JP2004014290A

JP2004014290A - Flat battery

Info

Publication number: JP2004014290A
Application number: JP2002165861A
Authority: JP
Inventors: Yuichi Kikuma; 菊間　祐一; Takashi Kato; 加藤　隆; Masami Suzuki; 鈴木　正美; Munehito Hayami; 早見　宗人
Original assignee: Toshiba Battery Co Ltd
Current assignee: FDK Twicell Co Ltd
Priority date: 2002-06-06
Filing date: 2002-06-06
Publication date: 2004-01-15
Anticipated expiration: 2022-06-06
Also published as: JP4035710B2

Abstract

<P>PROBLEM TO BE SOLVED: To provide a flat square-type battery in which a sealing property is improved by preventing movement of a side wall part of an encapsulating case caulked by a caulking process in sealing, and its bottom flat part from having strained deformation. <P>SOLUTION: In the flat square-type battery in which both a metal sheathing case and a metal inner package case are fitted via an insulation gasket, and the encapsulating case has at least two or more peripheral linear parts at the periphery of sealing structure caulked by caulking process, and the edge of each peripheral linear part is connected by the peripheral curved part of nearly circular shape, the encapsulating case is provided with an inner and an outer bottom faces having flat faces, and the side wall part extended from the periphery of the bottom in vertical upper direction is provided with the inner side face and the outer side face, each of which is connected by the inner and the outer bottom faces respectively and the bottom curved part of arc shape. Furthermore, an outer face radius R1 of the bottom curved part corresponding to the peripheral curved part and that of an outer face radius R2 corresponding to the peripheral linear part satisfy the relationship of R1 < R2. Thus, the sidewall material of the encapsulating case when caulking sealing is prevented from moving, and also the distortion deformation of the bottom flat part is prevented, thereby the sealing is improved. <P>COPYRIGHT: (C)2004,JPO

Description

【０００１】
【発明の属する技術分野】
本発明は扁平角形電池に係わり、特に底部平坦面の変形を防止し、かつ密閉性を向上させる扁平角形電池に関する。
【０００２】
【従来の技術】
近年、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されており、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。このような要求に対し、特願平１１−２４０９６４号や特願平１１−２４１２９０号に示すように、負極端子を兼ねる金属製の負極ケースと、正極端子を兼ねる金属製の正極ケースが絶縁ガスケットを介し嵌合され、さらに前記正極ケースまたは負極ケースが加締め加工により加締められた封口構造を有し、その内部に少なくとも正極、セパレータ、負極を含む発電要素と、非水電解質を内包した扁平形非水電解質二次電池において、扁平形電池の扁平面に垂直な方向の断面を見た場合に、少なくとも３面以上の正極と負極がセパレータを介し対向している正負極対向面を有する電極群が収納され、かつ、この電極群内の正負極対向面積の総和が絶縁ガスケットの開口面積よりも大きくした扁平形非水電解質二次電池が小型化の要求を満たす電池として提案されている。
【０００３】
さらに、近年では、液晶をはじめとした表示装置を有する小型機器は、薄型化を進める一方、表示装置の小型化には実使用上限度があるため、機器全体に占める表示装置の占有面積比率を極力大きくして、機器全体を小型化することが検討されている。この表示装置の多くは角形状を有していることから、この形状に機器を合わせるため機器全体が角形状を有するものが多くなっており、機器内での電池の搭載には扁平角形電池が望まれている。
【０００４】
また、前述した対向面積を拡大した電極群を実現する方法として、生産性、経済性の面から薄肉電極をセパレータを介して捲回し、さらにこれを押しつぶすことで扁平形の電極群を得る方法が多く採用されている。この場合、得られる電極群は扁平角形状となり、この電極群を内包し、さらに高容量化を実現するためには、周縁部に少なくとも２つ以上の直線部を有し、各直線部の端部が略円弧状曲線部により結ばれている角形や小判形に代表される扁平角形電池を形成する必要がある。
【０００５】
しかしながら、このような角形状を有する金属製の外装ケースと内装ケースが絶縁ガスケットを介し嵌合され、さらに外装ケースを加締め加工により封口部を形成する場合、周縁曲線部に対応する側壁部および底面曲線部の外面半径Ｒ１部は強度が高く、底面下方向への加締め圧力はその周辺部へ分散するためケース側壁部の材料の底面平坦部内方向への移動は抑えられる。しかし、周縁直線部に対応する側壁部および底面曲線部の外面半径Ｒ２部は強度が低く、前記加締め圧力は底面垂直方向に集中し、ケース側壁部の材料が底面平坦部内方向に移動してしまうことにより、部分的な材料余りにより平坦部に歪みを生じていた。さらにこのような材料の移動により加締め部の開口端までの高さが低くなることで、所定の加締め寸法を得ることができなくなり、封口性が低下するなどの課題があった。
【０００６】
【発明が解決しようとする課題】
本発明は、上記状況に鑑みてなされたもので、その課題は加締め加工により加締められた封口時の外装ケース側壁部の移動を防止し、かつ底面平坦部の歪み変形を防止することで、封口性を向上した扁平角形電池を提供することである。
【０００７】
【課題を解決するための手段】
本発明者等は鋭意研究を重ねた結果、下記に述べるような結論に到達した。　金属製の外装ケースと金属製の内装ケースが、絶縁ガスケットを介し嵌合され、さらに外周側に配置された前記外装ケースが加締め加工により加締められた封口構造の周縁部に少なくとも２つ以上の直線部（以後、周縁直線部Ｂとする）を有し、各直線部の端部が略円弧状曲線部（以後、周縁曲線部Ａとする）により結ばれている扁平角形電池において、前記外装ケースは平坦面を有する内底面と外底面を有し、該底面周縁部より垂直上方向に延伸した側壁面は内側面と外側面を有するとともにそれぞれ該内底面および該外底面と、円弧状の底面曲線部で結ばれており、周縁曲線部Ａに対応する底面曲線部の外面半径Ｒ１と周縁直線部Ｂに対応する底面曲線部の外面半径Ｒ２を、Ｒ１＜Ｒ２の関係とすることで、加締め封口時の外装ケース側壁部材料の移動を防止し、底面平坦部の変形を抑え、封口性を向上できることを見出した。
【０００８】
すなわち、外装ケース開口端上方より加締め型を押さえ付けることで加締めによる封口部を形成するが、この際の加締め圧力は外装ケースの開口端を加締め型に沿って内方向へ折り曲げるとともに、その反力として外装ケースの側壁部を底面方向に押し下げる力を生じる。更には、加締め型と側壁部の摩擦力も同様に底面方向への力を生じさせる。
【０００９】
電池形状がコイン型のように周縁部の強度が全て均一であれば、底面方向へ生じた圧力はケース側壁部を均一に押し下げることから、底面平坦部へケース側壁部の材料の移動も均一となり、部分的な材料余りが生じることなく、底部平坦部の変形を押さえることが可能である。しかし、電池形状が角形のように周縁部の強度が均一でない場合、強度の高い部分の周囲への分散圧力も合わせて強度の低い部分に集中し、底部平坦面へのケース側壁部材料の移動も不均一となる。そのため材料余りによる底部平坦面の変形を生じるとともに、ケースの加締め寸法が一定でなくなり、封口性が低下してしまう。すなわち、角形電池の周縁曲線部Ａは周縁直線部Ｂより強度が高いことから、加締め圧力による材料の移動は周縁直線部Ｂに集中し、底面平坦部での材料余りによる変形が生じてしまうことになる。
【００１０】
本発明によれば、扁平角形電池において、周縁曲線部Ａに対応する前記外面半径Ｒ１と周縁直線部Ｂに対応する前記外面半径Ｒ２の関係を、Ｒ１＜Ｒ２とすることで、底面方向に生じた加締め圧力による側壁部材料の移動を均一化するようにし、コイン型と同様に底部平坦面の変形を生じることなく、所定の加締め寸法とすることが可能となり、封口性も良好となる。
【００１１】
さらに好ましくは、Ｒ２／Ｒ１が１．１以上であり、前記外装ケースを構成する部材の板厚ｔに対する前記外面半径Ｒ１およびＲ２の比が１以上３以下とすることで、封口部形状の安定化による封口性向上が期待できる。ここで、板厚ｔに対するＲ１、Ｒ２の比が１よりも小さい場合、加締め圧力は側壁部下方向のみとなり、加締め後の電池周縁部にバリが発生する場合がある。また、逆に３以上となった場合は、Ｒ２／Ｒ１が１．１以上であってもＲ１部およびＲ２部の変形が大きく、所定の加締め寸法を得ることができず、封口性が保てなくなる。
【００１２】
ここで、本発明は扁平角形電池の封口構造について、詳しくは外装ケースの形状を改良し、底面平坦部の歪み変形を防止するとともに、封口性を向上することに主点をおいたものであり、前述の電極構造および電極構成については限定されるものではなく、電極構造については、前述した捲回方式だけでなく、積層方式、ペレット方式等、あるいは従来の構造を採用した場合でも本発明と同様の効果が期待できる。
また、耐食性の向上を目的にステンレスからなる正極ケース内面にアルミもしくはアルミ合金層を配してもよい。この場合、正極ケースの強度が低下することから、加締め圧力による材料の移動により電池底面平坦部の変形や電池周縁部のバリが発生し易くなるが、本発明の範囲とすることで所定の加締め寸法を得ることができ、良好な封口性を確保できる。
【００１３】
【発明の実施の形態】
以下、本発明の実施例及び比較例について、リチウム二次電池に採用した場合を例に説明する。
（実施例１）
本実施例１の扁平角形電池の断面図を図１、その平面図を図２に示す。すなわち、図に示すように、本実施例１の扁平角形電池は内面に金属ネット８が溶接された外装ケース４内に、ポリエチレン微多孔膜からなるセパレータ３を介して正極作用物質層１と負極作用物質２を渦巻状に捲回した電極群の正極作用物質層１が金属ネット８に接するように収納し、一方内面に金属ネット７が溶接された内装ケースの金属ネット７が電極群の負極作用物質層２に接するように収納し、さらに内装ケース６と外装ケース４の周辺の間に絶縁ガスケット５を介して、加締め加工により液密に封口されている。
【００１４】
以下、本実施例１の扁平角形リチウム二次電池の製造方法を説明する。
まず、ＬｉＣｏＯ_２１００質量部に対し導電材としてアセチレンブラック５質量部と黒鉛粉末５質量部を加え、結着剤としてポリフッ化ビニリデンを５質量部加え、Ｎ‐メチルピロリドンで希釈、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１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となるまで塗工、乾燥を繰り返し、両面塗工正極を作製した。次に、この電極体の片面の端から１０ｍｍ部分の作用物質含有層を除去し、アルミ層を剥き出し通電部とし、幅１９ｍｍ、長さ２００ｍｍ、厚さ０．１５ｍｍの長さに切り出した正極板を作製した。
【００１５】
次に、正負極通電部面を外周巻き終わり側とし、これら正極と負極の間に厚さ２５μｍのポリエチレン微多孔膜からなるセパレータ３を介し渦巻状に捲回し、扁平形電池の扁平面に対し水平方向に正負極対向部をもつように一定方向に捲回電極の中心部の空間がなくなるまで加圧した。
【００１６】
作製した電極群を８５℃で１２ｈ乾燥した後、ステンレス製の金属ネット７を内面に溶接し、絶縁ガスケット５と一体化した内装ケース（負極金属ケース）６の内底面に電極群の片面塗工負極板２の未塗工側が金属ネット７に接するように配置し、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の割合で混合した溶媒に支持塩としてＬｉＰＦ_６を１ｍｏｌ／ｌの割合で溶解せしめた非水電解質を注液し、さらに電極群の片面塗工正極板１の未塗工側に接するようにステンレス製の金属ネット８が内面に溶接された板厚０．２５ｍｍのステンレスからなる外装ケース（正極ケース）４を嵌合し、上下反転後、正極ケース４に加締め加工を実施し、封口し、厚さ３．２ｍｍ、縦３０ｍｍ、横３０ｍｍの実施例１の扁平角形非水電解質二次電池を製作した。この際の外装ケースのＲ１、Ｒ２および板厚ｔはそれぞれ０．５０ｍｍ、０．５５ｍｍ、０．２５ｍｍとし、加締め後の電池底面部から側壁部開口端高さｈは２．５ｍｍとした。
【００１７】
（実施例２）
外装ケースＲ１、Ｒ２および板厚ｔはそれぞれ０．２５ｍｍ、０．２８ｍｍ、０．２５ｍｍとしたこと以外は実施例１と同様に電池を作製した。
【００１８】
（実施例３）
外装ケースＲ１、Ｒ２および板厚ｔはそれぞれ０．６８ｍｍ、０．７５ｍｍ、０．２５ｍｍとしたこと以外は実施例１と同様に電池を作製した。
【００１９】
（比較例１）
外装ケースＲ１、Ｒ２および板厚ｔはそれぞれ０．５０ｍｍ、０．５０ｍｍ、０．２５ｍｍとしたこと以外は実施例１と同様に電池を作製した。
【００２０】
（比較例２）
外装ケースＲ１、Ｒ２および板厚ｔはそれぞれ０．２０ｍｍ、０．２２ｍｍ、０．２５ｍｍとしたこと以外は実施例１と同様に電池を作製した。
【００２１】
（比較例３）
外装ケースＲ１、Ｒ２および板厚ｔはそれぞれ０．７０ｍｍ、０．８０ｍｍ、０．２５ｍｍとしたこと以外は実施例１と同様に電池を作製した。
【００２２】
上述したようにして作製した本実施例及び比較例の電池３００個について、底面バリの発生および底部平坦面の変形／歪の発生を観察した。また、これらの電池において４．２Ｖ、１０ｍＡの定電流定電圧で４８ｈ初充電を実施し、３日間室温で放置後、６０℃‐９３％ＲＨの雰囲気下で３０日間貯蔵し、電解液の漏液について確認した。
【００２３】
外面半径Ｒ１およびＲ２、Ｒ２／Ｒ１、板厚ｔ、Ｒ１／ｔ、Ｒ２／ｔを表１に、更に底面周縁部バリ発生数、底部平坦面変形発生数、貯蔵後漏液発生数を表２に示した。
【００２４】
【表１】

【００２５】
【表２】

【００２６】
上記表１，２より明らかなように、本実施例の電池は加締め加工の際の底面方向に生じる加締め圧力による側壁部材料の移動が、電池周縁部全体で均一化するため、底部平坦面の変形を生じることなく、封口性も良好となった。また、比較例２では、図４に示すようにＲ１、Ｒ２ともに、外装ケース材料板厚ｔより小さくしていることから、加締め時の側壁部下方向への圧力により周縁部バリ９が発生した。比較例３では、Ｒ２／ｔが３．０を超えており、平坦面の変形は発生していないが、Ｒ２部が変形しており加締めが不充分となり漏液が発生した。
【００２７】
なお、本発明の実施例は、非水電解質に非水溶媒を用いた扁平形非水溶媒二次電池を用いて、正極ケースを外装ケースとした場合の加締め加工により封口する扁平角形電池について説明したが、正負極電極を入れ替え、外装ケースとして負極ケースを配置することも可能であり、また、他の電池系への適用も可能であって、要は扁平角形の加締め封口の電池に適用しても本発明と同様の効果が得られる。
【００２８】
【発明の効果】
以上説明したとおり、本発明によれば、加締め封口時の外装ケース側壁部材料の移動を防止し、底面平坦部の歪み変形を防止するとともに、封口性を向上した工業的価値の非常に大きな扁平角形電池を提供することができる。
【図面の簡単な説明】
【図１】本実施例１の電池の断面図。
【図２】本実施例１の電池の平面図。
【図３】本実施例１の電池の封口部の断面図。
【図４】比較例２の電池の周縁部バリ発生を示す概略図。
【符号の説明】
１…正極作用物質含有層（塗工電極）、２…負極作用物質含有層（塗工電極）、３…セパレータ、４…外装ケース（正極ケース）、５…絶縁ガスケット、６…内装ケース（負極ケース）、７…金属ネット（負極側）、８…金属ネット（正極側）、９…周縁部バリ、Ａ…周縁曲線部、Ｂ…周縁直線部、Ｒ１…周縁曲線部に対応した外装ケース底面曲線部の外面半径、Ｒ２…周縁直線部に対応した外装ケース底面曲線部の外面半径。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a flat prismatic battery, and more particularly, to a flat prismatic battery that prevents deformation of a flat bottom surface and improves sealing performance.
[0002]
[Prior art]
In recent years, the miniaturization of devices used has been accelerated, especially for small information terminals such as mobile phones and PDAs, and there is a demand for miniaturization of secondary batteries as main power supplies. In response to such demands, as shown in Japanese Patent Application Nos. 11-240964 and 11-241290, 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 are provided with an insulating gasket. The positive electrode case or the negative electrode case has a sealing structure in which the positive electrode case or the negative electrode case is caulked by caulking, and a power generating element including at least the positive electrode, the separator, and the negative electrode therein, and a flat body including a nonaqueous electrolyte. In a non-aqueous electrolyte secondary battery, an electrode having a positive / negative electrode facing surface in which at least three or more positive electrodes and a negative electrode face each other with a separator therebetween when a cross section in a direction perpendicular to the flat surface of the flat battery is viewed. A flat non-aqueous electrolyte secondary battery in which a group is housed and the sum of the positive and negative electrode facing areas in this electrode group is larger than the opening area of the insulating gasket satisfies the demand for miniaturization It has been proposed as a pond.
[0003]
Furthermore, in recent years, small devices having a display device such as a liquid crystal device have been reduced in thickness, while the miniaturization of the display device has an upper limit of actual use. It is being studied to reduce the size of the entire device by making it as large as possible. Since many of these display devices have a square shape, many devices have a square shape in order to fit the device to this shape, and a flat prismatic battery is used for mounting a battery in the device. Is desired.
[0004]
Further, as a method of realizing an electrode group having an enlarged facing area as described above, a method of winding a thin electrode through a separator from the viewpoint of productivity and economy and obtaining a flat electrode group by further crushing the thin electrode is known. Many are adopted. In this case, the obtained electrode group has a flattened rectangular shape, and in order to include the electrode group and realize a higher capacity, at least two or more linear portions are provided on the peripheral portion, and the end of each linear portion is provided. It is necessary to form a flat rectangular battery typified by a rectangular shape or an oval shape whose parts are connected by a substantially arc-shaped curved portion.
[0005]
However, when the metal outer case and the inner case having such a square shape are fitted via an insulating gasket, and further forming a sealing portion by caulking the outer case, a side wall corresponding to the peripheral curved portion and The outer radius R1 portion of the bottom curved portion has high strength, and the crimping pressure downward in the bottom surface is dispersed to its peripheral portion, so that the material of the case side wall portion is prevented from moving inward in the flat bottom portion. However, the outer radius R2 of the side wall portion and the bottom curved portion corresponding to the peripheral straight portion has low strength, the caulking pressure is concentrated in the vertical direction of the bottom surface, and the material of the case side wall portion moves inward in the bottom flat portion. As a result, the flat portion is distorted due to partial material surplus. Further, such a movement of the material lowers the height of the caulked portion to the opening end, so that a predetermined caulked dimension cannot be obtained, and there is a problem that the sealing property is reduced.
[0006]
[Problems to be solved by the invention]
The present invention has been made in view of the above circumstances, and an object of the present invention is to prevent movement of an outer case side wall portion at the time of sealing by caulking, and to prevent distortion deformation of a flat bottom portion. Another object of the present invention is to provide a flat battery having improved sealing properties.
[0007]
[Means for Solving the Problems]
As a result of intensive studies, the present inventors have reached the following conclusions. A metal outer case and a metal inner case are fitted via an insulating gasket, and at least two or more are provided on the peripheral edge of the sealing structure in which the outer case disposed on the outer peripheral side is crimped by crimping. (Hereinafter referred to as a peripheral straight line portion B), and the ends of each linear portion are connected by a substantially arc-shaped curved portion (hereinafter referred to as a peripheral curved portion A). The outer case has an inner bottom surface and an outer bottom surface having a flat surface, and a side wall surface extending vertically upward from the peripheral edge of the bottom surface has an inner side surface and an outer side surface, and the inner bottom surface and the outer bottom surface respectively have an arc shape. The outer surface radius R1 of the bottom curved portion corresponding to the peripheral curved portion A and the outer surface radius R2 of the bottom curved portion corresponding to the peripheral straight portion B are defined by a relationship of R1 <R2. , External case side when caulking To prevent movement of the member fees, suppress deformation of the bottom flat portion, it was found to be improved sealing properties.
[0008]
In other words, the sealing portion is formed by crimping by pressing the crimping die from above the outer case opening end, and the crimping pressure at this time is such that the opening end of the outer case is bent inward along the crimping die. As a reaction force, a force is generated to push down the side wall of the outer case in the bottom direction. Furthermore, the frictional force between the crimping die and the side wall also causes a force in the bottom direction.
[0009]
If the battery has a uniform shape like a coin, the pressure generated in the bottom direction uniformly pushes down the case side wall, so that the material on the case side wall moves evenly to the flat bottom. In addition, it is possible to suppress the deformation of the bottom flat portion without generating any excess material. However, when the strength of the peripheral portion is not uniform, such as a rectangular battery, the dispersion pressure around the high strength portion is also concentrated on the low strength portion, and the material of the case side wall material moves to the flat bottom surface. Also becomes non-uniform. For this reason, the bottom flat surface is deformed due to the excess material, and the caulking dimension of the case is not constant, so that the sealing performance is reduced. That is, since the peripheral curved portion A of the prismatic battery has higher strength than the peripheral linear portion B, the movement of the material due to the caulking pressure is concentrated on the peripheral linear portion B, and the deformation due to the excess material in the flat bottom portion occurs. Will be.
[0010]
According to the present invention, in the flat prismatic battery, the relationship between the outer surface radius R1 corresponding to the peripheral curved portion A and the outer surface radius R2 corresponding to the peripheral linear portion B is defined as R1 <R2, thereby causing the relationship in the bottom direction. The uniform movement of the side wall material due to the caulking pressure is achieved, and a predetermined caulking dimension can be obtained without deformation of the bottom flat surface like a coin type, and the sealing property is also improved. .
[0011]
More preferably, R2 / R1 is 1.1 or more, and the ratio of the outer surface radii R1 and R2 to the plate thickness t of the member constituting the outer case is 1 or more and 3 or less, so that the shape of the sealing portion is stabilized. It can be expected that the sealing property will be improved by the conversion. Here, when the ratio of R1 and R2 to the plate thickness t is smaller than 1, the caulking pressure is only in the downward direction of the side wall portion, and burrs may be generated at the periphery of the battery after caulking. On the other hand, when the ratio is 3 or more, even if R2 / R1 is 1.1 or more, the deformation of the R1 portion and the R2 portion is large, a predetermined caulking dimension cannot be obtained, and the sealing property is maintained. Lost.
[0012]
Here, the present invention is mainly concerned with the sealing structure of a flat prismatic battery, in which the shape of the outer case is improved, the distortion of the flat bottom portion is prevented, and the sealing property is improved. The electrode structure and the electrode configuration described above are not limited, and the electrode structure is not limited to the above-described winding method, but may be a laminate method, a pellet method, or a conventional structure. Similar effects can be expected.
An aluminum or aluminum alloy layer may be provided on the inner surface of the positive electrode case made of stainless steel for the purpose of improving corrosion resistance. In this case, since the strength of the positive electrode case is reduced, deformation of the flat portion of the battery bottom surface and burrs on the peripheral portion of the battery are likely to occur due to the movement of the material due to the crimping pressure. A caulking dimension can be obtained, and a good sealing property can be secured.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, Examples and Comparative Examples of the present invention will be described by taking as an example a case where the invention is applied to a lithium secondary battery.
(Example 1)
FIG. 1 is a cross-sectional view of the flat prismatic battery according to the first embodiment, and FIG. 2 is a plan view thereof. That is, as shown in the figure, the flat prismatic battery of Example 1 has the positive electrode active material layer 1 and the negative electrode in the outer case 4 in which the metal net 8 is welded to the inner surface via the separator 3 made of a polyethylene microporous film. The positive electrode active material layer 1 of the electrode group in which the active substance 2 is spirally wound is housed so as to be in contact with the metal net 8, and the metal net 7 of the interior case in which the metal net 7 is welded to the inner surface is the negative electrode of the electrode group. It is housed so as to be in contact with the active substance layer 2, and furthermore, it is liquid-tightly sealed by caulking between the inner case 6 and the outer case 4 via an insulating gasket 5.
[0014]
Hereinafter, a method for manufacturing the flat rectangular lithium secondary battery of the first embodiment will be described.
First, to 100 parts by mass of LiCoO ₂ , 5 parts by mass of acetylene black and 5 parts by mass of graphite powder were added as conductive materials, 5 parts by mass of polyvinylidene fluoride was added as a binder, and the mixture was diluted and mixed with N-methylpyrrolidone. A positive electrode mixture was obtained. Next, this positive electrode mixture was applied to one surface of a 0.02 mm thick aluminum foil serving as a positive electrode current collector by a doctor blade method and dried to form a positive electrode active substance-containing layer 1 on the aluminum foil surface. . Thereafter, coating and drying were repeated until the coating thickness of the positive electrode active substance-containing layer reached 0.15 mm on both sides, to produce a double-side coated positive electrode. Next, the positive electrode plate cut out to a length of 19 mm, a length of 200 mm, and a thickness of 0.15 mm was removed by removing the active material-containing layer of 10 mm from the end of one side of the electrode body, exposing the aluminum layer to serve as a current-carrying part. Was prepared.
[0015]
Next, the current-carrying surface of the positive and negative electrodes is set to the outer peripheral winding end side, and spirally wound between the positive electrode and the negative electrode with a separator 3 made of a 25 μm-thick polyethylene microporous film interposed therebetween, with respect to the flat surface of the flat battery. Pressure was applied in a certain direction until the space at the center of the wound electrode was exhausted so that the positive and negative electrode facing portions were provided in the horizontal direction.
[0016]
After drying the produced electrode group at 85 ° C. for 12 hours, a metal net 7 made of stainless steel is welded to the inner surface, and one side of the electrode group is coated on the inner bottom surface of an interior case (negative metal case) 6 integrated with the insulating gasket 5. LiPF ₆ was dissolved at a rate of 1 mol / l as a supporting salt in a solvent in which the uncoated side of the negative electrode plate 2 was in contact with the metal net 7 and ethylene carbonate and methyl ethyl carbonate were mixed at a volume ratio of 1: 1. The immersed non-aqueous electrolyte is injected, and a metal net 8 made of stainless steel is welded to the inner surface of the single-side coated positive electrode plate 1 of the electrode group so as to be in contact with the uncoated side thereof. After fitting the outer case (positive case) 4 and turning it upside down, the positive case 4 is crimped and sealed, and the flat rectangular non-aqueous water of Example 1 having a thickness of 3.2 mm, a length of 30 mm and a width of 30 mm is obtained. An electrolyte secondary battery was manufactured. At this time, R1 and R2 and the plate thickness t of the outer case were 0.50 mm, 0.55 mm and 0.25 mm, respectively, and the height h of the side wall opening from the bottom surface of the battery after crimping was 2.5 mm.
[0017]
(Example 2)
A battery was produced in the same manner as in Example 1, except that the outer cases R1, R2 and the thickness t were 0.25 mm, 0.28 mm, and 0.25 mm, respectively.
[0018]
(Example 3)
A battery was produced in the same manner as in Example 1, except that the outer cases R1, R2 and the thickness t were 0.68 mm, 0.75 mm, and 0.25 mm, respectively.
[0019]
(Comparative Example 1)
A battery was produced in the same manner as in Example 1, except that the outer cases R1, R2 and the plate thickness t were 0.50 mm, 0.50 mm, and 0.25 mm, respectively.
[0020]
(Comparative Example 2)
A battery was produced in the same manner as in Example 1, except that the outer cases R1, R2 and the plate thickness t were 0.20 mm, 0.22 mm, and 0.25 mm, respectively.
[0021]
(Comparative Example 3)
A battery was produced in the same manner as in Example 1, except that the outer cases R1, R2 and the thickness t were 0.70 mm, 0.80 mm, and 0.25 mm, respectively.
[0022]
For the 300 batteries of the present example and the comparative example manufactured as described above, the occurrence of burrs on the bottom surface and the occurrence of deformation / strain on the flat surface at the bottom were observed. In addition, these batteries were initially charged at a constant current and a constant voltage of 4.2 V and 10 mA for 48 hours, left at room temperature for 3 days, stored in an atmosphere of 60 ° C. and 93% RH for 30 days, and leaked electrolyte. The liquid was checked.
[0023]
Table 1 shows the outer radii R1 and R2, R2 / R1, plate thickness t, R1 / t, and R2 / t, and Table 2 shows the number of burrs generated at the bottom edge, the number of deformations at the bottom flat surface, and the number of leaks after storage. It was shown to.
[0024]
[Table 1]

[0025]
[Table 2]

[0026]
As is clear from Tables 1 and 2, the battery of this example has a flat bottom because the movement of the side wall material due to the crimping pressure generated in the bottom direction during the crimping process is uniform over the entire periphery of the battery. There was no deformation of the surface, and the sealing property was also good. Further, in Comparative Example 2, as shown in FIG. 4, since both R1 and R2 were smaller than the thickness t of the outer case material, the peripheral portion burr 9 was generated due to the downward pressure of the side wall portion during caulking. . In Comparative Example 3, R2 / t exceeded 3.0, and the flat surface was not deformed, but the R2 portion was deformed and crimping was insufficient to cause liquid leakage.
[0027]
Incidentally, the embodiment of the present invention, using a flat non-aqueous solvent secondary battery using a non-aqueous solvent for the non-aqueous electrolyte, for a flat prismatic battery that is sealed by caulking when the positive electrode case is an outer case Although described, it is also possible to replace the positive and negative electrodes and arrange a negative electrode case as an outer case, and it is also possible to apply to other battery systems, in other words, to a flat rectangular caulked sealing battery. Even if applied, the same effect as the present invention can be obtained.
[0028]
【The invention's effect】
As described above, according to the present invention, the movement of the outer case side wall material at the time of caulking and sealing is prevented, the distortion deformation of the bottom flat portion is prevented, and the industrial value of improving the sealing property is extremely large. A flat prismatic battery can be provided.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a battery according to a first embodiment.
FIG. 2 is a plan view of the battery of the first embodiment.
FIG. 3 is a sectional view of a sealing portion of the battery according to the first embodiment.
FIG. 4 is a schematic diagram showing generation of peripheral burr of a battery of Comparative Example 2.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Positive active material containing layer (coated electrode), 2 ... Negative active material containing layer (coated electrode), 3 ... separator, 4 ... outer case (positive case), 5 ... insulating gasket, 6 ... inner case (negative electrode) Case), 7: Metal net (negative electrode side), 8: Metal net (positive electrode side), 9: Peripheral part burr, A: Peripheral curved part, B: Peripheral straight part, R1: Peripheral curved part corresponding to the perimeter curved part Outer surface radius of curved portion, R2... Outer surface radius of outer case bottom curved portion corresponding to peripheral straight portion.

Claims

A metal outer case and a metal inner case are fitted via an insulating gasket, and the outer case has at least two or more peripheral straight-line portions at a peripheral portion of a sealing structure which is caulked by caulking. In a flat rectangular battery in which ends of respective peripheral straight portions are connected by a substantially arc-shaped peripheral curved portion, the outer case has an inner bottom surface and an outer bottom surface having a flat surface, and is perpendicular to the periphery of the bottom surface. The upwardly extending side wall portion has an inner side surface and an outer side surface, and is connected to the inner bottom surface and the outer bottom surface by an arc-shaped bottom curved portion, and the outer surface of the bottom curved portion corresponding to the peripheral curved portion. A flat rectangular battery, wherein a radius R1 and an outer surface radius R2 of a curved bottom surface portion corresponding to a peripheral straight line portion satisfy a relationship of R1 <R2.

2. The ratio of the outer surface radii R1 and R2 to the plate thickness t of the member constituting the outer case is 1 or more and 3 or less, wherein R2 / R1 is 1.1 or more. Flat batteries.