JP4453882B2

JP4453882B2 - Flat non-aqueous electrolyte secondary battery

Info

Publication number: JP4453882B2
Application number: JP24096499A
Authority: JP
Inventors: 正美鈴木; 宗人早見; 和男宇田川; 将貴志子田; 清人依田
Original assignee: Hitachi Maxell Energy Ltd
Current assignee: Hitachi Maxell Energy Ltd
Priority date: 1999-08-27
Filing date: 1999-08-27
Publication date: 2010-04-21
Anticipated expiration: 2019-08-27
Also published as: JP2001068160A

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係り、特に、重負荷放電特性の向上した扁平形非水電解質二次電池に関する。
【０００２】
【従来の技術】
正極作用物質にＭｎＯ_２やＶ_２Ｏ_５などの金属酸化物、あるいはフッ化黒鉛などの無機化合物、あるいはポリアニリンやポリアセン構造体などの有機化合物を用い、負極に金属リチウム、あるいはリチウム合金、あるいはポリアセン構造体などの有機化合物、あるいはリチウムを吸蔵、放出可能な炭素質材料、あるいはチタン酸リチウムやリチウム含有珪素酸化物のような酸化物を用い、電解質にプロピレンカーボネート、エチレンカーボネート、ブチレンカーボネート、ジエチルカーボネート、ジメチルカーボネート、メチルエチルカーボネート、ジメトキシエタン、γ−ブチルラクトンなどの非水溶媒にＬｉＣｌＯ_４、ＬｉＰＦ_６、ＬｉＢＦ_４、ＬｉＣＦ_３ＳＯ_３、ＬｉＮ（ＣＦ_３ＳＯ_２）_２、ＬｉＮ（Ｃ_２Ｆ_５ＳＯ_２）_２などの支持塩を溶解した非水電解質を用いたコイン形やボタン形などの電池総高に対して電池最外径が長い扁平形非水電解質二次電池は既に商品化されており、放電電流が数〜数十μＡ程度の軽負荷で放電が行われるＳＲＡＭやＲＴＣのバックアップ用電源や電池交換不要腕時計の主電源といった用途に適用されている。
【０００３】
これらのコイン形やボタン形などの扁平形非水電解質二次電池は、一般に図２に示したような構造を有する。すなわち、負極端子を兼ねる金属製の負極ケース５と、正極端子を兼ねる金属製の正極ケース１が、絶縁ガスケット６を介し嵌合され、さらに正極ケース１が加締め加工により加締められた封口構造を有し、その内部に絶縁ガスケット６の開口径より一回り直径が小さいタブレット状の正極２及び負極４をそれぞれ１枚ずつ非水電解質を含浸させた単層または多層のセパレータ３を介し、対向配置された構成をなしている。
【０００４】
上述したコイン形やボタン形などの扁平形非水電解質二次電池は製造が簡便であり、量産性に優れ、長期信頼性や安全性に優れるという長所を持っている。また、構造が簡便であることから、これらの電池の最大の特徴として小型化が可能であることが挙げられる。
【０００５】
一方、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、これに伴い主電源である二次電池についても小形化を図ることが必須とされている。従来、これらの電源には正極作用物質にコバルト酸リチウムなどのリチウム含有酸化物、負極に炭素質材料を用いたリチウムイオン二次電池や、正極作用物質にオキシ水酸化ニッケル、負極作用物質に水素吸蔵合金を用いたニッケル水素二次電池などのアルカリ二次電池が使用されてきたが、これらの電池は金属箔または金属ネットからなる集電体に作用物質層を塗布または充填し電極を形成後、電極中心部にタブ端子を溶接した後、捲回、または積層して電極群とし、さらに電極群の中心部から取り出したタブ端子を複雑に曲げ加工を行い、安全素子や封口ピン、電池缶などに溶接して電池を製作していた。
【０００６】
上述したようにこれらの電池は、複雑な製造工程を経て製作されるため作業性が劣り、また部品の小型化も困難であり、さらに、タブ端子のショート防止に電池内に空間を設けたり、安全素子などの多数の部品を電池内に組込む必要があり、電池の小型化に際しても現状ではほぼ限界に達していた。
【０００７】
【発明が解決しようとする課題】
そこで、本発明者らは電池の小型化に際し円筒形や角形のリチウムイオン二次電池やニッケル水素二次電池の小型化ではなく、前段に述べた扁平形非水電解質二次電池の高出力を図ることを試みた。まず、本発明者らは、正極作用物質に高容量で高電位なコバルト酸リチウムを、負極作用物質に高容量で電圧平坦性の良好な黒鉛化した炭素質材料をそれぞれ使用し、従来の扁平形非水電解質二次電池の製造及び構造に従い、正極及び負極をガスケットより一回り小さいタブレット状に成形加工し、電池を作製した。
【０００８】
しかしながら、このように作製された電池は従来の扁平形非水電解質二次電池に比べ優れた特性は得られたものの、小型携帯機器の主電源として要求される大電流で放電した場合の特性に対しては遥かに不十分であり、小型携帯機器の主電源としては到底満足できるレベルではなかった。
【０００９】
小型の扁平形非水電解質二次電池の重負荷放電特性を如何にして従来にないレベルまで引き上げるかが本発明の課題であり、重負荷放電特性が格段に優れた扁平形非水電解質二次電池を提供することが本発明の目的である。
【００１０】
【課題を解決するための手段】
本発明者らは前述の扁平形非水電解質二次電池の重負荷放電特性の向上に関し鋭意研究を重ねた結果、従来の扁平形非水電解質二次電池に比べ電極面積を格段に大きくすることで重負荷放電特性が飛躍的に向上することを見出した。
【００１１】
すなわち、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板と負極板がセパレータを介し対向配置している電極群を含む発電要素と、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、前記電極群内の正極板の作用物質含有層と負極板の作用物質含有層との対向面積（以下、「正負極の対向面積」や、単に「対向面積」と省略する場合がある。）を、前記絶縁ガスケットの開口面積よりも大きくすることで、重負荷放電特性が著しく優れた扁平形非水電解質二次電池を提供できることを見出した。
【００１２】
重負荷放電特性を向上させるためには電極面積を増大させることが有効であると推察されるが、従来の扁平形非水電解質二次電池ではタブレット状の正極及び負極をそれぞれ１枚ずつ絶縁ガスケットに内接する形で電池内に収容していたため、正負極がセパレータを介し対向する対向面積はどうしても絶縁ガスケットの開口面積より一回りほど小さくせざるを得なかった。ガスケットを肉薄にするなどして多少の電極面積の拡大を図ることは可能であるが、ガスケットの開口面積を上回るような対向面積を持つ電極を電池内に収納することは理論的に不可能であった。
【００１３】
そこで、本発明者らは従来技術からの大胆な発想の転換を図り、コイン形やボタン形などの非常に小さな扁平形電池の電池ケース内に電極を多層配置することで、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大きな電極群を収納することを可能にした。つまり、円筒形や角形などの容積の大きな二次電池では数十層を有する電極を収納している例があるが、これらの電池は前述のように構造が複雑であり、そのままの電池の電池構造をコイン形やボタン形などの小型の扁平形非水電解質二次電池に適用することは困難であった。また、たとえ適用したとしても小型であることや生産性に優れるといった扁平形非水電解質二次電池の利点を維持することは不可能であるため、コイン形やボタン形などの小型の扁平形非水電解質二次電池に絶縁ガスケットの開口面積よりも大きな正負極の対向面積を有する電極群を収納しようという取組みは過去にされなかった。
【００１４】
以下、如何にして本発明者らが本発明の扁平形非水電解質二次電池を実現したかを説明する。まず、正負極の対向面積がガスケットの開口面積より大きな電極を扁平形非水電解質二次電池内に収納する形態については種々の形態が考えられるが、その中で扁平形電池の扁平面に対して平行に正負極対向部を持つように電極を積層した電極群として収納するのが好ましいことが分かった。なぜなら、優れた重負荷放電特性を得るためには、電極面積を極力大きくとることと、部品点数を極力減らし、小さな電池内のスペースを有効に活用し、電極群と放電に必要な量の非水電解質を電池内に収納する必要があり、上記したような扁平面に対して平行に正負極対向部を持つように電極を積層した電極群とするような収納方法、例えば正極板の作用物質含有層と負極板の作用物質含有層とがセパレータを介し対向している正負極対向面を少なくとも５面有する電極群とするような収納方法とすることでこれらを実現できることが分かった。また、この収納方法によると電極を除く電池の組立方法が従来のタブレット状電極を用いた扁平形電池の製造方法に近く、従来の生産設備の一部流用が可能である上、生産性やコストといった実用面においても優れており量産する上でも好ましい。
【００１５】
次に、実際に電極群を作製、収納する方法については、電極の一部に通電部を設けた正極板並びに負極板を用意し、セパレータを介し正極板及び負極板を積層する際に、正極板の通電部がセパレータの配置されている箇所よりも外側に露出し、負極板の通電部が、正極板の通電部が露出している位置に対向する位置において、セパレータの配置されている箇所よりも外側に露出する形で積層した後、正極は正極同士、負極は負極同士おのおのの通電部を溶接などの方法により電気的に接続し電極群を形成し、電池内に収納する。正極板の通電部と負極板の通電部とを上記のように配置することで、コイン形やボタン形などの小さな扁平形非水電解質二次電池においても、正極板の通電部と負極板の通電部との接触による内部ショートを防止できる。
【００１６】
次に、電極群と外部端子を兼ねる電池金属ケースとの接続方法について説明する。前述したように、円筒形や角形などの比較的大きなリチウムイオン二次電池では電極群の中心部や巻き芯部にタブ端子を溶接してそれを曲げ加工して安全素子や封口ピンに溶接し集電を行っている。しかしながら、曲げ工程は工程自体が複雑なため生産性に劣る上、内部ショートを防止するため電池内に空間を持たせたり、電極群との間に絶縁板を挿入する必要があった。また、タブ端子を電極に溶接している部分に応力が加わるとセパレータを突き破ったり、電極の変形が起こるため絶縁テープで保護したり、巻き芯部に空間を設ける必要があり、電池の内容積を有効に使用することはできなかった。そのため、電池の内容積が小さなコイン形やボタン形の扁平形非水電解質二次電池ではこれらの集電方法は適用できず、新たな集電方法を考案する必要があった。
【００１７】
そこで、本発明者らは電極群の最外部に位置する正極板において、導電性を有する正極構成材を露出させ、電極群の最外部に位置する負極板において、導電性を有する負極構成材を露出させた形状を持つ電極群を作製し、おのおのの電極構成材を正極及び負極の電池ケースに接触させることにより、電極群と電池ケースの集電を確保することを見出した。この方法によれば、電極群と電池ケース間に無駄な空間や絶縁板を設ける必要もなく、放電容量を増やすことができる。また、電池ケースや電極とタブ端子がショートを起こすこともなく、安全性や信頼性も優れている。
【００１８】
また、本発明のような封口構造を持つ扁平形電池では電池ケースの加締め加工により、負極ケースと正極ケースの扁平面に対し垂直方向に応力が加わっており、本集電方法によると電極群の平面方向に均一な加圧力が加わり、充放電を円滑に行うことができる。なお、電極群の電極構成材露出部と電極ケースの接触は直接、接していてもよいし、金属箔や金属ネット、金属粉末、炭素フィラー、導電性塗料などを介し電気的に間接的に接していてもよい。
【００１９】
次に、電極については正極板、負極板とも、肉薄電極の作製が行い易いという点で金属箔にスラリー状の合剤を塗布、乾燥したものがよく、さらにそれを圧延したものを用いることもできる。上記のような金属箔に作用物質を含む合剤層を塗工した電極を用いる場合は、電極群の内部に用いる電極は金属箔の両面に作用物質含有層を形成したものを用いるのが、容積効率の上から好ましく、電極群の両端の電池ケースに接触する電極構成材露出部については作用物質含有層でも構わないが、接触抵抗を低減させるために電極構成材のうち、特に金属箔を露出させるのが好ましい。これに関してはこの部分に限り片面にのみ作用物質含有層を形成した電極を用いてもよいし、一旦両面に作用物質含有層を形成した後、片面のみ作用物質含有層を除去してもよい。
【００２０】
一方、本発明電池は電極を含めた電池の構造に主点をおいたものであり、正極作用物質については限定されるものではなく、ＭｎＯ_２、Ｖ_２Ｏ_５、Ｎｂ_２Ｏ_５、ＬｉＴｉ_２Ｏ_４、Ｌｉ_４Ｔｉ_５Ｏ_１２、ＬｉＦｅ_２Ｏ_４、ＬｉＭｎ_２Ｏ_４、Ｌｉ_４Ｍｎ_５Ｏ_１２、Ｌｉ_０．３３ＭｎＯ_２、コバルト酸リチウム、ニッケル酸リチウム、マンガン酸リチウムなどの金属酸化物、あるいはフッ化黒鉛、ＦｅＳ_２などの無機化合物、あるいはポリアニリンやポリアセン構造体などの有機化合物などあらゆるものが適用可能である。ただし、この中で作動電位が高く、サイクル特性に優れるという点でコバルト酸リチウム、ニッケル酸リチウム、マンガン酸リチウムやそれらの混合物やそれらの元素の一部を他の金属元素で置換したリチウム含有酸化物がより好ましく、長期間に亘り使用されることもある扁平形非水電解質二次電池においては高容量で電解液や水分との反応性が低く化学的に安定であるという点でコバルト酸リチウムがさらに好ましい。
【００２１】
また、本発明電池の負極作用物質については限定されるものではなく、金属リチウム、あるいはＬｉ−Ａｌ、Ｌｉ−Ｉｎ、Ｌｉ−Ｓｎ、Ｌｉ−Ｓｉ、Ｌｉ−Ｇｅ、Ｌｉ−Ｂｉ、Ｌｉ−Ｐｂなどのリチウム合金、あるいはポリアセン構造体などの有機化合物、あるいはリチウムを吸蔵、放出可能な炭素質材料、あるいはＮｂ_２Ｏ_５、ＬｉＴｉ_２Ｏ_４、Ｌｉ_４Ｔｉ_５Ｏ_１２やＬｉ含有珪素酸化物やＬｉ含有錫酸化物のような酸化物、Ｌｉ_３Ｎのような窒化物などあらゆるものが適用可能であるが、サイクル特性に優れ、作動電位が低く、高容量であるという点でＬｉを吸蔵、放出可能な炭素質材料が好ましく、特に放電末期においても電池作動電圧の低下が少ないという点で天然黒鉛や人造黒鉛、膨張黒鉛、メソフェーズピッチ焼成体、メソフェーズピッチ繊維焼成体などのｄ_００２の面間隔が０．３３８ｎｍ以下の黒鉛構造が発達した炭素質材料がより好ましい。
【００２２】
なお、上記した本発明電池では主としてコイン形やボタン形などの電池総高に対して電池最外径が長い扁平形電池について説明したが、本発明電池はこれのみに限定するものではなく、小判形や角形などの特殊形状を有する扁平形電池にも本発明と同様に適用できる。
【００２３】
【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詳細に説明する。
（参考例１）
参考例１の電池の製造方法を図１の断面図を参照して説明する。
【００２４】
まず、ＬｉＣｏＯ_２１００重量部に対し、導電剤としてアセチレンブラック５重量部と黒鉛粉末５重量部を加え、結着剤としてポリフッ化ビニリデン５重量部を加え、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（導電性を有する正極構成材）２ａである厚さ０．０２ｍｍのアルミニウム箔の片面にドクターブレード法により塗工、乾燥を行い、アルミニウム箔表面に正極作用物質含有層２ｂを形成した。以後、作用物質含有層の塗膜厚さが０．３９ｍｍとなるまで塗工、乾燥を繰り返し、片面塗工正極板を作製した。次に、この片面塗工正極板と同様の方法によりアルミニウム箔の両面に正極作用物質含有層の塗膜厚さが片面当たり０．３９ｍｍとなるように両面塗工し正極板を作製した。
【００２５】
次に、黒鉛化メソフェーズピッチ炭素繊維粉末１００重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重量部添加し、イオン交換水で希釈、混合して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（導電性を有する負極構成材）４ａである厚さ０．０２ｍｍの銅箔に作用物質含有層４ｂの厚さが０．３９ｍｍとなるように正極の場合と同様に塗工、乾燥を繰り返し実施し、片面塗工負極板を作製した。次に、この片面塗工負極板と同様の方法により銅箔の両面に負極作用物質含有層の塗膜厚さが片面当たり０．３９ｍｍとなるように両面塗工負極板を作製した。
【００２６】
これらの電極を幅１３ｍｍ、長さ１３ｍｍの正方形の一辺に幅６ｍｍ、長さ２ｍｍの張り出し部が付いた形状に切り出し、次にこの張り出し部に形成された作用物質含有層をこそげ落とし、アルミニウム層または銅層をむき出しとして通電部とし、幅１３ｍｍ、長さ１３ｍｍの作用物質含有層が形成された両面及び片面塗工の正極板及び負極板を作製した。
【００２７】
次に、片面塗工正極板の正極作用物質含有層形成部に厚さ２５μｍのポリエチレン微多孔膜からなるセパレータ３を介し両面塗工負極板を通電部が先の正極板と対向する位置に設置し、さらに、セパレータ３を介し、両面塗工正極板を通電部が先の正極板と同方向に向くように設置し、さらにセパレータ３を介し、このセパレータ面に負極作用物質含有層４ｂが接するように片面塗工負極板の通電部が先の負極板と同方向に向くように設置し、正極通電部及び負極通電部をそれぞれ溶接し、電極群を作製した。
【００２８】
作製した電極群を８５℃で１２ｈ乾燥した後、開口径が２０ｍｍであり、開口面積が３．１４ｃｍ^２である絶縁ガスケット６を一体化した負極金属ケース５の内底面に電極群の片面塗工負極板の未塗工側（すなわち、負極集電体４ａ）が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の未塗工側（すなわち正極集電体２ａ）に接するようにステンレス製の正極ケース１を嵌合し、上下反転後、正極ケースに加締め加工を実施し、封口して厚さ３ｍｍ、直径φ２４．５ｍｍの参考例１の扁平形非水電解質二次電池を作製した。この電池のセパレータを介した正極板の作用物質含有層と負極板の作用物質含有層との対向面の面数は計３面であり、正極板の作用物質含有層と負極板の作用物質含有層との対向面積の総和は５．１ｃｍ^２である。
【００２９】
（実施例２）
電極群内の正極板及び負極板の片面当たりの作用物質含有層の塗膜厚さがそれぞれ０．２２ｍｍであり、かつ電極群中間部の両面塗工正極板及び両面塗工負極板の積層枚数がそれぞれ２枚であること以外は参考例１と同様に電池を作製した。この電池のセパレータを介した正極板の作用物質含有層と負極板の作用物質含有層との対向面の面数は計５面であり、正極板の作用物質含有層と負極板の作用物質含有層との対向面積の総和は８．５ｃｍ^２である。
【００３０】
（実施例３）
電極群内の正極板及び負極板の片面当たりの作用物質含有層の塗膜厚さがそれぞれ０．１５ｍｍであり、かつ電極群中間部の両面塗工正極板及び両面塗工負極板の積層枚数がそれぞれ３枚であること以外は参考例１と同様に電池を作製した。この電池のセパレータを介した正極板の作用物質含有層と負極板の作用物質含有層との対向面の面数は計７面であり、正極板の作用物質含有層と負極板の作用物質含有層との対向面積の総和は１１．８ｃｍ^２である。
【００３１】
（実施例４）
電極群内の正極板及び負極板の片面当たりの作用物質含有層の塗膜厚さがそれぞれ０．１１ｍｍであり、かつ電極群中間部の両面塗工正極板及び両面塗工負極板の積層枚数がそれぞれ４枚であること以外は参考例１と同様に電池を作製した。この電池のセパレータを介した正極板の作用物質含有層と負極板の作用物質含有層との対向面の面数は計９面であり、正極板の作用物質含有層と負極板の作用物質含有層との対向面積の総和は１５．２ｃｍ^２である。
【００３２】
（比較例１）
ＬｉＣｏＯ_２１００重量部に対し導電剤としてアセチレンブラック５重量部と黒鉛粉末５重量部を加え、結着剤としてポリ４フッ化エチレン５重量部を加え、混合後、粉砕し、顆粒状の正極合剤を得た。次にこの正極顆粒合剤を、直径１９ｍｍ、厚さ１．１５ｍｍに加圧成形を行い、正極タブレットとした。
【００３３】
次に黒鉛化メソフェーズピッチ炭素繊維粉末１００重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重量部を添加、混合、乾燥後、さらに粉砕し顆粒状の負極合剤を得た。この負極顆粒合剤を、直径１９ｍｍ、厚さ１．１５ｍｍに加圧成形し、負極タブレットとした。
【００３４】
次に、これらの正負極タブレットを８５℃で１２ｈ乾燥した後、開口面積３．１４ｃｍ^２の絶縁ガスケットを一体化した負極ケースに負極タブレット、ポリプロピレンからなる厚さ０．２ｍｍのポリプロピレン不織布、正極タブレットの順に配置し、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、さらにステンレス製の正極ケースを嵌合し、上下反転後、正極ケースに加締め加工を実施し、厚さ３ｍｍ、直径φ２４．５ｍｍの比較例１の扁平形非水電解質二次電池を作製した。この電池のセパレータを介した正負極対向面の面数は１面であり、正負極の対向面積の総和は２．８ｃｍ^２である。
【００３５】
（比較例２）
電極群内の正極板及び負極板が片面塗工電極板のみであり、作用物質含有層の塗膜厚さがそれぞれ１．２４ｍｍであること以外は参考例１と同様に電池を作製した。この電池のセパレータを介した正極板の作用物質含有層と負極板の作用物質含有層との対向面の面数は計１面であり、正極板の作用物質含有層と負極板の作用物質含有層との対向面積の総和は１．７ｃｍ^２である。
【００３６】
以上の通り作製した本実施例、参考例及び比較例の電池について、４．２Ｖ、３ｍＡの定電流定電圧で４８ｈ初充電を実施した。その後、３０ｍＡの定電流で３．０Ｖまで放電を実施し重負荷放電容量を求めた。その結果を表１に示す。
【００３７】
【表１】

【００３８】
表１より明らかであるが、本実施例の各電池は比較例１の従来の顆粒合剤成形法により作製したタブレット状の電極を用いた正負極の対向面積がガスケットの開口面積よりも小さい電池や比較例２の正極板の作用物質含有層と負極板の作用物質含有層との対向面が１面しかなく、対向面積が小さい電池に比べ、著しく重負荷放電時の放電容量が大きい。
【００３９】
なお、本発明の実施例では、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説明したが、非水電解質にポリマー電解質を用いたポリマー二次電池や固体電解質を用いた固体電解質二次電池についても当然適用可能であり、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、電池形状については正極ケースの加締め加工により封口するコイン形非水電解質をもとに説明したが、正負極電極を入れ替え、負極ケースの加締め加工により封口することも可能である。さらに、電池形状についても真円である必要はなく小判形や角形などの特殊形状を有する扁平形非水電解質二次電池においても適用可能である。
【００４０】
【発明の効果】
以上説明したように、本発明によれば、扁平形電池の持つ電池サイズが小さく、かつ生産性に優れるという利点を維持したまま、重負荷放電時の放電容量が従来の電池に対し格段に大きくすることができるので、工業的価値の優れた扁平形非水電解質二次電池を提供することができる。
【図面の簡単な説明】
【図１】参考例の電池の断面図。
【図２】比較例１の電池の断面図。
【符号の説明】
１正極ケース
２正極
２ａ正極集電体
２ｂ正極作用物質含有層
３セパレータ
４負極
４ａ負極集電体
４ｂ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, and more particularly to a flat nonaqueous electrolyte secondary battery with improved heavy load discharge characteristics.
[0002]
[Prior art]
A metal oxide such as MnO ₂ and V ₂ O ₅ , an inorganic compound such as fluorinated graphite, or an organic compound such as polyaniline or a polyacene structure is used as the positive electrode active material, and metal lithium, lithium alloy, or polyacene is used as the negative electrode. Organic compounds such as structures, carbonaceous materials capable of occluding and releasing lithium, or oxides such as lithium titanate and lithium-containing silicon oxide, and propylene carbonate, ethylene carbonate, butylene carbonate, diethyl carbonate as electrolytes LiClO ₄ , LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) _{2 in} a non-aqueous solvent such as dimethyl carbonate, methyl ethyl carbonate, dimethoxyethane, and γ-butyl lactone , A flat non-aqueous electrolyte secondary with a battery outer diameter that is long relative to the total height of the battery, such as a coin shape or a button shape, using a non-aqueous electrolyte in which a supporting salt such as LiN (C ₂ F ₅ SO ₂ ) ₂ is dissolved Batteries have already been commercialized and are applied to applications such as SRAM and RTC backup power sources that discharge at a light load with a discharge current of several to several tens of μA, and main power sources for wristwatches that do not require battery replacement.
[0003]
These flat non-aqueous electrolyte secondary batteries such as coins and buttons generally have a structure as shown in FIG. That is, a sealing structure in which a metal negative electrode case 5 also serving as a negative electrode terminal and a metal positive electrode case 1 also serving as a positive electrode terminal are fitted via an insulating gasket 6 and the positive electrode case 1 is further crimped by crimping. The tablet-like positive electrode 2 and negative electrode 4 each having a diameter slightly smaller than the opening diameter of the insulating gasket 6 are respectively opposed to each other through a single-layer or multi-layer separator 3 impregnated with a non-aqueous electrolyte. It has an arranged configuration.
[0004]
The flat non-aqueous electrolyte secondary batteries such as the coin type and the button type described above have advantages that they are easy to manufacture, have excellent mass productivity, and have excellent long-term reliability and safety. In addition, since the structure is simple, the biggest feature of these batteries is that they can be miniaturized.
[0005]
On the other hand, downsizing of devices used has been accelerated mainly in small information terminals such as mobile phones and PDAs, and accordingly, it is essential to reduce the size of the secondary battery as the main power source. Conventionally, these power sources have lithium-ion secondary batteries using lithium-containing oxides such as lithium cobaltate as a positive electrode active substance, carbonaceous materials as a negative electrode, nickel oxyhydroxide as a positive electrode active substance, and hydrogen as a negative electrode active substance. Alkaline secondary batteries such as nickel metal hydride secondary batteries using occlusion alloys have been used, but these batteries are used after applying or filling an active material layer on a current collector made of metal foil or metal net to form an electrode. After the tab terminal is welded to the center part of the electrode, it is wound or laminated to form an electrode group, and the tab terminal taken out from the center part of the electrode group is bent in a complicated manner to produce a safety element, sealing pin, battery can The battery was manufactured by welding to the above.
[0006]
As described above, these batteries are manufactured through a complicated manufacturing process, so the workability is inferior, and it is difficult to reduce the size of the parts. Many components such as safety elements need to be incorporated into the battery, and the current limit has been reached when the battery is downsized.
[0007]
[Problems to be solved by the invention]
Therefore, the present inventors have not reduced the size of the cylindrical or square lithium ion secondary battery or nickel metal hydride secondary battery when reducing the size of the battery, but increased the output of the flat nonaqueous electrolyte secondary battery described in the previous stage. I tried to plan. First, the present inventors used a high-capacity, high-potential lithium cobaltate as the positive electrode active material, and a graphitized carbonaceous material with a high capacity and good voltage flatness as the negative-electrode active material. In accordance with the manufacture and structure of the non-aqueous electrolyte secondary battery, the positive electrode and the negative electrode were molded into a tablet that was slightly smaller than the gasket, to produce a battery.
[0008]
However, although the battery manufactured in this way has superior characteristics compared to the conventional flat non-aqueous electrolyte secondary battery, it has characteristics when discharged at a large current required as a main power source for small portable devices. It was far from sufficient, and it was not a satisfactory level as a main power source for small portable devices.
[0009]
It is the subject of the present invention how to raise the heavy load discharge characteristics of a small flat nonaqueous electrolyte secondary battery to an unprecedented level, and the flat nonaqueous electrolyte secondary battery with outstanding heavy load discharge characteristics is outstanding. It is an object of the present invention to provide a battery.
[0010]
[Means for Solving the Problems]
As a result of intensive studies on the improvement of the heavy load discharge characteristics of the above-described flat nonaqueous electrolyte secondary battery, the present inventors have made the electrode area much larger than that of the conventional flat nonaqueous electrolyte secondary battery. It has been found that the heavy load discharge characteristics are dramatically improved.
[0011]
That is, a metal negative electrode case that also serves as a negative electrode terminal and a metal positive electrode case that also serves as a positive electrode terminal are fitted via an insulating gasket, and the positive electrode case or the negative electrode case is further crimped by crimping A flat nonaqueous electrolyte secondary battery including a non-aqueous electrolyte and a power generation element including an electrode group in which at least a positive electrode plate and a negative electrode plate are opposed to each other via a separator. The area of opposition of the active substance-containing layer of the positive electrode plate and the active substance-containing layer of the negative electrode plate (hereinafter sometimes referred to as “opposite area of the positive and negative electrodes” or simply “opposite area”) is the insulating gasket. It was found that a flat non-aqueous electrolyte secondary battery with significantly excellent heavy load discharge characteristics can be provided by making the opening area larger than the above.
[0012]
In order to improve heavy-load discharge characteristics, it is speculated that increasing the electrode area is effective, but in conventional flat non-aqueous electrolyte secondary batteries, one tablet-shaped positive electrode and one negative electrode are insulated gaskets. Therefore, the facing area where the positive and negative electrodes face each other through the separator inevitably has to be smaller than the opening area of the insulating gasket. Although it is possible to increase the electrode area somewhat by making the gasket thinner, it is theoretically impossible to store an electrode with an opposing area that exceeds the opening area of the gasket in the battery. there were.
[0013]
Therefore, the present inventors have made a bold change from the prior art, and arranged the electrodes in a battery case of a very small flat battery such as a coin shape or a button shape, so that the positive electrode in the electrode group is arranged. It is possible to accommodate an electrode group in which the total area of the negative electrode facing area is larger than the opening area of the insulating gasket. In other words, there are examples in which a secondary battery having a large volume, such as a cylindrical shape or a rectangular shape, contains electrodes having several tens of layers. However, these batteries have a complicated structure as described above, and the batteries of the batteries as they are. It has been difficult to apply the structure to a small flat nonaqueous electrolyte secondary battery such as a coin shape or a button shape. In addition, even if applied, it is impossible to maintain the advantages of flat nonaqueous electrolyte secondary batteries such as small size and excellent productivity. No attempt has been made in the past to accommodate an electrode group having a positive and negative electrode facing area larger than the opening area of the insulating gasket in the water electrolyte secondary battery.
[0014]
Hereinafter, how the present inventors have realized the flat nonaqueous electrolyte secondary battery of the present invention will be described. First, various forms are conceivable for accommodating an electrode in which the opposing area of the positive and negative electrodes is larger than the opening area of the gasket in the flat nonaqueous electrolyte secondary battery. It was found that it is preferable to store the electrodes as a group of electrodes stacked so as to have the positive and negative electrode facing portions in parallel. This is because, in order to obtain excellent heavy load discharge characteristics, the electrode area should be made as large as possible, the number of parts should be reduced as much as possible, the space in the small battery should be used effectively, and the electrode group and the amount required for discharge should be reduced. It is necessary to store the water electrolyte in the battery, and a storage method such as an electrode group in which electrodes are laminated so as to have a positive and negative electrode facing portion parallel to the flat surface as described above, for example, an active substance of a positive electrode plate It was found that these can be realized by adopting a storage method in which the electrode group has at least five positive and negative electrode facing surfaces in which the containing layer and the active substance containing layer of the negative electrode plate face each other with a separator interposed therebetween. In addition, according to this storage method, the battery assembly method excluding the electrodes is similar to the conventional flat battery manufacturing method using tablet-like electrodes, and it is possible to divert part of the conventional production equipment, as well as productivity and cost. In terms of practical use, it is excellent in terms of mass production.
[0015]
Next, regarding the method of actually producing and storing the electrode group, a positive electrode plate and a negative electrode plate provided with a current-carrying part in part of the electrode are prepared, and when the positive electrode plate and the negative electrode plate are laminated via a separator, Where the current-carrying part of the plate is exposed outside the part where the separator is arranged, and the part where the separator is arranged in a position where the current-carrying part of the negative electrode plate faces the position where the current-carrying part of the positive electrode plate is exposed After being laminated so as to be exposed to the outside, the positive electrode is electrically connected to each other by the positive electrode, and the negative electrode is electrically connected to each other by a method such as welding to form an electrode group and housed in the battery. By arranging the current-carrying part of the positive electrode plate and the current-carrying part of the negative electrode plate as described above, even in a small flat nonaqueous electrolyte secondary battery such as a coin shape or a button shape, Internal short circuit due to contact with the current-carrying part can be prevented.
[0016]
Next, a method for connecting the electrode group and the battery metal case that also serves as an external terminal will be described. As described above, in a relatively large lithium ion secondary battery such as a cylindrical shape or a rectangular shape, a tab terminal is welded to the center portion or winding core portion of the electrode group, bent, and then welded to a safety element or a sealing pin. I am collecting current. However, since the process itself is complicated, the bending process is inferior in productivity, and it is necessary to provide a space in the battery or to insert an insulating plate between the electrodes in order to prevent an internal short circuit. In addition, if stress is applied to the part where the tab terminal is welded to the electrode, the separator will break through or the electrode will be deformed, so it is necessary to protect it with insulating tape, or to provide a space in the winding core. Could not be used effectively. Therefore, these current collection methods cannot be applied to a coin-type or button-type flat non-aqueous electrolyte secondary battery having a small battery internal volume, and it is necessary to devise a new current collection method.
[0017]
Therefore, the present inventors expose the positive electrode constituent material having conductivity in the positive electrode plate located at the outermost part of the electrode group, and the negative electrode constituent material having conductivity in the negative electrode plate located at the outermost part of the electrode group. It was found that an electrode group having an exposed shape was prepared, and each electrode component was brought into contact with the positive and negative battery cases, thereby ensuring current collection between the electrode group and the battery case. According to this method, there is no need to provide a useless space or an insulating plate between the electrode group and the battery case, and the discharge capacity can be increased. In addition, the battery case or electrode and the tab terminal do not cause a short circuit, and the safety and reliability are excellent.
[0018]
Further, in a flat battery having a sealing structure as in the present invention, stress is applied in a direction perpendicular to the flat surface of the negative electrode case and the positive electrode case by the caulking process of the battery case. A uniform applied pressure is applied in the plane direction, and charging and discharging can be performed smoothly. In addition, the contact between the electrode component exposed portion of the electrode group and the electrode case may be in direct contact, or in indirect electrical contact through a metal foil, metal net, metal powder, carbon filler, conductive paint, or the like. It may be.
[0019]
Next, as for the electrode, both the positive electrode plate and the negative electrode plate are preferably prepared by applying a slurry mixture to a metal foil and drying it in that it is easy to produce a thin electrode. it can. When using an electrode in which a mixture layer containing an active substance is applied to the metal foil as described above, an electrode used inside the electrode group is one in which an active substance-containing layer is formed on both sides of the metal foil. It is preferable from the viewpoint of volumetric efficiency, and the electrode component exposed portion that contacts the battery case at both ends of the electrode group may be an active substance-containing layer, but in order to reduce contact resistance, among the electrode components, particularly metal foil is used. It is preferable to expose. In this regard, an electrode in which an active substance-containing layer is formed only on one side may be used only in this portion, or after an active substance-containing layer is once formed on both sides, the active substance-containing layer may be removed only on one side.
[0020]
On the other hand, the battery of the present invention focuses on the structure of the battery including the electrode, and the positive electrode active material is not limited. MnO ₂ , V ₂ O ₅ , Nb ₂ O ₅ , LiTi ₂ Metal oxides such as O ₄ , Li ₄ Ti ₅ O ₁₂ , LiFe ₂ O ₄ , LiMn ₂ O ₄ , Li ₄ Mn ₅ O ₁₂ , Li _0.33 MnO ₂ , lithium cobaltate, lithium nickelate, lithium manganate Alternatively, any of inorganic compounds such as graphite fluoride and FeS ₂ or organic compounds such as polyaniline and polyacene structures can be applied. However, lithium-containing oxides in which lithium cobaltate, lithium nickelate, lithium manganate, mixtures thereof, or some of these elements are substituted with other metal elements are high in terms of operating potential and excellent cycle characteristics. Lithium cobaltate is a flat type non-aqueous electrolyte secondary battery that is more preferable and may be used for a long period of time because it has a high capacity, is low in reactivity with electrolytes and moisture, and is chemically stable. Is more preferable.
[0021]
Further, the negative electrode active substance of the battery of the present invention is not limited, and is lithium metal, Li—Al, Li—In, Li—Sn, Li—Si, Li—Ge, Li—Bi, Li—Pb, or the like. Lithium alloys, organic compounds such as polyacene structures, carbonaceous materials capable of occluding and releasing lithium, Nb ₂ O ₅ , LiTi ₂ O ₄ , Li ₄ Ti ₅ O ₁₂ , Li-containing silicon oxides and Li Oxides such as tin oxide and nitrides such as Li ₃ N can be applied, but Li is occluded and released in terms of excellent cycle characteristics, low operating potential, and high capacity. Possible carbonaceous materials are preferable, and natural graphite, artificial graphite, expanded graphite, mesophase pitch fired body, in particular, because the decrease in battery operating voltage is small even at the end of discharge Carbonaceous material spacing of d _002, such as mesophase pitch fiber sintered bodies following graphite structure 0.338nm has developed is more preferable.
[0022]
In the above-described battery of the present invention, a flat battery having a battery outer diameter that is long with respect to the total battery height such as a coin shape or a button shape has been described. However, the battery of the present invention is not limited to this and is not limited to a small size. The present invention can also be applied to a flat battery having a special shape such as a shape or a square.
[0023]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, examples and comparative examples of the present invention will be described in detail.
(Reference Example 1)
A method for manufacturing the battery of Reference Example 1 will be described with reference to the cross-sectional view of FIG.
[0024]
First, to 100 parts by weight of LiCoO ₂ , 5 parts by weight of acetylene black and 5 parts by weight of graphite powder are added as a conductive agent, 5 parts by weight of polyvinylidene fluoride is added as a binder, and diluted and mixed with N-methylpyrrolidone. A slurry-like positive electrode mixture was obtained. Next, this positive electrode mixture is coated on one side of a 0.02 mm thick aluminum foil, which is a positive electrode current collector (conductive positive electrode constituent material) 2a, and dried by a doctor blade method. A positive electrode active material-containing layer 2b was formed on the substrate. Thereafter, coating and drying were repeated until the coating thickness of the active substance-containing layer became 0.39 mm, to produce a single-side coated positive electrode plate. Next, by applying the same method as this single-side coated positive electrode plate, both surfaces of the aluminum foil were coated so that the coating thickness of the positive electrode active material-containing layer was 0.39 mm per one side to produce a positive electrode plate.
[0025]
Next, 2.5 parts by weight of styrene butadiene rubber (SBR) and carboxymethyl cellulose (CMC) are added as binders to 100 parts by weight of graphitized mesophase pitch carbon fiber powder, diluted with ion-exchanged water, mixed and slurried. A negative electrode mixture was obtained. When this negative electrode mixture is used as a positive electrode so that the thickness of the active substance-containing layer 4b is 0.39 mm on a copper foil having a thickness of 0.02 mm which is a negative electrode current collector (negative electrode constituent material having conductivity) 4a Similarly, coating and drying were repeated to produce a single-side coated negative electrode plate. Next, a double-sided coated negative electrode plate was prepared by the same method as this single-sided coated negative plate so that the coating thickness of the negative electrode active material-containing layer on both sides of the copper foil was 0.39 mm per side.
[0026]
These electrodes were cut into a shape having a protruding portion with a width of 6 mm and a length of 2 mm on one side of a square having a width of 13 mm and a length of 13 mm, and then the active substance-containing layer formed on the protruding portion was scraped off to obtain an aluminum layer. Alternatively, a copper layer was exposed to form an energization portion, and a positive electrode plate and a negative electrode plate coated on both sides and one side, on which an active substance-containing layer having a width of 13 mm and a length of 13 mm was formed, were produced.
[0027]
Next, a double-sided coated negative electrode plate is placed on the positive electrode active material containing layer forming part of the single-sided coated positive electrode plate through a separator 3 made of a polyethylene microporous film having a thickness of 25 μm at a position where the energizing part faces the positive electrode plate. Furthermore, the double-sided coated positive electrode plate is placed through the separator 3 so that the current-carrying part faces in the same direction as the previous positive electrode plate, and the negative electrode active substance-containing layer 4b is in contact with the separator surface through the separator 3. In this way, the current-carrying part of the single-side coated negative electrode plate was placed so as to face the same direction as the previous negative electrode plate, and the positive electrode current-carrying part and the negative electrode current-carrying part were welded respectively to produce an electrode group.
[0028]
After the produced electrode group was dried at 85 ° C. for 12 hours, one-side coating of the electrode group was applied to the inner bottom surface of the negative electrode metal case 5 integrated with the insulating gasket 6 having an opening diameter of 20 mm and an opening area of 3.14 cm ^2. uncoated side of the negative electrode plate (i.e., the negative electrode current collector 4a) arranged so that contact, the volume of ethylene carbonate and methyl ethyl carbonate ratio of 1: a LiPF ₆ 1 mol as a supporting salt in a mixed solvent at a ratio of 1 / The nonaqueous electrolyte dissolved at a ratio of 1 is injected, and the stainless steel positive electrode case 1 is fitted so as to be in contact with the uncoated side of the single-side coated positive electrode plate of the electrode group (that is, the positive electrode current collector 2a). Then, after flipping upside down, the positive electrode case was crimped and sealed to produce a flat nonaqueous electrolyte secondary battery of Reference Example 1 having a thickness of 3 mm and a diameter of 24.5 mm. The total number of opposing surfaces of the active substance-containing layer of the positive electrode plate and the active substance-containing layer of the negative electrode plate through the separator of this battery is three, and the active substance-containing layer of the positive electrode plate and the active substance content of the negative electrode plate are contained. The sum total of the area facing the layer is 5.1 cm ² .
[0029]
(Example 2)
The coating thickness of the active substance-containing layer per one side of the positive electrode plate and the negative electrode plate in the electrode group is 0.22 mm, respectively, and the number of laminated double-coated positive electrode plates and double-coated negative electrode plates in the middle part of the electrode group A battery was prepared in the same manner as in Reference Example 1 except that the number of each was two. The total number of opposing surfaces of the active substance-containing layer of the positive electrode plate and the active substance-containing layer of the negative electrode plate through the battery separator is five, and the active substance-containing layer of the positive electrode plate and the active substance content of the negative electrode plate are contained. The sum total of the area facing the layer is 8.5 cm ² .
[0030]
(Example 3)
The coating thickness of the active substance-containing layer per one side of the positive electrode plate and the negative electrode plate in the electrode group is 0.15 mm, respectively, and the number of laminated double-coated positive electrode plates and double-coated negative electrode plates in the middle part of the electrode group A battery was produced in the same manner as in Reference Example 1 except that the number of each was three. The total number of opposing surfaces of the active substance-containing layer of the positive electrode plate and the active substance-containing layer of the negative electrode plate through the separator of the battery is seven, and the active substance-containing layer of the positive electrode plate and the active substance content of the negative electrode plate are contained. The sum total of the area facing the layer is 11.8 cm ² .
[0031]
Example 4
The coating thickness of the active substance-containing layer per one side of the positive electrode plate and the negative electrode plate in the electrode group is 0.11 mm, respectively, and the number of laminated double-coated positive electrode plates and double-coated negative electrode plates in the middle part of the electrode group A battery was prepared in the same manner as in Reference Example 1 except that the number of each was four. The total number of opposing surfaces of the active substance-containing layer of the positive electrode plate and the active substance-containing layer of the negative electrode plate through the separator of the battery is nine, and the active substance-containing layer of the positive electrode plate and the active substance content of the negative electrode plate are contained. The sum total of the area facing the layer is 15.2 cm ² .
[0032]
(Comparative Example 1)
Add 5 parts by weight of acetylene black and 5 parts by weight of graphite powder as a conductive agent to 100 parts by weight of LiCoO ₂ , add 5 parts by weight of polytetrafluoroethylene as a binder, mix, grind, An agent was obtained. Next, this positive electrode granule mixture was pressure-molded to a diameter of 19 mm and a thickness of 1.15 mm to obtain a positive electrode tablet.
[0033]
Next, 2.5 parts by weight of styrene butadiene rubber (SBR) and carboxymethyl cellulose (CMC) as binders are added to 100 parts by weight of graphitized mesophase pitch carbon fiber powder, mixed, dried, and further pulverized to form granules. A negative electrode mixture was obtained. This negative electrode granule mixture was pressure-molded to a diameter of 19 mm and a thickness of 1.15 mm to obtain a negative electrode tablet.
[0034]
Next, after drying these positive and negative electrode tablets at 85 ° C. for 12 hours, a negative electrode case integrated with an insulating gasket having an opening area of 3.14 cm ² , a negative electrode tablet, a polypropylene non-woven fabric having a thickness of 0.2 mm, and a positive electrode tablet In this order, a nonaqueous electrolyte in which LiPF ₆ was dissolved at a rate of 1 mol / l as a supporting salt was poured into a solvent in which ethylene carbonate and methyl ethyl carbonate were mixed at a volume ratio of 1: 1. The positive electrode case was fitted, and after inverting upside down, the positive electrode case was crimped to produce a flat nonaqueous electrolyte secondary battery of Comparative Example 1 having a thickness of 3 mm and a diameter of 24.5 mm. The number of the positive and negative electrode facing surfaces through the separator of this battery is one, and the total of the facing areas of the positive and negative electrodes is 2.8 cm ² .
[0035]
(Comparative Example 2)
A battery was fabricated in the same manner as in Reference Example 1 except that the positive electrode plate and the negative electrode plate in the electrode group were only single-sided coated electrode plates, and the coating thickness of the active substance-containing layer was 1.24 mm. The total number of opposing surfaces of the active substance-containing layer of the positive electrode plate and the active substance-containing layer of the negative electrode plate through the battery separator is one, and the active substance-containing layer of the positive electrode plate and the active substance content of the negative electrode plate are contained. The sum total of the area facing the layer is 1.7 cm ² .
[0036]
The batteries of this example, reference example, and comparative example manufactured as described above were initially charged for 48 hours at a constant current and a constant voltage of 4.2 V and 3 mA. Thereafter, discharging was performed to 3.0 V at a constant current of 30 mA, and the heavy load discharge capacity was determined. The results are shown in Table 1.
[0037]
[Table 1]

[0038]
As is apparent from Table 1, each battery of the present example is a battery in which the opposing area of the positive and negative electrodes using the tablet-like electrode produced by the conventional granule mixture molding method of Comparative Example 1 is smaller than the opening area of the gasket. In addition, the active material containing layer of the positive electrode plate of Comparative Example 2 and the active material containing layer of the negative electrode plate have only one facing surface, and the discharge capacity during heavy load discharge is significantly larger than a battery having a small facing area.
[0039]
In the examples of the present invention, a flat nonaqueous solvent secondary battery using a nonaqueous solvent as a nonaqueous electrolyte has been described. However, a polymer secondary battery or a solid electrolyte using a polymer electrolyte as a nonaqueous electrolyte is described. Naturally, the present invention can also be applied to a solid electrolyte secondary battery using a polymer thin film, and a polymer thin film or a solid electrolyte membrane can be used instead of the resin separator. Further, the battery shape has been described based on the coin-type non-aqueous electrolyte that is sealed by crimping the positive electrode case, but it is also possible to replace the positive and negative electrodes and seal the negative electrode case by the crimping process. Further, the battery shape does not have to be a perfect circle, and can be applied to a flat nonaqueous electrolyte secondary battery having a special shape such as an oval shape or a square shape.
[0040]
【The invention's effect】
As described above, according to the present invention, the discharge capacity at the time of heavy load discharge is significantly larger than that of the conventional battery while maintaining the advantages that the flat battery has a small battery size and excellent productivity. Therefore, a flat nonaqueous electrolyte secondary battery having excellent industrial value can be provided.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a battery of a reference example.
2 is a cross-sectional view of a battery of Comparative Example 1. FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Positive electrode case 2 Positive electrode 2a Positive electrode collector 2b Positive electrode active material content layer 3 Separator 4 Negative electrode 4a Negative electrode current collector 4b Negative electrode active material content layer 5 Negative electrode case 6 Insulation gasket

Claims

A metal negative electrode case that also functions as a negative electrode terminal and a metal positive electrode case that also functions as a positive electrode terminal are fitted via an insulating gasket, and the positive electrode case or the negative electrode case is further crimped by caulking. And a flat nonaqueous electrolyte secondary battery containing a non-aqueous electrolyte and a power generation element including an electrode group in which at least a positive electrode plate and a negative electrode plate are laminated in a multilayer manner with a separator interposed therebetween. ,
The positive electrode plate contains a positive electrode active substance formed by applying and drying a slurry-like positive electrode mixture containing at least a positive electrode active substance on one or both sides of a metal foil which is a positive electrode constituent material having conductivity. Having an active substance-containing layer, and having a current-carrying part in which a part of the positive electrode constituent material is exposed without the active substance-containing layer being present,
The negative electrode plate contains a negative electrode active substance formed by applying and drying a slurry-like negative electrode mixture containing at least a negative electrode active substance on one or both sides of a metal foil which is a negative electrode constituent material having conductivity. Having an active substance-containing layer, and having a current-carrying part where a part of the negative electrode constituent material is exposed without the active substance-containing layer being present,
In the electrode group, the positive electrode plate, the negative electrode plate, and the separator are laminated in parallel to the flat surface of the battery, and each energization portion of the positive electrode plate is exposed to the outside of the place where the separator is disposed. And each energization part of the negative electrode plate is exposed to the outside of the position where the separator is disposed at a position opposite to the position where each energization part of the positive electrode plate is exposed. The negative electrode plates are connected to each other by electrical connection of the current-carrying portions, and the active substance-containing layer of the positive electrode plate and the active substance of the negative electrode plate are opposed to each other with the separator interposed therebetween. There are at least five surfaces facing the containing layer,
The facing area between the active substance-containing layer of the positive electrode plate and the active substance-containing layer of the negative electrode plate in the electrode group is larger than the opening area of the insulating gasket,
The positive electrode plate located at the outermost part of the electrode group has a positive electrode constituent material having conductivity exposed on the outermost surface of the electrode group, and the positive electrode constituent material is directly or electrically connected to the positive electrode case. Connected to and / or
The negative electrode plate located at the outermost part of the electrode group has a conductive negative electrode component exposed on the outermost surface of the electrode group, and the negative electrode component is directly or electrically connected to the negative electrode case. A flat non-aqueous electrolyte secondary battery characterized by being connected to.

The positive electrode plate has an active substance-containing layer formed on both sides of the metal foil, and the active substance-containing layer is not pre-coated on the surface directly or electrically in contact with the metal positive electrode case, or flat-shaped non-aqueous electrolyte secondary battery according to claim 1, wherein having the removed structure after application.

The negative electrode plate has an active substance-containing layer formed on both sides of the metal foil, and the active substance-containing layer is not pre-coated on the surface directly or electrically in contact with the metal negative electrode case, or flat-shaped non-aqueous electrolyte secondary battery according to claim 1, wherein having the removed structure after application.

2. The flat nonaqueous electrolyte secondary battery according to claim 1, wherein the positive electrode active material is a lithium-containing oxide.

The flat nonaqueous electrolyte secondary battery according to claim 4 , wherein the positive electrode active material is lithium cobalt oxide.

2. The flat nonaqueous electrolyte secondary battery according to claim 1, wherein the negative electrode active substance is a carbonaceous material.

The flat nonaqueous electrolyte secondary battery according to claim 6, wherein the negative electrode active material is a carbonaceous material having a d ₀₀₂ plane spacing of 0.338 nm or less.