JP3988901B2

JP3988901B2 - Organic electrolyte secondary battery

Info

Publication number: JP3988901B2
Application number: JP36352597A
Authority: JP
Inventors: 美奈子岩崎; 秀章弓場; 房次喜多; 和伸松本
Original assignee: Hitachi Maxell Energy Ltd
Current assignee: Maxell Ltd
Priority date: 1997-12-15
Filing date: 1997-12-15
Publication date: 2007-10-10
Anticipated expiration: 2017-12-15
Also published as: JPH11176478A

Description

【０００１】
【発明の属する技術分野】
本発明は、有機電解液二次電池に関するものであり、さらに詳しくは、安全性を確保するための特定の構造を有する有機電解液二次電池に関するものである。
【０００２】
【従来の技術】
有機電解液二次電池は電解液の溶媒として有機溶媒を用いた二次電池であり、この有機電解液二次電池は、容量が大きく、かつ高電圧、高エネルギー密度、高出力であることから、ますます需要が増える傾向にある。
【０００３】
そして、この電池の有機電解液（以下、電池を表すとき以外は、単に「電解液」という）の溶媒としては、これまで、エチレンカーボネートなどの環状エステルやそれにジメチルカーボネート、プロピオン酸メチルなどのエステルを混合したものが用いられてきた。
【０００４】
しかしながら、本発明者らの検討によれば、この有機電解液二次電池は、今後さらに高容量化を図った場合やユーザーから要求される仕様によっては、電池の構造についてさらに工夫をしていかないと、安全性が低下するおそれのあることが判明した。これを詳しく説明すると、通常、この種の電池では、保護回路などで過充電を防止することによって内部短絡を起こさないようにする対策がとられているし、また通常の内部短絡では電池が発熱するだけで異常事態には至らないようにされているが、異常使用を想定して釘刺し試験を行ってみたところ、安全性に欠ける場合のあることが判明した。すなわち、釘刺し試験では、電池の圧壊や外部短絡に比べて少ない部分で電池を確実に短絡させるので、短絡部位に電流が集中し、より発熱しやすくなり、電池が部分的に急速に高温になりやすいため、セパレータのフューズ（溶融による目づまり）のばらつきが生じやすく、また短絡部位での電解液と負極との反応による発熱が多くなるので、この釘刺し試験は通常の使用条件では生じ得ないような安全性の欠如も見出し得るほどに苛酷な安全性確認試験である。従って、この釘刺し試験で安全性が確認できれば、異常使用に遭遇した場合でも安全性が確保されるものと考えられる。
【０００５】
また、釘刺し試験は室温で行うよりも４５℃の高温状態で行う方が、電池がより高温にまで上昇しやすく、電池の熱暴走反応が生じやすい。さらに、１／２釘刺しのように、釘を電池の途中で止める方が、短絡部分が少なくなり電流がより集中して発熱しやすい。従って、この釘刺し試験を４５℃で行い、１／２釘刺しにすると、安全性を確認するための試験として非常に苛酷な試験となり、そのような苛酷な条件下の試験で安全性が確認できれば、実使用で充分な安全性が確保できるものと考えられる。
【０００６】
【発明が解決しようとする課題】
ところで、カーボンなどのリチウムを脱挿入できる化合物を負極活物質として用いた場合、金属リチウムを用いる場合よりも高温での電解液との反応性がはるかに低下し、電池の安全性が改善される。しかし、最近の高容量化への流れにより電池のエネルギー密度は今後ますます高くなる傾向にあるため、苛酷な安全性確認試験である釘刺し試験においても優れた安全性を示し得るようにしておくことが必要であり、そのためには電池の内部構造を発火しにくい構造に変更しておくことが必要であることがわかってきた。
【０００７】
従って、本発明は、今後の高容量化に備え、苛酷な安全性確認試験である釘刺し試験においても充分に安全性が確認できるように電池の構造を改良し、安全性の優れた有機電解液二次電池を提供することを目的とする。
【０００８】
【課題を解決するための手段】
本発明は、金属箔からなる正極集電体の少なくとも一方の面に活物質含有塗膜を形成してなる正極と、金属箔からなる負極集電体の少なくとも一方の面に活物質含有塗膜を形成してなる負極とを、セパレータを介して巻回した巻回構造の電極体、および有機電解液を電池缶に収容してなり、正極活物質、充電時の開路電圧がＬｉ基準で４Ｖ以上を示すリチウム複合酸化物であり、有機電解液中に鎖状エステルが全電解液溶媒中で５０体積％を超えて含まれている有機電解液二次電池において、上記巻回構造の電極体における正極の少なくとも最外周部に活物質含有塗膜を形成せず正極集電体のみの部分を設け、かつ上記巻回構造の電極体における負極の少なくとも最外周部に活物質含有塗膜を形成せず負極集電体のみの部分を設け、上記部分の正極集電体と負極集電体とをセパレータを介して配置させ、かつ上記巻回構造の電極体の巻回外径の最小値を放電状態において電池缶の内径より０．４〜０．７ｍｍ小さくすることによって、上記課題を解決したものである。
【０００９】
以下、本発明を完成するに至った経過および上記構成にすることによって安全性を向上させることができる理由を詳細に説明する。
【００１０】
一般に現在の有機電解液二次電池の巻回構造の電極体は、正極集電体となるアルミニウム箔の両面に活物質含有塗膜を形成したシート状の正極と、負極集電体となる銅箔の両面に活物質含有塗膜を形成したシート状の負極と２枚のセパレータとを、負極、セパレータ、正極、セパレータの順に積み重ね、負極が正極より外周側になるように渦巻状に巻回したものである。
【００１１】
本発明者らは、有機電解液二次電池として最も普及しているリチウムイオン二次電池を入手し、釘刺し試験を行ったところ、通常の市販のリチウムイオン二次電池では危険性が低いのに対し、電池のエネルギー密度を上げていくと危険性が高くなっていくことが判明した。これらの電池の負極には通常炭素材料などのリチウムを脱挿入できる化合物が使用されているが、負極が過充電されてリチウムが多少でも電着した場合、約１００℃付近から電解液と電着リチウムやリチウムが挿入された炭素材料との間で発熱反応が生じる。
【００１２】
また、正極でも、リチウムが脱離することによって、電解液との反応開始温度が低くなり、負極の反応熱により正極の熱暴走温度に達すると、電池は異常発熱を起こす。このような連続反応を伴う発熱現象があるため、通常使用条件での電池の負極の充放電可能な容量が電池の単位体積あたり９６ｍＡｈ／ｃｍ³（満充電において）を越えた場合には、電池が過充電された時の安全性が低下する。つまり、負極の単位体積あたりの放電可能な容量が多いほど、過充電時に発熱が生じた場合に電池の単位体積あたりの発熱量が多くなり、電池温度が正極の熱暴走温度にまで上昇する可能性が高くなる。従って、本発明では、負極の単位体積あたりの容量が大きい電池において、負極と電解液との発熱反応が生じた場合でも、その発熱によって電池の温度が正極の熱暴走反応にまで上昇しないように電池の構造を改良して、負極の単位体積当たりの容量が大きい高容量の電池でも、充分な安全性を確保できるようにしたのである。
【００１３】
本発明において、巻回構造の電極体における正極の少なくとも最外周部に活物質含有塗膜を形成せずに正極集電体のみの部分を設け、かつ巻回構造の電極体における負極の少なくとも最外周部に活物質含有塗膜を形成せずに負極集電体のみの部分を設け、上記部分の正極集電体と負極集電体とをセパレータを介して配置させることによって安全性を向上させることができる理由は、現在のところ必ずしも明確でないが、次のように考えられる。
【００１４】
前記のように、負極活物質として炭素材料のようなリチウムを脱挿入できる化合物を用いることによって、電解液と負極との高温での反応性は負極活物質としてリチウムを用いていた場合よりも低くなっているが、負極の充放電可能な容量が増えることにより電解液との反応性が増加して、発熱量が多くなり、電池の温度が上昇しやすくなる。しかし、巻回構造の電極体における正極および負極のそれぞれの少なくとも最外周部に活物質含有塗膜を形成せず正極集電体と負極集電体の部分のみを設けておくと、それらの集電体のみの部分によって放熱が早くなり、正極が熱暴走温度に達しにくくなって、電池が異常発熱を起こしにくくなり、電池の安全性が向上する。
【００１５】
【発明の実施の形態】
上記のように、巻回構造の電極体における正極と負極のそれぞれの最外周部に設ける正極集電体と負極集電体のみの部分は、巻回構造の電極体において１周以上であることが好ましく、また２周以下であることが好ましい。すなわち、上記のような正極集電体と負極集電体のみの部分を１周以上にすることによって、放熱を早くし、電池の安全性を充分に向上させることができ、また、それらの集電体のみの部分を２周以下にすることによって、電池のエネルギー密度の大幅な低下を防止することができる。
【００１６】
また、巻回構造の電極体の最外周部におけるセパレータをなくすと、負極集電体が直接電池缶の内壁と接触することになって放熱がより早くなり、電池の安全性を向上させる効果がより一層顕著に発現する。
【００１７】
本発明において、正極活物質としては、ＬｉＮｉＯ_２、ＬｉＣｏＯ_２、ＬｉＭｎ_２Ｏ_４などの充電時の開路電圧がＬｉ基準で４Ｖ以上を示すリチウム複合酸化物を用いる。
【００１８】
正極活物質として充電時の開路電圧がＬｉ基準で４Ｖ以上を示すリチウム複合酸化物を用いることで、高エネルギー密度が得られる。また、充電したＬｉＣｏＯ_２やＬｉＮｉＯ_２は電解液との反応開始温度がＬｉＭｎ_２Ｏ_４などより低く、負極の発熱によって正極の熱暴走温度に達しやすいので、正極活物質としてＬｉＣｏＯ_２やＬｉＮｉＯ_２を用いる場合には、本発明の効果が特に顕著に発現する。
【００１９】
そして、正極は、たとえば、上記の正極活物質にたとえば鱗片状黒鉛やカーボンブラックなどの導電助剤や、たとえばポリフッ化ビニリデンやポリテトラフルオロエチレンなどの結着剤などを適宜添加し、溶剤で塗材化した活物質含有塗材をアルミニウム箔などの金属箔からなる正極集電体に塗布し、乾燥して、活物質含有塗膜を形成することによって作製される。ただし、本発明においては、前記のように巻回構造の電極体において正極の少なくとも最外周部となる部分には活物質含有塗膜を形成せず正極集電体のみの部分を残しておく。
【００２０】
本発明において、負極に用いる材料としては、リチウムイオンをドープ、脱ドープできるものであればよく、本発明においては、そのようなリチウムイオンをドープ、脱ドープできる物質を負極活物質という。そして、この負極活物質としては、特に限定されることはないが、たとえば、黒鉛、熱分解炭素類、コークス類、ガラス状炭素類、有機高分子化合物の焼成体、メソカーボンマイクロビーズ、炭素繊維、活性炭などの炭素材料、Ｓｉ、Ｓｎ、Ｉｎなどの合金、またはＬｉに近い低電位で充放電できるＳｉ、Ｓｎ、Ｉｎなどの酸化物などを用いるのが好ましい。
【００２１】
負極活物質として炭素材料を用いる場合、該炭素材料としては下記の特性を持つものが好ましい。すなわち、その（００２）面の層間距離ｄ₀₀₂は、３．５Å以下が好ましく、より好ましくは３．４５Å以下、さらに好ましくは３．４Å以下である。また、ｃ軸方向の結晶子の大きさＬｃは、３０Å以上が好ましく、より好ましくは８０Å以上、さらに好ましくは２５０Å以上である。そして、平均粒径は８〜１５μｍ、特に１０〜１３μｍが好ましく、純度は９９．９％以上が好ましい。
【００２２】
負極は、たとえば、上記の負極活物質にたとえばポリフッ化ビニリデンやポリテトラフルオロエチレンなどの結着剤を適宜添加し、さらに要すれば導電助剤を適宜添加し、溶剤で塗材化し、この活物質含有塗材を銅箔などからなる負極集電体に塗布し、乾燥して、活物質含有塗膜を形成することによって作製される。ただし、本発明においては、前記のように巻回構造の電極体において負極の最外周部となる部分には活物質含有塗膜を形成せず、負極集電体のみの部分を残しておく。
【００２３】
上記正極や負極の集電体となる金属箔としては、たとえば、アルミニウム箔、銅箔、ニッケル箔、ステンレス鋼箔などが用いられるが、正極集電体となる金属箔としては特にアルミニウム箔が好ましく、また負極集電体となる金属箔としては特に銅箔が好ましい。
【００２４】
本発明において、電解液は、主溶媒として鎖状エステルを用いる。これにより、電解液の粘度を下げ、イオン伝導度を高めることができる。このような鎖状エステルとしては、たとえば、ジメチルカーボネート、ジエチルカーボネート、メチルエチルカーボネート、プロピオン酸メチルなどの鎖状のＣＯＯ−結合を有する有機溶媒が挙げられる。主溶媒というのは、これらの鎖状エステルを含んだ全電解液溶媒中で鎖状エステルが５０体積％を超えることを意味する。鎖状エステルが６５体積％を超えると、従来技術では４．４Ｖ充電後の釘刺し試験での電池の安全性が低下するが、本発明によれば、そのように鎖状エステルが６５体積％を超える場合でも安全性を確保でき、本発明の効果が顕著に発現する。
【００２５】
そして、鎖状エステルが７０体積％を超えると、従来技術では電池の安全性がより低下しやすくなるので、本発明の効果がより一層顕著に発現するようになり、鎖状エステルが７５体積％を超えると、従来技術では電池の安全性がさらに低下しやすくなるので、本発明の効果がさらに一層顕著に発現するようになる。また、鎖状エステルがメチル基を有する場合も従来技術では電池の安全性が低下しやすくなるので、本発明の効果がより一層顕著に発現する。
【００２６】
また、上記鎖状エステルに下記の誘電率が高いエステル（誘電率３０以上）を混合して用いると、鎖状エステルだけで用いる場合よりも、サイクル特性や電池の負荷特性が向上するので、電池としてはより好ましいものとなる。このような誘電率の高いエステルとしては、たとえば、プロピレンカーボネート（ＰＣ）、エチレンカーボネート（ＥＣ）、ブチレンカーボネート（ＢＣ）、ガンマーブチロラクトン（γ−ＢＬ）、エチレングリコールサルファイト（ＥＧＳ）などが挙げられ、特に環状構造のものが好ましく、とりわけ環状のカーボネートが好ましく、エチレンカーボネート（ＥＣ）が最も好ましい。
【００２７】
上記誘電率の高いエステルは電解液の全溶媒中の４０体積％未満が好ましく、より好ましくは３０体積％以下、さらに好ましくは２５体積％以下である。そして、これらの誘電率の高いエステルによる安全性の向上は、上記誘電率の高いエステルが電解液の全溶媒中で１０体積％以上になると顕著になり、２０体積％に達するとさらに顕著になる。
【００２８】
上記誘電率の高いエステル以外に併用可能な溶媒としては、たとえば１，２−ジメトキシエタン（ＤＭＥ）、１，３−ジオキソラン（ＤＯ）、テトラヒドロフラン（ＴＨＦ）、２−メチル−テトラヒドロフラン（２Ｍｅ−ＴＨＦ）、ジエチルエーテル（ＤＥＥ）などが挙げられる。そのほか、アミンイミド系有機溶媒や、含イオウまたは含フッ素系有機溶媒なども用いることができる。
【００２９】
電解液の電解質としては、たとえばＬｉＣｌＯ₄、ＬｉＰＦ₆、ＬｉＢＦ₄、ＬｉＡｓＦ₆、ＬｉＳｂＦ₆、ＬｉＣＦ₃ＳＯ₃、ＬｉＣ₄Ｆ₉ＳＯ₃、ＬｉＣＦ₃ＣＯ₂、Ｌｉ₂Ｃ₂Ｆ₄（ＳＯ₃）₂、ＬｉＮ（ＣＦ₃ＳＯ₂）₂、ＬｉＣ（ＣＦ₃ＳＯ₂）₃、ＬｉＣ_nＦ_2n+1ＳＯ₃（ｎ≧２）、ＬｉＮ（Ｒｆ₃ＯＳＯ₂）₂（ここで、Ｒｆはフルオロアルキル基）などが単独でまたは２種以上混合して用いられるが、特にＬｉＰＦ₆やＬｉＣ₄Ｆ₉ＳＯ₃などが充放電特性が良好なことから好ましい。電解液中における電解質の濃度は、特に限定されるものではないが、濃度を１ｍｏｌ／ｌ以上にすると安全性が向上するので好ましく、１．２ｍｏｌ／ｌ以上がさらに好ましい。また、電解液中における電解質の濃度が１．７ｍｏｌ／ｌ以下であると良好な電気特性が保たれるので好ましく、１．５ｍｏｌ／ｌ以下であることがさらに好ましい。
【００３０】
本発明は、電池の形状のいかんにかわらず適用でき、どのような形状の電池にも適用可能であるが、特に円筒形、楕円筒形、角筒形などの筒形電池に適用するのが適している。そして、巻回構造の電極体を上記のような円筒形電池や楕円筒形電池に適するように円筒状や楕円筒状にしたときに、前記のように、その巻回外径の最小値を放電状態において電池缶の内径より０．４〜０．７ｍｍ小さくする。すなわち、巻回構造の電極体の巻回外径の最小値を放電状態において電池缶の内径より０．４ｍｍ以上小さくすることによって、電池の容量が高くなっても釘刺し試験での安全性が確保でき、また、巻回構造の電極体の巻回外径の最小値を放電状態において電池缶の内径より０．７ｍｍ以下で小さくすることによって、電池の容量が大きく減少するのを防止することができる。
【００３１】
【実施例】
つぎに、実施例をあげて本発明をより具体的に説明する。ただし、本発明はそれらの実施例のみに限定されるものではない。
【００３２】
実施例１
メチルエチルカーボネートとエチレンカーボネートとを体積比３：１で混合し、この混合溶媒に対してＬｉＰＦ₆を１．０ｍｏｌ／ｌ溶解させて、組成が１．０ｍｏｌ／ｌＬｉＰＦ₆／ＥＣ：ＭＥＣ（１：３体積比）で示される電解液を調製した。上記電解液におけるＥＣはエチレンカーボネートの略称であり、ＭＥＣはメチルエチルカーボネートの略称である。従って、上記電解液を示す１．０ｍｏｌ／ｌＬｉＰＦ₆／ＥＣ：ＭＥＣ（１：３体積比）は、体積比でメチルエチルカーボネート３に対してエチレンカーボネート１の割合の混合溶媒にＬｉＦＰ₆を１．０ｍｏｌ／ｌ相当溶解させたものであることを示している。
【００３３】
これとは別に、正極活物質としてのＬｉＮｉＯ₂に対して導電助剤として燐片状黒鉛を重量比１００：７で加えて混合し、この混合物と、ポリフッ化ビニリデンをＮ−メチルピロリドンに溶解させた溶液とを混合してスラリー状の塗材にした。この正極活物質含有塗材を７０メッシュの網を通過させて大きなものを取り除いた後、厚さ２０μｍのアルミニウム箔からなる正極集電体の両面に均一に塗付し、加熱して乾燥した。ただし、これより作られる正極を負極やセパレータなどと共に巻回構造の電極体にした時に、正極の最外周部となる部分には上記活物質含有塗材の塗布を行わず、無地部、つまり、正極集電体のみの部分を５０ｍｍとした。このシート状の電極体を圧縮成形した後、切断し、幅３ｍｍのリード体を溶接して、シート状の正極を作製した。
【００３４】
つぎに、黒鉛系炭素材料（ただし、００２面の層間距離ｄ₀₀₂＝３．３７Å、ｃ軸方向の結晶子の大きさＬｃ＝９５０Å、平均粒径１０μｍ、純度９９．９％という特性を持つ炭素材料）を、ポリフッ化ビニリデンをＮ−メチルピロリドンに溶解させた溶液と混合してスラリー状の塗材にし、その負極活物質含有塗材を厚さ１０μｍの帯状の銅箔からなる負極集電体の両面に均一に塗付して乾燥した。ただし、これより作られる負極を前記正極やセパレータなどと共に巻回構造の電極体にした時に、負極の最外周部となる部分には上記負極活物質含有塗材の塗布を行わず、無地部、つまり、負極集電体のみの部分を５０ｍｍとした。このシート状の電極体を圧縮成形後、切断した後、幅３ｍｍのリード体を溶接して、シート状の負極を作製した。
【００３５】
上記シート状の正極を厚さ２５μｍの微孔性ポリエチレンフィルムからなるセパレータを介して上記シート状の負極に積み重ねて、電極板積層体にし、これを負極が正極より外周側になるようにしつつ渦巻状に巻回して渦巻状の巻回構造の電極体とした。ただし、上記巻回構造の電極体における最外周部分にはセパレータを配置しなかった。従って、この巻回構造の電極体の最外周部は負極集電体の銅箔で構成されている。この巻回構造の電極体を外径１８ｍｍの有底円筒状の電池缶内に充填し、正極および負極のリード体の溶接を行った。つぎに電解液を電池ケース内に注入し、電解液がセパレータなどに充分に浸透した後、封口し、予備充電、エイジングを行い、図１に概略構造を示す筒形の有機電解液二次電池を作製した。また、その電池の巻回構造の電極体の最外周部およびその近傍の詳細を図２に示した。
【００３６】
なお、この電池の負極の充放電容量は、この電池の通常充電条件（１６００ｍＡで充電し４．２Ｖに達した後は４．２Ｖの定電圧で充電する操作を２時間３０分行う）では、９６ｍＡｈ／ｃｍ³であった。また、この電池を２．７５Ｖまで１６００ｍＡで放電した後、分解し、巻回構造の電極体の巻回外径を調べたところ最小値が１６．４ｍｍであり、その最小値部分と電池缶の内径との差は０．５ｍｍであった。
【００３７】
ここで、この電池の概略構造を図１に基づいて説明すると、１は前記のシート状の正極で、２はシート状の負極である。ただし、図１では、繁雑化を避けるため、正極１や負極２の作製にあたって使用した集電体としての金属箔などは図示していない。そして、これらの正極１と負極２はセパレータ３を介して渦巻状に巻回され、渦巻状の巻回構造の電極体として上記の電解液４と共に電池缶５内に収容されている。
【００３８】
電池缶５はステンレス鋼製で、負極端子を兼ねており、電池缶５の底部には上記渦巻状の巻回構造の電極体の挿入に先立って、ポリプロピレンからなる絶縁体６が配置されている。封口板７はアルミニウム製で、円板状をしていて、中央部に薄肉部７ａを厚み方向の両端面より内部側に設け、かつ上記薄肉部７ａの周囲に電池内圧を防爆弁９に作用させるための圧力導入口７ｂとしての孔が設けられている。そして、この薄肉部７ａの上面に防爆弁９の突出部９ａが溶接され、溶接部分１１を構成している。なお、上記の封口板７に設けた薄肉部７ａや防爆弁９の突出部９ａなどは、図面上での理解がしやすいように、切断面のみを図示しており、切断面後方の輪郭線は図示を省略している。また、封口板７の薄肉部７ａと防爆弁９の突出部９ａとの溶接部分１１も、図面上での理解が容易なように、実際よりは誇張した状態に図示している。
【００３９】
端子板８は、圧延鋼製で表面にニッケルメッキが施され、周縁部が鍔状になった帽子状をしており、この端子板８にはガス排出孔８ａが設けられている。防爆弁９は、アルミニウム製で、円板状をしており、その中央部には発電要素側（図１では、下側）に先端部を有する突出部９ａが設けられ、その突出部９ａの下面が、前記したように、封口板７の薄肉部７ａの上面に溶接され、溶接部分１１を構成している。絶縁パッキング１０は、ポリプロピレン製で、環状をしており、封口板７の周縁部の上部に配置され、その上部に防爆弁９が配置していて、封口板７と防爆弁９とを絶縁するとともに、両者の間から電解液が漏れないように両者の間隙を封止している。環状ガスケット１２はポリプロピレン製で、リード体１３はアルミニウム製で、前記封口板７と正極１とを接続し、渦巻状電極体の上部には絶縁体１４が配置され、負極２と電池缶５の底部とはニッケル製のリード体１５で接続されている。
【００４０】
前記のように、電池缶５の底部には絶縁体６が配置され、前記正極１、負極２およびセパレータ３からなる渦巻状の巻回構造の電極体や、電解液４、電極体上部の絶縁体１４などは、この電池缶５内に収容され、それらの収容後、電池缶５の開口端近傍部分に底部が内方に突出した環状の溝が形成される。そして、上記電池缶５の開口部に、封口板７、絶縁パッキング１０、防爆弁９が挿入された環状ガスケット１２を入れ、さらにその上から端子板８を挿入し、電池缶５の溝から先の部分を内方に締め付けることによって、電池缶５の開口部が封口されている。ただし、上記のような電池組立にあたっては、あらかじめ負極２と電池缶５とをリード体１５で接続し、正極１と封口板７とをリード体１３で接続しておくことが好ましい。
【００４１】
上記のようにして組み立てられた電池においては、封口板７の薄肉部７ａと防爆弁９の突出部９ａとが溶接部分１１で接触し、防爆弁９の周縁部と端子板８の周縁部とが接触し、正極１と封口板７とは正極側のリード体１３で接続されているので、正極１と端子板８とはリード体１３、封口板７、防爆弁９およびそれらの溶接部分１１によって電気的接続が得られ、電路として正常に機能する。
【００４２】
そして、電池に異常事態が起こり、電池内部にガスが発生して電池の内圧が上昇した場合には、その内圧上昇により、防爆弁９の中央部が内圧方向（図１では、上側の方向）に変形し、それに伴って溶接部分１１で一体化されている薄肉部７ａに剪断力が働いて、該薄肉部７ａが破断するか、または防爆弁９の突出部９ａと封口板７の薄肉部７ａとの溶接部分１１が剥離し、それによって、正極１と端子板８との電気的接続が消失して、電流が遮断できるように設計されている。
【００４３】
なお、上記防爆弁９には薄肉部９ｂが設けられており、たとえば、充電が極度に進行して電解液や活物質などの発電要素が分解し、大量のガスが発生した場合は、防爆弁９が変形して、防爆弁９の突出部９ａと封口板７の薄肉部７ａとの溶接部分１１が剥離した後、この防爆弁９に設けた薄肉部９ｂが開裂してガスを端子板８のガス排出孔８ａから電池外部に排出させて電池の破裂を防止することができるように設計されている。
【００４４】
つぎに、上記電池の巻回構造の電極体の最外周部およびその近傍（すなわち、図１のＡの近傍に相当する部分）を図２に基づいて説明すると、正極１はアルミニウム箔からなる正極集電体１ａの両面に活物質含有塗膜１ｂを形成することによって作製されているが、その最外周部では活物質含有塗膜１ｂを形成せず正極集電体１ａのみの部分が設けられている。また、負極２は銅箔からなる負極集電体２ａの両面に活物質含有塗膜２ｂを形成することによって作製されているが、その最外周部では活物質含有塗膜２ｂを形成せず負極集電体２ａのみの部分が設けられている。
【００４５】
セパレータ３は正極１と負極２との間およびそれら正極１と負極２の最外周部における正極集電体２ａと負極集電体２ｂとの間に配置しているが、巻回構造の電極体の最外周部には配置しておらず、負極集電体２ａが直接電池缶５の内壁に接触している。なお、前記のように、放電状態においては、巻回構造の電極体の巻回外径の最小値と電池缶の内径との間には０．５ｍｍの差があるが、充電時には電極が膨張することと、渦巻状の巻回構造の電極体では真正な円形ではないこともあって、電極体の最外周部の負極集電体２ａは電池缶５の内壁に直接接触している。
【００４６】
この実施例１の電池における正極１の最外周部の活物質含有塗膜１ｂを形成せず正極集電体１ａのみの部分は巻回構造の電極体の外周部において約１周に相当し、また負極２の最外周部の活物質含有塗膜２ｂを形成せず負極集電体２ａのみの部分は巻回構造の電極体の外周部において約１周に相当する。
【００４７】
実施例２
正極１の最外周部における活物質含有塗膜１ｂを形成しない部分を正極集電体１ａの外面側にし、その内面側には活物質含有塗膜１ｂを形成した以外は、実施例１と同様にして筒形の有機電解液二次電池を作製した。
【００４８】
この実施例２の電池の巻回構造の電極体の最外周部およびその近傍を図３に基づいて説明すると、正極１の最外周部においては外面側のみが活物質含有塗膜１ｂを形成せず正極集電体１ａのみになっていて、その内面側には活物質含有塗膜１ｂが形成されている。そして、それ以外は図２に示す場合と同様に構成されている。
【００４９】
この実施例２の電池を２．７５Ｖまで１６００ｍＡで放電した後、分解し、その巻回構造の電極体の巻回外径を調べたところ最小値が１６．４ｍｍであり、その最小値部分と電池缶５の内径との差は０．５ｍｍであった。
【００５０】
実施例３
巻回構造の電極体の最外周部にセパレータ３が配置するようにした以外は、実施例１と同様にして筒形の有機電解液二次電池を作製した。
【００５１】
この実施例３の電池缶の巻回構造の電極体の最外周部およびその近傍を図４に基づいて説明すると、巻回構造の電極体の最外周部にセパレータ３が配置していて、負極集電体２ａと電池缶５の内壁との間にセパレータ３が介在している。そして、それ以外は図２に示す場合と同様に構成されている。
【００５２】
実施例４
実施例３と同様の構成であるが、その正極１の活物質含有塗膜１ｂの形成部分を２０ｍｍ短くし、かつ負極２の活物質含有塗膜２ｂの形成部分を２０ｍｍ短くした以外は、実施例３と同様にして筒形の有機電解液二次電池を作製した。
【００５３】
この実施例４の電池を２．７５Ｖまで１６００ｍＡで放電した後、分解し、巻回構造の電極体の巻回外径を調べたところ最小値が１６．２ｍｍであり、その最小値部分と電池缶５の内径との差は０．７ｍｍであった。
【００５４】
比較例１
活物質含有塗膜１ｂを形成しない部分を２ｍｍ残して正極集電体１ａに活物質含有塗膜１ｂを形成し、また、負極２側のリード体１５を取り付けるために負極２の最外周部に活物質含有塗膜２ｂを形成しない部分を５ｍｍ残して負極集電体２ａに活物質含有塗膜２ｂを形成し、かつ巻回構造の電極体の最外周部にもセパレータ３が配置するようにした以外は、実施例１と同様にして筒形の有機電解液二次電池を作製した。
【００５５】
この比較例１の電池の巻回構造の電極体の最外周部およびその近傍を図５に基づいて説明すると、正極１の最外周部も上記のように活物質含有塗膜１ｂが形成され、負極２の最外周部もリード体１５との接触部となる部分を除き活物質含有塗膜２ｂが形成され、かつセパレータ３が巻回構造の電極体の最外周部に配置していて、電池缶５と負極２の最外周部との間にセパレータ３が介在している。
【００５６】
この比較例１の電池を２．７５Ｖまで１６００ｍＡで放電した後、分解し、巻回構造の電極体の巻回外径を調べたところ最小値が１６．４ｍｍであり、その最小値部分と電池缶５の内径との差は０．５ｍｍであった。
【００５７】
比較例２
比較例１と同様の構成であるが、その正極１の活物質含有塗膜１ｂの形成部分を２０ｍｍ短くし、かつ負極２の活物質含有塗膜２ｂの形成部分を２０ｍｍ短くした以外は、比較例１と同様にして筒形の有機電解液二次電池を作製した。
【００５８】
この比較例２の電池を２．７５Ｖまで１６００ｍＡで放電した後、分解し、巻回構造の電極体の巻回外径を調べたところ最小値が１６．２ｍｍであり、その最小値部分と電池缶５の内径との差は０．７ｍｍであった。
【００５９】
上記実施例１〜４および比較例１〜２の電池を、１６００ｍＡで２．７５Ｖまで放電した後１６００ｍＡで充電し、４．４Ｖに達した後は４．４Ｖの定電圧に保つ条件で２時間３０分充電を行った。その後、電池を４５℃の恒温槽に入れて２時間後に取り出し、電池ホルダの上に置き、１／２釘刺し試験を行った。すなわち、直径３ｍｍのステンレス鋼製釘を電池の側面から電池の直径の１／２のところまで突き刺し、各電池２０個中で異常発熱する電池の数を調べた。その結果を表１に示す。表１中において結果を示す数値の分母は試験に供した電池個数であり、分子は異常発熱した電池個数である。なお、上記の異常発熱とは電池表面温度が１５０℃以上になった場合をいう。
【００６０】
【表１】

【００６１】
表１に示すように、実施例１〜４は、比較例１〜２に比べて、異常発熱する電池個数がはるかに少なく、高い安全性を有していた。すなわち、上記のような４５℃で２時間放置し、１／２釘刺しを行うという苛酷な条件下の釘刺し試験では、異常発熱する電池個数が１／５以下（上記のように２０個試験した場合は異常発熱する電池個数が４個以下）であれば、充分に高い安全性を有していると判断されるが、実施例１〜４は、いずれも、異常発熱する電池個数がそれ以下であり、充分に高い安全性を有していた。
【００６２】
上記実施例では、円筒形の有機電解液二次電池について安全性を調べたが、角筒形の有機電解液二次電池など、円筒形以外の形状の電池についても、本発明によれば、上記円筒形の有機電解液二次電池と同様の高い安全性を得ることができる。
【００６３】
【発明の効果】
以上説明したように、本発明では、高容量化を図った場合においても、安全性の高い有機電解液二次電池を提供することができた。
【図面の簡単な説明】
【図１】本発明に係る有機電解液二次電池の一例を概略的に示す断面図である。
【図２】実施例１の電池の巻回構造の電極体の最外周部およびその近傍を拡大して示す断面図である。
【図３】実施例２の電池の巻回構造の電極体の最外周部およびその近傍を拡大して示す断面図である。
【図４】実施例３の電池の巻回構造の電極体の最外周部およびその近傍を拡大して示す断面図である。
【図５】比較例１の電池の巻回構造の電極体の最外周部およびその近傍を拡大して示す断面図である。
【符号の説明】
１正極
１ａ正極集電体
１ｂ活物質含有塗膜
２負極
２ａ負極集電体
２ｂ活物質含有塗膜
３セパレータ
４電解液
５電池缶[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an organic electrolyte secondary battery, and more particularly to an organic electrolyte secondary battery having a specific structure for ensuring safety.
[0002]
[Prior art]
The organic electrolyte secondary battery is a secondary battery using an organic solvent as a solvent for the electrolyte, and this organic electrolyte secondary battery has a large capacity, high voltage, high energy density, and high output. Demand is increasing.
[0003]
As a solvent for the organic electrolyte solution of this battery (hereinafter simply referred to as “electrolyte” except when representing the battery), cyclic esters such as ethylene carbonate and esters such as dimethyl carbonate and methyl propionate have been used so far. A mixture of these has been used.
[0004]
However, according to the study by the present inventors, this organic electrolyte secondary battery does not further devise the structure of the battery when the capacity is further increased or depending on the specifications required by the user. As a result, it has been found that there is a possibility that safety may be lowered. This will be explained in detail. Normally, in this type of battery, measures are taken to prevent an internal short circuit by preventing overcharging by a protection circuit, etc., and the battery is heated by a normal internal short circuit. However, when a nail penetration test was conducted on the assumption of abnormal use, it was found that safety may be lacking. In other words, in the nail penetration test, the battery is reliably short-circuited with fewer parts compared to battery crushing or external short-circuiting, so that the current concentrates at the short-circuited part and more easily generates heat, and the battery partially rises to high temperature. This is likely to cause variations in separator fuses (clogging due to melting), and more heat is generated by the reaction between the electrolyte and the negative electrode at the short-circuit site, so this nail penetration test can occur under normal operating conditions. It is a safety confirmation test that is so severe that a lack of safety can be found. Therefore, if safety can be confirmed by this nail penetration test, it is considered that safety is ensured even when abnormal use is encountered.
[0005]
Further, when the nail penetration test is performed at a high temperature of 45 ° C. rather than at room temperature, the battery is likely to rise to a higher temperature and a thermal runaway reaction of the battery is likely to occur. Further, when the nail is stopped in the middle of the battery as in the case of 1/2 nail penetration, the number of short-circuited portions is reduced and the current is more concentrated and heat is easily generated. Therefore, when this nail penetration test is performed at 45 ° C. and a half nail penetration is performed, it becomes a very severe test as a test for confirming safety, and safety is confirmed by a test under such severe conditions. If possible, it is considered that sufficient safety can be secured by actual use.
[0006]
[Problems to be solved by the invention]
By the way, when a compound capable of removing and inserting lithium, such as carbon, is used as the negative electrode active material, the reactivity with the electrolyte at a high temperature is much lower than when metallic lithium is used, and the safety of the battery is improved. . However, as the energy density of batteries tends to increase in the future due to the recent trend toward higher capacities, it should be possible to show excellent safety even in the nail penetration test, which is a severe safety confirmation test. It has been found that it is necessary to change the internal structure of the battery to a structure that does not easily ignite.
[0007]
Therefore, the present invention improves the structure of the battery so that the safety can be sufficiently confirmed even in the nail penetration test, which is a severe safety confirmation test, in preparation for a future increase in capacity, and an organic electrolysis having excellent safety. An object is to provide a liquid secondary battery.
[0008]
[Means for Solving the Problems]
The present invention relates to a positive electrode in which an active material-containing coating film is formed on at least one surface of a positive electrode current collector made of a metal foil, and an active material-containing coating film on at least one surface of a negative electrode current collector made of a metal foil. A negative electrode formed by forming an electrode body with a wound structure wound through a separator and an organic electrolyte solution in a battery can, and a positive electrode active material, an open circuit voltage during charging is 4 V on a Li basis In the organic electrolyte secondary battery, which is a lithium composite oxide having the above structure, and the chain ester is contained in the organic electrolyte in an amount of more than 50% by volume in the entire electrolyte solvent, the electrode body having the above-described winding structure The active material-containing coating film is not formed on at least the outermost peripheral portion of the positive electrode in FIG. 5, but only the positive electrode current collector is provided, and the active material-containing coating film is formed on at least the outermost peripheral portion of the negative electrode in the electrode body having the winding structure Without providing the part of the negative electrode current collector only, the above part The positive electrode current collector and the negative electrode current collector are disposed via a separator, and the minimum winding outer diameter of the electrode body having the winding structure is 0.4 to 0.7 mm from the inner diameter of the battery can in a discharged state. The problem is solved by reducing the size.
[0009]
Hereinafter, the process that led to the completion of the present invention and the reason why the safety can be improved by using the above configuration will be described in detail.
[0010]
In general, an electrode body having a wound structure of a current organic electrolyte secondary battery includes a sheet-like positive electrode having an active material-containing coating film formed on both surfaces of an aluminum foil serving as a positive electrode current collector, and a copper serving as a negative electrode current collector. A sheet-like negative electrode with active material-containing coating film formed on both sides of the foil and two separators are stacked in the order of negative electrode, separator, positive electrode and separator, and wound in a spiral shape so that the negative electrode is on the outer peripheral side of the positive electrode It is a thing.
[0011]
The present inventors obtained the most popular lithium ion secondary battery as an organic electrolyte secondary battery and conducted a nail penetration test. The risk is low in ordinary commercially available lithium ion secondary batteries. On the other hand, it was found that the risk increases as the energy density of the battery increases. The negative electrode of these batteries usually uses a compound capable of removing and inserting lithium such as a carbon material. However, when the negative electrode is overcharged and lithium is electrodeposited to some extent, the electrolyte and electrodeposition are started from around 100 ° C. An exothermic reaction occurs between lithium and a carbon material into which lithium is inserted.
[0012]
In addition, even at the positive electrode, the reaction start temperature with the electrolytic solution is lowered due to the elimination of lithium, and when the thermal runaway temperature of the positive electrode is reached by the reaction heat of the negative electrode, the battery generates abnormal heat. Since there is an exothermic phenomenon with such a continuous reaction, the chargeable / dischargeable capacity of the negative electrode of the battery under normal use conditions is 96 mAh / cm per unit volume of the battery. ^Three If it exceeds (at full charge), the safety when the battery is overcharged decreases. In other words, the more dischargeable capacity per unit volume of the negative electrode, the more heat is generated per unit volume of the battery when heat is generated during overcharging, and the battery temperature can rise to the thermal runaway temperature of the positive electrode. Increases nature. Therefore, in the present invention, in a battery having a large capacity per unit volume of the negative electrode, even if an exothermic reaction between the negative electrode and the electrolyte occurs, the temperature of the battery does not rise to the thermal runaway reaction of the positive electrode due to the heat generation. The battery structure has been improved so that sufficient safety can be ensured even with a high capacity battery having a large capacity per unit volume of the negative electrode.
[0013]
In the present invention, at least the outermost peripheral portion of the positive electrode in the wound structure electrode body is provided with only the positive electrode current collector without forming the active material-containing coating film, and at least the outermost of the negative electrode in the wound structure electrode body. Improve safety by providing only the negative electrode current collector without forming an active material-containing coating film on the outer periphery, and arranging the positive electrode current collector and the negative electrode current collector in the above part via a separator. The reason why this is possible is not necessarily clear at present, but can be considered as follows.
[0014]
As described above, by using a compound capable of removing and inserting lithium, such as a carbon material, as the negative electrode active material, the reactivity between the electrolyte and the negative electrode at a high temperature is lower than when lithium is used as the negative electrode active material. However, as the capacity of the negative electrode that can be charged and discharged increases, the reactivity with the electrolyte increases, the amount of heat generation increases, and the temperature of the battery easily rises. However, if the active material-containing coating film is not formed on at least the outermost periphery of each of the positive electrode and the negative electrode in the wound electrode body, only the positive electrode current collector and the negative electrode current collector are provided. Heat dissipation is quickened only by the electric body, the positive electrode is less likely to reach the thermal runaway temperature, the battery is less likely to generate abnormal heat, and the safety of the battery is improved.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
As described above, the portion of the positive electrode current collector and the negative electrode current collector provided on the outermost periphery of each of the positive electrode and the negative electrode in the wound electrode body has one or more turns in the wound electrode body. Is preferable, and it is preferable that it is 2 or less. That is, by making the portion of only the positive electrode current collector and the negative electrode current collector as described above one or more rounds, the heat dissipation can be accelerated and the safety of the battery can be sufficiently improved. By making the portion of the electric body only two or less, it is possible to prevent a significant decrease in the energy density of the battery.
[0016]
Also, if the separator at the outermost periphery of the electrode body with a wound structure is eliminated, the negative electrode current collector is in direct contact with the inner wall of the battery can, so that heat dissipation is faster and the effect of improving battery safety is achieved. It is even more pronounced.
[0017]
In the present invention, as the positive electrode active material, LiNiO ₂ LiCoO ₂ , LiMn ₂ O ₄ A lithium composite oxide having an open circuit voltage of 4 V or more on the basis of Li is used.
[0018]
A high energy density can be obtained by using a lithium composite oxide having an open circuit voltage during charging of 4 V or more on the basis of Li as the positive electrode active material. In addition, the charged LiCoO ₂ And LiNiO ₂ The reaction start temperature with the electrolyte is LiMn ₂ O ₄ Since it is easy to reach the thermal runaway temperature of the positive electrode due to the heat generation of the negative electrode, LiCoO as a positive electrode active material ₂ And LiNiO ₂ In particular, the effect of the present invention is remarkably exhibited.
[0019]
For example, the positive electrode is appropriately coated with a solvent by appropriately adding, for example, a conductive aid such as flake graphite or carbon black, or a binder such as polyvinylidene fluoride or polytetrafluoroethylene to the positive electrode active material. The active material-containing coating material is applied to a positive electrode current collector made of a metal foil such as an aluminum foil and dried to form an active material-containing coating film. However, in the present invention, the active material-containing coating film is not formed on at least the outermost peripheral portion of the positive electrode in the wound electrode body as described above, and only the positive electrode current collector is left.
[0020]
In the present invention, the material used for the negative electrode may be any material that can be doped and dedoped with lithium ions. In the present invention, a material that can be doped and dedoped with lithium ions is referred to as a negative electrode active material. The negative electrode active material is not particularly limited. For example, graphite, pyrolytic carbons, cokes, glassy carbons, organic polymer compound fired bodies, mesocarbon microbeads, carbon fibers It is preferable to use carbon materials such as activated carbon, alloys such as Si, Sn, and In, or oxides such as Si, Sn, and In that can be charged and discharged at a low potential close to Li.
[0021]
When a carbon material is used as the negative electrode active material, the carbon material preferably has the following characteristics. That is, the interlayer distance d of the (002) plane ₀₀₂ Is preferably 3.5 mm or less, more preferably 3.45 mm or less, and still more preferably 3.4 mm or less. The crystallite size Lc in the c-axis direction is preferably 30 mm or more, more preferably 80 mm or more, and further preferably 250 mm or more. The average particle size is preferably 8 to 15 μm, particularly preferably 10 to 13 μm, and the purity is preferably 99.9% or more.
[0022]
For example, for the negative electrode, for example, a binder such as polyvinylidene fluoride or polytetrafluoroethylene is appropriately added to the negative electrode active material, and if necessary, a conductive additive is appropriately added, and a coating material is formed with a solvent. The material-containing coating material is applied to a negative electrode current collector made of copper foil or the like, and dried to form an active material-containing coating film. However, in the present invention, as described above, the active material-containing coating film is not formed on the outermost peripheral portion of the negative electrode in the wound electrode body, and only the negative electrode current collector is left.
[0023]
As the metal foil to be the current collector for the positive electrode or the negative electrode, for example, aluminum foil, copper foil, nickel foil, stainless steel foil or the like is used, and the aluminum foil is particularly preferable as the metal foil to be the current collector for the positive electrode. In addition, a copper foil is particularly preferable as the metal foil serving as the negative electrode current collector.
[0024]
In the present invention, the electrolytic solution uses a chain ester as a main solvent. Thereby, the viscosity of electrolyte solution can be lowered | hung and ion conductivity can be raised. Examples of such chain esters include organic solvents having a chain-like COO-bond such as dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, and methyl propionate. The main solvent means that the chain ester exceeds 50% by volume in the total electrolyte solution containing these chain esters. If the chain ester exceeds 65% by volume, the prior art reduces the safety of the battery in the nail penetration test after 4.4V charge, but according to the present invention, such a chain ester is 65% by volume. Even in the case of exceeding, safety can be ensured, and the effects of the present invention are remarkably exhibited.
[0025]
And when chain ester exceeds 70 volume%, since the safety | security of a battery will fall more easily in a prior art, the effect of this invention comes to express more notably, and chain ester is 75 volume%. In the case of exceeding the above, the safety of the battery is more likely to be lowered in the conventional technique, so that the effect of the present invention is more remarkably exhibited. Further, even when the chain ester has a methyl group, the safety of the battery is easily lowered in the conventional technique, and thus the effect of the present invention is more remarkably exhibited.
[0026]
In addition, when the above-mentioned chain ester is mixed with the following ester having a high dielectric constant (dielectric constant of 30 or more), cycle characteristics and battery load characteristics are improved as compared with the case where only the chain ester is used. Is more preferable. Examples of the ester having a high dielectric constant include propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate (BC), gamma-butyrolactone (γ-BL), ethylene glycol sulfite (EGS), and the like. In particular, those having a cyclic structure are preferred, especially cyclic carbonates are preferred, and ethylene carbonate (EC) is most preferred.
[0027]
The ester having a high dielectric constant is preferably less than 40% by volume, more preferably 30% by volume or less, and still more preferably 25% by volume or less in the total solvent of the electrolytic solution. The improvement in safety due to these esters having a high dielectric constant becomes significant when the ester having a high dielectric constant becomes 10% by volume or more in the total solvent of the electrolytic solution, and becomes more significant when it reaches 20% by volume. .
[0028]
Examples of solvents that can be used in combination with esters having a high dielectric constant include 1,2-dimethoxyethane (DME), 1,3-dioxolane (DO), tetrahydrofuran (THF), and 2-methyl-tetrahydrofuran (2Me-THF). , Diethyl ether (DEE) and the like. In addition, amine imide organic solvents, sulfur-containing or fluorine-containing organic solvents, and the like can also be used.
[0029]
As an electrolyte of the electrolytic solution, for example, LiClO _Four , LiPF ₆ , LiBF _Four , LiAsF ₆ , LiSbF ₆ , LiCF _Three SO _Three , LiC _Four F ₉ SO _Three , LiCF _Three CO ₂ , Li ₂ C ₂ F _Four (SO _Three ) ₂ , LiN (CF _Three SO ₂ ) ₂ , LiC (CF _Three SO ₂ ) _Three , LiC _n F _{2n + 1} SO _Three (N ≧ 2), LiN (Rf _Three OSO ₂ ) ₂ (Where Rf is a fluoroalkyl group) or the like may be used alone or in combination of two or more. ₆ And LiC _Four F ₉ SO _Three Are preferable because of good charge / discharge characteristics. The concentration of the electrolyte in the electrolytic solution is not particularly limited, but a concentration of 1 mol / l or more is preferable because safety is improved, and 1.2 mol / l or more is more preferable. In addition, when the concentration of the electrolyte in the electrolytic solution is 1.7 mol / l or less, good electrical characteristics are maintained, and it is more preferable that the concentration is 1.5 mol / l or less.
[0030]
The present invention can be applied regardless of the shape of the battery, and can be applied to batteries of any shape. However, the present invention is particularly applicable to cylindrical batteries such as cylindrical, elliptical, and rectangular cylinders. Is suitable. And when the electrode body of the wound structure is made into a cylindrical shape or an elliptical cylindrical shape so as to be suitable for the cylindrical battery or the elliptical cylindrical battery as described above, the minimum value of the wound outer diameter is set as described above. In the discharged state, it is 0.4 to 0.7 mm smaller than the inner diameter of the battery can. That is, by making the minimum value of the wound outer diameter of the electrode body with a wound structure 0.4 mm or more smaller than the inner diameter of the battery can in the discharged state, safety in the nail penetration test can be achieved even when the battery capacity increases. In addition, it is possible to prevent the battery capacity from greatly decreasing by reducing the minimum value of the wound outer diameter of the electrode body having a wound structure to 0.7 mm or less from the inner diameter of the battery can in the discharged state. Can do.
[0031]
【Example】
Next, the present invention will be described more specifically with reference to examples. However, this invention is not limited only to those Examples.
[0032]
Example 1
Methyl ethyl carbonate and ethylene carbonate are mixed at a volume ratio of 3: 1, and LiPF is added to the mixed solvent. ₆ Is dissolved at 1.0 mol / l, and the composition is 1.0 mol / l LiPF. ₆ An electrolytic solution represented by / EC: MEC (1: 3 volume ratio) was prepared. EC in the electrolytic solution is an abbreviation for ethylene carbonate, and MEC is an abbreviation for methyl ethyl carbonate. Therefore, 1.0 mol / l LiPF indicating the above electrolyte ₆ / EC: MEC (1: 3 volume ratio) is LiFP in a mixed solvent with a ratio of ethylene carbonate 1 to methyl ethyl carbonate 3 by volume ratio. ₆ Is dissolved in an amount equivalent to 1.0 mol / l.
[0033]
Separately, LiNiO as a positive electrode active material ₂ As a conductive aid, flake graphite was added at a weight ratio of 100: 7 and mixed, and this mixture was mixed with a solution in which polyvinylidene fluoride was dissolved in N-methylpyrrolidone to form a slurry-like coating material I made it. This positive electrode active material-containing coating material was passed through a 70-mesh net to remove a large one, and then uniformly applied to both surfaces of a positive electrode current collector made of an aluminum foil having a thickness of 20 μm, and heated and dried. However, when the positive electrode made from this is made into an electrode body with a wound structure together with the negative electrode and the separator, the portion that becomes the outermost peripheral portion of the positive electrode is not coated with the active material-containing coating material, that is, the plain portion, that is, The portion of the positive electrode current collector alone was 50 mm. This sheet-like electrode body was compression-molded and then cut, and a lead body having a width of 3 mm was welded to produce a sheet-like positive electrode.
[0034]
Next, a graphite-based carbon material (however, the interlayer distance d on the 002 plane) ₀₀₂ = 3.37 Å, a crystallite size in the c-axis direction Lc = 950 Å, a carbon material having characteristics of an average particle size of 10 µm and a purity of 99.9%), a solution in which polyvinylidene fluoride is dissolved in N-methylpyrrolidone The negative electrode active material-containing coating material was uniformly applied to both sides of a negative electrode current collector made of a strip-shaped copper foil having a thickness of 10 μm and dried. However, when the negative electrode made from this is made into an electrode body with a winding structure together with the positive electrode and the separator, the negative electrode active material-containing coating material is not applied to the portion that becomes the outermost peripheral portion of the negative electrode, That is, the portion of the negative electrode current collector alone was 50 mm. After this sheet-like electrode body was compression molded and cut, a lead body having a width of 3 mm was welded to produce a sheet-like negative electrode.
[0035]
The sheet-like positive electrode is stacked on the sheet-like negative electrode through a separator made of a microporous polyethylene film having a thickness of 25 μm to form an electrode plate laminate, and this is spirally wound so that the negative electrode is on the outer peripheral side of the positive electrode An electrode body having a spiral winding structure was obtained. However, no separator was disposed on the outermost peripheral portion of the electrode body having the winding structure. Therefore, the outermost peripheral part of the electrode body having the winding structure is constituted by the copper foil of the negative electrode current collector. The wound electrode body was filled into a bottomed cylindrical battery can with an outer diameter of 18 mm, and the positive and negative lead bodies were welded. Next, an electrolytic solution is injected into the battery case, and after the electrolyte has sufficiently penetrated into the separator and the like, sealing is performed, precharging and aging are performed, and a cylindrical organic electrolyte secondary battery having a schematic structure shown in FIG. Was made. Further, FIG. 2 shows details of the outermost peripheral part of the electrode body of the battery winding structure and the vicinity thereof.
[0036]
The charge / discharge capacity of the negative electrode of this battery is the normal charge condition of this battery (the operation of charging at a constant voltage of 4.2 V is performed for 2 hours and 30 minutes after charging at 1600 mA and reaching 4.2 V). 96 mAh / cm ^Three Met. In addition, after discharging this battery to 2.75 V at 1600 mA, the battery was disassembled, and the wound outer diameter of the electrode body having a wound structure was examined. The minimum value was 16.4 mm. The difference from the inner diameter was 0.5 mm.
[0037]
Here, the schematic structure of this battery will be described with reference to FIG. 1. 1 is the above-mentioned sheet-like positive electrode, and 2 is the sheet-like negative electrode. However, in FIG. 1, in order to avoid complication, a metal foil or the like as a current collector used for manufacturing the positive electrode 1 and the negative electrode 2 is not illustrated. The positive electrode 1 and the negative electrode 2 are spirally wound via a separator 3 and are housed in a battery can 5 together with the electrolyte 4 as an electrode body having a spiral winding structure.
[0038]
The battery can 5 is made of stainless steel and also serves as a negative electrode terminal, and an insulator 6 made of polypropylene is disposed at the bottom of the battery can 5 prior to the insertion of the spirally wound electrode body. . The sealing plate 7 is made of aluminum and has a disk shape. A thin portion 7a is provided in the center portion on the inner side from both end faces in the thickness direction, and the internal pressure of the battery acts on the explosion-proof valve 9 around the thin portion 7a. A hole is provided as a pressure introduction port 7b. And the protrusion part 9a of the explosion-proof valve 9 is welded to the upper surface of this thin part 7a, and the welding part 11 is comprised. Note that the thin-walled portion 7a provided on the sealing plate 7 and the protruding portion 9a of the explosion-proof valve 9 are shown only on the cut surface for easy understanding on the drawing, and the contour line behind the cut surface is shown. Is not shown. In addition, the welded portion 11 between the thin-walled portion 7a of the sealing plate 7 and the protruding portion 9a of the explosion-proof valve 9 is also shown in an exaggerated state so as to facilitate understanding on the drawing.
[0039]
The terminal board 8 is made of rolled steel, has a nickel plating on the surface, and has a hat shape with a peripheral edge portion, and the terminal board 8 is provided with a gas discharge hole 8a. The explosion-proof valve 9 is made of aluminum and has a disk shape, and a projection 9a having a tip on the power generation element side (lower side in FIG. 1) is provided at the center of the explosion-proof valve 9. As described above, the lower surface is welded to the upper surface of the thin portion 7 a of the sealing plate 7 to constitute the welded portion 11. The insulating packing 10 is made of polypropylene and has an annular shape. The insulating packing 10 is arranged at the upper part of the peripheral portion of the sealing plate 7, and the explosion-proof valve 9 is arranged at the upper portion thereof, so that the sealing plate 7 and the explosion-proof valve 9 are insulated. At the same time, the gap between the two is sealed so that the electrolyte does not leak from between them. The annular gasket 12 is made of polypropylene, the lead body 13 is made of aluminum, the sealing plate 7 and the positive electrode 1 are connected, an insulator 14 is disposed on the upper part of the spiral electrode body, and the negative electrode 2 and the battery can 5 The bottom is connected by a lead body 15 made of nickel.
[0040]
As described above, the insulator 6 is disposed at the bottom of the battery can 5, and the spirally wound electrode body including the positive electrode 1, the negative electrode 2, and the separator 3, the electrolyte solution 4, and the insulation of the upper part of the electrode body. The body 14 and the like are accommodated in the battery can 5, and after the accommodation, an annular groove having a bottom protruding inward is formed in the vicinity of the opening end of the battery can 5. Then, an annular gasket 12 in which a sealing plate 7, an insulating packing 10, and an explosion-proof valve 9 are inserted is inserted into the opening of the battery can 5, and a terminal plate 8 is further inserted over the annular gasket 12. The opening of the battery can 5 is sealed by tightening the portion inward. However, in assembling the battery as described above, it is preferable that the negative electrode 2 and the battery can 5 are connected in advance by the lead body 15 and the positive electrode 1 and the sealing plate 7 are connected by the lead body 13 in advance.
[0041]
In the battery assembled as described above, the thin portion 7a of the sealing plate 7 and the protruding portion 9a of the explosion-proof valve 9 are in contact with each other at the welded portion 11, and the peripheral portion of the explosion-proof valve 9 and the peripheral portion of the terminal plate 8 are Are in contact with each other, and the positive electrode 1 and the sealing plate 7 are connected by the lead body 13 on the positive electrode side. Therefore, the positive electrode 1 and the terminal plate 8 are connected to the lead body 13, the sealing plate 7, the explosion-proof valve 9, and their welded portions 11. Provides an electrical connection and functions normally as an electrical circuit.
[0042]
When an abnormal situation occurs in the battery and gas is generated inside the battery to increase the internal pressure of the battery, the central portion of the explosion-proof valve 9 is moved in the internal pressure direction (upward direction in FIG. 1) due to the increase in the internal pressure. Accordingly, a shearing force is applied to the thin portion 7a integrated at the welded portion 11 to break the thin portion 7a, or the protruding portion 9a of the explosion-proof valve 9 and the thin portion of the sealing plate 7 It is designed so that the welded part 11 with 7a is peeled off, whereby the electrical connection between the positive electrode 1 and the terminal plate 8 is lost and the current can be interrupted.
[0043]
The explosion-proof valve 9 is provided with a thin-walled portion 9b. For example, when a large amount of gas is generated due to decomposition of a power generation element such as an electrolyte or an active material due to extreme progress of charging, the explosion-proof valve 9 is deformed, and the welded portion 11 between the projecting portion 9a of the explosion-proof valve 9 and the thin-walled portion 7a of the sealing plate 7 is peeled off, and then the thin-walled portion 9b provided on the explosion-proof valve 9 is cleaved to release the gas to the terminal plate 8 The battery is designed to be discharged from the gas discharge hole 8a to the outside of the battery to prevent the battery from bursting.
[0044]
Next, the outermost peripheral part of the electrode body of the battery winding structure and the vicinity thereof (that is, the part corresponding to the vicinity of A in FIG. 1) will be described with reference to FIG. 2. The positive electrode 1 is a positive electrode made of an aluminum foil. The active material-containing coating film 1b is formed on both surfaces of the current collector 1a, but the active material-containing coating film 1b is not formed on the outermost periphery, and only the positive electrode current collector 1a is provided. ing. Moreover, although the negative electrode 2 is produced by forming the active material containing coating film 2b on both surfaces of the negative electrode collector 2a which consists of copper foil, the active material containing coating film 2b is not formed in the outermost periphery part, but a negative electrode Only the current collector 2a is provided.
[0045]
The separator 3 is disposed between the positive electrode 1 and the negative electrode 2 and between the positive electrode current collector 2a and the negative electrode current collector 2b at the outermost periphery of the positive electrode 1 and the negative electrode 2, but the electrode body has a winding structure. The negative electrode current collector 2 a is in direct contact with the inner wall of the battery can 5. As described above, in the discharged state, there is a difference of 0.5 mm between the minimum value of the outer diameter of the wound electrode body and the inner diameter of the battery can, but the electrode expands during charging. The negative electrode current collector 2 a at the outermost periphery of the electrode body is in direct contact with the inner wall of the battery can 5 because the electrode body having a spiral winding structure is not a true circle.
[0046]
In the battery of Example 1, the active material-containing coating film 1b on the outermost peripheral portion of the positive electrode 1 is not formed, and the portion of the positive electrode current collector 1a alone corresponds to about one turn in the outer peripheral portion of the wound electrode body. Moreover, the active material containing coating film 2b of the outermost peripheral part of the negative electrode 2 is not formed, and the part of only the negative electrode current collector 2a corresponds to about one turn in the outer peripheral part of the wound electrode body.
[0047]
Example 2
Except that the portion of the outermost peripheral portion of the positive electrode 1 where the active material-containing coating film 1b is not formed is the outer surface side of the positive electrode current collector 1a, and the active material-containing coating film 1b is formed on the inner surface side. Thus, a cylindrical organic electrolyte secondary battery was produced.
[0048]
The outermost peripheral part of the electrode body of the battery winding structure of Example 2 and the vicinity thereof will be described with reference to FIG. 3. Only the outer surface side of the positive electrode 1 forms the active material-containing coating film 1b. Only the positive electrode current collector 1a is formed, and an active material-containing coating film 1b is formed on the inner surface side thereof. The rest of the configuration is the same as that shown in FIG.
[0049]
The battery of Example 2 was discharged at 1600 mA up to 2.75 V, then disassembled, and the winding outer diameter of the electrode body having the winding structure was examined. As a result, the minimum value was 16.4 mm. The difference from the inner diameter of the battery can 5 was 0.5 mm.
[0050]
Example 3
A cylindrical organic electrolyte secondary battery was produced in the same manner as in Example 1 except that the separator 3 was arranged on the outermost peripheral portion of the wound electrode body.
[0051]
The outermost peripheral portion of the electrode body having the winding structure of the battery can of Example 3 and the vicinity thereof will be described with reference to FIG. 4. The separator 3 is disposed on the outermost peripheral portion of the electrode body having the winding structure, and the negative electrode A separator 3 is interposed between the current collector 2 a and the inner wall of the battery can 5. The rest of the configuration is the same as that shown in FIG.
[0052]
Example 4
Although it is the same structure as Example 3, it implemented except that the formation part of the active material containing coating film 1b of the positive electrode 1 was shortened by 20 mm, and the formation part of the active material containing coating film 2b of the negative electrode 2 was shortened by 20 mm. A cylindrical organic electrolyte secondary battery was produced in the same manner as in Example 3.
[0053]
The battery of this Example 4 was discharged to 1.75 mA up to 2.75 V, then disassembled, and the wound outer diameter of the wound electrode body was examined. The minimum value was 16.2 mm. The difference from the inner diameter of the can 5 was 0.7 mm.
[0054]
Comparative Example 1
The active material-containing coating film 1b is formed on the positive electrode current collector 1a, leaving 2 mm of the portion where the active material-containing coating film 1b is not formed, and the negative electrode 2 has a lead body 15 attached to the outermost peripheral portion of the negative electrode 2 The active material-containing coating film 2b is formed on the negative electrode current collector 2a, leaving 5 mm of the portion where the active material-containing coating film 2b is not formed, and the separator 3 is also disposed on the outermost peripheral portion of the wound electrode body. A cylindrical organic electrolyte secondary battery was produced in the same manner as in Example 1 except that.
[0055]
When the outermost peripheral part of the electrode body of the wound structure of the battery of Comparative Example 1 and the vicinity thereof are described with reference to FIG. 5, the active material-containing coating film 1b is also formed on the outermost peripheral part of the positive electrode 1 as described above. An active material-containing coating film 2b is formed on the outermost peripheral portion of the negative electrode 2 except for a portion that is in contact with the lead body 15, and the separator 3 is disposed on the outermost peripheral portion of the electrode body having a wound structure. A separator 3 is interposed between the can 5 and the outermost periphery of the negative electrode 2.
[0056]
The battery of Comparative Example 1 was discharged to 1.75 mA up to 2.75 V, then disassembled, and the winding outer diameter of the wound electrode body was examined. The minimum value was 16.4 mm. The difference from the inner diameter of the can 5 was 0.5 mm.
[0057]
Comparative Example 2
Although it is the structure similar to the comparative example 1, except that the formation part of the active material containing coating film 1b of the positive electrode 1 was shortened by 20 mm, and the formation part of the active material containing coating film 2b of the negative electrode 2 was shortened by 20 mm, A cylindrical organic electrolyte secondary battery was produced in the same manner as in Example 1.
[0058]
The battery of Comparative Example 2 was discharged at 1600 mA up to 2.75 V, then disassembled, and the winding outer diameter of the wound electrode body was examined. The minimum value was 16.2 mm. The difference from the inner diameter of the can 5 was 0.7 mm.
[0059]
The batteries of Examples 1 to 4 and Comparative Examples 1 and 2 were discharged at 1600 mA to 2.75 V, charged at 1600 mA, and after reaching 4.4 V, maintained at a constant voltage of 4.4 V for 2 hours. Charging was performed for 30 minutes. Then, the battery was put into a 45 degreeC thermostat and taken out after 2 hours, and it put on the battery holder, and the 1/2 nail penetration test was done. That is, a stainless steel nail having a diameter of 3 mm was pierced from the side of the battery to half the diameter of the battery, and the number of batteries that abnormally generated heat in 20 batteries was examined. The results are shown in Table 1. In Table 1, the denominator of the numerical value indicating the result is the number of batteries subjected to the test, and the numerator is the number of batteries that have abnormally heated. In addition, said abnormal heat generation means the case where the battery surface temperature becomes 150 degreeC or more.
[0060]
[Table 1]

[0061]
As shown in Table 1, Examples 1 to 4 had a much lower number of batteries that generated abnormal heat than Comparative Examples 1 and 2, and had high safety. That is, in the nail penetration test under the severe condition of being left at 45 ° C. for 2 hours and performing a half nail penetration as described above, the number of batteries that generate abnormal heat is 1/5 or less (as described above, 20 pieces test If the number of batteries that abnormally generate heat is 4 or less), it is judged that the safety is sufficiently high. However, in all of Examples 1 to 4, the number of batteries that abnormally generate heat is the same. It was as follows and had sufficiently high safety.
[0062]
In the above embodiment, the safety of a cylindrical organic electrolyte secondary battery was investigated, but according to the present invention, a battery having a shape other than a cylindrical shape, such as a rectangular organic electrolyte secondary battery, The same high safety as that of the cylindrical organic electrolyte secondary battery can be obtained.
[0063]
【The invention's effect】
As described above, according to the present invention, a highly safe organic electrolyte secondary battery can be provided even when the capacity is increased.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view schematically showing an example of an organic electrolyte secondary battery according to the present invention.
2 is an enlarged cross-sectional view showing an outermost peripheral portion of the electrode body having a battery winding structure of Example 1 and the vicinity thereof. FIG.
FIG. 3 is an enlarged cross-sectional view showing an outermost peripheral portion of an electrode body having a battery winding structure according to a second embodiment and the vicinity thereof.
4 is an enlarged cross-sectional view showing an outermost peripheral portion of an electrode body having a battery winding structure according to Example 3 and the vicinity thereof. FIG.
5 is an enlarged cross-sectional view showing an outermost peripheral portion and its vicinity of an electrode body having a battery winding structure according to Comparative Example 1. FIG.
[Explanation of symbols]
1 Positive electrode
1a Positive electrode current collector
1b Active material-containing coating film
2 Negative electrode
2a Negative electrode current collector
2b Active material-containing coating film
3 Separator
4 Electrolytic solution
5 Battery can

Claims

A positive electrode formed by forming an active material-containing coating on at least one surface of a positive electrode current collector made of metal foil, and an active material-containing coating formed on at least one surface of a negative electrode current collector made of metal foil a negative electrode comprising an electrode body winding structure by winding via a separator, and an organic electrolyte Ri Na housed in a battery can and the positive electrode active material, the open circuit voltage during charging than 4V based on Li lithium complex is an oxide, an organic electrolyte secondary battery containing chain ester that contains more than 50 vol% in the total electrolyte in a solvent in the organic electrolyte solution, the electrode of the winding structure shown The active material-containing coating film is not formed on at least the outermost peripheral portion of the positive electrode in FIG. 5, but only the positive electrode current collector is provided, and the active material-containing coating film is formed on at least the outermost peripheral portion of the negative electrode in the wound electrode body. Without providing a part for the negative electrode current collector alone, And the minimum winding outer diameter of the electrode body having the winding structure is 0.4 to 0.7 mm smaller than the inner diameter of the battery can in the discharged state. Organic electrolyte secondary battery characterized by.

A positive electrode current collector having a capacity capable of charging / discharging the negative electrode at full charge of 96 mAh / cm ³ or more per unit volume of the battery and not forming the active material-containing coating film and the active material-containing coating film are formed. The organic electrolyte secondary battery according to claim 1, wherein the negative electrode current collector that is not present is present in the wound structure electrode body one or more times.

3. The organic material according to claim 1, wherein the carbon material used as the negative electrode active material has an (002) plane interlayer distance d ₀₀₂ of 3.5 mm or less and a crystallite size in the c-axis direction of 30 mm or more. Electrolyte secondary battery.

The organic electrolyte secondary battery according to any one of claims 1 to 3, wherein the chain ester contained in the organic electrolyte has a methyl group .

5. The organic electrolyte secondary battery according to claim 1, wherein the organic electrolyte contains a cyclic structure ester having a dielectric constant of 30 or more in an amount of less than 40% by volume in the total electrolyte solvent.