JP2004273388A

JP2004273388A - Cylindrical storage battery

Info

Publication number: JP2004273388A
Application number: JP2003066266A
Authority: JP
Inventors: Teruhito Nagae; 輝人長江; Yasuhiro Kudo; 康洋工藤
Original assignee: Sanyo Electric Co Ltd
Current assignee: Sanyo Electric Co Ltd
Priority date: 2003-03-12
Filing date: 2003-03-12
Publication date: 2004-09-30

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cylindrical storage battery with safety improved through securing a gas channel even if the temperature of the battery rises abnormally. <P>SOLUTION: The cylindrical storage battery is provided with a spiral-shaped electrode group having a winding core space part 10a remaining after winding cores used in forming the spiral-shaped electrode group at a center part are removed, and is characterised in that the METSUKE (weight per area) of separators 11a (12a, 13a, 14a, 15a, 16a) arranged at the winding core space part 10a is smaller than that of separators arranged at an electrode facing part. Thus, if the METSUKE of the separators arranged at the winding core space part 10a is small, the fiber volume existing there 10a can be reduced. With this, when an abnormal heat is generated before the separators are molten, it becomes hard for a gas exhaust port fitted at a sealing body to be choked, and the time needed for choking can be elongated. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

【０００１】
【発明の属する技術分野】
本発明は、ニッケル−水素蓄電池、ニッケル−カドミウム蓄電池などのアルカリ蓄電池あるいはリチウムイオン電池などの非水電解質電池に係り、特に、正極と負極との間にセパレータを介在させて渦巻状に巻回した渦巻状電極群を円筒形外装缶内に備えた円筒形蓄電池に関する。
【０００２】
【従来の技術】
一般に、ニッケル−水素蓄電池、ニッケル−カドミウム蓄電池などのアルカリ蓄電池あるいはリチウムイオン電池などの非水電解質電池は、正極と負極の間にセパレータを介在させ、これらを渦巻状に巻回して電極群を形成した後に上下端に集電体を接続して電極体を形成する。この電極体を円筒状の金属製外装缶（電池缶）に収納し、正極用集電体より延出する集電リード板を封口体下面に溶接し、電解液を注入した後、外装缶の開口部に絶縁ガスケットを介在させて封口体を装着することにより密閉して構成されている。
【０００３】
このような電池に用いられるセパレータにおいては、耐酸化性に優れ、かつ電解液に対する耐性に優れるとともに、充分な量の電解液を保持でき、電解液を保持した状態で充分なガス透過性を有することが要望されている。このようなセパレータに用いられる材質としては、ナイロンなどのポリアミド系繊維や、ポリプロピレン、ポリエチレンなどのポリオレフィン系樹脂繊維が使用されている。
【０００４】
【発明が解決しようとする課題】
ところで、ポリアミド系樹脂繊維やポリオレフィン系樹脂繊維は８０〜１２０℃付近に軟化点を有している。このため、過充電時やハイレートの放電時、あるいは誤使用等によって、電池内部の温度がこの軟化点を超える温度まで上昇すると、ポリアミド系樹脂繊維やポリオレフィン系樹脂繊維からなるセパレータの軟化が始まる。セパレータが軟化した後、冷えて固化すると、固化した部分の開孔は閉塞されることとなる。すると、電池内でガスが発生すると、発生したガスの通路が閉塞されて、電池膨れが生じるという問題を生じた。
【０００５】
また、セパレータが軟化し、さらに電池内部温度が上昇して、セパレータの融点まで温度上昇すると、溶融した樹脂が電池内の空間部に沿って、即ち、渦巻状に巻回された電極群の中心部（電池内で空間部が形成されている部分）に沿って這い上がるようになる。すると、外装缶（電池缶）の開口部を封止する封口体に設けられたガスの排気口を溶融した樹脂が塞ぐ事態も生じて、電池の内部圧力が異常に上昇し、電池缶の膨れ等の電池の変形も生じるようになる。
【０００６】
そこで、本発明は上記問題点を解消するためになされたものであって、電池の温度が異常に上昇しても、ガス通路を確保できるようにして安全性が向上した円筒形蓄電池を提供することを目的とする。
【０００７】
【課題を解決するための手段】
上記目的を達成するため、本発明の円筒形蓄電池は、中心部に渦巻状電極群を形成する際に用いられた巻芯が除去された後に残存した巻芯空間部を有する渦巻状電極群を備え、かつ巻芯空間部に配置されたセパレータの目付は電極対向部に配置されたセパレータの目付よりも小さいことを特徴とする。
【０００８】
このように、巻芯空間部に配置されたセパレータの目付が電極対向部に配置されたセパレータの目付よりも小さいと、巻芯空間部に存在する繊維量を少なくすることが可能となる。これにより、セパレータが溶融するまでの異常発熱が発生した場合、封口体に設けられているガス排気口が閉塞されにくくなるとともに、閉塞されるまでの時間を長くすることが可能となる。これにより、この種のセパレータを用いた電池の安全性が向上することとなる。この場合、電極対向部に配置されたセパレータの目付も低減すると、繊維量が低減した分だけ電解液の保持量が低減するようになる。この結果、電池特性を維持することができなくなるとともに、耐ショート性も低下するという不具合も発生するようになるので好ましくない。
【０００９】
また、巻芯空間部に配置されたセパレータの厚みを電極対向部に配置されたセパレータの厚みよりも薄くすると、巻芯空間部の空間容積が増加するようになるので、缶底側から電池上部への排気通路を大きくすることが可能となる。これにより、セパレータが溶融するには至らないが、高率（ハイレート）で連続的に充電された電池内部において多量のガスが発生するような異常が発生した場合に、電池内部のガスは缶底側に滞留することなく安全弁に到達するできるようになる。この結果、電池の温度が異常に上昇した場合の安全性を向上させることが可能となる。
【００１０】
この場合も、電極対向部に配置されたセパレータの厚みも薄くすると、この部分のセパレータの見かけ密度も減少して、電解液の保持量が低減して電池特性を維持することができなくなるので好ましくない。なお、巻芯空間部の空間容積が増加すると、この巻芯空間に溶接電極を挿入して集電タブと缶底とを溶接する場合においては、缶底での溶接性が向上するので好ましい。
【００１１】
また、巻芯空間部に配置されたセパレータの目付および厚みを電極対向部に配置されたセパレータの目付および厚みよりも小さくすると、巻芯空間部に存在する繊維量を少なくすることが可能になるとともに、巻芯空間部の空間容積を増加させることが可能となる。これにより、封口体に設けられているガス排気口が閉塞されにくくなるとともに、缶底側から電池上部への排気通路を大きくすることが可能となり、さらに、巻芯空間部に溶接電極を容易に挿入することが可能となるので、缶底での溶接性が向上する。
【００１２】
さらに、巻芯空間部に配置されたセパレータが電極対向部に配置されたセパレータの目付よりも小さく、かつ厚みも薄くなるように二重化（２枚のセパレータを貼り合わせること）されていると、巻芯空間部に存在する繊維量が少なくなるとともに、巻芯空間部の空間容積も大きくなる。これにより、封口体に設けられているガス排気口が閉塞されにくくなるとともに、缶底側から電池上部への排気通路も大きくなるため、この種のセパレータを用いた電池の安全性がさらに向上することとなる。
【００１３】
【発明の実施の形態】
以下に、本発明をニッケル−水素蓄電池に適用した場合の実施の形態を図１および図２に基づいて説明する。なお、図１はセパレータの断面を模式的に示す断面図である。また、図２は図１のセパレータを用いて形成された渦巻状電極群を外装缶内に収容した状態の横断面を模式的に示す断面図である。
【００１４】
１．セパレータの作製
（１）実施例１
ポリエチレン繊維（ＰＥ：融点は１３８℃）とポリプロピレン繊維（ＰＰ：融点は１６０℃）を所定の配合比率となるように配合した。ついで、これらの繊維を空気中に飛散させて金網で捕集して湿式抄紙した後、圧延して目付が４０ｇ／ｍ^２で、厚みが０．１０ｍｍの第１基布１１ａを作製した。また、上述と同様に湿式抄紙した後、圧延して、目付が２０ｇ／ｍ^２で、厚みが０．０５ｍｍの第２基布１１ｂを作製した。ついで、第１基布１１ａの上に第２基布１１ｂを配置して、これらを張り合わせた。このとき、後に正、負極とともに渦巻状に巻回された際に、巻芯空間部１０ａ（図２参照）に第１基布１１ａのみが配置されるように張り合わせた（二重化した）後、親水化処理して、図１（ａ）に示すような実施例１のセパレータ１１を作製した。
【００１５】
（２）実施例２
海成分がポリエチレンテレフタレート（ＰＥＴ）で、島成分がポリプロピレン（ＰＰ）からなる海島型繊維を所定の配合比率となるように配合した後、これらの繊維を空気中に飛散させて金網で捕集して湿式抄紙した。ついで、後に正、負極とともに渦巻状に巻回された際に、巻芯空間部１０ａ（図２参照）に配置される部分１２ａの海成分（ＰＥＴ）をアルカリにて溶脱した。この後、圧延し、親水化処理して、巻芯空間部１０ａに配置される部分１２ａの目付が４０ｇ／ｍ^２で、その他の部分の目付が６０ｇ／ｍ^２で、厚みが０．１５ｍｍの実施例２のセパレータ１２を、図１（ｂ）に示すように作製した。
【００１６】
（３）実施例３
海成分がポリアミドで、島成分がポリプロピレン（ＰＰ）からなる海島型繊維を所定の配合比率となるように配合した後、これらの繊維を空気中に飛散させて金網で捕集して湿式抄紙した。ついで、後に正、負極とともに渦巻状に巻回された際に、巻芯空間部１０ａ（図２参照）に配置される部分１３ａの海成分（ポリアミド）をアルカリにて溶脱した。この後、圧延し、親水化処理して、巻芯空間部１０ａに配置される部分１３ａの目付が４０ｇ／ｍ^２で、その他の部分の目付が６０ｇ／ｍ^２で、厚みが０．１５ｍｍの実施例３のセパレータ１３を、図１（ｃ）に示すように作製した。
【００１７】
（４）実施例４
ポリエチレン繊維（ＰＥ：融点は１３８℃）とポリプロピレン繊維（ＰＰ：融点は１６０℃）を所定の配合比率となるように配合した。この後、これらの繊維を空気中に飛散させて金網で捕集して湿式抄紙した後、圧延して目付が６０ｇ／ｍ^２で、厚みが０．１５ｍｍの基布を作製した。ついで、後に正、負極とともに渦巻状に巻回された際に、巻芯空間部１０ａ（図２参照）に配置される部分１４ａを凹凸があるローラで圧延して、この部分１４ａの厚みが０．１２ｍｍになるように圧延した。この後、親水化処理して、図１（ｄ）に示すような実施例４のセパレータ１４を作製した。
【００１８】
（５）実施例５
ポリエチレン繊維（ＰＥ：融点は１３８℃）とポリプロピレン繊維（ＰＰ：融点は１６０℃）を所定の配合比率となるように配合した。この後、これらの繊維を空気中に飛散させて金網で捕集して湿式抄紙した後、圧延して目付が６０ｇ／ｍ^２で、厚みが０．１５ｍｍの基布を作製した。ついで、後に正、負極とともに渦巻状に巻回された際に、巻芯空間部１０ａ（図２参照）に配置される部分１５ａのみに熱を加えて加圧して、この部分１５ａの厚みを０．１２ｍｍに低減させた。この後、親水化処理して、図１（ｅ）に示すような実施例５のセパレータ１５を作製した。
【００１９】
（６）実施例６
海成分がポリエチレンテレフタレート（ＰＥＴ）で、島成分がポリプロピレン（ＰＰ）からなる海島型繊維を所定の配合比率となるように配合した後、これらの繊維を空気中に飛散させて金網で捕集して湿式抄紙した。ついで、後に正、負極とともに渦巻状に巻回された際に、巻芯空間部１０ａ（図２参照）に配置される部分１６ａの海成分（ＰＥＴ）をアルカリにて溶脱した。この後、圧延して、巻芯空間部１０ａに配置される部分１６ａの目付が４０ｇ／ｍ^２で、その他の部分の目付が６０ｇ／ｍ^２で、厚みが０．１５ｍｍの基布を作製した。ついで、この基布の巻芯空間部１０ａに配置される部分１６ａを凹凸があるローラで圧延して、この部分１６ａの厚みを０．１２ｍｍに圧延した。この後、親水化処理して、図１（ｆ）に示すような実施例６のセパレータ１６を作製した。
【００２０】
（７）比較例１
海成分がポリアミドで、島成分がポリプロピレン（ＰＰ）からなる海島型繊維を所定の配合比率となるように配合した後、これらの繊維を空気中に飛散させて金網で捕集して湿式抄紙して基布とした。ついで、この基布の海成分（ポリアミド）をアルカリにて溶脱した。この後、圧延した後、親水化処理して、目付が４０ｇ／ｍ^２で、厚みが０．１０ｍｍの比較例１のセパレータ１７を、図１（ｇ）に示すように作製した。
【００２１】
（８）比較例２
ポリエチレン繊維（ＰＥ：融点は１３８℃）とポリプロピレン繊維（ＰＰ：融点は１６０℃）を所定の配合比率となるように配合した。この後、これらの繊維を空気中に飛散させて金網で捕集して湿式抄紙した後、圧延して目付が６０ｇ／ｍ^２で厚みが０．１５ｍｍの基布を作製した。ついで、この基布を凹凸があるローラで加圧して、厚みを０．１２ｍｍに圧延した。この後、親水化処理して、目付が４０ｇ／ｍ^２で、厚みが０．１０ｍｍの比較例２のセパレータ１８を、図１（ｈ）に示すように作製した。
【００２２】
（９）比較例３
ポリエチレン繊維（ＰＥ：融点は１３８℃）とポリプロピレン繊維（ＰＰ：融点は１６０℃）を所定の配合比率となるように配合した。この後、これらの繊維を空気中に飛散させて金網で捕集して湿式抄紙し、圧延した後、親水化処理して、目付が６０ｇ／ｍ^２で、厚みが０．１５ｍｍの比較例３のセパレータ１９を、図１（ｉ）に示すように作製した。
【００２３】
２．ニッケル正極の作製
水酸化ニッケルを主成分とする正極活物質粉末１００質量部と、０．２質量％のヒドロキシプロピルセルロースを溶解させた水溶液５０質量部とを混合して正極活物質スラリーを調製した。この正極活物質スラリーを多孔度９５％の発泡ニッケル２１に充填し、乾燥させた後、これを圧延してニッケル正極２０を作製した。なお、電池の公称容量が１５００ｍＡｈになるように正極活物質スラリーを発泡ニッケル２１に充填した。
【００２４】
３．水素吸蔵合金負極の作製
水素吸蔵合金粉末にポリテトラフルオロエチレン（ＰＴＦＥ）などの結着剤と、適量の水とを加えて混合し、水素吸蔵合金ペーストを調製した。ついで、この水素吸蔵合金ペーストを負極基板（パンチングメタル）３１の両面に塗布し、乾燥した後、所定の厚みとなるようにプレスして水素吸蔵合金負極３０を作製した。なお、電極容量が２２５０ｍＡｈになるように水素吸蔵合金ペーストをパンチングメタル３１に充填した。
【００２５】
４．ニッケル−水素蓄電池の作製
ついで、上述のように作製したニッケル正極２０の上に、上述のように作製した各セパレータ１１（１２，１３，１４，１５，１６，１７，１８，１９）を配置した。また、上述のように作製した水素吸蔵合金負極３０の上に、各セパレータ１１（１２，１３，１４，１５，１６，１７，１８，１９）を配置した。ついで、これらを重ね合わせた後、２枚のセパレータ１１（１２，１３，１４，１５，１６，１７，１８，１９）の端部１１ａ（１２ａ，１３ａ，１４ａ，１５ａ，１６ａ，１７ａ，１８ａ，１９ａ）を図示しない巻芯のスリット部に狭持した。
【００２６】
ついで、巻芯を所定の回数だけ巻回して、ニッケル正極２０、セパレータ１１（１２，１３，１４，１５，１６，１７，１８，１９）、水素吸蔵合金負極３０およびセパレータ１１（１２，１３，１４，１５，１６，１７，１８，１９）を渦巻き状に巻き取った。この後、巻芯を引き抜くことにより渦巻状電極群１０を作製した。この場合、巻芯を引き抜くことにより渦巻状電極群１０の中心部に巻芯空間部１０ａが形成されることとなる。ついで、これらの電極群１０の上端部に正極集電体（図示せず）を溶接し、下端部に負極集電体（図示せず）を溶接した後、これらを有底筒状の外装缶４０内にそれぞれ挿入した。
【００２７】
この後、負極集電体を外装缶４０の内底面に溶接するとともに、正極集電体から延出する集電リード板の先端部を安全弁を内蔵する封口体（図示せず）の底面に溶接し、外装缶４０内に所定量の電解液（水酸化カリウム（ＫＯＨ）と水酸化リチウム（ＬｉＯＨ）と水酸化ナトリウム（ＮａＯＨ）の混合水溶液）を注入した。ついで、封口体を外装缶４０の開口部に絶縁ガスケットを介して載置し、外装缶４０の開口部の端部を内方にかしめることによって電池を密閉して、公称容量１５００ｍＡｈのＡＡサイズの各ニッケル−水素蓄電池Ａ〜ＦおよびＸ〜Ｚを作製した。
【００２８】
なお、セパレータ１１を用いたものを電池Ａとし、セパレータ１２を用いたものを電池Ｂとし、セパレータ１３を用いたものを電池Ｃとし、セパレータ１４を用いたものを電池Ｄとし、セパレータ１５を用いたものを電池Ｅとし、セパレータ１６を用いたものを電池Ｆとし、セパレータ１７を用いたものを電池Ｘとし、セパレータ１８を用いたものを電池Ｙとし、セパレータ１９を用いたものを電池Ｚとした。
【００２９】
５．試験
（１）短絡試験
各１００００個の電極群をそれぞれ外装缶４０内に挿入した状態で、正、負極間の絶縁抵抗を測定して、この抵抗値が１．５ｋΩ以下を短絡と判定して、短絡が発生した電池の個数を求めた。ついで、求めた短絡発生個数に基づいて短絡発生率（％）を算出すると、下記の表１に示すような結果が得られた。
【００３０】
（２）缶底溶接性試験
各１００００個の電極群を外装缶４０内に挿入した状態で、それぞれの負極集電体をそれぞれの外装缶４０の内底面に溶接した際に、溶接不良が発生した個数を求めた。ついで、求めた溶接不良発生個数に基づいて溶接不良発生率（％）を算出すると、下記の表１に示すような結果が得られた。
【００３１】
（３）ガスバーナー燃焼による安全性試験
まず、上述のようにして作製した各ニッケル−水素蓄電池Ａ〜ＦおよびＸ〜Ｚを用いて、これらの各電池を、２５℃の温度雰囲気で、１２０ｍＡの充電電流で１６時間充電した後、１時間休止し、２４０ｍＡの放電電流で放電終止電圧が１．０Ｖになるまで放電した後、１時間休止する。この充放電を３回繰り返して各電池Ａ〜ＦおよびＸ〜Ｚを活性化した。
【００３２】
ついで、上述のように活性化した各ニッケル−水素蓄電池Ａ〜ＦおよびＸ〜Ｚをそれぞれ１００００個ずつ用いて、２５℃の温度雰囲気で１５００ｍＡの充電電流で充電を行い、満充電に達した後、電池電圧が１０ｍＶ低下（−ΔＶ＝１０ｍＶ）した時点で充電を１時間休止させた。この後、ガスバーナーを燃焼させ、電池温度を２５０℃に上昇させて、封口体が外れた電池の個数の割合（封口体外れ率）を求めると、下記の表１に示すような結果となった。
【００３３】
（４）高率充電時の安全性試験
また、上述のように活性化した各ニッケル−水素蓄電池Ａ〜ＦおよびＸ〜Ｚをそれぞれ１００００個ずつ用いて、２５℃の温度雰囲気で６０００ｍＡの充電電流で短絡が発生するまで充電を行い、短絡が発生した時点で封口体が外れた電池の個数の割合（封口体外れ発生率）を求めると、下記の表１に示すような結果となった。
【００３４】
（５）サイクル寿命試験
上述のようにして活性化した各ニッケル−水素蓄電池Ａ〜ＦおよびＸ〜Ｚをそれぞれ１００００個ずつ用いて、２５℃の温度雰囲気で１５００ｍＡの充電電流で充電し、満充電に達した後、電池電圧が１０ｍＶ低下（−ΔＶ＝１０ｍＶ）した時点で充電を１時間休止させる。ついで、１５００ｍＡの放電電流で電池電圧が１．０Ｖになるまで放電させるという充放電サイクルを繰り返して行い、初期容量との比率が６０％に達したサイクル（回）をサイクル寿命として求めると、下記の表１に示すような結果となった。
【００３５】
【表１】

【００３６】
上記表１の結果から明らかなように、目付（６０ｇ／ｍ^２）および厚み（０．１５ｍｍ）が均一なセパレータ１９を用いた電池Ｚにおいては、缶底溶接不良発生率が０．１０％で、ガスバーナー燃焼時の封口体外れ率が１５％で、６Ａ高率充電時の封口体外れ率が１０％と大きいことが分かる。これは、巻芯空間部１０ａに存在するセパレータ１９ａの厚みが０．１５ｍｍと大きいために、巻芯空間部１０ａの容積が減少して溶接電極を巻芯空間部１０ａに挿入する際に、巻芯空間部１０ａに存在するセパレータ１９ａが邪魔になったためと考えられる。
また、巻芯空間部１０ａに存在するセパレータ１９ａの目付が６０ｇ／ｍ^２と大きいために、巻芯空間部１０ａに存在する繊維量が多くなる。これにより、ガスバーナー燃焼時や高率充電時に、セパレータ１９が溶融するまでの異常発熱が発生した場合、溶融した繊維が封口体に設けられているガス排気口を閉塞して、封口体外れが生じたと考えられる。
【００３７】
また、目付（６０ｇ／ｍ^２）および厚み（０．１２ｍｍ）が均一なセパレータ１８を用いた電池Ｙにおいては、ガスバーナー燃焼時の封口体外れ率が１５％と大きく、サイクル寿命が４００サイクルと小さいことが分かる。これは、巻芯空間部１０ａに存在するセパレータ１８ａの目付が６０ｇ／ｍ^２と大きいために、巻芯空間部１０ａに存在する繊維量が多くなる。これにより、ガスバーナー燃焼時にセパレータ１８が溶融するまでの異常発熱が発生した場合、溶融した繊維が封口体に設けられているガス排気口を閉塞して、封口体外れが生じたと考えられる。また、電極対向部のセパレータ１８の厚みが０．１２ｍｍと小さいために、電解液の保持量が少なくなって、サイクル寿命が小さくなったと考えられる。
【００３８】
さらに、目付（４０ｇ／ｍ^２）および厚み（０．１０ｍｍ）が均一なセパレータ１７を用いた電池Ｘにおいては、短絡発生率が０．１０％と大きく、かつサイクル寿命も４００サイクルと小さいことが分かる。これは、セパレータ１７の目付は４０ｇ／ｍ^２と小さく、かつ厚みが０．１２ｍｍと小さいために、正極と負極が直接接触しやすくなったためと考えられる。また、電極対向部のセパレータ１７の目付は４０ｇ／ｍ^２と小さく、かつ厚みが０．１２ｍｍと小さいために、電解液の保持量が少なくなって、サイクル寿命が小さくなったと考えられる。
【００３９】
これに対して、巻芯空間部１０ａの厚みが０．１２ｍｍのセパレータ１４，１５を用いた電池Ｄ，Ｅにおいては、ガスバーナー燃焼時の封口体外れ率が１５％と大きい反面、短絡発生率は０．０２％で、缶底溶接不良発生率は０．０３％で、６Ａ高率充電時の封口体外れ率は３％と小さく、サイクル寿命は５００サイクルと大きいことが分かる。これは、巻芯空間部１０ａに配置されたセパレータ１４ａ，１５ａに圧延処理が施されて厚みが薄くなっているので、巻芯空間部の空間容積が増加するようになる。
【００４０】
この結果、缶底側から電池上部への排気通路を大きくすることが可能となり、セパレータ１４，１５が溶融するには至らないが、高率（ハイレート）で連続的に充電された電池内部において多量のガスが発生するような異常が発生した場合に、電池内部のガスは缶底側に滞留することなく安全弁に到達するできるようになったためと考えられる。
【００４１】
これにより、電池の温度が異常に上昇した場合の安全性を向上させることが可能となるが、巻芯空間部１０ａ以外の電極対向部分のセパレータ１４，１５も圧延処理すると、この部分のセパレータの見かけ密度も減少して、電解液の保持量が低減して電池特性を維持することができなくなるので好ましくない。この場合、巻芯空間部１０ａの空間容積が増加するので、この巻芯空間部１０ａに溶接棒を挿入して集電タブと缶底とを溶接する場合の溶接性が向上する。
【００４２】
また、巻芯空間部１０ａの目付が４０ｇ／ｍ^２のセパレータ１２，１３を用いた電池Ｂ，Ｃにおいては、缶底溶接不良発生率は０．１０％と大きい反面、短絡発生率は０．０２％で、ガスバーナー燃焼時の封口体外れ率が４％で、６Ａ高率充電時の封口体外れ率は３％と小さく、サイクル寿命は５００サイクルと大きいことが分かる。これは、巻芯空間部１０ａに配置されたセパレータ１２ａ，１３ａに目付低減処理が施されているので、巻芯空間部１０ａに存在する繊維量を少なくすることが可能となる。
【００４３】
これにより、セパレータ１４ａ，１５ａが溶融するまでの異常発熱が発生しても、封口体に設けられているガス排気口が閉塞されにくくなったためと考えられる。この場合、巻芯空間部１０ａ以外の電極対向部のセパレータ１４，１５の目付も低減すると、繊維量が低減した分だけ電解液の保持量が低減して電池特性を維持することができなくなるとともに、耐ショート性も低下するという不具合も発生するようになるので好ましくない。
【００４４】
また、巻芯空間部１０ａの目付が４０ｇ／ｍ^２で厚みが０．１２ｍｍのセパレータ１６を用いた電池Ｆにおいては、短絡発生率は０．０２％で、缶底溶接不良発生率は０．０３％で、ガスバーナー燃焼時の封口体外れ率は２％で、６Ａ高率充電時の封口体外れ率は２％と小さく、サイクル寿命は５００サイクルと大きいことが分かる。これは、巻芯空間部１０ａに配置されたセパレータ１６ａは目付低減処理が施されているとともに圧延処理が施されているので、巻芯空間部１０ａに存在する繊維量を少なくすることが可能になるとともに、巻芯空間部１０ａの空間容積も増加するようになる。これにより、封口体に設けられているガス排気口が閉塞されにくくなるとともに、缶底側から電池上部への排気通路も大きくなったためと考えられる。
【００４５】
さらに、巻芯空間部１０ａに目付が４０ｇ／ｍ^２で厚みが０．１０ｍｍの第１基布１１ａのみが存在するようにした貼り合わせセパレータ１１を用いた電池Ａにおいては、短絡発生率は０．０２％で、缶底溶接不良発生率は０．０１％で、ガスバーナー燃焼時の封口体外れ率は１％で、６Ａ高率充電時の封口体外れ率は１％と小さく、サイクル寿命は５００サイクルと大きいことが分かる。これは、巻芯空間部１０ａに配置されたセパレータ１１ａは目付が小さく、かつ厚みも薄いために、巻芯空間部１０ａに存在する繊維量は少なく、かつ巻芯空間部１０ａの空間容積も大きい。これにより、封口体に設けられているガス排気口が閉塞されにくくなるとともに、缶底側から電池上部への排気通路も大きくなったためと考えられる。
【００４６】
【発明の効果】
上述のように、本発明においては、巻芯空間部１０ａに配置されたセパレータの目付が小さいか、厚みが薄いか、あるいは目付が小さくかつ厚みが薄く形成されているので、巻芯空間部１０ａに存在する繊維量を少なくすることが可能となったり、あるいは巻芯空間部１０ａの空間容積を増大させたり、さらに巻芯空間部１０ａでの繊維量が少なくかつ空間容積を増大させることが可能となる。これにより、セパレータが溶融するまでの異常発熱が発生した場合、封口体に設けられているガス排気口が閉塞されにくくなるとともに、閉塞されるまでの時間を長くすることが可能となる。また、缶底側から電池上部への排気通路も大きくなる。これにより、この種のセパレータを用いた電池の安全性が向上することとなる。さらに、巻芯空間部１０ａの空間容積が増加するので、溶接棒を容易に挿入することができるようになるので、缶底での溶接性が向上する。
【００４７】
なお、上述した実施形態においては、本発明の好ましい例としてニッケル−水素蓄電池に適用する例について説明したが、本発明はニッケル−水素蓄電池に限らず、ニッケル−カドミウム蓄電池などの他のアルカリ蓄電池、あるいはリチウムイオン電池などの非水電解質電池に適用できることは明らかである。さらに、上述した実施形態においては、本発明を円筒型の蓄電池に適用した例について説明したが、本発明はこれに限らず、巻回電極群を備える各種の形状の蓄電池に本発明を適用できることもいうまでもない。
【図面の簡単な説明】
【図１】セパレータの断面を模式的に示す断面図である。
【図２】図１のセパレータを用いて形成された渦巻状電極群を外装缶内に収容した状態の横断面を模式的に示す断面図である。
【符号の説明】
１０…渦巻状電極群、１０ａ…巻芯空間部、１１，１２，１３，１４，１５，１６，１７，１８，１９…セパレータ、１１ａ…第１基布、１２ａ…第２基布、１３ａ，１４ａ，１５ａ，１６ａ，１７ａ，１８ａ，１９ａ…巻芯空間部に配置されるセパレータ、２０…ニッケル正極、２１…発泡ニッケル、３０…水素吸蔵合金負極、３１…負極基板（パンチングメタル）、４０…外装缶（電池缶）[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a nickel-hydrogen storage battery, a non-aqueous electrolyte battery such as an alkaline storage battery such as a nickel-cadmium storage battery or a lithium ion battery, and particularly, spirally wound with a separator interposed between a positive electrode and a negative electrode. The present invention relates to a cylindrical storage battery provided with a spiral electrode group in a cylindrical outer can.
[0002]
[Prior art]
In general, alkaline storage batteries such as nickel-hydrogen storage batteries and nickel-cadmium storage batteries or non-aqueous electrolyte batteries such as lithium-ion batteries have a separator interposed between a positive electrode and a negative electrode, and these are spirally wound to form an electrode group. After that, a current collector is connected to the upper and lower ends to form an electrode body. The electrode body is housed in a cylindrical metal outer can (battery can), a current collecting lead plate extending from the positive electrode current collector is welded to the lower surface of the sealing body, and an electrolyte is injected. It is hermetically sealed by mounting a sealing body with an insulating gasket interposed in the opening.
[0003]
The separator used in such a battery has excellent oxidation resistance, and is excellent in resistance to an electrolytic solution, can hold a sufficient amount of the electrolytic solution, and has sufficient gas permeability in a state in which the electrolytic solution is held. It is desired. As a material used for such a separator, polyamide fibers such as nylon and polyolefin resin fibers such as polypropylene and polyethylene are used.
[0004]
[Problems to be solved by the invention]
By the way, polyamide resin fibers and polyolefin resin fibers have a softening point at around 80 to 120 ° C. For this reason, when the temperature inside the battery rises to a temperature exceeding this softening point due to overcharging, high-rate discharging, misuse, or the like, the softening of the separator made of polyamide resin fibers or polyolefin resin fibers starts. When the separator softens and then cools and solidifies, the opening in the solidified portion is closed. Then, when gas is generated in the battery, the passage of the generated gas is closed, and there is a problem that the battery swells.
[0005]
Also, when the separator softens and the temperature inside the battery rises to the melting point of the separator, the melted resin flows along the space inside the battery, that is, the center of the spirally wound electrode group. Crawling along the portion (the portion where the space is formed in the battery). Then, a situation occurs in which the molten resin blocks the gas exhaust port provided in the sealing body that seals the opening of the outer can (battery can), and the internal pressure of the battery rises abnormally, causing the battery can to swell. And the like.
[0006]
Therefore, the present invention has been made to solve the above problems, and provides a cylindrical storage battery having improved safety by securing a gas passage even when the temperature of the battery abnormally rises. The purpose is to:
[0007]
[Means for Solving the Problems]
In order to achieve the above object, the cylindrical storage battery of the present invention includes a spiral electrode group having a core space remaining after the core used in forming the spiral electrode group in the center is removed. It is characterized in that the basis weight of the separator provided and arranged in the core space is smaller than the basis weight of the separator arranged in the electrode facing part.
[0008]
As described above, when the basis weight of the separator disposed in the core space is smaller than the basis weight of the separator disposed in the electrode facing portion, the amount of fibers existing in the core space can be reduced. Accordingly, when abnormal heat generation occurs until the separator is melted, the gas exhaust port provided in the sealing body is less likely to be closed, and the time until the gas outlet is closed can be lengthened. Thereby, the safety of the battery using this kind of separator is improved. In this case, if the basis weight of the separator disposed at the electrode facing portion is also reduced, the amount of retained electrolyte is reduced by the amount of the reduced fiber amount. As a result, the battery characteristics cannot be maintained, and the short-circuit resistance also deteriorates, which is not preferable.
[0009]
Also, if the thickness of the separator arranged in the core space is made thinner than the thickness of the separator arranged in the electrode facing part, the space volume of the core space will increase, so that the top of the battery from the bottom of the can It is possible to enlarge the exhaust passage to the air. As a result, if the separator does not melt, but an abnormality occurs such that a large amount of gas is generated inside the battery continuously charged at a high rate (high rate), the gas inside the battery is removed from the bottom of the can. The safety valve can be reached without stagnation on the side. As a result, it is possible to improve safety when the temperature of the battery abnormally rises.
[0010]
Also in this case, if the thickness of the separator disposed in the electrode facing portion is also reduced, the apparent density of the separator in this portion is also reduced, and the amount of the electrolyte held is reduced, and the battery characteristics cannot be maintained. Absent. In addition, when the space volume of the core space is increased, when the current collecting tab and the can bottom are welded by inserting a welding electrode into the core space, weldability at the can bottom is improved, which is preferable.
[0011]
When the basis weight and the thickness of the separator arranged in the core space are smaller than the basis weight and the thickness of the separator arranged in the electrode facing part, the amount of fibers present in the core space can be reduced. At the same time, the space volume of the core space can be increased. This makes it difficult for the gas exhaust port provided in the sealing body to be closed, and makes it possible to enlarge the exhaust passage from the bottom of the can to the upper part of the battery. Further, the welding electrode can be easily provided in the core space. Since it becomes possible to insert, the weldability at the bottom of the can is improved.
[0012]
Furthermore, if the separator arranged in the core space is smaller than the basis weight of the separator arranged in the electrode facing part and is made thinner so that the thickness becomes thinner (the two separators are bonded together), As the amount of fibers existing in the core space decreases, the volume of the core space also increases. As a result, the gas exhaust port provided in the sealing body is less likely to be blocked, and the exhaust passage from the bottom of the can to the upper part of the battery is increased, so that the safety of the battery using this type of separator is further improved. It will be.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
An embodiment in which the present invention is applied to a nickel-hydrogen storage battery will be described below with reference to FIGS. FIG. 1 is a cross-sectional view schematically showing a cross section of the separator. FIG. 2 is a cross-sectional view schematically showing a cross section in a state where a spiral electrode group formed using the separator of FIG. 1 is housed in an outer can.
[0014]
1. Production of separator
(1) Example 1
Polyethylene fiber (PE: melting point: 138 ° C.) and polypropylene fiber (PP: melting point: 160 ° C.) were blended at a predetermined blending ratio. Next, these fibers are scattered in the air, collected by a wire mesh, wet-laid, and then rolled to have a basis weight of 40 g / m2. ² Thus, a first base cloth 11a having a thickness of 0.10 mm was produced. Further, after the wet papermaking is performed in the same manner as described above, the paper is rolled to have a basis weight of 20 g / m ² Thus, a second base cloth 11b having a thickness of 0.05 mm was produced. Next, the second base cloth 11b was arranged on the first base cloth 11a, and these were attached to each other. At this time, after being wound together with the positive and negative electrodes in a spiral shape, the first base cloth 11a is laminated (duplexed) so that only the first base cloth 11a is disposed in the core space 10a (see FIG. 2). The separator 11 of Example 1 as shown in FIG.
[0015]
(2) Example 2
After blending sea-island type fibers having a sea component of polyethylene terephthalate (PET) and an island component of polypropylene (PP) at a predetermined blending ratio, these fibers are scattered in the air and collected by a wire mesh. And wet papermaking. Then, when the spiral was wound together with the positive and negative electrodes later, the sea component (PET) of the portion 12a disposed in the core space 10a (see FIG. 2) was leached with alkali. Thereafter, the core is rolled and subjected to a hydrophilic treatment, and the basis weight of the portion 12a arranged in the core space 10a is 40 g / m2. ² And the basis weight of other parts is 60 g / m ² Then, the separator 12 of Example 2 having a thickness of 0.15 mm was produced as shown in FIG.
[0016]
(3) Example 3
After blending sea-island type fibers having a sea component of polyamide and an island component of polypropylene (PP) so as to have a predetermined blending ratio, these fibers were scattered in the air, collected by a wire mesh, and wet-laid. . Subsequently, when the spiral was wound together with the positive and negative electrodes later, the sea component (polyamide) in the portion 13a disposed in the core space 10a (see FIG. 2) was leached with alkali. Thereafter, rolling and hydrophilization treatment are performed, and the weight of the portion 13a arranged in the core space 10a is 40 g / m2. ² And the basis weight of other parts is 60 g / m ² Then, the separator 13 of Example 3 having a thickness of 0.15 mm was produced as shown in FIG.
[0017]
(4) Example 4
Polyethylene fiber (PE: melting point: 138 ° C.) and polypropylene fiber (PP: melting point: 160 ° C.) were blended at a predetermined blending ratio. Thereafter, these fibers are scattered in the air, collected by a wire mesh, wet-laid, and then rolled to have a basis weight of 60 g / m2. ² Thus, a base cloth having a thickness of 0.15 mm was produced. Then, when subsequently wound in a spiral shape together with the positive and negative electrodes, the portion 14a disposed in the core space 10a (see FIG. 2) is rolled by a roller having irregularities so that the thickness of the portion 14a is reduced to zero. .12 mm. Thereafter, a hydrophilic treatment was performed to produce a separator 14 of Example 4 as shown in FIG.
[0018]
(5) Example 5
Polyethylene fiber (PE: melting point: 138 ° C.) and polypropylene fiber (PP: melting point: 160 ° C.) were blended at a predetermined blending ratio. Thereafter, these fibers are scattered in the air, collected by a wire mesh, wet-laid, and then rolled to have a basis weight of 60 g / m2. ² Thus, a base cloth having a thickness of 0.15 mm was produced. Then, when the spiral is wound together with the positive and negative electrodes later, heat is applied only to the portion 15a disposed in the core space 10a (see FIG. 2), and the thickness of the portion 15a is reduced to 0. .12 mm. Thereafter, the separator 15 of Example 5 as shown in FIG.
[0019]
(6) Example 6
After blending sea-island type fibers having a sea component of polyethylene terephthalate (PET) and an island component of polypropylene (PP) at a predetermined blending ratio, these fibers are scattered in the air and collected by a wire mesh. And wet papermaking. Then, when the spiral was wound together with the positive and negative electrodes later, the sea component (PET) of the portion 16a disposed in the core space 10a (see FIG. 2) was leached with alkali. Thereafter, rolling is performed, and the weight of the portion 16a arranged in the core space 10a is 40 g / m2. ² And the basis weight of other parts is 60 g / m ² Thus, a base cloth having a thickness of 0.15 mm was produced. Then, the portion 16a of the base cloth disposed in the core space 10a was rolled with a roller having irregularities, and the thickness of the portion 16a was rolled to 0.12 mm. Thereafter, the separator 16 of Example 6 as shown in FIG.
[0020]
(7) Comparative example 1
After blending sea-island fibers having a sea component of polyamide and an island component of polypropylene (PP) so as to have a predetermined blending ratio, these fibers are scattered in the air, collected by a wire mesh, and subjected to wet papermaking. To make a base cloth. Next, the sea component (polyamide) of the base fabric was leached with an alkali. After this, after rolling, it is subjected to a hydrophilic treatment to give a basis weight of 40 g / m. ² The separator 17 of Comparative Example 1 having a thickness of 0.10 mm was produced as shown in FIG.
[0021]
(8) Comparative example 2
Polyethylene fiber (PE: melting point: 138 ° C.) and polypropylene fiber (PP: melting point: 160 ° C.) were blended at a predetermined blending ratio. Thereafter, these fibers are scattered in the air, collected by a wire mesh, wet-laid, and then rolled to have a basis weight of 60 g / m2. ² To produce a base cloth having a thickness of 0.15 mm. Next, the base fabric was pressed with a roller having irregularities to roll the base fabric to a thickness of 0.12 mm. Then, it is subjected to a hydrophilic treatment, and the basis weight is 40 g / m. ² Then, the separator 18 of Comparative Example 2 having a thickness of 0.10 mm was produced as shown in FIG.
[0022]
(9) Comparative example 3
Polyethylene fiber (PE: melting point: 138 ° C.) and polypropylene fiber (PP: melting point: 160 ° C.) were blended at a predetermined blending ratio. Thereafter, these fibers are scattered in the air, collected by a wire mesh, wet-laid, rolled, and then subjected to a hydrophilic treatment to give a basis weight of 60 g / m2. ² Then, a separator 19 of Comparative Example 3 having a thickness of 0.15 mm was produced as shown in FIG.
[0023]
2. Preparation of nickel positive electrode
A positive electrode active material slurry was prepared by mixing 100 parts by mass of a positive electrode active material powder containing nickel hydroxide as a main component and 50 parts by mass of an aqueous solution in which 0.2% by mass of hydroxypropyl cellulose was dissolved. This positive electrode active material slurry was filled into foamed nickel 21 having a porosity of 95%, dried, and then rolled to produce a nickel positive electrode 20. The positive electrode active material slurry was filled in the foamed nickel 21 so that the battery had a nominal capacity of 1500 mAh.
[0024]
3. Preparation of hydrogen storage alloy negative electrode
A binder such as polytetrafluoroethylene (PTFE) and an appropriate amount of water were added to the hydrogen storage alloy powder and mixed to prepare a hydrogen storage alloy paste. Next, this hydrogen storage alloy paste was applied to both surfaces of a negative electrode substrate (punched metal) 31, dried, and then pressed to a predetermined thickness to produce a hydrogen storage alloy negative electrode 30. The punching metal 31 was filled with the hydrogen storage alloy paste so that the electrode capacity was 2250 mAh.
[0025]
4. Production of nickel-hydrogen storage battery
Next, the separators 11 (12, 13, 14, 15, 16, 17, 18, and 19) manufactured as described above were arranged on the nickel positive electrode 20 manufactured as described above. Each separator 11 (12, 13, 14, 15, 16, 17, 18, 19) was disposed on the hydrogen storage alloy negative electrode 30 produced as described above. Then, after these are overlaid, the ends 11a (12a, 13a, 14a, 15a, 16a, 17a, 18a, 18a, 18a, 18a, 12a, 13a, 14a, 15 19a) was held between slit portions of a winding core (not shown).
[0026]
Next, the core is wound a predetermined number of times, and the nickel positive electrode 20, the separator 11 (12, 13, 14, 15, 16, 17, 18, 19), the hydrogen storage alloy negative electrode 30, and the separator 11 (12, 13, 14, 15, 16, 17, 18, 19) were spirally wound. Thereafter, the spirally wound electrode group 10 was manufactured by extracting the core. In this case, the core space is formed in the center of the spiral electrode group 10 by extracting the core. Next, a positive electrode current collector (not shown) is welded to the upper end of the electrode group 10, and a negative electrode current collector (not shown) is welded to the lower end thereof. 40, respectively.
[0027]
Thereafter, the negative electrode current collector is welded to the inner bottom surface of the outer can 40, and the end of the current collecting lead plate extending from the positive electrode current collector is welded to the bottom surface of a sealing body (not shown) containing a safety valve. Then, a predetermined amount of an electrolytic solution (a mixed aqueous solution of potassium hydroxide (KOH), lithium hydroxide (LiOH), and sodium hydroxide (NaOH)) was injected into the outer can 40. Next, the sealing body is placed on the opening of the outer can 40 via an insulating gasket, and the end of the opening of the outer can 40 is crimped inward to seal the battery, and the AA size with a nominal capacity of 1500 mAh. Of the nickel-hydrogen storage batteries A to F and X to Z were manufactured.
[0028]
The battery using the separator 11 is referred to as a battery A, the battery using the separator 12 is referred to as a battery B, the battery using the separator 13 is referred to as a battery C, the battery using the separator 14 is referred to as a battery D, and the battery 15 using the separator 15. A battery E using the separator 16, a battery F using the separator 16, a battery X using the separator 17, a battery Y using the separator 18, and a battery Z using the separator 19. did.
[0029]
5. test
(1) Short circuit test
With each of the 10,000 electrode groups inserted into the outer can 40, the insulation resistance between the positive electrode and the negative electrode was measured, and when the resistance value was 1.5 kΩ or less, it was determined that the battery was short-circuited. Was determined. Next, when the short-circuit occurrence rate (%) was calculated based on the obtained number of short-circuit occurrences, the results shown in Table 1 below were obtained.
[0030]
(2) Can bottom weldability test
When each negative electrode current collector was welded to the inner bottom surface of each outer can 40 in a state in which each 10,000 electrode groups were inserted into the outer can 40, the number of defective weldings was determined. Next, when the welding failure occurrence rate (%) was calculated based on the obtained welding failure occurrence number, the results shown in Table 1 below were obtained.
[0031]
(3) Safety test by gas burner combustion
First, using the nickel-hydrogen storage batteries A to F and X to Z manufactured as described above, these batteries were charged at a temperature of 25 ° C. and a charging current of 120 mA for 16 hours. After the discharge, the battery is discharged at a discharge current of 240 mA until the discharge end voltage becomes 1.0 V, and then the operation is paused for 1 hour. This charge / discharge was repeated three times to activate each of the batteries A to F and X to Z.
[0032]
Next, using each of the 10000 nickel-hydrogen storage batteries A to F and X to Z activated as described above, charging was performed at a charging current of 1500 mA in a temperature atmosphere of 25 ° C., and a full charge was obtained. When the battery voltage dropped by 10 mV (−ΔV = 10 mV), charging was suspended for 1 hour. Thereafter, the gas burner was burned, the battery temperature was raised to 250 ° C., and the ratio of the number of batteries in which the sealing body was removed (the rate of removal of the sealing body) was determined. The results shown in Table 1 below were obtained. Was.
[0033]
(4) Safety test during high rate charging
Using each of the 10000 nickel-hydrogen storage batteries A to F and X to Z activated as described above, charging was performed at a temperature of 25 ° C. with a charging current of 6000 mA until a short circuit occurred. When the ratio of the number of batteries in which the sealing member was detached (occurrence of detachment of the sealing member) was determined at the time when the occurrence of, the results shown in Table 1 below were obtained.
[0034]
(5) Cycle life test
After each of the nickel-hydrogen storage batteries A to F and X to Z activated as described above was charged at a charging current of 1500 mA in a temperature atmosphere of 25 ° C. using 10,000 each, the battery was fully charged. When the voltage drops by 10 mV (−ΔV = 10 mV), charging is suspended for one hour. Next, a charge / discharge cycle of discharging the battery with a discharge current of 1500 mA until the battery voltage becomes 1.0 V is repeatedly performed, and a cycle (times) in which the ratio to the initial capacity reaches 60% is obtained as a cycle life. The results are as shown in Table 1.
[0035]
[Table 1]

[0036]
As apparent from the results in Table 1, the basis weight (60 g / m ² In the battery Z using the separator 19 having a uniform thickness (0.15 mm) and a uniform thickness (0.15 mm), the rate of occurrence of defective welding at the bottom of the can was 0.10%, the rate of detachment of the sealing body during combustion of the gas burner was 15%, and the It can be seen that the detachment rate of the sealing body at the rate charging is as large as 10%. This is because when the thickness of the separator 19a existing in the core space 10a is as large as 0.15 mm, the volume of the core space 10a is reduced, and when the welding electrode is inserted into the core space 10a, the winding is performed. It is considered that the separator 19a existing in the core space 10a was in the way.
The separator 19a in the core space 10a has a basis weight of 60 g / m2. ² Therefore, the amount of fibers existing in the core space 10a increases. Thus, when abnormal heat generation occurs until the separator 19 is melted during gas burner combustion or high-rate charging, the melted fibers close the gas exhaust port provided in the sealing body, and the sealing body may come off. Probably caused.
[0037]
In addition, the basis weight (60 g / m ² ) And the battery Y using the separator 18 having a uniform thickness (0.12 mm), the rate of detachment of the sealing body during combustion of the gas burner was as large as 15%, and the cycle life was as small as 400 cycles. This is because the basis weight of the separator 18a existing in the core space 10a is 60 g / m2. ² Therefore, the amount of fibers existing in the core space 10a increases. Accordingly, when abnormal heat is generated until the separator 18 is melted during the combustion of the gas burner, it is considered that the melted fiber closes the gas exhaust port provided in the sealing body and the sealing body comes off. Further, it is considered that since the thickness of the separator 18 at the electrode facing portion is as small as 0.12 mm, the amount of retained electrolyte is reduced, and the cycle life is shortened.
[0038]
Furthermore, the basis weight (40 g / m ² ) And the battery X using the separator 17 having a uniform thickness (0.10 mm), the short circuit occurrence rate is as large as 0.10% and the cycle life is as small as 400 cycles. The basis weight of the separator 17 is 40 g / m. ² It is considered that the positive electrode and the negative electrode became easy to directly contact with each other because the thickness was as small as 0.12 mm. The basis weight of the separator 17 at the electrode facing portion is 40 g / m. ² Is small and the thickness is as small as 0.12 mm, it is considered that the holding amount of the electrolyte is reduced and the cycle life is shortened.
[0039]
On the other hand, in the batteries D and E using the

separators

14 and 15 having the thickness of the core space 10a of 0.12 mm, the sealing member detachment rate at the time of burning the gas burner is as large as 15%, but the short circuit occurrence rate is large. Is 0.02%, the occurrence rate of defective welding at the bottom of the can is 0.03%, the rate of detachment of the sealing body during charging at a high rate of 6A is as small as 3%, and the cycle life is as large as 500 cycles. This is because the

separators

14a and 15a arranged in the core space 10a are subjected to a rolling process to reduce the thickness, so that the space volume of the core space increases.
[0040]
As a result, it is possible to enlarge the exhaust passage from the bottom of the can to the top of the battery, and the

separators

14 and 15 do not melt, but a large amount of the battery is continuously charged at a high rate (high rate). It is considered that when an abnormality such as the generation of the above-mentioned gas occurs, the gas inside the battery can reach the safety valve without staying at the bottom of the can.
[0041]
This makes it possible to improve the safety when the temperature of the battery rises abnormally. However, if the

separators

14 and 15 in the electrode-facing portions other than the core space 10a are also rolled, the separators in this portion will be The apparent density also decreases, and the amount of retained electrolyte decreases, making it impossible to maintain battery characteristics. In this case, since the space volume of the core space 10a increases, the weldability in the case where a welding rod is inserted into the core space 10a and the current collecting tab and the can bottom are welded is improved.
[0042]
In addition, the basis weight of the core space 10a is 40 g / m. ² In the batteries B and C using the

separators

12 and 13 described above, the rate of occurrence of defective welding at the bottom of the can was as large as 0.10%, but the rate of occurrence of short circuit was 0.02%, and the rate of detachment of the sealing body during gas burner combustion was low. It can be seen that at 4%, the rate of detachment of the sealing body during charging at a high rate of 6A is as small as 3%, and the cycle life is as large as 500 cycles. This is because the weight reduction process is applied to the

separators

12a and 13a arranged in the core space 10a, so that the amount of fibers existing in the core space 10a can be reduced.
[0043]
This is considered to be due to the fact that even if abnormal heat generation occurs until the

separators

14a and 15a are melted, the gas exhaust port provided in the sealing body is hardly blocked. In this case, if the basis weights of the

separators

14 and 15 in the electrode facing portions other than the core space 10a are also reduced, the amount of retained electrolyte is reduced by the reduced fiber amount, and battery characteristics cannot be maintained. However, a disadvantage that the short-circuit resistance is also reduced is undesirably caused.
[0044]
In addition, the basis weight of the core space 10a is 40 g / m. ² In the battery F using the separator 16 having a thickness of 0.12 mm, the short circuit occurrence rate is 0.02%, the can bottom welding failure occurrence rate is 0.03%, and the sealing body detachment rate during gas burner combustion is It can be seen that at 2%, the rate of detachment of the sealing body during charging at a high rate of 6A is as small as 2%, and the cycle life is as large as 500 cycles. This is because the separator 16a disposed in the core space 10a has been subjected to the weight reduction process and the rolling process, so that the amount of fibers existing in the core space 10a can be reduced. At the same time, the space volume of the core space 10a also increases. This is considered to be due to the fact that the gas exhaust port provided in the sealing body was less likely to be closed, and the exhaust passage from the bottom of the can to the upper part of the battery was enlarged.
[0045]
Furthermore, the basis weight of the core space 10a is 40 g / m. ² In the battery A using the laminated separator 11 in which only the first base cloth 11a having a thickness of 0.10 mm is present, the short-circuit occurrence rate is 0.02% and the can bottom welding failure occurrence rate is 0.1%. It can be seen that the rate of detachment of the sealing body at the time of combustion of the gas burner is 1%, the rate of detachment of the sealing body at the time of charging at a high rate of 6A is as small as 1%, and the cycle life is as large as 500 cycles. This is because the separator 11a arranged in the core space 10a has a small basis weight and a small thickness, so that the amount of fibers existing in the core space 10a is small and the space volume of the core space 10a is large. . This is considered to be due to the fact that the gas exhaust port provided in the sealing body was less likely to be closed, and the exhaust passage from the bottom of the can to the upper part of the battery was enlarged.
[0046]
【The invention's effect】
As described above, in the present invention, since the basis weight of the separator disposed in the core space 10a is small, the thickness is small, or the basis weight is small and the thickness is small, the core space 10a It is possible to reduce the amount of fibers existing in the core space, or to increase the space volume of the core space 10a, and further to reduce the amount of fibers in the core space 10a and increase the space volume. It becomes. Accordingly, when abnormal heat generation occurs until the separator is melted, the gas exhaust port provided in the sealing body is less likely to be closed, and the time until the gas outlet is closed can be lengthened. In addition, the exhaust passage from the bottom of the can to the top of the battery also becomes large. Thereby, the safety of the battery using this kind of separator is improved. Further, since the space volume of the core space 10a increases, the welding rod can be easily inserted, so that the weldability at the bottom of the can is improved.
[0047]
In the above-described embodiment, an example in which the present invention is applied to a nickel-hydrogen storage battery as a preferred example of the present invention has been described.However, the present invention is not limited to a nickel-hydrogen storage battery, and other alkaline storage batteries such as nickel-cadmium storage batteries, Alternatively, it is apparent that the present invention can be applied to a nonaqueous electrolyte battery such as a lithium ion battery. Furthermore, in the above-described embodiment, an example in which the present invention is applied to a cylindrical storage battery has been described. However, the present invention is not limited to this, and the present invention can be applied to storage batteries of various shapes including a wound electrode group. Needless to say.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view schematically showing a cross section of a separator.
FIG. 2 is a cross-sectional view schematically showing a cross section in a state where a spiral electrode group formed using the separator of FIG. 1 is housed in an outer can.
[Explanation of symbols]
Reference numeral 10: spiral electrode group, 10a: core space, 11, 12, 13, 14, 15, 16, 17, 18, 19 ... separator, 11a: first base cloth, 12a: second base cloth, 13a, 14a, 15a, 16a, 17a, 18a, 19a ... separators arranged in the core space, 20 ... nickel positive electrode, 21 ... nickel foam, 30 ... hydrogen storage alloy negative electrode, 31 ... negative electrode substrate (punching metal), 40 ... Outer can (battery can)

Claims

A cylindrical storage battery provided with a spirally wound electrode group spirally wound with a separator interposed between a positive electrode and a negative electrode in a cylindrical outer can,
The spiral electrode group includes a core space part remaining after the core used in forming the spiral electrode group is removed at the center,
The weight of the separator arranged in the core space portion is smaller than the mass of the separator arranged in the electrode facing portion.

A cylindrical storage battery provided with a spirally wound electrode group spirally wound with a separator interposed between a positive electrode and a negative electrode in a cylindrical outer can,
The spiral electrode group includes a core space part remaining after the core used in forming the spiral electrode group is removed at the center,
A cylindrical storage battery, wherein the thickness of the separator arranged in the core space is smaller than the thickness of the separator arranged in the electrode facing part.

A cylindrical storage battery provided with a spirally wound electrode group spirally wound with a separator interposed between a positive electrode and a negative electrode in a cylindrical outer can,
The spiral electrode group includes a core space part remaining after the core used in forming the spiral electrode group is removed at the center,
The basis weight and thickness of the separator arranged in the core space portion are smaller than the basis weight and thickness of the separator arranged in the electrode facing portion.

A cylindrical storage battery provided with a spirally wound electrode group spirally wound with a separator interposed between a positive electrode and a negative electrode in a cylindrical outer can,
The spiral electrode group includes a core space part remaining after the core used in forming the spiral electrode group is removed at the center,
A cylindrical storage battery, wherein two separators are attached so that the basis weight and the thickness of the separator arranged in the core space are smaller than the basis weight and the thickness of the separator arranged in the electrode facing part. .