JP2004342478A

JP2004342478A - Flat type non-aqueous electrolyte secondary battery

Info

Publication number: JP2004342478A
Application number: JP2003138288A
Authority: JP
Inventors: Koji Kano; 幸司加納; Munehito Hayami; 宗人早見; Masami Suzuki; 正美鈴木
Original assignee: Toshiba Battery Co Ltd
Current assignee: FDK Twicell Co Ltd
Priority date: 2003-05-16
Filing date: 2003-05-16
Publication date: 2004-12-02

Abstract

<P>PROBLEM TO BE SOLVED: To improve safety against vibration and falling in a flat type non-aqueous electrolyte secondary battery having a wound electrode group. <P>SOLUTION: This is a flat type non-aqueous electrolyte secondary battery that has a sealed structure in which a negative electrode case made of metal serving also as a negative electrode terminal and a positive electrode terminal made of metal serving also as a positive electrode terminal are fitted and sealed through an insulating gasket, and contains inside an electrode group made by winding a positive electrode, a negative electrode, and a separator of belt shape, and an electrolyte. Each width of the belt-shaped positive electrode, negative electrode, and separator constituting the electrode group is made: positive electrode width<negative electrode width<separator width, and the width of the separator is made longer by 0.5 mm-2.0 mm respectively from the both side edge of the width of the negative electrode. Thereby, degradation of discharge capacity, leakage of a liquid, and fracture or the like can be prevented against vibration and falling. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【０００１】
【発明の属する技術分野】
本発明は扁平形非水電解質二次電池に関し、さらに詳しくは振動や落下に対して優れた安定性を有する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化しており、それらの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し、扁平形非水電解質二次電池において正負極対向面を増加させて従来のものより正負極対向面積を大きくし、小型でかつ容量アップしたものが開発されている（例えば特許文献１および特許文献２参照。）。
【０００３】
これを詳しく説明すると、上記扁平形非水電解質二次電池は、負極端子を兼ねる負極ケースと正極端子を兼ねる正極ケースが絶縁ガスケットを介して嵌合されてカシメ加工によりカシメられた封口構造をしており、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液とを内包している。そして該正極と負極はセパレータを介して対向して帯状となっており、これが捲回して電極群を構成している。このように構成したことで、正負極対向面積が従来の扁平形非水電解質二次電池に比べて大幅に増加している。そして上記電池は、電極群の一方の外面に導電性を有する正極構成材を露出させて、その正極構成材を直接正極ケースに接続し、同様に他の一方の外面に導電性を有する負極構成材を露出させてその負極構成材を直接負極ケースに接続している。そのため、円筒形電池のように電極群の中心から取り出したタブ端子を複雑に曲げ加工して安全素子や封口ピン、電池缶などに溶接して集電する、という複雑な工程を必要としない。
【０００４】
しかしながら、これらの扁平形非水電解質二次電池では、上記したように電極群と電極ケースとを直接接触させて集電しているため、当該電池電圧によっては電極群の厚み方向の変化が起こったときに電池ケース内部で電極群の移動が起こり、電池ケースとのストレスにより短絡を起こすことがある。また、電池の構成上、電極群端部は中央部と比べると機械強度的に弱く、強い衝撃を与えるとセパレータを突き破り内部短絡を起こす危険性がある。
【０００５】
【特許文献１】
特開２００１−０６８１６０号公報
【特許文献２】
特開２００１−０６８１４３号公報
【０００６】
【発明が解決しようとする課題】
本発明は上記状況に対処してなされたもので、上記の捲回した電極群を有する正負極対向面積を増加させた扁平形非水電解質二次電池において、振動や落下に対する安全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】
本発明は、上記の正負極対向面積を増加させた扁平形非水電解質二次電池において、電極群を構成する正極、負極およびセパレータの各幅を正極＜負極＜セパレータとし、かつセパレータの幅を負極の幅の両端部よりそれぞれ０．５ｍｍないし２．０ｍｍ長くすることによって上記目的を達成した。
【０００８】
すなわち本発明は、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端子が、絶縁ガスケットを介して嵌合され、さらに前記正極ケースまたは負極ケースがカシメ加工によりカシメられた封口構造を有し、その内部に帯状の正極、負極およびセパレータを捲回してなる電極群と非水電解質とを内包してなる扁平形非水電解質二次電池において、電極群を構成する帯状の正極、負極およびセパレータの各幅が、正極幅＜負極幅＜セパレータ幅の関係を有し、かつセパレータの幅が負極の幅の両側端よりそれぞれ０．５ｍｍ〜２．０ｍｍ長くなっていることを特徴とする。
【０００９】
正極、負極およびセパレータの幅について上記のように規定したのは、次の理由による。
セパレータは正極と負極とを絶縁することが目的であるので、少なくとも正極全面を覆う状態になっていなくてはならず、したがって正極面積よりも大きい。また、正極と負極との関係で言うと、負極は正極全面を覆う状態でなければならない。その理由は、充電時には正極内部からリチウムが放出され、負極にリチウムが挿入されるが、対向面に負極物質が存在しない場合には、負極集電体に金属としてリチウムが析出し、それによって電池の放電容量が減少し、正極と負極の容量バランスが変化し、サイクル特性が劣化するからであり、また、内部短絡が起きる可能性があるからでもある。
【００１０】
したがって電極幅は、（正極）＜（セパレータ）で、かつ（正極）＜（負極）となるのが好ましい。また、電極群の幅方向の両端はセパレータを負極より長くすることによって、より確実に絶縁できる。したがって（セパレータ）＞（負極）であることが好ましい。その際、セパレータ幅の負極幅に対する余剰分は、片側で０．５ｍｍ〜２．０ｍｍづつ、したがって幅全体では１．０ｍｍ〜４．０ｍｍであることが好ましいことがわかった。なお、片側余剰分は、より好ましくは０．７５〜２．０ｍｍである。片側余剰分が０．５ｍｍより少ないときは、電極群製造工程で微量の巻きずれが起こり不良品が発生しやすい。また、不良品にならない場合でも振動や落下で内部短絡を起こす可能性がある。２．０ｍｍを超える場合は、電池組立工程で正極と絶縁ガスケットの間にセパレータがかみこまれるおそれが生じ、また、絶縁性は高くなるがセパレータ占有面積が増加するので、エネルギー密度が低下する。
【００１１】
また、捲回した電極群の最外周の露出した部分、すなわち電極群の最外周の正負極ケースに固定されていない部分は、巻き止めテープや接着剤で絶縁固定されていることが望ましい。これは、本発明の扁平形非水電解質二次電池では電池ケースが正極端子および負極端子となっているので、電極群の巻き終わり部分をしっかり固定し、絶縁する必要があるからである。この絶縁テープの基材は電解液やリチウムイオンに安定なものであればよく、例えば絶縁性の樹脂または電子伝導性の低い無機材料で作られたものがよい。
【００１２】
【発明の実施の形態】
以下、本発明の実施例について説明する。
（実施例１）
図１は本実施例の電池の断面図である。この図を参照しながら本実施例の電池の製造方法を説明する。
【００１３】
まず、ＬｉＣｏＯ_２１００質量部に対し導電剤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のアルミ箔の両面にドクターブレード法により塗工し、乾燥して、アルミ箔表面に正極作用物質含有層を形成した。この正極作用物質含有層を形成したアルミ箔を２０ｍｍ幅に切断して正極を作製した。次に、この正極の片面の端から１０ｍｍの部分の作用物質含有層を除去してアルミ箔を剥き出しにし、これを集電部とした。このようにして、幅２０ｍｍ、長さ２００ｍｍ、厚さ０．１５ｍｍの正極板２を作製した。
【００１４】
次に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（ＳＢＲ）とカルボキシメチルセルロース（ＣＭＣ）をそれぞれ２．５質量部を添加し、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。得られた負極合剤を負極集電体である厚さ０．０２ｍｍの銅箔に作用物質含有層の厚さが０．１５ｍｍとなるように正極の場合と同様に塗工、乾燥を行い、銅箔表面に負極作用物質含有層を形成した。この負極作用物質含有層を形成した銅箔を２１ｍｍ幅に切断して負極を作製した。次に、この負極の片面の端から２３ｍｍの部分の作用物質含有層を除去して銅箔を剥き出しにし、これを集電部とした。このようにして、幅２１ｍｍ、長さ２２０ｍｍ、厚さ０．１５ｍｍの負極板４を作製した。
【００１５】
次に、正負極集電部面を外周巻き終わり側とし、正極と負極との間に厚さ２５μｍで幅２３ｍｍのポリエチレン微多孔膜からなるセパレータ３を介在させて渦巻状に捲回した。このとき、セパレータは負極より幅広とし、負極の幅より両側でそれぞれ１．０ｍｍ長くなるようにした。この捲回した電極を、電池の扁平方向に正負極対向面が並ぶように加圧し、中心部の空間がなくなるまでこれを行って扁平状とした。
【００１６】
その後、正極の外周端部とその内側にあるセパレータとさらにその内側にある負極とを、ポリエステル粘着テープ７で図１のように電極群の外側面が隠れるように被覆した。同様にして負極の外周端部がある外側面についてもポリエステル粘着テープ７で被覆した。
【００１７】
絶縁ガスケット６と一体化した負極ケース５の内面にニッケル製金属ネット８を溶接し、この金属ネット８に接するように電極群を配置する。このとき電極群の負極板４の未塗工面すなわち負極板集電部が金属ネット８に接するように行う。そしてエチレンカーボネートとγ−ブチルラクトンを体積比１：３の割合で混合した溶媒に支持塩としてＬｉＢＦ_４１．５ｍｏｌ／ｌ溶解した非水電解質を注液し、０．１ｍｍのアルミニウム製金属ネット９が内面に溶接された正極ケース１（板厚０．２５ｍｍ内面アルミニウム−外側ステンレスのクラッド材）を嵌合する。このとき電極群の正極板２の未塗工面すなわち正極板集電部が金属ネット９に接するように行う。嵌合後、上下反転し、正極ケース１をカシメて封口する。このようにして厚さ３．２ｍｍ、縦３０ｍｍ、横３０ｍｍの扁平角形非水電解質二次電池を作製した。
【００１８】
（実施例２）
正極板の幅を２１ｍｍ、負極板の幅を２２ｍｍ、セパレータの幅を２３ｍｍとし、セパレータは負極板の両側からそれぞれ０．５ｍｍ出るようにした。それ以外は実施例１と同様にして扁平角形非水電解質二次電池を作製した。
【００１９】
（実施例３）
正極板の幅を１８ｍｍ、負極板の幅を１９ｍｍ、セパレータの幅を２３ｍｍとし、セパレータは負極板の両側からそれぞれ２ｍｍ出るようにした。それ以外は実施例１と同様にして扁平角形非水電解質二次電池を作製した。
【００２０】
（実施例４）
正極板の幅を１９ｍｍ、負極板の幅を２０ｍｍ、セパレータの幅を２３ｍｍとし、セパレータは負極板の片側から１ｍｍ、他の片側から２ｍｍ出るようにした。それ以外は実施例１と同様にして扁平角形非水電解質二次電池を作製した。
【００２１】
（実施例５）
正極板の幅を１９．５ｍｍ、負極板の幅を２０．５ｍｍ、セパレータの幅を２３ｍｍとし、セパレータは負極板の片側から０．５ｍｍ、他の片側から２ｍｍ出るようにした。それ以外は実施例１と同様にして扁平角形非水電解質二次電池を作製した。
【００２２】
（比較例１）
正極板の幅を１６ｍｍ、負極板の幅を１７ｍｍ、セパレータの幅を２３ｍｍとし、セパレータは負極板の両側からそれぞれ３ｍｍ出るようにした。それ以外は実施例１と同様にして扁平角形非水電解質二次電池を作製した。
【００２３】
（比較例２）
正極板の幅を１８ｍｍ、負極板の幅を１９ｍｍ、セパレータの幅を２３ｍｍとし、セパレータは負極板の片側から１ｍｍ、他の片側から３ｍｍ出るようにした。それ以外は実施例１と同様にして扁平角形非水電解質二次電池を作製した。
【００２４】
（比較例３）
正極板の幅を２１．４ｍｍ、負極板の幅を２２．４ｍｍ、セパレータの幅を２３ｍｍとし、セパレータは負極板の両側からそれぞれ０．３ｍｍ出るようにした。それ以外は実施例１と同様にして扁平角形非水電解質二次電池を作製した。
【００２５】
（比較例４）
正極板の幅を１８ｍｍ、負極板の幅を１９ｍｍ、セパレータの幅を２３ｍｍとし、セパレータは負極板の片側から０．３ｍｍ、他の片側から３．７ｍｍ出るようにした。それ以外は実施例１と同様にして扁平角形非水電解質二次電池を作製した。
【００２６】
上記の実施例および比較例で作製した各２００個の電池について、４．２Ｖ、１５ｍＡの定電流定電圧で２４時間初充電を実施し、３日間室温で放置した後、開路電圧を測定した。表１に開路電圧が４．０Ｖ以下であった電池（以下、△ＯＶ不良と示す）の個数を示す。また、充電後３日間放置した電池のうち、漏液が確認された電池の個数を示す。
【００２７】
次に、開路電圧が４．０Ｖ以下であった電池および漏液が確認されなかった電池について、以下のように放電容量測定、振動試験、および落下試験を行った。いずれも結果を表１に示す。
【００２８】
放電容量測定：一旦１５ｍＡで３．０Ｖまでの放電を３サイクル行い、３回の放電の平均値を放電容量とした。
振動試験：電池を変形させないようにして確実に振動装置のプラットホームに固定する。振動は７Ｈｚから２００Ｈｚの対数掃引のサインカーブ波形とし、７Ｈｚに戻るまでを１５分間とする。対数掃引速度は、７Ｈｚから１８Ｈｚに達するまでピーク加速度を９．８ｍ／ｓｅｃ^２に維持する。その後、振幅を０．８ｍｍ（合計変位１．６ｍｍ）に保ち、ピーク加速度が７８．４ｍ／ｓｅｃ^２となるまで振動を増加する（約５０Ｈｚ）。その後振動が２００Ｈｚにあがるまで７８．４のピーク加速度を維持する。試験は、電池の正極ケースを上、負極ケースを上、カシメ部を上（または下）とした３種類を４回、計１２回繰り返した。試験後、電池質量の減少、漏液、破裂、破断および発火がなく、かつ開路電圧が試験前の９０％以上というすべての条件を満たした電池を合格とし、５０個中の不合格数を表１に示した。
【００２９】
落下試験：
電池を１．９ｍの高さからコンクリートの床に自由落下させた。これを１０回行い、試験後、電池質量の減少、漏液、破裂、破断および発火がなく、かつ開路電圧が試験前の９０％以上というすべての条件を満たした電池を合格とし、５０個中の不合格数を表１に示した。
【００３０】
【表１】

【００３１】
表１に示すように、負極幅に対するセパレータ幅の余剰量が０．５ｍｍ未満の比較例３および４では、充電後の△ＯＶ不良が確認された。また、充電後に漏液が見られた比較例１および２の電池を分解調査したところ、セパレータが絶縁ガスケットと正極ケースの間にかみ込んでいることがわかった。
【００３２】
振動試験と落下試験では、比較例３および４で不良数が多く存在しているが、これは開路電圧が低下したものである。これらの電池を分解した結果、電極群端面のセパレータの溶融が認められた。これらの現象は、通常の使用時にはセパレータの存在により、正極と負極、正極と負極ケース、負極と負極ケース、をそれぞれ絶縁しているが、捲回軸に対して垂直な電解群端面のセパレータ余剰量が少ない場合、振動や衝撃を加えることによって短絡に至ることがあると考えられる。
【００３３】
したがって、セパレータ余剰量を多くすれば振動や衝撃に対するこのような現象は減少するが、セパレータの機械的強度が低いので、セパレータ余剰量を多くすると封口部へのかみ込みが起こる可能性が高まる。また、セパレータ余剰量を増やすためには容積の制限の問題から電極の幅を狭くしなければならず（比較例１、２）、電極面積の減少により放電容量が低下するという問題がある。
【００３４】
これらの結果から、負極幅に対するセパレータの余剰量を０．５ｍｍ以上、２．０ｍｍ以下、とすることで、電池容量が高く、製造性が良好で、振動や衝撃に強い電池が得られることがわかつた。
【００３５】
なお、上記実施例では非水電解質に非水溶媒を用いたが、非水電解質としてポリマー電解質を用いても、固体電解質を用いてもよい。また、樹脂製セパレータの代わりにポリマー薄膜や固体電解質膜を用いることも可能である。また、電池形状に関しては、正極ケースのカシメ加工による封口構造を説明したが、負極ケースのカシメ加工による封口構造でもよく、さらに電池形状も正方形以外に直方形や小判形、円形コイン形など、特殊形状を有する扁平形非水電解質二次電池に適用可能である。
【００３６】
【発明の効果】
以上説明したように、本発明によれば、捲回した電極群を有する扁平形非水電解質二次電池の衝撃や振動に対する安全性を向上させ、信頼性の高い上記扁平形非水電解質電池を提供することができる。
【図面の簡単な説明】
【図１】本発明の一実施例である扁平形非水電解質二次電池の断面図。
【符号の説明】
１…正極ケース、２…正極、３…セパレータ、４…負極、５…負極ケース、６…絶縁ガスケット、７…絶縁テープ、８…負極集電体、９…正極集電体。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a flat non-aqueous electrolyte secondary battery, and more particularly to a flat non-aqueous electrolyte secondary battery having excellent stability against vibration and dropping.
[0002]
[Prior art]
The miniaturization of devices used has been accelerating, especially for small information terminals such as mobile phones and PDAs, and there is a demand for miniaturization of secondary batteries, which are the main power supplies for these devices. In order to cope with such a situation, a flat nonaqueous electrolyte secondary battery has been developed in which the positive / negative electrode facing surface is increased to increase the positive / negative electrode facing area as compared with the conventional type, and that the battery is small and has an increased capacity (for example, See Patent Literature 1 and Patent Literature 2.)
[0003]
More specifically, the flat nonaqueous electrolyte secondary battery has a sealing structure in which a negative electrode case also serving as a negative electrode terminal and a positive electrode case also serving as a positive electrode terminal are fitted via an insulating gasket and caulked by caulking. And a power generation element including at least a positive electrode, a separator, and a negative electrode and a non-aqueous electrolyte. The positive electrode and the negative electrode face each other with a separator interposed therebetween and have a band shape, which is wound to form an electrode group. With this configuration, the positive and negative electrode facing areas are greatly increased as compared with the conventional flat nonaqueous electrolyte secondary battery. In the battery, the positive electrode component having conductivity is exposed on one outer surface of the electrode group, and the positive electrode component is directly connected to the positive electrode case, and the negative electrode component having conductivity on the other outer surface is similarly formed. The material is exposed and the negative electrode component is directly connected to the negative electrode case. For this reason, there is no need for a complicated process in which a tab terminal taken out from the center of an electrode group is complicatedly bent and welded to a safety element, a sealing pin, a battery can, or the like to collect current as in a cylindrical battery.
[0004]
However, in these flat nonaqueous electrolyte secondary batteries, since the electrode group and the electrode case are brought into direct contact to collect current as described above, a change in the thickness direction of the electrode group occurs depending on the battery voltage. In such a case, the electrode group may move inside the battery case, and a short circuit may occur due to stress with the battery case. In addition, due to the structure of the battery, the end of the electrode group is weaker in mechanical strength than the center, and there is a danger that a strong impact will break through the separator and cause an internal short circuit.
[0005]
[Patent Document 1]
JP 2001-068160 A [Patent Document 2]
JP-A-2001-068143
[Problems to be solved by the invention]
The present invention has been made in view of the above circumstances, and in a flat non-aqueous electrolyte secondary battery having an increased positive / negative electrode facing area having the above-mentioned wound electrode group, improves safety against vibration and dropping. It is intended for that purpose.
[0007]
[Means for Solving the Problems]
The present invention relates to a flat nonaqueous electrolyte secondary battery having an increased positive electrode / negative electrode facing area, wherein each width of a positive electrode, a negative electrode, and a separator constituting an electrode group is defined as positive electrode <negative electrode <separator, and the width of the separator is The above object was achieved by making the width of the negative electrode 0.5 mm to 2.0 mm longer than both ends.
[0008]
That is, in the present invention, a metal negative electrode case also serving as a negative electrode terminal and a metal positive electrode terminal also serving as a positive electrode terminal were fitted via an insulating gasket, and the positive electrode case or the negative electrode case was caulked by caulking. In a flat non-aqueous electrolyte secondary battery including a non-aqueous electrolyte and an electrode group formed by winding a band-shaped positive electrode, a negative electrode, and a separator therein, the band-shaped band forming the electrode group The width of each of the positive electrode, the negative electrode, and the separator has a relationship of positive electrode width <negative electrode width <separator width, and the width of the separator is 0.5 mm to 2.0 mm longer than both ends of the width of the negative electrode. Features.
[0009]
The reason why the widths of the positive electrode, the negative electrode, and the separator are specified as described above is as follows.
Since the purpose of the separator is to insulate the positive electrode and the negative electrode, the separator must be in a state of covering at least the entire surface of the positive electrode, and is therefore larger than the positive electrode area. In terms of the relationship between the positive electrode and the negative electrode, the negative electrode must be in a state of covering the entire surface of the positive electrode. The reason is that during charging, lithium is released from the inside of the positive electrode and lithium is inserted into the negative electrode, but when no negative electrode material is present on the opposite surface, lithium is deposited as metal on the negative electrode current collector, thereby This is because the discharge capacity decreases, the capacity balance between the positive electrode and the negative electrode changes, the cycle characteristics deteriorate, and an internal short circuit may occur.
[0010]
Therefore, the electrode width preferably satisfies (positive electrode) <(separator) and (positive electrode) <(negative electrode). In addition, both ends in the width direction of the electrode group can be more reliably insulated by making the separator longer than the negative electrode. Therefore, it is preferable that (separator)> (negative electrode). At that time, it was found that the surplus of the separator width with respect to the negative electrode width was preferably 0.5 mm to 2.0 mm on one side, and thus it was preferable that the entire width was 1.0 mm to 4.0 mm. The excess on one side is more preferably 0.75 to 2.0 mm. If the surplus on one side is less than 0.5 mm, a small amount of winding deviation occurs in the electrode group manufacturing process, and defective products are likely to occur. In addition, even if it does not become a defective product, there is a possibility that an internal short circuit may occur due to vibration or drop. If it exceeds 2.0 mm, the separator may be caught between the positive electrode and the insulating gasket in the battery assembling step, and the insulating property is increased but the area occupied by the separator is increased, so that the energy density is reduced.
[0011]
It is preferable that the outermost exposed portion of the wound electrode group, that is, the outermost portion of the electrode group that is not fixed to the positive / negative electrode case is insulated and fixed with a tape or an adhesive. This is because, in the flat nonaqueous electrolyte secondary battery of the present invention, since the battery case has a positive electrode terminal and a negative electrode terminal, it is necessary to firmly fix the winding end portion of the electrode group and insulate it. The base material of the insulating tape may be any material as long as it is stable to an electrolytic solution or lithium ions. For example, a material made of an insulating resin or an inorganic material having low electron conductivity is preferable.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, examples of the present invention will be described.
(Example 1)
FIG. 1 is a cross-sectional view of the battery of this embodiment. The method of manufacturing the battery according to the present embodiment will be described with reference to FIG.
[0013]
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 agents, 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 both surfaces of a 0.02 mm thick aluminum foil as a positive electrode current collector by a doctor blade method, and dried to form a positive electrode active substance-containing layer on the surface of the aluminum foil. The aluminum foil on which the positive electrode active substance-containing layer was formed was cut into a width of 20 mm to prepare a positive electrode. Next, the active material-containing layer at a portion 10 mm from one end of the positive electrode was removed to expose the aluminum foil, which was used as a current collector. Thus, a positive electrode plate 2 having a width of 20 mm, a length of 200 mm, and a thickness of 0.15 mm was produced.
[0014]
Next, 2.5 parts by mass of styrene-butadiene rubber (SBR) and carboxymethylcellulose (CMC) were added as binders to 100 parts by mass of the graphitized mesophase pitch carbon fiber powder, and diluted and mixed with ion-exchanged water. A negative electrode mixture was obtained. The obtained negative electrode mixture is applied to a 0.02 mm-thick copper foil as a negative electrode current collector in the same manner as in the case of the positive electrode so that the thickness of the active substance-containing layer becomes 0.15 mm, and dried, A negative electrode active material containing layer was formed on the copper foil surface. The copper foil on which the negative electrode active material-containing layer was formed was cut into a width of 21 mm to prepare a negative electrode. Next, the active material-containing layer at a portion 23 mm from one end of the negative electrode was removed to expose the copper foil, which was used as a current collector. Thus, a negative electrode plate 4 having a width of 21 mm, a length of 220 mm, and a thickness of 0.15 mm was produced.
[0015]
Next, the positive and negative electrode current collector surfaces were wound around the end of the outer periphery, and a separator 3 made of a polyethylene microporous film having a thickness of 25 μm and a width of 23 mm was interposed between the positive electrode and the negative electrode, and spirally wound. At this time, the separator was wider than the negative electrode, and was longer by 1.0 mm on both sides than the width of the negative electrode. The wound electrode was pressed so that the positive and negative electrode facing surfaces were lined up in the flat direction of the battery, and this was performed until there was no space in the center, thereby obtaining a flat shape.
[0016]
Thereafter, the outer peripheral end of the positive electrode, the separator inside the positive electrode, and the negative electrode further inside the positive electrode were covered with a polyester adhesive tape 7 so as to hide the outer surface of the electrode group as shown in FIG. Similarly, the outer surface on which the outer peripheral end of the negative electrode was located was covered with the polyester adhesive tape 7.
[0017]
A nickel metal net 8 is welded to the inner surface of the negative electrode case 5 integrated with the insulating gasket 6, and an electrode group is arranged so as to be in contact with the metal net 8. At this time, the process is performed so that the uncoated surface of the negative electrode plate 4 of the electrode group, that is, the negative electrode current collector is in contact with the metal net 8. Then, a non-aqueous electrolyte in which 1.5 mol / l of LiBF ₄ was dissolved as a supporting salt was injected into a solvent in which ethylene carbonate and γ-butyl lactone were mixed at a volume ratio of 1: 3, and a 0.1 mm aluminum metal net 9 was used. Is fitted to the positive electrode case 1 (plate thickness 0.25 mm, inner surface aluminum-outside stainless steel clad material) welded to the inner surface. At this time, the process is performed so that the uncoated surface of the positive electrode plate 2 of the electrode group, that is, the positive electrode plate current collector contacts the metal net 9. After fitting, it is turned upside down, and the positive electrode case 1 is swaged and sealed. Thus, a flat rectangular nonaqueous electrolyte secondary battery having a thickness of 3.2 mm, a length of 30 mm, and a width of 30 mm was produced.
[0018]
(Example 2)
The width of the positive electrode plate was set to 21 mm, the width of the negative electrode plate was set to 22 mm, and the width of the separator was set to 23 mm. Except for this, a flat rectangular non-aqueous electrolyte secondary battery was manufactured in the same manner as in Example 1.
[0019]
(Example 3)
The width of the positive electrode plate was set to 18 mm, the width of the negative electrode plate was set to 19 mm, and the width of the separator was set to 23 mm. Except for this, a flat rectangular non-aqueous electrolyte secondary battery was manufactured in the same manner as in Example 1.
[0020]
(Example 4)
The width of the positive electrode plate was 19 mm, the width of the negative electrode plate was 20 mm, and the width of the separator was 23 mm. The separator protruded 1 mm from one side of the negative electrode plate and 2 mm from the other side. Except for this, a flat rectangular non-aqueous electrolyte secondary battery was manufactured in the same manner as in Example 1.
[0021]
(Example 5)
The width of the positive electrode plate was 19.5 mm, the width of the negative electrode plate was 20.5 mm, and the width of the separator was 23 mm. The separator protruded 0.5 mm from one side of the negative electrode plate and 2 mm from the other side. Except for this, a flat rectangular non-aqueous electrolyte secondary battery was manufactured in the same manner as in Example 1.
[0022]
(Comparative Example 1)
The width of the positive electrode plate was set to 16 mm, the width of the negative electrode plate was set to 17 mm, the width of the separator was set to 23 mm, and the separator protruded 3 mm from both sides of the negative electrode plate. Except for this, a flat rectangular non-aqueous electrolyte secondary battery was manufactured in the same manner as in Example 1.
[0023]
(Comparative Example 2)
The width of the positive electrode plate was 18 mm, the width of the negative electrode plate was 19 mm, and the width of the separator was 23 mm. The separator protruded 1 mm from one side of the negative electrode plate and 3 mm from the other side. Except for this, a flat rectangular non-aqueous electrolyte secondary battery was manufactured in the same manner as in Example 1.
[0024]
(Comparative Example 3)
The width of the positive electrode plate was 21.4 mm, the width of the negative electrode plate was 22.4 mm, the width of the separator was 23 mm, and the separator protruded 0.3 mm from both sides of the negative electrode plate. Except for this, a flat rectangular non-aqueous electrolyte secondary battery was manufactured in the same manner as in Example 1.
[0025]
(Comparative Example 4)
The width of the positive electrode plate was 18 mm, the width of the negative electrode plate was 19 mm, and the width of the separator was 23 mm. The separator protruded 0.3 mm from one side of the negative electrode plate and 3.7 mm from the other side. Except for this, a flat rectangular nonaqueous electrolyte secondary battery was manufactured in the same manner as in Example 1.
[0026]
Each of the 200 batteries produced in the above Examples and Comparative Examples was initially charged at a constant current and voltage of 4.2 V and 15 mA for 24 hours, left at room temperature for 3 days, and then the open circuit voltage was measured. Table 1 shows the number of batteries having an open circuit voltage of 4.0 V or less (hereinafter referred to as △ OV failure). In addition, among the batteries left for 3 days after charging, the number of batteries for which leakage was confirmed is shown.
[0027]
Next, the discharge capacity measurement, the vibration test, and the drop test were performed on the battery having the open circuit voltage of 4.0 V or less and the battery in which the liquid leakage was not confirmed, as follows. Table 1 shows the results.
[0028]
Discharge capacity measurement: Discharge up to 3.0 V was performed once at 15 mA for 3 cycles, and the average value of the three discharges was taken as the discharge capacity.
Vibration test: Secure the battery to the platform of the vibration device without deforming it. The vibration is a sine curve waveform of logarithmic sweep from 7 Hz to 200 Hz, and it takes 15 minutes to return to 7 Hz. The logarithmic sweep speed maintains the peak acceleration at 9.8 m / sec ² from 7 Hz to 18 Hz. Thereafter, the amplitude is kept at 0.8 mm (total displacement 1.6 mm), and the vibration is increased (about 50 Hz) until the peak acceleration becomes 78.4 m / sec ² . Thereafter, the peak acceleration of 78.4 is maintained until the vibration rises to 200 Hz. The test was repeated four times, three times with the positive electrode case of the battery up, the negative electrode case up, and the crimped portion up (or down), for a total of 12 times. After the test, a battery that met all the conditions of no battery loss, liquid leakage, rupture, rupture and ignition, and an open circuit voltage of 90% or more before the test was accepted, and the number of rejects out of 50 was shown. 1 is shown.
[0029]
Drop test:
The battery was allowed to fall freely from a height of 1.9 m onto a concrete floor. This test was performed 10 times, and after the test, the battery was judged to be acceptable if it did not lose the battery mass, leak, rupture, break or ignite, and satisfied all the conditions that the open-circuit voltage was 90% or more of that before the test. Table 1 shows the number of rejects.
[0030]
[Table 1]

[0031]
As shown in Table 1, in Comparative Examples 3 and 4 where the surplus amount of the separator width with respect to the negative electrode width was less than 0.5 mm, ΔOV failure after charging was confirmed. In addition, when the batteries of Comparative Examples 1 and 2, in which a liquid leak was observed after charging, were disassembled and investigated, it was found that the separator was stuck between the insulating gasket and the positive electrode case.
[0032]
In the vibration test and the drop test, the number of defects was large in Comparative Examples 3 and 4, but this was because the open circuit voltage was reduced. As a result of disassembling these batteries, melting of the separator on the end face of the electrode group was observed. These phenomena are that, during normal use, the presence of the separator insulates the positive electrode and the negative electrode, the positive electrode and the negative electrode case, and the negative electrode and the negative electrode case, respectively. When the amount is small, it is considered that a short circuit may be caused by applying vibration or impact.
[0033]
Therefore, if the excess amount of the separator is increased, such a phenomenon with respect to vibration and impact is reduced, but the mechanical strength of the separator is low. Further, in order to increase the surplus amount of the separator, the width of the electrode must be reduced due to the problem of volume limitation (Comparative Examples 1 and 2), and there is a problem that the discharge capacity is reduced due to the decrease in the electrode area.
[0034]
From these results, by setting the surplus amount of the separator with respect to the negative electrode width to 0.5 mm or more and 2.0 mm or less, it is possible to obtain a battery with high battery capacity, good manufacturability, and resistance to vibration and impact. Wakata.
[0035]
In the above embodiment, a non-aqueous solvent is used as the non-aqueous electrolyte. However, a polymer electrolyte or a solid electrolyte may be used as the non-aqueous electrolyte. Further, a polymer thin film or a solid electrolyte membrane can be used instead of the resin separator. In addition, regarding the battery shape, the sealing structure by crimping of the positive electrode case was explained, but the sealing structure by crimping of the negative electrode case may be used. The present invention is applicable to a flat nonaqueous electrolyte secondary battery having a shape.
[0036]
【The invention's effect】
As described above, according to the present invention, the safety of a flat non-aqueous electrolyte secondary battery having a wound electrode group with respect to shock and vibration is improved, and the flat non-aqueous electrolyte battery having high reliability is provided. Can be provided.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a flat nonaqueous electrolyte secondary battery according to one embodiment of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Positive electrode case, 2 ... Positive electrode, 3 ... Separator, 4 ... Negative electrode, 5 ... Negative electrode case, 6 ... Insulating gasket, 7 ... Insulating tape, 8 ... Negative electrode collector, 9 ... Positive electrode collector.

Claims

A metal negative electrode case also serving as a negative electrode terminal, and a metal positive electrode terminal also serving as a positive electrode terminal are fitted via an insulating gasket, and further have a sealing structure in which the positive electrode case or the negative electrode case is swaged by swaging. In a flat non-aqueous electrolyte secondary battery including a non-aqueous electrolyte and an electrode group formed by winding a band-shaped positive electrode, a negative electrode, and a separator therein, a band-shaped positive electrode, a negative electrode, and a separator constituting the electrode group Wherein each width of the negative electrode has a relationship of positive electrode width <negative electrode width <separator width, and the width of the separator is 0.5 mm to 2.0 mm longer than both ends of the width of the negative electrode. Non-aqueous electrolyte secondary battery.

2. The flat nonaqueous electrolyte secondary battery according to claim 1, wherein the exposed outermost end portion of the electrode group is insulated and fixed with a tape or an adhesive.

The outermost positive electrode end and negative electrode end of the electrode group formed by winding the strip-shaped positive electrode, negative electrode, and separator are made of a conductive component having no active substance, and are directly or electrically connected to the positive electrode case and the negative electrode case. The flat nonaqueous electrolyte secondary battery according to claim 1, wherein the secondary battery is in partial contact.