JP2003092143A - Lithium polymer battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obstruct the generation of cracks in a polymer electrolyte layer in manufacturing and in charge/discharge of a secondary battery and enhance energy density of the secondary battery. SOLUTION: A polymer electrolyte layer 17 is interposed between a positive active material layer 13 of a positive sheet 11 and a negative active material layer 16 of a negative sheet 14, and the positive sheet and the negative sheet are stacked. A laminate 20 is folded back once or two or more times in zigzag to form a lithium polymer battery 10. A negative current collector foil 15 and the polymer electrolyte layer are folded back in a belt, with no disconnection, and the negative active material layer is formed on the negative current collector foil so that the folded part of the negative current collector foil is divided with a negative slit 18. The positive sheet has an area corresponding to the folded back area of the negative current collector foil, and interposed between polymer electrolyte layers other than the folded part of the negative current collector foil.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a lithium ion polymer secondary battery in which a positive electrode sheet and a negative electrode sheet are laminated with a polymer electrolyte layer interposed.

[0002]

2. Description of the Related Art Conventionally, as this type of battery, an active material of a positive electrode sheet having an active material formed on the surface of a positive electrode current collector foil,
Disclosed is a lithium ion polymer secondary battery in which a positive electrode sheet and a negative electrode sheet are laminated with a polymer electrolyte layer interposed between the active material formed on the surface of the negative electrode current collector foil and the active material of the negative electrode sheet. (Japanese Patent Laid-Open No. 2001-28273)
issue). In this lithium-ion polymer secondary battery, the negative electrode sheet is in the form of a strip, and the polymer electrolyte layer is laminated on the surface of the active material, and the polymer sheet is folded once or twice or more. A plurality of positive electrode sheets each having an area corresponding to the folded area are sandwiched between the electrolyte layers. Further, a polymer electrolyte layer is laminated on the surface of the active material of the sandwiched positive electrode sheets.

In the lithium ion polymer secondary battery having such a structure, since the strip-shaped negative electrode sheet having an enlarged area is folded, the discharge capacity can be increased in a relatively small and thin state. Further, since a plurality of positive electrode sheets each having an area corresponding to the folded area are sandwiched between the polymer electrolyte layers, the negative electrode sheet at the fold portion does not bend, and the negative electrode sheet may bend to prevent internal deformation. Can prevent short circuit. Further, since the polymer electrolyte layer is formed on the strip-shaped negative electrode sheet, the active materials in the plurality of positive electrode sheets sandwiched between the polymer electrolyte layers share the same electrolyte, respectively. The internal impedance is made uniform and the cycle characteristics can be improved.

[0004]

However, in the lithium ion polymer secondary battery disclosed in the above-mentioned Japanese Patent Laid-Open No. 2001-28273, a polymer electrolyte layer is laminated on the surface of the active material of the strip-shaped negative electrode sheet, and When the positive electrode sheet is sandwiched between the polymer electrolyte layers excluding the folds of the negative electrode sheet and folded, tensile stress acts on the polymer electrolyte layer by the active material of the negative electrode sheet located on the mountain fold side of the negative electrode current collector foil. Therefore, cracks are likely to occur, and when cracks occur, cycle characteristics may be deteriorated. Further, in the above-mentioned conventional lithium ion polymer secondary battery, due to the volume change accompanying the charge and discharge of the battery, tensile stress is applied to the polymer electrolyte layer by the active material of the negative electrode sheet located on the mountain fold side of the negative electrode current collector foil as described above. Since it works, cracks are likely to occur, and when the cracks occur, cycle characteristics may deteriorate. Further, in the above-mentioned conventional lithium ion polymer secondary battery, since the active material of the positive electrode sheet does not exist at the fold of the negative electrode sheet, the active material of the negative electrode sheet located at the fold of the negative electrode sheet contributes to occlusion and release of lithium ions. However, there is a problem that the energy density of the battery is lowered. The object of the present invention is to prevent the generation of cracks in the polymer electrolyte layer during manufacturing and charging and discharging,
It is to provide a lithium polymer battery capable of improving energy density.

[0005]

The invention according to claim 1 is
As shown in FIG. 1, the positive electrode active material layer 1 of the positive electrode sheet 11 in which the positive electrode active material layer 13 is formed on the surface of the positive electrode current collector foil 12.
3 and the negative electrode active material layer 16 of the negative electrode sheet 14 having the negative electrode active material layer 16 formed on the surface of the negative electrode current collector foil 15,
This is an improvement of a lithium polymer battery in which a positive electrode sheet 11 and a negative electrode sheet 14 are laminated with a polymer electrolyte layer 17 interposed, and the laminate 20 is folded by one bending or by folding twice or more. The characteristic structure is that the negative electrode current collector foil 15 and the polymer electrolyte layer 17 are folded in a continuous band shape, and the negative electrode active material layer 16 is folded into the negative electrode current collector foil 15.
Are formed on the negative electrode current collector foil 15 so as to be divided by providing the negative electrode slits 18 at the bent portions, and the positive electrode sheets 11 each have an area corresponding to the folded area of the negative electrode current collector foil 15 and the negative electrode. The current collector foil 15 is sandwiched between the polymer electrolyte layers 17 excluding the bent portions.

In the lithium polymer battery described in claim 1, a tensile stress is applied to the polymer electrolyte layer 17 on the mountain fold side of the negative electrode current collector foil 15 in the bent portion of the negative electrode current collector foil 15 when the battery 10 is manufactured. Although acting, the polymer electrolyte layer 17 is deformed so as to enter the negative electrode slit 18, so that the tensile stress is reduced. Battery 1
When charge and discharge of 0 are repeated, the negative electrode active material layer 16 expands and contracts due to the absorption and release of lithium ions into the negative electrode active material layer 16 to change in volume, and the negative electrode active material layer 16 expands to form a polymer electrolyte layer 17. Although the tensile stress acts, the polymer electrolyte layer 17 is deformed so as to enter the negative electrode slit 18, so that the tensile stress is reduced. Further, even if the positive electrode active material layer 13 does not exist in the bent portion of the negative electrode current collector foil 15 and the negative electrode active material layer 16 exists in this bent portion, the negative electrode active material layer 16 absorbs and releases lithium ions. Therefore, the unnecessary portion of the negative electrode active material layer 16 is removed by providing the negative electrode slit 18 in the bent portion of the negative electrode current collector foil 15. In addition, it is preferable that the negative electrode slit 18 is provided on either one or both of the mountain fold side and the valley fold side of the negative electrode current collector foil 15 among the bent portions of the negative electrode current collector foil 15.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Next, a first embodiment of the present invention will be described with reference to the drawings. As shown in FIG. 1, a lithium polymer battery 10 (lithium ion polymer secondary battery)
Is formed by folding the laminated body 20 obtained by interposing the polymer electrolyte layer 17 between the positive electrode sheet 11 and the negative electrode sheet 14 by folding a plurality of times. The positive electrode sheet 11 includes a positive electrode current collector foil 12 and a positive electrode active material layer 13 formed on the surface of the positive electrode current collector foil 12, and the negative electrode sheet 14 includes a negative electrode current collector foil 15 and the negative electrode current collector foil 15. The negative electrode active material layer 16 formed on the surface of the electric foil 15. The polymer electrolyte layer 17 is interposed between the positive electrode active material layer 13 formed on the surface of the positive electrode current collector foil 12 and the negative electrode active material layer 16 formed on the surface of the negative electrode current collector foil 15. . The negative electrode current collector foil 15 and the polymer electrolyte layer 17 are formed in a strip shape. By forming the negative electrode current collector foil 15 in a strip shape as described above, the discharge capacity can be expanded.

The negative electrode active material layer 16 is a negative electrode current collector foil 15.
It is formed on the negative electrode current collector foil 15 so as to be divided by providing the negative electrode slit 18 at the bent portion. The negative electrode slits 18 are provided on the first negative electrode slit 18a provided on the mountain fold side of the negative electrode current collector foil 15 in the folded portion of the negative electrode current collector foil 15 and on the valley fold side of the negative electrode current collector foil 15. The second negative electrode slit 18b. These slits 1
The width of 8a and 18b is 0.5 to 8 mm, preferably 1 to 5
It is set in the range of mm. The slits 18a, 18b
Is limited to 0.5 to 8 mm, the width is 0.5 m
If it is less than m, the generation of cracks in the polymer electrolyte layer 17 at the bent portion of the negative electrode current collector foil 15 cannot be sufficiently prevented, and if it exceeds 8 mm, the energy density is lowered.

On the other hand, each of the positive electrode sheets 11 is a negative electrode current collector.
A negative electrode having an area corresponding to the folded area of the body foil 15.
Of the polymer electrolyte layer 17 excluding the bent portion of the collector foil 15.
Sandwiched between each. In addition, as the negative electrode current collector foil 15
Include Cu foil, which is used as the active material of the negative electrode active material layer 16.
Examples include carbon-based active materials. Also, the positive electrode current collector foil 1
Examples of 2 include Al foil, which is an active material of the positive electrode active material layer 13.
LiCoO as quality ₂Is mentioned. Furthermore, polymer
Polyethylene oxide, polyfluoride as the degrading layer 17
Examples thereof include vinylidene.

A method of manufacturing the lithium polymer battery 10 having the above structure will be described. Preparation of Negative Electrode Sheet 14 and Formation of Polymer Electrolyte Layer 17 First, the active material contained in the negative electrode active material layer 16 is dispersed and mixed in a solution to prepare a negative electrode active material slurry. Next, this slurry is intermittently applied to the upper surface of the strip-shaped negative electrode current collector foil 15 by a doctor blade method, a screen printing method or the like and dried (FIG. 6B). At this time, one side edge 16a of the negative electrode active material layer 16 is made to coincide with one side edge 15a of the negative electrode current collector foil 15, and the other side edge 16b of the negative electrode active material layer 16 is changed to the negative electrode current collector foil 15. A plurality of negative electrode active material layers 16 are formed on the upper surface of the negative electrode current collector foil 15 at predetermined intervals (negative electrode slits 18) while being shifted inward by a predetermined distance from the other side edge 15b. As a result, the negative electrode sheet 14 is manufactured. The polymer electrolyte layer 17 is formed on the upper surface of the negative electrode sheet 14, that is, the upper surfaces of the plurality of negative electrode active material layers 16 by continuously applying an electrolyte slurry by a doctor blade method or the like and drying (FIG. 6 ( c)). The polymer electrolyte layer 17 is formed in a strip shape having an area that covers the plurality of negative electrode active material layers 16.

Preparation of Positive Electrode Sheet 11 and Formation of Polymer Electrolyte Layer 17 First, the active material contained in the positive electrode active material layer 13 is dispersed and mixed in a solution to prepare a positive electrode active material slurry. Next, this slurry is continuously applied to the upper surface of the strip-shaped positive electrode current collector foil 12 by a doctor blade method or the like and dried (FIG. 5).
(B)). At this time, one side edge 13 of the positive electrode active material layer 13
a is aligned with one side edge 12a of the positive electrode current collector foil 12,
Further, the positive electrode active material layer 13 of the positive electrode current collector foil 12 is moved in a state where the other side edge 13b of the positive electrode active material layer 13 is displaced inward by a predetermined distance from the other side edge 12b of the positive electrode current collector foil 12. It is formed like a strip on the upper surface. Next, the electrolyte slurry is continuously applied to the upper surface of the strip-shaped positive electrode active material layer 13 by a doctor blade method or the like and dried to form the polymer electrolyte layer 17 (FIG. 5C). The polymer electrolyte layer 17 is formed in a band shape having an area that covers the positive electrode active material layer 13. Further, the strip-shaped positive electrode current collector foil 12 on which the positive electrode active material layer 13 and the polymer electrolyte layer 17 are formed corresponds to the folded area of the negative electrode current collector foil 15 together with the positive electrode active material layer 13 and the polymer electrolyte layer 17. Cut to have area. As a result, a plurality of positive electrode sheets 11 having a predetermined area and having the polymer electrolyte layer 17 formed on the surface thereof are produced.

Thermocompression bonding of the negative electrode sheet 14 and the positive electrode sheet 11. First, a plurality of positive electrode sheets 11 with the polymer electrolyte layer 17 on the lower side are provided on the negative electrode sheet 14 with the strip-shaped polymer electrolyte layer 17 on the upper side. Laminated bodies 20 are produced by arranging the folded portions of the foil 15 at predetermined intervals (FIG. 4). Next, between the pair of rollers 19 and 19 which are heated to a predetermined temperature and rotate in the direction of the solid line arrow, the laminated body 20 is provided.
Is inserted from the direction indicated by the dashed arrow. As a result, the positive electrode sheet 11 and the negative electrode sheet 14 are thermocompression bonded with the polymer electrolyte layer 17 interposed. The plurality of positive electrode sheets 11 are arranged on the negative electrode sheet 14 such that the other side edge 15b of the strip-shaped negative electrode current collector foil 15 projects from one side edge 12a of the plurality of positive electrode current collector foils 12. Positive electrode current collector foil 12
The other side edge 12b is arranged so as to project from one side edge 15a of the strip-shaped negative electrode current collector foil 15.

Folding of Laminated Body 20 The above thermocompression-bonded laminated body 20 is folded by folding at the folded portion of the negative electrode current collector foil 15. That is, as shown in FIG. 3, the negative electrode current collector foil 1 on which the positive electrode sheet 11 is not disposed
Fold the folded parts of 5 alternately in zigzags. Thereby, the other side edge 15b of the strip-shaped negative electrode current collector foil 15 projects from one side edge 12a of the plurality of positive electrode current collector foils 12, and the other side edge 12b of the plurality of positive electrode current collector foils 12 is striped. The negative electrode current collector foil 15 is laminated in a state of protruding from one side edge 15a. In the laminated body 20 thus folded, a plurality of positive electrode sheets 11 having an area corresponding to the folded area are sandwiched between the polymer electrolyte layers 17 excluding the folded portion of the negative electrode current collector foil 15. In addition, from one side edge 12a of the plurality of positive electrode current collector foils 12, the negative electrode current collector foils 1
5, the protruding portion 15c which is the other side edge 15b protrudes in a zigzag bent state, and one end of the negative electrode terminal 21 is fixed to the protruding portion 15c by a fastener 22 that is fixed through the protruding portion 15c bent in a zigzag manner. Is fixed. Further, from one side edge 15a of the negative electrode current collector foil 15, the protrusions 12c which are the other side edges 12b of the plurality of positive electrode current collector foils 12 respectively protrude, and the protrusions 12c penetrate the protrusions 12c. One end of the positive electrode terminal 23 is fixed by the stopper 22 that is fixed by fixing.

Sealing of Folded Laminated Body 20 The laminated body 20 which is folded and has the negative electrode terminal 21 and the positive electrode terminal 22 has a pair of package sheets 24, 2 made of aluminum foil laminated with polypropylene.
It is sealed by 4 (FIGS. 1-3). Specifically, the laminated body 20 having the above-mentioned folded and negative electrode terminal 21 and positive electrode terminal 23 has a pair of package sheets 2 in a vacuum atmosphere.
The periphery of 4, 24 is sealed by thermocompression bonding. At this time, the other end of the positive electrode terminal 23 and the other end of the negative electrode terminal 21 are thermocompression-bonded so as to project from the pair of package sheets 24, 24 to the outside. The lithium polymer battery 10 manufactured in this way obtains desired power by using the other end of the positive electrode terminal 23 and the other end of the negative electrode terminal 21 protruding from the package sheets 24, 24 as the terminals of the battery 10. You can

In the lithium polymer battery 10 thus constructed, adjacent negative electrode active material layers 16 are divided by the negative electrode slits 18 at the bent portion of the strip-shaped negative electrode current collector foil 15, so that heat is generated. When the pressure-bonded laminated body 20 is folded, a tensile stress acts on the polymer electrolyte layer 17 having a smaller elastic coefficient than the negative electrode current collector foil 15 on the mountain fold side of the negative electrode current collector foil 15. It is reduced by deforming the electrolyte layer 17 so as to enter the negative electrode slit 18. As a result, when the battery 10 is manufactured,
That is, it is possible to prevent the generation of cracks in the polymer electrolyte layer 17 when the laminated body 20 is folded, and thus it is possible to prevent the cycle characteristics of the battery 10 from being deteriorated.

When the battery 10 is repeatedly charged and discharged, the negative electrode active material layer 16 expands and contracts due to the absorption and release of lithium ions into the negative electrode active material layer 16 to change its volume. The change in volume is absorbed by the presence of the negative electrode slit 18. Specifically, although the tensile stress acts on the polymer electrolyte layer 17 due to the expansion of the negative electrode active material layer 16, the polymer electrolyte layer 17 is deformed so as to enter the negative electrode slit 18, so that the tensile stress is reduced. . As a result, it is possible to prevent the generation of cracks in the polymer electrolyte layer 17 during charge / discharge of the battery 10, and thus it is possible to prevent deterioration of the cycle characteristics of the battery 10. Further, even if the positive electrode active material layer 13 does not exist in the bent portion of the negative electrode current collector foil 15 and the negative electrode active material layer 16 exists in this bent portion, the negative electrode active material layer 16 absorbs and releases lithium ions. Does not contribute to. Therefore, the negative electrode current collector foil 15
By providing the negative electrode slit 18 in the bent portion, unnecessary portions of the negative electrode active material layer 16 are removed. As a result, the energy density of the battery 10 can be improved.

7 and 8 show a second embodiment of the present invention. 7 and 8, the same reference numerals as those in FIGS. 1 and 4 indicate the same parts. In this embodiment, first, both surfaces of the strip-shaped negative electrode current collector foil 15 are intermittently coated with a negative electrode active material slurry by a doctor blade method, a screen printing method or the like and dried to form a plurality of negative electrode active material layers 16 respectively. Then, the negative electrode sheet 54 is formed. Then, the electrolytic slurry is continuously applied to both surfaces of the strip-shaped negative electrode current collector foil 15 by the doctor blade method so as to cover the plurality of negative electrode active material layers 16 and dried to form a pair of strip-shaped polymer electrolyte layers 1
7 and 17 are formed respectively.

On the other hand, on both sides of the strip-shaped positive electrode current collector foil 12,
The positive electrode active material slurry is continuously applied by a doctor blade method and dried to form a pair of positive electrode active material layers 13 and 13, respectively. Then, the electrolytic slurry is continuously applied to both surfaces of the strip-shaped positive electrode current collector foil 12 by the doctor blade method so as to cover the strip-shaped positive electrode active material layer 13 and dried to form a pair of strip-shaped polymer electrolyte layers 17 and 17. After each formation, the strip-shaped positive electrode current collector foil 12 is cut together with the positive electrode active material layer 13 and the polymer electrolyte layer 16 so as to have an area corresponding to the folded area of the negative electrode current collector foil 15. As a result, a plurality of positive electrode sheets 51 having a predetermined area and having the polymer electrolyte layer 17 formed on both surfaces thereof are produced.

Next, on the upper surface of the strip-shaped negative electrode sheet 54,
After arranging the plurality of positive electrode sheets 51 at a predetermined pitch and arranging the plurality of positive electrode sheets 51 at a predetermined pitch on the lower surface of the negative electrode sheet 54 at a predetermined pitch, a pair of rollers 19, By thermocompression bonding at 19, a laminate 60 is produced (FIG. 8). Further, this laminated body 60
Fold multiple times by folding. That is, the negative electrode sheet 54
After the laminated body 60 is folded so that the upper surface of the positive electrode sheet 51 located on the upper surface of one end of the positive electrode sheet 51 is adjacent to and faces the upper surface of the negative electrode sheet 54 on which the positive electrode sheet 51 is not disposed via the polymer electrolyte layer 17. The negative electrode sheet 5 located on the lower surface near one end of the negative electrode sheet 54 is adjacent to the lower surface of the negative electrode sheet 54, and the positive electrode sheet 51 is not arranged on the lower surface.
4. The laminated body 60 is folded so as to face the lower surface via the polymer electrolyte layer 17. This operation is repeated to produce the folded laminated body 60. The configuration and manufacturing method other than the above are the first
It is the same as the embodiment.

In the lithium polymer battery 50 thus constructed, the negative electrode sheets 54 and the positive electrode sheets 51 are alternately laminated, so that the energy density of the lithium polymer battery 50 can be improved. In this case, although two strip-shaped polymer electrolyte layers 17 are required, the laminate 6
When the number of folds of 0 is 3 or more, cycle characteristics can be improved.

In the first and second embodiments, the negative electrode slits are provided on both the mountain fold side and the valley fold side of the negative electrode current collector foil in the folded portion of the negative electrode current collector foil. The slit may be provided on one of the folded side of the negative electrode current collector foil and on the mountain fold side or the valley fold side of the negative electrode current collector foil. Further, in the first and second embodiments, the case where the sandwiched positive electrode sheet 11 has the polymer electrolyte layer 17 on the surface of the positive electrode active material layer 13 has been described. If the positive electrode sheet can be laminated via the polymer electrolyte layer, the polymer electrolyte layer need not be formed in advance on the surface of the positive electrode active material layer of the positive electrode sheet. Furthermore, in the first embodiment, an example (FIG. 4) in which two layers of the active material layer and the polymer electrolyte layer are provided on one surface of the positive electrode sheet and one surface of the negative electrode sheet, respectively, is shown. In the second embodiment, an example in which two layers of the active material and the polymer electrolyte layer are provided on both surfaces of the positive electrode sheet and the negative electrode sheet (FIG. 8) is shown, but the present invention is not limited to these, and the strip-shaped negative electrode sheet is also provided. 2 of negative electrode active material layer and polymer electrolyte layer on both sides of
Each layer may be provided, and two layers of a positive electrode active material layer and a polymer electrolyte layer may be provided on one surface of a plurality of positive electrode sheets,
Alternatively, two layers of a positive electrode active material layer and a polymer electrolyte layer may be respectively provided on both surfaces of a plurality of positive electrode sheets, and two layers of a negative electrode active material layer and a polymer electrolyte layer may be provided on one surface of a strip-shaped negative electrode sheet. However, the sheet having two layers of the active material layer and the polymer electrolyte layer only on one surface is preferably a strip-shaped negative electrode sheet.

[0022]

EXAMPLES Next, examples of the present invention will be described in detail together with comparative examples. Example 1 First, a plurality of positive electrode sheets 11 were produced (FIG. 5). That is, 70 g of LiCoO ₂ powder and 4 g of graphite powder (trade name; Ketjen Black) are dispersed and mixed in a N-methylpyrrolidone solution of polyvinylidene fluoride,
A positive electrode active material slurry was prepared. On the other hand, 40 g of vinylidene fluoride-hexafluoropropylene copolymer (manufactured by Elf Atchem, Kynar 2810; product containing hexafluoropropylene 12 wt%) was added to dimethyl carbonate 20.
It was dissolved in 0 g at 60 ° C., and 80 g of an electrolytic solution was further stirred and mixed to prepare an electrolyte slurry. Next, the positive electrode current collector foil 12 made of Al having a width of 10 cm and a length of 1 m is continuously coated with the positive electrode active material slurry by a doctor blade method and dried to form a positive electrode active material layer on the upper surface of the positive electrode current collector foil 12. 13 was formed, and the electrolyte slurry was continuously applied so as to cover the positive electrode active material layer 13 and dried to form a polymer electrolyte layer 17. The strip-shaped positive electrode current collector foil 12 on which the positive electrode active material layer 13 and the polymer electrolyte layer 17 are formed is used as the positive electrode active material layer 13
And with the polymer electrolyte layer 17, the width and length having the polymer electrolyte layer 17 are 10 cm and 10 c.
m positive electrode sheets 11 were obtained.

On the other hand, a strip-shaped negative electrode sheet 14 was prepared (FIG. 6). That is, a negative electrode active material slurry in which 50 g of scaly natural graphite powder is dispersed and mixed in a N-methylpyrrolidone solution of polyvinylidene fluoride on the upper surface of a negative electrode current collector foil 15 made of Cu having a width of 10 cm and a length of 1 m is prepared by a doctor. A plurality of negative electrode active material layers 16 were formed on the upper surface of the negative electrode current collector foil 15 by intermittent coating using a blade method and drying. Next, this negative electrode active material layer 1
6 is continuously applied by a doctor blade method so as to cover 6 and dried to form a polymer electrolyte layer 17, and a strip-shaped negative electrode sheet 1 having the polymer electrolyte layer 17 is formed.
4 was produced.

A plurality of positive electrode sheets 11 with the polymer electrolyte layer 17 on the lower side are placed on the negative electrode sheet 14 with the strip-shaped polymer electrolyte layer 17 on the upper side at predetermined intervals at the bent portions of the negative electrode current collector foil 15. The laminated body 20 was produced by thermocompression bonding in a state of being opened and arranged (FIG. 4). This laminate 20 was folded by folding at the folded portion of the negative electrode current collector foil 15. That is, as shown in FIG. 3, the folded portion of the negative electrode current collector foil 15 on which the positive electrode sheet 11 was not arranged was alternately bent in a zigzag manner and folded. Thus, a lithium polymer battery 10 was obtained in which ten positive electrode sheets 11 each having a width of 10 cm and a length of 10 cm were sandwiched between the polymer electrolyte layers 17 of the strip-shaped negative electrode sheet 14 having a folding area of 10 cm in width and 10 cm in length. . This battery 10 is referred to as Example 1.

Comparative Example 1 The same procedure as in Example 1 was repeated.
A positive electrode sheet was prepared. Then, the strip-shaped negative electrode sheet obtained by the same procedure as in Example 1 was cut to have a width of 10
Ten negative electrode sheets having a cm length of 10 cm were obtained. Next, the single negative electrode sheet was thermocompression-bonded to the single positive electrode sheet via the polymer electrolyte layer to prepare 10 sets of laminates. These 10 sets of laminates were further laminated to obtain a lithium polymer battery in which the opposing areas of the positive electrode sheet and the negative electrode sheet were substantially the same as in Example 1. This battery was designated as Comparative Example 1.

Comparative Example 2 A negative electrode sheet having a continuous negative electrode active material layer, that is, a negative electrode slit is not provided by continuously applying a negative electrode active material slurry on the upper surface of a negative electrode current collector foil by a doctor blade method and drying. A lithium polymer battery was obtained in the same manner as in Example 1 except that a negative electrode sheet was prepared. This secondary battery was designated as Comparative Example 2.

<Comparative Test> The cycle characteristics of the capacity retention of the lithium polymer batteries of Example 1, Comparative Example 1 and Comparative Example 2 were measured by a charge / discharge tester. The result is shown in FIG.

<Evaluation> As is clear from the results shown in FIG.
The gradient in the cycle characteristics of the lithium polymer battery in Example 1 is gentler than that in Comparative Examples 1 and 2, and the cycle characteristic of the capacity retention rate of Example 1 is the capacity retention rate of Comparative Examples 1 and 2. It was found that the cycle characteristics were improved. It is considered that this is because in Example 1, the generation of cracks in the polymer electrolyte layer in the bent portion of the negative electrode current collector foil was prevented.

[0029]

As described above, according to the present invention, the negative electrode current collector foil and the polymer electrolyte layer are folded in a continuous strip shape, and the negative electrode active material layer is formed at the bent portion of the negative electrode current collector foil. It is formed on the negative electrode current collector foil so as to be divided by providing slits, and the positive electrode sheet has an area corresponding to the folding area of the negative electrode current collector foil, and the bent portion of the negative electrode current collector foil is excluded. Since the positive electrode sheet was sandwiched between the polymer electrolyte layers, even if tensile stress acts on the polymer electrolyte layer on the mountain fold side of the negative electrode current collector foil during manufacturing of the battery, the polymer electrolyte layer may penetrate into the negative electrode slit. And the tensile stress is reduced. As a result, cracks in the polymer electrolyte layer can be prevented from occurring during the production of the battery, so that the cycle characteristics of the battery can be prevented from being deteriorated.

When the battery is repeatedly charged and discharged, the negative electrode active material layer expands and contracts due to the absorption and release of lithium ions into the negative electrode active material layer to change in volume, and the negative electrode active material layer expands to cause the polymer electrolyte layer to expand. Although the tensile stress acts on the polymer electrolyte layer, the polymer electrolyte layer is deformed so as to penetrate into the negative electrode slit, so that the tensile stress is reduced.
As a result, it is possible to prevent the generation of cracks in the polymer electrolyte layer during charge / discharge of the battery, so that it is possible to prevent deterioration of the cycle characteristics of the battery. Furthermore, the positive electrode active material layer does not exist in the bent portion of the negative electrode current collector foil, and even if the negative electrode active material layer exists in the bent portion, the negative electrode active material layer does not contribute to occlusion and release of lithium ions. By providing the negative electrode slit in the bent portion of the negative electrode current collector foil, the unnecessary portion of the negative electrode active material layer is removed. As a result, the energy density of the battery can be improved.

[Brief description of drawings]

FIG. 1 is a sectional view taken along the line AA of FIG. 2 showing a lithium polymer battery according to a first embodiment of the present invention.

FIG. 2 is a cross-sectional view taken along line BB of FIG. 1 showing the battery.

FIG. 3 is an exploded perspective view showing a state immediately before sealing the battery.

FIG. 4 is a perspective view showing a state immediately before the positive electrode sheet is thermocompression bonded to the negative electrode sheet.

FIG. 5 is a diagram showing a manufacturing process of the positive electrode sheet.

FIG. 6 is a diagram showing a manufacturing process of the negative electrode sheet.

FIG. 7 is a sectional view corresponding to FIG. 1, showing a second embodiment of the present invention.

FIG. 8 is a perspective view showing a state immediately before the positive electrode sheet is thermocompression bonded to the negative electrode sheet.

FIG. 9 is a diagram showing cycle characteristics of capacity retention of the lithium polymer batteries of Example 1 and Comparative Example 1.

[Explanation of symbols]

10,50 Lithium polymer battery 11,51 Positive electrode sheet 12 Positive electrode current collector foil 13 Positive electrode active material layer 14,54 Negative electrode sheet 15 Negative electrode current collector foil 16 Negative electrode active material layer 17 Polymer electrolyte layer 18 Negative slit 20,60 laminate

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Akio Mizuguchi             1002-14 Mukoyama, Naka-machi, Naka-gun, Ibaraki Prefecture             Terari Co., Ltd.             Inside (72) Inventor Akihiro Higami             1002-14 Mukoyama, Naka-machi, Naka-gun, Ibaraki Prefecture             Terari Co., Ltd.             Inside F term (reference) 5H029 AJ03 AJ11 AK03 AL07 AM03                       AM16 BJ04 BJ15 CJ03 CJ22                       HJ12                 5H050 AA08 AA14 BA15 CA08 CB08                       DA02 DA03 FA06 GA03 GA22                       HA12

Claims (2)

[Claims] 1. A positive electrode active material layer on the surface of the positive electrode current collector foil (12).
The positive electrode active material layer (1) of the positive electrode sheet (11) on which (13) is formed
3) and the negative electrode active material layer (16) of the negative electrode sheet (14) having the negative electrode active material layer (16) formed on the surface of the negative electrode current collector foil (15), the polymer electrolyte layer (17 ) And the positive electrode sheet (1
1) and the negative electrode sheet (14) are laminated, the laminate (20)
In a lithium polymer battery in which the negative electrode current collector foil (15) and the polymer electrolyte layer (17) are folded in a belt-like continuous state, The negative electrode active material layer (16) is respectively formed on the negative electrode current collector foil (15) so as to be divided by providing a negative electrode slit (18) at a bent portion of the negative electrode current collector foil (15), The positive electrode sheet (11) has an area corresponding to the folding area of the negative electrode current collector foil (15), and the negative electrode current collector foil.
A lithium polymer battery, which is sandwiched between the polymer electrolyte layers (17) excluding the bent portions of (15). 2. The negative electrode slit (18) is provided on either one or both of the mountain fold side and the valley fold side of the negative electrode current collector foil (15) among the bent portions of the negative electrode current collector foil (15). The lithium polymer battery according to claim 1.