomodate the encapsulation section to, further improve the sealed effect of encapsulation section.

In one embodiment, the packaging section comprises a first packaging sub-section, a second packaging sub-section and a third packaging sub-section which are sequentially connected, the first packaging sub-section is connected to the transition section, one end, far away from the first packaging sub-section, of the second packaging sub-section is bent towards the aluminum-plastic film main body, and one end, far away from the second packaging sub-section, of the third packaging sub-section is bent towards the second packaging sub-section.

By adopting the technical scheme, the packaging section is specifically divided into three subsections, namely a first packaging subsection, a second packaging subsection and a third packaging subsection in sequence, and the packaging section is bent according to actual requirements.

In one embodiment, an adhesive layer is disposed between the second package sub-section and the third package sub-section.

By adopting the technical scheme, the third packaging subsegment is prevented from rebounding relative to the second packaging subsegment by the adhesive layer.

In one embodiment, the included angle a between the encapsulation section and the thickness direction of the aluminum-plastic film ranges from 0 ° to 60 °.

Through adopting above-mentioned technical scheme, contained angle a can make the encapsulation section obtain suitable effect of buckling in above-mentioned scope.

In one embodiment, the aluminum-plastic film main body is formed by buckling two aluminum-plastic films with punched pits, and the length L from the bent packaging section to the transition section is greater than half of the thickness of the battery core wrapped by the aluminum-plastic film main body.

By adopting the technical scheme, the transition section and the packaging section are both positioned in the middle of the thickness direction of the aluminum-plastic film main body, so that the length L from the packaging section to the transition section after bending is greater than half of the thickness of the electric core wrapped by the aluminum-plastic film main body.

In one embodiment, the aluminum-plastic film main body is formed by buckling an aluminum-plastic film with a punched pit and another aluminum-plastic film without punched pit, and the length L from the bent packaging section to the transition section is greater than the thickness of the aluminum-plastic film main body wrapping the battery core.

By adopting the technical scheme, the transition section and the packaging section are both positioned on one side of the thickness direction of the aluminum-plastic film main body, so that the length L from the packaging section to the transition section after bending is larger than the thickness of the battery core wrapped by the aluminum-plastic film main body.

The utility model also provides a laminate polymer battery, including a plurality of electric cores, still include a plurality of foretell plastic-aluminum membrane packaging structure, each plastic-aluminum membrane packaging structure encapsulates in corresponding electric core.

The utility model has the advantages that: the utility model provides a laminate polymer battery, on the basis that has above-mentioned plastic-aluminum membrane packaging structure, tensile strength is higher, and life is longer.

In one embodiment, a buffer layer is disposed between two adjacent aluminum plastic film packaging structures.

Through adopting above-mentioned technical scheme, reduce the impact of two adjacent electric cores to and increase the interval between two adjacent plastic-aluminum membrane packaging structure, make plastic-aluminum membrane packaging structure's side seal limit have sufficient space of placing, can not influence each other.

Drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for the embodiments or the prior art descriptions will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings without creative efforts.

Fig. 1 is a schematic structural diagram of an aluminum-plastic film package structure according to an embodiment of the present invention;

fig. 2 is a schematic structural diagram of an aluminum-plastic film package structure according to an embodiment of the present invention;

fig. 3 is a schematic structural diagram of an aluminum-plastic film package structure according to another embodiment of the present invention;

fig. 4 is the utility model provides a laminate polymer battery's schematic structure diagram.

Wherein, in the figures, the respective reference numerals:

the packaging structure comprises an aluminum-plastic film packaging structure 100, an aluminum-plastic film main body 10, a side sealing edge 20, a transition section 21, a packaging section 22, a first packaging subsection 221, a second packaging subsection 222, a third packaging subsection 223, an adhesive layer 224, a battery cell 200 and a buffer layer 300.

Detailed Description

Reference will now be made in detail to the embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the drawings are exemplary and intended to be used for explaining the present invention, and should not be construed as limiting the present invention.

In the description of the present invention, it is to be understood that the terms "length", "width", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", and the like indicate orientations or positional relationships based on those shown in the drawings, and are merely for convenience of description and simplicity of description, and do not indicate or imply that the device or element being referred to must have a particular orientation, be constructed and operated in a particular orientation, and thus, should not be construed as limiting the present invention.

Furthermore, the terms "first", "second" and "first" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of the present invention, "a plurality" means two or more unless specifically limited otherwise.

In the present invention, unless otherwise expressly stated or limited, the terms "mounted," "connected," and "fixed" are to be construed broadly and may, for example, be fixedly connected, detachably connected, or integrally formed; can be mechanically or electrically connected; either directly or indirectly through intervening media, either internally or in any other relationship. The specific meaning of the above terms in the present invention can be understood according to specific situations by those skilled in the art.

Referring to fig. 1, an aluminum-plastic film package structure 100 of the present application includes an aluminum-plastic film main body 10 for wrapping a battery cell 200, and a side sealing edge 20 formed by extending the aluminum-plastic film main body 10 outward. The side sealing edge 20 includes a transition section 21 connected to the aluminum plastic film main body 10 and a sealing section 22 extending outward from the transition section 21. Here, the transition section 21 is a portion of the side edge 20 that is not heat-sealed, and the sealing section 22 is a portion of the side edge 20 that is heat-sealed, and is also an effective portion for achieving leakage prevention of the aluminum plastic film sealing structure 100, so that the length of the sealing section 22 determines the tensile strength of the side edge 20. The height of the bent packaging section 22 to the transition section 21 exceeds the boundary of the aluminum plastic film main body 10 wrapping the battery core 200 in the thickness direction. It can be understood that, in order to ensure the sealing performance of the aluminum plastic film main body 10 and shorten the overall width of the aluminum plastic film packaging structure 100, the packaging section 22 needs to be bent, and the height from the end of the bent packaging section 22 far away from the transition section 21 to the transition section 21 should exceed the boundary of the aluminum plastic film main body 10 in the thickness direction after wrapping the battery cell 200.

The utility model provides an aluminum-plastic film packaging structure 100, including aluminum-plastic film main part 10 and side banding 20, wherein, side banding 20 includes changeover portion 21 and encapsulation section 22 again, here, encapsulation section 22 carries out the effective structure section of encapsulation for side banding 20, the height H through buckling back to changeover portion 21 with encapsulation section 22 surpasses in aluminum-plastic film main part 10 parcel electric core 200 the length of encapsulation section 22 in the ascending border of thickness side, thereby obtain the longer side banding 20 of effective encapsulation length, and like this, make the tensile strength of side banding 20 improve.

In one embodiment, the height of the encapsulation section 22 from the bending to the transition section 21 exceeds the boundary range of the aluminum plastic film main body 10 wrapping the battery cell 200 in the thickness direction, and is 0.1mm to 1 mm. It will be appreciated that the length of the encapsulated section 22 is defined using quantitative specific data. For example, the height H can be 0.1mm, 0.2mm, 0.3mm, 0.4mm, 0.5mm, 0.6mm, 0.7mm, 0.8mm, 0.9mm, 1.0mm, and the like. In addition, within the above range, the side seals 20 can obtain an appropriate tensile strength, and the side seals 20 do not interfere with each other due to an excessively long length after the series and parallel lamination of the pouch batteries.

Referring to fig. 2, in one embodiment, the encapsulation section 22 is bent at least twice to be close to the aluminum-plastic film main body 10. Through adopting above-mentioned technical scheme, utilize the mode of buckling to accomodate encapsulation section 22 to, further improve encapsulation section 22's sealed effect.

With continued reference to fig. 2, the encapsulation section 22 includes a first encapsulation section 221, a second encapsulation section 222 and a third encapsulation section 223 sequentially connected, the first encapsulation section is connected to the transition section 21, an end of the second encapsulation section 222 far from the first encapsulation section 221 is bent toward the aluminum-plastic film main body 10, and an end of the third encapsulation section 223 far from the second encapsulation section 222 is bent toward the second encapsulation section 222. It can be understood that the encapsulation section 22 is specifically divided into three subsections, namely a first encapsulation subsection 221, a second encapsulation subsection 222 and a third encapsulation subsection 223, and the bending is performed according to actual requirements.

Referring to fig. 2, in one embodiment, an adhesive layer 224 is disposed between the second package sub-section 222 and the third package sub-section 223. By adopting the above technical solution, the adhesive layer 224 is used to prevent the third package subsegment from springing back relative to the second package subsegment 222.

Referring to fig. 2 and 3, in an embodiment, an included angle a between the package segment 22 and the thickness direction of the aluminum-plastic film is in a range of 0 ° to 60 °. Specifically, the included angle a may be 0 °, 5 °, 10 °, 15 °, 20 °, 25 °, 30 °, 35 °, 40 °, 45 °, 50 °, 60 °, and the like, and the included angle a may enable the package segment 22 to obtain a proper bending effect within the above range.

Referring to fig. 2, in an embodiment, the aluminum-plastic film main body 10 is formed by fastening two aluminum-plastic films each having a punched hole, and the length L from the bending of the encapsulation section 22 to the transition section 21 is greater than a half of the thickness of the aluminum-plastic film main body 10 wrapping the battery cell 200. It is understood that the length L is the length of the folded encapsulation section 22, i.e. the distance between the end of the folded encapsulation section 22 away from the transition section 21 and the end where the folded encapsulation section is connected to the transition section 21. By adopting the above technical scheme, the transition section 21 and the encapsulation section 22 are both located in the middle of the thickness direction of the aluminum-plastic film main body 10, and therefore, the length L from the bending of the encapsulation section 22 to the transition section 21 should be greater than half of the thickness of the aluminum-plastic film main body 10 wrapping the battery cell 200.

Referring to fig. 3, the difference from the above embodiment is that the aluminum-plastic film main body 10 is formed by buckling an aluminum-plastic film with a punched hole and another aluminum-plastic film without punched hole, so that the transition section 21 and the encapsulation section 22 are both located on one side of the aluminum-plastic film main body 10 in the thickness direction. Similarly, the length L from the bent packaging section 22 to the transition section 21 is greater than the thickness of the aluminum-plastic film main body 10 wrapping the battery cell 200.

Referring to fig. 4, the present invention further provides a flexible package battery, which includes a plurality of battery cells 200 and a plurality of the above aluminum plastic film package structures 100, wherein each aluminum plastic film package structure 100 is packaged in a corresponding battery cell 200.

The utility model provides a laminate polymer battery, on the basis that has above-mentioned plastic-aluminum membrane packaging structure 100, tensile strength is higher, and life is longer.

Referring to fig. 4, in an embodiment, a buffer layer 300 is disposed between two adjacent aluminum plastic film package structures 100. As can be appreciated, the buffer layer 300 can reduce the impact of two adjacent battery cells 200 and increase the distance between two adjacent aluminum-plastic film package structures 100, so that the side sealing edge 20 of the aluminum-plastic film package structure 100 has enough space for placing without affecting each other.

The test procedure was as follows:

example 1, cell 200 size (thickness width length) was selected to be 6.9mm 88mm 267mm, and the cell 200 was wrapped with two aluminum plastic films each having a punched hole, the aluminum plastic films having a thickness of 1.5 mm. The height H of the package section 22 of the side sealing edge 20 after being bent twice is 3.7mm, and the boundary of the package section, which exceeds the aluminum-plastic film main body 10 and wraps the battery cell 200 in the thickness direction, is 3.7-6.9\ 2-1.5-0.1 mm.

Example 2, cell 200 size (thickness width length) was selected to be 6.9mm 88mm 267mm, and the cell 200 was wrapped with two aluminum plastic films each having a punched hole, the aluminum plastic films having a thickness of 1.5 mm. The height H of the package section 22 of the side sealing edge 20 after being bent twice is 3.8mm, and the boundary of the package section, which exceeds the aluminum-plastic film main body 10 and wraps the battery cell 200 in the thickness direction, is 3.8-6.9\ 2-1.5-0.2 mm.

Example 3, a cell 200 size (thickness width length) of 6.9mm 88mm 267mm was selected, and the cell 200 was wrapped with two aluminum plastic films each having a punched hole, the aluminum plastic films having a thickness of 1.5 mm. The height H of the package section 22 of the side sealing edge 20 after being bent twice is 3.9mm, and the boundary of the package section, which exceeds the aluminum-plastic film main body 10 and wraps the battery cell 200 in the thickness direction, is 3.9-6.9\ 2-1.5-0.3 mm.

Example 4, a cell 200 size (thickness width length) of 6.9mm 88mm 267mm was selected and the cell 200 was wrapped with two aluminum plastic films each having a punched hole, the aluminum plastic films having a thickness of 1.5 mm. The height H of the package section 22 of the side sealing edge 20 after being bent twice is 4.0mm, and the boundary of the package section, which exceeds the aluminum-plastic film main body 10 and wraps the battery cell 200 in the thickness direction, is 4.0-6.9\ 2-1.5-0.4 mm.

Example 5, cell 200 size (thickness width length) was selected to be 6.9mm 88mm 267mm, and the cell 200 was wrapped with two aluminum plastic films each having a punched hole, the aluminum plastic films having a thickness of 1.5 mm. The height H of the package section 22 of the side sealing edge 20 after being bent twice is 4.1mm, and the boundary of the package section, which exceeds the aluminum-plastic film main body 10 and wraps the battery cell 200 in the thickness direction, is 4.1-6.9\ 2-1.5-0.5 mm.

Example 6, cell 200 size (thickness width length) was selected to be 6.9mm 88mm 267mm, and the cell 200 was wrapped with two aluminum plastic films each having a punched hole, the aluminum plastic films having a thickness of 1.5 mm. The height H of the package section 22 of the side sealing edge 20 after being bent twice is 4.2mm, and the boundary of the package section, which exceeds the aluminum-plastic film main body 10 and wraps the battery cell 200 in the thickness direction, is 4.2-6.9\ 2-1.5-0.6 mm.

Example 7, a cell 200 size (thickness width length) of 6.9mm 88mm 267mm was selected and the cell 200 was wrapped with two aluminum plastic films each having a punched hole, the aluminum plastic films having a thickness of 1.5 mm. The height H of the package section 22 of the side sealing edge 20 after being bent twice is 4.3mm, and the boundary of the package section, which exceeds the aluminum-plastic film main body 10 and wraps the battery cell 200 in the thickness direction, is 4.3-6.9\ 2-1.5-0.7 mm.

Example 8, a cell 200 size (thickness width length) of 6.9mm 88mm 267mm was selected and the cell 200 was wrapped with two aluminum plastic films each having a punched hole, the aluminum plastic films having a thickness of 1.5 mm. The height H of the package section 22 of the side sealing edge 20 after being bent twice is 4.4mm, and the boundary of the package section, which exceeds the aluminum-plastic film main body 10 and wraps the battery cell 200 in the thickness direction, is 4.4-6.9\ 2-1.5-0.8 mm.

Example 9, cell 200 size (thickness width length) was selected to be 6.9mm 88mm 267mm, and the cell 200 was wrapped with two aluminum plastic films each having a punched hole, the aluminum plastic films having a thickness of 1.5 mm. The height H of the package section 22 of the side sealing edge 20 after being bent twice is 4.5mm, and the boundary of the package section, which exceeds the aluminum-plastic film main body 10 and wraps the battery cell 200 in the thickness direction, is 4.5-6.9\ 2-1.5-0.9 mm.

Example 10, cell 200 size (thickness width length) was selected to be 6.9mm 88mm 267mm, and the cell 200 was wrapped with two aluminum plastic films each having a punched hole, the aluminum plastic films having a thickness of 1.5 mm. The height H of the package section 22 of the side sealing edge 20 after being bent twice is 4.6mm, and the boundary of the package section, which exceeds the aluminum-plastic film main body 10 and wraps the battery cell 200 in the thickness direction, is 4.6-6.9\ 2-1.5-1.0 mm.

Comparative example 1, cell 200 size (thickness width length) was selected to be 6.9mm 88mm 267mm, and the cell 200 was wrapped with two aluminum plastic films each having a punched hole, the aluminum plastic films having a thickness of 1.5 mm. The height H of the package section 22 of the side sealing edge 20 after being bent twice is 3.3mm, and the boundary of the package section, which is lower than the boundary of the electrical core 200 wrapped by the aluminum-plastic film main body 10 in the thickness direction, is 6.9\2+1.5-3.3 mm ═ 0.3 mm.

Comparative example 1, cell 200 size (thickness width length) was selected to be 6.9mm 88mm 267mm, and the cell 200 was wrapped with two aluminum plastic films each having a punched hole, the aluminum plastic films having a thickness of 1.5 mm. The height H of the package section 22 of the side sealing edge 20 after being bent twice is 3.0mm, and the boundary of the package section, which is lower than the boundary of the electrical core 200 wrapped by the aluminum-plastic film main body 10 in the thickness direction, is 6.9\2+ 1.5-3.0-0 mm.

The above examples 1 to 10, as well as comparative examples 1, 2 were subjected to a tensile strength test of the side-seals 20, which achieved a process that remained a single variable, i.e. only the height H was varied, with the following test results:

in conclusion, as shown by the data of the tensile strength of the side seals 20 of examples 1 to 10 and the data of the tensile strength of the side seals 20 of comparative examples 1 to 2, the tensile strength of the side seal 20 of the comparative example is lower than that of the data in each example, which shows that the effective seal length of the side seal 20 is defined by bending the encapsulation section 22 of the side seal 20 until the height H of the transition section 21 exceeds the boundary of the aluminum plastic film main body 10 wrapping the battery cell 200 in the thickness direction, so that the tensile strength of the side seal 20 can be improved, and, along with the increase of height H, tensile strength also constantly increases, however, height H has the increase upper limit, surpasss too much and easily influences the position of placing of laminate in series-parallel connection of laminate in-process of laminate of soft-packaged battery, and finally, the length overlength of side banding 20 needs to occupy more accommodation space, influences the volume energy density of battery package. Meanwhile, the calendar life of the soft package battery is also in direct proportion to the tensile strength of the side seal edge 20.

The above description is only exemplary of the present invention and should not be construed as limiting the present invention, and any modifications, equivalents and improvements made within the spirit and principles of the present invention are intended to be included within the scope of the present invention.

Claims (10)

1. The utility model provides an aluminum-plastic film packaging structure, including the aluminum-plastic film main part that is used for wrapping up electric core and by the side banding that the aluminum-plastic film main part outwards extended and formed, the side banding including connect in the changeover portion of aluminum-plastic film main part and by the outside encapsulation section that extends of changeover portion, its characterized in that: the height from the bent packaging section to the transition section exceeds the boundary of the aluminum-plastic film main body wrapping the battery cell in the thickness direction.

2. The aluminum-plastic film packaging structure of claim 1, wherein: the height from the bent packaging section to the transition section exceeds the boundary range of the aluminum plastic film main body wrapped battery cell in the thickness direction by 0.1-1 mm.

3. The aluminum-plastic film packaging structure of claim 1, wherein: the packaging section is close to the aluminum-plastic film main body after being bent at least twice.

4. The aluminum-plastic film packaging structure of claim 3, wherein: the packaging section comprises a first packaging sub-section, a second packaging sub-section and a third packaging sub-section which are sequentially connected, the first packaging sub-section is connected to the transition section, one end, far away from the first packaging sub-section, of the second packaging sub-section is bent towards the aluminum-plastic film main body, and one end, far away from the second packaging sub-section, of the third packaging sub-section is bent towards the second packaging sub-section.

5. The aluminum-plastic film packaging structure of claim 4, wherein: and an adhesive layer is arranged between the second packaging subsection and the third packaging subsection.

6. The aluminum-plastic film packaging structure of claim 1, wherein: the range of an included angle a between the packaging section and the thickness direction of the aluminum-plastic film is 0-60 degrees.

7. The aluminum-plastic film packaging structure of claim 1 or 6, wherein: the aluminum-plastic film main part is formed by buckling two aluminum-plastic films with punched pits, and the length L of the transition section after the packaging section is bent is larger than half of the thickness of the electric core wrapped by the aluminum-plastic film main part.

8. The aluminum-plastic film packaging structure of claim 1 or 6, wherein: the aluminum-plastic film main body is formed by buckling an aluminum-plastic film with a punched hole and another aluminum-plastic film without punched hole, and the length L from the bent packaging section to the transition section is larger than the thickness of the aluminum-plastic film main body wrapping the battery core.

9. The utility model provides a laminate polymer battery, includes a plurality of electric cores, its characterized in that: the battery cell structure further comprises a plurality of aluminum-plastic film packaging structures according to any one of claims 1 to 8, wherein each aluminum-plastic film packaging structure is packaged in a corresponding battery cell.

10. The pouch cell according to claim 9, wherein: and a buffer layer is arranged between every two adjacent aluminum-plastic film packaging structures.

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