JP4901017B2

JP4901017B2 - Flat nonaqueous electrolyte secondary battery with lead terminals

Info

Publication number: JP4901017B2
Application number: JP2001125780A
Authority: JP
Inventors: 宗人早見; 祐一菊間
Original assignee: Hitachi Maxell Energy Ltd
Current assignee: Hitachi Maxell Energy Ltd
Priority date: 2001-04-24
Filing date: 2001-04-24
Publication date: 2012-03-21
Anticipated expiration: 2021-04-24
Also published as: JP2002324584A

Description

【０００１】
【発明の属する技術分野】
本発明は扁平形非水電解質二次電池に係わり、特に、リード端子を電極ケース面に溶接したリード端子付扁平形非水電解質二次電池に関する。
【０００２】
【従来の技術】
正極作用物質にＭｎＯ₂やＶ₂Ｏ₅などの金属酸化物、あるいはフッ化黒鉛などの無機化合物、あるいはポリアニリンやポリアセン構造体などの有機化合物を用い、負極に金属リチウム、あるいはリチウム合金、あるいはポリアセン構造体などの有機化合物、あるいはリチウムを吸蔵、放出可能な炭素質材料、あるいはチタン酸リチウムやリチウム含有珪素酸化物のような酸化物を用い、電解質にプロピレンカーボネート、エチレンカーボネート、ブチレンカーボネート、ジエチルカーボネート、ジメチルカーボネート、メチルエチルカーボネート、ジメトキシエタン、γ−ブチルラクトンなどの非水溶媒にＬｉＣｌＯ₄、ＬｉＰＦ₆、ＬｉＢＦ₄、ＬｉＣＦ₃ＳＯ₃、ＬｉＮ（ＣＦ₃ＳＯ₂）₂、ＬｉＮ（Ｃ₂Ｆ₅ＳＯ₂）₂などの支持塩を溶解した非水電解質を用いたコイン形やボタン形の扁平形非水電解質二次電池は、既に商品化されており、放電電流が数〜数十μＡ程度の軽負荷で放電が行われるＳＲＡＭやＲＴＣのバックアップ用電源や電池交換不要腕時計の主電源といった用途に適用されている。
【０００３】
これらコイン形やボタン形の扁平形非水電解質二次電池は、主用途が軽負荷での放電のため、図６に示す構造をしており、正極１４、及び負極１５は、ペレット形状をしたものが一般的である。
【０００４】
しかし、図６に示すような従来の扁平形非水電解質二次電池では、負極端子を兼ねる金属製の負極ケース５と、正極端子を兼ねる金属製の正極ケース１が、絶縁ガスケット６を介し嵌合され、さらに正極ケース１または負極ケース５が加締め加工により加締められた封口構造を有し、その内部に少なくとも正極１４、セパレータ３、負極１５を含む発電要素と、非水電解質が内包されているが、正極１４、及び負極１５がペレット形状をしているため、リード端子を溶接する際、溶接に十分な熱を発生させても、正極または負極がペレット形状のため正極１４及び負極１５の間に設けられたセパレータ３まで発生した熱が到達せず、セパレータ３の穴あき、収縮などの問題は起こらなかった。
【０００５】
一方、携帯電話やＰＤＡなどの小型情報端末を中心に使用機器の小型化が加速しており、主電源である二次電池についても小型化を図ることが要求されている。このような要求に対し、特開２０００−６８１６０号や、特開２００１−６８１４３号に示すような負極端子を兼ねる金属製の負極ケースと、正極端子を兼ねる金属製の正極ケースが、絶縁ガスケットを介し嵌合され、さらに正極ケースまたは負極ケースが加締め加工により加締められた封口構造を有し、その内部に少なくとも正極、セパレータ、負極を含む発電要素と、非水電解質を内包した扁平形非水電解質二次電池において、扁平形電池の扁平面に垂直な方向の断面を見た場合に、少なくとも３面以上の正極と負極がセパレータを介して対向している正負極対向面を有した電極群が収納され、かつ、電極群内の正負極対向面積の総和が絶縁ガスケットの開口面積よりも大きくする構造の扁平形非水電解質二次電池が小型化の要求を満たす電池として開発されている。
【０００６】
ところで、これらの扁平形非水電解質二次電池を機器に組み込む場合、その多くは正極ケース及び負極ケースの外側にリード端子を抵抗溶接にて溶接し、端子部と機器とをはんだ付けして組み込むのが一般的である。しかし、前述したように正極、負極、セパレータからなる合剤層の厚さが１．０ｍｍ以下である電極群を積層もしくは捲回し、電池内に内包する扁平形非水電解質二次電池では、一枚の電極の厚さが１ｍｍ以下の薄い正負極電極と０．５ｍｍ以下のポリエチレン、ポリプロピレン製などの薄膜セパレータを介して、積層または捲回された電極群を直接、正極及び負極ケースに接触させ、ケースと電極の集電を取っている。この電池系において抵抗溶接を行うために、ケースに３００〜４５０Ｖ程度の電圧を印加した場合、溶接時に発生する熱が電池ケースを通じて電極、セパレータにまで到達してしまい、セパレータの穴あき、収縮を起こし、容量劣化や電池内ショートを起こしたり、また、溶接部分に電圧が集中するため溶接部分に通じる電極が集電体から剥げ落ちるなどの不具合が生じ、電池としての機能の低下を引き起こす。
【０００７】
一方、溶接時の出力を下げた場合、前述したような不具合は起こらなくなるが、溶接強度が弱くなるため、リード端子がとれたり、電池とリード端子の接触が悪くなってしまう。また、リード端子の溶接方法をレーザー溶接などに変更しても熱の発生は抑えられず、同様の不具合を招くというような問題がある。
【０００８】
【発明が解決しようとする課題】
本発明は上記情況に対処するためになされたもので、その課題は正極、負極、セパレータからなる電極層を積層もしくは捲回した電極群を電池内に内包する扁平形非水電解質二次電池において、前記電極層の厚さは１．０ｍｍ以下であり、リード端子溶接により発生する熱による、電池内の電極、セパレータの破壊を抑制し、容量劣化や電池内ショートを防止できるリード端子を備えたリード端子付扁平形非水電解質二次電池を提供するものである。
【０００９】
【課題を解決するための手段】
上記課題を解決するために、本発明は、外部回路に接続するリード端子を電池に溶接するリード端子付扁平形非水電解質二次電池において、前記リード端子の電池への溶接位置は電極群が接触している部分を避けた電池ケースの周辺部とし、また、リード端子は帯状または環状の金属板を用いた構成としている。
【００１０】
まず、本発明電池は電極を含めた電池の構造に主点をおいたものであり、正極作用物質については限定されるものではなく、ＭｎＯ₂、Ｖ₂Ｏ₅、ＬｉＴｉ₂Ｏ₄、Ｌｉ₄Ｔｉ₅Ｏ₁₂、ＬｉＦｅ₂Ｏ₄、コバルト酸リチウム、ニッケル酸リチウム、マンガン酸リチウムなどの金属酸化物、あるいはフッ化黒鉛、ＦｅＳ₂などの無機化合物、あるいはポリアニリンやポリアセン構造体などの有機化合物などあらゆる物が適用可能である。ただし、この中で作用電位が高く、サイクル特性に優れるという点でコバルト酸リチウム、ニッケル酸リチウム、マンガン酸リチウムやそれらの混合物やそれらの元素の一部を他の金属元素で置換したリチウム含有酸化物がより好ましく、長期間に渡り使用されることもある扁平形非水電解質二次電池においては高容量で電解液や水分との反応性が低く化学的に安定であるという点でコバルト酸リチウムがさらに好ましい。
【００１１】
また、本発明電池の負極作用については限定されるものではなく、金属リチウム、あるいはＬｉ−Ａｌ、Ｌｉ−Ｉｎ、Ｌｉ−Ｓｎ、Ｌｉ−Ｓｉ、Ｌｉ−Ｇｅ、Ｌｉ−Ｂｉ、Ｌｉ−Ｐｂなどのリチウム合金、あるいはポリアセン構造体などの有機化合物、あるいはリチウムを吸蔵、放出可能な炭素質材料、あるいはＮｂ₂Ｏ₅、ＬｉＴｉ₂Ｏ₄、Ｌｉ₄Ｔｉ₅Ｏ₁₂やＬｉ含有珪素酸化物のような酸化物などあらゆるものが適用可能であるが、サイクル特性に優れ、作動電位が低く、高容量であるという点でＬｉを吸蔵、放出可能な炭素質材料が好ましく、特に放電末期においても電池作動電圧の低下が少ないという点で天然黒鉛や人造黒鉛、膨張黒鉛、メソフェーズピッチ焼成体、メソフェーズピッチ繊維焼成体などのｄ₀₀₂面の面間隔が０．３３８ｎｍ以下の黒鉛構造が発達した炭素質材料がより好ましい。
【００１２】
さらに、電極については正負極とも従来の顆粒合剤の成形方式や金属ネットの金属基盤に合剤を充填する方法を用いてもよいが肉薄電極の作製が行い易いという点で金属箔にスラリー状の合剤を塗布、乾燥したものがよく、さらにそれを圧延したものを用いることもできる。このような金属箔に作用物質を含む合剤層を塗工した電極を用いる場合は、電極群の内部に用いる電極は金属箔の両面に作用物質層を形成したものを用いるのが、容積効率の上から好ましく、電極群の両端の金属ネットに接触する電極構成材露出部については接触抵抗を低減させるために電極構成材の内、特に金属箔を露出させるのが好ましい。これに関してはこの部分に限り片面にのみ作用物質層を形成した電極を用いてもよいし、一旦、両面に作用物質層を形成した後、片面のみ作用物質層を除去してもよい。
【００１３】
また、電池に溶接するリード端子の材料については、導電性の得られるものであればいずれのものでもよいが、その汎用性などからステンレス製のものが好ましい。また、端子の厚さ、形状についても特に限定されるものではない。
【００１４】
【発明の実施の形態】
以下、本発明の実施例及び比較例について詳細に説明する。
図１は本発明の実施例１の断面図であり、図２は図１の電池ケース周辺部の拡大図である。
【００１５】
図に示すように、本実施例１の扁平形非水電解質二次電池は、負極端子を兼ねる金属製の負極ケース５と、正極端子を兼ねる金属製の正極ケース１が、絶縁ガスケット６を介し嵌合され、さらに正極ケース１または負極ケース５が加締め加工により加締められた封口構造を有し、その内部に少なくとも正極作用物質含有層２、セパレータ３、負極作用物質含有層４を含む発電要素と、非水電解質を内包しており、さらに正極ケース１にはリード端子７を、また負極ケース５にはリード端子８が溶接されている。
【００１６】
本実施例においては、図３で示される帯状の厚さ０．２ｍｍのステンレスの金属板からなるリード端子７、８を用い、このリード端子７、８の溶接位置９、１０は図２に示すように、電極群が接触している部分を避けた負極ケース５の範囲Ｂ内であり、また正極ケース１での電極群が接触している部分を避けた範囲Ａ内である。
【００１７】
次に、本実施例電池の製造方法について説明する。
まず、ＬｉＣｏＯ₂１００質量部に対し導電材としてアセチレンブラック５質量部と黒鉛粉末５質量部を加え、結着剤としてポリフッ化ビニリデンを５質量部加え、Ｎ−メチルピロリドンで希釈、混合し、スラリー状の正極合剤を得た。次に、この正極合剤を、正極集電体である厚さ０．０２ｍｍのアルミ箔の片面にドクターブレード法により塗工、乾燥を行い、アルミ箔表面に正極作用物質含有層２を形成した。以後、正極作用物質含有層の塗膜厚さが両面で０．１５ｍｍとなるまで塗工、乾燥を繰り返し、両面塗工正極を作製した。次に、この電極体の片面の端から１０ｍｍ部分の作用物質含有層を除去し、アルミ層を剥き出し通電部とし、幅１５ｍｍ、長さ１２０ｍｍ、厚さ０．１５ｍｍの長さに切り出した正極板を作製した。
【００１８】
次に、黒鉛化メソフェーズピッチ炭素繊維粉末１００質量部に結着剤としてスチレンブタジエンゴム（ＳＢＲ）とカルボキシメチルセルロース（ＣＭＣ）をそれぞれ２．５質量部を添加し、イオン交換水で希釈、混合し、スラリー状の負極合剤を得た。得られた負極合剤を負極集電体である厚さ０．０２ｍｍの銅箔に負極作用物質含有層４の厚さが０．１５ｍｍとなるように正極の場合と同様に塗工、乾燥を繰り返し実施し両面塗工負極を作製した。次に、この集電体の片面の端から１０ｍｍ部分の作用物質含有層を除去し、銅層を剥き出し通電部とし、幅１５ｍｍ、長さ１２０ｍｍ、厚さ０．１５ｍｍの長さに切り出した負極板を作製した。
【００１９】
次に、正負極通電部面を外周巻き終わり側とし、これら正極と負極の間に厚さ２５μｍのポリエチレン微多孔膜からなるセパレータ３を介し渦巻状に捲回し、扁平形電池の扁平面に対し水平方向に正負極対向部を持つように一定方向に捲回電極の中心部の空間がなくなるまで加圧した。
【００２０】
作製した電極群を８５℃で１２ｈ乾燥した後、絶縁ガスケット６を一体化した負極金属ケース５の内底面に電極群の片面塗工負極板の未塗工側が金属ネットに接する用に配置し、エチレンカーボネートとメチルエチルカーボネートを体積比１：１の割合で混合した溶媒に支持塩としてＬｉＰＦ₆を１ｍｏｌ／ｌの割合で溶解せしめた非水電解質を注液し、さらにステンレス製の正極ケース１を嵌合し、上下反転後、正極ケースに加締め加工を実施し、封口し、厚さ３ｍｍ、直径φ２４．５ｍｍの実施例の扁平形非水電解質二次電池を製作した。また、これらの電池において４．２Ｖ、３ｍＡの定電流定電圧で４８ｈ初充電を実施した。
【００２１】
表１は扁平形電池の正極ケース側を、表２は負極ケース側を図５のごとき従来の溶接位置と、図２の本実施例のごとく電極群を内包した部分を避けた面に溶接した場合とを溶接エネルギー毎に比較したものである。比較数は各１０００個、電圧テスター及び端子引張り試験により評価を行った。ここでの、内部短絡不良とは、溶接により電圧が４．０Ｖを下回ったものをさし、また、溶接不良とは引張り試験で、２．９Ｎ以下の強度しか得られなかったものをさす。
【００２２】
【表１】

【００２３】
【表２】

【００２４】
本発明の他の実施例として、図４に示すように、厚さ０．２ｍｍのステンレスの金属板からなるリード端子１２が図２に示すように電極群を内包した部分を避けた周辺部の面（溶接位置）１３にシリーズスポット溶接によって固着されている場合について、上記図３の帯状の金属板からなるリード端子を用いた場合と同様の内部短絡不良と溶接不良についての評価を行って、その結果を表３、表４に示した。
【００２５】
【表３】

【００２６】
【表４】

【００２７】
溶接機はセイワ製溶接機ＭＣ−１６０Ｂを使用し、従来の溶接は出力を正極ケース４８０Ｖ、負極ケース３５０Ｖとしている。従来の溶接位置では、溶接電圧が低いと、内部短絡不良は起きないが、溶接不良が多くなる。溶接出力を高くすると、溶接不良は減少するが、内部短絡が増加する。本実施例の溶接条件では電極群を内包した部分を避けた電極ケースの周辺部で溶接しているため、出力を上げても内部短絡は起こさない。このため、出力を従来の３０％向上させても溶接の悪影響がない。
【００２８】
なお、本発明の実施例では、図３や図４のような帯状または環状のリード端子を使用したが、リード端子自体の形状を規定するものではなく、電池を搭載する電子機器などにより、適宜形状を変更することができる。また、リード端子の先端にリード線付コネクタを接合したリード端子でも本実施例と同様な効果が得られる。
【００２９】
また、本発明の実施例は、非水電解質に非水溶媒を用いた扁平形非水溶媒二次電池を用いたが、電池形状については正極ケースの加締め加工により封口するコイン形非水電解質二次電池をもとに説明したが、正負極電極を入れ替え、負極ケースの加締め加工により封口することも可能である。さらに、電池形状についても円形のコイン形である必要はなく小判形などの特殊形状を有する扁平形非水電解質二次電池においても適用可能である。
【００３０】
【発明の効果】
以上説明したように、本発明によれば正極電極、負極電極、セパレータからなる電極群を内包した部分を避けた電池ケース周辺部にリード端子を溶接することにより、内部活物質に影響を及ぼすことなく、溶接を行うことができ、また、溶接出力を従来よりもおよそ３０％上げることができ、しかも溶接不良を減少させ、溶接強度を安定させることができるという、非常に大きな工業的価値を有するリード端子付扁平形非水電解質二次電池を提供することができる。
【図面の簡単な説明】
【図１】本発明の実施例１の扁平形非水電解質二次電池の断面図。
【図２】図１のリード端子溶接位置の拡大断面図。
【図３】図１に用いるリード端子の斜視図。
【図４】本発明の他の実施例に用いるリード端子の斜視図。
【図５】従来のリード端子付き扁平形非水電解質二次電池の断面図。
【図６】従来の扁平形非水電解質二次電池の断面図。
【符号の説明】
１…正極ケース、２…正極作用物質含有層（塗工電極）、３…セパレータ、４…負極作用物質含有層（塗工電極）、５…負極ケース、６…絶縁ガスケット、７，８，１２…リード端子、９，１０，１３…溶接位置、１４…正極、１５…負極。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a flat non-aqueous electrolyte secondary battery, and more particularly to a flat non-aqueous electrolyte secondary battery with a lead terminal in which a lead terminal is welded to an electrode case surface.
[0002]
[Prior art]
A metal oxide such as MnO ₂ or V ₂ O ₅ , an inorganic compound such as fluorinated graphite, or an organic compound such as polyaniline or a polyacene structure is used as the positive electrode active material, and metal lithium, lithium alloy, or polyacene is used as the negative electrode Organic compounds such as structures, carbonaceous materials capable of occluding and releasing lithium, or oxides such as lithium titanate and lithium-containing silicon oxide, and propylene carbonate, ethylene carbonate, butylene carbonate, diethyl carbonate as electrolytes LiClO ₄ , LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ ) in a non-aqueous solvent such as dimethyl carbonate, methyl ethyl carbonate, dimethoxyethane, and γ-butyl lactone. a supporting salt such as SO ₂₎ ₂ Coin-shaped and button-shaped flat non-aqueous electrolyte secondary batteries using the non-aqueous electrolyte that have been solved have already been commercialized, such as SRAMs that discharge at light loads with a discharge current of about several to several tens of μA. It is applied to applications such as RTC backup power supplies and main power supplies for wristwatches that do not require battery replacement.
[0003]
These coin-shaped and button-shaped flat non-aqueous electrolyte secondary batteries have the structure shown in FIG. 6 because the main application is discharge under light load, and the positive electrode 14 and the negative electrode 15 have a pellet shape. Things are common.
[0004]
However, in the conventional flat nonaqueous electrolyte secondary battery as shown in FIG. 6, the metal negative electrode case 5 also serving as the negative electrode terminal and the metal positive electrode case 1 also serving as the positive electrode terminal are fitted via the insulating gasket 6. In addition, the positive electrode case 1 or the negative electrode case 5 has a sealing structure in which the positive electrode case 1 or the negative electrode case 5 is crimped, and a power generation element including at least the positive electrode 14, the separator 3, and the negative electrode 15 and a nonaqueous electrolyte are included therein. However, since the positive electrode 14 and the negative electrode 15 have a pellet shape, the positive electrode 14 and the negative electrode 15 have a pellet shape because the positive electrode or the negative electrode has a pellet shape even when sufficient heat is generated when welding the lead terminals. The generated heat did not reach the separator 3 provided between them, and problems such as perforation and shrinkage of the separator 3 did not occur.
[0005]
On the other hand, downsizing of devices used is accelerating mainly on small information terminals such as mobile phones and PDAs, and secondary batteries as a main power source are required to be downsized. In response to such a demand, a metal negative electrode case that also serves as a negative electrode terminal and a metal positive electrode case that also serves as a positive electrode terminal as shown in Japanese Patent Laid-Open No. 2000-68160 and Japanese Patent Laid-Open No. 2001-68143 have insulating gaskets. And a positive electrode case or a negative electrode case, which has a sealing structure in which a positive electrode case or a negative electrode case is crimped by caulking, and a power generation element including at least a positive electrode, a separator, and a negative electrode, and a non-aqueous electrolyte In a water electrolyte secondary battery, an electrode having positive and negative electrode facing surfaces in which at least three positive and negative electrodes face each other through a separator when a cross section in a direction perpendicular to the flat surface of the flat battery is viewed A flat nonaqueous electrolyte secondary battery with a structure in which the group is housed and the sum of the positive and negative electrode facing areas in the electrode group is larger than the opening area of the insulating gasket meets the requirements for downsizing. It has been developed as a battery.
[0006]
By the way, when these flat-type nonaqueous electrolyte secondary batteries are incorporated into devices, many of them are assembled by welding lead terminals to the outside of the positive electrode case and the negative electrode case by resistance welding, and soldering the terminal portion and the device. It is common. However, as described above, in a flat non-aqueous electrolyte secondary battery in which a mixture of electrodes having a thickness of 1.0 mm or less consisting of a positive electrode, a negative electrode, and a separator is laminated or wound, The laminated or wound electrode group is directly brought into contact with the positive and negative electrode cases through a thin positive and negative electrode having a thickness of 1 mm or less and a thin film separator made of polyethylene or polypropylene having a thickness of 0.5 mm or less. , Collecting current for case and electrode. In order to perform resistance welding in this battery system, when a voltage of about 300 to 450 V is applied to the case, the heat generated during welding reaches the electrode and the separator through the battery case, causing the separator to perforate and shrink. This causes problems such as capacity deterioration, short circuit in the battery, and voltage concentration at the welded part, so that the electrode leading to the welded part is peeled off from the current collector, resulting in deterioration of the battery function.
[0007]
On the other hand, when the output at the time of welding is lowered, the above-described problems do not occur, but the welding strength is weakened, so that the lead terminal can be removed or the contact between the battery and the lead terminal is deteriorated. Further, even if the lead terminal welding method is changed to laser welding or the like, there is a problem in that the generation of heat cannot be suppressed and the same problem is caused.
[0008]
[Problems to be solved by the invention]
The present invention has been made to cope with the above situation, and the problem is that in a flat type nonaqueous electrolyte secondary battery in which an electrode group in which an electrode layer composed of a positive electrode, a negative electrode, and a separator is laminated or wound is included in the battery. The electrode layer has a thickness of 1.0 mm or less, and has lead terminals that can suppress the destruction of electrodes and separators in the battery due to heat generated by lead terminal welding, and prevent capacity deterioration and short-circuit in the battery. A flat nonaqueous electrolyte secondary battery with lead terminals is provided.
[0009]
[Means for Solving the Problems]
In order to solve the above problems, the present invention provides a lead flat-shaped non-aqueous electrolyte secondary battery with terminals for welding a lead terminal to the battery to be connected to an external circuit, the welding position the electrode group into the battery of the lead terminals The peripheral part of the battery case avoiding the contact part is used, and the lead terminal is configured to use a band-shaped or annular metal plate.
[0010]
First, the battery of the present invention has a main structure in the structure of the battery including the electrode, and the positive electrode active substance is not limited. MnO ₂ , V ₂ O ₅ , LiTi ₂ O ₄ , Li ₄ Metal oxides such as Ti ₅ O ₁₂ , LiFe ₂ O ₄ , lithium cobaltate, lithium nickelate and lithium manganate, inorganic compounds such as fluorinated graphite and FeS ₂ , organic compounds such as polyaniline and polyacene structures, etc. Everything is applicable. However, lithium-containing oxides in which lithium cobaltate, lithium nickelate, lithium manganate, mixtures thereof, or some of these elements are replaced with other metal elements in terms of high working potential and excellent cycle characteristics. Lithium cobaltate is a flat type non-aqueous electrolyte secondary battery that is more preferable and may be used for a long period of time because it is chemically stable with a high capacity and low reactivity with electrolyte and moisture. Is more preferable.
[0011]
Further, the negative electrode action of the battery of the present invention is not limited, and may be metal lithium, Li-Al, Li-In, Li-Sn, Li-Si, Li-Ge, Li-Bi, Li-Pb, or the like. Lithium alloys, organic compounds such as polyacene structures, carbonaceous materials capable of occluding and releasing lithium, or Nb ₂ O ₅ , LiTi ₂ O ₄ , Li ₄ Ti ₅ O ₁₂ and Li-containing silicon oxides Any material such as oxide can be applied, but a carbonaceous material that can occlude and release Li is preferable in terms of excellent cycle characteristics, low operating potential, and high capacity, and in particular, the battery operating voltage even at the end of discharge. The surface spacing of the _d002 plane of natural graphite, artificial graphite, expanded graphite, mesophase pitch fired body, mesophase pitch fiber fired body, etc. is 0.3 because A carbonaceous material with a developed graphite structure of 38 nm or less is more preferable.
[0012]
Furthermore, for the electrodes, both the positive and negative electrodes may be formed using a conventional granule mixture molding method or a method of filling the metal base of the metal net with a mixture. It is preferable to apply and dry the mixture, and it is also possible to use a rolled product. When using an electrode in which a mixture layer containing an active substance is applied to such a metal foil, the electrode used inside the electrode group is one in which an active substance layer is formed on both sides of the metal foil. From the above, it is preferable to expose the metal foil, particularly the metal foil, in order to reduce the contact resistance of the electrode component exposed portions that are in contact with the metal nets at both ends of the electrode group. In this regard, an electrode in which an active substance layer is formed only on one side may be used only in this portion, or after an active substance layer is once formed on both sides, the active substance layer may be removed only on one side.
[0013]
In addition, the lead terminal material to be welded to the battery may be any material as long as conductivity is obtained, but stainless steel is preferable in view of its versatility. Further, the thickness and shape of the terminal are not particularly limited.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, examples and comparative examples of the present invention will be described in detail.
FIG. 1 is a cross-sectional view of the first embodiment of the present invention, and FIG. 2 is an enlarged view of the periphery of the battery case of FIG.
[0015]
As shown in the figure, in the flat nonaqueous electrolyte secondary battery of Example 1, a metal negative electrode case 5 also serving as a negative electrode terminal and a metal positive electrode case 1 also serving as a positive electrode terminal are interposed via an insulating gasket 6. The power generation includes a sealing structure in which the positive electrode case 1 or the negative electrode case 5 is crimped by caulking, and includes at least the positive electrode active substance-containing layer 2, the separator 3, and the negative electrode active substance-containing layer 4 therein. The element and the nonaqueous electrolyte are included, and the lead terminal 7 is welded to the positive electrode case 1 and the lead terminal 8 is welded to the negative electrode case 5.
[0016]
In the present embodiment,

lead terminals

7 and 8 made of a stainless steel metal plate with a thickness of 0.2 mm shown in FIG. 3 are used, and

welding positions

9 and 10 of the

lead terminals

7 and 8 are shown in FIG. Thus, it is in the range B of the negative electrode case 5 that avoids the portion where the electrode group is in contact, and is in the range A that avoids the portion where the electrode group in the positive electrode case 1 is in contact.
[0017]
Next, a method for manufacturing the battery of this example will be described.
First, 5 parts by mass of acetylene black and 5 parts by mass of graphite powder are added as conductive materials to 100 parts by mass of LiCoO ₂ , 5 parts by mass of polyvinylidene fluoride is added as a binder, diluted with N-methylpyrrolidone, mixed and slurried. A positive electrode mixture was obtained. Next, this positive electrode mixture was applied to one surface of a 0.02 mm thick aluminum foil as a positive electrode current collector by a doctor blade method and dried to form a positive electrode active substance-containing layer 2 on the aluminum foil surface. . Thereafter, coating and drying were repeated until the coating film thickness of the positive electrode active material-containing layer became 0.15 mm on both sides, to produce a double-sided coated positive electrode. Next, a 10 mm portion of the active substance-containing layer is removed from the end of one side of the electrode body, the aluminum layer is stripped to form a current-carrying portion, and a positive electrode plate cut out to a length of 15 mm in width, 120 mm in length, and 0.15 mm in thickness. Was made.
[0018]
Next, 2.5 parts by mass of styrene butadiene rubber (SBR) and carboxymethyl cellulose (CMC) are added as binders to 100 parts by mass of graphitized mesophase pitch carbon fiber powder, respectively, diluted with ion-exchanged water, mixed, A slurry-like negative electrode mixture was obtained. The obtained negative electrode mixture was applied and dried in the same manner as in the case of the positive electrode so that the thickness of the negative electrode active material-containing layer 4 was 0.15 mm on a 0.02 mm thick copper foil as a negative electrode current collector. It carried out repeatedly and produced the double-sided coating negative electrode. Next, a 10 mm portion of the active substance-containing layer was removed from one end of the current collector, and the copper layer was stripped to form a current-carrying portion. The negative electrode was cut into a length of 15 mm, a length of 120 mm, and a thickness of 0.15 mm. A plate was made.
[0019]
Next, the positive and negative electrode current-carrying part surface is the outer winding end side, and the coil is wound between the positive electrode and the negative electrode with a separator 3 made of a polyethylene microporous film having a thickness of 25 μm, to the flat surface of the flat battery. Pressurization was performed in a certain direction so that there was no space at the center of the wound electrode so as to have a positive and negative electrode facing part in the horizontal direction.
[0020]
After the produced electrode group was dried at 85 ° C. for 12 hours, the uncoated side of the single-side coated negative electrode plate of the electrode group was placed on the inner bottom surface of the negative electrode metal case 5 integrated with the insulating gasket 6, A non-aqueous electrolyte in which LiPF ₆ was dissolved as a supporting salt at a rate of 1 mol / l was poured into a solvent in which ethylene carbonate and methyl ethyl carbonate were mixed at a volume ratio of 1: 1. After fitting and turning upside down, the positive electrode case was crimped, sealed, and a flat nonaqueous electrolyte secondary battery having a thickness of 3 mm and a diameter of 24.5 mm was produced. In addition, these batteries were initially charged for 48 hours at a constant current and a constant voltage of 4.2 V and 3 mA.
[0021]
Table 1 welds the flat battery side of the positive electrode case, and Table 2 welds the negative electrode case side to the conventional welding position as shown in FIG. 5 and the surface avoiding the part containing the electrode group as shown in FIG. The case is compared for each welding energy. Each of the comparison numbers was evaluated by 1000 pieces, a voltage tester, and a terminal tensile test. Here, the internal short circuit failure means that the voltage is lower than 4.0 V by welding, and the welding failure means that the strength of only 2.9 N or less was obtained in the tensile test.
[0022]
[Table 1]

[0023]
[Table 2]

[0024]
As another embodiment of the present invention, as shown in FIG. 4, the lead terminal 12 made of a stainless steel plate having a thickness of 0.2 mm avoids the portion including the electrode group as shown in FIG. For the case of being fixed to the surface (welding position) 13 by series spot welding, the same internal short-circuit failure and poor welding as in the case of using the lead terminal made of the strip-shaped metal plate in FIG. The results are shown in Tables 3 and 4.
[0025]
[Table 3]

[0026]
[Table 4]

[0027]
The welding machine uses a Seiwa welding machine MC-160B, and the conventional welding uses a positive electrode case 480V and a negative electrode case 350V. In the conventional welding position, if the welding voltage is low, the internal short circuit failure does not occur, but the welding failure increases. Increasing the welding power reduces weld defects but increases internal shorts. In the welding conditions of the present embodiment, since the welding is performed at the periphery of the electrode case that avoids the portion including the electrode group, an internal short circuit does not occur even if the output is increased. For this reason, there is no adverse effect of welding even if the output is improved by 30% of the conventional value.
[0028]
In the embodiment of the present invention, a strip-like or annular lead terminal as shown in FIGS. 3 and 4 is used. However, the shape of the lead terminal itself is not defined. The shape can be changed. In addition, the same effect as in the present embodiment can be obtained with a lead terminal in which a lead wire connector is joined to the tip of the lead terminal.
[0029]
Further, in the examples of the present invention, a flat type nonaqueous solvent secondary battery using a nonaqueous solvent for the nonaqueous electrolyte was used, but the coin shape nonaqueous electrolyte was sealed by crimping the positive electrode case with respect to the battery shape. Although described based on the secondary battery, it is also possible to replace the positive and negative electrodes and seal them by caulking the negative electrode case. Furthermore, the battery shape does not need to be a circular coin shape, and can be applied to a flat nonaqueous electrolyte secondary battery having a special shape such as an oval shape.
[0030]
【Effect of the invention】
As described above, according to the present invention, the lead terminal is welded to the periphery of the battery case avoiding the portion including the electrode group composed of the positive electrode, the negative electrode, and the separator, thereby affecting the internal active material. The welding power can be increased, and the welding power can be increased by about 30% compared to the conventional technique. Further, it has a very large industrial value in that welding defects can be reduced and welding strength can be stabilized. A flat nonaqueous electrolyte secondary battery with lead terminals can be provided.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a flat nonaqueous electrolyte secondary battery according to Example 1 of the present invention.
FIG. 2 is an enlarged cross-sectional view of a lead terminal welding position in FIG. 1;
FIG. 3 is a perspective view of a lead terminal used in FIG.
FIG. 4 is a perspective view of a lead terminal used in another embodiment of the present invention.
FIG. 5 is a cross-sectional view of a conventional flat nonaqueous electrolyte secondary battery with lead terminals.
FIG. 6 is a cross-sectional view of a conventional flat nonaqueous electrolyte secondary battery.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Positive electrode case, 2 ... Positive electrode active material content layer (coating electrode), 3 ... Separator, 4 ... Negative electrode active material content layer (coating electrode), 5 ... Negative electrode case, 6 ... Insulating gasket, 7, 8, 12 ... lead terminal, 9, 10, 13 ... welding position, 14 ... positive electrode, 15 ... negative electrode.

Claims

A metal negative electrode case that also functions as a negative electrode terminal and a metal positive electrode case that also functions as a positive electrode terminal are fitted via an insulating gasket, and the positive electrode case or the negative electrode case is further crimped by caulking. A lead terminal formed by laminating or winding an electrode layer including at least a positive electrode, a negative electrode, and a thin film separator, and welding a lead terminal containing a nonaqueous electrolyte and connected to an external circuit to the electrode case In the attached flat nonaqueous electrolyte secondary battery, the thickness of the electrode layer is 1.0 mm or less, and the welding position of the lead terminal to the electrode case avoids the portion where the positive electrode and the negative electrode group are in contact with each other. A flat non-aqueous electrolyte secondary battery with lead terminals, characterized by being in the periphery of the positive electrode and negative electrode case.

2. The flat nonaqueous electrolyte secondary battery with a lead terminal according to claim 1, wherein the lead terminal is a strip-shaped or annular metal plate.