JP4178269B2

JP4178269B2 - Flat battery

Info

Publication number: JP4178269B2
Application number: JP2002349489A
Authority: JP
Inventors: 宗人早見
Original assignee: Toshiba Battery Co Ltd
Current assignee: FDK Twicell Co Ltd
Priority date: 2002-12-02
Filing date: 2002-12-02
Publication date: 2008-11-12
Anticipated expiration: 2022-12-02
Also published as: JP2004185889A

Description

【０００１】
【発明の属する技術分野】
本発明は、電池ケースに改良を加えて密閉性を向上させた扁平形非水電解質二次電池に関する。
【０００２】
【従来の技術】
携帯電話やPDAなどの小型情報端末を中心に使用機器の小型化が加速しており、主電源である二次電池についても小型化を図ることが要求されている。このような状況に対応して、扁平形非水電解質二次電池においても、小型でありながら重負荷時の放電容量を大きくするために、正負極を捲回または積層して正負極対向面積を大きくしたものが発明されている（例えば、特許文献１および特許文献２参照）。
【０００３】
上記のような扁平形非水電解質二次電池において、さらに高容量化を図るためには、電池内の電極群以外の占める空間を極力少なくして、容積を有効に活用できるような形状にすることが望ましい。それには、例えば角形や小判形のような、２辺以上の直線部をもち、それぞれの直線部の接点が曲線部で結ばれているような形状がよい。
【０００４】
【特許文献１】
特開2001-068160号
【特許文献２】
特開2001-068143号
【０００５】
【発明が解決しようとする課題】
しかしながら、このような形状にした場合、次のような問題点があることがわかった。一般に扁平形電池では金属製負極ケースと金属製正極ケースとが絶縁ガスケットを介して嵌合して作製されており、その際正極ケースまたは負極ケース（以後、正極ケースの場合について説明する）の開口端部を中心に向かって折り曲げる方法をとっている。しかしながら、前記したような角形や小判形のような形状とする場合には、正極ケースの開口端部を折り曲げて縮口するときに、正極ケースの直線部から曲線部に向かう部分で肉寄せや歪が発生しやすい。この場合、直線部と曲線部を同じように曲げようとすると、正極ケースの側面部や底部にかかる力が不均一となり、正極ケースに凹みや歪みなどの変形が生じて、密閉性が低下する。これに対して、直線部の縮口率を曲線部より小さくなるように曲げようとすると、直線部での密閉性が低下する。
【０００６】
本発明はこのような問題に対処してなされたもので、例えば角形や小判形のような、２辺以上の直線部をもち、直線部と直線部とが曲線部で結ばれているような形状の扁平形電池において、密閉性を向上させることを目的としたものである。
【０００７】
【課題を解決するための手段】
すなわち本発明は、負極端子を兼ねる金属製負極ケースおよび正極端子を兼ねる金属製正極ケースがそれぞれ２辺以上の直線部をもちかつ直線部と直線部とが曲線により結ばれている形状をしているとともに、前記直線部の高さが曲線部の高さの 1.04 〜 1.11 であり、上記負極正極いずれかのケースの開口部がカシメ加工により折り曲げられ、それによって絶縁ガスケットを介して両ケースが嵌合した封口構造をしている扁平形電池において、上記カシメ加工されたケースの底面から正極負極いずれかのケースの直線部までの高さが電池総高の0.8〜1.0であり、かつ曲線部における高さの1.03〜1.14であることを特徴とする。
【０００８】
前記したように、直線部の縮口の圧力を曲線部より弱くすれば、そのケースに凹みや歪みなどの変形がなくなるが、そうすると直線部における絶縁ガスケットの締めが弱くなり、密閉性が悪くなる。それを解決するために、本発明では、カシメ加工するケースの高さ、すなわちケース底面から開口部の端部までの高さ、を直線部において曲線部より高くすることによって、縮口の弱さを補い、密閉性を維持した。
【０００９】
このケースの直線部の高さは、電池総高に対して０．８〜１．０の場合（殆どの場合この範囲に入る）、曲線部の高さに対して１．０３〜１．４４が好ましい。これよりも曲線部が低いと曲線部の縮口力が不足して封口性が低下する。逆にこれよりも曲線部が高いと直線部に凹みや歪みが生じてしまう。
【００１０】
【発明の実施の形態】
（実施例１）
図１に本実施例の電池の断面図を示す。
まず、正極合剤を作成する。LiCoO₂ 100質量部に導電剤としてアセチレンブラック５質量部、黒鉛粉末５質量部を加え、結着剤としてポリフッ化ビニリデン５質量部を加え、Ｎ―メチルピロリドンで希釈して混合し、スラリー状の正極合剤を得た。次にこの正極合剤を、正極集電体である厚さ0.02mmのアルミ箔の片面にドクターブレード法により塗工・乾燥を行い、アルミ箔表面に正極作用物質含有層２を形成した。以後、正極作用物質含有層の塗膜厚さが両面で0.15mmになるまで塗工・乾燥を繰り返し、両面塗工正極を作成した。次にこの正極体の片面の端から10mm部分の作用物質含有層を除去し、このアルミ層を剥き出しにした部分を通電部とした。このようにして幅19mm、長さ200mm、厚さ0.15mmの正極板を作成した。
【００１１】
次に、負極合剤を作成する。黒鉛化メソフェーズピッチ炭素繊維粉末100質量部に、結着剤としてスチレンブタジエンゴムとカルボキシセルロースをそれぞれ2.5質量部添加し、イオン交換水で希釈・混合し、スラリー状の負極合剤を得た。この負極合剤を、負極集電体である厚さ0.02mmの銅箔に、作用物質層の厚さが両面で0.15mmとなるまで正極の場合と同様に塗工・乾燥を繰り返して、両面塗工負極を作成した。次に、この負極体の片面の端から23mm部分の作用物質含有層４を除去し、この銅層を剥き出しにした部分を通電部とした。このようにして幅20mm、長さ220mm、厚さ0.15mmの負極板を作成した。
【００１２】
上記の正・負極板の通電部面をそれぞれ外周巻き終わり側として、正極と負極の間にセパレータ３（25μｍのポリエチレン微多孔膜）を介して渦巻き状に捲回し、捲回電極の中心部に空間がなくなるまでこの捲回電極を一定方向に加圧し、電池の扁平面に対して水平方向に正負極対向部をもつようにした。この作成した電極群を85℃で12時間乾燥した後、この電極群を、絶縁ガスケット６を一体化した金属製負極ケース５の内底面に負極通電部が接するように配置し、次に非水電解質をこれに注液した。非水電解質はエチレンカーボネートとメチルエチルカーボネートを体積比１：１で混合した溶媒に、支持塩としてLiPF₆を1mol/lの割合で溶解せしめたものである。
【００１３】
次に、上記の負極ケースに、直線部の高さ（図４参照）2.8mm、曲線部の高さ（図３参照）2.7mmの、内側をアルミニウムでクラッドされているステンレス製正極ケース（以下、「アルミクラッドステンレス製正極ケース」）１を嵌合し、上下反転した後正極ケースのカシメ加工を行った。直線部と曲線部とで高さが異なる正極ケースの斜め上から見た状態を図２に示す。図２に示すように、曲線部の開口部端部は凹状となっている。
【００１４】
これによって厚さ3.2mm、縦30mm、横30mmの角形の扁平形非水電解質二次電池を製作した。この電池でカシメにより折り曲げられた正極ケースの底面から開口端部までの高さは、直線部で2.5mm、曲線部で2.4mmとなる。
【００１５】
（実施例２）
アルミクラッドステンレス製正極ケースを、直線部の高さ2.9mm、曲線部の高さ2.7mmとし、それ以外はすべて実施例１と同様にして角形の扁平形非水電解質二次電池を製作した。この電池でカシメにより折り曲げられた正極ケースの底面から開口端部までの高さは、直線部で2.6mm、曲線部で2.4mmとなる。
【００１６】
（実施例３）
アルミクラッドステンレス製正極ケースを、直線部の高さ3.0mm、曲線部の高さ2.7mmとし、それ以外はすべて実施例１と同様にして角形の扁平形非水電解質二次電池を製作した。この電池でカシメにより折り曲げられた正極ケースの底面から開口端部までの高さは、直線部で2.8mm、曲線部で2.4mmとなる。
【００１７】
（比較例１）
アルミクラッドステンレス製正極ケースを、直線部の高さ2.7mm、曲線部の高さ2.7mmとし、それ以外はすべて実施例１と同様にして角形の扁平形非水電解質二次電池を製作した。この電池でカシメにより折り曲げられた正極ケースの底面から開口端部までの高さは、直線部で2.4mm、曲線部で2.4mmとなる。
【００１８】
（比較例２）
アルミクラッドステンレス製正極ケースを、直線部の高さ3.1mm、曲線部の高さ2.7mmとし、それ以外はすべて実施例１と同様にして角形の扁平形非水電解質二次電池を製作した。この電池でカシメにより折り曲げられた正極ケースの底面から開口端部までの高さは、直線部で2.9mm、曲線部で2.4mmとなる。
【００１９】
上記実施例１〜３および比較例１〜２の電池各100個について変形歪みを調べた後、4.2V、10mAの定電流定電圧で48時間初充電を実施し、温度60℃-湿度93%の雰囲気中３０日間貯蔵した。貯蔵後の電解液の漏液個数を調べた。結果を表１に示す。
【００２０】
【表１】

【００２１】
表１で明らかなように、比較例１の電池は正極ケースの直線部に歪みが生じ、その部分で電解液の漏出が発生した。比較例２の電池は曲線部の縮口力が不足して封口性が低下し、その部分から漏液が生じた。これに対して実施例の電池では歪み変形も漏液も生じなかった。
【００２２】
なお、上記実施例では電解液に非水溶媒を用いた扁平形非水電解質二次電池について説明したが、電解液に水溶性溶媒を用いたものでも、また充電を行わない一次電池でも、本発明は適用できる。
【００２３】
さらに、電池形状としては正極ケースのカシメ加工により封口する角形コイン状について説明したが、負極ケースをカシメ加工するものでもよく、また小判形でもよい。
【００２４】
【発明の効果】
以上説明したように、本発明によれば、例えば角形や小判形のような、電池ケースの形状が少なくとも２辺の直線部とそれらとつながる曲線部とを有する扁平形電池において、封口加工による歪みを減少させ、密封性を向上させる効果がある。
【図面の簡単な説明】
【図１】本発明の実施例１の電池の断面図。
【図２】本発明の実施例１の電池の一部を斜め上から見た図。
【図３】本発明の実施例１の電池の曲線部の断面図。
【図４】本発明の実施例１の電池の直線部の断面図。
【符号の説明】
１…正極ケース、２…正極作用物質含有層、３…セパレータ、４…負極作用物質含有層、５…負極ケース、６…絶縁ガスケット。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a flat nonaqueous electrolyte secondary battery in which the battery case is improved to improve hermeticity.
[0002]
[Prior art]
Downsizing of devices used has been accelerating mainly on small information terminals such as mobile phones and PDAs, and secondary batteries as a main power source are required to be downsized. In response to such a situation, even in a flat type non-aqueous electrolyte secondary battery, in order to increase the discharge capacity under heavy load while being small, the positive and negative electrodes are wound or stacked to increase the area facing the positive and negative electrodes. Larger ones have been invented (see, for example, Patent Document 1 and Patent Document 2).
[0003]
In the flat type nonaqueous electrolyte secondary battery as described above, in order to further increase the capacity, the space occupied by the battery other than the electrode group is reduced as much as possible so that the volume can be effectively utilized. It is desirable. For this purpose, for example, a shape such as a square shape or an oval shape having two or more straight portions and the contact points of the respective straight portions being connected by curved portions is preferable.
[0004]
[Patent Document 1]
JP 2001-068160 [Patent Document 2]
JP-A-2001-068143 [0005]
[Problems to be solved by the invention]
However, it has been found that such a shape has the following problems. In general, a flat battery is manufactured by fitting a metal negative electrode case and a metal positive electrode case through an insulating gasket. At that time, an opening of the positive electrode case or the negative electrode case (hereinafter, the case of the positive electrode case will be described). The method is to bend the end toward the center. However, in the case of a shape such as a square shape or an oval shape as described above, when the opening end of the positive electrode case is folded and shrunk, the portion of the positive electrode case facing the curved portion from the straight line portion or Distortion is likely to occur. In this case, if the straight portion and the curved portion are bent in the same manner, the force applied to the side surface portion and bottom portion of the positive electrode case becomes non-uniform, and the positive electrode case is deformed such as a dent or a distortion, thereby reducing the sealing performance. . On the other hand, if it tries to bend so that the shrinkage ratio of a linear part may become smaller than a curved part, the sealing performance in a linear part will fall.
[0006]
The present invention has been made to cope with such a problem. For example, it has two or more straight portions such as a square shape and an oval shape, and the straight portion and the straight portion are connected by a curved portion. The object is to improve the sealing performance of a flat battery having a shape.
[0007]
[Means for Solving the Problems]
That is, the present invention has a shape in which a metal negative electrode case also serving as a negative electrode terminal and a metal positive electrode case also serving as a positive electrode terminal each have two or more straight portions, and the straight portion and the straight portion are connected by a curve. In addition, the height of the straight portion is 1.04 to 1.11 of the height of the curved portion , and the opening of either case of the negative electrode or the positive electrode is bent by caulking, whereby both cases are fitted via an insulating gasket. In a flat battery having a combined sealing structure, the height from the bottom surface of the crimped case to the straight portion of either positive or negative electrode case is 0.8 to 1.0 of the total battery height, and in the curved portion The height is 1.03 to 1.14.
[0008]
As described above, if the pressure at the constriction at the straight portion is made weaker than that at the curved portion, the case will not be deformed, such as dents or distortion, but the insulation gasket at the straight portion will be weakened and the sealing performance will be poor. . In order to solve this problem, in the present invention, the height of the case to be crimped, that is, the height from the bottom of the case to the end of the opening is made higher than the curved portion in the straight portion, thereby reducing the weakness of the mouth. To maintain hermeticity.
[0009]
In this case, when the height of the straight portion is 0.8 to 1.0 with respect to the total battery height (in most cases, this range), 1.03 to 1.44 with respect to the height of the curved portion. Is preferred. If the curved portion is lower than this, the curving force of the curved portion is insufficient and the sealing performance is lowered. On the other hand, if the curved portion is higher than this, a dent or distortion occurs in the straight portion.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
(Example 1)
FIG. 1 shows a cross-sectional view of the battery of this example.
First, a positive electrode mixture is prepared. Add 5 parts by mass of acetylene black and 5 parts by mass of graphite powder as a conductive agent to 100 parts by mass of LiCoO ₂ , add 5 parts by mass of polyvinylidene fluoride as a binder, dilute and mix with N-methylpyrrolidone, A positive electrode mixture was obtained. Next, this positive electrode mixture was coated and dried on one side of a 0.02 mm thick aluminum foil as a positive electrode current collector by a doctor blade method to form a positive electrode active substance-containing layer 2 on the aluminum foil surface. Thereafter, coating and drying were repeated until the coating film thickness of the positive electrode active material-containing layer became 0.15 mm on both sides, to prepare a double-sided coated positive electrode. Next, the active substance-containing layer of 10 mm from the edge of one side of the positive electrode was removed, and the portion where the aluminum layer was exposed was used as a current-carrying portion. In this way, a positive electrode plate having a width of 19 mm, a length of 200 mm, and a thickness of 0.15 mm was produced.
[0011]
Next, a negative electrode mixture is prepared. 2.5 parts by mass of styrene butadiene rubber and carboxycellulose as binders were added to 100 parts by mass of graphitized mesophase pitch carbon fiber powder, and diluted and mixed with ion-exchanged water to obtain a slurry-like negative electrode mixture. This negative electrode mixture was applied to a 0.02 mm thick copper foil as a negative electrode current collector, and coating and drying were repeated as in the case of the positive electrode until the active material layer thickness was 0.15 mm on both sides. A coated negative electrode was prepared. Next, the active substance-containing layer 4 in a 23 mm portion was removed from one end of the negative electrode body, and the portion where the copper layer was exposed was used as an energizing portion. In this way, a negative electrode plate having a width of 20 mm, a length of 220 mm, and a thickness of 0.15 mm was prepared.
[0012]
With the current-carrying surface of the positive and negative electrode plates as the outer winding end side, the coil is wound spirally between the positive electrode and the negative electrode via the separator 3 (25 μm polyethylene microporous film), The wound electrode was pressed in a certain direction until there was no space, and had a positive and negative electrode facing portion in the horizontal direction with respect to the flat surface of the battery. After the created electrode group was dried at 85 ° C. for 12 hours, this electrode group was placed so that the negative electrode energizing portion was in contact with the inner bottom surface of the metal negative electrode case 5 integrated with the insulating gasket 6, and then non-aqueous Electrolyte was poured into this. The non-aqueous electrolyte is obtained by dissolving LiPF ₆ as a supporting salt at a rate of 1 mol / l in a solvent in which ethylene carbonate and methyl ethyl carbonate are mixed at a volume ratio of 1: 1.
[0013]
Next, the above-mentioned negative electrode case is made of a stainless steel positive electrode case (hereinafter referred to as 2.8 mm) having a straight portion height (see FIG. 4) of 2.8 mm and a curved portion height (see FIG. 3) of 2.7 mm. The “aluminum-clad stainless steel positive electrode case”) 1 was fitted and turned upside down, and then the positive electrode case was crimped. FIG. 2 shows a state in which the positive electrode case having different heights in the straight line portion and the curved portion is viewed from above. As shown in FIG. 2, the end of the opening of the curved portion is concave.
[0014]
As a result, a rectangular flat nonaqueous electrolyte secondary battery having a thickness of 3.2 mm, a length of 30 mm, and a width of 30 mm was manufactured. The height from the bottom surface of the positive electrode case bent by caulking in this battery to the open end is 2.5 mm at the straight portion and 2.4 mm at the curved portion.
[0015]
(Example 2)
A square flat nonaqueous electrolyte secondary battery was manufactured in the same manner as in Example 1 except that the aluminum-clad stainless steel positive electrode case had a straight portion height of 2.9 mm and a curved portion height of 2.7 mm. The height from the bottom surface of the positive electrode case bent by caulking in this battery to the open end is 2.6 mm at the straight portion and 2.4 mm at the curved portion.
[0016]
(Example 3)
A square flat nonaqueous electrolyte secondary battery was manufactured in the same manner as in Example 1 except that the aluminum-clad stainless steel positive electrode case had a straight portion height of 3.0 mm and a curved portion height of 2.7 mm. The height from the bottom surface of the positive electrode case bent by caulking in this battery to the open end is 2.8 mm at the straight portion and 2.4 mm at the curved portion.
[0017]
(Comparative Example 1)
A square flat nonaqueous electrolyte secondary battery was manufactured in the same manner as in Example 1 except that the aluminum-clad stainless steel positive electrode case had a straight portion height of 2.7 mm and a curved portion height of 2.7 mm. The height from the bottom surface of the positive electrode case bent by caulking in this battery to the open end is 2.4 mm at the straight portion and 2.4 mm at the curved portion.
[0018]
(Comparative Example 2)
A square flat nonaqueous electrolyte secondary battery was manufactured in the same manner as in Example 1 except that the aluminum-clad stainless steel positive electrode case had a straight portion height of 3.1 mm and a curved portion height of 2.7 mm. The height from the bottom surface of the positive electrode case bent by caulking in this battery to the open end is 2.9 mm at the straight portion and 2.4 mm at the curved portion.
[0019]
After examining the deformation strain for each of the batteries of Examples 1 to 3 and Comparative Examples 1 and 2, the initial charge was performed for 48 hours at a constant current and a constant voltage of 4.2 V, 10 mA, and the temperature was 60 ° C. and the humidity was 93%. For 30 days. The number of electrolyte leaks after storage was examined. The results are shown in Table 1.
[0020]
[Table 1]

[0021]
As is clear from Table 1, the battery of Comparative Example 1 was distorted at the straight portion of the positive electrode case, and electrolyte leakage occurred at that portion. In the battery of Comparative Example 2, the curving force at the curved portion was insufficient, the sealing performance was lowered, and liquid leakage occurred from that portion. On the other hand, neither distortion nor leakage occurred in the battery of the example.
[0022]
In the above embodiment, a flat non-aqueous electrolyte secondary battery using a non-aqueous solvent as an electrolytic solution has been described. However, even a battery using a water-soluble solvent as an electrolytic solution or a primary battery that does not perform charging may be used. The invention is applicable.
[0023]
Furthermore, as the battery shape, a rectangular coin shape that is sealed by caulking of the positive electrode case has been described, but the negative electrode case may be caulked and may be oval.
[0024]
【The invention's effect】
As described above, according to the present invention, in a flat battery in which the shape of the battery case has, for example, a square part or an oval shape, the straight part having at least two sides and a curved part connected thereto, distortion caused by sealing processing Is effective in improving the sealing performance.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a battery according to Example 1 of the present invention.
FIG. 2 is a view of a part of the battery of Example 1 of the present invention as viewed obliquely from above.
FIG. 3 is a cross-sectional view of a curved portion of the battery of Example 1 of the present invention.
FIG. 4 is a cross-sectional view of a straight portion of the battery according to Example 1 of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Positive electrode case, 2 ... Positive electrode active material content layer, 3 ... Separator, 4 ... Negative electrode active material content layer, 5 ... Negative electrode case, 6 ... Insulation gasket.

Claims

The metal negative electrode case that also serves as the negative electrode terminal and the metal positive electrode case that also serves as the positive electrode terminal each have a shape in which the straight part has two or more sides and the straight part and the straight part are connected by a curve, and the straight line The height of the part is 1.04 to 1.11 of the height of the curved part , and the opening part of one of the negative electrode and the positive electrode is bent by caulking so that both cases are fitted via an insulating gasket. In the flat battery
The height from the bottom surface of the caulked case to the straight portion of either positive or negative electrode case is 0.8 to 1.0 of the total battery height and 1.03 to 1.14 of the height in the curved portion. Flat battery.

The flat battery according to claim 1, wherein the end of the opening of any case of the positive electrode and the negative electrode to be crimped has a concave shape at the curved portion.

The flat battery according to claim 1, wherein the flat battery is a flat nonaqueous electrolyte secondary battery, and the positive electrode case is crimped.