JP4622019B2

JP4622019B2 - Flat battery

Info

Publication number: JP4622019B2
Application number: JP2000011452A
Authority: JP
Inventors: 義高松政; 昌彦小川; 英明吉尾; 裕明 ▲今▼西
Original assignee: Panasonic Corp; Matsushita Electric Industrial Co Ltd
Current assignee: Panasonic Corp; Panasonic Holdings Corp
Priority date: 1999-01-20
Filing date: 2000-01-20
Publication date: 2011-02-02
Anticipated expiration: 2020-01-20
Also published as: JP2001093489A

Description

【０００１】
【発明の属する技術分野】
本発明は、電解質を保持したセパレータ材料にポリマーを用いた、いわゆるリチウムポリマー二次電池等に適用される、薄い樹脂フィルム主体のラミネートシートで袋状外装ケースを構成し、これで積層一体化した扁平な積層電極部分を包み込んだ電池に関する。さらに詳しくは、外装ケースの一部に施すシート状の安全弁部材に関するものである。
【０００２】
【従来の技術】
樹脂フィルムの間に金属箔を配して全体を積層一体化したラミネートシートからなる外装ケースを使用した電池は、従来より知られている。
【０００３】
図５は、このラミネートシート製外装ケースを用いた従来の電池の断面構造を示している。即ち、図５に示す従来例は、１枚の負極板２の両側にセパレータ３を介して２枚の正極板１を積層一体化した積層電極４を備え、一対のラミネートシート１５，１６の周囲Ｐ（図５では対向する２辺のＰ１とＰ３を示す）を加熱溶着することにより、前記積層電極４を密封する外装ケース１７を構成したものである。正極板１は正極集電体１ａの片面に正極活物質層１ｂを塗着して構成され、負極板２は負極集電体２ａの両面に負極活物質層２ｂを塗着して構成されている。この負極板２の両側にそれぞれポリマー製なるセパレータ３を介して正極板１を配して全体を積層一体化することにより積層電極４が構成される。
【０００４】
前記正極集電体１ａには図示しないが正極リードが接続され、その先端部はラミネートシート１５，１６相互のシール部の１カ所を通過して外部に引き出されている。負極集電体２ａにも同様に負極リードが接続され、その先端部はシール部を通過して外部に引き出されている。
【０００５】
一対のラミネートシート１５，１６は、金属箔、例えばアルミニウム箔の一方面側に熱溶着樹脂層、例えばポリプロピレンフィルムを、他方面側に機械的強度に優れた樹脂層、例えば伸延処理したポリアミドフィルムまたはポリエチレンテレフタレートフィルムをそれぞれ積層一体化して形成されたもので、ラミネートシート１５，１６相互間のシールは熱溶着樹脂層どうしの熱溶着によってなされる。具体的な熱溶着は、その重ねた周囲Ｐの熱溶着樹脂層を密着させた状態で、加熱冶具により加圧、加熱することで行われる。
【０００６】
【発明が解決しようとする課題】
前記のようなラミネートシート製外装ケースを用いた電池は、通常の使用状態においては優れた密閉性を発揮する。しかし電池の異常使用時、特に過充電や異常高温での放置状態においては、電池の発熱や外部の温度上昇によりそれまで電極やポリマーセパレータに保持されていた電解液が分解してガスが発生し、外装ケースの内圧が高まって外装ケースが著しく変形することで、ケース内部の積層電極自体も変形し始めて内部短絡に至るという問題があった。このため、ラミネートシート製外装ケースのシール部の一部に他の部分よりも剥離強度の小さい（弱い）部分を設け、ケース内部のガス圧力が前記剥離強度を上回ったときここを剥離させ、ケース内側からガスを逃がすことが、例えば特開平１０−５５７９２号公報で提案されている。この例はケース内部のガス圧力を感知して変形し始めたケースのシール部の一部を開放するもので、前記の小さい剥離強度と変形による電池の内部短絡発生とを関連づけることが難しく、内部短絡発生以前に確実にケースシール部を開放させることはできない。
【０００７】
本発明の主たる目的は、樹脂フィルム主体のラミネートシート製外装ケースの一部に温度感知タイプの安全弁部材を設けることで、電池の異常使用時、特に過充電や異常高温放置状態において、その異常高温を感知して安全弁が開弁動作し、電池内部で発生したガスを速やかに外部に放出することにより高い安全性を備えた電池を提供することにある。
【０００８】
【課題を解決するための手段】
本発明の電池の構成は、それぞれシート状またはフィルム状の正極板、電解質を保持するポリマー製セパレータおよび負極板を積層一体化した扁平な積層電極を、アルミニウム箔を中央に配してその両面に樹脂フィルムを接合したラミネートシート、好ましくは内側から外側に向けて順にポリプロピレンフィルム、アルミニウム箔、二軸延伸処理したポリアミド（ナイロン）フィルムまたはポリエチレンテレフタレートフィルムをラミネートしたシートにより形成された外装ケースに封入するとともに、前記正極板および負極板にそれぞれ一端が接続された正極リードおよび負極リードを、前記外装ケースのシール部の一部より外部に引き出し、正極リード部または負極リード部かあるいは両者間のシール部の一部に、ポリプロピレンよりも実質的に融点の低い樹脂からなる温度感知タイプの安全弁部材を組み込んだものである。
【０００９】
ここでの安全弁部材は、前記外装ケースのシール部の一部に、ラミネートシートの最内側樹脂フィルムであるポリプロピレンと熱溶着性を有する樹脂フィルム、例えばポリプロピレンを上下の外層とし、ポリプロピレンよりも低融点の樹脂フィルム、例えば変性ポリエチレンフィルムを内層にもつ３層構造の多層シートを一体に組み込んだものである。あるいはまたポリプロピレンよりも低融点の樹脂、例えばエチレンアクリル酸共重合体（ＥＡＡ）の単独樹脂シートからなる安全弁部材をシール部の一部に組み込んだものである。
【００１０】
これにより、短絡や過充電などの電池の誤使用や、異常高温での放置状態における電池温度の上昇によって、ラミネートシートのシール部の一部に安全弁として組み込まれた多層シートの低融点フィルムか、またはＥＡＡのシートが軟化溶融を開始し、電池内の圧力上昇によってその形状を変形し始めて、多層シートのフィルム間またはラミネートシートのシール部を開口させることができる。従って電池内で圧力上昇したガスは、この開口したシール部から速やかにケース外部に排出でき、電池の急激な温度上昇や電池内圧の急上昇を効果的に抑制し、これらに起因した電池の内部短絡を防止することが可能となる。
【００１１】
多層シートの配置位置としては、外部へ引き出される正極リード、負極リード間のラミネートシートのシール部以外に、多層シートが正極リード、負極リードの両方あるいは、どちらか一方のリードをとり囲むように取り付けられ、その表面部分が外装ケース最内側のポリプロピレンフィルムと熱溶着されている場合においても、前記同様に安全弁部材としての機能を果たすことができる。また多層シートの内層をなす低融点樹脂フィルムとしては、前記の変性ポリエチレンのほかに、ＥＡＡ、エチレンメタクリル酸共重合体（ＥＭＡ）、変性ポリプロピレンおよびポリアリレートを用いることができる。
【００１２】
さらに、ＥＡＡ、変性ポリプロピレン、ポリアリレートなどを用いる場合は、多層シートの１層としてのほか、前記のようにそれ単独で安全弁部材とすることができる。単独で安全弁部材として用いる熱溶着樹脂フィルムあるいはシートは、ケースのシール部に挟み込むことからその厚さは２０μｍ〜１００μｍが好ましく、さらにその融点はケースを構成するラミネートシートのそれよりも適度な温度間隔、例えば２０℃〜４０℃低い８０℃〜１１０℃にあることが、電池の急激な温度上昇や電池内圧の上昇につれた温度に感応して軟化溶融変形し、ガスを外部に逃がす経路を作って、ケースの変形に起因した電池の内部短絡を防止する上からも好ましい。
【００１３】
また、前記３層構造の多層シートの場合、より温度に感応し易くするには内層の樹脂フィルムを、低融点樹脂群の中から異なった融点の２種を選んで併用し、これらとその外側の外層樹脂フィルムとの融点差をはっきりさせるとよい。
【００１４】
さらに多層シートの外層をなす熱溶着樹脂フィルムとしては、ラミネートシートと溶着し合い、この間を液密、気密に保つ上からラミネートシートと同タイプの樹脂フィルム、もしくはラミネートシートの内層樹脂フィルムとの熱溶着性が良好な樹脂フィルムが好ましい。
【００１５】
【発明の実施の形態】
以下、図面を引用して本発明の実施形態について説明する。ここでの実施形態は、扁平なリチウムポリマー二次電池に適用した例を示すもので、図１〜図４によって説明する。なお、図には従来例と共通する要素には同一の符号を付した。本実施形態に示すラミネートシート製の袋状外装ケースを用いたリチウムポリマー二次電池は、図１の平面図に示すように、扁平な積層電極４の正極側リード接続部１ｃに接続された正極リード８、負極リード接続部２ｃに接続された負極リード９のそれぞれの先端を外装ケースの外部に引き出している。このために１枚のラミネートシートをその中央折り曲げ線Ｔに沿って長さ方向に２つ折りにした２面５，６で積層電極４を包み込み、前記中央折り曲げ線Ｔの辺を除く３辺Ｐ１、Ｐ２、Ｐ３を熱溶着によりシールした袋状の外装ケース７で密封している。このとき、リード引き出し部である１辺Ｐ２のシール部、詳しくは正極リードと負極リードの間の一部に、ラミネートシート最内側のポリプロピレンフィルムよりも低融点の変性ポリエチレンフィルムと、その外側に配したラミネートシートのポリプロピレンフィルムと同タイプのポリプロピレンフィルムの合計３層からなる多層シート１０を挟み込んで、辺Ｐ２のシール時に同時熱溶着して、安全弁部材としている。ここでの積層電極４および外装ケースのシール構造は、図１のＡ−Ａ線に沿った断面図である図２に示すように構成されている。
【００１６】
図３は、前記２枚のポリプロピレンフィルムと１枚の変性ポリエチレンフィルムの３層を一体にラミネートした多層シートの断面図である。この多層シートの厚さは、ケース側のラミネートシートの厚さや熱溶着条件にも影響されるが、熱溶着後でも安全弁部材として機能する３層一体構造を維持するためにはポリプロピレンフィルムの厚さは１０μｍ〜５０μｍ、ポリエチレンフィルムのそれは２０μｍ〜１００μｍに保つとよい。
【００１７】
また図２において、積層電極４は、従来例同様１枚の負極板２の両側にポリマー製セパレータ３を介して２枚の正極板１を、積層一体化して約６００μｍの厚さに構成されている。具体的には、２枚の正極板１は、それぞれ正極活物質１ｂを正極集電体１ａの片面に塗着して構成され、同じく負極板２は中央の負極集電体２ａの両面に負極活物質２ｂを塗着して構成される。そして正極板１と負極板２との間に電解液を保持するポリマー製フィルムからなるセパレータ３を配して全体を熱溶着により一体化している。なおセパレータ３には、ポリマー製フィルムのほか多孔質シートからなる担体に、電解液を含んで自らがゲル状態を呈するポリマーを塗着、含浸させたものを用いることもできる。
【００１８】
さらに、正極集電体１ａはアルミニウムまたは導電性材料にアルミニウムをコーティングした素材のパンチングメタルまたはラスメタルからなり、その表面に導電性炭素材であるアセチレンブラックまたはケッチェンブラックと、結着材であるポリフッ化ビニリデンとの混合物を塗着一体化させたものである。また、負極集電体２ａは銅、ニッケルまたは導電性材料に銅あるいはニッケルをコーティングした素材のパンチングメタルまたはラスメタルからなり、その表面に正極集電体１ａと同様の導電性炭素材を塗着一体化させている。
【００１９】
前記の正極活物質層１ｂおよび負極活物質層２ｂは、活物質粉末、導電剤およびポリマー溶液からなるペーストを正極、負極集電体にそれぞれ塗着、乾燥して作製した。
【００２０】
積層電極４を構成する２枚の正極板１の集電体１ａのそれぞれには、図１に示すように、一方側に偏位（図では上方向）した位置に、正極リード８を接続するための正極側リード接続部１ｃが延出形成され、負極板２の負極集電体２ａにも他方側（下方向）に偏位した位置に負極リード９を接続するための負極側リード接続部２ｃが延出形成されている。正極側リード接続部１ｃにはアルミニウム薄板で形成されたリボン状正極リード８が、負極側リード接続部２ｃには銅薄板で形成されたリボン状負極リード９が、それぞれ溶接点Ｓで抵抗溶接または超音波溶接されている。
【００２１】
この実施形態では、図２に示すように、正極板１は２枚用いているので、それぞれの正極側リード接続部１ｃは、上下に重なり１本のリボン状正極リード８に溶接点Ｓで同時に接合される。このように構成される積層電極４をより多くの枚数積層して１つの積層電池を構成する場合には、積層枚数に対応して正極側リード接続部１ｃ、負極側リード接続部２ｃの複数を接合すればよい。
【００２２】
前記正極リード８および負極リード９の一部には、図１に示すように、金属との接着性のよい熱溶着性樹脂として変性ポリプロピレンフィルム１２，１３がそれぞれ取り付けられている。この変性ポリプロピレンフィルム１２，１３は、２枚のフィルムによりそれぞれリード８，９を挟んで重ね合わせ、温度２００℃、圧力０．１ＭＰａを加えた状態を３０秒間維持して液密、気密に取り付けた。このフィルム１２，１３は、外装ケース７の１辺のシール部Ｐ２の通過位置に対応してシール部よりも広幅でリード８，９を被覆したものである。通常のポリプロピレンでは金属との接着性に乏しいが、酸変性処理などによってポリプロピレン骨格に官能基を導入して変性ポリプロピレンとすることにより、対金属接着性が向上し、前記のように加熱、加圧が加えられることによってそれぞれ正極リード８、負極リード９の表面に完全に接着してリード８，９の表面の一部を被覆する。
【００２３】
また、多層シート１０はラミネートシートのシール部Ｐ２のシール幅よりも長い短冊状に切断し、リード８，９を被覆する変性ポリプロピレンフィルム１２，１３の間のシール部Ｐ２の一部に、シール部Ｐ２を横断するように挟み込む。そして、熱溶着によるシール部Ｐ２の形成時に、リード８，９を被覆する変性ポリプロピレンフィルム１２，１３と同時にこの多層シート１０を溶着すると作業性が向上する。
【００２４】
このように変性ポリプロピレンフィルム１２，１３で被覆された正極リード８、負極リード９および多層シート１０を折り重ねられる２面のラミネートシート５，６の端縁で挟んでシールすると、１辺Ｐ２のシール部ではシート内層のポリプロピレンおよび多層シートの外装ポリプロピレンとの樹脂相互の熱溶着と同時に、各リード８，９の通過部位ではポリプロピレンと変性ポリプロピレンフィルム１２，１３とが熱溶着される。
【００２５】
従って、一辺Ｐ２のシール部から各リード８，９を外部に引き出しても、この部分の外装ケース７としての密閉性は十分に保持される。
【００２６】
また図４に示すように安全弁部材として作用する多層シート１０は、各リード８，９のそれぞれの一部を取り囲むように、金属との接着性のよい熱溶着樹脂として施してもよい。またその設置は両方のリードではなく一方のリードにのみ取り付けてもよい。この場合、多層シート１０は２枚のフィルム状に切断し、少なくとも一方のリード８または９を挟んで重ね合わせ、温度２００℃、圧力０．１ＭＰａを加えた状態を３０秒間維持して液密、気密に取り付けた。
【００２７】
安全弁部材として機能し、ラミネートシートの熱溶着側フィルムである変性ポリプロピレンよりも低融点である多層シートの内層熱溶着樹脂としては、前記の変性ポリエチレンのほか、ＥＡＡ、エチレンメタクリル酸共重合体、変性ポリプロピレンおよびポリアリレートの群から選ばれた１種が使用できる。
【００２８】
また、ケースをなすラミネートシートには、アルミニウム箔等の金属箔を中央に配して、その両面に熱溶着樹脂フィルムを接合したものが使用でき、その熱溶着側樹脂フィルムとしては、ポリプロピレン、変性ポリプロピレンが使用できる。ラミネートシートの外側樹脂フィルムとしては、ポリエチレンテレフタレート、熱溶着性ポリイミド、ポリメタクリル酸メチル、伸延処理したポリアミド（ナイロン）等の樹脂、あるいはこれらの２種以上の樹脂を共重合させたものを採用することができる。このような金属箔を含むラミネートシートは、金属箔によりガスバリアー性や光遮断性が向上し、最内側樹脂層の熱溶着によるシールが容易となる特徴を備えている。
【００２９】
次にラミネートシートの３辺の熱溶着シールにより形成される袋状外装ケース７で、扁平な積層電極４を密封したリチウムポリマー二次電池を、その作製手順に沿って次に説明する。
【００３０】
上述のように正極側リード接続部１ｃおよび負極側リード接続部２ｃにそれぞれ一端が溶接された正極リード８、負極リード９に前記変性ポリプロピレンフィルム１２，１３が熱溶着によって取り付けられた積層電極４は、２つ折りされたラミネートシートの２面５，６が対向する２辺のシール部Ｐ１、Ｐ３が熱溶着によりシールされて封筒状に形成された外装ケース７内に挿入される。
【００３１】
ついで積層電極４を内包して封筒状になった外装ケース７のまだシールされていない残り１辺のシール部Ｐ２から所定量の電解液が注入され、各リード８，９の間のシール部Ｐ２に多層シート１０を挟みこんだ後、この１辺Ｐ２も熱溶着する。
【００３２】
このとき、正極リード８および負極リード９の一部を被覆する変性ポリプロピレンフィルム１２，１３も同時に溶着され、正極リード８および負極リード９の先端部が外装ケース７から突出するようになる。このようにして作製した本発明の電池をａ、および安全弁部材を持たない従来電池をｂとして、これらの安全性について評価を行なった。
【００３３】
試験方法としては、昇温装置付きの恒温槽を用いて一定の温度上昇速度（５℃／分）で１６０℃まで昇温し、さらに１６０℃で３時間放置することとし、そのときの電池の内部短絡の発生数を評価した。
評価電池ａ，ｂは各２０個ずつ用意し、試験した結果を（表１）に示す。
【００３４】
【表１】

【００３５】
（表１）より明らかなように本発明の電池ａは内部短絡が十分に防止されていることがわかる。一方、従来電池ｂでは評価資料の６０％で内部短絡が発生していた。
【００３６】
従来電池ｂでは電池が異常高温に放置された状態において、電池内で電解液などの分解により大量のガスが発生し、それに伴い薄く平坦であった電池の外装ケースが中高状態（焼餅形状）に膨らんで変形する。このときケース内の積層電極も外装ケースの変形に追従するように変形し始めて正極、負極間で短絡を生じ、ガス発生が増長される。
【００３７】
それに対して本発明の電池ａでは、異常高温状態のガス発生による電池内圧の上昇に対して、外装ケースのシール部に挟みこまれた多層シートの低融点樹脂フィルムが、温度上昇により軟化溶融すると共に電池内の圧力で変形し始めて多層シート間が開き、実質的にシール部が開口して、内部ガスを速やかに外部へ排出できるために外装ケースの変形を抑制でき、このケース変形に追従する積層電極の変形をなくして内部短絡を防止することができる。
【００３８】
次に低融点の熱溶着性樹脂シートとしてＥＡＡシートを単独で用いた安全弁部材の例を説明する。
【００３９】
図１同様に、積層電極４を１枚のラミネートシートをその中央折り曲げ線Ｔに沿って長さ方向に２つ折りにした状態で包み、この中央折り曲げ線Ｔの辺を除く３辺Ｐ１、Ｐ２、Ｐ３を熱溶着によりシールした袋状外装ケース７で積層電極４を密封する際、リード引き出し部であるＰ２辺のシール部には、正極リードと負極リードの間に、ラミネートシートの熱溶着側であるポリプロピレンフィルムよりも低融点で短冊状をしたＥＡＡシート１０を挟み込み、同時に熱溶着して安全弁部材とした。
【００４０】
また図４に示すように、各リード８，９のそれぞれの一部に、金属との接着性のよい熱溶着性樹脂として、かつまた安全弁として作用するＥＡＡシート１０を施してもよい。その配置位置としては上記の両方のリードのほか、一方のリードに取り付けるだけであってもよい。その配置の方法は、前記のラミネートシートの配置のそれと同じでよい。
【００４１】
この例でも安全弁部材として機能し、ラミネートシートの熱溶着側変性ポリプロピレンよりも低融点の熱溶着樹脂としては、ＥＡＡのほか、前記のエチレンメタクリル酸共重合体、変性ポリプロピレン、変性ポリエチレン、およびポリアリレートの群から選ばれた１種が使用できる。
【００４２】
扁平な電池の組立は、積層電極４を収容して封筒状になった外装ケース７のまだシールされていない残り１辺のＰ２から所定量の電解液が注入され、各リード８，９の間のシール部に短冊状のＥＡＡシートを挟み込んだ後、この１辺Ｐ２を熱溶着シールすることでなされる。このとき、正極リード８および負極リード９の一部を被覆する変性ポリプロピレンフィルム１２，１３も同時に溶着され、正極リード８および負極リード９の先端部が外装ケース７から外部に突出するようになる。このようにして作製した本発明の電池をａ１とし、ＥＡＡシート１０を各リード８，９の一部に熱溶着して被覆し、その被覆部をシール部Ｐ２部に熱溶着して作製した電池をｂ１、および安全弁部材を持たない従来電池をｃとして、これらの安全性について評価を行った。
【００４３】
試験方法としては、前記同様昇温装置付きの恒温槽を用いて一定温度上昇速度（５℃／分）で１６０℃まで昇温し、さらに１６０℃で３時間放置することとした。そのときの電池の内部短絡発生数で評価した。
【００４４】
評価電池ａ１，ｂ１およびｃは各２０個づつ用意し、試験した結果を（表２）に示す。
【００４５】
【表２】

【００４６】
（表２）より明らかなように本発明の電池ａ１およびｂ１については、内部短絡を十分に防止していることがわかる。また、従来電池ｃでは電池総数の６０％で内部短絡が発生した。
【００４７】
従来電池ｃでは、異常高温下に放置された状態において、電池内で電解液などの分解により大量のガスが発生し、それに伴い外装ケースが扁平状態から中高状態に膨らんで変形する。このときケース内の積層電極も外装ケースの変形に追従するように変形し始めて正極、負極間で短絡を生じるためである。
【００４８】
それに対して本発明の電池ａ１およびｂ１では、異常高温状態下でのガス発生による電池内圧の上昇に対して、外装ケースのシール部分の一部に組み込まれたＥＡＡシートが温度上昇により軟化溶融を開始すると共に電池内圧力で変形し始めてシール部が開口し、ここから内部ガスを速やかに外部へ排出するためにケースの変形を抑制でき、積層電極の変形をなくして内部短絡の発生を防止することができる。
【００４９】
【発明の効果】
以上の説明のとおり本発明によれば、樹脂フィルム主体のラミネートシート製外装ケースのシール部に、ラミネートシートの熱溶着側樹脂フィルムよりも低融点の樹脂シートか、熱溶着側樹脂フィルムと同タイプのフィルムを上下外層に配し、この熱溶着側樹脂フィルムよりも低融点の樹脂フィルムを内層に配した多層シートを組み込んで安全弁部材とした。従って、電池の異常高温放置などにおいて、温度を感知して安全弁部分を開放し、外装ケース内部のガスを逃がしてケース膨れに起因した電極の変形による内部短絡を抑制し、信頼性の高い扁平電池を提供することができる。
【図面の簡単な説明】
【図１】本発明の実施例における扁平電池の構成を示す平面図
【図２】図１のＡ−Ａ線に沿った断面図
【図３】多層シートの断面図
【図４】本発明の安全弁部材の別な形態を示す平面図
【図５】従来の扁平電池の断面略図
【符号の説明】
１正極板
２負極板
３セパレータ
４積層電極
７外装ケース
８正極リード
９負極リード
１０多層シート
１２変性ポリプロピレンフィルム
１３変性ポリプロピレンフィルム[0001]
BACKGROUND OF THE INVENTION
In the present invention, a bag-like outer case is formed of a laminate sheet mainly composed of a thin resin film, which is applied to a so-called lithium polymer secondary battery using a polymer as a separator material holding an electrolyte, and laminated and integrated with this. The present invention relates to a battery enclosing a flat laminated electrode portion. More specifically, the present invention relates to a sheet-like safety valve member applied to a part of an exterior case.
[0002]
[Prior art]
A battery using an exterior case made of a laminate sheet in which a metal foil is disposed between resin films and laminated as a whole is known.
[0003]
FIG. 5 shows a cross-sectional structure of a conventional battery using the laminate sheet outer case. That is, the conventional example shown in FIG. 5 includes a laminated electrode 4 in which two positive plates 1 are laminated and integrated on both sides of a single negative plate 2 with separators 3 therebetween, and a periphery of a pair of laminated sheets 15 and 16. The outer case 17 that seals the laminated electrode 4 is configured by heat-welding P (showing two opposite sides P1 and P3 in FIG. 5). The positive electrode plate 1 is configured by applying a positive electrode active material layer 1b to one surface of a positive electrode current collector 1a, and the negative electrode plate 2 is configured by applying a negative electrode active material layer 2b to both surfaces of the negative electrode current collector 2a. Yes. A laminated electrode 4 is configured by arranging the positive electrode plate 1 on both sides of the negative electrode plate 2 via polymer separators 3 and laminating and integrating the whole.
[0004]
Although not shown, a positive electrode lead is connected to the positive electrode current collector 1a, and a tip portion of the positive electrode current collector 1a passes through one seal portion between the laminate sheets 15 and 16 and is drawn to the outside. Similarly, a negative electrode lead is connected to the negative electrode current collector 2a, and a tip portion thereof passes through the seal portion and is drawn to the outside.
[0005]
The pair of laminate sheets 15 and 16 are made of a metal foil, for example, an aluminum foil, a heat-welded resin layer, for example, a polypropylene film on one side, and a resin layer with excellent mechanical strength, for example, a stretched polyamide film, on the other side. It is formed by laminating and integrating polyethylene terephthalate films, and the laminate sheets 15 and 16 are sealed by heat welding between the heat-welded resin layers. Specific heat welding is performed by pressurizing and heating with a heating jig in a state where the heat-welded resin layers around the overlapped surrounding P are in close contact with each other.
[0006]
[Problems to be solved by the invention]
A battery using the laminate sheet outer case as described above exhibits excellent hermeticity in a normal use state. However, when the battery is abnormally used, especially when it is left overcharged or at an extremely high temperature, the electrolyte solution previously held by the electrode or polymer separator is decomposed and gas is generated due to the heat generated by the battery or the external temperature rise. As the internal pressure of the outer case increases and the outer case deforms significantly, there is a problem that the laminated electrode itself inside the case starts to deform and leads to an internal short circuit. For this reason, a part of the sealing portion of the laminate sheet outer case is provided with a part having a smaller (weaker) peel strength than the other parts, and the case is peeled off when the gas pressure inside the case exceeds the peel strength. For example, Japanese Patent Laid-Open No. 10-55792 proposes to let gas escape from the inside. In this example, the gas pressure inside the case is sensed to open a part of the seal part of the case, and it is difficult to relate the small peel strength to the internal short circuit occurrence of the battery due to the deformation. The case seal cannot be reliably opened before the occurrence of a short circuit.
[0007]
The main purpose of the present invention is to provide a temperature sensing type safety valve member in a part of the resin film-based laminate sheet outer case, so that the battery is abnormally used, especially in an overcharged or abnormally high temperature standing state. It is to provide a battery with high safety by opening the safety valve upon sensing the above, and quickly releasing the gas generated inside the battery to the outside.
[0008]
[Means for Solving the Problems]
The configuration of the battery of the present invention consists of a sheet-like or film-like positive electrode plate, a polymer separator for holding an electrolyte, and a flat laminated electrode obtained by laminating and integrating a negative electrode plate, with an aluminum foil placed in the center on both sides. Sealed in an outer case formed by a laminate sheet bonded with a resin film , preferably a sheet laminated with a polypropylene film, an aluminum foil, a biaxially stretched polyamide (nylon) film or a polyethylene terephthalate film in order from the inside to the outside. In addition, a positive electrode lead and a negative electrode lead, one end of which is connected to each of the positive electrode plate and the negative electrode plate, are drawn out from a part of the seal part of the outer case, and the positive electrode lead part or the negative electrode lead part or a seal part between them Than some polypropylene Qualitatively those incorporating a temperature sensing type of safety valve member made of low melting point resin.
[0009]
In this case, the safety valve member has a heat sealable resin film, for example, polypropylene, which is the innermost resin film of the laminate sheet, in a part of the seal portion of the outer case, and has a lower melting point than polypropylene, for example, polypropylene. A multi-layer sheet having a three-layer structure having a resin film, for example, a modified polyethylene film as an inner layer, is integrally incorporated. Alternatively, a safety valve member made of a single resin sheet of a resin having a lower melting point than polypropylene, for example, ethylene acrylic acid copolymer (EAA) is incorporated in a part of the seal portion.
[0010]
Due to the battery misuse such as short circuit and overcharge, or due to the rise in battery temperature when left at abnormally high temperature, the low melting point film of the multilayer sheet incorporated as a safety valve in a part of the seal part of the laminate sheet, Alternatively, the sheet of EAA starts to soften and melt, and its shape starts to be deformed by the increase in pressure in the battery, so that the gap between the films of the multilayer sheet or the seal portion of the laminate sheet can be opened. Therefore, the gas whose pressure has increased in the battery can be quickly discharged outside the case from this open seal, effectively suppressing the rapid temperature rise of the battery and the rapid increase in the internal pressure of the battery. Can be prevented.
[0011]
The multi-layer sheet is placed so that the multi-layer sheet surrounds both the positive lead and / or negative lead, in addition to the laminate sheet seal between the positive lead and negative lead that are drawn to the outside. Even when the surface portion is heat-welded to the innermost polypropylene film of the outer case, it can function as a safety valve member as described above. In addition to the modified polyethylene, EAA, ethylene methacrylic acid copolymer (EMA), modified polypropylene, and polyarylate can be used as the low melting point resin film forming the inner layer of the multilayer sheet.
[0012]
Further, when EAA, modified polypropylene, polyarylate, or the like is used, it can be used alone as a safety valve member as described above, as well as a single layer of a multilayer sheet. The thickness of the heat-welded resin film or sheet used alone as a safety valve member is preferably 20 μm to 100 μm because it is sandwiched between the seal portions of the case, and its melting point is a moderate temperature interval than that of the laminate sheet constituting the case. For example, a temperature of 80 ° C. to 110 ° C., which is lower by 20 ° C. to 40 ° C., softens, melts and deforms in response to a sudden rise in battery temperature or a rise in battery internal pressure, and creates a path for gas to escape to the outside. It is also preferable from the viewpoint of preventing internal short circuit of the battery due to deformation of the case.
[0013]
In addition, in the case of the multilayer sheet having the three-layer structure, in order to make it more sensitive to temperature, the inner layer resin film is used in combination with two different melting points selected from the low melting point resin group. It is better to clarify the difference in melting point from the outer layer resin film.
[0014]
Furthermore, as the heat-welded resin film that forms the outer layer of the multilayer sheet, the laminate sheet is welded together, and the space between the two is liquid-tight and air-tight. A resin film having good weldability is preferred.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. The embodiment here shows an example applied to a flat lithium polymer secondary battery, and will be described with reference to FIGS. In the figure, the same reference numerals are assigned to elements common to the conventional example. As shown in the plan view of FIG. 1, the lithium polymer secondary battery using the laminated sheet bag-shaped outer case shown in the present embodiment has a positive electrode connected to the positive electrode side lead connecting portion 1 c of the flat laminated electrode 4. Lead ends of the lead 8 and the negative electrode lead 9 connected to the negative electrode lead connecting portion 2c are drawn out of the outer case. For this purpose, the laminated electrode 4 is wrapped by two

surfaces

5 and 6 obtained by folding one laminate sheet in the longitudinal direction along the center fold line T, and three sides P1 excluding the side of the center fold line T, P2 and P3 are sealed with a bag-shaped outer case 7 sealed by heat welding. At this time, a modified polyethylene film having a lower melting point than that of the innermost polypropylene film on the inner side of the laminate sheet and an outer side of the seal portion on one side P2, which is a lead lead-out portion, specifically, a part between the positive electrode lead and the negative electrode lead. A multilayer sheet 10 composed of a total of three layers of the same type of polypropylene film as the laminated sheet is sandwiched and heat-welded simultaneously when the side P2 is sealed to form a safety valve member. The laminated electrode 4 and the sealing structure of the outer case here are configured as shown in FIG. 2 which is a cross-sectional view taken along the line AA of FIG.
[0016]
FIG. 3 is a cross-sectional view of a multilayer sheet obtained by integrally laminating three layers of the two polypropylene films and one modified polyethylene film. The thickness of the multilayer sheet is influenced by the thickness of the laminate sheet on the case side and the heat welding conditions, but in order to maintain a three-layer integrated structure that functions as a safety valve member even after the heat welding, the thickness of the polypropylene film Is 10 μm to 50 μm, and that of the polyethylene film is preferably 20 μm to 100 μm.
[0017]
In FIG. 2, a laminated electrode 4 is formed to have a thickness of about 600 μm by laminating and integrating two positive plates 1 with polymer separators 3 on both sides of a single negative plate 2 as in the conventional example. Yes. Specifically, the two positive electrode plates 1 are each configured by coating the positive electrode active material 1b on one surface of the positive electrode current collector 1a, and the negative electrode plate 2 is similarly formed on both surfaces of the central negative electrode current collector 2a. The active material 2b is applied and configured. And the separator 3 which consists of a polymer film which hold | maintains electrolyte solution is arrange | positioned between the positive electrode plate 1 and the negative electrode plate 2, and the whole is integrated by heat welding. In addition, the separator 3 can also use the thing which apply | coated and impregnated the polymer which shows electrolyte solution itself in the support | carrier consisting of a porous sheet other than a polymer film, and which shows a gel state itself.
[0018]
Further, the positive electrode current collector 1a is made of a punching metal or a lath metal made of aluminum or a conductive material coated with aluminum, and acetylene black or ketjen black, which is a conductive carbon material, and a polyfluoride, which is a binder, on the surface thereof. A mixture with vinylidene chloride is integrated by coating. The negative electrode current collector 2a is made of a punching metal or a lath metal made of copper, nickel or a conductive material coated with copper or nickel, and a conductive carbon material similar to that of the positive electrode current collector 1a is applied to the surface of the negative electrode current collector 2a. It has become.
[0019]
The positive electrode active material layer 1b and the negative electrode active material layer 2b were prepared by applying a paste made of an active material powder, a conductive agent, and a polymer solution to the positive electrode and the negative electrode current collector, respectively, and drying.
[0020]
As shown in FIG. 1, a positive electrode lead 8 is connected to each of the current collectors 1a of the two positive electrode plates 1 constituting the laminated electrode 4 at a position displaced to one side (upward in the drawing). And a negative electrode side lead connection portion for connecting the negative electrode lead 9 to the negative electrode current collector 2a of the negative electrode plate 2 at a position displaced to the other side (downward). 2c is extended and formed. A ribbon-like positive electrode lead 8 formed of an aluminum thin plate is formed on the positive electrode-side lead connecting portion 1c, and a ribbon-shaped negative electrode lead 9 formed of a copper thin plate is formed on the negative electrode-side lead connecting portion 2c at a welding point S, respectively. Ultrasonic welding.
[0021]
In this embodiment, as shown in FIG. 2, since two positive electrode plates 1 are used, each positive electrode side lead connecting portion 1c is overlapped one above the other at the welding point S to one ribbon-like positive electrode lead 8 at the same time. Be joined. When a stacked battery is configured by stacking a larger number of stacked electrodes 4 configured in this way, a plurality of positive electrode side lead connection portions 1c and a plurality of negative electrode side lead connection portions 2c are provided corresponding to the number of stacked layers. What is necessary is just to join.
[0022]
As shown in FIG. 1, modified

polypropylene films

12 and 13 are attached to a part of the positive electrode lead 8 and the negative electrode lead 9 as a heat-welding resin having good adhesion to metal. The modified

polypropylene films

12 and 13 were overlapped with the leads 8 and 9 sandwiched between two films, respectively, and were attached in a liquid-tight and air-tight manner while maintaining a temperature of 200 ° C. and a pressure of 0.1 MPa for 30 seconds. . The

films

12 and 13 cover the leads 8 and 9 so as to be wider than the seal portion corresponding to the passing position of the seal portion P2 on one side of the outer case 7. Ordinary polypropylene has poor adhesion to metal, but by introducing a functional group into the polypropylene skeleton by acid modification treatment, etc., modified polypropylene improves adhesion to metal and is heated and pressurized as described above. Is completely adhered to the surfaces of the positive electrode lead 8 and the negative electrode lead 9 so as to cover a part of the surface of the leads 8 and 9, respectively.
[0023]
The multilayer sheet 10 is cut into a strip longer than the seal width of the seal portion P2 of the laminate sheet, and a seal portion is formed on a part of the seal portion P2 between the modified

polypropylene films

12 and 13 covering the leads 8 and 9. Insert so as to cross P2. When the multi-layer sheet 10 is welded simultaneously with the modified

polypropylene films

12 and 13 covering the leads 8 and 9 when the seal portion P2 is formed by heat welding, workability is improved.
[0024]
When the positive electrode lead 8, the negative electrode lead 9, and the multilayer sheet 10 coated with the modified

polypropylene films

12 and 13 are sandwiched between the edges of the two

laminated sheets

5 and 6 to be sealed, the seal of one side P2 is obtained. At the same time, the resin and the

laminated polypropylene film

12 and 13 are thermally welded at the passage portions of the leads 8 and 9 at the same time as the resin is thermally welded to the inner layer polypropylene and the exterior polypropylene of the multilayer sheet.
[0025]
Therefore, even if the leads 8 and 9 are pulled out from the seal portion on one side P2, the sealing performance of the portion as the outer case 7 is sufficiently maintained.
[0026]
Further, as shown in FIG. 4, the multilayer sheet 10 acting as a safety valve member may be applied as a heat-welded resin having good adhesiveness with a metal so as to surround each of the leads 8 and 9. Moreover, the installation may be performed only on one lead instead of both leads. In this case, the multilayer sheet 10 is cut into two films, overlapped by sandwiching at least one lead 8 or 9, and maintained in a state of applying a temperature of 200 ° C. and a pressure of 0.1 MPa for 30 seconds, and being liquid-tight. Installed airtight.
[0027]
In addition to the above-mentioned modified polyethylene, EAA, ethylene methacrylic acid copolymer, modified as the inner layer heat-welded resin of the multilayer sheet that functions as a safety valve member and has a lower melting point than the modified polypropylene that is the heat-welded side film of the laminate sheet One selected from the group of polypropylene and polyarylate can be used.
[0028]
In addition, the laminate sheet that forms the case can be used with a metal foil such as an aluminum foil placed in the center and bonded with a heat-welded resin film on both sides thereof. Polypropylene can be used. As the outer resin film of the laminate sheet, a resin such as polyethylene terephthalate, heat-weldable polyimide, polymethyl methacrylate, stretched polyamide (nylon), or a copolymer of these two or more resins is employed. be able to. The laminate sheet including such a metal foil has characteristics that the gas barrier property and the light blocking property are improved by the metal foil, and the sealing by the thermal welding of the innermost resin layer is facilitated.
[0029]
Next, a lithium polymer secondary battery in which the flat laminated electrode 4 is sealed with a bag-like outer case 7 formed by heat-sealing seals on the three sides of the laminate sheet will be described along the manufacturing procedure thereof.
[0030]
As described above, the laminated electrode 4 in which the modified

polypropylene films

12 and 13 are attached to the positive electrode lead 8 and the negative electrode lead 9 respectively welded to the positive electrode side lead connecting portion 1c and the negative electrode side lead connecting portion 2c by heat welding. The seal portions P1 and P3 on the two sides facing the two

surfaces

5 and 6 of the folded laminate sheet are sealed by thermal welding and inserted into an envelope case 7 formed in an envelope shape.
[0031]
Then, a predetermined amount of electrolyte is injected from the remaining unsealed seal portion P2 of the envelope case 7 that encloses the laminated electrode 4 and has an envelope shape, and the seal portion P2 between the leads 8 and 9 is injected. After sandwiching the multilayer sheet 10, the one side P2 is also thermally welded.
[0032]
At this time, the modified

polypropylene films

12 and 13 covering a part of the positive electrode lead 8 and the negative electrode lead 9 are also welded at the same time, so that the leading ends of the positive electrode lead 8 and the negative electrode lead 9 protrude from the outer case 7. The safety of the battery of the present invention thus produced was evaluated as a, and the conventional battery without a safety valve member as b.
[0033]
As a test method, the temperature was increased to 160 ° C. at a constant temperature increase rate (5 ° C./min) using a thermostatic chamber equipped with a temperature increasing device, and further left at 160 ° C. for 3 hours. The number of occurrences of internal short circuit was evaluated.
Twenty evaluation batteries a and b were prepared for each, and the test results are shown in Table 1.
[0034]
[Table 1]

[0035]
As is clear from Table 1, it can be seen that the battery a of the present invention sufficiently prevents internal short circuit. On the other hand, in the conventional battery b, an internal short circuit occurred in 60% of the evaluation data.
[0036]
In the conventional battery b, when the battery is left at an abnormally high temperature, a large amount of gas is generated due to decomposition of the electrolyte solution in the battery, and the thin and flat battery outer case is changed to a medium-high state (cauterized shape). Swells and deforms. At this time, the laminated electrode in the case also begins to deform so as to follow the deformation of the outer case, causing a short circuit between the positive electrode and the negative electrode, and gas generation is increased.
[0037]
On the other hand, in the battery a of the present invention, the low-melting point resin film of the multilayer sheet sandwiched between the seal portions of the outer case is softened and melted by the temperature rise against the increase in the battery internal pressure due to the generation of gas at an abnormally high temperature. At the same time, it begins to deform due to the pressure inside the battery, the space between the multilayer sheets opens, the seal part opens substantially, and the internal gas can be discharged quickly to the outside, so that deformation of the outer case can be suppressed, and this case deformation is followed. An internal short circuit can be prevented by eliminating the deformation of the laminated electrode.
[0038]
Next, an example of a safety valve member using an EAA sheet alone as a low melting point heat-welding resin sheet will be described.
[0039]
As in FIG. 1, the laminated electrode 4 is wrapped in a state in which one laminate sheet is folded in the longitudinal direction along the central fold line T, and three sides P 1, P 2, excluding the side of the central fold line T, When the laminated electrode 4 is sealed with the bag-like outer case 7 in which P3 is sealed by thermal welding, the P2 side seal portion, which is the lead lead-out portion, is interposed between the positive electrode lead and the negative electrode lead on the heat welding side of the laminate sheet. A strip of EAA sheet 10 having a melting point lower than that of a certain polypropylene film was sandwiched and heat-welded at the same time to obtain a safety valve member.
[0040]
Further, as shown in FIG. 4, an EAA sheet 10 that acts as a heat-welding resin with good adhesion to metal and also as a safety valve may be applied to a part of each of the leads 8 and 9. As for the arrangement position, in addition to both the above-mentioned leads, it may be attached only to one lead. The arrangement method may be the same as that of the laminate sheet.
[0041]
Also in this example, it functions as a safety valve member, and as the heat-melting resin having a lower melting point than the heat-bonding-side modified polypropylene of the laminate sheet, in addition to EAA, the above-mentioned ethylene methacrylic acid copolymer, modified polypropylene, modified polyethylene, and polyarylate One selected from the group of can be used.
[0042]
A flat battery is assembled by injecting a predetermined amount of electrolyte from P2 on the remaining unsealed side of the envelope case 7 containing the laminated electrode 4 and in the form of an envelope, between the leads 8 and 9. This is done by sandwiching a strip-shaped EAA sheet in the seal portion and then heat sealing this one side P2. At this time, the modified

polypropylene films

12 and 13 covering a part of the positive electrode lead 8 and the negative electrode lead 9 are also welded at the same time, and the leading ends of the positive electrode lead 8 and the negative electrode lead 9 protrude from the outer case 7 to the outside. The battery of the present invention thus produced is designated as a1, and the EAA sheet 10 is thermally welded and coated on a part of each lead 8 and 9, and the covered part is thermally welded to the seal part P2 part. B1 and a conventional battery having no safety valve member as c, and the safety was evaluated.
[0043]
As a test method, the temperature was raised to 160 ° C. at a constant temperature increase rate (5 ° C./min) using a thermostatic bath equipped with a temperature raising device as described above, and further left at 160 ° C. for 3 hours. Evaluation was made based on the number of internal short-circuit occurrences at that time.
[0044]
Twenty evaluation batteries a1, b1 and c were prepared for each, and the test results are shown in Table 2.
[0045]
[Table 2]

[0046]
As is clear from Table 2, it can be seen that the batteries a1 and b1 of the present invention sufficiently prevent internal short circuit. Further, in the conventional battery c, an internal short circuit occurred in 60% of the total number of batteries.
[0047]
In the conventional battery c, a large amount of gas is generated due to decomposition of the electrolytic solution or the like in the battery left in an abnormally high temperature, and the outer case is swelled and deformed from a flat state to a middle to high state. This is because the laminated electrode in the case also starts to deform so as to follow the deformation of the outer case and causes a short circuit between the positive electrode and the negative electrode.
[0048]
On the other hand, in the batteries a1 and b1 of the present invention, the EAA sheet incorporated in a part of the seal portion of the outer case is softened and melted by the temperature rise against the rise in the battery internal pressure due to gas generation under an abnormally high temperature condition. Starts to be deformed by the internal pressure of the battery, and the seal part opens, from which the internal gas can be quickly discharged to the outside, so that the deformation of the case can be suppressed, and the occurrence of an internal short circuit can be prevented by eliminating the deformation of the laminated electrode. be able to.
[0049]
【The invention's effect】
As described above, according to the present invention, the sealing part of the resin sheet-based laminate sheet outer case is a resin sheet having a lower melting point than the heat-welding side resin film of the laminate sheet, or the same type as the heat-welding side resin film. A multilayered sheet in which a film having a lower melting point than that of the heat-welding side resin film is disposed in the inner layer is incorporated into a safety valve member. Therefore, when the battery is left at an abnormally high temperature, the safety valve is opened by sensing the temperature, the gas inside the outer case is released, and internal short circuit due to deformation of the electrode due to the case swelling is suppressed, and a highly reliable flat battery Can be provided.
[Brief description of the drawings]
1 is a plan view showing a configuration of a flat battery in an embodiment of the present invention. FIG. 2 is a cross-sectional view taken along line AA in FIG. 1. FIG. 3 is a cross-sectional view of a multilayer sheet. Fig. 5 is a plan view showing another form of the safety valve member. Fig. 5 is a schematic cross-sectional view of a conventional flat battery.
DESCRIPTION OF SYMBOLS 1 Positive electrode plate 2 Negative electrode plate 3 Separator 4 Laminated electrode 7 Exterior case 8 Positive electrode lead 9 Negative electrode lead 10 Multilayer sheet 12 Modified polypropylene film 13 Modified polypropylene film

Claims

Each of the sheet-like or film-like positive electrode plate, a flat separator electrode made by laminating and integrating the polymer separator holding the electrolyte and the negative electrode plate is a laminate sheet in which an aluminum foil is arranged in the center and resin films are bonded to both sides. In the battery in which the positive electrode lead and the negative electrode lead, which are housed in the formed bag-shaped outer case and whose one ends are connected to the positive electrode plate and the negative electrode plate, are drawn out from the seal portion of the outer case, the outer case A safety valve member is incorporated in a part of the seal part, and the safety valve member is made of a heat-welded resin sheet having a melting point lower than that of the heat-welded resin film on the inner surface of the laminate sheet, , Ethylene acrylic acid copolymer, ethylene methacrylic acid copolymer, modified polypropylene, modified polymer One kind is flat batteries selected from the group consisting of ethylene and polyarylate.

Each of the sheet-like or film-like positive electrode plate, a flat separator electrode made by laminating and integrating the polymer separator holding the electrolyte and the negative electrode plate is a laminate sheet in which an aluminum foil is arranged in the center and resin films are bonded to both sides. The positive electrode lead is configured to be folded in half at the center in the length direction and sealed in a bag-like outer case in which the edges of the remaining three sides are thermally welded, and one end is connected to each of the positive electrode plate and the negative electrode plate In the battery in which the lead and the negative electrode lead are drawn out from the seal portion on one side of the outer case, a safety valve member is incorporated in a part of the seal portion of the outer case, and the safety valve member An outer layer resin film that is thermally welded to the welding side resin film is disposed on the upper and lower outer layers, and the inner layer is a heat welding side resin on the inner surface of the laminate sheet. The outer layer resin film constituting the multilayer sheet is composed of an inner layer resin film having a lower melting point than that of the film, and the whole is integrated. A flat battery characterized by being formed of the same material as a resin film.

The flat battery according to claim 2, wherein the thickness of the inner layer resin film of the multilayer sheet is thicker than the thickness of the outer layer resin film located outside thereof.

The flat battery according to claim 2, wherein each film of the multilayer sheet is in a state in which an interface of each resin film is thermally welded.

3. The flat battery according to claim 2, wherein the multilayer sheet has a thickness of 40 [mu] m to 200 [mu] m, the outer resin film is made of polypropylene having a thickness of 10 [mu] m to 50 [mu] m, and the inner resin film is made of polyethylene having a thickness of 20 [mu] m to 100 [mu] m.

The flat battery according to claim 2, wherein the safety valve member made of a multilayer sheet is incorporated in a seal portion of the outer case in a state of surrounding at least one of the positive electrode lead and the negative electrode lead.

The low-melting-point heat-welded resin sheet forming the safety valve member is heat-welded so as to surround at least one of the positive electrode lead and the negative electrode lead, and the surface portion thereof is a heat-welded resin film on the inner surface of the laminate sheet constituting the outer case The flat battery according to claim 1, which is heat-welded.

2. The flat battery according to claim 1, wherein the heat-melting resin sheet having a low melting point has a thickness of 20 μm to 100 μm and a melting point of 80 ° C. to 110 ° C. 3.

Each has a sheet-like or film-like positive electrode plate, a polymer separator that holds an electrolyte, and a laminated electrode in which a negative electrode plate is laminated and integrated, and a bag-like outer case in which this laminated electrode is sealed. From one in which a laminate sheet laminated with polypropylene film, aluminum foil, stretched polyamide film or polyethylene terephthalate film is folded in two at the center in the length direction and the edges of the remaining three sides are heat welded In the battery in which the positive electrode lead and the negative electrode lead, one end of which is connected to each of the positive electrode plate and the negative electrode plate, are drawn out from the seal portion on one side of the case, the case seal portion between the positive electrode lead and the negative electrode lead Is a resin sheet with a lower melting point than polypropylene film. Flat battery safety valve member is integrally welded.

The flat battery according to claim 9, wherein the resin sheet having a melting point lower than that of the polypropylene film is made of an ethylene acrylic acid copolymer.