JP2003187874A - Flat battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a flat battery which can reduce defect caused by electrode plate breaking or active material layer removing from electrodes when the electrodes are inserted and set in a battery case, and enables good discharging characteristic by improving nonaqueous electrolyte soakage to the electrodes. <P>SOLUTION: An adhesive tape 5 which has at least one opening or an adhesive tape which is made of base material having permeability for the nonaqueous electrolyte, is stuck on soles of the electrodes 7 which are disposed on an electrode inserting side of the battery case. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention suppresses damage to an electrode plate and dropping of an active material layer when inserting an electrode group into a battery case, and a non-aqueous electrolyte solution for the electrode group housed in the battery case. Relates to a flat battery excellent in liquid injection property.

[0002]

2. Description of the Related Art In recent years, with the remarkable reduction in size, weight and thickness of cordless devices such as mobile phones and notebook personal computers, lithium ion secondary batteries, which are small, lightweight and have high energy density, have become the mainstream as a driving power source. ing. Among them, from the viewpoint of effective use of space, a thin flat battery, particularly a lithium ion secondary battery using an aluminum prismatic battery case that also satisfies the demand for weight reduction, is in the spotlight.

In these flat batteries, the positive electrode plate, the negative electrode plate and the separator are extremely thin, and the electrode group in which the positive electrode plate and the negative electrode plate are spirally wound through the separator is housed in the battery case. The battery case is formed so as to have an upper opening and a rectangular cross section. The electrode group is accommodated through the opening, and after the nonaqueous electrolytic solution is injected and impregnated, the opening is used as a sealing plate. It is configured to have a sealed mouth.

In a flat battery, the core material of the electrode plate and the separator are made as thin as possible in order to achieve further thinning or higher capacity, and the amount of the separator in the core or outermost periphery of the electrode group is used. Is reduced, or the pressure applied to the electrode group is increased to reduce the thickness of the electrode group. Further, in the portion corresponding to the outer peripheral portion of the positive electrode group, the active material was applied only to one surface located on the inner surface side of the electrode group, and the other surface did not contribute to the discharge reaction, so the core material of the aluminum foil was exposed. There is also known a method of effectively utilizing an active material by forming a structure.

The electrode group as described above is filled with the active material at a high density and has a large amount of the active material. Therefore, when the electrode group is inserted into the battery case, the active material layer is liable to drop off and the battery capacity is lowered. It is one of the causes of the deterioration of characteristics such as. further,
The area of the battery case opening has been reduced due to the progress of thinning, and there is a possibility that the bottom surface of the electrode group may be damaged when the electrode group is housed in the battery case. In order to suppress the occurrence of such defects, a method of fixing with an adhesive tape is adopted. Specifically, as is clear from the perspective view of the electrode group shown in FIG. 4, the electrode group 7 is wound with the positive electrode core material 1 exposed at the outermost periphery, and the electrode group 7 is wound with the adhesive tape 3. A method of binding and fixing the terminal end or the entire circumference of the group is adopted. As a result, the electrode group 7 is prevented from bulging due to the looseness of the winding, and the electrode plate is prevented from being displaced or damaged when it is inserted into the battery case.

[0006]

However, in the above construction, the pressure-sensitive adhesive tape only prevents the electrode group from bulging due to loose winding, and when it is inserted into the battery case, the electrode group 7, especially the bottom portion. The corners of No. 4 come into contact with the battery case, causing damage to the electrode group 7 and dropping of the active material layer.
Therefore, a method has been proposed in which an adhesive tape 15 having a width larger than the bottom surface is attached to the bottom surface located on the insertion side of the electrode group 7 shown in FIG. 5 to cover the bottom surface of the electrode group 7 and the vicinity of the bottom surface of the side surface. ing. In this method, the adhesive tape 15
If the thickness of the electrode is large, the thickness of the electrode group also increases, which hinders high capacity, and an extremely thin adhesive tape is required. Usually, the adhesive tape 15 is made of polypropylene resin or polyimide resin as a base material, and has a thickness of 20 including adhesive.
It is set to -60 μm. Furthermore, a resin material that is stable with respect to the non-aqueous electrolyte is used.

Adhesive tape 15 in the battery manufacturing process
Is formed wider than the electrode group 7 and is attached only to the bottom surface. Then, when the electrode group 7 is inserted into the case, the portion protruding from the electrode group is bent along the shape of the electrode group and covers the vicinity of the bottom surface of the side surface. Thereby, the electrodes exposed at the bottom surface of the electrode group 7 and the end faces of the separator are prevented from coming into contact with and being damaged by the case and the active material layer from falling off.

The electrode group 7 having the above structure is covered with the adhesive tape 3 along its side surface, and the bottom surface is also covered with the adhesive tape 15. Therefore, in the process of injecting the electrolytic solution after inserting the electrode group 7 into the battery case, it becomes difficult for the electrolytic solution flowing between the electrode group 7 and the battery case to flow into the electrode group 7. Can be confirmed. In particular, in the electrode plate group in which the active material is packed with a high density or wound with a high binding force, the above phenomenon becomes remarkable, and the positive and negative electrode plates and the separator are not impregnated with sufficient electrolytic solution, and the discharge rate characteristic There is a problem that causes deterioration.

In order to solve the above problems, it is an object of the present invention to provide a flat battery which suppresses damage to the electrode group when it is inserted into a battery case and at the same time does not cause deterioration of discharge rate characteristics. To do.

[0010]

In order to achieve the above object, the flat battery of the present invention has a bottomed battery case having an upper opening in which an electrode group including a positive and negative electrode plate and a separator is inserted and housed. An opening of a battery case is hermetically sealed, and the electrode group has an adhesive tape having at least one opening attached to a bottom surface located on the insertion side into the battery case. The shape of the opening is not limited to a circular shape, a substantially quadrangular shape, or the like as long as it does not hinder the permeation of the electrolytic solution and does not damage the electrode group during insertion into the battery case. Further, the adhesive tape may be divided into two or more parts and attached to each other to form a slit-shaped opening in the divided part of the adhesive tape. The area of these openings is preferably set to 1% or more of the area of the bottom surface of the electrode group.

Further, the flat battery of the present invention comprises a bottomed battery case having an upper opening in which an electrode group including positive and negative electrode plates and a separator is inserted and housed, and the opening of the battery case is hermetically sealed. The electrode group has an adhesive tape attached to the bottom surface located on the insertion side into the battery case, the adhesive tape including a base material and an adhesive layer having permeability to a non-aqueous electrolyte, Moreover, it is characterized in that a region where the pressure-sensitive adhesive layer is not formed is formed.

The area of the area where the adhesive layer is not formed in the adhesive tape is preferably 1% or more of the area of the bottom surface of the electrode group, and the base material of the adhesive tape is the same material as the separator. Is preferred.

By adopting each of the above-mentioned constitutions, it is possible to greatly suppress the damage of the electrode group and the dropping of the active material layer when the electrode group is inserted and stored in the battery case, and at the same time, the non-aqueous electrolyte solution The non-aqueous electrolyte that has flowed between the electrode group and the case at the time of injection flows into the electrode group through the opening of the adhesive tape attached to the bottom of the electrode group. The positive and negative electrode plates and the separator are supplied with the electrolytic solution as designed, and a flat battery having excellent discharge rate characteristics can be obtained.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Preferred embodiments of the present invention will be described below with reference to FIGS.

FIG. 1 is a principal view of an adhesive tape in which an opening formed of a circular hole is formed on the bottom surface of an electrode group, and a perspective view of an electrode group to which the adhesive tape is attached. FIG. It is a perspective view of the electrode group which stuck the tape and formed the slit-shaped opening part. Further, FIG. 3 is a main surface and a side view of a pressure-sensitive adhesive tape including a base material that transmits a non-aqueous electrolyte and a pressure-sensitive adhesive layer, and is a perspective view of the adhesive tape attached.

The structure of the electrode group in this embodiment will be described in detail below. In this electrode group, a positive and negative electrode plate and a separator are wound, and an active material layer is formed only on the inner surface side on the outermost periphery, and a positive electrode plate whose outer surface side is an uncoated portion is positioned. Therefore, the positive electrode core material is exposed on the side surface of the electrode group.

The electrode group 7 shown in FIG. 1 has an adhesive tape 5 having an opening formed by a circular hole 6 on the bottom surface. Therefore, when the electrode group is inserted into and housed in the bottomed battery case having an open upper portion, damage to the electrode group and dropping of the active material layer are suppressed. Further, after accommodating the electrode group at a predetermined position in the battery case, non-aqueous electrolysis is injected. At this time, the electrolytic solution flowing into the electrode group and the battery case reaches the bottom surface of the battery case. Then, the electrolytic solution moves to the electrode group through the opening formed in the adhesive tape, and the positive electrode plate and the separator are impregnated there. Therefore, since the electrolytic solution injected into the battery case reaches the positive and negative electrode plates and the separator efficiently and reliably, the discharge rate characteristics and the like are not deteriorated.

The area of the circular hole forming the opening of the adhesive tape is 1% or more of the bottom area of the electrode group. This ratio is a ratio necessary for impregnating the positive and negative electrode plates and the separator with the electrolytic solution flowing along the inner surface of the battery case and existing on the bottom surface of the battery case. The upper limit of the ratio is 20
% Or less is preferable. If it exceeds 20%, the fluidity from the bottom of the battery case to the electrode group will not change,
Problems and difficulties such as breakage of the active material layer when the battery case is inserted and dropping of the active material layer, workability of the adhesive tape, and deterioration of workability associated with attachment become remarkable. Further, there is no limitation on the shape and number of the openings. A circular shape, an elliptical shape, a rectangular shape, or the like can be used. The opening may be one or more, and the forming position is not particularly limited. Preferably, in the case of one place, 2 in the center
If there are more than one place, they are evenly provided from the center to the left and right.

On the other hand, in the electrode group shown in FIG. 2, the adhesive tape is divided into two or more and attached to the bottom surface. The adhesive tape is divided to form slit-shaped openings. The electrolytic solution existing on the bottom surface of the battery case moves to the electrode group side through the slit-shaped opening. Moreover, when the battery pack is inserted into the battery case, the electrode group, especially the bottom surface, is prevented from being damaged and the active material layer is prevented from falling off.

The cross-sectional area of the slit-shaped opening 8 is 1% or more of the bottom area of the electrode group. Considering the ease of sticking the bottom adhesive tape of the electrode group in manufacturing, it is advantageous that the slit-shaped opening 8 is wide, but the slit-shaped opening 8 is
If the width of the electrode is wide, the electrode plate may be flipped over when the electrode group is inserted into the battery case. Therefore, the width is preferably 20% or less of the cross-sectional area of the bottom portion, and the position where the slit is provided is not particularly limited. Although not provided, it is preferable to provide them in the central portion in the case of one location and in the left and right evenly from the central portion in the case of two or more locations.

Furthermore, in the electrode group shown in FIG. 3, an adhesive tape having permeability to the non-aqueous electrolyte is attached to the bottom surface. This adhesive tape uses a resin material having a permeability to a non-aqueous electrolyte as a base material, and an adhesive layer is formed on the base material to impart adhesiveness. The resin material used for this base material is preferably the same material as the separator in consideration of the organic electrolyte solution resistance and the adhesiveness of the separator. Then, an area in which the adhesive layer is not formed on the base material is formed, and the electrolytic solution permeates through the area. The area of the region where the adhesive layer is not formed is 1% or more with respect to the bottom area of the electrode group. On the other hand, the upper limit value of the unformed area is preferably 20% or less. If this value is exceeded, the adhesive force between the electrode group and the adhesive tape will be reduced, resulting in misalignment or the like during insertion into the battery case. Further, the unformed area may be formed in a stripe shape or a dot shape as well as the structure formed in the central portion of the adhesive tape as shown in FIG. 3, and a uniform adhesive force can be obtained in the entire adhesive tape. Any configuration will do.

It is essential that the material of the base material that constitutes the adhesive tape is a material that is permeable to the non-aqueous electrolyte solution, such as a polyolefin resin such as polyethylene resin or polypropylene resin, or polytetrafluoroethylene (PTF).
E), fluorine-based resins such as tetrafluoroethylene / hexafluoropropylene copolymer (FEP) and tetrafluoroethylene / perfluoroalkoxyethylene copolymer (PFA), glass cloth, and the like can be used. Preferably, the same material as the separator is selected as described above,
It is a non-woven fabric of olefin resin such as polyethylene resin and polypropylene resin. The thickness of the substrate is preferably in the range of 15 μm to 40 μm from the viewpoint of strength and high capacity. The pressure-sensitive adhesive applied to this base material to form the pressure-sensitive adhesive layer is at least one selected from isobutyl rubber, styrene-butadiene rubber, silicon resin, and acrylic resin. The thickness of the adhesive layer is preferably in the range of 15 μm to 70 μm from the viewpoint of adhesiveness to the bottom of the electrode group and high capacity.

The electrode group shown in FIGS. 1 to 3 is housed in a battery case, and then, a process of injecting and impregnating a non-aqueous electrolyte solution and a process of sealing an opening of the battery case with a sealing plate are performed. Completed as a flat battery. The electrode group according to this embodiment is a flat electrode group in which a positive electrode plate and a negative electrode plate are insulated via a separator. Hereinafter, the components of the electrode group and the configuration of the electrolytic solution will be described in detail.

The positive electrode plate is made of a foil made of aluminum or aluminum alloy or a foil that has been lathed or etched, and the positive electrode active material and the binder are used on one or both sides of the current collector as the solvent, if necessary. Apply paste that is kneaded and dispersed,
It can be manufactured by drying and rolling. The positive electrode plate preferably has a thickness of 130 μm to 200 μm and is flexible.

As the positive electrode active material, for example, a lithium-containing transition metal compound capable of accepting lithium ions as a guest is used. For example, a composite metal oxide of at least one metal selected from cobalt, manganese, nickel, chromium, iron and vanadium and lithium, L
iCoO ₂ , LiMnO ₂ , LiNiO ₂ , LiCo _x Ni
_(1-x) O ₂ (0 <x <1), LiCrO ₂ , αLiFe
O ₂ , LiVO _{2 and the} like are preferable.

Examples of the binder include a fluororesin material which maintains adhesion between active materials, a polymer material having a polyalkylene oxide skeleton, and a styrene-butadiene copolymer. As the fluorine-based resin material, polyvinylidene fluoride (PVDF), a copolymer P (VDF-) of vinylidene fluoride (VDF) and hexafluoropropylene (HFP).
HFP) is preferred. Further, as a conductive agent added as needed, a carbon-based conductive material such as acetylene black, graphite, carbon fiber or the like is preferable.

As the solvent, a solvent capable of dissolving the binder is suitable, and in the case of the non-aqueous binder, acetone, cyclohexanone, N-methyl-2-pyrrolidone (NMP), methyl ethyl ketone (MEK) and other non-solvents are used. A water solvent alone or a mixed solvent obtained by mixing these is preferable, and water is preferable in the case of an aqueous binder.

On the other hand, the negative electrode plate was prepared by kneading and dispersing a negative electrode active material and a binder and, if necessary, a conductive agent in a solvent on one side or both sides of a collector made of a copper foil or a lathed or etched foil. It can be prepared by applying a paste, drying and rolling. The thickness of the negative electrode plate is 140 μm to 210 μm.
m, and is preferably flexible.

As the negative electrode active material, for example, a material containing graphite having a graphite type crystal structure capable of absorbing and desorbing lithium ions, such as natural graphite or artificial graphite is used. In particular, it is preferable to use a carbon material having a graphite type crystal structure in which the lattice spacing (d ₀₀₂ ) of the lattice plane (002) is 3.350 to 3.400 Å.

As the binder, the solvent, and the conductive agent which can be added if necessary, those similar to the positive electrode can be used.

Further, as the separator, a microporous polyolefin resin such as polyethylene resin or polypropylene resin is preferable.

On the other hand, the non-aqueous electrolytic solution is composed of a non-aqueous solvent and an electrolyte, and the non-aqueous solvent contains a cyclic carbonate and a chain carbonate as main components. Examples of the cyclic carbonate include ethylene carbonate (E
It is preferably at least one selected from C), propylene carbonate (PC), and butylene carbonate (BC). The chain carbonate is preferably at least one selected from dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC) and the like. As the electrolyte, for example, a lithium salt having a strong electron-withdrawing property is used, and for example, LiPF ₆ or Li
BF ₄ , LiClO ₄ , LiAsF ₆ , LiCF ₃ SO ₃ ,
LiN (SO ₂ CF ₃ ) ₂ , LiN (SO ₂ C ₂ F ₅ ) ₂ , L
iC (SO ₂ CF _{3) 3} and the like. These electrolytes may be used alone or in combination of two or more. These electrolytes are preferably dissolved in the non-aqueous solvent at a concentration of 0.5 to 1.5M.

[0033]

The present invention will be described in detail with reference to examples and comparative examples, but these do not limit the present invention in any way.

Example 1 50 parts by weight of lithium cobalt oxide (LiCoO ₂ ) powder as a positive electrode active material, 1.5 parts by weight of acetylene black as a conductive agent, and 5 parts as a binder.
7 parts by weight of 0% by weight polyfluorinated ethylene (PTFE) dispersion aqueous solution and 41.5 parts by weight of 1% by weight aqueous solution of carboxymethylcellulose ammonium salt as a thickener were added, kneaded and dispersed to prepare a positive electrode paste. . 0.3% of this positive electrode paste was applied to both sides of a core material made of aluminum foil having a thickness of 20 μm by using a die coater.
It was applied so as to have a thickness of 5 mm, dried and then heated to 200 ° C. to sinter the PTFE particles of the binder. It should be noted that, when the electrode group is constructed, the portion corresponding to the outermost periphery is configured to be applied only on one side. After that, roll pressure was applied until the thickness of the positive electrode plate was 0.15 mm, and the positive electrode plate was obtained by cutting into a predetermined size with a width of 42 mm and a length of 466 mm. An aluminum lead 10 was welded to the positive electrode core material 1, and an insulating tape 11 was attached and covered thereon.

On the other hand, graphite powder 100 is used as the negative electrode active material.
5 parts by weight of a binder solution consisting of a styrene-butadiene copolymer was added to parts by weight and kneaded and dispersed to prepare a paste for negative electrode. This negative electrode paste is applied to both sides of a core material made of a copper foil having a thickness of 10 μm using a die coater, dried, and then roll-pressed to a thickness of 0.15 mm to give a width of 44 mm.
mm and a length of 447 mm were cut into a predetermined size to obtain a strip-shaped negative electrode plate. A lead 12 made of nickel was welded to the negative electrode core material, and an insulating tape was attached and covered thereon. As the separator 2, a polyethylene resin microporous film cut into a width of 46 mm and a thickness of 27 μm was used.

Next, one end of the separator is sandwiched between the slits of the core jig having an elliptical cross section with slits on the short axis, and the core jig is rotated to move the outer circumference of the core jig. One positive electrode plate and one negative electrode plate were wound with a separator interposed therebetween to form an electrode group having an elliptical cross section. The positive electrode core material on the outer periphery of the electrode group was fixed with an adhesive tape 3 for fixing the electrode group having a base material made of polypropylene resin and having a width of 40 mm and a length of 16 mm. As described above, a part of the positive electrode plate is coated with the active material only on one surface, and the positive electrode plate is wound so that the uncoated portion of the active material is located on the outermost outer surface of the electrode group. Therefore, when the electrode group is formed, the positive electrode core material 1 is exposed, and the positive electrode core material is fixed to the electrode body 7 with the adhesive tape 3.

Further, in the state where the step of fixing with the adhesive tape is completed, the electrode group is extracted from the winding jig, and the electrode group is sandwiched between a pair of flat plates parallel to the major axis of the electrode group. The electrode group 7 having a flat cross section was constituted by pressurizing and deforming with a pressure of 5 MPa.

Next, an adhesive tape was stuck on the bottom surface of the electrode group 7. This adhesive tape used a base material made of polypropylene resin and having a thickness of 30 μm. The pressure-sensitive adhesive layer formed on the base material was made of silicone resin and had a thickness of 30 μm. The obtained adhesive tape 5 was cut so that the major axis was 38 mm and the minor axis was 16 mm.

Further, the pressure-sensitive adhesive tape of this example has an opening formed by providing a circular hole 6 having a diameter of 1.5 mm in the central portion as shown in FIG. The area of this opening corresponds to 1% of the bottom area of the electrode group 7. Further, the adhesive tape 5 is bent and attached at the dotted line portion. As a result, it is attached to the bottom surface located on the insertion side into the battery case and the vicinity of the bottom surface of the side surface adjacent to this bottom surface.

After that, the electrode group 7 was inserted into a battery case made of an aluminum alloy, and then the positive electrode lead 10 was used as a sealing plate and the negative electrode lead 12 was electrically connected to a mounting hole in the central portion of the sealing plate via an insulating gasket. Each washer was laser-welded to the washer attached in an insulated state. The sealing plate was fitted into a predetermined position of the opening of the battery case, and the periphery thereof was fixed to the inner peripheral surface of the battery case by laser welding. After that, 3.4 g of the non-aqueous electrolyte was injected and impregnated into the battery case through the liquid injection hole of the sealing plate, and then the sealing member was inserted into the liquid injection hole of the sealing plate, and A flat battery having a width of 34 mm, a thickness of 6 mm, and a height of 50 mm and a capacity of 950 mAh was completed by laser welding with a sealing plate to obtain a battery A.

The non-aqueous electrolytic solution was prepared by mixing lithium hexafluorophosphate (LiP) as an electrolyte in a mixed solvent of an equal amount of ethylene carbonate and ethyl methyl carbonate.
F ₆ ) having a concentration of 1.0 mol / l was used.

Similarly, the diameter of the circular hole 6 is 0.5 m.
m, 2.0 mm, 4.0 mm, 5.4 mm (same as the minor axis dimension of the electrode group), in addition to the circular hole, 2.0 mm in the minor axis direction of the electrode group, 16.7 mm in the major axis direction. A pressure-sensitive adhesive tape having an opening formed into a shape was prepared. A flat-type battery was prepared in which these adhesive tapes were attached to the bottom surface of the electrode group and the battery A was used for other configurations. The obtained batteries were designated as Battery B to Battery F, respectively. The areas of the openings for the electrode group 7 in the batteries B to F are 0.5% and 1.
They were 9%, 7.5%, 13.7% and 20.0%.

(Example 2) Using an electrode group manufactured in the same manner as in Example 1, an adhesive tape was divided into two and attached to the bottom surface located on the insertion side into the battery case, and a slit-shaped opening was formed. Formed. The base material of this adhesive tape is made of polytetrafluoroethylene (PTFE) resin and has a thickness of 20 μm.
m. A styrene-butadiene rubber (SBR) was used as the adhesive applied to the base material, and the adhesive layer was formed to have a thickness of 30 μm. The obtained tape was used in Example 1.
Similarly to the above, the major axis was cut to 18.5 mm and the minor axis to 16 mm to prepare an adhesive tape. This was attached to the bottom surface of the electrode group so that a slit-shaped gap 8 of 1.0 mm was formed in the central portion. The obtained battery was named battery G. The cross-sectional area of the aperture ratio when this slit was provided was 3.2% with respect to the cross-sectional area of the bottom of the electrode group.

(Example 3) A battery was prepared by using an electrode group prepared in the same manner as in Example 1 and using an adhesive tape having an area where an adhesive layer was not formed on the bottom surface located on the insertion side into the battery case. did. The base material 13 of this adhesive tape is made of glass cloth and has a thickness of 20 μm. Also, the adhesive 14
Is made of an acrylic resin containing butyl acrylate as a main component, and was applied so as to have a thickness of 40 μm. The obtained tape was cut to have a major axis of 38 mm and a minor axis of 16 mm. At this time, a portion of the tape having a width of 2.0 mm to which the adhesive 14 is not applied, that is, an unformed region of the adhesive layer, is provided at the center of the tape, and this unformed region is located at the center of the bottom surface of the electrode group. Then, it was attached to the bottom of the electrode. Batteries having the same configurations as those of the batteries A to G were manufactured. This was designated as Battery H. The area of the non-formed area not coated with the adhesive 14 is 6.
It was 5%.

Furthermore, a battery I was prepared in the same manner as the battery H except that a microporous film made of polyethylene resin, which was the same material as the separator, was used as the base material 13. The ratio of the unformed region in this battery was 6.5% with respect to the bottom area of the electrode group.

(Comparative Example) A comparative battery prepared in the same manner as in Example 1 using an adhesive tape having no opening and no adhesive layer-formed region on the bottom surface of the electrode group to be inserted into the battery case. It was created. At this time, as the adhesive tape,
A polypropylene resin having a thickness of 30 μm is used as a base material, and an adhesive layer made of a silicone resin is formed with a thickness of 30 μm.
It was obtained by cutting into 8 mm and a minor axis of 16 mm. The other structure is the same as that of the battery A in this embodiment, and the adhesive tape 15 is used.
Is bent and attached to the bottom surface of the electrode group 7. The obtained comparative battery was designated as comparative battery J.

A comparative battery was also prepared in which the entire bottom surface of the electrode group was not covered with the adhesive tape. The pressure-sensitive adhesive tape attached to the bottom surface of the electrode group was the same as in Comparative Battery J, and a polypropylene resin, a substrate having a thickness of 30 μm, and an adhesive layer having a thickness of 30 μm formed on a silicon resin was used. This tape was cut into a long axis of 30 mm and a short axis of 16 mm and attached to the bottom surface of the electrode group. Since the bottom adhesive tape of the electrode group has a width of 30 mm, the curved portions on both sides of the electrode group 7 are the portions not covered with this tape. The obtained battery was used as a comparative battery K. The area of the uncovered portion of the bottom surface of the electrode group was 2.9%.

With respect to each of the 20 flat cells of Examples 1 to 3 and Comparative Example thus obtained, the prepared battery was disassembled, the electrode group was removed from the battery case, and the bottom of the battery case was removed. The weight of the remaining non-aqueous electrolytic solution was measured, and for each 1000 cells, the defective rate due to electrode plate damage or peeling or dropping of the active material layer after inserting the electrode group into the battery case was visually inspected and compared. The results are shown in Table 1.

Table 1 shows the results of the discharge rate of 2 C at 20 ° C. obtained for each of the 20 cells of the flat battery as follows. Charging is performed by constant current-constant voltage charging for 2 hours at 4.2V, constant current charging of 950mA (1CmA) until the battery voltage reaches 4.2V, and then the current value is attenuated to 45mA (0mA. The battery was charged to reach a discharge end voltage of 3.0 V at a constant current of 190 mA (0.2 CmA), after being charged to 0.05 CmA). Next, after charging in the same manner as above, the battery was discharged to a discharge end voltage of 3.0 V with a constant current of 1900 mA (2 CmA), and a discharge rate of 2 C was (capacity at 2 CmA discharge) / (0.2 CmA discharge). Capacity).

[0050]

[Table 1]

As is clear from Table 1, in the comparative battery K in which the curvature portions at both ends of the bottom portion on the side of the cross section of the electrode group to be inserted into the battery case are not covered, the electrode group is inserted and stored in the battery case. At this time, 0.5% of defects occurred in this portion due to damage of the electrode group and dropping of the active material layer. On the other hand, in each of the batteries in this example, the entire bottom surface was covered and the adhesive tape having the opening or the region where the adhesive layer was not formed was used, and therefore the defective rate was 0.

In the case of Battery B in which the area of the opening is less than 1.0% of the bottom area of the electrode group, a few drops of the non-aqueous electrolyte solution remains at the bottom of the 3-cell battery case in 20 cells. 1.0%
In the case of Battery A and Battery C to Battery F described above, the nonaqueous electrolytic solution does not remain at the bottom of the battery case, the discharge rate characteristics of 2C are excellent, and the ratio to the cross-sectional area of the bottom surface of the electrode group is high. I found that it didn't change.

Further, the adhesive tape is divided into at least two pieces, and a battery G having an adhesive tape having slit-shaped openings attached to the divided surface, a base material permeable to a non-aqueous electrolyte and an adhesive agent are used. Battery H and battery I with adhesive tape
It was found that 2C of the battery I using the same material as the separator as the base material had a slightly higher discharge rate.
Then, it was found that in the battery J in which the adhesive tape was not provided with holes or slit-shaped openings, the nonaqueous electrolytic solution remained at the bottom of the battery case, and the discharge rate characteristic at 2C deteriorates.

[0054]

As described above, according to the flat battery of the present invention, when the electrode group is inserted into and stored in the battery case, the damage due to the electrode group and the defect due to the dropping of the active material layer can be significantly suppressed. Furthermore, the electrolyte that flows between the electrode group and the battery case during the injection of the non-aqueous electrolyte reaches the electrode group through the opening of the adhesive tape, and the electrolyte can be effectively used, and the flat surface with excellent charge and discharge characteristics can be used. A shaped battery can be provided.

[Brief description of drawings]

FIG. 1A is a schematic view showing a bottom surface of an adhesive tape according to an embodiment of the present application, and FIG. 1B is a perspective view of an electrode group according to the embodiment of the present application.

FIG. 2 is a perspective view of an electrode group according to another embodiment of the present application.

FIG. 3A is a schematic view showing the configuration of an adhesive tape according to yet another embodiment of the present application, and FIG. 3B is a perspective view of an electrode group according to the embodiment of the present application.

FIG. 4 is a perspective view showing an external shape of an electrode group.

FIG. 5 is a perspective view showing a configuration of a conventional electrode group.

[Explanation of symbols]

1 Positive electrode core material 2 separator 3 adhesive tape 4 Bottom of electrode group 5 adhesive tape 6 circular holes 7 electrode group 8 openings 9 Adhesive tape (divided pieces) 10 Positive electrode lead 11 insulating tape 12 Negative electrode lead 13 Base material 14 Adhesive layer

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Hirofumi Sato             1006 Kadoma, Kadoma-shi, Osaka Matsushita Electric             Sangyo Co., Ltd. F-term (reference) 5H028 AA06 BB03 CC02 CC12 CC22                       CC26                 5H029 AJ00 AK03 AL07 AM03 AM07                       BJ03 BJ04 BJ14 DJ04

Claims (6)

[Claims] 1. A flat-type battery in which an electrode group including a positive and negative electrode plate and a separator is inserted and housed in a bottomed battery case having an upper opening, and the opening of the battery case is hermetically sealed. The flat battery is characterized in that the electrode group has an adhesive tape having at least one opening attached to the bottom surface located on the insertion side into the battery case. 2. The flat battery according to claim 1, wherein the adhesive tape is divided and attached in two or more parts, and the divided part of the adhesive tape forms a slit-shaped opening. 3. The flat battery according to claim 1, wherein the area of the opening formed in the adhesive tape is 1% or more of the area of the bottom surface of the electrode group. 4. A flat battery, wherein an electrode group including a positive and negative electrode plate and a separator is inserted and housed in a bottomed battery case having an upper opening, and the opening of the battery case is hermetically sealed. The electrode group has an adhesive tape attached to the bottom surface located on the insertion side into the battery case, and the adhesive tape is
A flat battery comprising a base material having permeability to a non-aqueous electrolyte and a pressure-sensitive adhesive layer, and forming a region where the pressure-sensitive adhesive layer is not formed. 5. The flat battery according to claim 4, wherein the adhesive tape has an area of an area where the adhesive layer is not formed, which is 1% or more of the area of the bottom surface of the electrode group. 6. The flat battery according to claim 4, wherein the adhesive tape uses a base material made of the same material as the separator.