JP4253886B2

JP4253886B2 - Flat type non-aqueous electrolyte battery and manufacturing method thereof

Info

Publication number: JP4253886B2
Application number: JP33873498A
Authority: JP
Inventors: 浩司芳澤; 薫井上; 宏和木宮; 肇西野; 正也大河内
Original assignee: Panasonic Corp; Matsushita Electric Industrial Co Ltd
Current assignee: Panasonic Corp; Panasonic Holdings Corp
Priority date: 1998-11-30
Filing date: 1998-11-30
Publication date: 2009-04-15
Anticipated expiration: 2018-11-30
Also published as: JP2000164259A

Description

【０００１】
【発明の属する技術分野】
本発明は，扁平形非水電解液電池の構成およびその製造法に関するものである。
【０００２】
【従来の技術】
近年，AV機器，パソコン等のコードレス化，ポータブル化に伴いその駆動用電源である電池に対し，小型，軽量，高エネルギー密度化の要望が強まっている。特にリチウム二次電池は高エネルギー密度を有する電池であり次世代の主力電池として期待され，その潜在的市場規模も大きい。また形状としては通信機の薄型化，あるいは，スペースの有効利用の観点からも角薄型の要望が高まっている。
【０００３】
従来角薄型リチウムイオン電池は，特開平8-32998号公報に示されるように，金属板をしぼり加工などで有底の角薄形電池ケースを作成し，その中に渦巻き状の極板群及び電解液を注入した後，開口部を塞ぐ封口板をレーザー溶接で封口する方法が一般的である。このような電池において，体積効率を向上させるために渦巻き電極群の巻軸の中心線が角形電池ケースの開口面と平行にしたもの（特開平7-47605号公報）等がある。
【０００４】
特に今日軽量化という意味からアルミニウムをケースに用いることが主流となりつつあるが，米国特許第555672号明細書ではケースのコーナー部分の厚みを厚くすることで，より薄板のケースでも強度を保つことができ電池の薄型化，軽量化が可能となるものも提案されている。さらに薄型化に対して様々な取り組みがなされ特に電池厚みに最も影響を及ぼす封口板構造について種々提案（特開平9-153367号公報，米国特許第5585207号明細書）がされている。これらの提案に示される封口板においては，封口板蓋板と端子を樹脂を介して絶縁しているが，端子はリベットでありこれをかしめることにより液密を保っている。また，生産性向上という意味から特開平7-57716号公報に示されるように，正極板及び負極板をテープ状のセパレータによって連続的に袋詰めにし各電極板間のセパレータ融着部で折り畳むことによって構成することが提案されている。最近ではポリマー電池に使用されるが，アルミニウム金属薄膜のラミネートシートを外装ケース（米国特許第5478668号明細書）として使用し薄型化の試みがなされている。
【０００５】
【発明が解決しようとする課題】
電池の角薄型が進み通信機用途では現在5mm程度のものに移行しつつあり，将来さらなる薄型化が要望されている。従来，角薄型リチウムイオン電池は，金属板をしぼり加工などで有底の角薄形電池ケースを作成し，その中に渦巻き状の極板群及び電解液を注入した後，開口部を塞ぐ封口板をレーザー溶接で封口する方法が一般的で，電池の薄型化に伴い当然封口板も薄くなり端子取り出しスペースが窮屈になる。
【０００６】
従って樹脂を絶縁層にして端子を兼ねたリベットでかしめる方式では非常に小さい部品となり耐漏液性の信頼性が極めて低くなるといった課題がある。また，封口板と外装ケースをレーザー溶接し封口する工程においても溶接スペースに余裕がなく高精度のレーザー溶接技術が必要となり生産性は低下する。量産化に際しては少しのレーザー軌道のズレや，ランプの消耗によるレーザー出力変動で不良率を著しく増加させるといった課題がある。
【０００７】
一方，特開平6-310144号公報や特開平3-129664号公報にその製造法や構造が詳細に示されるような扁平形コイン電池では正負極の対峙面積すなわち反応面積が小さすぎることや，活物質層の厚みが０．２から１．７ｍｍと厚いこと等の要因で極めて小さな電流しか取り出せないといった課題がある。
【０００８】
本発明はこのような課題を解決し，扁平形電池で，かつ十分な電流を取り出せ，さらに極めて生産性の良い電池構成及びその製造法を提供するものである。
【０００９】
【課題を解決するための手段】
金属箔にリチウムを吸蔵・放出可能な正極材料を含む合剤ペーストを塗工した薄い正極板と，同様に金属箔にリチウムを吸蔵・放出できる負極材料を含む合剤ペーストを塗工した薄い負極板を，ポリエチレンなどの樹脂からなる微多孔膜であるセパレーターを介して渦巻き状に巻回し極板群を構成する。
【００１０】
この極板群をプレスなどで断面が長円形になるように扁平状に成形する。このことにより，扁平形の極板群で，かつ，薄型極板を使用するので正負極の対向面積（反応面積）が大きく，従来の粉体合剤をプレスしペレット状に成形したものに比較し大きな電流を取り出す事ができる。
【００１１】
あるいは，エキスパンドメタルの薄板にリチウムを吸蔵・放出可能な正極材料の合剤あるいは負極材料の合剤を塗り込み圧延して作成した薄型極板を短冊状に切断し，これらを樹脂製のセパレータを介して積層して，さらに熱を加え加圧接合し一体化した極板群とする事でも上述の場合とほぼ同様な効果を得ることができる。
【００１２】
上記のようにして作成した扁平形極板群に電解液を含浸させ金属ケースでかしめ封口する。このとき正極ケースは内面がアルミニウムまたはアルミニウム合金であり負極ケースはステンレス，ニッケル，銅のいずれかとした方が好ましい。このことで電解液による金属ケースの腐食などの劣化を抑制することができる。
【００１３】
また，極板群とケースは正負極それぞれの極で接触する事で集電は可能であるが，極板から取り出された金属集電体をケースに溶接すればより確実に電気的導通が確保され電池を長期に保存した場合に内部抵抗の増加を抑えることが可能である。扁平形の正極及び負極ケースを対向させ樹脂製のガスケットを介してかしめ封口をする事で，厚みが５ｍｍ以下のような極めて薄い扁平形の電池であっても，レーザー溶接や薄型のかしめ封口板を用いないために，高信頼性の電池を生産性よく製造できる。このとき樹脂製のガスケットはポリフェニレンスルフィド樹脂を用いると，高強度及び耐高温性でかつ耐薬品性の樹脂であるので，封口強度を増加させると共に電池の高温での耐漏液性を向上させることができる。
【００１４】
【発明の実施の形態】
（参考例１）
以下，本発明の参考例を図面を参照しながら説明する。
【００１５】
図１は，本発明の扁平形電池の構造断面図である。１は正極ケースでステンレスとアルミニウムのクラッド材を用い，アルミニウムの面が電池の内側になるように成形した。２は負極ケースでステンレス材を使用した。３は正極ケースと負極ケースを絶縁するガスケットでポリプロピレン製である。４は正極板，５は負極板，６はセパレーターである。
【００１６】
図１に示した本発明の扁平形非水電解液電池は以下のようにして作製した。正極板は，活物質であるLiCoO₂に導電剤としてカーボンブラックを，結着剤としてポリ四フッ化エチレンの水性ディスパージョンを固形分の重量比で100：3：10の割合で混合したものをアルミニウム箔の両面に塗着，乾燥し，圧延した後所定の大きさに切断したものである。
【００１７】
負極板は，炭素質材料を主材料とし，これとスチレンブタジエンゴム系結着剤とを重量比で100：5の割合で混合したものを銅箔の両面に塗着，乾燥，圧延した後所定の大きさに切断したものである。セパレーターはポリエチレン製の微多孔フィルムである。正極板，負極板をセパレータを介して巻き回し，断面長円形の極板群に加圧成形する。
【００１８】
次にこの極板群に電解液を含浸させる。含浸は密閉容器の中で電解液に極板群を浸し，容器を60ｍｍHgまで減圧に引き１０秒間ホールドし大気圧に戻す作業を，３回繰り返した。電解液には，エチレンカーボネート（EC）とジエチルカーボネート（DEC）をモル比で１：３で混合した溶媒に溶質として六フッ化リン酸リチウムを１モル／ｌの濃度で溶解したものを用いた。液の含浸した極板群を正極ケースに入れ，ガスケットを封口部分にはめ込んだ負極ケースをかぶせ封口金型に挿入し油圧プレスでかしめ封口を行った。
【００１９】
図１に示すように正極板と正極ケース及び負極板と負極ケースは接触し電気的導通を確保している。つまり扁平形極板群の最外周側面部は片面に正極が露出し，もう片面は負極板が露出した構成にした。電池のサイズは図２に外観を示すが，長辺側が５０ｍｍ，短辺側が３０ｍｍで電池厚みが３ｍｍである。また，四角のＲは５ｍｍとした。図３にこの電池を4．1Vの定電圧充電（最大電流500mA）を２時間行い，80mA,400mA及び800mAの３種類の定電流で放電した結果を示した。図より400mAの電流値でも電池容量が約400mAhの放電容量があり，セルラーフォンなどの用途に十分使用可能であることがわかる。
【００２０】
以上のことより，本参考例で示したような構成の電池を作成することで，扁平形電池で，かつ十分な電流を取り出せ，さらに極めて生産性の良い電池を提供する事が可能となる。
【００２１】
参考例では極板群の最外周に極板部分を露呈し，ケースと接触させることで電気的導通を確保したが，正極板及び負極板から金属リードを取り出した場合は極板群の最外周がセパレータでもかまわない。取り出したリードをそれぞれのケースに接触あるいは溶接することで電気的導通を確保する事ができる。正極に関してはアルミニウムのリード線を使用する場合が多いが，このリードをケースに超音波溶接する場合等はケース内面の溶接面も同一材料のアルミニウムの方が溶接強度，信頼性の面で有利である。また，４Ｖ系の活物質を用いるなど高電位の場合は腐食などによる劣化を押さえるためにもアルミニウムあるいはアルミニウム合金である方が望ましい。
【００２２】
参考例で示した構成の場合は，極板群の最外周は反応に関与しない部分で，活物質を必要としない。従ってスペースの有効利用の観点からも最外周の極板合剤を剥離し集電体である金属箔を露呈させこれをケースと接触させる方が有利である。このようにする場合のケースと極板も接点部分の拡大図を図４に示した。１は正極ケースで，１ａが内面のアルミニウム層，１ｂがステンレス層である。２は負極ケース，７は負極集電体である銅箔，８は負極合剤層で，９が負極板と負極ケースの接触面である。１０は正極の集電体であるアルミニウム箔，１１は正極合剤で，１２が正極板と正極ケースの接触面である。
【００２３】
（実施例１）
極板の集電体とケースを溶接することのメリットについて説明する。電池の製造工程は増加し生産性は多少低下するが，溶接する事で電池を長期に保存した場合の電池内部抵抗の増加を低減し信頼性のより高い電池を供給できる。図５は集電体とケースを溶接した場合の接点部の拡大図である。図に示すように極板群の最外周末端部に合剤の未塗着部を設け，その部分をケースと溶接した（１３，１４）。図の１３が負極溶接点で１４が正極溶接点である。溶接方法は超音波溶接法を用いた。以上のようにして作成した電池を６０℃の環境下で３ヶ月保存した。６０℃に温度を上げるのは，室温で保存する場合の加速試験である。一般に６０℃，２０日保存が室温の１年保存相当に匹敵するといわれている。比較のために末端部を溶接していない電池も同条件で保存した。（表１）に保存後の電池の内部抵抗を測定した結果を示した。数値はn=５の平均値を示している。
【００２４】
【表１】

【００２５】
（表１）より明らかなように溶接した場合，長期保存後の内部抵抗の増加を低減させることができる。
【００２６】
ガスケットの材質としてポリフェニレン樹脂を用いることのメリットについて説明する。ガスケットの樹脂材料としては一般にポリプロピレン（ＰＰ）が非水電解液電池で使用されている。この樹脂は成形性が良くコストも低いためコイン型リチウム電池などに広く用いられているが，電池高温保存時の劣化が課題とされている。
【００２７】
また，強度が低く変形が大きいため，かしめ封口部の樹脂に用いる場合は５０〜７０％の圧縮率になるまで圧縮している。圧縮率が大きいと樹脂が組成変形を起こし必要な封口部の弾性が確保できず高温での長期間の保存において漏液を招いたりする。従って，熱的に比較的安定な樹脂で，樹脂の変形量は小さい方が良く，樹脂の圧縮率を３０％程度までに下げることが望ましい。
【００２８】
本実施例では約２０種の樹脂から耐有機溶剤性などの既存データを参照し，ポリプロピレン（ＰＰ），ポリエチレンテレフタレート（ＰＥＴ）及びポリフェニレンスルフィド（ＰＰＳ）樹脂の３種に絞り込み評価した。これらの樹脂を用いて電池を作製し高温保存時の電池漏液試験を行うことで樹脂の選定を行った。（表２）に熱衝撃試験1000サイクル時の漏液率を示した。熱衝撃試験は，-50℃で１時間保存した後100℃で１時間保存する工程を１サイクルとした。
【００２９】
【表２】

【００３０】
（表２）より明らかなように本発明のような構造においてはＰＰＳ樹脂を用いた場合，従来用いられてきたＰＰ樹脂に比較し飛躍的に耐漏液性が向上する。
【００３１】
なお，本実施例では扁平形で横断面角形の電池としたがその他，横断面円形などでも同様の効果がある。
【００３２】
（実施例２）
図６は，積層極板群とした場合の扁平形電池の構造断面図である。実施例１と同様に，２０は正極ケースでステンレスとアルミニウムのクラッド材を用い，アルミニウムの面が電池の内側になるように成形した。２１は負極ケースでステンレス材を使用した。２２は正極ケースと負極ケースを絶縁するガスケットでポリプロピレン製である。１５は正極板，１６は負極板，１７はセパレーターである。１８は正極金属集電体で１９は負極金属集電体で，それぞれ積層極板間で連結されている。
【００３３】
図６に示した本発明の扁平形非水電解液電池は以下のようにして作製した。正極板はアルミニウムのエキスパンドメタルを集電体にしLiCoO₂を活物質とする正極合剤を塗布乾燥したのち圧延し厚みを規定寸法にしたものである。ケースに接触する正極板は接触する面には合剤を塗布せず片面塗着とするがその他は両面塗着である。
【００３４】
負極板は銅のエキスパンドメタルを集電体にし黒鉛を含む負極合剤を塗布乾燥したのち圧延し厚みを規定寸法にしたものである。正極板同様，ケースに接触する負極板は接触する面には合剤を塗布せず片面塗着とするがその他は両面塗着である。理由は，電池内の空間体積を有効に活用するために片面塗着とした。セパレータはポリマー電解質シートからなる。
【００３５】
これら正極板及び負極板をセパレータを介して図のように積層し熱加圧することで一体化して積層極板群とした。極板間の電気的導通は図に示すように各極板に未塗着部を設け，正負極各々反対側で集電体同士を溶接する事で確保する。極板の集電体とケースを溶接する場合はこの部分を利用しケースと溶接する。溶接する効果は実施例１と同様，長期保存後の内部抵抗の増加を低減させることができる。
【００３６】
次にこの極板群に電解液を含浸させる。積層極板中に可塑剤等が含まれる場合は，可塑剤を抽出する工程を経てから注液工程に進む。本実施例では可塑剤としてジブチルフタレート，抽出剤としてジエチルエーテルを用いた。含浸は密閉容器の中で電解液に極板群を浸し，容器を60ｍｍHgまで減圧に引き１０秒間ホールドし大気圧に戻す作業を，３回繰り返した。
【００３７】
電解液には，エチレンカーボネート（EC）とジエチルカーボネート（DEC）をモル比で１：３で混合した溶媒に溶質として六フッ化リン酸リチウムを１モル／ｌの濃度で溶解したものを用いた。液の含浸した極板群を正極ケースに入れ，ガスケットを封口部分にはめ込んだ負極ケースをかぶせ封口金型に挿入し油圧プレスでかしめ封口を行った。電池のサイズは実施例１同様の長辺側が５０ｍｍ，短辺側が３０ｍｍで電池厚みが３ｍｍである。また，四角のＲは５ｍｍとした。
【００３８】
このようにして作成した扁平形電池は容量は300mAhと実施例１に比較し低下したが，１時間率放電電流（１Ｃ）は十分に取り出し可能であった。以上のことより，本実施例で示したような構成の電池を作成することで，扁平形電池で，かつ十分な電流を取り出せ，さらに極めて生産性の良い電池を提供する事が可能となる。
【００３９】
積層極板の場合，本実施例では極板を積層した後熱加圧により一体化したが，一体化しない場合は極板群をホールドするような樹脂製の袋に収納されている方が電解液注液工程などでバラバラになることもなく電池を製造する面で都合がよい。そのために，ポリエチレン，ポリプロピレン，フッ素樹脂樹脂製の微多孔フィルムで作成した袋に積層極板群を挿入する事で上記のような問題を解決する。樹脂の種類は電解液に対して耐薬品性があり比較的安価なものを選んだ。
【００４０】
また，微多孔フィルムとしたのは電解液注液時に極板に電解液が含浸しやすくするためと，熱を多少加えることでフィルムが収縮しより極板群を強固にホールドする効果があるためである。本実施例では熱加圧をしない場合を対象に樹脂製袋に収納する検討を行ったが，熱加圧し極板を一体化したものにおいてもより強固にホールドする等の効果があり同様に有用である。
【００４１】
なお，本実施例では扁平で横断面角形の電池としたがその他横断面円形などでも同様の効果がある。
【００４２】
【発明の効果】
以上のように本発明によれば，5mm以下の様な非常に薄い扁平形電池であっても，十分な電流を取り出せ，さらに従来の一般的な角薄型リチウム２次電池のようにレーザー溶接などの高度な要素技術を必要としないため，極めて生産性の良い電池を提供する事が可能となる。
【図面の簡単な説明】
【図１】本発明の扁平形電池の構造断面図
【図２】（Ａ）同電池の側面図
（Ｂ）同電池の上面図
【図３】同電池の放電特性図
【図４】（ａ）負極板と負極ケースとの接触面の要部拡大図
（ｂ）正極板と正極ケースとの接触面の要部拡大図
【図５】（ａ）負極集電体と負極ケースとの溶接点の要部拡大図
（ｂ）正極集電体と正極ケースとの溶接点の要部拡大図
【図６】本発明の他の扁平形電池の構造断面図
【符号の説明】
１正極ケース
１ａアルミニウム層
１ｂステンレス層
２負極ケース
３ガスケット
４正極板
５負極板
６セパレータ
７銅箔（負極集電体）
１０アルミニウム箔（正極集電体）[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a configuration of a flat nonaqueous electrolyte battery and a method for manufacturing the same.
[0002]
[Prior art]
In recent years, along with the cordless and portable use of AV equipment and personal computers, there has been a growing demand for smaller, lighter, and higher energy density batteries for the power source for driving them. In particular, the lithium secondary battery is a battery having a high energy density and is expected as a next-generation main battery, and its potential market size is also large. In addition, there is a growing demand for a thin shape from the viewpoint of thin communication equipment or effective use of space.
[0003]
In conventional rectangular thin lithium ion batteries, as shown in Japanese Patent Application Laid-Open No. 8-32998, a bottomed rectangular thin battery case is made by squeezing a metal plate, and a spiral electrode plate group and A method of sealing the sealing plate that closes the opening by laser welding after injecting the electrolyte is common. In such a battery, in order to improve volumetric efficiency, there is a battery whose center line of the spiral electrode group is parallel to the opening surface of the rectangular battery case (Japanese Patent Laid-Open No. 7-47605).
[0004]
In particular, the use of aluminum for cases is becoming the mainstream today in the sense of weight reduction. However, in US Pat. No. 555672, by increasing the thickness of the corners of the case, the strength can be maintained even in thinner cases. A battery that can be made thinner and lighter has been proposed. In addition, various efforts have been made to reduce the thickness, and various proposals have been made regarding a sealing plate structure that most affects the battery thickness (Japanese Patent Laid-Open No. 9-153367, US Pat. No. 5,585,207). In the sealing plates shown in these proposals, the sealing plate cover plate and the terminal are insulated via a resin, but the terminal is a rivet and is kept liquid-tight by caulking it. Further, as shown in Japanese Patent Application Laid-Open No. 7-57716, the positive electrode plate and the negative electrode plate are continuously packed with a tape-shaped separator and folded at the separator fusion portion between the electrode plates in order to improve productivity. It has been proposed that Recently, it is used in polymer batteries, but attempts have been made to reduce the thickness by using an aluminum metal thin film laminate sheet as an outer case (US Pat. No. 5,478,668).
[0005]
[Problems to be solved by the invention]
As battery corners are becoming thinner, they are currently shifting to 5 mm for communications equipment, and further reductions in the future are demanded. Conventionally, a rectangular thin lithium-ion battery has a bottomed rectangular thin battery case made by squeezing a metal plate, and a spiral electrode plate and electrolyte are injected into it, and then the opening is closed. The method of sealing the plate by laser welding is common, and as the battery becomes thinner, the sealing plate becomes naturally thinner and the terminal take-out space becomes tight.
[0006]
Therefore, the method of caulking with a rivet that also serves as a terminal by using a resin as an insulating layer has a problem that the reliability becomes very small because the component becomes very small. Also, in the process of sealing the sealing plate and the outer case by laser welding, there is no room for welding space, and high-precision laser welding technology is required, resulting in reduced productivity. In mass production, there are problems such as slight deviation of laser trajectory and significant increase in defect rate due to laser output fluctuation due to lamp wear.
[0007]
On the other hand, in a flat coin battery whose manufacturing method and structure are described in detail in JP-A-6-310144 and JP-A-3-129664, the opposing area of the positive and negative electrodes, that is, the reaction area is too small. There is a problem that only a very small current can be taken out due to factors such as the thickness of the material layer being as thick as 0.2 to 1.7 mm.
[0008]
The present invention solves such a problem, and provides a battery configuration and a method for manufacturing the same that are flat batteries, can obtain a sufficient current, and have extremely high productivity.
[0009]
[Means for Solving the Problems]
A thin positive plate coated with a mixture paste containing a positive electrode material capable of inserting and extracting lithium into a metal foil, and a thin negative electrode coated with a mixture paste containing a negative electrode material capable of inserting and extracting lithium into a metal foil as well. The plate is wound in a spiral shape through a separator, which is a microporous film made of a resin such as polyethylene, to constitute an electrode plate group.
[0010]
This electrode plate group is formed into a flat shape by a press or the like so that the cross section becomes an oval. Because of this, the flat electrode group and the use of thin electrode plates, the area of the positive and negative electrodes facing each other (reaction area) is large. Compared to conventional powder mixtures pressed into pellets A large current can be taken out.
[0011]
Alternatively, a thin electrode plate made by applying and rolling a positive electrode material mixture or a negative electrode material mixture capable of inserting and extracting lithium into a thin sheet of expanded metal is cut into strips, and these are separated by a resin separator. The same effect as in the above case can be obtained by stacking the electrode plates together and applying pressure to form an electrode plate group integrated by pressure bonding.
[0012]
The flat electrode group produced as described above is impregnated with an electrolytic solution and caulked and sealed with a metal case. At this time, the positive electrode case is preferably made of aluminum or an aluminum alloy, and the negative electrode case is preferably made of stainless steel, nickel, or copper. This can suppress deterioration such as corrosion of the metal case caused by the electrolytic solution.
[0013]
In addition, the current can be collected by contacting the electrode plate group and the case at the positive and negative electrodes. However, if the metal current collector taken out from the electrode plate is welded to the case, electrical conduction is more reliably ensured. When the battery is stored for a long period of time, it is possible to suppress an increase in internal resistance. Even if the battery is extremely thin, such as 5 mm or less, the flat positive electrode and negative electrode case are facing each other and sealed with a resin gasket. Therefore, a highly reliable battery can be manufactured with high productivity. At this time, if a polyphenylene sulfide resin is used for the resin gasket, it is a high-strength, high-temperature-resistant and chemical-resistant resin, so that it can increase the sealing strength and improve the leakage resistance of the battery at high temperatures. it can.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
( Reference Example 1)
Hereinafter, reference examples of the present invention will be described with reference to the drawings.
[0015]
FIG. 1 is a structural sectional view of a flat battery of the present invention. 1 is a positive electrode case using a clad material of stainless steel and aluminum, and molded so that the aluminum surface is inside the battery. 2 is a negative electrode case made of stainless steel. 3 is a gasket for insulating the positive electrode case and the negative electrode case, and is made of polypropylene. 4 is a positive electrode plate, 5 is a negative electrode plate, and 6 is a separator.
[0016]
The flat nonaqueous electrolyte battery of the present invention shown in FIG. 1 was produced as follows. The positive electrode plate is made by mixing LiCoO ₂ as an active material with carbon black as a conductive agent and an aqueous dispersion of polytetrafluoroethylene as a binder in a weight ratio of 100: 3: 10. It is applied to both sides of aluminum foil, dried, rolled, and then cut into a predetermined size.
[0017]
The negative electrode plate is mainly composed of a carbonaceous material, and this is mixed with a styrene butadiene rubber binder at a weight ratio of 100: 5. It is cut to the size of. The separator is a microporous film made of polyethylene. The positive electrode plate and the negative electrode plate are wound through a separator, and pressed into an electrode plate group having an oval cross section.
[0018]
Next, the electrode group is impregnated with an electrolytic solution. For the impregnation, the electrode plate group was immersed in an electrolyte solution in a sealed container, the container was decompressed to 60 mmHg, held for 10 seconds, and returned to atmospheric pressure three times. The electrolyte used was a solution in which lithium hexafluorophosphate was dissolved at a concentration of 1 mol / l as a solute in a solvent in which ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed at a molar ratio of 1: 3. . The electrode plate group impregnated with the liquid was placed in the positive electrode case, and the negative electrode case with the gasket fitted in the sealing part was put over and inserted into the sealing mold, and the sealing was carried out by caulking with a hydraulic press.
[0019]
As shown in FIG. 1, the positive electrode plate and the positive electrode case, and the negative electrode plate and the negative electrode case are in contact with each other to ensure electrical conduction. In other words, the outermost side surface of the flat electrode plate group has a structure in which the positive electrode is exposed on one side and the negative electrode is exposed on the other side. As shown in FIG. 2, the size of the battery is 50 mm on the long side, 30 mm on the short side, and 3 mm in thickness. The square R was 5 mm. Fig. 3 shows the results of discharging this battery at a constant voltage of 4.1V (maximum current of 500mA) for 2 hours and discharging at three constant currents of 80mA, 400mA and 800mA. From the figure, it can be seen that even with a current value of 400 mA, the battery capacity is about 400 mAh, which is sufficient for applications such as cellular phones.
[0020]
From the above, it is possible to provide a battery that is a flat battery, can obtain a sufficient current, and has extremely high productivity by making a battery having the configuration shown in this reference example.
[0021]
In the reference example, the electrode plate portion was exposed on the outermost periphery of the electrode plate group and contacted with the case to ensure electrical continuity. However, when metal leads were taken out from the positive electrode plate and the negative electrode plate, the outermost periphery of the electrode plate group was May be a separator. Electrical conduction can be ensured by contacting or welding the taken-out lead to each case. For the positive electrode, an aluminum lead wire is often used, but when this lead is ultrasonically welded to the case, it is advantageous in terms of welding strength and reliability that the inner surface of the case is made of aluminum of the same material. is there. In addition, in the case of a high potential such as using a 4V-based active material, aluminum or an aluminum alloy is preferable in order to suppress deterioration due to corrosion or the like.
[0022]
In the case of the configuration shown in the reference example, the outermost periphery of the electrode plate group is a part not involved in the reaction and does not require an active material. Therefore, from the viewpoint of effective use of the space, it is advantageous to peel off the outermost electrode plate mixture to expose the metal foil as a current collector and to bring it into contact with the case. FIG. 4 shows an enlarged view of the contact portion of the case and the electrode plate in this case. 1 is a positive electrode case, 1a is an inner aluminum layer, and 1b is a stainless steel layer. 2 is a negative electrode case, 7 is a copper foil as a negative electrode current collector, 8 is a negative electrode mixture layer, and 9 is a contact surface between the negative electrode plate and the negative electrode case. 10 is an aluminum foil as a positive electrode current collector, 11 is a positive electrode mixture, and 12 is a contact surface between the positive electrode plate and the positive electrode case.
[0023]
Example 1
The merit of welding the current collector of the electrode plate and the case will be described. Although the manufacturing process of the battery increases and the productivity slightly decreases, welding increases the internal resistance of the battery when the battery is stored for a long period of time, so that a battery with higher reliability can be supplied. FIG. 5 is an enlarged view of the contact portion when the current collector and the case are welded. As shown in the figure, an uncoated portion of the mixture was provided at the outermost peripheral end portion of the electrode plate group, and the portion was welded to the case (13, 14). In the figure, 13 is a negative electrode welding point and 14 is a positive electrode welding point. As a welding method, an ultrasonic welding method was used. The battery prepared as described above was stored in an environment of 60 ° C. for 3 months. Increasing the temperature to 60 ° C is an accelerated test for storage at room temperature. In general, it is said that storage at 60 ° C. for 20 days is equivalent to storage for 1 year at room temperature. For comparison, a battery whose end was not welded was also stored under the same conditions. Table 1 shows the results of measuring the internal resistance of the battery after storage. The numerical value has shown the average value of n = 5.
[0024]
[Table 1]

[0025]
When it is welded as apparent from (Table 1), the increase in internal resistance after long-term storage can be reduced.
[0026]
The merit of using polyphenylene resin as the material of the gasket will be described. Polypropylene (PP) is generally used in nonaqueous electrolyte batteries as the gasket resin material. Since this resin has good moldability and low cost, it is widely used for coin-type lithium batteries and the like. However, deterioration during storage at high temperatures is a problem.
[0027]
In addition, since the strength is low and the deformation is large, when the resin is used in the caulking sealing portion, the compression is performed until the compression rate is 50 to 70%. If the compressibility is high, the resin undergoes compositional deformation and the necessary elasticity of the sealing portion cannot be ensured, resulting in leakage during long-term storage at high temperatures. Therefore, it is preferable that the resin is thermally stable and the deformation amount of the resin is small, and it is desirable to reduce the compressibility of the resin to about 30%.
[0028]
In this example, existing data such as organic solvent resistance was referred to from about 20 kinds of resins, and evaluation was made by narrowing down to three kinds of polypropylene (PP), polyethylene terephthalate (PET) and polyphenylene sulfide (PPS) resins. Batteries were produced using these resins, and the resin was selected by conducting a battery leakage test during high-temperature storage. (Table 2) shows the liquid leakage rate during 1000 cycles of the thermal shock test. In the thermal shock test, the process of storing at -50 ° C for 1 hour and then storing at 100 ° C for 1 hour was defined as one cycle.
[0029]
[Table 2]

[0030]
As apparent from Table 2, when the PPS resin is used in the structure of the present invention, the leakage resistance is dramatically improved as compared with the conventionally used PP resin.
[0031]
In the present embodiment, the battery has a flat shape and a square cross section, but the same effect can be obtained with a circular cross section.
[0032]
(Example 2)
FIG. 6 is a structural cross-sectional view of a flat battery in the case of a laminated electrode plate group. Similar to Example 1, 20 is a positive electrode case made of a clad material of stainless steel and aluminum, and molded so that the aluminum surface is inside the battery. 21 is a negative electrode case made of stainless steel. A gasket 22 for insulating the positive electrode case and the negative electrode case is made of polypropylene. Reference numeral 15 is a positive electrode plate, 16 is a negative electrode plate, and 17 is a separator. Reference numeral 18 denotes a positive electrode metal current collector, and reference numeral 19 denotes a negative electrode metal current collector, which are connected between the laminated electrode plates.
[0033]
The flat nonaqueous electrolyte battery of the present invention shown in FIG. 6 was produced as follows. The positive electrode plate is obtained by applying and drying a positive electrode mixture containing aluminum expanded metal as a current collector and LiCoO ₂ as an active material, and then rolling it to a specified dimension. The positive electrode plate in contact with the case is coated on one side without applying a mixture on the contacting surface, but the other side is double-sided coating.
[0034]
The negative electrode plate is obtained by applying a copper expanded metal as a current collector, applying and drying a negative electrode mixture containing graphite, and rolling it to a specified dimension. As with the positive electrode plate, the negative electrode plate that contacts the case is not coated with a mixture on the contact surface, but single-sided coating, but the other is double-sided coating. The reason was to apply single-sided coating in order to effectively use the space volume in the battery. The separator is made of a polymer electrolyte sheet.
[0035]
The positive electrode plate and the negative electrode plate were laminated as shown in the figure through a separator and integrated by heating and pressing to form a laminated electrode plate group. As shown in the figure, electrical conduction between the electrode plates is ensured by providing an uncoated portion on each electrode plate and welding the current collectors on the opposite sides of the positive and negative electrodes. When welding the current collector of the electrode plate and the case, use this part to weld the case. As in Example 1, the effect of welding can reduce the increase in internal resistance after long-term storage.
[0036]
Next, the electrode group is impregnated with an electrolytic solution. When the laminated electrode plate contains a plasticizer or the like, the process proceeds to the liquid injection process after the process of extracting the plasticizer. In this example, dibutyl phthalate was used as a plasticizer and diethyl ether was used as an extractant. For the impregnation, the electrode plate group was immersed in an electrolyte solution in a sealed container, the container was decompressed to 60 mmHg, held for 10 seconds, and returned to atmospheric pressure three times.
[0037]
The electrolyte used was a solution in which lithium hexafluorophosphate was dissolved at a concentration of 1 mol / l as a solute in a solvent in which ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed at a molar ratio of 1: 3. . The electrode plate group impregnated with the liquid was placed in the positive electrode case, and the negative electrode case with the gasket fitted in the sealing part was put over and inserted into the sealing mold, and the sealing was carried out by caulking with a hydraulic press. The size of the battery is 50 mm on the long side, 30 mm on the short side and the thickness of the battery is 3 mm as in Example 1. The square R was 5 mm.
[0038]
The flat battery thus produced had a capacity of 300 mAh, which was lower than that of Example 1, but the 1-hour discharge current (1C) could be taken out sufficiently. From the above, it is possible to provide a battery with a flat battery and a sufficiently high current by producing a battery having a configuration as shown in this embodiment, and having extremely high productivity.
[0039]
In the case of a laminated electrode plate, in this embodiment, the electrode plates are laminated and integrated by heat and pressure, but if not integrated, it is better to store them in a resin bag that holds the electrode plate group. It is convenient in terms of manufacturing the battery without being separated in the liquid injection process. Therefore, the above-mentioned problems are solved by inserting the laminated electrode plate group into a bag made of a microporous film made of polyethylene, polypropylene, or fluororesin resin. The resin type was selected from chemicals that are resistant to electrolytes and relatively inexpensive.
[0040]
In addition, the microporous film is used because it is easy to impregnate the electrode plate with the electrolyte during the injection of the electrolyte, and because the film contracts by applying a little heat, it has the effect of holding the electrode group firmly. It is. In this example, a study was made to store the product in a resin bag for the case where heat pressurization is not performed. It is.
[0041]
In this embodiment, the battery is flat and has a square cross section, but the same effect can be obtained with other circular cross sections.
[0042]
【The invention's effect】
As described above, according to the present invention, sufficient current can be taken out even with a very thin flat battery of 5 mm or less, and laser welding or the like as in the case of a conventional general rectangular thin lithium secondary battery. Therefore, it is possible to provide batteries with extremely high productivity.
[Brief description of the drawings]
1 is a cross-sectional view of the structure of a flat battery of the present invention. FIG. 2A is a side view of the battery. FIG. 1B is a top view of the battery. ) Enlarged view of the main part of the contact surface between the negative electrode plate and the negative electrode case (b) Enlarged view of the main part of the contact surface between the positive electrode plate and the positive electrode case [FIG. 5] (a) Welding point between the negative electrode current collector and the negative electrode case (B) Enlarged view of the main part of the welding point between the positive electrode current collector and the positive electrode case [FIG. 6] Cross-sectional view of the structure of another flat battery of the present invention [Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Positive electrode case 1a Aluminum layer 1b Stainless steel layer 2 Negative electrode case 3 Gasket 4 Positive electrode plate 5 Negative electrode plate 6 Separator 7 Copper foil (negative electrode collector)
10 Aluminum foil (positive electrode current collector)

Claims

A flat battery that seals a metal positive electrode case and a negative electrode case through a resin gasket that electrically insulates them, and contains an organic electrolyte in which lithium salt is dissolved, and lithium is occluded.・ A positive electrode plate coated with a releasable positive electrode material on a metal current collector and a negative electrode plate coated with a negative electrode material capable of occluding and releasing lithium on a metal current collector are spirally wound through a separator. And at least one of the current collectors of the positive electrode plate and the negative electrode plate is provided with an uncoated portion of the mixture at the outermost peripheral end portion of the electrode plate group, and the uncoated portion is welded to the metal case A flat non-aqueous electrolyte battery.

The flat nonaqueous electrolyte battery according to claim 1, wherein at least one metal current collector of the positive electrode plate and the negative electrode plate is exposed on the outermost periphery of the electrode plate group.

The flat nonaqueous electrolyte battery according to claim 1, wherein an inner surface of the positive electrode case is aluminum or an aluminum alloy.

The flat nonaqueous electrolyte battery according to claim 1, wherein the inner surface of the negative electrode case is made of stainless steel, nickel, or copper.

The flat nonaqueous electrolyte battery according to claim 1, wherein the resin gasket is a polyphenylene sulfide resin.

It is a flat battery that seals a metal positive electrode case and negative electrode case with a resin gasket that electrically insulates them, and contains an organic electrolyte containing lithium salt and occluded lithium. laminated electrode of the cathode material capable of laminated via a separator and a negative electrode plate of the negative electrode material a positive electrode plate and a lithium was coated wear can occlude and release was applied to the surfaces of the metal current collector on a metal current collector And a non-coated portion provided on each electrode plate, the uncoated portions are welded to the opposite sides of the positive and negative electrodes, and the welded portion and the metal case are welded to each other. battery.

The flat nonaqueous electrolyte battery according to claim 6 , wherein an inner surface of the positive electrode case is aluminum or an aluminum alloy.

The flat nonaqueous electrolyte battery according to claim 6 , wherein the inner surface of the negative electrode case is made of stainless steel, nickel, or copper.

7. The flat nonaqueous electrolyte battery according to claim 6, wherein the laminated electrode plate group is housed in a resin bag.

The flat nonaqueous electrolyte battery according to claim 9 , wherein the resin bag is a microporous film.

The flat non-aqueous electrolyte battery according to claim 9 , wherein the resin bag contains at least one of polyethylene, polypropylene, and fluororesin.

The flat nonaqueous electrolyte battery according to claim 6 , wherein the resin gasket is a polyphenylene sulfide resin.

A positive electrode plate using a positive electrode material capable of occluding and releasing lithium and a negative electrode plate using a negative electrode material capable of occluding and releasing lithium are spirally wound through a separator to form an electrode plate group; A step of forming the plate group into an oval cross section, a step of impregnating the electrode plate group with an organic electrolytic solution in which a lithium salt is dissolved, a step of inserting the electrode plate group into the positive electrode or negative electrode case, and a gasket A method for producing a flat nonaqueous electrolyte battery having a step of caulking and sealing with another metal case through
A step of forming the electrode plate group to have an oval cross section, a step of impregnating the electrode plate group with an organic electrolyte solution in which a lithium salt is dissolved, a step of inserting the electrode plate group into the positive electrode or negative electrode case, During any one of the steps of caulking and sealing with the other metal case through the gasket, at least one of the current collectors of the positive electrode plate and the negative electrode plate is not mixed with the outermost peripheral end portion of the electrode plate group. A method for producing a flat non-aqueous electrolyte battery in which a coated portion is provided and a step of welding the uncoated portion to a metal case is added .

A step of forming a laminated electrode in which a positive electrode plate using a positive electrode material capable of inserting and extracting lithium and a negative electrode plate using a negative electrode material capable of inserting and extracting lithium are laminated via a separator; A step of integrating by joining, a step of impregnating an electrode plate group with an organic electrolyte solution in which a lithium salt is dissolved, a step of inserting the electrode plate group into a positive or negative electrode case, and another metal case through a gasket A method for producing a flat nonaqueous electrolyte battery having a step of caulking and sealing ,
The process of integrating the laminated electrodes by thermal bonding, the process of impregnating the electrode group with an organic electrolyte solution in which lithium salt is dissolved, the process of inserting the electrode group into the positive or negative electrode case, and the gasket Between any one of the metal case and the caulking and sealing step, each electrode plate is further provided with an uncoated portion, and the uncoated portions are welded to each other on the opposite sides of the positive and negative electrodes. A method for manufacturing a flat non-aqueous electrolyte battery in which a process for welding each of them is added .

The process of integrating the laminated electrodes by thermal bonding, the process of impregnating the electrode group with an organic electrolyte solution in which lithium salt is dissolved, the process of inserting the electrode group into the positive or negative electrode case, and the gasket 15. The method for producing a flat nonaqueous electrolyte battery according to claim 14, wherein a step of housing the laminated electrode plate group in a resin bag is added between one of the steps of sealing with the metal case.