JP3580287B2 - Lithium secondary battery and its non-aqueous electrolyte - Google Patents
Lithium secondary battery and its non-aqueous electrolyte Download PDFInfo
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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Description
【０００１】
【発明の属する技術分野】
本発明は、電池の過充電防止などの安全性およびサイクル特性、電気容量、保存特性などの電池特性にも優れたリチウム二次電池を提供することができる新規なリチウム二次電池、および、そのリチウム二次電池の安全性を確保する方法、更には、安全性の高いリチウム二次電池用電解液に関する。
【０００２】
【従来の技術】
近年、リチウム二次電池は小型電子機器などの駆動用電源として広く使用されている。また、小型ビデオカメラ、携帯電話、ノート型パソコンなどの携帯用電子・通信機器のみならず、自動車用の電源としての期待も大きい。このリチウム二次電池は、主に正極、非水電解液および負極から構成されており、特に、ＬｉＣｏＯ２などのリチウム複合酸化物を正極とし、炭素材料又はリチウム金属を負極としたリチウム二次電池が好適に使用されている。そして、そのリチウム二次電池用電解液の非水溶媒としては、エチレンカーボネート（ＥＣ）、プロピレンカーボネート（ＰＣ）などのカーボネート類が好適に使用されている。
【０００３】
このようなリチウム二次電池は、通常の作用電圧を上回るような過充電時に、正極からは過剰なリチウムが放出されると同時に、負極では過剰なリチウムの析出が生じて、デンドライトが生じる。そのため、正・負極の両極が化学的に不安定化する。正・負極の両極が化学的に不安定になると、やがては非水電解液中のカーボネート類と作用して分解し、急激な発熱反応が起こる。これによって、電池が異常に発熱し、電池の安全性が損なわれるという問題を生じる。このような状況は、リチウム二次電池のエネルギー密度が増加するほど重要な問題となる。
【０００４】
このような問題を解決するため、電解液中に添加剤として少量の芳香族化合物を添加することによって、過充電に対して安全性を確保できるようにしたものが、例えば、特開平７−３０２６１４号公報において提案された。この特開平７−３０２６１４号公報では、電解液の添加剤として、分子量５００以下で満充電時の正極電位よりも貴な電位に可逆性酸化還元電位を有するようなπ電子軌道を持つアニソール誘導体などを使用している。また、特開２０００−１５６２４３号公報では、ビフェニルや４，４’−ジメチルビフェニルなどを使用している。このようなアニソール誘導体やビフェニル誘導体は、電池内でレドックスシャトルすることにより、過充電に対して電池の安全性を確保している。
【０００５】
また、特開平９−１０６８３５号公報では、負極に炭素材料を用い、電解液の添加剤として、ビフェニル、３−Ｒ−チオフェン、３−クロロチオフェン、フランを約１〜４％使用して、電池の最大作動電圧を超える電圧でビフェニルなどが重合することによって、電池の内部抵抗を大きくして、過充電に対して電池の安全性を確保する方法が提案されている。また、特開平９−１７１８４０号公報では、同様に、ビフェニル、３−Ｒ−チオフェン、３−クロロチオフェン、フランを使用して、電池の最大作動電圧を超える電圧でビフェニルなどが重合することによって気体を発生させ、内部電気切断装置を作動させることにより内部短絡を生じさせて、過充電に対して電池の安全性を確保する方法が提案されている。また、特開平１０−３２１２５８号公報では、同様に、ビフェニル、３−Ｒ−チオフェン、３−クロロチオフェン、フランを使用して、電池の最大作動電圧を超える電圧でビフェニルなどが重合することによって、導電性ポリマーを発生させることにより、内部短絡を生じさせて過充電に対して電池の安全性を確保する方法が提案されている。
【０００６】
しかしながら、特開平１１−１６２５１２号公報では、ビフェニルなどを添加した電池において、４．１Ｖを越える電圧上限までサイクルが繰り返されたり、４０℃以上の高温で長期間暴露される充放電状態では、サイクル特性などの電池特性を悪化させる傾向があり、添加量の増大に伴って、その傾向は顕著になるという問題点があることが記載されている。そこで、２，２−ジフェニルプロパンなどを添加する電解液が提案され、電池の最大作動電圧を超える電圧で２，２−ジフェニルプロパンなどが重合することによって、気体を発生させて内部電気切断装置を作動させたり、導電性ポリマーを発生させることにより、内部短絡を生じさせて、過充電に対して電池の安全性を確保する方法が提案されている。
【０００７】
【発明が解決しようとする課題】
しかしながら、特開平７−３０２６１４号公報や特開２０００−１５６２４３号公報に提案されたアニソール誘導体やビフェニル誘導体は、レドックスシャトルにより過充電に対して有効に作用するのに対して、サイクル特性や保存特性に悪影響を及ぼすという問題を生じた。提案されているアニソール誘導体やビフェニル誘導体は、４０℃以上の高温や通常作動電圧で使用している場合に、局部的に少し高い電圧にさらされると充放電と共に徐々にアニソール誘導体やビフェニル誘導体が分解し、本来の電池特性が低下するという問題がある。したがって、通常の充放電と共に徐々にアニソール誘導体やビフェニル誘導体が分解して少なくなってしまうために、３００サイクル後に過充電試験を行うと、安全を十分確保できないこともある。
【０００８】
また、特開平９−１０６８３５号公報、特開平９−１７１８４０号公報、特開平１０−３２１２５８号公報に提案されたビフェニル、３−Ｒ−チオフェン、３−クロロチオフェン、フランも同様に、過充電に対しては有効に作用するのに対して、前記の特開平１１−１６２５１２号公報で指摘されているように、サイクル特性や保存特性に悪影響を及ぼし、ビフェニル添加量と共に顕著になるという問題を生じた。これは、ビフェニルなどが４．５Ｖ以下の電位で酸化分解されるために、４０℃以上の高温や通常作動電圧で使用している場合にも局部的に少し高い電圧にさらされると、徐々にビフェニルなどが分解して少なくなってしまうためにサイクル寿命が低下してしまう。更には、充放電と共に徐々にビフェニルなどが分解して少なくなってしまうために、３００サイクル後に過充電試験を行うと、安全を十分確保できないこともある。
【０００９】
更には、特開平１１−１６２５１２号公報に提案された２，２−ジフェニルプロパンを添加した電池は、ビフェニルを添加した電池ほど過充電に対する安全性は良くないものの、何も添加しない電池よりも過充電に対する安全性は良い。また、２，２−ジフェニルプロパンを添加した電池は、ビフェニルを添加した電池より優れたサイクル特性が得られるものの、何も添加しない電池よりもサイクル特性は悪いことが記載されている。よって、ビフェニルを添加した電池よりも良好なサイクル特性を得るためには、安全性の一部を犠牲にすることが許容できることが述べられている。このため、過充電防止などの安全性およびサイクル特性、電気容量、保存特性などの電池特性は必ずしも満足なものではないのが現状である。
【００１０】
本発明は、前記のようなリチウム二次電池用電解液に関する課題を解決し、電池の過充電防止などの安全性およびサイクル特性、電気容量などの電池特性にも優れたリチウム二次電池を構成することができるリチウム二次電池用の非水電解液、およびそれを用いたリチウム二次電池を提供することを目的とする。
【００１１】
【課題を解決するための手段】
本発明は、コバルトまたはニッケルを含有するリチウムとの複合酸化物からなる正極、リチウム金属、リチウム合金またはリチウムを吸蔵、放出可能な材料からなる負極、および非水溶媒に電解質が溶解されている非水電解液からなるリチウム二次電池において、該非水電解液中に０．１重量％〜１０重量％のｔｅｒｔ−アルキルベンゼン誘導体および０．１重量％〜１．５重量％のビフェニル誘導体を含有することを特徴するリチウム二次電池に関する。
【００１２】
また、本発明は、コバルトまたはニッケルを含有するリチウムとの複合酸化物からなる正極、リチウム金属、リチウム合金またはリチウムを吸蔵、放出可能な材料からなる負極、および非水溶媒に電解質が溶解されている非水電解液からなるリチウム二次電池用電解液において、該非水電解液中に０．１重量％〜１０重量％のｔｅｒｔ−アルキルベンゼン誘導体および０．１重量％〜１．５重量％のビフェニル誘導体を含有することを特徴するリチウム二次電池用電解液に関する。
【００１３】
従来の過充電防止の機構としては、４．５Ｖ付近の電位でレドックスシャトルする方法、４．５Ｖ以下の電位で重合することによって、電池の内部抵抗を大きくする方法、気体を発生させて内部電気切断装置を作動させることにより内部短絡を生じさせたり、導電性ポリマーを発生させることにより内部短絡を生じさせて、過充電に対する電池の安全性を確保する方法が知られている。
【００１４】
一方、本発明の過充電防止の機構は、非水電解液中に含有される前記ｔｅｒｔ−アルキルベンゼン誘導体が、リチウムに対して＋４．６Ｖ〜＋５．０Ｖの電位で酸化分解することにより、過充電時に正極中のコバルトまたはニッケルの溶出が促進され、そのコバルトまたはニッケルが負極上に析出することによって、負極上に析出したリチウム金属と非水電解液中のカーボネートとの反応を未然に抑制するものと考えられる。また、本発明において、場合によっては、電池内部でコバルトまたはニッケルが負極に析出することにより内部短絡を起こし、過充電防止効果を発現するものと考えられる。その結果、電池の安全性が十分確保されるものと推定される。さらに、本発明において、ｔｅｒｔ−アルキルベンゼン誘導体と共に、ビフェニル誘導体を０．１重量％〜１．５重量％と少量添加することによって、前記ｔｅｒｔ−アルキルベンゼン誘導体の過充電防止作用を助長し、かつ、従来低下することが知られていた電池特性を向上させるという予期しない効果が発現される。
【００１５】
さらに、非水電解液中に含有される前記ｔｅｒｔ−アルキルベンゼン誘導体は、リチウムに対する酸化電位が＋４．６Ｖ〜＋５．０Ｖと高いために、４０℃以上の高温や通常作動電圧で充放電を繰り返しても、電圧が局部的に４．２Ｖを越えて、前記ｔｅｒｔ−アルキルベンゼン誘導体が分解することがない。また、０．１重量％〜１．５重量％と少量のビフェニル誘導体のみでは、過充電防止効果は発現しないものの、ビフェニル誘導体の分解がわずかであるために、ｔｅｒｔ−アルキルベンゼン誘導体と併用することにより、逆に電池特性が向上することを見出した。更には、３００サイクル後に過充電試験を行うと、前記ｔｅｒｔ−アルキルベンゼン誘導体の過充電防止作用により、安全を十分確保できる。これにより、電池の過充電防止などの安全性に優れているだけではなく、サイクル特性、電気容量、保存特性などの電池特性にも優れたリチウム二次電池を提供することができるものと考えられる。
【００１６】
【発明の実施の形態】
非水溶媒に電解質が溶解されている電解液に含有されるｔｅｒｔ−アルキルベンゼン誘導体としては、以下のような化合物が挙げられる。
例えば、ｔｅｒｔ−ブチルベンゼン、１−フルオロ−４−ｔｅｒｔ−ブチルベンゼン、１−クロロ−４−ｔｅｒｔ−ブチルベンゼン、１−ブロモ−４−ｔｅｒｔ−ブチルベンゼン、１−ヨード−４−ｔｅｒｔ−ブチルベンゼン、５−ｔｅｒｔ−ブチル−ｍ−キシレン、４−ｔｅｒｔ−ブチルトルエン、３，５−ジ−ｔｅｒｔ−ブチルトルエン、１，３−ジ−ｔｅｒｔ−ブチルベンゼン、１，４−ジ−ｔｅｒｔ−ブチルベンゼン、１，３，５−トリ−ｔｅｒｔ−ブチルベンゼン、ｔｅｒｔ−ペンチルベンゼン、（１−エチル−１−メチルプロピル）ベンゼン、（１，１−ジエチルプロピル）ベンゼン、（１，１−ジメチルブチル）ベンゼン、（１−エチル−１−メチルブチル）ベンゼン、（１−エチル−１−エチルブチル）ベンゼン、（１，１，２−トリメチルプロピル）ベンゼン、１−フルオロ−４−ｔｅｒｔ−ペンチルベンゼン、１−クロロ−４−ｔｅｒｔ−ペンチルベンゼン、１−ブロモ−４−ｔｅｒｔ−ペンチルベンゼン、１−ヨード−４−ｔｅｒｔ−ペンチルベンゼン、５−ｔｅｒｔ−ペンチル−ｍ−キシレン、１−メチル−４−ｔｅｒｔ−ペンチルベンゼン、３，５−ジ−ｔｅｒｔ−ペンチルトルエン、１，３−ジ−ｔｅｒｔ−ペンチルベンゼン、１，４−ジ−ｔｅｒｔ−ペンチルベンゼン、１，３，５−トリ−ｔｅｒｔ−ペンチルベンゼンなどのｔｅｒｔ−アルキルベンゼン誘導体の少なくとも一種以上であることが好ましい。
また、前記ビフェニル誘導体として、ビフェニル、ｏ−テルフェニル、ｍ−テルフェニル、ｐ−テルフェニル、４−メチルビフェニル、４−エチルビフェニル、４−ｔｅｒｔ−ブチルビフェニルなどを使用することができ、特に酸化電位が４．８〜５．０Ｖと高い前記ｔｅｒｔ−ブチルベンゼン等の一部を酸化電位が４．５Ｖと低いｏ−テルフェニルに代えることにより、過充電防止効果を向上させることができる。なお、例えばｔｅｒｔ−ブチルベンゼンの一部をｏ−テルフェニルに代える場合、ｔｅｒｔ−ブチルベンゼンの含有量はｏ−テルフェニルの重量に対して１０倍量以下が好ましく、好ましくは０．３〜５倍量、特に０．５〜３倍量が好ましい。前記したように酸化電位の異なる少なくとも２種類の前記ｔｅｒｔ−アルキルベンゼン誘導体と前記ビフェニル誘導体とを併用することにより、過充電防止効果を高めることができる上に、電池特性を向上させることもできるようになる。
【００１７】
前記ｔｅｒｔ−アルキルベンゼン誘導体の含有量は、過度に多いと、電解液の電導度などが変わり電池性能が低下することがあり、過度に少ないと、十分な過充電効果が得られないので、電解液の重量に対して０．１重量％〜１０重量％、特に１〜５重量％の範囲とするのがよい。
【００１８】
また、前記ビフェニル誘導体の含有量は、過度に多いと、通常使用時に電池内でビフェニル誘導体の分解が起こり、電池性能が低下することがあり、過度に少ないと、十分な過充電効果や電池性能が得られないので、電解液の重量に対して０．１重量％〜１．５重量％、特に０．３重量％〜０．９重量％とするのがよい。
【００１９】
本発明で使用される非水溶媒としては、例えば、エチレンカーボネート（ＥＣ）、プロピレンカーボネート（ＰＣ）、ブチレンカーボネート（ＢＣ）、ビニレンカーボネート（ＶＣ）などの環状カーボネート類や、γ−ブチロラクトンなどのラクトン類、ジメチルカーボネート（ＤＭＣ）、メチルエチルカーボネート（ＭＥＣ）、ジエチルカーボネート（ＤＥＣ）などの鎖状カーボネート類、テトラヒドロフラン、２−メチルテトラヒドロフラン、１，４−ジオキサン、１，２−ジメトキシエタン、１，２−ジエトキシエタン、１，２−ジブトキシエタンなどのエーテル類、アセトニトリルなどのニトリル類、プロピオン酸メチル、ピバリン酸メチル、ピバリン酸オクチルなどのエステル類、ジメチルホルムアミドなどのアミド類が挙げられる。
【００２０】
これらの非水溶媒は、１種類で使用してもよく、また２種類以上を組み合わせて使用してもよい。非水溶媒の組み合わせは特に限定されないが、例えば、環状カーボネート類と鎖状カーボネート類との組み合わせ、環状カーボネート類とラクトン類との組み合わせ、環状カーボネート類３種類と鎖状カーボネート類との組み合わせなど種々の組み合わせが挙げられる。
【００２１】
本発明で使用される電解質としては、例えば、ＬｉＰＦ６、ＬｉＢＦ４、ＬｉＣｌＯ４、ＬｉＮ（ＳＯ２ＣＦ３）２、ＬｉＮ（ＳＯ２Ｃ２Ｆ５）２、ＬｉＣ（ＳＯ２ＣＦ３）３、ＬｉＰＦ４（ＣＦ３）２、ＬｉＰＦ３（Ｃ２Ｆ５）３、ＬｉＰＦ３（ＣＦ３）３、ＬｉＰＦ３（ｉｓｏ−Ｃ３Ｆ７）３、ＬｉＰＦ５（ｉｓｏ−Ｃ３Ｆ７）などが挙げられる。これらの電解質は、１種類で使用してもよく、２種類以上組み合わせて使用してもよい。これら電解質は、前記の非水溶媒に通常０．１〜３Ｍ、好ましくは０．５〜１．５Ｍの濃度で溶解されて使用される。
【００２２】
本発明の電解液は、例えば、前記の非水溶媒を混合し、これに前記の電解質を溶解し、前記ｔｅｒｔ−アルキルベンゼン誘導体のうち少なくとも１種とビフェニル誘導体のうち少なくとも１種とを溶解することにより得られる。
【００２３】
本発明の電解液は、二次電池の構成部材、特にリチウム二次電池の構成部材として好適に使用される。二次電池を構成する電解液以外の構成部材については特に限定されず、従来使用されている種々の構成部材を使用できる。
【００２４】
例えば、正極活物質としてはコバルトまたはニッケルを含有するリチウムとの複合金属酸化物が使用される。このような複合金属酸化物としては、例えば、ＬｉＣｏＯ２、ＬｉＮｉＯ２、ＬｉＣｏ１−ｘＮｉｘＯ２（０．０１＜ｘ＜１）などが挙げられる。また、ＬｉＣｏＯ２とＬｉＭｎ２Ｏ４、ＬｉＣｏＯ２とＬｉＮｉＯ２、ＬｉＭｎ２Ｏ４とＬｉＮｉＯ２のように適当に混ぜ合わせて使用しても良い。
【００２５】
正極は、前記の正極活物質をアセチレンブラック、カーボンブラックなどの導電剤およびポリテトラフルオロエチレン（ＰＴＦＥ）、ポリフッ化ビニリデン（ＰＶＤＦ）、スチレンとブタジエンの共重合体（ＳＢＲ）、アクリロニトリルとブタジエンの共重合体（ＮＢＲ）、カルボキシメチルセルロース（ＣＭＣ）などの結着剤と混練して正極合剤とした後、この正極材料を集電体としてのアルミニウムやステンレス製の箔やラス板に圧延して、５０℃〜２５０℃程度の温度で２時間程度真空下で加熱処理することにより作製される。
【００２６】
負極（負極活物質）としては、リチウム金属やリチウム合金、またはリチウムを吸蔵・放出可能な炭素材料〔熱分解炭素類、コークス類、グラファイト類（人造黒鉛、天然黒鉛など）、有機高分子化合物燃焼体、炭素繊維〕、または複合スズ酸化物などの物質が使用される。特に、格子面（００２）の面間隔（ｄ００２）が０．３３５〜０．３４０ｎｍ（ナノメーター）である黒鉛型結晶構造を有する炭素材料を使用することが好ましい。なお、炭素材料のような粉末材料はエチレンプロピレンジエンターポリマー（ＥＰＤＭ）、ポリテトラフルオロエチレン（ＰＴＦＥ）、ポリフッ化ビニリデン（ＰＶＤＦ）、スチレンとブタジエンの共重合体（ＳＢＲ）、アクリロニトリルとブタジエンの共重合体（ＮＢＲ）、カルボキシメチルセルロース（ＣＭＣ）などの結着剤と混練して負極合剤として使用される。
【００２７】
リチウム二次電池の構造は特に限定されるものではなく、単層又は複層の正極、負極、セパレータを有するコイン型電池やポリマー電池、さらに、ロール状の正極、負極およびロール状のセパレータを有する円筒型電池や角型電池などが一例として挙げられる。なお、セパレータとしては公知のポリオレフィンの微多孔膜、織布、不織布などが使用される。
【００２８】
本発明におけるリチウム二次電池は、最大作動電圧が４．２Ｖより大きい場合にも長期間にわたり、優れたサイクル特性を有しており、特に最大作動電圧が４．３Ｖのような場合にも優れたサイクル特性を有している。カットオフ電圧は、２．０Ｖ以上とすることができ、さらに２．５Ｖ以上とすることができる。電流値については特に限定されるものではないが、通常０．１〜３Ｃの定電流放電で使用される。また、本発明におけるリチウム二次電池は、−４０〜１００℃と広い範囲で充放電することができるが、好ましくは０〜８０℃である。
【００２９】
【実施例】
次に、実施例および比較例を挙げて、本発明を具体的に説明する。
実施例１
〔電解液の調製〕
ＥＣ／ＰＣ／ＤＥＣ（容量比）＝３０／５／６５の非水溶媒を調製し、これにＬｉＰＦ６を１Ｍの濃度になるように溶解して電解液を調製した後、さらにｔｅｒｔ−ブチルベンゼンおよびビフェニルを電解液に対して、それぞれ２．５重量％、０．９重量％となるように加えた。
【００３０】
〔リチウム二次電池の作製および電池特性の測定〕
ＬｉＣｏＯ２（正極活物質）を９０重量％、アセチレンブラック（導電剤）を５重量％、ポリフッ化ビニリデン（結着剤）を５重量％の割合で混合し、これに１−メチル−２−ピロリドンを加えてスラリー状にしてアルミ箔上に塗布した。その後、これを乾燥し、加圧成形して正極を調製した。人造黒鉛（負極活物質）を９５重量％、ポリフッ化ビニリデン（結着剤）を５重量％の割合で混合し、これに１−メチル−２−ピロリドンを加えてスラリー状にして銅箔上に塗布した。その後、これを乾燥し、加圧成形して負極を調製した。そして、ポリプロピレン微多孔性フィルムのセパレータを用い、上記の電解液を注入して１８６５０サイズの円筒型電池（直径１８ｍｍ、高さ６５ｍｍ）を作製した。電池には、圧力開放口および内部電流遮断装置を設けた。
この１８６５０電池を用いて、サイクル試験するために、高温（４５℃）下、１．４５Ａ（１Ｃ）の定電流で４．２Ｖまで充電した後、終止電圧４．２Ｖとして定電圧下に合計３時間充電した。次に１．４５Ａ（１Ｃ）の定電流下、終止電圧２．５Ｖまで放電し充放電を繰り返した。初期放電容量は、１Ｍ ＬｉＰＦ６＋ＥＣ／ＰＣ／ＤＥＣ（容量比）＝３０／５／６５を電解液として用いた場合（比較例１）と比較して同等であった。３００サイクル後の電池特性を測定したところ、初期放電容量を１００％としたときの放電容量維持率は８４．４％であった。また、高温保存特性も良好であった。さらに、サイクル試験を３００回繰り返した１８６５０電池を用いて、常温（２０℃）下、満充電状態から２．９Ａ（２Ｃ）の定電流で続けて充電することにより、過充電試験を行った。この時、電流遮断時間は２２分、電流遮断後の電池の最高表面温度は６７℃であった。１８６５０サイズの円筒型電池の材料条件および電池特性を表１に示す。
【００３１】
実施例２
ビフェニルの使用量を電解液に対して０．５重量％としたほかは実施例１と同様に円筒型電池を作製した。１８６５０サイズの円筒型電池の材料条件および３００サイクル後の放電容量維持率、電流遮断時間、電流遮断後の電池の最高表面温度を表１に示す。
【００３２】
実施例３
ビフェニルの使用量を電解液に対して１．３重量％としたほかは実施例１と同様に円筒型電池を作製した。１８６５０サイズの円筒型電池の材料条件および３００サイクル後の放電容量維持率、電流遮断時間、電流遮断後の電池の最高表面温度を表１に示す。
【００３３】
実施例４
ビフェニルに代えてｏ−テルフェニルを電解液に対して０．９重量％使用したほかは実施例１と同様に円筒型電池を作製した。１８６５０サイズの円筒型電池の材料条件および３００サイクル後の放電容量維持率、電流遮断時間、電流遮断後の電池の最高表面温度を表１に示す。
【００３４】
実施例５
ｔｅｒｔ−ブチルベンゼンに代えてｔｅｒｔ−ペンチルベンゼンを電解液に対して２．５重量％使用し、またビフェニルに代えて４−エチルビフェニルを電解液に対して０．９重量％使用したほかは実施例１と同様に円筒型電池を作製した。１８６５０サイズの円筒型電池の材料条件および３００サイクル後の放電容量維持率、電流遮断時間、電流遮断後の電池の最高表面温度を表１に示す。
【００３５】
実施例６
ｔｅｒｔ−アルキルベンゼン誘導体として、ｔｅｒｔ−ブチルベンゼンおよびｔｅｒｔ−ペンチルベンゼンを電解液に対してそれぞれ２重量％ずつ使用し、またビフェニル誘導体として４−メチルビフェニルを電解液に対して０．５重量％使用したほかは実施例１と同様に円筒型電池を作製した。１８６５０サイズの円筒型電池の材料条件および３００サイクル後の放電容量維持率、電流遮断時間、電流遮断後の電池の最高表面温度を表１に示す。
【００３６】
比較例１
ｔｅｒｔ−アルキルベンゼン誘導体およびビフェニル誘導体を全く添加しなかったほかは実施例１と同様に円筒型電池を作製した。１８６５０サイズの円筒型電池の材料条件および３００サイクル後の放電容量維持率、電流遮断時間、電流遮断後の電池の最高表面温度を表１に示す。
【００３７】
比較例２
ビフェニルを電解液に対して１．３重量％使用し、ｔｅｒｔ−アルキルベンゼン誘導体を全く使用しなかったほかは実施例１と同様に円筒型電池を作製した。１８６５０サイズの円筒型電池の材料条件および３００サイクル後の放電容量維持率、電流遮断時間、電流遮断後の電池の最高表面温度を表１に示す。
【００３８】
比較例３
ビフェニルを電解液に対して４重量％使用し、ｔｅｒｔ−アルキルベンゼン誘導体を全く使用しなかったほかは比較例２と同様に円筒型電池を作製した。１８６５０サイズの円筒型電池の材料条件および３００サイクル後の放電容量維持率、電流遮断時間、電流遮断後の電池の最高表面温度を表１に示す。
【００３９】
実施例７
正極活物質として、ＬｉＣｏＯ２に代えてＬｉＮｉ０．８Ｃｏ０．２Ｏ２を使用したほかは実施例５と同様に、１８６５０サイズの円筒型電池を作製した。１８６５０サイズの円筒型電池の材料条件および３００サイクル後の放電容量維持率、電流遮断時間、電流遮断後の電池の最高表面温度を表１に示す。
【００４０】
比較例４
ｔｅｒｔ−アルキルベンゼン誘導体およびビフェニル誘導体を全く添加しなかったほかは実施例７と同様に、１８６５０サイズの円筒型電池を作製し、電池性能を測定した。１８６５０サイズの円筒型電池の材料条件および電池特性を表１に示す。
【００４１】
実施例８
ｔｅｒｔ−ブチルベンゼンに代えて４−フルオロ−ｔｅｒｔ−ペンチルベンゼンを電解液に対して３．０重量％使用したほかは実施例１と同様に円筒型電池を作製した。１８６５０サイズの円筒型電池の材料条件および３００サイクル後の放電容量維持率、電流遮断時間、電流遮断後の電池の最高表面温度を表１に示す。
【００４２】
比較例５
トルエンを電解液に対して３．０重量％使用し、ビフェニルを電解液に対して０．５重量％使用したほかは比較例１と同様に円筒型電池を作製した。１８６５０サイズの円筒型電池の材料条件および３００サイクル後の放電容量維持率、電流遮断時間、電流遮断後の電池の最高表面温度を表１に示す。
【００４３】
比較例６
ｎ−ブチルベンゼンを電解液に対して３．０重量％使用し、ビフェニルを電解液に対して０．５重量％使用したほかは比較例１と同様に円筒型電池を作製した。１８６５０サイズの円筒型電池の材料条件および３００サイクル後の放電容量維持率、電流遮断時間、電流遮断後の電池の最高表面温度を表１に示す。
【００４４】
比較例７
ジ−ｎ−ブチルフタレートを電解液に対して３．０重量％使用し、ビフェニルを電解液に対して０．５重量％使用したほかは比較例１と同様に円筒型電池を作製した。１８６５０サイズの円筒型電池の材料条件および３００サイクル後の放電容量維持率、電流遮断時間、電流遮断後の電池の最高表面温度を表１に示す。
【００４５】
比較例８
４−フルオロトルエンを電解液に対して３．０重量％使用し、ビフェニルを電解液に対して０．５重量％使用したほかは比較例１と同様に円筒型電池を作製した。１８６５０サイズの円筒型電池の材料条件および３００サイクル後の放電容量維持率、電流遮断時間、電流遮断後の電池の最高表面温度を表１に示す。
【００４６】
以上の実施例は、過充電時にいずれも負極上に十分なコバルトまたはニッケルが析出していた。本発明の有機化合物を添加した電池は、比較例の電池よりも過充電に対する安全性およびサイクル特性が良いことがわかる。
【００４７】
【表１】
なお、本発明は記載の実施例に限定されず、発明の趣旨から容易に類推可能な様々な組み合わせが可能である。特に、上記実施例の溶媒の組み合わせは限定されるものではない。更には、上記実施例は１８６５０サイズの円筒型電池に関するものであるが、本発明は角型、アルミラミネート型、コイン型の電池にも適用される。
【００４９】
【発明の効果】
本発明によれば、電池の過充電防止などの安全性およびサイクル特性と電気容量などの電池特性に優れたリチウム二次電池を提供することができる。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention is a novel lithium secondary battery capable of providing a lithium secondary battery excellent in battery characteristics such as safety and cycle characteristics such as prevention of overcharge of the battery, electric capacity, storage characteristics, and the like. The present invention relates to a method for ensuring the safety of a lithium secondary battery, and further relates to a highly safe electrolyte for a lithium secondary battery.
[0002]
[Prior art]
In recent years, lithium secondary batteries have been widely used as power sources for driving small electronic devices and the like. In addition, there are great expectations not only for portable electronic and communication devices such as small video cameras, mobile phones, and notebook computers, but also as power sources for automobiles. This lithium secondary battery is mainly composed of a positive electrode, a non-aqueous electrolyte and a negative electrode. 2 Lithium secondary batteries using a lithium composite oxide as a positive electrode and a carbon material or lithium metal as a negative electrode are suitably used. As the non-aqueous solvent for the lithium secondary battery electrolyte, carbonates such as ethylene carbonate (EC) and propylene carbonate (PC) are preferably used.
[0003]
In such a lithium secondary battery, at the time of overcharging that exceeds a normal working voltage, excessive lithium is released from the positive electrode, and at the same time, excessive lithium is precipitated at the negative electrode, and dendrites are generated. Therefore, both the positive and negative electrodes become chemically unstable. If both the positive and negative electrodes become chemically unstable, they will eventually act on carbonates in the non-aqueous electrolyte and decompose, causing a rapid exothermic reaction. As a result, a problem arises in that the battery generates abnormal heat and the safety of the battery is impaired. Such a situation becomes more important as the energy density of the lithium secondary battery increases.
[0004]
In order to solve such a problem, a method in which a small amount of an aromatic compound is added as an additive to an electrolytic solution to ensure safety against overcharging is disclosed in, for example, JP-A-7-302614. Was proposed in Japanese Patent Publication No. In JP-A-7-302614, an anisole derivative having a π-electron orbit having a molecular weight of 500 or less and having a reversible oxidation-reduction potential at a noble potential higher than the positive electrode potential at the time of full charge as an additive of an electrolytic solution is disclosed. You are using In Japanese Patent Application Laid-Open No. 2000-156243, biphenyl, 4,4'-dimethylbiphenyl and the like are used. Such an anisole derivative or biphenyl derivative ensures the safety of the battery against overcharging by redox shuttle in the battery.
[0005]
Japanese Patent Application Laid-Open No. 9-106835 discloses a battery using a carbon material for a negative electrode, and using about 1 to 4% of biphenyl, 3-R-thiophene, 3-chlorothiophene, and furan as additives for an electrolytic solution. A method has been proposed in which the internal resistance of a battery is increased by polymerizing biphenyl or the like at a voltage exceeding the maximum operating voltage of the battery to ensure the safety of the battery against overcharging. Also, in Japanese Patent Application Laid-Open No. 9-171840, similarly, biphenyl, 3-R-thiophene, 3-chlorothiophene, and furan are used to polymerize biphenyl and the like at a voltage exceeding the maximum operating voltage of the battery. A method has been proposed in which an internal short circuit is caused by operating the internal electric disconnection device to generate an internal short circuit, thereby ensuring the safety of the battery against overcharging. In Japanese Patent Application Laid-Open No. Hei 10-32258, similarly, biphenyl, 3-R-thiophene, 3-chlorothiophene, and furan are used to polymerize biphenyl and the like at a voltage exceeding the maximum operating voltage of the battery. A method has been proposed in which a conductive polymer is generated to cause an internal short circuit to ensure the safety of the battery against overcharging.
[0006]
However, in Japanese Patent Application Laid-Open No. H11-162512, in a battery to which biphenyl or the like is added, the cycle is repeated up to a voltage upper limit exceeding 4.1 V, or the battery is exposed to a high temperature of 40 ° C. or more for a long period of time. It is described that there is a problem that battery characteristics such as characteristics tend to be deteriorated, and the tendency becomes remarkable as the added amount increases. Therefore, an electrolytic solution to which 2,2-diphenylpropane or the like is added has been proposed, and by polymerizing 2,2-diphenylpropane or the like at a voltage exceeding the maximum operating voltage of the battery, a gas is generated to generate an internal electric cutting device. A method has been proposed in which an internal short circuit is generated by operating or generating a conductive polymer to ensure the safety of the battery against overcharging.
[0007]
[Problems to be solved by the invention]
However, while the anisole derivatives and biphenyl derivatives proposed in JP-A-7-302614 and JP-A-2000-156243 effectively act on overcharging by a redox shuttle, the cycle characteristics and the storage characteristics are improved. Has a problem of adversely affecting The proposed anisole and biphenyl derivatives decompose slowly when charged and discharged when exposed to a slightly higher voltage when used at a high temperature of 40 ° C or higher or at a normal operating voltage. However, there is a problem that the original battery characteristics deteriorate. Therefore, since the anisole derivative and the biphenyl derivative are gradually decomposed and reduced with normal charge and discharge, safety may not be sufficiently secured when an overcharge test is performed after 300 cycles.
[0008]
Similarly, biphenyl, 3-R-thiophene, 3-chlorothiophene, and furan proposed in JP-A-9-106835, JP-A-9-171840, and JP-A-10-321258 also suffer from overcharging. On the other hand, while it works effectively, as pointed out in the above-mentioned JP-A-11-162512, it adversely affects the cycle characteristics and the storage characteristics, and causes a problem that it becomes remarkable with the added amount of biphenyl. Was. This is because biphenyl and the like are oxidatively decomposed at a potential of 4.5 V or less, so that even when used at a high temperature of 40 ° C. or more or at a normal operating voltage, if they are locally exposed to a slightly higher voltage, they are gradually reduced. Since biphenyl and the like are decomposed and reduced, the cycle life is reduced. Furthermore, since biphenyl and the like are gradually decomposed and reduced during charging and discharging, safety may not be sufficiently secured when an overcharge test is performed after 300 cycles.
[0009]
Furthermore, the battery to which 2,2-diphenylpropane is added, which is proposed in Japanese Patent Application Laid-Open No. H11-162512, is not as safe as the battery to which biphenyl is added, but has a higher safety than the battery to which nothing is added. The safety for charging is good. Further, it is described that a battery to which 2,2-diphenylpropane is added has better cycle characteristics than a battery to which biphenyl is added, but has worse cycle characteristics than a battery to which nothing is added. Therefore, it is stated that it is acceptable to sacrifice a part of safety in order to obtain better cycle characteristics than the battery to which biphenyl is added. Therefore, at present, safety such as overcharge prevention and battery characteristics such as cycle characteristics, electric capacity and storage characteristics are not always satisfactory.
[0010]
The present invention solves the problems relating to the electrolyte for a lithium secondary battery as described above, and constitutes a lithium secondary battery excellent in battery characteristics such as safety and cycle characteristics such as prevention of overcharge of the battery and electric capacity. Rechargeable lithium battery Non-aqueous electrolyte for use and lithium secondary battery using the same The purpose is to provide.
[0011]
[Means for Solving the Problems]
The present invention provides a positive electrode made of a composite oxide with lithium containing cobalt or nickel, a negative electrode made of a material capable of occluding and releasing lithium metal, a lithium alloy or lithium, and a non-aqueous solvent in which an electrolyte is dissolved in a non-aqueous solvent. In a lithium secondary battery comprising an aqueous electrolyte, the non-aqueous electrolyte contains 0.1% to 10% by weight of a tert-alkylbenzene derivative and 0.1% to 1.5% by weight of a biphenyl derivative. A lithium secondary battery characterized by the following.
[0012]
Further, the present invention provides a positive electrode comprising a composite oxide with lithium containing cobalt or nickel, a negative electrode comprising a lithium metal, a lithium alloy or a material capable of occluding and releasing lithium, and an electrolyte dissolved in a non-aqueous solvent. Of a tert-alkylbenzene derivative and 0.1% to 1.5% by weight of a tert-alkylbenzene derivative and 0.1% to 1.5% by weight of a biphenyl electrolyte in a non-aqueous electrolyte. The present invention relates to an electrolyte for a lithium secondary battery, comprising a derivative.
[0013]
As a conventional mechanism for preventing overcharging, a method of redox shuttle at a potential of about 4.5 V, a method of increasing the internal resistance of a battery by polymerizing at a potential of 4.5 V or less, and a method of generating gas to generate internal electricity There is known a method in which an internal short circuit is generated by operating a cutting device, or an internal short circuit is generated by generating a conductive polymer to ensure the safety of a battery against overcharging.
[0014]
On the other hand, the mechanism for preventing overcharge according to the present invention is that the tert-alkylbenzene derivative contained in the non-aqueous electrolyte is oxidatively decomposed at a potential of +4.6 V to +5.0 V with respect to lithium, thereby overcharging. Sometimes the elution of cobalt or nickel in the positive electrode is promoted, and the cobalt or nickel precipitates on the negative electrode, thereby suppressing the reaction between the lithium metal deposited on the negative electrode and the carbonate in the non-aqueous electrolyte. it is conceivable that. Further, in the present invention, in some cases, it is considered that cobalt or nickel is deposited on the negative electrode inside the battery to cause an internal short circuit, thereby exhibiting an overcharge prevention effect. As a result, it is estimated that the safety of the battery is sufficiently ensured. Furthermore, in the present invention, the biphenyl derivative is added in a small amount of 0.1% by weight to 1.5% by weight together with the tert-alkylbenzene derivative, thereby promoting the overcharge preventing action of the tert-alkylbenzene derivative. An unexpected effect of improving battery characteristics, which has been known to decrease, is exhibited.
[0015]
Further, the tert-alkylbenzene derivative contained in the non-aqueous electrolyte has a high oxidation potential with respect to lithium of +4.6 V to +5.0 V, and thus is repeatedly charged and discharged at a high temperature of 40 ° C. or higher or a normal operating voltage. Even when the voltage locally exceeds 4.2 V, the tert-alkylbenzene derivative does not decompose. In addition, although a small amount of 0.1 to 1.5% by weight of only a biphenyl derivative does not exhibit an overcharge preventing effect, the biphenyl derivative is slightly decomposed, so that it is used in combination with a tert-alkylbenzene derivative. On the contrary, it has been found that the battery characteristics are improved. Further, if an overcharge test is performed after 300 cycles, safety can be sufficiently ensured by the overcharge preventing action of the tert-alkylbenzene derivative. This is considered to provide a lithium secondary battery that is not only excellent in safety such as prevention of overcharging of the battery, but also excellent in battery characteristics such as cycle characteristics, electric capacity, and storage characteristics. .
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
Examples of the tert-alkylbenzene derivative contained in the electrolytic solution in which the electrolyte is dissolved in the non-aqueous solvent include the following compounds.
For example, tert-butylbenzene, 1-fluoro-4-tert-butylbenzene, 1-chloro-4-tert-butylbenzene, 1-bromo-4-tert-butylbenzene, 1-iodo-4-tert-butylbenzene , 5-tert-butyl-m-xylene, 4-tert-butyltoluene, 3,5-di-tert-butyltoluene, 1,3-di-tert-butylbenzene, 1,4-di-tert-butylbenzene , 1,3,5-tri-tert-butylbenzene, tert-pentylbenzene, (1-ethyl-1-methylpropyl) benzene, (1,1-diethylpropyl) benzene, (1,1-dimethylbutyl) benzene , (1-ethyl-1-methylbutyl) benzene, (1-ethyl-1-ethylbutyl) benzene, (1,1 2-trimethylpropyl) benzene, 1-fluoro-4-tert-pentylbenzene, 1-chloro-4-tert-pentylbenzene, 1-bromo-4-tert-pentylbenzene, 1-iodo-4-tert-pentylbenzene , 5-tert-pentyl-m-xylene, 1-methyl-4-tert-pentylbenzene, 3,5-di-tert-pentyltoluene, 1,3-di-tert-pentylbenzene, 1,4-di- It is preferably at least one or more tert-alkylbenzene derivatives such as tert-pentylbenzene and 1,3,5-tri-tert-pentylbenzene.
Further, as the biphenyl derivative, biphenyl, o-terphenyl, m-terphenyl, p-terphenyl, 4-methylbiphenyl, 4-ethylbiphenyl, 4-tert-butylbiphenyl and the like can be used. The overcharge prevention effect can be improved by replacing a part of the tert-butylbenzene or the like having a high potential of 4.8 to 5.0 V with o-terphenyl having a low oxidation potential of 4.5 V. For example, when part of tert-butylbenzene is replaced with o-terphenyl, the content of tert-butylbenzene is preferably not more than 10 times the weight of o-terphenyl, and more preferably 0.3 to 5 times. Double amount, especially 0.5 to 3 times amount is preferable. As described above, by using at least two kinds of the tert-alkylbenzene derivatives having different oxidation potentials and the biphenyl derivative in combination, the overcharge prevention effect can be improved and the battery characteristics can be improved. Become.
[0017]
When the content of the tert-alkylbenzene derivative is excessively large, the conductivity of the electrolytic solution and the like may be changed and battery performance may be reduced. When the content is excessively small, a sufficient overcharge effect may not be obtained. Is preferably in the range of 0.1% by weight to 10% by weight, particularly 1 to 5% by weight, based on the weight of
[0018]
In addition, when the content of the biphenyl derivative is excessively large, the biphenyl derivative is decomposed in the battery during normal use, and the battery performance may be deteriorated. When the content is excessively small, a sufficient overcharge effect or battery performance may be obtained. Is not obtained, the content is preferably 0.1% by weight to 1.5% by weight, particularly 0.3% by weight to 0.9% by weight based on the weight of the electrolytic solution.
[0019]
Examples of the non-aqueous solvent used in the present invention include cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC) and vinylene carbonate (VC), and lactones such as γ-butyrolactone. , Linear carbonates such as dimethyl carbonate (DMC), methyl ethyl carbonate (MEC) and diethyl carbonate (DEC), tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, 1,2-dimethoxyethane, 1,2 Ethers such as -diethoxyethane and 1,2-dibutoxyethane; nitriles such as acetonitrile; esters such as methyl propionate, methyl pivalate and octyl pivalate; and amides such as dimethylformamide. .
[0020]
These non-aqueous solvents may be used alone or in combination of two or more. The combination of the non-aqueous solvents is not particularly limited, and examples thereof include various combinations such as a combination of a cyclic carbonate and a chain carbonate, a combination of a cyclic carbonate and a lactone, and a combination of three kinds of cyclic carbonates and a chain carbonate. Combinations.
[0021]
As the electrolyte used in the present invention, for example, LiPF 6 , LiBF 4 , LiClO 4 , LiN (SO 2 CF 3 ) 2 , LiN (SO 2 C 2 F 5 ) 2 , LiC (SO 2 CF 3 ) 3 , LiPF 4 (CF 3 ) 2 , LiPF 3 (C 2 F 5 ) 3 , LiPF 3 (CF 3 ) 3 , LiPF 3 (Iso-C 3 F 7 ) 3 , LiPF 5 (Iso-C 3 F 7 ). These electrolytes may be used alone or in combination of two or more. These electrolytes are used after being dissolved in the above non-aqueous solvent at a concentration of usually 0.1 to 3M, preferably 0.5 to 1.5M.
[0022]
For example, the electrolyte solution of the present invention is obtained by mixing the above non-aqueous solvent, dissolving the above electrolyte therein, and dissolving at least one of the tert-alkylbenzene derivatives and at least one of the biphenyl derivatives. Is obtained by
[0023]
The electrolytic solution of the present invention is suitably used as a constituent member of a secondary battery, particularly as a constituent member of a lithium secondary battery. The constituent members other than the electrolytic solution constituting the secondary battery are not particularly limited, and various constituent members conventionally used can be used.
[0024]
For example, a composite metal oxide with lithium containing cobalt or nickel is used as the positive electrode active material. As such a composite metal oxide, for example, LiCoO 2 , LiNiO 2 , LiCo 1-x Ni x O 2 (0.01 <x <1). Also, LiCoO 2 And LiMn 2 O 4 , LiCoO 2 And LiNiO 2 , LiMn 2 O 4 And LiNiO 2 May be used by appropriately mixing them.
[0025]
For the positive electrode, a conductive agent such as acetylene black or carbon black, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), a copolymer of styrene and butadiene (SBR), or a copolymer of acrylonitrile and butadiene is used as the positive electrode. After kneading with a binder such as polymer (NBR) and carboxymethylcellulose (CMC) to form a positive electrode mixture, this positive electrode material is rolled into aluminum or stainless steel foil or lath plate as a current collector, It is produced by performing a heat treatment under a vacuum at a temperature of about 50 ° C. to 250 ° C. for about 2 hours.
[0026]
As the negative electrode (negative electrode active material), lithium metal or lithium alloy, or a carbon material capable of occluding and releasing lithium (pyrolytic carbons, cokes, graphites (artificial graphite, natural graphite, etc.), organic polymer compound combustion) Body, carbon fiber], or a composite tin oxide. In particular, the spacing (d) of the lattice plane (002) 002 ) Is preferably a carbon material having a graphite-type crystal structure having a diameter of 0.335 to 0.340 nm (nanometers). Powder materials such as carbon materials include ethylene propylene diene terpolymer (EPDM), polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), a copolymer of styrene and butadiene (SBR), and a copolymer of acrylonitrile and butadiene. It is used as a negative electrode mixture by kneading with a binder such as a polymer (NBR) and carboxymethyl cellulose (CMC).
[0027]
The structure of the lithium secondary battery is not particularly limited, and has a single-layer or multilayer positive electrode, a negative electrode, a coin-type battery or a polymer battery having a separator, and further has a roll-shaped positive electrode, a negative electrode, and a roll-shaped separator. Examples include a cylindrical battery and a square battery. As the separator, a known microporous polyolefin membrane, woven fabric, nonwoven fabric, or the like is used.
[0028]
The lithium secondary battery according to the present invention has excellent cycle characteristics for a long time even when the maximum operating voltage is higher than 4.2 V, and is particularly excellent even when the maximum operating voltage is 4.3 V. Cycle characteristics. The cutoff voltage can be 2.0 V or higher, and can be 2.5 V or higher. Although the current value is not particularly limited, it is usually used at a constant current discharge of 0.1 to 3C. Further, the lithium secondary battery of the present invention can be charged and discharged in a wide range of -40 to 100 ° C, but is preferably 0 to 80 ° C.
[0029]
【Example】
Next, the present invention will be specifically described with reference to Examples and Comparative Examples.
Example 1
(Preparation of electrolyte solution)
A non-aqueous solvent of EC / PC / DEC (volume ratio) = 30/5/65 was prepared, and LiPF 6 Was dissolved to a concentration of 1M to prepare an electrolytic solution, and then tert-butylbenzene and biphenyl were further added to the electrolytic solution at 2.5% by weight and 0.9% by weight, respectively. .
[0030]
[Production of lithium secondary battery and measurement of battery characteristics]
LiCoO 2 90% by weight (positive electrode active material), 5% by weight of acetylene black (conductive agent), and 5% by weight of polyvinylidene fluoride (binder), and 1-methyl-2-pyrrolidone was added thereto. To form a slurry and apply it on an aluminum foil. Thereafter, this was dried and pressed to prepare a positive electrode. 95% by weight of artificial graphite (negative electrode active material) and 5% by weight of polyvinylidene fluoride (binder) were mixed, and 1-methyl-2-pyrrolidone was added thereto to form a slurry to form a slurry on a copper foil. Applied. Thereafter, this was dried and molded under pressure to prepare a negative electrode. Then, using a separator made of a polypropylene microporous film, the above-mentioned electrolytic solution was injected to produce a 18650-size cylindrical battery (diameter 18 mm, height 65 mm). The battery was provided with a pressure release port and an internal current interrupter.
In order to perform a cycle test using this 18650 battery, the battery was charged to 4.2 V at a constant current of 1.45 A (1 C) at a high temperature (45 ° C.), and then a final voltage of 4.2 V was obtained under a constant voltage of 3 V. Charged for hours. Next, under a constant current of 1.45 A (1 C), the battery was discharged to a final voltage of 2.5 V, and charging and discharging were repeated. Initial discharge capacity is 1M LiPF 6 + EC / PC / DEC (volume ratio) = 30/5/65 was equivalent to the case where the electrolyte was used (Comparative Example 1). When the battery characteristics after 300 cycles were measured, the discharge capacity retention ratio when the initial discharge capacity was 100% was 84.4%. The high-temperature storage characteristics were also good. Further, an overcharge test was performed by continuously charging the battery from a fully charged state at a constant current of 2.9 A (2 C) at room temperature (20 ° C.) using an 18650 battery obtained by repeating the cycle test 300 times. At this time, the current interruption time was 22 minutes, and the maximum surface temperature of the battery after the current interruption was 67 ° C. Table 1 shows the material conditions and battery characteristics of the 18650-size cylindrical battery.
[0031]
Example 2
A cylindrical battery was produced in the same manner as in Example 1 except that the amount of biphenyl used was 0.5% by weight with respect to the electrolytic solution. Table 1 shows the material conditions of the 18650-size cylindrical battery, the discharge capacity retention rate after 300 cycles, the current interruption time, and the maximum surface temperature of the battery after the current interruption.
[0032]
Example 3
A cylindrical battery was produced in the same manner as in Example 1 except that the amount of biphenyl used was 1.3% by weight based on the electrolyte. Table 1 shows the material conditions of the 18650-size cylindrical battery, the discharge capacity retention rate after 300 cycles, the current interruption time, and the maximum surface temperature of the battery after the current interruption.
[0033]
Example 4
A cylindrical battery was produced in the same manner as in Example 1 except that 0.9% by weight of o-terphenyl was used in place of biphenyl with respect to the electrolytic solution. Table 1 shows the material conditions of the 18650-size cylindrical battery, the discharge capacity retention rate after 300 cycles, the current interruption time, and the maximum surface temperature of the battery after the current interruption.
[0034]
Example 5
The procedure was performed except that tert-pentylbenzene was used in place of tert-butylbenzene in an amount of 2.5% by weight based on the electrolyte, and 4-ethylbiphenyl was used in place of biphenyl in an amount of 0.9% by weight of the electrolyte. A cylindrical battery was produced in the same manner as in Example 1. Table 1 shows the material conditions of the 18650-size cylindrical battery, the discharge capacity retention rate after 300 cycles, the current interruption time, and the maximum surface temperature of the battery after the current interruption.
[0035]
Example 6
As a tert-alkylbenzene derivative, tert-butylbenzene and tert-pentylbenzene were used in an amount of 2% by weight with respect to the electrolyte, and as a biphenyl derivative, 4-methylbiphenyl was used in an amount of 0.5% by weight with respect to the electrolyte. Otherwise, a cylindrical battery was manufactured in the same manner as in Example 1. Table 1 shows the material conditions of the 18650-size cylindrical battery, the discharge capacity retention rate after 300 cycles, the current interruption time, and the maximum surface temperature of the battery after the current interruption.
[0036]
Comparative Example 1
A cylindrical battery was produced in the same manner as in Example 1, except that no tert-alkylbenzene derivative or biphenyl derivative was added. Table 1 shows the material conditions of the 18650-size cylindrical battery, the discharge capacity retention rate after 300 cycles, the current interruption time, and the maximum surface temperature of the battery after the current interruption.
[0037]
Comparative Example 2
A cylindrical battery was produced in the same manner as in Example 1 except that biphenyl was used in an amount of 1.3% by weight based on the electrolytic solution, and no tert-alkylbenzene derivative was used. Table 1 shows the material conditions of the 18650-size cylindrical battery, the discharge capacity retention rate after 300 cycles, the current interruption time, and the maximum surface temperature of the battery after the current interruption.
[0038]
Comparative Example 3
A cylindrical battery was produced in the same manner as in Comparative Example 2 except that biphenyl was used in an amount of 4% by weight based on the electrolytic solution and no tert-alkylbenzene derivative was used. Table 1 shows the material conditions of the 18650-size cylindrical battery, the discharge capacity retention rate after 300 cycles, the current interruption time, and the maximum surface temperature of the battery after the current interruption.
[0039]
Example 7
LiCoO as a positive electrode active material 2 Instead of LiNi 0.8 Co 0.2 O 2 A 18650-size cylindrical battery was produced in the same manner as in Example 5 except for using. Table 1 shows the material conditions of the 18650-size cylindrical battery, the discharge capacity retention rate after 300 cycles, the current interruption time, and the maximum surface temperature of the battery after the current interruption.
[0040]
Comparative Example 4
A cylindrical battery of 18650 size was prepared in the same manner as in Example 7 except that no tert-alkylbenzene derivative and biphenyl derivative were added, and the battery performance was measured. Table 1 shows the material conditions and battery characteristics of the 18650-size cylindrical battery.
[0041]
Example 8
A cylindrical battery was produced in the same manner as in Example 1, except that 3.0% by weight of 4-fluoro-tert-pentylbenzene was used in the electrolyte instead of tert-butylbenzene. Table 1 shows the material conditions of the 18650-size cylindrical battery, the discharge capacity retention rate after 300 cycles, the current interruption time, and the maximum surface temperature of the battery after the current interruption.
[0042]
Comparative Example 5
A cylindrical battery was produced in the same manner as in Comparative Example 1, except that toluene was used in an amount of 3.0% by weight based on the electrolyte and biphenyl was used in an amount of 0.5% by weight based on the electrolyte. Table 1 shows the material conditions of the 18650-size cylindrical battery, the discharge capacity retention rate after 300 cycles, the current interruption time, and the maximum surface temperature of the battery after the current interruption.
[0043]
Comparative Example 6
A cylindrical battery was produced in the same manner as in Comparative Example 1, except that 3.0% by weight of n-butylbenzene was used in the electrolytic solution and 0.5% by weight of biphenyl was used in the electrolytic solution. Table 1 shows the material conditions of the 18650-size cylindrical battery, the discharge capacity retention rate after 300 cycles, the current interruption time, and the maximum surface temperature of the battery after the current interruption.
[0044]
Comparative Example 7
A cylindrical battery was produced in the same manner as in Comparative Example 1, except that 3.0% by weight of di-n-butyl phthalate was used in the electrolytic solution and 0.5% by weight of biphenyl was used in the electrolytic solution. Table 1 shows the material conditions of the 18650-size cylindrical battery, the discharge capacity retention rate after 300 cycles, the current interruption time, and the maximum surface temperature of the battery after the current interruption.
[0045]
Comparative Example 8
A cylindrical battery was produced in the same manner as in Comparative Example 1, except that 3.0% by weight of 4-fluorotoluene was used in the electrolytic solution and 0.5% by weight of biphenyl was used in the electrolytic solution. Table 1 shows the material conditions of the 18650-size cylindrical battery, the discharge capacity retention rate after 300 cycles, the current interruption time, and the maximum surface temperature of the battery after the current interruption.
[0046]
In each of the above examples, sufficient cobalt or nickel was deposited on the negative electrode during overcharge. It can be seen that the battery to which the organic compound of the present invention is added has better safety against overcharge and better cycle characteristics than the battery of the comparative example.
[0047]
[Table 1]
It should be noted that the present invention is not limited to the described embodiments, and various combinations that can be easily analogized from the gist of the invention are possible. In particular, the combinations of the solvents in the above examples are not limited. Further, the above embodiment relates to a cylindrical battery of 18650 size, but the present invention is also applicable to a square battery, an aluminum laminate battery, and a coin battery.
[0049]
【The invention's effect】
According to the present invention, safety and cycle characteristics such as overcharge prevention of a battery When A lithium secondary battery having excellent battery characteristics such as electric capacity can be provided.
Claims (8)
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| TW579613B (en) * | 2001-09-27 | 2004-03-11 | Nisshin Spinning | Nonaqueous electrolyte secondary cell, power supply comprising the secondary cell, portable device, transportable or movable machine, electric apparatus for home use, and method for charging nonaqueous electrolyte secondary cell |
| JP3914048B2 (en) | 2001-12-21 | 2007-05-16 | 日立マクセル株式会社 | Non-aqueous secondary battery and portable device using the same |
| DE602004031086D1 (en) * | 2003-02-27 | 2011-03-03 | Mitsubishi Chem Corp | WATER-FREE ELECTROLYTIC SOLUTION AND LITHIUM SECONDARY BATTERY |
| US7083878B2 (en) | 2003-02-27 | 2006-08-01 | Mitsubishi Chemical Corporation | Nonaqueous electrolytic solution and lithium secondary battery |
| US7700232B2 (en) * | 2004-03-19 | 2010-04-20 | Ube Industries, Ltd. | Nonaqueous electrolytic solution for lithium secondary battery |
| US7811710B2 (en) * | 2004-04-01 | 2010-10-12 | 3M Innovative Properties Company | Redox shuttle for rechargeable lithium-ion cell |
| DE102004018249B3 (en) | 2004-04-15 | 2006-03-16 | Infineon Technologies Ag | Method for processing a workpiece on a workpiece carrier |
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