JP3544889B2

JP3544889B2 - Sealed battery

Info

Publication number: JP3544889B2
Application number: JP09391199A
Authority: JP
Inventors: 裕之長谷部; 則雄高見; 隆久大崎; 基神田
Original assignee: Toshiba Corp
Current assignee: Toshiba Corp
Priority date: 1999-03-31
Filing date: 1999-03-31
Publication date: 2004-07-21
Anticipated expiration: 2019-03-31
Also published as: JP2000285955A

Description

【０００１】
【発明の属する技術分野】
本発明は、薄型形状の密閉型電池の構成方法に関するものであり、更に詳しくは、電極とセパレータからなる電極群を、融着面を有する外装材で覆った薄型形状の密閉型電池に関するものである。
【０００２】
【従来の技術】
長らくポータブル機器用電源として広く用いられてきた密閉型鉛電池やニッケルカドミウム二次電池に代えて、近年ニッケル水素二次電池やリチウムイオン二次電池という新型の高容量二次電池が開発され、ポータブル機器用電源として広く用いられるようになった。これらの電池により、ポータブル機器の稼動時間が長くなり利便性が増したとともに、ポータブル機器の小型化、軽量化が進んだ。
【０００３】
しかし、ニッケル水素二次電池においては充電末期に発生する酸素ガスにより電池内圧が上昇し、電池が膨張する。そのため、この防止策として強固な金属製の容器に収納されて使用されている。またリチウムイオン二次電池では、通常の充放電ではガスの発生はないため電池膨張は生じないが、初充電時にガスが発生し電池が膨張する。この膨張量は少ないものの、リチウムイオン二次電池では電解液が非水溶媒であるため液抵抗が大きく、正極と負極の間隔が若干でも広がると電池特性が極端に低下するため、ニッケル水素二次電池同様強固な金属製容器に収納されて実用に供されている。
【０００４】
従来の使用用途では金属製の容器であってもその厚さが問題となることはなかったが、近年の電子機器の実装技術の進歩と、部品の小型化により、電池に従来以上に薄型の要求が強くなっている。この要求にこたえるため、厚さが５ｍｍ以下の金属容器が開発されているが、金属板を絞り込んで作成する缶ではそろそろ限界が見え始めている。
【０００５】
このような金属容器に収納された電池の薄型化の限界を打破するために、リチウムイオン二次電池においては、このような薄型電池を従来と全く異なる方法で作成する事により解決しようとする試みが行われ始めている。この方法は２通りあり、一つは活物質をゲル化材とともに集電体へ塗布し、これを同じくゲル化材を塗布したセパレータを介して積層したのち、ゲル化材へ電解液を含浸させる、ゲルポリマー電池と呼ばれる手法であり、もう一つは、有機固体電解質を介して、両極を積層したるポリマー電池である。しかし、両者とも電池、特に電極の作成方法が従来と全く異なる為、性能が不十分である他、エネルギー密度が缶に収納した従来型の電池よりも低くなってしまうという問題が顕在化してきており、実用にいたっているとは言えない状況である。
【０００６】
【発明が解決しようとする課題】
本発明は、上述の薄型電池の重量の問題と、ポリマー電池の電池特性上の問題を同時に解決するする電池作成手法を提供することを課題としている。
【０００７】
【課題を解決するための手段】
本願発明者らは、上述の問題を解決する構造を鋭意研究した結果、電極とセパレータからなる電極群を電極群構成後に加熱圧着させる構造が非常に効果的であることを見出し、本願を出願するに至った。
【０００８】
本発明の電池は正極と負極とをセパレータを介して積層した電極群を内面に
融着面を有する薄膜で覆った密閉型電池において、前記セパレータは、少なくもその表面の一部がポリエチレンで覆われており、前記電極群を構成後、加熱圧着することにより、前記電極と前記セパレータが少なくともその一部において相互に融着することを特徴とする密閉型電池である。
【０００９】
また、前記電池がアルカリ水溶液を電解液として用いるアルカリ電池であってもかまわない。
【００１０】
このような密閉型電池を構成する電池構成としては、特段限定する必要はなく、ニッケル水素二次電池、リチウムイオン二次電池等の新型高容量二次電池は勿論、従来から広く使用されてきている、ニッケルカドミウム二次電池に対しても適用可能である。そのため、電極材料としても、ニッケル水素二次電池の場合であれば、正極に焼結式やペースト式の水酸化ニッケル電極を負極にＬａＮｉ５系やラーベス相の水素吸蔵合金電極を、リチウムイオン二次電池であれば、正極にＬｉＣｏＯ_２、ＬｉＮｉＯ_２、ＬｉＭｎＯ_２、ＬｉＭｎ_２Ｏ_４等の材料を、負極にコークス、グラファイト、金属Ｌｉ等の使用が可能である。
【００１１】
また電解液も特段限定されるものではなく、上述の電池系に適合した電解液を適宜選択して使用することが可能である。例えば、ニッケル水素二次電池であればＫＯＨ、ＮａＯＨ、ＬｉＯＨ等のアルカリ水溶液を単独ないしは混合した電解液を、リチウムイオン二次電池であればＥＣ，ＰＣ，ＭＥＣ，ＤＭＣ，ＤＥＣ等の炭酸エステルにＬｉＰＦ６やＬＩＢＦ４等の支持塩を適当量加えたものを使用する。勿論ここに記した以外の組み合わせでも、電池系として成り立つものであれば使用可能である。
【００１２】
セパレータもその選択を特に限定する必要はないが、外装材との融着が可能となる材料を選択する必要がある。しかし、何ら特殊な材料を選択する必要はなく、ニッケル水素二次電池あればナイロンやポリプロピレンの不織布を、リチウムイオン二次電池であれば、ポリエチレンやポリプロピレンの多孔膜を使用すればよい。
【００１３】
外装材も非水電解液系電池の場合にはアルミ等のバリア層を挿入した多層膜が好ましいが、ニッケル水素二次電池のような水系電解液の場合にはポリプロピレンのような、ポリオレフィンの膜で十分である。また融着面の材料も特に特殊な材料を使用する必要はなく、多くの場合、ポリエチレンやポリプロピレンのようなポリオレフィンやアイオノマーで使用可能である。
【００１４】
（作用）
本願の電池の作成の一例を図１に示す。このように、予め集電体に活物質を添着させて作成した正極２と負極４を、合成樹脂からなるセパレータ３を介して積層し、電極群を構成する。ついでこの電極群を内面に融着材層を有する外装材にて包み、圧迫しながら熱を加えることによりセパレータの一部が融解し前記電極と熱融着させ、電極群が一体化される。図１では電極が正負極各一枚の電極群を示しているが、複数層積層することや、長尺電極を捲回して作成した電極群でも同様の手法により電極群の一体化が行える。
【００１５】
ついで、電解液を注入した後、外装材１を完全密閉させて電池を完成させる。
【００１６】
このような構成の電池とすることにより、充電末期や初充電時の発生ガスによる電池内圧の上昇により電極間隔が広がることや、電池形状が膨張することを抑制することが可能となり、電極間隔の拡大に起因する電池特性の劣化を抑制することが可能となる。
【００１７】
つまり、本願に示す、電極とセパレータ積層したる電極群を加熱圧着させることにより、電極群を一体化させるとう簡便な手法により、ポリマー電池のような特殊な電極をまったく使用することなく、薄型でエネルギー密度の高いリチウムイオン二次電池を提供することが可能となるほか、従来金属缶以外では実現が実質的に不可能であったニッケル水素二次電池や、ニッケルカドミウム二次電池の薄型化が可能となった。
【００１８】
また、金属缶のような缶成形上の限界もないため、厚さ１ｍｍ以下の電池の作成も容易である他、電池に柔軟性を付与できるという特徴を有している。
【００１９】
以下実施例をもとに詳細に説明を行う。
【００２０】
【発明の実施の形態】
（実施例）
下記の方法によりニッケル水素二次電池用の正極と負極を作成した。
【００２１】
正極：
水酸化ニッケル９０ｇと一酸化コバルト１０ｇに練り剤としてポリアクリル酸ナトリウム０．１７５ｇとＣＭＣ０．１５ｇ、更にＰＴＦＥを３．５ｇを加え、十分混合した後、水を加えて更に混練しニッケル活物質ペーストを調製する。次いで、これらのペーストを三次元構造を有するニッケル発泡基板（住友電工製セルメット）へ擦り込んだ後、温風乾燥器中に放置することで乾燥を行う。十分乾燥の後、二段式圧延機を用いて、所定の厚みまでプレスを行ない、最後に打ち抜きプレスにより、４０ｍｍ×６０ｍｍに打ち抜いた。この電極の重量から求めた水酸化ニッケル含有量を基にして算出された理論容量は約１０００ｍＡｈである。
【００２２】
負極：
まずＬｍＮｉ_４．０Ｃｏ_０．４Ｍｎ_０．３Ａｌ_０．３１００ｇにケッチェンブ
ラック１ｇ、更に練り剤としてＣＭＣ０．１ｇ、ポリアクリル酸ナトリウム０．３ｇ及びＰＴＦＥ２ｇを加え十分混合した後、水を加えて水素吸蔵合金活物質ペーストを作成する。ついで、このペーストを正極と同様に三次元構造を有するニッケル発泡基板（住友電工製セルメット）へ擦り込んだ後、温風乾燥器中で放置することで乾燥を行う。十分乾燥の後、二段式圧延機を用いて、所定の厚みまでプレスを行い、最後に打ち抜きプレスにより、４２ｍｍ×６２ｍｍに打ち抜いた。
【００２３】
ついでこれらの電極を使用して、以下詳述する比較例１、実施例１、実施例２、実施例３の電極群を作成した。
【００２４】
比較例１：上述の電極をポリプロピレン製の不織布セパレータを介して積層したものをＰＥＴ製フィルムの表面にアイオノマー製の熱融着面を形成したラミネートフィルムにより外部を覆った。ついでラミネートフィルムの周辺部を注液用の開口部を除いて熱融着により密着させた後、注液用の未融着部からシリンジにより８規定の水酸化カリウム水溶液を注入し、電解液が電極群に十分吸収されるまで放置した。その後注液に使用した未融着部を熱融着により密着することで比較例１の密閉型電池を作成した。電池断面を図２に示す。なお、ラミネートフィルムの熱融着はアイオノマーの融点よりは高く、セパレータ２３を構成するポリプロピレンの融点よりは低温である１０５℃で行い、さらに、ラミネートフィルム周辺部に限定して加熱したため、電極とセパレータ、電極とアイオノマーの融着は生じていない。ここで、２１は外装材、２２は正極、２３はセパレータ、２４は負極である。
【００２５】
実施例１：上述の電極をポリプロピレン製の芯材をポリエチレンで薄く覆った繊維により作成された不織布セパレータを介して積層した電極群をＰＥＴ製フィルムの表面にアイオノマー製の熱融着面を形成したラミネートフィルムにより外部を覆った。ラミネートフィルム外面より電極群を圧迫しながら１４０℃に加熱し、セパレータ中のポリエチレンを融解してセパレータと電極を、またアイオノマーを融解して電極とラミネートフィルムをそれぞれ熱融着させた。ついでラミネートフィルムの周辺部を注液用の開口部を除いて熱融着により密着させた後、注液用の未融着部からシリンジにより８規定の水酸化カリウム水溶液を注入し、電解液が電極群に十分吸収されるまで放置した。その後注液に使用した未融着部を熱融着により密着することで実施例１の密閉型電池を作成した。電池断面を図３に示す。図２と同一部分は同一番号を付しその詳細説明は省略した。尚、３０は熱融着層である。
【００２６】
実施例２：上述の電極をポリプロピレン製の不織布セパレータを介して積層した。この際、電極とセパレータの間にポリエチレンの微粒子を散布しながら積層を行った。このようにして作成した電極群をＰＥＴ製フィルムの表面にアイオノマー製の熱融着面を形成したラミネートフィルムにより外部を覆った。ラミネートフィルム外面より電極群を圧迫しながら１４０℃に加熱し、セパレータと電極の間に散布したポリエチレンを融解してセパレータと電極をポリエチレン微粒子の散布個所において、またアイオノマーを融解して電極とラミネートフィルムをそれぞれ熱融着させた。ついでラミネートフィルムの周辺部を注液用の開口部を除いて熱融着により密着させた後、注液用の未融着部からシリンジにより８規定の水酸化カリウム水溶液を注入し、電解液が電極群に十分吸収されるまで放置した。その後注液に使用した未融着部を熱融着により密着することで実施例２の密閉型電池を作成した。電池断面を図３に示す。
【００２７】
実施例３：上述の電極をポリプロピレン製の不織布セパレータを介して積層した。この際、電極とセパレータの間にポリプロピレンの芯材の表面を薄くポリエチレンで覆った短繊維を散布しながら積層を行った。このようにして作成した電極群をＰＥＴ製フィルムの表面にアイオノマー製の熱融着面を形成したラミネートフィルムにより外部を覆った。ラミネートフィルム外面より電極群を圧迫しながら１４０℃に加熱し、セパレータと電極の間に散布した短繊維のポリエチレンを融解してセパレータと電極を、またアイオノマーを融解して電極とラミネートフィルムをそれぞれ熱融着させた。ついでラミネートフィルムの周辺部を注液用の開口部を除いて熱融着により密着させた後、注液用の未融着部からシリンジにより８規定の水酸化カリウム水溶液を注入し、電解液が電極群に十分吸収されるまで放置した。その後注液に使用した未融着部を熱融着により密着することで実施例３の密閉型電池を作成した。電池断面を図３に示す。
【００２８】
これらの電池を１Ａの電流で１時間２０分充電した後、１Ａの電流で０．８Ｖまで放電する充放電を繰り返し行い、初期の放電容量に対する、サイクル進行に伴う放電容量の変化を測定したその結果を図４に示す。
【００２９】
図４より明らかなとおり、実施例の電池ではサイクル進行に伴う容量低下が少ないのに対し、比較例の電池では、急激に容量が低下している。この原因を探るため、電池の外形検査を行なったところ、表１に示すように、実施例の電池ではその厚さの変化が少ないのに対し、比較例１の電池では大きく膨らんでいることがわかった。
【００３０】
このことと、透過Ｘ線撮影の結果から、比較例１の電池で容量低下が大きかったのは、充電末期に正極で発生する酸素ガスにより電池内圧が上昇し、周辺部でのみ固定されている比較例１の電池では電池の膨れを抑制する事ができず、電極間隔が広がってしまい放電容量が低下したものと考えられる。これに対し、実施例の各電池では手法こそ異なるものの電極とセパレータ、外装材が少なくともその一部において相互に結着されているため、電池の膨張が抑制され、容量低下が少なかったものと考えられる。
【００３１】
【表１】

（比較例２〜３、実施例４）
下記の方法によりリチウムイオン二次電池用の正極と負極を作製した。
【００３２】
正極：
ＬｉＣｏＯ_２１００ｇへ導電材としてアセチレンブラックを６ｇ添加し、ＰＶｄＦ３ｇ（固形分）とともに十分混連しペースト化したものを、アルミ箔へ塗布し、乾燥・プレスを行って作成した。この電極を３００ｍｍ×５０ｍｍに切り出し使用した。この正極の活物質量から算出される理論容量は８００ｍＡｈである。
【００３３】
負極：
繊維状グラファイトであるＭＣＦ１００ｇへＰＶｄＦを６ｇ（固形分）添加し、十分混練し、ペーストとしたものを銅箔へ塗布し、乾燥・プレスをおこなって作製した。この電極を３４０ｍｍ×５２ｍｍに切り出して使用した。
【００３４】
これらの電極を外径２０ｍｍの巻き芯にポリエチレン製の多孔性膜セパレータにより絶縁しながら捲回した。この際、正負両電極とセパレータの間に融点９２℃のアイオノマーの粉末を散布しながら積層を行なった。このようにして捲回した電極を巻き芯から抜き取り、押しつぶすことにより偏平な電極群を作成した。この電極群をアイオノマーとアルミ箔のラミネート材にて外部を覆った。その後、ラミネートフィルム外面より電極群を圧迫しながら１００℃に加熱し、セパレータと電極との間をアイオノマーの散布個所において、また電極群とラミネートフィルム内面のアイオノマーを熱融着し、ついでラミネートフィルム外周部を注液用の場所を残して電極周辺部にあわせて熱融着した。その後、外周部の注液用の個所からシリンジによりエチレンカーボネートとメチルエチルカーボネートを等量混合したものへ１モルのＬｉＰＦ６を溶解させたものを電解液として注液し、注液穴を熱融着し塞いだ。この電池を実施例４とする。
【００３５】
上記実施例４とアイオノマー粉末を散布しない以外はまったく同一の手順で作成した電池を比較例２とする。
【００３６】
また、上記実施例４のアイオノマー粉末の代わりにポリエチレンの粉末を散布し、熱融着温度をポリエチレンの融点以上である１４０℃で行った電池を比較例３とする。
【００３７】
これらを４００ｍＡの電流で４．２Ｖまで定電流で、４．２Ｖになってからは定電圧で充電を計５時間行なった後、８００ｍＡで３Ｖまで放電するサイクルを繰り返し、サイクル進行に伴う放電容量の変化を測定した。その結果を図５に示す。
【００３８】
図５より、アイオノマー粉末により電極とセパレータを熱融着させた実施例４の電池ではほとんど劣化は観察されないが、熱融着を行なっていない比較例２では急激な劣化が生じていることが、またポリエチレン粉末で熱融着を行った比較例３ではサイクル初期から、全く容量が得られていないことがわかる。この原因を調査するため、サイクル後の電池を解体し、観察したところ実施例４の電池では電極群が一体化し正負極間が密着しているのに対し、比較例２の電池では負極上に多くの放電し残りの金属リチウムの析出が観察された。このことから、融着させなかった比較例２では充放電サイクルの進行に伴い電極間隔が広がり電流分布が不均一となってしまい金属リチウムの析出が生じ、その結果サイクル進行に伴い容量低下が起こったものと考えられる。
【００３９】
また、比較例３ではポリエチレン粉末による熱融着が行われていることから電極群は実施例同様強固に一体化されているものの、電池のインピーダンス測定の結果、インピーダンスが非常に高いことが確認された。その後電池を強制的に解体しセパレータを走査型電子顕微鏡にて観察したところセパレータに予め設けられている微細孔がほとんど全て収縮し閉孔していることがわかった。このことから、比較例３の電池では熱融着にポリエチレン粉末を使用し、融着温度を１４０℃と高くしたためセパレータの有する安全機構であるシャットダウン機構が作用し閉孔してしまい、イオンの移動が妨げられてしまい電池として機能しなかったものと考えられる。
【００４０】
このことより、熱融着に使用する熱融着樹脂はセパレータの閉孔温度より低温で融着しうるものを選択することが必要であることがわかる。
【００４１】
【発明の効果】
電極とセパレータを相互に熱融着するという簡便にして効果的な電池構成手法を見出すことにより、ポリマー電池のような特殊な電極をまったく使用することなく、薄型でエネルギー密度の高いリチウムイオン二次電池を提供することが可能となるほか、従来金属缶以外では実現が実質的に不可能であったニッケル水素二次電池や、ニッケルカドミウム二次電池の薄型化が可能となった。
【００４２】
また、金属缶のような缶成形上の限界もないため、厚さ１ｍｍ以下の電池の作成も容易という特徴を有しており、その工業的寄与は大なる物がある。
【図面の簡単な説明】
【図１】本発明の一構成例を示す図。
【図２】比較例１の電池の一部を示す電池断面図。
【図３】実施例１〜３の電池の一部を示す電池断面図。
【図４】実施例１〜３、比較例１の電池の充放電サイクル特性図。
【図５】実施例４、比較例２の電池の充放電サイクル特性図。
【符号の説明】
１外装材
２正極
３セパレータ
４負極[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for forming a thin sealed battery, and more particularly, to a thin sealed battery in which an electrode group including an electrode and a separator is covered with an exterior material having a fusion surface. is there.
[0002]
[Prior art]
In recent years, new high-capacity rechargeable batteries such as nickel-metal hydride rechargeable batteries and lithium-ion rechargeable batteries have been developed instead of sealed lead batteries and nickel-cadmium rechargeable batteries, which have been widely used as power supplies for portable devices. It has been widely used as a power supply for equipment. These batteries have increased the operating time of portable devices and increased convenience, and also made portable devices smaller and lighter.
[0003]
However, in a nickel-hydrogen secondary battery, the internal pressure of the battery increases due to oxygen gas generated at the end of charging, and the battery expands. Therefore, as a preventive measure, it is used by being housed in a strong metal container. In a lithium ion secondary battery, gas is not generated during normal charge / discharge, so that the battery does not expand. However, gas is generated at the time of initial charging, and the battery expands. Although the amount of expansion is small, the lithium ion secondary battery has a large liquid resistance because the electrolyte is a non-aqueous solvent, and even if the distance between the positive electrode and the negative electrode is slightly widened, the battery characteristics are extremely deteriorated. It is stored in a strong metal container like a battery and put to practical use.
[0004]
In conventional applications, the thickness of the metal container did not matter even with metal containers, but recent advances in electronic device mounting technology and downsizing of components have made it possible to use thinner batteries than ever before. The demands are getting stronger. To meet this demand, metal containers having a thickness of 5 mm or less have been developed. However, the limits of a metal can made by squeezing a metal plate are beginning to appear.
[0005]
In order to overcome the limitation of thinning of batteries housed in such metal containers, in lithium-ion secondary batteries, attempts to solve such thin batteries by making them completely different from conventional methods Is beginning to take place. This method has two methods. One is to apply an active material to a current collector together with a gelling material, and stack this through a separator coated with the gelling material, and then impregnate the gelling material with an electrolytic solution. The other is a polymer battery in which both electrodes are laminated via an organic solid electrolyte. However, in both cases, the method of forming the battery, particularly the electrode, is completely different from the conventional method, so that the performance is insufficient and the problem that the energy density is lower than that of the conventional battery stored in a can has become apparent. And it is not in practical use.
[0006]
[Problems to be solved by the invention]
SUMMARY OF THE INVENTION An object of the present invention is to provide a battery manufacturing method that simultaneously solves the above-described problem of the weight of a thin battery and the problem of the battery characteristics of a polymer battery.
[0007]
[Means for Solving the Problems]
The inventors of the present application have conducted intensive studies on a structure that solves the above-described problem, and as a result, have found that a structure in which an electrode group including an electrode and a separator is heat-pressed after forming the electrode group is extremely effective, and filed an application with the present application. Reached.
[0008]
The battery of the present invention is a sealed battery in which an electrode group in which a positive electrode and a negative electrode are laminated with a separator interposed therebetween is covered with a thin film having a fused surface on an inner surface, wherein the separator has at least a part of its surface covered with polyethylene. The sealed battery is characterized in that the electrodes and the separator are at least partially fused to each other by heat-compression bonding after forming the electrode group.
[0009]
Further, the battery may be an alkaline battery using an alkaline aqueous solution as an electrolytic solution.
[0010]
There is no particular limitation on the battery configuration that constitutes such a sealed battery, and new high-capacity secondary batteries such as nickel-metal hydride secondary batteries and lithium-ion secondary batteries have been widely used in the past as well. The present invention is also applicable to nickel cadmium secondary batteries. Therefore, in the case of a nickel-metal hydride secondary battery, a sintered or pasted nickel hydroxide electrode is used for the positive electrode, a LaNi5 or Laves phase hydrogen storage alloy electrode is used for the negative electrode, and a lithium ion secondary battery is used as the electrode material. In the case of a battery, materials such as LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , and LiMn ₂ O ₄ can be used for the positive electrode, and coke, graphite, metallic Li, and the like can be used for the negative electrode.
[0011]
Also, the electrolyte is not particularly limited, and an electrolyte suitable for the above-described battery system can be appropriately selected and used. For example, in the case of a nickel-hydrogen secondary battery, an electrolyte solution containing an alkali aqueous solution such as KOH, NaOH, or LiOH alone or in a mixture is used. In the case of a lithium-ion secondary battery, an electrolytic solution of EC, PC, MEC, DMC, DEC, or the like is used. A solution obtained by adding an appropriate amount of a supporting salt such as LiPF6 or LIBF4 is used. Of course, combinations other than those described here can be used as long as they can be realized as a battery system.
[0012]
It is not necessary to particularly limit the selection of the separator, but it is necessary to select a material that can be fused with the exterior material. However, there is no need to select any special material. For a nickel-hydrogen secondary battery, a nonwoven fabric of nylon or polypropylene may be used, and for a lithium-ion secondary battery, a porous film of polyethylene or polypropylene may be used.
[0013]
In the case of a non-aqueous electrolyte battery, the exterior material is preferably a multilayer film in which a barrier layer such as aluminum is inserted, but in the case of an aqueous electrolyte such as a nickel-hydrogen secondary battery, a polyolefin film such as polypropylene is used. Is enough. Further, it is not necessary to use a special material for the material of the fusion surface, and in many cases, a polyolefin such as polyethylene or polypropylene or an ionomer can be used.
[0014]
(Action)
One example of the preparation of the battery of the present application is shown in FIG. As described above, the positive electrode 2 and the negative electrode 4 which are prepared by previously adhering the active material to the current collector are stacked via the separator 3 made of a synthetic resin to form an electrode group. Next, the electrode group is wrapped in an exterior material having a fusion material layer on the inner surface, and heat is applied while pressing, so that a portion of the separator is melted and thermally fused with the electrode, whereby the electrode group is integrated. Although FIG. 1 shows one electrode group for each of the positive electrode and the negative electrode, the electrode group can be integrated by a similar method in a case where a plurality of layers are stacked or an electrode group formed by winding a long electrode.
[0015]
Next, after injecting the electrolytic solution, the exterior material 1 is completely sealed to complete the battery.
[0016]
With the battery having such a configuration, it is possible to suppress the electrode interval from expanding due to an increase in the battery internal pressure due to the gas generated at the end of charging or the initial charging, and to suppress the battery shape from expanding. It is possible to suppress deterioration of battery characteristics due to the expansion.
[0017]
In other words, as shown in the present application, the electrode group formed by laminating the electrode and the separator is heat-pressed, and a simple method of integrating the electrode group is achieved without using any special electrode such as a polymer battery. In addition to being able to provide lithium-ion secondary batteries with high energy density, nickel-metal hydride secondary batteries and nickel cadmium secondary batteries, which were practically impossible to achieve with anything other than metal cans, have become thinner. It has become possible.
[0018]
Further, since there is no limit in forming a can as in a metal can, it is easy to produce a battery having a thickness of 1 mm or less, and the battery has flexibility.
[0019]
Hereinafter, the embodiment will be described in detail.
[0020]
BEST MODE FOR CARRYING OUT THE INVENTION
(Example)
A positive electrode and a negative electrode for a nickel-metal hydride secondary battery were prepared by the following method.
[0021]
Positive electrode:
To a mixture of 90 g of nickel hydroxide and 10 g of cobalt monoxide, 0.175 g of sodium polyacrylate, 0.15 g of CMC, and 3.5 g of PTFE are added as kneading agents, and 3.5 g of PTFE is sufficiently mixed. Is prepared. Next, these pastes are rubbed on a nickel foam substrate having a three-dimensional structure (Celmet, manufactured by Sumitomo Electric Industries, Ltd.), and then dried by being left in a hot-air dryer. After sufficient drying, pressing was performed to a predetermined thickness using a two-stage rolling mill, and finally punching was performed to 40 mm x 60 mm by a punching press. The theoretical capacity calculated based on the nickel hydroxide content obtained from the weight of this electrode is about 1000 mAh.
[0022]
Negative electrode:
First, 100 g of LmNi _4.0 Co _0.4 Mn _0.3 Al _0.3, 1 g of ketjen black, 0.1 g of CMC as a kneading agent, _0.3 g of sodium polyacrylate and 2 g of PTFE are added and mixed well, and then water is added. In addition, a hydrogen storage alloy active material paste is prepared. Next, the paste is rubbed on a nickel foam substrate (Celmet, manufactured by Sumitomo Electric Industries, Ltd.) having a three-dimensional structure in the same manner as the positive electrode, and dried by leaving it in a hot-air dryer. After sufficient drying, pressing was performed to a predetermined thickness using a two-stage rolling mill, and finally punching was performed to 42 mm × 62 mm by a punching press.
[0023]
Then, using these electrodes, electrode groups of Comparative Example 1, Example 1, Example 2, and Example 3 described in detail below were prepared.
[0024]
COMPARATIVE EXAMPLE 1 The above-described electrode was laminated via a polypropylene nonwoven fabric separator, and the outside was covered with a laminate film having a heat-sealed surface made of an ionomer formed on the surface of a PET film. Then, the peripheral portion of the laminated film was adhered by heat fusion except for the opening for liquid injection, and then an 8N aqueous potassium hydroxide solution was injected with a syringe from the unfused portion for liquid injection, and the electrolytic solution was removed. It was left until it was sufficiently absorbed by the electrode group. Thereafter, the unfused portion used for the injection was adhered by heat fusion to produce a sealed battery of Comparative Example 1. FIG. 2 shows a cross section of the battery. The heat-sealing of the laminated film was performed at 105 ° C., which was higher than the melting point of the ionomer and lower than the melting point of the polypropylene constituting the separator 23, and further, heating was performed only in the peripheral portion of the laminated film. No fusion between the electrode and the ionomer occurred. Here, 21 is an exterior material, 22 is a positive electrode, 23 is a separator, and 24 is a negative electrode.
[0025]
Example 1: An electrode group in which the above-described electrodes were laminated via a nonwoven fabric separator made of a fiber in which a polypropylene core material was thinly covered with polyethylene, and a heat-sealed surface made of an ionomer was formed on the surface of a PET film. The outside was covered with a laminate film. The laminate was heated to 140 ° C. while compressing the electrode group from the outer surface, and the polyethylene in the separator was melted to fuse the separator and the electrode, and the ionomer was melted to fuse the electrode and the laminate film. Then, the peripheral portion of the laminated film was adhered by heat fusion except for the opening for liquid injection, and then an 8N aqueous potassium hydroxide solution was injected with a syringe from the unfused portion for liquid injection, and the electrolytic solution was removed. It was left until it was sufficiently absorbed by the electrode group. Thereafter, the unfused portion used for the liquid injection was adhered by heat fusion to produce a sealed battery of Example 1. FIG. 3 shows a cross section of the battery. 2 are denoted by the same reference numerals, and detailed description thereof is omitted. Incidentally, reference numeral 30 denotes a heat fusion layer.
[0026]
Example 2: The above-mentioned electrodes were laminated via a nonwoven fabric separator made of polypropylene. At this time, lamination was performed while fine particles of polyethylene were being sprayed between the electrode and the separator. The outside of the electrode group thus prepared was covered with a laminate film having a heat-sealed surface made of an ionomer formed on the surface of a PET film. Heat to 140 ° C while compressing the electrode group from the outer surface of the laminate film, melt the polyethylene sprayed between the separator and the electrode, melt the separator and the electrode at the place where the polyethylene fine particles are sprayed, and melt the ionomer and melt the electrode and the laminate film. Were heat-sealed. Then, the peripheral portion of the laminated film was adhered by heat fusion except for the opening for liquid injection, and then an 8N aqueous potassium hydroxide solution was injected with a syringe from the unfused portion for liquid injection, and the electrolytic solution was removed. It was left until it was sufficiently absorbed by the electrode group. Thereafter, the unfused portion used for the injection was brought into close contact by heat fusion to produce a sealed battery of Example 2. FIG. 3 shows a cross section of the battery.
[0027]
Example 3: The above-mentioned electrodes were laminated via a nonwoven fabric separator made of polypropylene. At this time, lamination was performed while spraying short fibers between the electrodes and the separator, the surfaces of the polypropylene core being thinly covered with polyethylene. The outside of the electrode group thus prepared was covered with a laminate film having a heat-sealed surface made of an ionomer formed on the surface of a PET film. The laminate is heated to 140 ° C while compressing the electrodes from the outer surface of the laminate film.The polyethylene of short fibers sprayed between the separator and the electrode is melted to heat the separator and the electrode, and the ionomer is melted to heat the electrode and the laminate film. Fused. Then, the peripheral portion of the laminated film was adhered by heat fusion except for the opening for liquid injection, and then an 8N aqueous potassium hydroxide solution was injected with a syringe from the unfused portion for liquid injection, and the electrolytic solution was removed. It was left until it was sufficiently absorbed by the electrode group. Thereafter, the unfused portion used for the liquid injection was adhered by heat fusion to produce a sealed battery of Example 3. FIG. 3 shows a cross section of the battery.
[0028]
These batteries were charged at a current of 1 A for 1 hour and 20 minutes, and then repeatedly charged and discharged at a current of 1 A to 0.8 V, and the change in the discharge capacity with the cycle progression with respect to the initial discharge capacity was measured. FIG. 4 shows the results.
[0029]
As is evident from FIG. 4, the capacity of the battery of the example is small with the progress of the cycle, whereas the capacity of the battery of the comparative example is sharply reduced. When the outer shape of the battery was inspected to find out the cause, as shown in Table 1, the change in thickness was small in the battery according to the example, while the battery according to Comparative Example 1 was greatly expanded. all right.
[0030]
From this and the results of transmission X-ray imaging, the reason for the large decrease in the capacity of the battery of Comparative Example 1 was that the internal pressure of the battery increased due to the oxygen gas generated at the positive electrode at the end of charging, and was fixed only in the peripheral portion. It is considered that the battery of Comparative Example 1 could not suppress the swelling of the battery, and the electrode gap was widened and the discharge capacity was reduced. On the other hand, in each of the batteries of the examples, although the method is different, it is considered that the electrodes, the separator, and the exterior material are bonded to each other in at least a part thereof, so that the expansion of the battery is suppressed and the capacity reduction is considered to be small. Can be
[0031]
[Table 1]

(Comparative Examples 2-3, Example 4)
A positive electrode and a negative electrode for a lithium ion secondary battery were produced by the following method.
[0032]
Positive electrode:
6 g of acetylene black as a conductive material was added to 100 g of LiCoO ₂ , and a paste obtained by sufficiently mixing with 3 g (solid content) of PVdF was applied to an aluminum foil, followed by drying and pressing to prepare. This electrode was cut out to a size of 300 mm × 50 mm and used. The theoretical capacity calculated from the amount of the active material of the positive electrode is 800 mAh.
[0033]
Negative electrode:
6 g (solid content) of PVdF was added to 100 g of MCF which was a fibrous graphite, kneaded well, and a paste was applied to a copper foil, followed by drying and pressing. This electrode was cut out to 340 mm × 52 mm and used.
[0034]
These electrodes were wound around a winding core having an outer diameter of 20 mm while insulating with a polyethylene porous membrane separator. At this time, lamination was performed while spraying ionomer powder having a melting point of 92 ° C. between the positive and negative electrodes and the separator. The electrode wound in this manner was removed from the winding core and crushed to form a flat electrode group. This electrode group was covered with an ionomer and an aluminum foil laminate. Then, the laminate is heated to 100 ° C. while pressing the electrode group from the outer surface of the laminate film. The ionomer between the electrode group and the inner surface of the laminate film is thermally fused between the separator and the electrode. The part was heat-sealed to the periphery of the electrode except for the place for liquid injection. Thereafter, a solution obtained by dissolving 1 mol of LiPF6 in a mixture of equal amounts of ethylene carbonate and methyl ethyl carbonate was injected as a liquid electrolyte from a location for liquid injection on the outer peripheral portion with a syringe, and the injection hole was thermally fused. I blocked it. This battery is referred to as Example 4.
[0035]
A battery prepared in exactly the same procedure as in Example 4 except that the ionomer powder was not sprayed is referred to as Comparative Example 2.
[0036]
Also, Comparative Example 3 is a battery in which polyethylene powder was sprayed instead of the ionomer powder of Example 4 and the heat fusion was performed at 140 ° C., which is equal to or higher than the melting point of polyethylene.
[0037]
After charging them at a constant current up to 4.2 V at a current of 400 mA and charging them at a constant voltage of 4.2 V for a total of 5 hours, a cycle of discharging them at 800 mA to 3 V is repeated, and the discharge capacity accompanying the progress of the cycle is repeated. Was measured. The result is shown in FIG.
[0038]
From FIG. 5, almost no deterioration was observed in the battery of Example 4 in which the electrode and the separator were heat-sealed with the ionomer powder, but rapid deterioration occurred in Comparative Example 2 in which heat-sealing was not performed. In Comparative Example 3 in which heat fusion was performed with polyethylene powder, no capacity was obtained from the beginning of the cycle. In order to investigate the cause, the battery after the cycle was disassembled and observed. As a result, the battery of Example 4 had the electrode group integrated and the positive and negative electrodes were in close contact with each other. Many discharges and precipitation of the remaining metallic lithium were observed. From this, in Comparative Example 2 in which no fusion was performed, the electrode spacing was widened with the progress of the charge / discharge cycle, the current distribution became uneven, and metal lithium was precipitated. As a result, the capacity was reduced with the progress of the cycle. It is thought that it was.
[0039]
Further, in Comparative Example 3, since the electrode group was firmly integrated as in the example because heat fusion was performed using polyethylene powder, the impedance was measured to be very high as a result of the impedance measurement of the battery. Was. Thereafter, the battery was forcibly disassembled and the separator was observed with a scanning electron microscope. As a result, it was found that almost all of the fine holes provided in the separator had shrunk and closed. From this, in the battery of Comparative Example 3, polyethylene powder was used for heat fusion, and the fusion temperature was raised to 140 ° C., so that the shutdown mechanism, which is a safety mechanism of the separator, acted to close the pores, and the ions were moved. It was considered that the battery did not function as a battery.
[0040]
This indicates that it is necessary to select a heat-sealing resin used for heat-sealing at a temperature lower than the pore closing temperature of the separator.
[0041]
【The invention's effect】
By finding a simple and effective battery construction method in which electrodes and separators are heat-sealed to each other, a lithium ion secondary battery with a low energy density and a low profile can be used without using any special electrodes such as polymer batteries. In addition to being able to provide batteries, it has become possible to reduce the thickness of nickel-metal hydride secondary batteries and nickel cadmium secondary batteries, which were practically impossible with other than metal cans.
[0042]
In addition, since there is no limit in forming a can like a metal can, a battery having a thickness of 1 mm or less is easily produced, and its industrial contribution greatly increases.
[Brief description of the drawings]
FIG. 1 is a diagram showing a configuration example of the present invention.
FIG. 2 is a cross-sectional view of a part of the battery of Comparative Example 1.
FIG. 3 is a battery cross-sectional view showing a part of the batteries of Examples 1 to 3.
FIG. 4 is a charge / discharge cycle characteristic diagram of the batteries of Examples 1 to 3 and Comparative Example 1.
FIG. 5 is a charge / discharge cycle characteristic diagram of the batteries of Example 4 and Comparative Example 2.
[Explanation of symbols]
1 Exterior material 2 Positive electrode 3 Separator 4 Negative electrode

Claims

In a sealed battery in which an electrode group in which a positive electrode and a negative electrode are stacked with a separator interposed therebetween is covered with a thin film having a fused surface on an inner surface, the separator has at least a part of its surface covered with polyethylene, A sealed battery wherein the electrode and the separator are at least partially fused to each other by heat-compression bonding after forming the electrode group.

Alkaline battery wherein the battery uses an aqueous alkaline solution as an electrolyte
The sealed battery according to claim 1, wherein

The sealed battery according to claim 1, wherein the battery uses a non-aqueous electrolyte as an electrolyte.