JP4656698B2

JP4656698B2 - Flat non-aqueous electrolyte secondary battery

Info

Publication number: JP4656698B2
Application number: JP2000183000A
Authority: JP
Inventors: 宗人早見; 正美鈴木; 和男宇田川
Original assignee: Hitachi Maxell Energy Ltd
Current assignee: Hitachi Maxell Energy Ltd
Priority date: 2000-06-19
Filing date: 2000-06-19
Publication date: 2011-03-23
Anticipated expiration: 2020-06-19
Also published as: JP2002008729A

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、リード端子溶接時のセパレータ、電極の損傷を防止する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、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、リチウム合金、ポリアセン構造体などの有機化合物、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−ブチロ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】
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。これに対し、特願平１１−２４０９６４号や特願平１１−２４１２９０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、さらに前記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平行な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している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提案されている。
【０００４】
しかしながら、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、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である。前述したように正極、負極、セパレータからなる電極層の厚さが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ている。
【０００５】
このような電池系において抵抗溶接を行うために、電池ケースに５００Ｖ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や収縮を起こし、容量劣化や電池内ショートを起こす。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。また、溶接時の出力を下げた場合、上記の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、リード端子が取れたり、電池とリード端子の接触が悪くなってしまうという不具合がある。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恐れがある。
【０００６】
【発明が解決しようとする課題】
本発明は、上記状況に鑑みてなされたもので、その目的は、リード端子溶接により発生する熱の集中を分散させ、電池ケース内の電極、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する扁平形非水電解質二次電池を提供することにある。
【０００７】
【課題を解決するための手段】
本発明者らは鋭意研究を重ねた結果、扁平形非水電解質二次電池において、正極及び負極ケースと電極群との間に、金属ネットを設けることにより、前記正極及び負極ケースに電池外部からリード端子を溶接するときに発生する熱の集中を分散させ、電池ケース内の電極及びセパレータの破壊を抑制できることを見出した。
【０００８】
すなわち、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、さらに前記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、集電体の表面に作用物質含有層を有する正極、集電体の表面に作用物質含有層を有する負極、シャットダウン機能のある薄膜セパレータを合わせた、厚さが１．０ｍｍ以下の電極層により形成され、かつ正極と負極との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な電極群と、非水電解質とを収納した扁平形非水電解質二次電池において、該正極または負極ケースと電極群との間に、金属ネットを設けることにより、リード端子溶接時により発生する熱の集中を分散させ、かつ電池ケースと電極群の距離を離すことで、電池内の電極やセパレータの破壊を抑制できることを見出した。
【０００９】
以下、本発明者らが本発明の扁平形非水電解質二次電池（以下単に電池と称する）を如何にして実現したかを説明する。
リード端子溶接時に発生する熱の集中を分散させるには電池ケース外部と電極群との距離を離すことが有効である。これには電池ケースと電極群との間に、導電性のある材料を挿入することで実現される。特に熱伝導を抑制するために金属ネットを用いることが好ましい。
【００１０】
金属ネットの形状は、電池ケースとの間に空隙が得られ、空隙内に電解液を取り込めるものが良い。金属ネットとしては金網、エキスパンドメタル、パンチドメタル、発泡体などが挙げられる。空隙内の電解液は、熱や電圧の集中を起き難くさせる作用がある。また、集電体の形や開口度には特に規制はない。
【００１１】
また、金属ネットの厚さは缶の厚さを足した厚さが問題になるが、その厚さが薄いと熱の集中を分散させる効果が薄くなり目的が達せられない。逆に、その厚さが厚いと熱の集中を分散させるのは可能であるが、電池内に組み込まれる電極が多く取り込めなくなり、電池容量の低下につながる。
これらを考慮して正極または負極ケースと金属ネットの合計の厚さは０．３０ｍｍ以上０．４５ｍｍ以下が適切である。
【００１２】
また、金属ネットはあらかじめ、電池ケースの内面に溶接すると密着性が向上し、優れた導電が得られるのでよい。金属ネットの材料に関してはいかなるものでも可能であるが、金属酸化物等の高電位を有する作用物質を正極に用いた場合、正極作用物質より卑な溶解電位を持つ金属ネットを用いると、電池保存中に高電位のために劣化が起こり電池の性能に影響を及ぼす。このため、正極側の金属ネットはアルミニウムやチタン、またはクロム、モリブデンを多く含むようなステンレス鋼がよい。負極側の金属ネットに関しては正極よりも電位がかなり卑であるため、正極ほど耐食性に配慮する必要はなく、ステンレス鋼やニッケル、銅などがあげられる。また電極群と金属ネットとの接触抵抗を下げるために金属ネットの表面に導電性塗料を塗布することが好ましい。
【００１３】
本発明の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、正極作用物質は特に限定されるものではない。すなわち、ＭｎＯ₂、Ｖ₂Ｏ₅、Ｎｂ₂Ｏ₅、ＬｉＴｉ₂Ｏ₄、ＬｉＴｉ₅Ｏ₁₂、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、この中で作動電位が高く、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、長期間に亘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。
【００１４】
また、本発明の電池の負極については特に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−Ｓｉ、Ｌｉ−Ｇｅ、Ｌｉ−Ｂｉ、Ｌｉ−Ｐｂなどのリチウム合金、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物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好ましい。
【００１５】
次に、本発明の電池の電極については、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も用いることもできる。また、前記のような金属箔に作用物質を含む合剤層（作用物質含有層）を塗工した電極を用いる場合、電極群の内部に用いる電極は金属箔の両面に作用物質含有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、この部分に限り片面にのみ作用物質含有層を形成した電極を用いてもよいし、一旦、両面に作用物質含有層を形成した後、片面のみ作用物質含有層を除去してもよい。
【００１６】
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良いが、その汎用性等からステンレス製のものが好ましい。また、端子の厚さ、形においても特に限定されるものではない。
【００１７】
【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。
（実施例１）
図１は本発明の実施例１の扁平形非水電解質二次電池の断面図である。
図において、本実施例１の扁平形非水電解質二次電池の電池ケースは、ステンレス製の金属ネット２が内面に溶接されたステンレス製の正極ケース１に、金属ネット６を内面に溶接し、絶縁ガスケット７を一体化した負極ケース５を嵌合しており、この電池ケース内には正極作用物質含有層３と負極作用物質含有層４の間にポリエチレン微多孔膜からなるセパレータ８を介し渦巻状に捲回された発電要素が収納されている。
【００１８】
次に、本実施例１の扁平形非水電解質二次電池の製造方法を説明する。
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。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３を形成した。以後、正極作用物質含有層３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に切り出した正極板を作製した。
【００１９】
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。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、銅層を剥き出し通電部とし、幅１５ｍｍ、長さ１２０ｍｍ、厚さ０．１５ｍｍに切り出した負極板を作製した。
【００２０】
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８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。
【００２１】
作製した電極群を８５℃で１２時間乾燥した後、厚さ０．０３ｍｍのステンレス製の金属ネット６を内面に溶接した、絶縁ガスケット７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ように配置し、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、さらに電極群の片面塗工正極板の未塗工側に接するように厚さ０．０３ｍｍのステンレス製の金属ネット２が内面に溶接された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１の扁平形非水電解質二次電池を製作した。正極及び負極ケースの厚さと該金属ネットの厚さの合計はそれぞれ０．２８ｍｍである。
【００２２】
（実施例２）
厚さが０．０５ｍｍの金属ネットを正極及び負極ケースの内面に溶接し、正極及び負極ケースの厚さと該金属ネットの厚さの合計がそれぞれ０．３０ｍｍである以外は実施例１と同様に電池を作製した。
【００２３】
（実施例３）
正極及び負極の作用物質含有層の厚さを０．１４ｍｍとし、厚さが０．１０ｍｍの金属ネットを正極及び負極ケースの内面に溶接し、正極及び負極ケースの厚さと該金属ネットの厚さの合計がそれぞれ０．３５ｍｍである以外は実施例１と同様に電池を作製した。
【００２４】
（実施例４）
正極及び負極の作用物質含有層の厚さを０．１３ｍｍとし、厚さが０．１５ｍｍの金属ネットを正極及び負極ケースの内面に溶接し、正極及び負極ケースの厚さと該金属ネットの厚さの合計がそれぞれ０．４０ｍｍである以外は実施例１と同様に電池を作製した。
【００２５】
（実施例５）
正極及び負極の作用物質含有層の厚さを０．１２ｍｍとし、厚さが０．２０ｍｍの金属ネットを正極及び負極ケースの内面に溶接し、正極及び負極ケースの厚さと該金属ネットの厚さの合計がそれぞれ０．４５ｍｍである以外は実施例１と同様に電池を作製した。
【００２６】
（実施例６）
正極及び負極の作用物質含有層の厚さを０．１０ｍｍとし、厚さが０．３０ｍｍの金属ネットを正極及び負極ケースの内面に溶接し、正極及び負極ケースの厚さと該金属ネットの厚さの合計がそれぞれ０．５５ｍｍである以外は実施例１と同様に電池を作製した。
【００２７】
（比較例１）
金属ネットを用いず、厚さが０．２５ｍｍの電池ケースの内面に導電性塗料を塗布した正極及び負極ケースを用いた以外は実施例１と同様に電池を作製した。
以上の通り作製した本実施例および比較例の電池３００個の正極、負極両電池ケースに厚さ０．２ｍｍのステンレス製のリード端子を４８０±１０Ｖの溶接出力で抵抗溶接を行った。これらの電池をランダムに５０個抜き取り、電池を分解し、正負極側のセパレータの穴あき、収縮、及び電極の剥げ落ち具合を観察した。また、これらの電池において、４．２Ｖ、３ｍＡの定電流定電圧で４８時間初充電を実施し、３日間室温で放置後、開路電圧を測定した。その後、３日後の開路電圧が４．０Ｖ以上であった電池を１ｍＡの定電流で３．０Ｖまで放電を実施し放電容量を求めた。
【００２８】
正負極側のセパレータの穴あき、収縮、及び電極の剥げ落ち発生率を表１に示した。また、初充電後、電池を３日間放置後の開路電圧と、その後、３日後の開路電圧が４．０Ｖ以上であった電池の放電容量の平均値を表２に示した。
【００２９】
表より明らかであるが本発明の各実施例の電池は、比較例１の電池に比べて電池にリード端子を抵抗溶接した後の正負極側のセパレータの穴あき、収縮、及び電極の剥げ落ちが大幅に改善されており、電池のショートも改善されている。なお、正極ケース及び負極ケースの厚さと該金属ネットの厚さの合計がそれぞれ０．３０ｍｍ以上である実施例に関しては、電池に比べて電池にリード端子を抵抗溶接した後の正負極側のセパレータ穴あき、収縮、及び電極の剥げ落ちが見られない。実施例１の電池は、抵抗溶接後の正極、負極側のセパレータの収縮が若干みられたが、電池内での内部短絡が起こる程のものではない。実施例２、３、４、５の電池においては金属ネットの厚さが最適であるため電池内に電極を多く詰め込め、高容量の電池が得られる。このため、正極及び負極ケースの厚さと該金属ネットの厚さの合計が０．３０ｍｍ以上０．４５ｍｍ以下のものが更によい。
【００３０】
【表１】

【００３１】
【表２】

【００３２】
なお、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て説明し、また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。
【００３３】
【発明の効果】
以上説明したとおり、本発明によれば、電池の高容量を維持したまま、電池にリード端子を抵抗溶接した後の正負極側のセパレータの穴あき、収縮、及び電極の剥げ落ちの不具合を解消できるので、工業的価値の非常に優れた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の電池の断面図。
【符号の説明】
１…正極ケース、２…金属ネット（正極側）、３…正極作用物質含有層、４…負極作用物質含有層、５…負極ケース、６…金属ネット（負極側）、７…絶縁ガスケット、８…セパレータ。[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 that prevents damage to a separator and electrodes during lead terminal welding.
[0002]
[Prior art]
Metal active materials such as MnO ₂ and V ₂ O ₅ , inorganic compounds such as fluorinated graphite, or organic compounds such as polyaniline and polyacene structures are used as the positive electrode active material, and metal lithium, lithium alloys, polyacene structures, etc. are used as the negative electrode Organic compounds, 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, dimethyl carbonate, LiClO ₄ , LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ and the like in a non-aqueous solvent such as methyl ethyl carbonate, dimethoxyethane, and γ-butyrolactone Coin using non-aqueous electrolyte in which the supporting salt of And button-type flat non-aqueous electrolyte secondary batteries have already been commercialized, and SRAM and RTC backup power sources that discharge at a light load with a discharge current of several to several tens of microamperes and battery replacement-free watches It is applied to uses such as main power.
[0003]
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. On the other hand, a metal negative electrode case also serving as a negative electrode terminal and a metal positive electrode case also serving as a positive electrode terminal as shown in Japanese Patent Application No. 11-240964 and Japanese Patent Application No. 11-241290 are fitted through an insulating gasket. A flat non-aqueous solution that has a sealing structure in which the positive electrode case or the negative electrode case is further crimped by caulking, and includes a power generation element including at least a positive electrode, a separator, and a negative electrode, and a non-aqueous electrolyte. In an electrolyte secondary battery, an electrode having positive and negative electrode facing surfaces in which at least three or more positive and negative electrodes face each other through a separator when viewed in a vertical direction parallel to the flat surface of the flat battery A flat non-aqueous electrolyte secondary battery 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 satisfies the requirements for downsizing To have been proposed.
[0004]
However, when these flat-type nonaqueous electrolyte secondary batteries are incorporated into equipment, many of them are built by welding the lead terminals to the outside of the positive and negative electrode cases by resistance welding, and soldering the terminal part and the equipment. Is common. As described above, in a flat nonaqueous electrolyte secondary battery in which an electrode group consisting of a positive electrode, a negative electrode, and a separator has a thickness of 1.0 mm or less and is laminated or wound, A positive and negative electrode having a thickness of 1 mm or less and a group of electrodes laminated or wound through a thin film separator made of polyethylene, polypropylene or the like having a thickness of 0.5 mm or less are directly brought into contact with the positive electrode and the negative electrode case.
[0005]
In order to perform resistance welding in such a battery system, when a voltage of about 500 V is applied to the battery case, heat generated during welding reaches the electrodes and the separator through the battery case, and the separator is perforated and contracted. Cause deterioration of capacity and short circuit in the battery. In addition, since the voltage concentrates on the welded portion, problems such as peeling off of the electrode leading to the welded portion from the current collector occur, and the function as a battery is reduced. Further, when the output during welding is lowered, the above-described problems do not occur, but since the welding strength is weakened, there is a problem that the lead terminal can be removed or the contact between the battery and the lead terminal is deteriorated. Moreover, even if the welding method of the lead terminal is changed to laser welding or the like, the generation of heat cannot be suppressed, and the same problem may be caused.
[0006]
[Problems to be solved by the invention]
The present invention has been made in view of the above circumstances, and its purpose is to disperse the concentration of heat generated by lead terminal welding, to suppress the destruction of electrodes and separators in the battery case, capacity deterioration and short circuit in the battery. It is an object of the present invention to provide a flat non-aqueous electrolyte secondary battery that prevents the above.
[0007]
[Means for Solving the Problems]
As a result of intensive studies, the present inventors have found that in a flat non-aqueous electrolyte secondary battery, a metal net is provided between the positive electrode and the negative electrode case and the electrode group, so that the positive electrode and the negative electrode case are externally attached to the positive electrode and the negative electrode case. It has been found that the concentration of heat generated when welding the lead terminals can be dispersed, and the destruction of the electrodes and separators in the battery case can be suppressed.
[0008]
That is, 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 are fitted via an insulating gasket, and the positive electrode case or the negative electrode case is further crimped by crimping has, at least in its interior, the combined positive electrode with an active substance-containing layer on the surface of the current collector, a negative electrode with an active substance-containing layer on the surface of the current collector, a thin film separator with a shutdown function, the thickness In a flat nonaqueous electrolyte secondary battery in which an electrode group formed by an electrode layer of 1.0 mm or less and the sum of the opposing areas of the positive electrode and the negative electrode is larger than the opening area of the insulating gasket and a nonaqueous electrolyte is accommodated In addition, by providing a metal net between the positive electrode or negative electrode case and the electrode group, the concentration of heat generated during welding of the lead terminals is dispersed, and the battery case is And by increasing the distance of the electrode group was found to be suppressed destruction of the electrodes and separators in the battery.
[0009]
Hereinafter, how the present inventors have realized the flat nonaqueous electrolyte secondary battery (hereinafter simply referred to as a battery) of the present invention will be described.
In order to disperse the concentration of heat generated during lead terminal welding, it is effective to increase the distance between the outside of the battery case and the electrode group. This is realized by inserting a conductive material between the battery case and the electrode group. In particular, it is preferable to use a metal net in order to suppress heat conduction.
[0010]
The shape of the metal net is preferably such that a gap is obtained between the battery case and the electrolytic solution can be taken into the gap. Examples of the metal net include a metal net, expanded metal, punched metal, and foam. The electrolyte in the gap has an effect of making it difficult for heat and voltage to concentrate. There are no particular restrictions on the shape and aperture of the current collector.
[0011]
In addition, the thickness of the metal net is a problem of adding the thickness of the can, but if the thickness is thin, the effect of dispersing the concentration of heat is reduced and the purpose cannot be achieved. On the contrary, if the thickness is large, it is possible to disperse the concentration of heat, but a large number of electrodes incorporated in the battery cannot be taken in, leading to a decrease in battery capacity.
Considering these, the total thickness of the positive electrode or negative electrode case and the metal net is appropriately 0.30 mm or more and 0.45 mm or less.
[0012]
In addition, when the metal net is previously welded to the inner surface of the battery case, the adhesion is improved, and excellent conductivity is obtained. Any material can be used for the metal net, but when an active substance such as a metal oxide is used for the positive electrode, it is possible to preserve the battery by using a metal net that has a lower dissolution potential than the positive electrode active substance. Deterioration occurs due to the high potential inside, affecting the performance of the battery. For this reason, the metal net on the positive electrode side is preferably made of aluminum, titanium, or stainless steel containing a large amount of chromium or molybdenum. Since the potential of the metal net on the negative electrode side is considerably lower than that of the positive electrode, it is not necessary to consider corrosion resistance as much as the positive electrode, and examples include stainless steel, nickel, and copper. In order to reduce the contact resistance between the electrode group and the metal net, it is preferable to apply a conductive paint to the surface of the metal net.
[0013]
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 particularly limited. That is, MnO ₂ , V ₂ O ₅ , Nb ₂ O ₅ , LiTi ₂ O ₄ , LiTi ₅ O ₁₂ , LiFe ₂ O ₄ , metal oxide such as lithium cobaltate, lithium nickelate, lithium manganate, or fluoride Any material such as an inorganic compound such as graphite or FeS ₂ or an organic compound such as polyaniline or polyacene structure is applicable. However, lithium-containing oxides in which lithium cobaltate, lithium nickelate, lithium manganate, mixtures thereof, or some of these elements are substituted with other metal elements are high in terms of operating potential and excellent cycle characteristics. In the flat non-aqueous electrolyte secondary battery, which is more preferable and may be used for a long period of time, cobalt acid is high in capacity, low in reactivity with electrolyte and moisture, and chemically stable. More preferred is lithium.
[0014]
Further, the negative electrode of the battery of the present invention is not particularly limited, lithium metal, or lithium alloys such as Li-Al, Li-In, Li-Si, Li-Ge, Li-Bi, Li-Pb, Alternatively, various materials such as Nb ₂ O ₅ , LiTi ₂ O ₄ , Li ₄ Ti ₅ O ₁₂ and oxides such as Li-containing silicon oxide can be applied, but they have excellent cycle characteristics, low operating potential, and high capacity. The carbonaceous material capable of occluding and releasing Li is preferable in that it is natural graphite, artificial graphite, expanded graphite, mesophase pitch fired body, mesophase pitch fiber, especially in that the battery operating voltage does not decrease much at the end of discharge. A carbonaceous material in which a graphite structure having a d ₀₀₂ plane interval of 0.338 nm or less such as a fired body is developed is preferable.
[0015]
Next, with respect to the electrodes of the battery of the present invention, both the positive and negative electrodes may use a conventional granule mixture molding method or a method of filling a metal base of a metal net with a mixture, but it is easy to produce a thin electrode. In that respect, it is preferable to apply a slurry mixture to a metal foil and dry it, and it is also possible to use a rolled product. In addition, when using an electrode in which a mixture layer containing an active substance (active substance-containing layer) is applied to the metal foil as described above, the electrode used inside the electrode group forms an active substance-containing layer on both sides of the metal foil. It is preferable from the viewpoint of volume efficiency that the exposed electrode components exposed to the metal nets at both ends of the electrode group are exposed to the metal foil, particularly the metal foil, in order to reduce the contact resistance. Is preferred. In this regard, an electrode in which an active substance-containing layer is formed only on one side may be used only in this portion, or after the active substance-containing layer is once formed on both sides, the active substance-containing layer may be removed only on one side. .
[0016]
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. Also, the thickness and shape of the terminal are not particularly limited.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, examples and comparative examples of the present invention will be described in detail.
Example 1
1 is a cross-sectional view of a flat nonaqueous electrolyte secondary battery according to Example 1 of the present invention.
In the figure, the battery case of the flat nonaqueous electrolyte secondary battery of Example 1 has a stainless steel positive electrode case 1 welded to the inner surface of a stainless steel metal net 2 and a metal net 6 welded to the inner surface. A negative electrode case 5 in which an insulating gasket 7 is integrated is fitted, and the battery case is spirally interposed between a positive electrode active substance-containing layer 3 and a negative electrode active substance-containing layer 4 via a separator 8 made of a polyethylene microporous film. A power generation element wound in a shape is stored.
[0018]
Next, a method for manufacturing the flat nonaqueous electrolyte secondary battery of Example 1 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. 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 3 on the aluminum foil surface. Thereafter, coating and drying were repeated until the coating film thickness of the positive electrode active material-containing layer 3 reached 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 was removed from one end of the electrode body, and the positive electrode plate was cut out to have a width of 15 mm, a length of 120 mm, and a thickness of 0.15 mm by stripping the aluminum layer. .
[0019]
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, and diluted and mixed with ion-exchanged water. 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. A 10 mm portion of the active substance-containing layer was removed from one end of the electrode body, and the copper layer was peeled off to form a current-carrying portion. A negative electrode plate cut out to a width of 15 mm, a length of 120 mm, and a thickness of 0.15 mm was produced.
[0020]
Next, the positive and negative electrode current-carrying surface is the end of the outer periphery winding, and the coil is wound between the positive electrode and the negative electrode with a separator 8 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.
[0021]
The prepared electrode group was dried at 85 ° C. for 12 hours, and then a 0.03 mm thick stainless steel metal net 6 was welded to the inner surface, and the electrode group was formed on the inner bottom surface of the negative electrode metal case 5 integrated with the insulating gasket 7. uncoated side of the single-side coated negative electrode plate is disposed in contact with the metal net, a volume of ethylene carbonate and methyl ethyl carbonate ratio of 1: a LiPF ₆ at a rate of 1 mol / l as a supporting salt to mixed solvent at a ratio of A non-aqueous electrolyte that has been dissolved is injected, and a stainless steel metal net 2 having a thickness of 0.03 mm is welded to the inner surface so as to be in contact with the uncoated side of the single-side coated positive electrode plate of the electrode group. After fitting the positive electrode case 1 and turning it upside down, the positive electrode case was crimped, sealed, and a flat nonaqueous electrolyte secondary battery of Example 1 having a thickness of 3 mm and a diameter of 24.5 mm was produced. The total thickness of the positive and negative electrode cases and the thickness of the metal net is 0.28 mm.
[0022]
(Example 2)
A metal net having a thickness of 0.05 mm is welded to the inner surfaces of the positive electrode and the negative electrode case, and the sum of the thickness of the positive electrode and the negative electrode case and the thickness of the metal net is 0.30 mm, respectively, as in Example 1. A battery was produced.
[0023]
(Example 3)
The thickness of the active substance containing layer of the positive electrode and the negative electrode is 0.14 mm, a metal net having a thickness of 0.10 mm is welded to the inner surfaces of the positive electrode and the negative electrode case, and the thickness of the positive electrode and the negative electrode case and the thickness of the metal net A battery was fabricated in the same manner as in Example 1 except that the total of each was 0.35 mm.
[0024]
Example 4
The thickness of the active substance containing layer of the positive electrode and the negative electrode is 0.13 mm, a metal net having a thickness of 0.15 mm is welded to the inner surfaces of the positive electrode and the negative electrode case, and the thickness of the positive electrode and the negative electrode case and the thickness of the metal net A battery was fabricated in the same manner as in Example 1 except that the total of each was 0.40 mm.
[0025]
(Example 5)
The thickness of the active substance containing layer of the positive electrode and the negative electrode is 0.12 mm, a metal net having a thickness of 0.20 mm is welded to the inner surfaces of the positive electrode and the negative electrode case, and the thickness of the positive electrode and the negative electrode case and the thickness of the metal net A battery was produced in the same manner as in Example 1 except that the total of each was 0.45 mm.
[0026]
(Example 6)
The thickness of the active substance-containing layer of the positive electrode and the negative electrode is 0.10 mm, a metal net having a thickness of 0.30 mm is welded to the inner surfaces of the positive electrode and the negative electrode case, and the thickness of the positive electrode and the negative electrode case and the thickness of the metal net A battery was produced in the same manner as in Example 1 except that the total of each was 0.55 mm.
[0027]
(Comparative Example 1)
A battery was produced in the same manner as in Example 1 except that a positive electrode and a negative electrode case in which a conductive paint was applied to the inner surface of a battery case having a thickness of 0.25 mm were used without using a metal net.
Resistive welding was performed with a welding output of 480 ± 10 V on a stainless steel lead terminal having a thickness of 0.2 mm on both the positive and negative battery cases of 300 batteries of this example and comparative example produced as described above. Fifty of these batteries were extracted at random, the batteries were disassembled, and the positive and negative separators were perforated, contracted, and the electrodes were peeled off. In these batteries, initial charging was performed for 48 hours at a constant current and a constant voltage of 4.2 V, 3 mA, and the open circuit voltage was measured after being left at room temperature for 3 days. Thereafter, the battery whose open circuit voltage after 3 days was 4.0 V or higher was discharged to 3.0 V at a constant current of 1 mA to obtain the discharge capacity.
[0028]
Table 1 shows the perforation and shrinkage of the positive and negative separators, and the rate of occurrence of electrode peeling. Table 2 shows the open circuit voltage after the battery was left for three days after the initial charge, and the average value of the discharge capacity of the battery after which the open circuit voltage after 3 days was 4.0 V or more.
[0029]
As is clear from the table, the batteries of the respective examples of the present invention had the positive and negative separators perforated and contracted after the lead terminals were resistance welded to the battery, and the electrodes were peeled off. Has been greatly improved, and battery shorts have also been improved. In addition, regarding the examples in which the total thickness of the positive electrode case and the negative electrode case and the thickness of the metal net is 0.30 mm or more, the separator on the positive and negative electrode side after resistance welding of the lead terminal to the battery as compared with the battery There is no perforation, shrinkage, or electrode peeling. In the battery of Example 1, some shrinkage of the positive electrode and negative electrode separators after resistance welding was observed, but the internal short circuit within the battery did not occur. In the batteries of Examples 2, 3, 4, and 5, since the thickness of the metal net is optimal, a large capacity battery can be obtained by packing many electrodes in the battery. For this reason, the thing whose total of the thickness of a positive electrode and negative electrode case and the thickness of this metal net is 0.30 mm or more and 0.45 mm or less is still better.
[0030]
[Table 1]

[0031]
[Table 2]

[0032]
In addition, the Example of this invention demonstrates using the flat type nonaqueous solvent secondary battery which used the nonaqueous solvent for the nonaqueous electrolyte, and about the shape of a battery, the coin type non-sealing is carried out by the crimping process of a positive electrode case. Although described based on the water electrolyte, 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.
[0033]
【The invention's effect】
As described above, according to the present invention, the problems of perforation and shrinkage of the separator on the positive and negative electrodes side after resistance welding of the lead terminal to the battery while maintaining the high capacity of the battery and the electrode peeling off are eliminated. Therefore, it is possible to provide a flat non-aqueous electrolyte secondary battery having an excellent industrial value.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a battery according to Example 1 of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Positive electrode case, 2 ... Metal net (positive electrode side), 3 ... Positive electrode active material content layer, 4 ... Negative electrode active material content layer, 5 ... Negative electrode case, 6 ... Metal net (negative electrode side), 7 ... Insulating gasket, 8 ... separator.

Claims

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 are fitted via an insulating gasket, and the positive electrode case or the negative electrode case has a sealing structure that is crimped by caulking, In a flat nonaqueous electrolyte secondary battery containing a nonaqueous electrolyte and an electrode group in which at least a positive electrode, a negative electrode, and a thin film separator are combined,
The positive electrode and the negative electrode have an active substance-containing layer on the surface of a current collector,
The sum total of the opposing areas of the positive electrode and the negative electrode in the electrode group is larger than the opening area of the insulating gasket,
The thickness of the electrode layer comprising the positive electrode, the negative electrode and the thin film separator in the electrode group is 1.0 mm or less,
A flat nonaqueous electrolyte secondary battery comprising a metal net provided between the positive electrode or negative electrode case and the electrode group.

The flat nonaqueous electrolyte secondary battery according to claim 1, wherein the inner surface of the positive electrode case or the inner surface of the negative electrode case and the metal net are welded.

The electrode group is flattened type nonaqueous electrolyte secondary battery according to claim 1 or 2, said electrode layer is an electrode group winding turn was wound structure spirally.