JP2004022336A - Electrolyte for secondary battery and secondary battery using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a lithium secondary battery endowed with an excellent energy density and characteristics such as electromotive force as well as excellent in cycle life and safety. <P>SOLUTION: Electrolyte containing sulfonic acid anhydride expressed in formula (1) is used as an aprotic organic solvent. In the formula, X denotes an alkylene group with the carbon number of 2 to 4 which may have a substituent, an alkenylene group with the carbon number of 2 to 4 which may have a substituent, an aromatic ring which may have a substituent, or a heterocycle which may have a substituent. <P>COPYRIGHT: (C)2004,JPO

Description

ここで、Ｘは、置換基を有しても良い炭素数２〜４のアルキレン基、置換基を有しても良い炭素数２〜４のアルケニレン基、置換基を有しても良い芳香族環、置換基を有しても良い複素環を示す。
【００３５】
なお、置換基としては、ハロゲン原子、置換もしくは未置換のアルキル基、置換もしくは未置換のアルコキシ基、置換もしくは未置換のシクロアルキル基、置換もしくは未置換のアリール基、置換もしくは未置換の複素環基を好ましいものとして例示できる。
【００３６】
具体的には、下記一般式（２）で示されるような化合物が有効である。
【００３７】
【化５】

ここで、Ｒ_１〜Ｒ_４はそれぞれ独立に、水素原子、ハロゲン原子、置換もしくは未置換のアルキル基、置換もしくは未置換のアルコキシ基、置換もしくは未置換のシクロアルキル基、置換もしくは未置換のアリール基、置換もしくは未置換の複素環基を示す。また、Ｒ１〜Ｒ４は互いに縮合して、置換基を有しても良いアリール環又は置換基を有しても良い複素環を形成しても良い。
【００３８】
さらに、スルホン酸無水物基が分子中に複数個有っても構わない。
【００３９】
本発明の一般式（１）の化合物の代表例を表１〜３に具体的に例示するが、本発明はこれらに限定するものではない。
【００４０】
【表１】

【００４１】
【表２】

【００４２】
【表３】

【００４３】
一般式（１）で示されるスルホン酸無水物の電解液に占める割合は特に限定されないが、電解液全体の０．０１〜１０ｗｔ％で含まれることが好ましい。０．０１ｗｔ未満の場合、十分な皮膜効果が得られにくい。１０ｗｔ％を越えると、電解液の粘性を高くすることなど抵抗が大きくなり好ましくはない。
【００４４】
本発明では、非プロトン性有機溶媒に一般式（１）のスルホン酸無水物を加え、更にイミドアニオンおよび遷移金属イオンを加えても良い。また、非プロトン性有機溶媒に電解質塩としてリチウム塩を溶解した電解液に、少なくともイミドアニオンと遷移金属とからなる金属錯体を加えても良い。
【００４５】
イミドアニオンと遷移金属イオンが存在する系の場合、充放電によりイミドアニオンと遷移金属との金属錯体が負極表面に形成される（２０００年電気化学秋季大会（２０００年９月、千葉工業大学、講演番号：２Ａ２４）、第４１回電池討論会（２０００年１１月、名古屋国際会議場、講演番号：１Ｅ０３））。
【００４６】
また、イミドアニオンと遷移金属イオンとの金属錯体が存在する場合、充放電に関係なく前記金属錯体が負極表面に吸着される。
【００４７】
このイミドアニオンと遷移金属イオンとの金属錯体と、スルホン酸無水物の二つの化合物が負極表面に存在することは次のような効果をもたらす。
【００４８】
負極表面には、溶媒分子との反応を引き起こすダングリングボンドと、反応性のない部位が存在している。添加するイミド塩によって生成する金属錯体や、イミド塩と遷移金属によって形成される金属錯体は前記反応性のない部位に吸着することによって安定化皮膜を形成し、リチウムイオン伝導を行う。
【００４９】
また、本発明で重要な添加物であるスルホン酸無水物は、負極表面での不働態皮膜形成に寄与し、結果として溶媒分子の分解を抑制する。また、スルホン酸無水物は負極や電解液に存在する微量の水分と反応し水分除去に有効である。
【００５０】
前記イミドアニオンの具体例としては、⁻Ｎ（Ｃ_ｎＦ_２ｎ＋１ＳＯ_２）（Ｃ_ｍＦ_２ｍ＋１ＳＯ_２）（ｎ，ｍは自然数）などがあげられる。
【００５１】
ここで用いる遷移金属としては、ランタノイド系遷移金属であることが好ましく、特に、ユーロピウム（Ｅｕ）、ネオジウム（Ｎｄ）、エルビウム（Ｅｒ）またはホルミウム（Ｈｏ）が好ましい。
【００５２】
イミドアニオン又はその金属錯体は電解液中に０．００５〜１０ｗｔ％で含まれることが好ましい。０．００５ｗｔ％未満では負極表面での皮膜形成に十分効果が得られないことがあり、また、１０ｗｔ％を越えると溶解しないだけでなく電解液の粘性を大きくすることあり、好ましくない。本発明においてより好ましくは、０．０５〜５ｗｔ％の範囲である。
【００５３】
また、一般式（１）に示すスルホン酸無水物が含まれる電解液に、更に一般式（１）に示す以外のスルホニル基を有する化合物を加えることも有効である。一般式（１）に示す以外のスルホニル基を有する化合物を加えることにより、粘度の調整や複合効果による皮膜の安定性向上や溶媒分子の抑制効果が大きくなる。
【００５４】
一般式（１）に示す以外のスルホニル基を有する化合物としては、具体的には、スルホラン（特開昭６０−１５４４７８号公報）、１，３−プロパンスルトンや１，４−ブタンスルトン（特開昭６２−１００９４８号公報、特開昭６３−１０２１７３号公報、特開平１１−３３９８５０号公報、特開２０００−３７２４号公報）、アルカンスルホン酸無水物（特開平１０−１８９０４１号公報）、１，３，２−ジオキサホスホラン−２−オキサイド誘導体（特開平１０−５０３４２号公報）、γ−スルトン化合物（特開２０００−２３５８６６号公報）、スルホレン誘導体（特開２０００−２９４２７８号公報）などがあげられるが、これらに限定されるものではない。なお、特に好ましくは、下記一般式（３）に示されるスルトン化合物である。
【００５５】
【化６】

ここで、ｎは０〜２の整数である。また、Ｒ_１〜Ｒ_６は、それぞれ独立に水素原子、炭素数１〜１２のアルキル基、炭素数３〜６のシクロアルキル基、炭素数６〜１２のアリール基を示す。
【００５６】
スルホニル基を有する化合物は電解液中に０．０１〜１０ｗｔ％で含まれることが好ましい。０．０１ｗｔ％未満では負極表面での皮膜形成に十分効果がない。１０ｗｔ％を越えると溶解しないだけでなく電解液の粘性を大きくするために好ましくない。本発明において、より好ましくは、０．０５〜５ｗｔ％の範囲である。
【００５７】
更に本発明によれば、前記一般式（１）に示すスルホン酸無水物が含まれる電解液中に、ビニレンカーボネート又はその誘導体を添加又は混合することで更にサイクル特性の改善を図ることができる。
【００５８】
ビニレンカボネート又はその誘導体は、例えば、特開平４−１６９０７５号公報、特開平７−１２２２９６号公報、特開平８−４５５４５号公報、特開平５−８２１３８号公報、特開平５−７４４８６号公報、特開平６−５２８８７号公報、特開平１１−２６０４０１号公報、特開２０００−２０８１６９号公報、特開２００１−３５５３０号公報、特開２０００−１３８０７１号公報に示される化合物を適宜使用することができる。
【００５９】
ビニレンカーボネート又はその誘導体を添加剤として使用する場合には、電解液中に０．０１〜１０ｗｔ％含ませることで効果が得られる。また、溶媒として用いる場合には１〜５０ｗｔ％含ませることで効果が得られる。
【００６０】
本発明で使用する非プロトン性有機溶媒は、環状カーボネート類、鎖状カーボネート類、脂肪族カルボン酸エステル類、γ−ラクトン類、環状エーテル類、鎖状エーテル類およびそれらのフッ化誘導体であり、これらから適宜１種あるいは２種以上の混合で使用される。
【００６１】
本発明において、リチウム塩としては、ＬｉＰＦ_６、ＬｉＢＦ_４、ＬｉＡｓＦ_６、ＬｉＳｂＦ_６、ＬｉＣｌＯ_４、ＬｉＡｌＣｌ_４、ＬｉＮ（Ｃ_ｎＦ_２ｎ＋１ＳＯ_２）（Ｃ_ｍＦ_２ｍ＋１ＳＯ_２）（ｎ，ｍは自然数）が好ましく、特に、ＬｉＰＦ_６、ＬｉＢＦ_４が好ましい。
【００６２】
また、本発明によれば、リチウムを活物質とする正極、負極を備えた上記二次電池用電解液を用いた二次電池が与えられる。
【００６３】
負極として、リチウムを吸蔵、放出できる材料、リチウム金属、リチウムと合金を形成することができる金属材料、酸化物材料等からなる負極活物質を用いる。
【００６４】
ここでリチウムを吸蔵、放出できる材料として炭素を含んだものが好ましく、特に、黒鉛、非晶質炭素であることが好ましい。
【００６５】
本発明では、更に負極と正極をセパレータを隔てて組み合わせ、電池外装体に挿入し、上記一般式（１）で示される化合物を含む電解液を含浸させた後、電池外装体を封止または封止後に、必要により電池を充電し、負極上に皮膜を形成させ、二次電池を提供する。
【００６６】
【発明の実施の形態】
図１に本発明に係る電池の一例について概略構造を示す。
【００６７】
本発明の電池は、正極集電体１１、リチウムイオンを吸蔵・放出し得る酸化物またはイオウ化合物、導電性高分子、安定化ラジカル化合物のいずれかまたは混合物からなる正極活物質を含有する層１２、リチウムイオンを吸蔵・放出する炭素材料または酸化物、リチウムと合金を形成する金属、リチウム金属自身のいずれかもしくはこれらの混合物からなる負極活物質を含有する層１３、負極集電体１４、電解液１５およびこれを含む多孔質セパレータ１６から構成されている。
【００６８】
ここで、一般式（１）で示されるスルホン酸無水物は電解液１５に含まれる。
【００６９】
本発明における電解液としては、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）、ビニレンカーボネート（ＶＣ）等の環状カーボネート類、ジメチルカーボネート（ＤＭＣ）、ジエチルカーボネート（ＤＥＣ）、エチルメチルカーボネート（ＥＭＣ）、ジプロピルカーボネート（ＤＰＣ）等の鎖状カーボネート類、ギ酸メチル、酢酸メチル、プロピオン酸エチル等の脂肪族カルボン酸エステル類、γ−ブチロラクトン等のγ−ラクトン類、１，２−エトキシエタン（ＤＥＥ）、エトキシメトキシエタン（ＥＭＥ）等の鎖状エーテル類、テトラヒドロフラン、２−メチルテトラヒドロフラン等の環状エーテル類、ジメチルスルホキシド、１，３−ジオキソラン、ホルムアミド、アセトアミド、ジメチルホルムアミド、アセトニトリル、プロピルニトリル、ニトロメタン、エチルモノグライム、リン酸トリエステル、トリメトキシメタン、ジオキソラン誘導体、スルホラン、メチルスルホラン、１，３−ジメチル−２−イミダゾリジノン、３−メチル−２−オキサゾリジノン、プロピレンカーボネート誘導体、テトラヒドロフラン誘導体、エチルエーテル、１，３−プロパンスルトン、アニソール、Ｎ−メチルピロリドン、フッ素化カルボン酸エステルなどの非プロトン性有機溶媒を一種又は二種以上を混合して使用し、これらの有機溶媒に溶解するリチウム塩を溶解させる。リチウム塩としては、リチウムイミド塩、ＬｉＰＦ_６、ＬｉＡｓＦ_６、ＬｉＡｌＣｌ_４、ＬｉＣｌＯ_４、ＬｉＢＦ_４、ＬｉＳｂＦ_６などがあげられる。
【００７０】
本発明において電解液に、性質の異なる添加剤を混合させて負極表面に性質の異なる皮膜を形成することも有効である。
【００７１】
具体的にはイミド化合物と遷移金属化合物を溶解させ、更に一般式（１）に示されるスルホン酸無水物を溶解させる場合と、遷移金属カチオンとイミドアニオンからなる金属錯体をあらかじめ溶解させ、更に一般式（１）に示されるスルホン酸無水物を溶解させる場合の二つの方法により作製される。
【００７２】
これらの方法はスルホン酸無水物による皮膜形成の他に、前者は、イミド化合物と遷移金属とが充放電過程を経て負極上で金属錯体を形成するものである。後者は金属錯体をあらかじめ合成し、これを電解液に溶解することで負極上に吸着させるものである。このイミドアニオンを含んだ金属錯体は電解液中で負極表面上に均一に皮膜を形成することによって、充電時に均一な電場を整え、平滑でスムーズなリチウム吸蔵または析出過程を与える。特に、リチウム金属を用いた場合、負極上に生成する皮膜は化学的、物理的に強固かつ低抵抗なものとなる。
【００７３】
表面膜の成分は、一部析出した遷移金属と、リチウムとイミドアニオンに含まれるフッ素の反応により生成したフッ化リチウムである。析出した遷移金属はリチウムと合金を形成することで安定化し、フッ化リチウムは化学的、物理的に安定な化合物である。
【００７４】
イミド化合物と遷移金属を溶解させ更に前記スルホン酸無水物を溶解させる場合、電解液に含まれるイミド化合物や遷移金属は、特に限定されないが、好ましくは電界液全体に対して、０．００５〜１０ｗｔ％が好ましい。０．００５ｗｔ％未満では、電極表面全体に添加剤の効果が行き渡らず、また１０Ｗｔ％を越えると電解液の粘性が増大するために液抵抗が大きくなるためである。この時、電解液全体に含まれるスルホン酸無水物は０．０１〜１０ｗｔ％が好ましい。０．０１ｗｔ％未満では、電極表面全体に添加剤の効果が行き渡らず、また１０Ｗｔ％を越えると電解液の粘性が増大するために液抵抗が大きくなるためである。
【００７５】
遷移金属カチオンとイミドアニオンからなる金属錯体をあらかじめ溶解させ、更に前記スルホン酸無水物を溶解させる場合電解液に含まれる金属錯体は、特に限定されないが、電界液全体に対して、０．００５〜１０ｗｔ％が好ましい。０．００５ｗｔ％未満では、電極表面全体に添加剤の効果が行き渡らず、また１０Ｗｔ％を越えると電解液の粘性が増大するために液抵抗が大きくなるためである。この時、電解液全体に含まれる前記スルホン酸無水物は０．０１〜１０ｗｔ％が好ましい。０．０１ｗｔ％未満では、電極表面全体に添加剤の効果が行き渡らず、また１０ｗｔ％を越えると電解液の粘性が増大するために液抵抗が大きくなるためである。
【００７６】
前記遷移金属としては、ランタノイド系遷移金属が好ましく、ユーロピウム（Ｅｕ）、ネオジウム（Ｎｄ）、エルビウム（Ｅｒ）、ホルミウム（Ｈｏ）のいずれかもしくは混合物が好ましい。これは、Ｅｕ、Ｎｄ、Ｅｒ、Ｈｏの酸化還元電位が黒鉛、合金、リチウム金属のそれと同じもしくは近く、リチウムよりも０Ｖ〜０．８Ｖ高い電位で還元可能であることによる。
【００７７】
このように負極活物質の酸化還元電位と近い金属を選択し、これらと安定な錯体を形成するアニオンを選ぶことにより、これらの金属が容易に還元されなくなる。従って、本発明で示したランタノイド系遷移金属カチオンとイミドアニオンからなる錯体は、負極と電解液の界面により安定に存在することができる。
【００７８】
イミドアニオンとしては、⁻Ｎ（Ｃ_ｎＦ_２ｎ＋１ＳＯ_２）（Ｃ_ｍＦ_２ｍ＋１ＳＯ_２）（ｎ，ｍは自然数）が好ましく、特に、アルミ腐食抑制の点からパーフルオロエチルスルフォニルイミドアニオン［⁻Ｎ（Ｃ_２Ｆ_５ＳＯ_２）_２］が好ましい。
【００７９】
さらに、皮膜が機械的に壊れた際には、その壊れた箇所において、負極表面のリチウムと負極表面に吸着した上記イミドアニオンとの反応生成物であるフッ化リチウムが、皮膜を修復する機能を有しており、皮膜が破壊された後においても、安定な表面化合物の生成を導く効果を有している。
【００８０】
本発明に係る負極は、上述のように、リチウム金属、リチウム合金または炭素材料や酸化物等のリチウムを吸蔵、放出できる材料により構成されている。
【００８１】
この炭素材料としては、リチウムを吸蔵する黒鉛、非晶質炭素、ダイヤモンド状炭素、カーボンナノチューブなど、あるいはこれらの複合物を用いることができる。
【００８２】
また、酸化物としては、酸化シリコン、酸化スズ、酸化インジウム、酸化亜鉛、酸化リチウム、リン酸、ホウ酸のいずれか、あるいはこれらの複合物を用いてもよく、特に酸化シリコンを含むことが好ましい。構造としてはアモルファス状態であることが好ましい。これは、酸化シリコンが安定で他の化合物との反応を引き起こさないため、またアモルファス構造が結晶粒界、欠陥といった不均一性に起因する劣化を導かないためである。成膜方法としては、蒸着法、ＣＶＤ法、スパッタリング法などの方法を用いることができる。
【００８３】
リチウム合金とは、リチウムおよびリチウムと合金形成可能な金属により構成される。例えば、Ａｌ、Ｓｉ、Ｐｂ、Ｓｎ、Ｉｎ、Ｂｉ、Ａｇ、Ｂａ、Ｃａ、Ｈｇ、Ｐｄ、Ｐｔ、Ｔｅ、Ｚｎ、Ｌａなどの金属とリチウムとの２元または３元以上の合金により構成される。リチウム金属やリチウム合金としては、特にアモルファス状のものが好ましい。これは、アモルファス構造により結晶粒界、欠陥といった不均一性に起因する劣化が起きにくいためである。
【００８４】
リチウム金属またはリチウム合金は、融液冷却方式、液体急冷方式、アトマイズ方式、真空蒸着方式、スパッタリング方式、プラズマＣＶＤ方式、光ＣＶＤ方式、熱ＣＶＤ方式、ゾルーゲル方式、などの適宜な方式で形成することができる。
【００８５】
本発明において、遷移金属カチオンとイミドアニオンからなる錯体を電解質溶液との界面に存在させると、負極は、金属、合金相の体積変化に対する柔軟性、イオン分布の均一性、物理的・化学的安定性に優れたものとなるので好ましい。その結果、デンドライト生成やリチウムの微粉化を効果的に防止することができ、サイクル効率と寿命が向上する。
【００８６】
また、負極として炭素材料や酸化物材料を用いたときにその表面に存在するダングリングボンドは化学的活性が高く、容易に溶媒を分解させることになる。この表面に、遷移金属カチオンとイミドアニオンからなる錯体を吸着させることによって、溶媒の分解が抑制され、不可逆容量が大きく減少するため、充放電効率が減少しない。
【００８７】
本発明において、正極活物質としては、例えば、ＬｉＣｏＯ_２、ＬｉＮｉＯ_２、ＬｉＭｎ_２Ｏ_４などのリチウム含有複合酸化物があげられ、これらのリチウム含有複合酸化物の遷移金属部分を他元素で置き換えたものでもよい。
【００８８】
また、金属リチウム対極電位で４．５Ｖ以上にプラトーを有するリチウム含有複合酸化物を用いることもできる。リチウム含有複合酸化物としては、スピネル型リチウムマンガン複合酸化物、オリビン型リチウム含有複合酸化物、逆スピネル型リチウム含有複合酸化物等が例示される。リチウム含有複合酸化物は、例えば下記一般式（４）で表される化合物とすることができる。
【００８９】
【化７】
Ｌｉ_ａ（Ｍ_ｘＭｎ_２−ｘ）Ｏ_４　　　　　　　　（４）
式中、０＜ｘ＜２、０＜ａ＜１．２である。Ｍは、Ｎｉ、Ｃｏ、Ｆｅ、ＣｒおよびＣｕよりなる群から選ばれる少なくとも一種である。
【００９０】
本発明における正極は、これらの活物質を、カーボンブラック等の導電性物質、ポリビニリデンフルオライド（ＰＶＤＦ）等の結着剤とともにＮ−メチル−２−ピロリドン（ＮＭＰ）等の溶剤中に分散混練し、これをアルミニウム箔等の基体上に塗布することにより得ることができる。
【００９１】
本発明に係るリチウム二次電池は、乾燥空気または不活性ガス雰囲気において、負極および正極を、セパレータを介して積層、あるいは積層したものを捲回した後に、電池缶に収容したり、合成樹脂と金属箔との積層体からなる可とう性フィルム等によって封口することによって電池を製造することができる。
【００９２】
なお、セパレータとしては、ポリプロピレン、ポリエチレン等のポリオレフィン、フッ素樹脂等の多孔性フィルムが用いられる。
【００９３】
本発明に係る二次電池の形状としては、特に制限はないが、例えば、円筒型、角型、コイン型などがあげられる。
【００９４】
【実施例】
（実施例１）
（電池の作製）
正極は正極集電体として厚み２０μｍのアルミニウム箔を用い、正極活物質としてＬｉＭｎ_２Ｏ_４を用いた。負極として負極集電体としての厚み１０μｍの銅箔上に負極活物質として厚み２０μｍリチウム金属を蒸着したものを用いた。また、電解質溶液は、溶媒としてＥＣとＤＥＣの混合溶媒（体積比：３０／７０）を用い、支持電解質としてＬｉＮ（Ｃ_２Ｆ_５ＳＯ_２）_２（以下、ＬｉＢＥＴＩと略記）を１ｍｏｌＬ^−１溶解し、さらに、スルホン酸無水物として上記表１に記載の化合物Ｎｏ．５を電解液中に１ｗｔ％含まれるように加えた。そして、負極と正極とをポリエチレンからなるセパレータを介して積層し、本実施例の二次電池を作製した。
【００９５】
（充放電サイクル試験）
温度２０℃において、充電レート０．０５Ｃ、放電レート０．１Ｃ、充電終止電圧４．２Ｖ、放電終止電圧３．０Ｖ、リチウム金属負極の利用率（放電深度）は３３％とした。容量維持率（％）は４００サイクル後の放電容量（ｍＡｈ）を、１０サイクル目の放電容量（ｍＡｈ）で割った値である。サイクル試験で得られた結果を下記表４に示す。
【００９６】
（実施例２〜４）
実施例１において、化合物Ｎｏ．５の代わりに、表４に示すスルホン酸無水物を用いる他は、実施例１と同様にして二次電池を作製した。以下、実施例１と同様に電池の特性を調べた。結果を表４に示す。
【００９７】
（比較例１）
実施例１において、化合物Ｎｏ．５を添加しない他は、実施例１と同様にして二次電池を作製した。以下、実施例１と同様に電池の特性を調べた。結果を表４に示す。
【００９８】
（比較例２）
実施例１において、化合物Ｎｏ．５に代えてメタンスルホン酸無水物を用いる他は、実施例１と同様にして二次電池を作製した。以下、実施例１と同様に電池の特性を調べた。結果を表４に示す。
【００９９】
【表４】

【０１００】
実施例１〜４に示した電池は、比較例１、２と比較して、サイクル試験後の容量維持率が向上していること、すなわちサイクル特性が改善していることが確認された。
【０１０１】
（実施例５）
実施例１において、支持電解質としてＬｉＢＥＴＩに代えてＬｉＰＦ_６を用い、負極として、黒鉛粉末に結着材としてＮ−メチル−２−ピロリドンに溶解したポリフッ化ビニリデンと導電付与材を混合しペースト状にしたものを銅箔に塗布し、乾燥させたものを用いる他は、実施例１と同様にして二次電池を作製した。以下、実施例１と同様に電池の特性を調べた。結果を表５に示す。
【０１０２】
（実施例６〜８）
実施例５において、化合物Ｎｏ．５に代えて表５に示すスルホン酸無水物を用いる他は、実施例５と同様にして二次電池を作製した。以下、実施例５と同様に電池の特性を調べた。結果を表５に示す。
【０１０３】
（比較例３）
実施例５において、化合物Ｎｏ．５を添加しない他は、実施例５と同様にして二次電池を作製した。以下、実施例５と同様に電池の特性を調べた。結果を表５に示す。
【０１０４】
【表５】

【０１０５】
実施例５〜８に示した電池は、比較例３と比較して、サイクル試験後の容量維持率が向上していること、すなわちサイクル特性が改善していることが確認された。
【０１０６】
（実施例９）
実施例５において、黒鉛に代えて非晶質炭素を用い、電解液の主溶媒をＰＣ／ＥＣ／ＤＥＣ（体積比：２０／２０／６０）とする他は、実施例５と同様にして二次電池を作製した。以下、実施例５と同様に電池の特性を調べた。結果を表６に示す。
【０１０７】
（実施例１０〜１２）
実施例９において、化合物Ｎｏ．５に代えて表６に示すスルホン酸無水物を用いる他は、実施例９と同様にして二次電池を作製した。以下、実施例９と同様に電池の特性を調べた。結果を表６に示す。
【０１０８】
（比較例４）
実施例９において、化合物Ｎｏ．５を添加しない他は、実施例９と同様にして二次電池を作製した。以下、実施例９と同様に電池の特性を調べた。結果を表６に示す。
【０１０９】
【表６】

【０１１０】
実施例９〜１２に示した電池は、比較例４と比較して、サイクル試験後の容量維持率が向上していること、すなわちサイクル特性が改善していることが確認された。
【０１１１】
（実施例１３）
実施例１において、電解液にさらに１，３−プロパンスルトン（以下、１，３−ＰＳと略記）が１ｗｔ％含まれるようにする他は、実施例１と同様にして二次電池を作製した。以下、実施例１と同様に電池の特性を調べた。結果を表７に示す。
【０１１２】
（実施例１４〜１６）
実施例１３において、化合物Ｎｏ．５に代えて表７に示すスルホン酸無水物を用いる他は、実施例１３と同様にして二次電池を作製した。以下、実施例１３と同様に電池の特性を調べた。結果を表７に示す。
【０１１３】
【表７】

【０１１４】
実施例１３〜１６に示した電池は、実施例１〜４及び比較例１と比較して、サイクル試験後の容量維持率が向上していること、すなわちサイクル特性が改善していることが確認された。これは、添加剤として使用した一般式（１）で示されるスルホン酸無水物と１，３−ＰＳとの複合効果によるものである。
【０１１５】
（実施例１７）
実施例５において、電解液にさらに１，３−プロパンスルトン（以下、１，３−ＰＳと略記）が１ｗｔ％含まれるようにする他は、実施例５と同様にして二次電池を作製した。以下、実施例５と同様に電池の特性を調べた。結果を表８に示す。
【０１１６】
（実施例１８〜２０）
実施例１７において、化合物Ｎｏ．５に代えて表８に示すスルホン酸無水物を用いる他は、実施例１７と同様にして二次電池を作製した。以下、実施例１７と同様に電池の特性を調べた。結果を表８に示す。
【０１１７】
【表８】

【０１１８】
実施例１７〜２０に示した電池は、実施例５〜８及び比較例３と比較して、サイクル試験後の容量維持率が向上していること、すなわちサイクル特性が改善していることが確認された。これは、添加剤として使用した一般式（１）で示されるスルホン酸無水物と１，３−ＰＳとの複合効果によるものである。
【０１１９】
（実施例２１）
実施例９において、電解液にさらに１，３−プロパンスルトン（以下、１，３−ＰＳと略記）が１ｗｔ％含まれるようにする他は、実施例９と同様にして二次電池を作製した。以下、実施例９と同様に電池の特性を調べた。結果を表９に示す。
【０１２０】
（実施例２２〜２４）
実施例２１において、化合物Ｎｏ．５に代えて表９に示すスルホン酸無水物を用いる他は、実施例２１と同様にして二次電池を作製した。以下、実施例２１と同様に電池の特性を調べた。結果を表９に示す。
【０１２１】
【表９】

【０１２２】
実施例２１〜２４に示した電池は、実施例９〜１２及び比較例４と比較して、サイクル試験後の容量維持率が向上していること、すなわちサイクル特性が改善していることが確認された。これは、添加剤として使用した一般式（１）で示されるスルホン酸無水物と１，３−ＰＳとの複合効果によるものである。
【０１２３】
（実施例２５〜２８）
実施例９において、電解液にさらにＣＦ_３ＳＯ_３ ⁻アニオンを持つ表１０に示すランタニド系遷移金属イオンの塩が０．３ｗｔ％含まれるようにする他は、実施例９と同様にして二次電池を作製した。以下、実施例９と同様に電池の特性を調べた。結果を表１０に示す。
【０１２４】
【表１０】

【０１２５】
実施例２５〜２８の電池は、いずれも比較例４及び実施例９と比較して、サイクル試験後の容量維持率が向上していること、すなわちサイクル特性が改善していることが確認された。
【０１２６】
（実施例２９〜３２）
実施例９において、電解液にさらに表１１に示すランタニド系遷移金属錯体が０．１ｗｔ％含まれるようにする他は、実施例９と同様にして二次電池を作製した。以下、実施例９と同様に電池の特性を調べた。結果を表１１に示す。
【０１２７】
【表１１】

【０１２８】
実施例２９〜３２の電池は、いずれも比較例４及び実施例９と比べ、サイクル特性が改善されたことが確認された。
【０１２９】
（実施例３３）
実施例９において、電解液にさらにビニレンカーボネート（以下、ＶＣと略記）が１ｗｔ％含まれるようにする他は、実施例９と同様にして二次電池を作製した。以下、実施例９と同様に電池の特性を調べた。結果を表１２に示す。
【０１３０】
（実施例３４〜３６）
実施例３３において、化合物Ｎｏ．５に代えて表１２に示すスルホン酸無水物を用いる他は、実施例３３と同様にして二次電池を作製した。以下、実施例３３と同様に電池の特性を調べた。結果を表１２に示す。
【０１３１】
【表１２】

実施例３３〜３６に示した電池は、比較例４や実施例９〜１２と比較して、サイクル試験後の容量維持率が向上していること、すなわちサイクル特性が改善していることが確認された。
【０１３２】
【発明の効果】
本発明によれば、非プロトン性溶媒に、少なくとも上記一般式（１）に示すスルホン酸無水物が含まれる電解液を使用して二次電池を作製した場合に、得られた二次電池は充放電効率に優れ、サイクル特性が良好な、安全性に優れたリチウム二次電池を得ることができる。
【図面の簡単な説明】
【図１】本発明に係る二次電池の概略構成図である。
【符号の説明】
１１　　　正極集電体
１２　　　正極活物質を含有する層
１３　　　負極活物質を含有する層
１４　　　負極集電体
１５　　　非水電解質溶液
１６　　　多孔質セパレータ[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a secondary battery electrolyte and a secondary battery using the same.
[0002]
[Prior art]
Non-aqueous electrolyte lithium-ion or lithium secondary batteries using carbon materials, oxides, lithium alloys or lithium metal for the negative electrode are attracting attention as power sources for mobile phones and notebook computers because of their high energy density .
[0003]
In this secondary battery, it is known that a film (hereinafter, referred to as a surface film) called a surface film, a protective film, an SEI, or a film is formed on the surface of the negative electrode. It is known that control of the surface film is indispensable for improving the performance of the negative electrode because the surface film has a large effect on charge / discharge efficiency, cycle life, and safety.
[0004]
It is necessary to reduce the irreversible capacity of carbon materials and oxide materials, and it is necessary to solve the problems of safety due to reduction of charge / discharge efficiency and generation of dendrites (dendritic crystals) in lithium metal and alloy negative electrodes.
[0005]
Various methods have been proposed as methods for solving these problems. For example, it has been proposed to suppress the generation of dendrites by providing a coating layer made of lithium fluoride or the like on the surface of lithium metal or a lithium alloy using a chemical reaction.
[0006]
JP-A-7-302617 discloses a technique in which a lithium negative electrode is exposed to an electrolytic solution containing hydrofluoric acid and the negative electrode is reacted with hydrofluoric acid to cover the surface with a lithium fluoride film. ing.
[0007]
Hydrofluoric acid is LiPF₆And a small amount of water. On the other hand, a surface film of lithium hydroxide or lithium oxide is formed on the surface of the lithium negative electrode by natural oxidation in air. When these react, a surface film of lithium fluoride is formed on the surface of the negative electrode.
[0008]
However, this lithium fluoride film is formed by utilizing the reaction between the electrode interface and the liquid, and the side reaction components easily mix into the surface film, and it is difficult to obtain a uniform film. In addition, there are cases where the surface film of lithium hydroxide or lithium oxide is not formed uniformly, or where there is a part where lithium is exposed, and in these cases, a uniform thin film cannot be formed. Alternatively, there is a safety problem due to the reaction of lithium with water or hydrogen fluoride. In addition, when the reaction is insufficient, unnecessary compound components other than the fluoride remain, which may adversely affect the ion conductivity.
[0009]
Furthermore, in the method of forming a fluoride layer using such a chemical reaction at the interface, the selection range of available fluorides and electrolytes is limited, and it is difficult to form a stable surface film with good yield. there were.
[0010]
In JP-A-8-250108, a mixed gas of argon and hydrogen fluoride is reacted with an aluminum-lithium alloy to obtain a lithium fluoride surface film on the negative electrode surface.
[0011]
However, when a surface film already exists on the surface of the lithium metal, particularly when a plurality of types of compounds are present, the reaction tends to be non-uniform, and it is difficult to form a uniform film of lithium fluoride. For this reason, it is difficult to obtain a lithium secondary battery having sufficient cycle characteristics.
[0012]
Japanese Patent Application Laid-Open No. H11-288706 discloses that a uniform film structure, that is, a surface film structure mainly composed of a material having a rock salt type crystal structure is formed on the surface of a lithium sheet in which (100) crystal planes are preferentially oriented. A forming technique is disclosed. By doing so, a uniform precipitation-dissolution reaction, that is, charge / discharge of the battery can be performed, dendrite precipitation of lithium metal can be suppressed, and the cycle life of the battery can be improved.
[0013]
It is stated that the material used for the surface film preferably has a halide of lithium, and it is preferable to use a solid solution of LiF and at least one selected from LiCl, LiBr and LiI.
[0014]
Specifically, in order to form a solid solution film of at least one of LiCl, LiBr, and LiI and LiF, a lithium sheet formed by pressing (rolling) and having a (100) crystal plane preferentially oriented is used. A negative electrode for a non-aqueous electrolyte battery is manufactured by immersing in an electrolyte containing at least one of chlorine molecules or chlorine ions, bromine molecules or bromine ions, iodine molecules or iodine ions and fluorine molecules or fluorine ions. .
[0015]
In the case of this technique, a rolled lithium metal sheet is used, and since the lithium sheet is easily exposed to the air, a film derived from moisture or the like is easily formed on the surface, and the existence of active points becomes non-uniform, and the intended purpose is obtained. It became difficult to form a stable surface film, and the effect of suppressing dendrite was not always sufficiently obtained.
[0016]
In addition, when a carbon material such as graphite or amorphous carbon capable of occluding and releasing lithium ions is used as a negative electrode, a technique for improving capacity and charge / discharge efficiency has been reported.
[0017]
Japanese Patent Application Laid-Open No. H5-223483 proposes a negative electrode in which a carbon material is coated with aluminum. Thereby, reductive decomposition of solvent molecules solvated with lithium ions on the carbon surface is suppressed, and deterioration of cycle life is suppressed. However, since aluminum reacts with a very small amount of water, there is a problem that the capacity is rapidly reduced when the cycle is repeated.
[0018]
Japanese Patent Application Laid-Open No. H5-275077 discloses a negative electrode in which the surface of a carbon material is coated with a thin film of a lithium ion conductive solid electrolyte. It is stated that this can suppress the decomposition of the solvent that occurs when the carbon material is used, and provide a lithium ion secondary battery that can use propylene carbonate in particular.
[0019]
However, cracks generated in the solid electrolyte due to stress changes at the time of lithium ion insertion and desorption lead to characteristic deterioration. In addition, due to non-uniformity such as crystal defects of the solid electrolyte, a uniform reaction cannot be obtained on the negative electrode surface, leading to a deterioration in cycle life.
[0020]
In Japanese Patent Application Laid-Open No. 2000-3724, the negative electrode is made of a material containing graphite, contains cyclic carbonate and chain carbonate as main components as an electrolytic solution, and contains 0.1 wt% or more and 4 wt% or less in the electrolytic solution. A secondary battery containing 1,3-propane sultone and / or 1,4-butane sultone is disclosed.
[0021]
Here, 1,3-propane sultone and 1,4-butane sultone contribute to the formation of a passive film on the surface of the carbon material, and passivate the active and highly crystallized carbon material such as natural graphite and artificial graphite. It is considered that the coating has the effect of suppressing the decomposition of the electrolytic solution without impairing the normal reaction of the battery.
[0022]
Naoi et al., 2000 Electrochemical Fall Conference (September 2000, Chiba Institute of Technology, lecture number: 2A24), 41st Battery Symposium (November 2000, Nagoya International Convention Center, lecture number: 1E03) Report on the effect of a complex of lanthanide transition metal such as europium and imide anion on lithium metal anode.
[0023]
Here, LiN (C) is used as a lithium salt in a mixed solvent of propylene carbonate or ethylene carbonate and 1,2-dimethoxyethane.₂F₅SO₂)₂Is further added to the electrolyte in which Eu (CF) is dissolved.₃SO₃)₃Was added as an additive, and Eu [(C) was added on the Li metal immersed in the electrolytic solution.₂F₅SO₂)₂]₃A surface film composed of a complex is formed.
[0024]
[Problems to be solved by the invention]
However, the above prior art has the following common problems.
[0025]
The surface film formed on the negative electrode surface is closely related to the charge / discharge efficiency, cycle life and safety by its properties, but there is no method capable of controlling the film for a long time.
[0026]
For example, when a surface film made of a lithium halide or a glassy oxide is formed on a layer made of lithium or an alloy thereof, the effect of suppressing dendrite can be obtained to a certain extent at the time of initial use, but when used repeatedly, The surface film is deteriorated and the function as a protective film is reduced.
[0027]
This is because a layer made of lithium or an alloy thereof changes its volume by absorbing and releasing lithium, while a film made of lithium halide and the like located on the top hardly changes its volume. It is considered that the internal stress is generated at the interface.
[0028]
It is considered that the generation of such internal stress particularly damages a part of the surface film made of lithium halide or the like, and reduces the function of suppressing dendrite.
[0029]
As for carbon materials such as graphite, as described above, compounds having a sulfonyl group such as 1,3-propane sultone are used as additives for the electrolytic solution. However, a sufficient film effect cannot be obtained, and solvent molecules or The charge due to the decomposition of the anion appears as an irreversible capacity component, leading to a decrease in the initial charge / discharge efficiency. Further, the composition, crystal state, stability, and the like of the film generated at this time have a great effect on the subsequent efficiency and cycle life.
[0030]
Further, the decomposition of the solvent of the electrolytic solution by the trace amount of water present in the graphite or the amorphous carbon negative electrode was promoted. When graphite or an amorphous carbon negative electrode is used, it is necessary to remove water molecules.
[0031]
In the method of forming an organic surface film on a Li metal surface studied by Naoi et al., Although a certain effect is obtained in improving the cycle life compared with the above-mentioned conventional technology, it is not yet sufficient.
[0032]
In this way, studies have been made to improve the charge / discharge efficiency and cycle life by forming a film on the negative electrode for secondary batteries, but no sufficient characteristics have yet been obtained, The biggest issue is how to form a film that leads to sufficient charge and discharge efficiency.
[0033]
[Means for Solving the Problems]
As a result of intensive studies, the present inventors have found that when a secondary battery is manufactured by applying an electrolytic solution containing at least a sulfonic anhydride represented by the general formula (1) to an aprotic solvent, It has been found that the obtained secondary battery has excellent charge / discharge efficiency and good cycle characteristics, and has led to the present invention.
[0034]
Embedded image

Here, X is an alkylene group having 2 to 4 carbon atoms which may have a substituent, an alkenylene group having 2 to 4 carbon atoms which may have a substituent, or an aromatic group which may have a substituent The ring and the heterocyclic ring which may have a substituent are shown.
[0035]
As the substituent, a halogen atom, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkoxy group, a substituted or unsubstituted cycloalkyl group, a substituted or unsubstituted aryl group, a substituted or unsubstituted heterocyclic ring The groups can be exemplified as preferred.
[0036]
Specifically, a compound represented by the following general formula (2) is effective.
[0037]
Embedded image

Where R₁~ R₄Are each independently a hydrogen atom, a halogen atom, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkoxy group, a substituted or unsubstituted cycloalkyl group, a substituted or unsubstituted aryl group, a substituted or unsubstituted heterocyclic group. Shows a ring group. Further, R1 to R4 may be condensed with each other to form an aryl ring which may have a substituent or a heterocyclic ring which may have a substituent.
[0038]
Further, a plurality of sulfonic anhydride groups may be present in the molecule.
[0039]
Representative examples of the compound of the general formula (1) of the present invention are specifically shown in Tables 1 to 3, but the present invention is not limited thereto.
[0040]
[Table 1]

[0041]
[Table 2]

[0042]
[Table 3]

[0043]
The proportion of the sulfonic anhydride represented by the general formula (1) in the electrolytic solution is not particularly limited, but is preferably contained at 0.01 to 10 wt% of the entire electrolytic solution. If it is less than 0.01 wt%, it is difficult to obtain a sufficient film effect. If it exceeds 10% by weight, the resistance increases, such as increasing the viscosity of the electrolytic solution, which is not preferable.
[0044]
In the present invention, the sulfonic anhydride of the general formula (1) may be added to the aprotic organic solvent, and an imide anion and a transition metal ion may be further added. Further, a metal complex comprising at least an imide anion and a transition metal may be added to an electrolytic solution obtained by dissolving a lithium salt as an electrolyte salt in an aprotic organic solvent.
[0045]
In the case of a system in which an imide anion and a transition metal ion are present, a metal complex of the imide anion and the transition metal is formed on the surface of the negative electrode by charge and discharge. No. 2A24), 41st Battery Symposium (November 2000, Nagoya International Congress Center, Lecture No .: 1E03)).
[0046]
When a metal complex of an imide anion and a transition metal ion is present, the metal complex is adsorbed on the negative electrode surface regardless of charge and discharge.
[0047]
The presence of the two compounds of the metal complex of the imide anion and the transition metal ion and the sulfonic anhydride on the negative electrode surface has the following effects.
[0048]
On the surface of the negative electrode, there are dangling bonds that cause a reaction with solvent molecules, and non-reactive sites. The metal complex formed by the imide salt to be added and the metal complex formed by the imide salt and the transition metal form a stabilized film by adsorbing to the non-reactive site, thereby performing lithium ion conduction.
[0049]
Further, the sulfonic anhydride, which is an important additive in the present invention, contributes to the formation of a passive film on the surface of the negative electrode, and as a result, suppresses the decomposition of solvent molecules. Further, the sulfonic anhydride reacts with a small amount of water present in the negative electrode and the electrolytic solution, and is effective in removing water.
[0050]
Specific examples of the imide anion include:⁻N (C_nF_{2n + 1}SO₂) (C_mF_{2m + 1}SO₂) (N and m are natural numbers).
[0051]
The transition metal used here is preferably a lanthanoid transition metal, particularly preferably europium (Eu), neodymium (Nd), erbium (Er) or holmium (Ho).
[0052]
The imide anion or its metal complex is preferably contained in the electrolyte at 0.005 to 10 wt%. If the amount is less than 0.005 wt%, a sufficient effect on the formation of a film on the negative electrode surface may not be obtained. On the other hand, if the amount exceeds 10 wt%, not only does not dissolve but also the viscosity of the electrolytic solution is increased, which is not preferable. In the present invention, it is more preferably in the range of 0.05 to 5 wt%.
[0053]
It is also effective to further add a compound having a sulfonyl group other than the general formula (1) to the electrolytic solution containing the sulfonic anhydride represented by the general formula (1). By adding a compound having a sulfonyl group other than those represented by the general formula (1), the effect of adjusting the viscosity, improving the stability of the film due to the composite effect, and suppressing the solvent molecules is increased.
[0054]
Specific examples of compounds having a sulfonyl group other than those represented by the general formula (1) include sulfolane (JP-A-60-154478), 1,3-propanesultone and 1,4-butanesultone (JP-A- 62-100948, JP-A-63-102173, JP-A-11-339850, JP-A-2000-3724), alkanesulfonic anhydride (JP-A-10-189041), 1,3 , 2-dioxaphosphorane-2-oxide derivative (JP-A-10-50342), γ-sultone compound (JP-A-2000-235866), sulfolene derivative (JP-A-2000-294278) and the like. However, the present invention is not limited to these. Particularly preferred is a sultone compound represented by the following general formula (3).
[0055]
Embedded image

Here, n is an integer of 0 to 2. Also, R₁~ R₆Each independently represents a hydrogen atom, an alkyl group having 1 to 12 carbon atoms, a cycloalkyl group having 3 to 6 carbon atoms, or an aryl group having 6 to 12 carbon atoms.
[0056]
The compound having a sulfonyl group is preferably contained in the electrolytic solution at 0.01 to 10% by weight. If the amount is less than 0.01 wt%, the film formation on the negative electrode surface is not sufficiently effective. Exceeding 10 wt% is not preferable because it not only dissolves but also increases the viscosity of the electrolytic solution. In the present invention, the content is more preferably in the range of 0.05 to 5 wt%.
[0057]
Further, according to the present invention, the cycle characteristics can be further improved by adding or mixing vinylene carbonate or a derivative thereof to the electrolytic solution containing the sulfonic anhydride represented by the general formula (1).
[0058]
Vinylene carbonate or a derivative thereof is described in, for example, JP-A-4-1690075, JP-A-7-122296, JP-A-8-45545, JP-A-5-82138, JP-A-5-74486, The compounds described in JP-A-6-52887, JP-A-11-260401, JP-A-2000-208169, JP-A-2001-35530, and JP-A-2000-138071 can be appropriately used. .
[0059]
When vinylene carbonate or a derivative thereof is used as an additive, the effect can be obtained by adding 0.01 to 10% by weight of the electrolyte solution. When used as a solvent, the effect can be obtained by adding 1 to 50% by weight.
[0060]
The aprotic organic solvents used in the present invention are cyclic carbonates, chain carbonates, aliphatic carboxylic acid esters, γ-lactones, cyclic ethers, chain ethers and fluorinated derivatives thereof, From these, one type or a mixture of two or more types is used as appropriate.
[0061]
In the present invention, as the lithium salt, LiPF₆, LiBF₄, LiAsF₆, LiSbF₆, LiClO₄, LiAlCl₄, LiN (C_nF_{2n + 1}SO₂) (C_mF_{2m + 1}SO₂) (N and m are natural numbers).₆, LiBF₄Is preferred.
[0062]
Further, according to the present invention, there is provided a secondary battery using the above electrolyte solution for a secondary battery, comprising a positive electrode and a negative electrode using lithium as an active material.
[0063]
As the negative electrode, a negative electrode active material including a material capable of inserting and extracting lithium, a lithium metal, a metal material capable of forming an alloy with lithium, and an oxide material is used.
[0064]
Here, a material containing carbon is preferable as a material capable of inserting and extracting lithium, and particularly, graphite and amorphous carbon are preferable.
[0065]
In the present invention, the negative electrode and the positive electrode are further combined with a separator interposed therebetween, inserted into a battery outer package, and impregnated with an electrolytic solution containing the compound represented by the general formula (1), and then the battery outer package is sealed or sealed. After stopping, the battery is charged if necessary, and a film is formed on the negative electrode to provide a secondary battery.
[0066]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 shows a schematic structure of an example of the battery according to the present invention.
[0067]
The battery of the present invention includes a positive electrode current collector 11, a layer 12 containing a positive electrode active material composed of any one or a mixture of an oxide or a sulfur compound capable of occluding and releasing lithium ions, a conductive polymer, and a stabilized radical compound. A layer 13 containing a negative electrode active material composed of any one of a carbon material or oxide that absorbs and releases lithium ions, a metal that forms an alloy with lithium, and lithium metal itself, or a mixture thereof; a negative electrode current collector 14; It is composed of a liquid 15 and a porous separator 16 containing it.
[0068]
Here, the sulfonic anhydride represented by the general formula (1) is contained in the electrolytic solution 15.
[0069]
Examples of the electrolyte in the present invention include cyclic carbonates such as propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate (BC), and vinylene carbonate (VC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl carbonate. Chain carbonates such as methyl carbonate (EMC) and dipropyl carbonate (DPC); aliphatic carboxylic acid esters such as methyl formate, methyl acetate and ethyl propionate; γ-lactones such as γ-butyrolactone; Chain ethers such as ethoxyethane (DEE) and ethoxymethoxyethane (EME), cyclic ethers such as tetrahydrofuran and 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolan, formamide, acetamide, Dimethylformamide, acetonitrile, propylnitrile, nitromethane, ethyl monoglyme, phosphoric acid triester, trimethoxymethane, dioxolane derivative, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, 3-methyl-2-oxazolidinone Aprotic organic solvents such as propylene carbonate derivatives, tetrahydrofuran derivatives, ethyl ether, 1,3-propane sultone, anisole, N-methylpyrrolidone, fluorinated carboxylic esters, or a mixture of two or more, The lithium salt dissolved in these organic solvents is dissolved. As the lithium salt, lithium imide salt, LiPF₆, LiAsF₆, LiAlCl₄, LiClO₄, LiBF₄, LiSbF₆And so on.
[0070]
In the present invention, it is also effective to mix additives having different properties with the electrolyte to form films having different properties on the negative electrode surface.
[0071]
Specifically, an imide compound and a transition metal compound are dissolved, and further, a sulfonic anhydride represented by the general formula (1) is dissolved. It is prepared by two methods for dissolving the sulfonic anhydride represented by the formula (1).
[0072]
In these methods, in addition to the formation of a film using a sulfonic anhydride, the former forms a metal complex on a negative electrode through a charge / discharge process between an imide compound and a transition metal. In the latter, a metal complex is synthesized in advance, and the metal complex is dissolved in an electrolytic solution to be adsorbed on a negative electrode. The metal complex containing the imide anion forms a uniform film on the surface of the negative electrode in the electrolytic solution, thereby providing a uniform electric field during charging and providing a smooth and smooth lithium occlusion or precipitation process. In particular, when lithium metal is used, the film formed on the negative electrode is chemically and physically strong and has low resistance.
[0073]
The component of the surface film is lithium fluoride generated by the reaction between a partially precipitated transition metal, lithium and fluorine contained in the imide anion. The deposited transition metal is stabilized by forming an alloy with lithium, and lithium fluoride is a chemically and physically stable compound.
[0074]
When dissolving the imide compound and the transition metal and further dissolving the sulfonic anhydride, the imide compound and the transition metal contained in the electrolytic solution are not particularly limited, but preferably 0.005 to 10 wt. % Is preferred. If the content is less than 0.005% by weight, the effect of the additive does not reach the entire electrode surface, and if the content exceeds 10% by weight, the viscosity of the electrolyte increases and the liquid resistance increases. At this time, the amount of the sulfonic anhydride contained in the entire electrolyte is preferably 0.01 to 10% by weight. If the content is less than 0.01 wt%, the effect of the additive does not spread over the entire electrode surface, and if it exceeds 10 Wt%, the viscosity of the electrolyte increases and the liquid resistance increases.
[0075]
When a metal complex composed of a transition metal cation and an imide anion is previously dissolved, and the sulfonic anhydride is further dissolved, the metal complex contained in the electrolytic solution is not particularly limited. 10 wt% is preferred. If the content is less than 0.005% by weight, the effect of the additive does not reach the entire electrode surface, and if the content exceeds 10% by weight, the viscosity of the electrolyte increases and the liquid resistance increases. At this time, the amount of the sulfonic anhydride contained in the entire electrolytic solution is preferably 0.01 to 10% by weight. If the content is less than 0.01 wt%, the effect of the additive does not reach the entire surface of the electrode, and if it exceeds 10 wt%, the viscosity of the electrolyte increases and the liquid resistance increases.
[0076]
As the transition metal, a lanthanoid transition metal is preferable, and any one or a mixture of europium (Eu), neodymium (Nd), erbium (Er), and holmium (Ho) is preferable. This is because the redox potentials of Eu, Nd, Er, and Ho are the same as or close to those of graphite, alloy, and lithium metal, and can be reduced at a potential higher by 0 V to 0.8 V than lithium.
[0077]
As described above, by selecting metals close to the oxidation-reduction potential of the negative electrode active material and selecting anions that form stable complexes with these metals, these metals are not easily reduced. Therefore, the complex comprising the lanthanoid transition metal cation and the imide anion shown in the present invention can be more stably present at the interface between the negative electrode and the electrolyte.
[0078]
As the imide anion,⁻N (C_nF_{2n + 1}SO₂) (C_mF_{2m + 1}SO₂) (N and m are natural numbers), and in particular, a perfluoroethylsulfonylimide anion [⁻N (C₂F₅SO₂)₂Is preferred.
[0079]
Further, when the film is mechanically broken, lithium fluoride, which is a reaction product between lithium on the negative electrode surface and the imide anion adsorbed on the negative electrode surface, has a function of repairing the film at the broken portion. And has an effect of leading to the generation of a stable surface compound even after the film is broken.
[0080]
As described above, the negative electrode according to the present invention is made of a material capable of inserting and extracting lithium, such as lithium metal, a lithium alloy, or a carbon material or an oxide.
[0081]
As the carbon material, graphite that absorbs lithium, amorphous carbon, diamond-like carbon, carbon nanotube, or the like, or a composite thereof can be used.
[0082]
Further, as the oxide, any of silicon oxide, tin oxide, indium oxide, zinc oxide, lithium oxide, phosphoric acid, boric acid, or a composite thereof may be used, and it is particularly preferable to include silicon oxide. . The structure is preferably in an amorphous state. This is because silicon oxide is stable and does not cause a reaction with another compound, and the amorphous structure does not lead to deterioration due to non-uniformity such as crystal grain boundaries and defects. As a film formation method, a method such as an evaporation method, a CVD method, or a sputtering method can be used.
[0083]
The lithium alloy is composed of lithium and a metal capable of forming an alloy with lithium. For example, it is composed of a binary or ternary alloy of lithium and a metal such as Al, Si, Pb, Sn, In, Bi, Ag, Ba, Ca, Hg, Pd, Pt, Te, Zn, and La. . As the lithium metal or lithium alloy, an amorphous material is particularly preferable. This is because deterioration due to non-uniformity such as crystal grain boundaries and defects hardly occurs due to the amorphous structure.
[0084]
Lithium metal or lithium alloy should be formed by an appropriate method such as a melt cooling method, a liquid quenching method, an atomizing method, a vacuum evaporation method, a sputtering method, a plasma CVD method, an optical CVD method, a thermal CVD method, a sol-gel method, etc. Can be.
[0085]
In the present invention, when a complex composed of a transition metal cation and an imide anion is present at the interface with the electrolyte solution, the negative electrode has flexibility with respect to the volume change of the metal and alloy phases, uniformity of ion distribution, physical and chemical stability. It is preferable because it has excellent properties. As a result, generation of dendrite and pulverization of lithium can be effectively prevented, and cycle efficiency and life are improved.
[0086]
When a carbon material or an oxide material is used as the negative electrode, the dangling bond existing on the surface thereof has high chemical activity and easily decomposes the solvent. By adsorbing a complex comprising a transition metal cation and an imide anion on this surface, the decomposition of the solvent is suppressed and the irreversible capacity is greatly reduced, so that the charge / discharge efficiency does not decrease.
[0087]
In the present invention, as the positive electrode active material, for example, LiCoO₂, LiNiO₂, LiMn₂O₄And the like. The transition metal portion of these lithium-containing composite oxides may be replaced with another element.
[0088]
Further, a lithium-containing composite oxide having a plateau at 4.5 V or more in terms of the counter electrode potential of metallic lithium can also be used. Examples of the lithium-containing composite oxide include a spinel-type lithium-manganese composite oxide, an olivine-type lithium-containing composite oxide, and an inverse spinel-type lithium-containing composite oxide. The lithium-containing composite oxide can be, for example, a compound represented by the following general formula (4).
[0089]
Embedded image
Li_a(M_xMn_2-x) O₄(4)
In the formula, 0 <x <2 and 0 <a <1.2. M is at least one selected from the group consisting of Ni, Co, Fe, Cr and Cu.
[0090]
In the positive electrode of the present invention, these active materials are dispersed and kneaded in a solvent such as N-methyl-2-pyrrolidone (NMP) together with a conductive material such as carbon black and a binder such as polyvinylidene fluoride (PVDF). Then, it can be obtained by applying this on a substrate such as an aluminum foil.
[0091]
Lithium secondary battery according to the present invention, in a dry air or an inert gas atmosphere, the negative electrode and the positive electrode, laminated through a separator, or after winding the laminated thing, or housed in a battery can, or synthetic resin A battery can be manufactured by sealing with a flexible film or the like made of a laminate with a metal foil.
[0092]
As the separator, a porous film such as a polyolefin such as polypropylene or polyethylene, or a fluororesin is used.
[0093]
The shape of the secondary battery according to the present invention is not particularly limited, and examples thereof include a cylindrical shape, a square shape, and a coin shape.
[0094]
【Example】
(Example 1)
(Production of battery)
The positive electrode uses a 20 μm thick aluminum foil as a positive electrode current collector, and LiMn as a positive electrode active material.₂O₄Was used. As a negative electrode, a 20 μm-thick lithium metal was deposited as a negative electrode active material on a 10 μm-thick copper foil as a negative electrode current collector. The electrolyte solution uses a mixed solvent of EC and DEC (volume ratio: 30/70) as a solvent, and LiN (C₂F₅SO₂)₂(Hereinafter abbreviated as LiBETI) in 1 molL^-1And dissolved as a sulfonic anhydride. 5 was added so that the electrolyte solution contained 1 wt%. Then, the negative electrode and the positive electrode were laminated with a separator made of polyethylene interposed therebetween, to produce a secondary battery of this example.
[0095]
(Charge / discharge cycle test)
At a temperature of 20 ° C., the charge rate was 0.05 C, the discharge rate was 0.1 C, the charge end voltage was 4.2 V, the discharge end voltage was 3.0 V, and the utilization rate (depth of discharge) of the lithium metal negative electrode was 33%. The capacity retention ratio (%) is a value obtained by dividing the discharge capacity (mAh) after 400 cycles by the discharge capacity (mAh) at the 10th cycle. Table 4 shows the results obtained in the cycle test.
[0096]
(Examples 2 to 4)
In Example 1, Compound No. A secondary battery was fabricated in the same manner as in Example 1 except that sulfonic anhydride shown in Table 4 was used instead of 5. Hereinafter, the characteristics of the battery were examined in the same manner as in Example 1. Table 4 shows the results.
[0097]
(Comparative Example 1)
In Example 1, Compound No. A secondary battery was fabricated in the same manner as in Example 1 except that No. 5 was not added. Hereinafter, the characteristics of the battery were examined in the same manner as in Example 1. Table 4 shows the results.
[0098]
(Comparative Example 2)
In Example 1, Compound No. A secondary battery was fabricated in the same manner as in Example 1, except that methanesulfonic anhydride was used instead of 5. Hereinafter, the characteristics of the battery were examined in the same manner as in Example 1. Table 4 shows the results.
[0099]
[Table 4]

[0100]
In the batteries shown in Examples 1 to 4, it was confirmed that the capacity retention ratio after the cycle test was improved as compared with Comparative Examples 1 and 2, that is, the cycle characteristics were improved.
[0101]
(Example 5)
In Example 1, LiPF was used as the supporting electrolyte instead of LiBETI.₆As a negative electrode, a mixture of polyvinylidene fluoride dissolved in N-methyl-2-pyrrolidone and a conductivity-imparting material as a binder in graphite powder was applied to a copper foil, and the paste was applied to a copper foil and dried. A secondary battery was fabricated in the same manner as in Example 1 except that the secondary battery was used. Hereinafter, the characteristics of the battery were examined in the same manner as in Example 1. Table 5 shows the results.
[0102]
(Examples 6 to 8)
In Example 5, Compound No. A secondary battery was fabricated in the same manner as in Example 5, except that sulfonic anhydride shown in Table 5 was used instead of 5. Hereinafter, the characteristics of the battery were examined in the same manner as in Example 5. Table 5 shows the results.
[0103]
(Comparative Example 3)
In Example 5, Compound No. A secondary battery was fabricated in the same manner as in Example 5, except that No. 5 was not added. Hereinafter, the characteristics of the battery were examined in the same manner as in Example 5. Table 5 shows the results.
[0104]
[Table 5]

[0105]
It was confirmed that the batteries shown in Examples 5 to 8 had an improved capacity retention ratio after the cycle test, that is, improved cycle characteristics, as compared with Comparative Example 3.
[0106]
(Example 9)
Example 5 was repeated in the same manner as in Example 5 except that amorphous carbon was used instead of graphite, and that the main solvent of the electrolytic solution was PC / EC / DEC (volume ratio: 20/20/60). A secondary battery was manufactured. Hereinafter, the characteristics of the battery were examined in the same manner as in Example 5. Table 6 shows the results.
[0107]
(Examples 10 to 12)
In Example 9, Compound No. A secondary battery was fabricated in the same manner as in Example 9, except that sulfonic anhydride shown in Table 6 was used instead of 5. Hereinafter, the characteristics of the battery were examined in the same manner as in Example 9. Table 6 shows the results.
[0108]
(Comparative Example 4)
In Example 9, Compound No. A secondary battery was fabricated in the same manner as in Example 9 except that No. 5 was not added. Hereinafter, the characteristics of the battery were examined in the same manner as in Example 9. Table 6 shows the results.
[0109]
[Table 6]

[0110]
It was confirmed that the batteries shown in Examples 9 to 12 had improved capacity retention after the cycle test, that is, improved cycle characteristics, as compared with Comparative Example 4.
[0111]
(Example 13)
A secondary battery was fabricated in the same manner as in Example 1, except that the electrolyte further contained 1 wt% of 1,3-propane sultone (hereinafter, abbreviated as 1,3-PS). . Hereinafter, the characteristics of the battery were examined in the same manner as in Example 1. Table 7 shows the results.
[0112]
(Examples 14 to 16)
In Example 13, Compound No. A secondary battery was fabricated in the same manner as in Example 13 except that sulfonic anhydride shown in Table 7 was used instead of 5. Hereinafter, the characteristics of the battery were examined in the same manner as in Example 13. Table 7 shows the results.
[0113]
[Table 7]

[0114]
It was confirmed that the batteries shown in Examples 13 to 16 had improved capacity retention after the cycle test, that is, improved cycle characteristics, as compared with Examples 1 to 4 and Comparative Example 1. Was done. This is due to the combined effect of the sulfonic anhydride represented by the general formula (1) used as an additive and 1,3-PS.
[0115]
(Example 17)
A secondary battery was fabricated in the same manner as in Example 5, except that the electrolyte further contained 1 wt% of 1,3-propane sultone (hereinafter, abbreviated as 1,3-PS). . Hereinafter, the characteristics of the battery were examined in the same manner as in Example 5. Table 8 shows the results.
[0116]
(Examples 18 to 20)
In Example 17, Compound No. A secondary battery was fabricated in the same manner as in Example 17, except that sulfonic anhydride shown in Table 8 was used instead of 5. Hereinafter, the characteristics of the battery were examined in the same manner as in Example 17. Table 8 shows the results.
[0117]
[Table 8]

[0118]
It was confirmed that the batteries shown in Examples 17 to 20 had improved capacity retention after the cycle test, that is, improved cycle characteristics, as compared with Examples 5 to 8 and Comparative Example 3. Was done. This is due to the combined effect of the sulfonic anhydride represented by the general formula (1) used as an additive and 1,3-PS.
[0119]
(Example 21)
In Example 9, a secondary battery was fabricated in the same manner as in Example 9, except that the electrolyte further contained 1 wt% of 1,3-propane sultone (hereinafter, abbreviated as 1,3-PS). . Hereinafter, the characteristics of the battery were examined in the same manner as in Example 9. Table 9 shows the results.
[0120]
(Examples 22 to 24)
In Example 21, Compound No. A secondary battery was fabricated in the same manner as in Example 21, except that sulfonic anhydride shown in Table 9 was used instead of 5. Hereinafter, the characteristics of the battery were examined in the same manner as in Example 21. Table 9 shows the results.
[0121]
[Table 9]

[0122]
It was confirmed that the batteries shown in Examples 21 to 24 had improved capacity retention after the cycle test, that is, improved cycle characteristics, as compared with Examples 9 to 12 and Comparative Example 4. Was done. This is due to the combined effect of the sulfonic anhydride represented by the general formula (1) used as an additive and 1,3-PS.
[0123]
(Examples 25 to 28)
In Example 9, the electrolytic solution further contains CF.₃SO₃ ⁻A secondary battery was fabricated in the same manner as in Example 9, except that a salt of a lanthanide-based transition metal ion shown in Table 10 having an anion was contained at 0.3 wt%. Hereinafter, the characteristics of the battery were examined in the same manner as in Example 9. Table 10 shows the results.
[0124]
[Table 10]

[0125]
In all of the batteries of Examples 25 to 28, it was confirmed that the capacity retention rate after the cycle test was improved, that is, the cycle characteristics were improved, as compared with Comparative Examples 4 and 9. .
[0126]
(Examples 29 to 32)
A secondary battery was fabricated in the same manner as in Example 9, except that the electrolyte further contained 0.1 wt% of the lanthanide-based transition metal complex shown in Table 11. Hereinafter, the characteristics of the battery were examined in the same manner as in Example 9. Table 11 shows the results.
[0127]
[Table 11]

[0128]
It was confirmed that all of the batteries of Examples 29 to 32 had improved cycle characteristics as compared with Comparative Example 4 and Example 9.
[0129]
(Example 33)
A secondary battery was fabricated in the same manner as in Example 9, except that the electrolyte further contained 1 wt% of vinylene carbonate (hereinafter abbreviated as VC). Hereinafter, the characteristics of the battery were examined in the same manner as in Example 9. Table 12 shows the results.
[0130]
(Examples 34 to 36)
In Example 33, Compound No. A secondary battery was fabricated in the same manner as in Example 33 except that sulfonic anhydride shown in Table 12 was used instead of 5. Hereinafter, the characteristics of the battery were examined in the same manner as in Example 33. Table 12 shows the results.
[0131]
[Table 12]

It was confirmed that the batteries shown in Examples 33 to 36 had improved capacity retention after the cycle test, that is, improved cycle characteristics, as compared with Comparative Example 4 and Examples 9 to 12. Was done.
[0132]
【The invention's effect】
According to the present invention, when a secondary battery is manufactured using an electrolytic solution containing at least the sulfonic anhydride represented by the general formula (1) in an aprotic solvent, the obtained secondary battery is A lithium secondary battery having excellent charge / discharge efficiency, good cycle characteristics, and excellent safety can be obtained.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of a secondary battery according to the present invention.
[Explanation of symbols]
11 current collector
12 Layer containing positive electrode active material
13—Layer containing negative electrode active material
14 negative electrode current collector
15 non-aqueous electrolyte solution
16 porous separator

Claims (20)

An electrolyte solution for a secondary battery, characterized in that the aprotic solvent contains at least a sulfonic anhydride represented by the following general formula (1).

Here, X is an alkylene group having 2 to 4 carbon atoms which may have a substituent, an alkenylene group having 2 to 4 carbon atoms which may have a substituent, or an aromatic group which may have a substituent The ring and the heterocyclic ring which may have a substituent are shown. The electrolyte solution for a secondary battery according to claim 1, wherein the sulfonic anhydride is a compound represented by the following general formula (2).

Here, R _{1 to} R ₄ are each independently a hydrogen atom, a halogen atom, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkoxy group, a substituted or unsubstituted cycloalkyl group, a substituted or unsubstituted aryl. Represents a group, a substituted or unsubstituted heterocyclic group. Further, R1 to R4 may be condensed with each other to form an aryl ring which may have a substituent or a heterocyclic ring which may have a substituent. 2. The electrolyte for a secondary battery according to claim 1, further comprising a compound having a sulfonyl group other than that represented by the general formula (1), together with the sulfonic anhydride represented by the general formula (1). 3. The electrolytic solution for a secondary battery according to claim 3, wherein the compound having a sulfonyl group other than that represented by the general formula (1) is a sultone compound represented by the following general formula (3).

Here, n is an integer of 0 to 2. R _{1 to} R ₆ each independently represent a hydrogen atom, an alkyl group having 1 to 12 carbon atoms, a cycloalkyl group having 3 to 6 carbon atoms, or an aryl group having 6 to 12 carbon atoms. The electrolytic solution for a secondary battery according to claim 1, wherein the aprotic organic solvent contains at least an imide anion, a transition metal ion, and a compound having a sulfonyl group represented by the general formula (1). The electrolytic solution in which a lithium salt is dissolved as an electrolyte salt in an aprotic organic solvent contains at least a metal complex comprising an imide anion and a transition metal and a sulfonic anhydride represented by the general formula (1). The electrolytic solution for a secondary battery according to the above. The electrolyte for a secondary battery according to any one of claims 1 to 6, wherein the electrolyte further contains vinylene carbonate or a derivative thereof. 7. The electrolyte for a secondary battery according to claim 5, wherein the transition metal is a lanthanoid transition metal. 9. The electrolyte for a secondary battery according to claim 8, wherein the lanthanoid transition metal is one selected from europium, neodymium, erbium or holmium. Imide anion is ^{_{- N (C n F 2n +}} 1 SO 2) (C m F 2m + 1 SO 2) (n, m are natural numbers) electrolyte solution for a secondary battery according to claim 5 or 6 is. The electrolytic solution for a secondary battery according to claim 1, wherein the sulfonic anhydride represented by the general formula (1) is contained in an amount of 0.01 to 10 wt% of the entire electrolytic solution. 7. The electrolyte for a secondary battery according to claim 5, wherein the imide anion or a metal complex thereof is contained in the electrolyte at 0.005 to 10 wt%. The aprotic organic solvent is selected from the group consisting of cyclic carbonates, chain carbonates, aliphatic carboxylic esters, γ-lactones, cyclic ethers, chain ethers, and fluorinated derivatives thereof. The electrolyte solution for a secondary battery according to any one of claims 1 to 12, comprising: The lithium salt was selected from LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiSbF ₆ , LiClO ₄ , LiAlCl ₄ , LiN (C _n F _{2n + 1} SO ₂ ) (C _m F _{2m + 1} SO ₂ ) (n and m are natural numbers) The electrolyte solution for a secondary battery according to claim 6, comprising: A secondary battery comprising at least a positive electrode and a negative electrode, wherein the secondary battery electrolytic solution according to any one of claims 1 to 14 is used. The secondary battery according to claim 15, wherein the positive electrode is made of a lithium-containing composite oxide capable of inserting and extracting lithium. 16. The negative electrode uses a negative electrode active material made of any one of a material capable of inserting and extracting lithium, a lithium metal, a metal material capable of forming an alloy with lithium, and an oxide material, or a mixture of two or more types. 2. The secondary battery according to 1. 18. The secondary battery according to claim 17, wherein a negative electrode containing carbon is used as the material capable of inserting and extracting lithium. 19. The secondary battery according to claim 18, wherein a material capable of occluding and releasing lithium is graphite. 19. The secondary battery according to claim 18, wherein a material capable of occluding and releasing lithium is an amorphous carbon.

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