JP2005018990A - Stacked lithium ion secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a stacked lithium ion secondary battery having a structure reasonably durable against unavoidable shock although a power generation element is stored in a soft battery case. <P>SOLUTION: This stacked lithium ion secondary battery 1 is composed by airtightly enclosing a cell 2 in the battery case 4 formed of a laminated armoring material 34. A fusion bonding margin 11 for keeping the inside of the case airtight is formed on the battery case 4. The outer peripheral part 11b out of the fusion bonding margin 11 is bent inward with respect to a battery plate surface direction WL. The inner peripheral part 11a out of the fusion bonding margin 11 is so adjusted as to project in the direction WL. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a stacked lithium ion secondary battery in which a plate-shaped power generation element is assembled by laminating a plurality of power generation units each including an electrode and a separator, and the power generation element is hermetically sealed in a soft container. .
[0002]
[Prior art]
Recently, in lithium ion secondary batteries (including the concept of a lithium polymer secondary battery) that can swell and hold an electrolyte in an electrode, there is little risk of liquid leakage. It has been carried out in a battery container made of a laminate exterior material. According to this method, since it is not necessary to use a metal container, it is easy to thin the battery. In addition, a laminated lithium ion secondary battery described later has a feature that the degree of freedom in shape is extremely high.
[0003]
The laminate exterior material is generally a laminate of resin on both sides of an aluminum foil. A heat-fusible resin such as polypropylene is laminated on the side exposed in the container. According to this configuration, the container can be sealed only by melting and solidifying the heat-fusible resin. A fusion allowance is formed at a location where the heat-fusible resin is melted and solidified. This fusion allowance must be at least several millimeters wide to prevent moisture from penetrating into the battery. In a small battery, the fusion allowance occupies a relatively large area. In view of this, attempts have been made to reduce the area substantially occupied by the battery by folding the fusion allowance exactly on the side of the battery (see Patent Documents 1 to 3 below).
[0004]
[Patent Document 1]
JP 2000-58013 A [Patent Document 2]
JP 2001-202931 A [Patent Document 3]
Japanese Patent Laid-Open No. 2001-357824
[Problems to be solved by the invention]
By the way, a plate-like lithium ion secondary battery using a soft battery container is originally thin and small in size, so the battery container is often used by being exposed. In such a case, an unavoidable impact may be applied to the battery when it is incorporated into an electric product or even during actual use, and the power generation element may be deformed.
[0006]
In particular, in a stacked lithium ion secondary battery, a plurality of power generation units composed of a positive electrode, a negative electrode, and a separator are individually manufactured, and the power generation element is assembled by stacking these units. Sometimes, characteristics such as charge / discharge cycle characteristics and internal resistance are easily deteriorated.
[0007]
An object of the present invention is to provide a stacked lithium ion secondary battery having a structure that can appropriately withstand inevitable impacts while a power generation element is housed in a soft battery container.
[0008]
[Means for solving the problems and actions / effects]
In order to solve the above problems, the present invention is an exterior material in which a plate-shaped power generation element is configured by laminating a plurality of power generation units including electrodes and separators, and a heat-fusible resin is laminated on a metal foil. In a laminated lithium ion secondary battery in which the power generation element is hermetically sealed to the constructed battery container, the upper and lower exterior materials are bonded together by melting and solidifying the heat-fusible resin located inside, and the air-tightness in the battery container Is formed along the shape of the power generation element, the outer peripheral portion of the fusion allowance is bent 90 degrees or more with respect to the battery plate surface direction, and the inner peripheral portion adjacent to the bent outer peripheral portion is the battery. It is characterized by being adjusted to project in the plate surface direction.
[0009]
In the present invention, a part of the fusion allowance formed on the outer periphery of the battery container is left a little without being bent, and functions as an impact absorption allowance against an external force from the battery plate surface direction. Certainly, from the standpoint of maximizing the substantial size of the battery, in other words, the dead space that does not directly contribute to power generation, it is better to bend the entire fusion allowance along its inner periphery. However, in the present invention, only the outer peripheral portion of the fusion allowance is bent, and the inner peripheral portion adjacent to the outer peripheral portion is adjusted so as to project in the battery plate surface direction. And even when a sudden mechanical impact is applied from the battery plate surface direction, this structure absorbs the kinetic energy of the impact to the inner peripheral portion of the flexible fusion allowance and mitigates the impact transmitted to the power generation element. Will be able to. Thereby, it can prevent that a deformation | transformation etc. arise in a power generation element, and deterioration of characteristics, such as charging / discharging cycling characteristics and internal resistance, is suppressed. Of course, since the dead space corresponding to the bent portion is reduced, the battery can be made compact.
[0010]
In a preferred embodiment, the fusion allowance is provided with a notch having a shape in which the fusion allowance is notched inwardly corresponding to each corner of the power generation element having a polygonal shape, and these notches are formed. Depending on the remaining width of the fusion allowance at the position, a folding line is formed that divides the fusion allowance into an outer peripheral portion and an inner peripheral portion. When an attempt is made to fold the fusion allowance formed corresponding to two adjacent sides of the polygonal power generation element, a crease or the like is formed. Therefore, a notch is provided corresponding to each corner of the power generation element. The formation position of the fold line is determined according to the remaining width of the fusion allowance at the notch (corresponding to the distance from the tip of the notch to the inside of the battery container). If the fusion allowance is bent along such a fold line, no crease or the like will occur. Since the crease is not formed, it is possible to expect an effect of smoothing work such as storage of the electric device in the battery storage portion.
[0011]
Moreover, it is preferable to give circular arc shape to the tip of a notch. If it does in this way, fracture of an exterior material advances from the tip of a notch, and it can prevent effectively that air leaks in a container.
[0012]
In addition, when a set of notch lines extending from both ends of the arc shape is virtually extended, the notch portions are formed so that they intersect to form an acute angle or the notch lines extend in parallel. It is even better if there is. In this way, a high moisture barrier property can be maintained. Lithium ion secondary batteries such as the present invention are very reluctant to the presence of moisture. Water reacts with lithium ions to produce an inactive compound, which deteriorates charge / discharge cycle characteristics. Moreover, it reacts with the lithium salt in the electrolytic solution to generate a gas such as hydrofluoric acid, which may cause deterioration of battery characteristics. Generally, since a metal foil such as aluminum exists in the thickness direction of the exterior material, water hardly permeates in that direction. Water enters the container from the cross section of the exterior material. The longer the distance from the cross section to the inside of the container, the higher the moisture barrier property. Therefore, if the notch is formed as described above, the distance from the cross section to the inside of the container can be made as long as possible, and a high moisture barrier property can be maintained.
[0013]
In a more preferred aspect, the battery container can be composed of a container main body in which a recess for accommodating the power generation element is formed, and a lid that covers the container main body. In this case, a fusion allowance is formed by the overlap of the opening peripheral edge of the recess in the container main body and the lid, and the outer peripheral portion of the fusion allowance is bent 90 degrees or more from the battery plate surface direction toward the container main body. By being fixed in contact with the side surface, a gap is formed, and an external force from the battery plate surface direction can be absorbed. If the fusion allowance is bent so that such a gap is formed, a rocking space for the fusion allowance is secured, and high shock absorption performance can be realized.
[0014]
Moreover, the aspect by which the outer peripheral part of the fusion allowance is folded by the container main body side, and is being fixed to the inner peripheral part is also suitable. By doing so, the thickness of the fusion allowance extending in the battery plate surface direction increases, and the rigidity of the fusion allowance increases.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
FIG. 1 is a schematic cross-sectional view of a lithium ion secondary battery 1 (hereinafter also simply referred to as battery 1) according to the present invention. The battery 1 has a structure in which a cell 2 as a power generation element is sealed in a battery container 4. The plate-like cell 2 is formed by laminating a plurality of individually generated power generation units 20 so that their outer peripheral edges are aligned in the vertical direction. FIG. 2 shows a schematic cross-sectional view of the power generation unit 20.
[0016]
As shown in FIG. 2, the power generation unit 20 has a bi-cell structure in which separators 3 and 3 are sandwiched between positive electrodes 7 and 7 and a negative electrode 10. The positive electrode 7 has a structure in which a positive electrode active material layer 6 is laminated on a positive electrode current collector 5. On the other hand, the negative electrode 10 has a structure in which negative electrode active material layers 9 and 9 are laminated on a negative electrode current collector 8. In the present embodiment, the negative electrode 10 is shared by the two separators 3 and 3 so that the sides of the separators 3 and 3 not facing the negative electrode 10 are individually covered with the positive electrodes 7 and 7. Yes. The area of the negative electrode 10 can be equal to that of the positive electrode 7, but is preferably larger than that of the positive electrode 7. Further, the separators 3 and 3 have a larger area than the electrodes 7 and 10. The arrangement of the positive electrode 7 and the negative electrode 10 may be interchanged. Various shapes such as a square and a polygon other than a square can be adopted as the shape of the cell 2.
[0017]
The positive electrode current collector 5 can be composed of a foil or a metal mesh made of Al or an Al alloy. The negative electrode current collector 8 can be composed of a foil or a metal mesh made of Cu or a Cu alloy. As the metal mesh, any of expanded metal, etching metal and punching metal can be used.
[0018]
The positive electrode active material layer 6 includes a positive electrode active material, a conductive additive, and a polymer substrate (polymer). Similarly, the negative electrode active material layer 9 includes a negative electrode active material, a conductive additive, and a polymer substrate. The separator 3, the positive electrode active material layer 6 and the negative electrode active material layer 9 have a porous form, and are impregnated with a nonaqueous electrolytic solution in which a lithium salt such as LiPF ₆ is dissolved in an organic solvent such as ethylene carbonate or propylene carbonate. Has been.
[0019]
Examples of the polymer substrate constituting the positive electrode active material layer 6 and the negative electrode active material layer 9 include fluororesins such as polyvinylidene fluoride (PVDF), hexafluoropropylene (HFP), polytetrafluoroethylene (PTEF), and the like. A copolymer of fluororesin can be used.
[0020]
As the positive electrode active material constituting the positive electrode active material layer 6, a lithium composite oxide containing a transition metal or a typical metal such as LiMnO ₂ , LiCoO ₂ , or LiNiO ₂ can be used. As the negative electrode active material constituting the negative electrode active material layer 9, a graphite-based carbon material such as a mesofuse carbon material is suitable. In addition, conductive carbon such as acetylene black can be used as the conductive auxiliary agent (conductive substance).
[0021]
The separator 3 is made of the same material as the polymer substrate contained in the positive electrode active material layer 6 and the negative electrode active material layer 9, for example, PVDF, HFP, or a copolymer thereof (mixed with a filler such as SiO ₂ or the like). May be) Alternatively, a microporous film such as polyethylene or polypropylene, a microporous film having a multi-layer structure in which polyethylene is sandwiched between polypropylene, a resin layer such as polyethylene or polypropylene, and a resin layer made of PVDF, HFP, or a copolymer thereof You may use the microporous film etc. which have.
[0022]
As shown in FIG. 1, one end of strip-shaped lead terminals 12 and 13 is connected to the cell 2. The other ends of the lead terminals 12 and 13 extend outward through the fusion allowance 11 (sealing portion) of the battery container 4. Specifically, one end of the positive lead terminal 12 is connected to the power outlet 50 of the positive current collector 5, and one end of the negative lead terminal 13 is connected to the power outlet 80 of the negative current collector 8. It is connected. The power extraction unit 50 of the positive electrode current collector 5 is provided in each of the power generation units 20, and the plurality of power extraction units 50 are bundled into one. The positive lead terminal 12 may be made of, for example, aluminum or an aluminum alloy. The lead terminal 13 for the negative electrode is preferably composed of copper, copper alloy, nickel, nickel alloy, nickel-plated copper, or nickel-plated copper alloy.
[0023]
As shown in FIG. 7, the battery container 4 that accommodates the cell 2 is composed of a flexible sheet-like exterior material 34 in which resin layers 31 and 33 are provided on both surfaces of a metal foil 32 such as an aluminum foil. Yes. As the resin layer 31 exposed to the outside of the battery container 4, for example, polyethylene terephthalate or biaxially stretched nylon is used. Materials with resistance and low water vapor permeability are used.
[0024]
As shown in FIG. 1, the upper and lower exterior members 34 are bonded together by the melting and solidification of the resin layer 33 that comes inside the container, and the fusion allowance 11 is formed. Specifically, as shown in FIG. 8, the battery container 4 can be composed of a container body 4 b having a recess 4 p for accommodating the cells 2 and a lid 4 a. After the cell 2 is accommodated in the recess 4p of the container body 4b, the lid 4a is covered. The lid portion 4a is disposed so as to completely close the opening of the concave portion 4p of the container body 4b, and the outer peripheral edge portions of the container body 4b and the lid portion 4a are sandwiched between seal bars 90 and 91 (heat fusion jig). The inner resin layers 33 and 33 are heated and melted by the seal bars 90 and 91. If the seal bars 90 and 91 are separated, the fused resin layers 33 and 33 of the container body 4b and the lid portion 4a are solidified while being united, whereby the fusion allowance 11 for maintaining airtightness in the battery container 4 is obtained. It is formed. In addition, there are a case where the cover part 4a and the container body 4b are integrally manufactured by molding one exterior material 34, and a case where the lid part 4a and the container body 4b are separately manufactured.
[0025]
The fusion allowance 11 is formed so as to surround the cell 2 as well as the lead-out positions of the lead terminals 12 and 13. FIG. 3 is a top view of the battery 1, and the formation position of the fusion allowance 11 in the battery 1 is represented by a geometric pattern. Reference numeral 14 denotes a resin film for enhancing insulation and airtightness at the lead terminal 12 and 13 extraction positions.
[0026]
As shown in FIG. 2, the battery 1 of the present invention is a laminated lithium ion secondary battery obtained by individually producing a plurality of power generation units 20 and laminating and pressing them. As shown in FIG. 3, there is no limitation on the shape of the cell 2, and a polygonal battery other than a square can be easily manufactured. The battery container 4 is formed according to the shape of the cell 2. That is, the fusion allowance 11 is provided along the shape of the cell 2. The battery 1 shown in FIG. 3 shows immediately after the fusion allowance 11 is formed. The fusion allowance 11 does not contribute to power generation, but greatly increases the area that the battery 1 substantially occupies. Therefore, as will be described below, the fusion allowance 11 can be bent in the thickness direction of the battery 1 to make the battery 1 compact.
[0027]
However, when the thin plate-like cell 2 is accommodated in the soft battery container 4 made of the laminate exterior material 34, the cell 2 is subjected to a sudden mechanical impact from the lateral direction (battery plate surface direction). May be deformed. Therefore, in the present invention, a part (inner peripheral part) inward of the fusion allowance 11 formed on the outer periphery of the battery case 4 is left without being bent, and this is made to function as an impact absorption allowance. As a result, both compactness and enhanced impact resistance can be achieved.
[0028]
FIG. 6 is a schematic cross-sectional view showing a bent form of the fusion allowance 11. Here, two preferred specific examples in which the outer peripheral portion 11b of the fusion allowance 11 is bent by 90 degrees or more with respect to the battery plate surface direction WL, and the substantial size (occupied area) of the battery 1 is reduced. Show. In the embodiment shown in FIG. 6A, the outer peripheral portion 11 b of the fusion allowance 11 formed so as to extend in the battery plate surface direction WL is in contact with the side surface 4 f of the container body 4 b constituting the battery container 4. It is bent. The bent fusion allowance 11 is fixed by fixing means (not shown) such as an adhesive tape, a heat shrink film, and an adhesive so that the outer peripheral portion 11b is held in contact with the side surface 4f of the container body 4b. . On the other hand, the inner peripheral portion 11a of the fusion allowance 11 is adjusted so as to project in the battery plate surface direction WL. As a result, a slight gap HS is formed between the side surface 4f of the container body 4b and the bent fusion allowance 11. The gap HS compensates for the flexibility of the fusion allowance 11 protruding in the battery plate surface direction WL, and contributes to further improvement in impact resistance.
[0029]
In the embodiment shown in FIG. 6B, the outer peripheral portion 11b is folded back approximately 180 degrees toward the container main body 4b constituting the battery container 4 so that the outer peripheral portion 11b is in contact with and overlapped with the inner peripheral portion 11a. The folded outer peripheral portion 11b is tightly fixed to the inner peripheral portion 11a with an adhesive or an adhesive tape. According to this embodiment, the thickness of the fusion allowance 11 is about twice that of the original, and the impact resistance of the fusion allowance 11 is improved. The widths of the outer peripheral portion 11b and the inner peripheral portion 11a do not need to coincide with each other. For example, the fusion allowance 11 may be bent so that the outer peripheral portion 11b extends along the side surface 4f of the container body 4b.
[0030]
By the way, as shown in FIG. 3, the fusion allowance 11 has a polygonal shape because of the relationship with the shape of the cell 2, and in the case where the fusion allowance 11 constituting two adjacent sides is used for bending, A crease is made. Moreover, adjustment of the formation position of a folding line (border of the outer peripheral part 11b and the inner peripheral part 11a) is also troublesome. Therefore, prior to the step of bending the fusion allowance 11, the notches 40 to 45 are formed at positions corresponding to the corners of the polygonal cell 2 as shown in FIG. As a result, the easiness of folding can be improved, and creases are less likely to occur.
[0031]
The fusion allowance 11 formed so as to correspond to each side of the cell 2 can be bent individually by providing the notches 40 to 45 at both ends. Further, for example, a folding line KL that divides the fusion allowance 11 into an outer peripheral portion 11b and an inner peripheral portion 11a is set across a pair of adjacent cutout portions such as the cutout portions 40 and 41. Remaining width d ₂ of the fusion Chakudai 11 in the formation position of the notch 40 and 41 determines the width of the inner circumferential edge to the fold line KL of Toruchakudai 11. That is, adjusting the depth of cut for forming the notches 40 to 45 is also used for determining the bending position.
[0032]
Specifically, each part can be adjusted as shown in the enlarged schematic diagram of FIG. First, forming a width _{d 1} of Toruchakudai 11, for example, it is desirable to adjust the 2.0mm or 6.0mm or less. If too small adjusting the formation width d ₁ of Toruchakudai 11, there is a possibility that sufficient water content permeability can not be obtained. Conversely, if too large adjusting the formation width d ₁ of Toruchakudai 11, so causing an increase in dead space is not preferable. In the forming position of the notch 42 (representative of all notch), it is desirable to secure a remaining width d ₂ of Toruchakudai 11 or more 0.5 mm. Too small a residual width d _2, moisture permeation into the container becomes active, after which there is a possibility to accelerate the deterioration of characteristics of the battery 1, the inner peripheral portion 11a of the fusion Chakudai 11 shown in FIG. 6 (a) the width D ₁ can not be sufficiently secure.
[0033]
Further, as shown in FIG. 5B, it is desirable that an appropriate concave arc shape is provided on the inner side of the battery container 4 at the bottom of the notch portion 42, that is, at the tip of the notch. The notch portion 42 can be formed by using a cutting blade. However, if the notch tip is sharp, the breakage may proceed from the notch tip during the bending work of the fusion allowance 11 or the like. As a result, air may leak into the battery case 4. On the other hand, as shown in FIGS. 5 (a) and 5 (b), when an arc shape is given to the notched cross section, breakage hardly occurs. The radius R ₁ of the arc can be set to, for example, about 0.1 mm. Further, it is also possible to impart a substantially equal radius of the circular arc shape remaining width d ₂ of Toruchakudai 11.
[0034]
In addition, as shown in FIG. 5B, the notch portion 42 is provided so that when a pair of notch lines extending from both ends of the arc shape are virtually extended, the notch lines intersect at an acute angle θ. It is preferable that That is, if the tip is notched at an acute angle while giving an arc shape to form the notched portion 42, the moisture permeation retaining effect and the fracture preventing effect can be maintained in a well-balanced manner. For the same reason, as shown in FIG. 5 (c), it is also preferable to provide a circular arc shape at the tip of the notch while providing a notch with a constant width.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view of a lithium ion secondary battery according to the present invention.
2 is a schematic cross-sectional view of a power generation unit constituting the battery of FIG.
3 is a top view of the battery of FIG. 1 before folding the fusion allowance.
4 is a top view of the battery of FIG. 1 after forming a notch.
FIG. 5 is a schematic diagram illustrating a form of forming a notch.
FIG. 6 is a schematic cross-sectional view showing a bending form of a fusion allowance.
FIG. 7 is a schematic cross-sectional view showing a configuration of an exterior material that is a material of a battery container.
FIG. 8 is a schematic cross-sectional view showing a procedure for sealing a battery container.
[Explanation of symbols]
1 Lithium ion secondary battery 2 cell (power generation element)
3 Separator 4 Battery container 4a Lid 4b Container body 4p Recess 4f Side surface 7 of container body Positive electrode 10 Negative electrode 11 Fusion allowance 11a Inner peripheral portion 11b of fusion allowance Outer peripheral portion 20 of fusion allowance Power generation unit 32 Metal foils 31, 33 Resin layer 34 exterior materials 40-45, 42 'notch KL fold line HS gap

Claims (6)

A plate-shaped power generation element is configured by laminating a plurality of power generation units each including an electrode and a separator, and the power generation element is placed in a battery container composed of an exterior material in which a heat-fusible resin is laminated on a metal foil. In a hermetically sealed multilayer lithium ion secondary battery,
A fusion allowance is formed along the shape of the power generating element so that the upper and lower exterior materials are bonded together by melting and solidifying the heat-fusible resin located on the inner side to maintain airtightness in the battery container,
The outer peripheral portion of the fusion allowance is bent 90 degrees or more with respect to the battery plate surface direction, and the inner peripheral portion adjacent to the bent outer peripheral portion is adjusted so as to protrude in the battery plate surface direction. A feature of a laminated lithium ion secondary battery. The fusion allowance is provided with a cutout portion having a shape in which the fusion allowance is notched inwardly corresponding to each corner of the power generation element having a polygonal shape,
The folding line for dividing the fusion allowance into the outer peripheral portion and the inner peripheral portion is formed according to the remaining width of the fusion allowance at the position where the notches are formed. Stacked lithium ion secondary battery. The laminated lithium ion secondary battery according to claim 2, wherein an arc shape is provided at the tip of the notch. When the set of notch lines extending from both ends of the arc shape is virtually extended, the notch portions are formed such that they intersect to form an acute angle or the notch lines extend in parallel. The laminated lithium ion secondary battery according to claim 3. The battery container is composed of a container main body in which a recess for accommodating the power generation element is formed, and a lid portion covering the container main body,
The fusion margin is formed by the overlap between the opening peripheral edge of the recess and the lid in the container body, and the outer peripheral portion of the fusion margin is bent 90 degrees or more from the battery plate surface direction toward the container body. 5. The gap according to claim 1, wherein a space is formed by contacting and fixing the side surface of the container body, and external force from the battery plate surface direction is absorbed. Stacked lithium ion secondary battery. The battery container is composed of a container main body in which a recess for accommodating the power generation element is formed, and a lid portion covering the container main body,
The fusion margin is formed by the overlap of the opening peripheral edge of the recess and the lid in the container body, and the outer peripheral portion of the fusion margin is folded to the container main body side and fixed to the inner peripheral portion. The laminated lithium ion secondary battery according to any one of claims 1 to 4.

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