JP4265169B2 - Secondary battery electrolyte and secondary battery using the same - Google Patents

Description

【００１９】
（ただし、上記一般式（１）において、Ｒ₁、Ｒ_２、およびＲ₃は、置換もしくは未置換のフェニル基、置換もしくは未置換の直鎖状乃至分岐状のアルキル基、置換もしくは未置換のシクロアルキル基を示す。また、Ｒ_１及びＲ_２が互いに縮合した環構造であってもよい。Ｘ⁻は、陰イオンを示す。）
【００２０】
本発明の二次電池用電解液は、非プロトン性溶媒を溶媒とし、これに上記式（１）で示されるスルホニウム塩が溶解または分散されている。よって、二次電池に用いた際にそのサイクル特性を向上させることができる。
【００２１】
本発明によれば、少なくとも正極と負極とを備えた二次電池であって、前記二次電池用電解液を含むことを特徴とする二次電池が提供される。本発明の二次電池は、電解液として上記式（１）で示されるスルホニウム塩を含む二次電池用電解液を含むため、サイクル特性が改善向上されたものである。
【００２２】
なお、本発明に係る二次電池用電解液は、溶媒に対し上記一般式（１）で示されるスルホニウム塩を溶解させる工程と、リチウム塩を溶解させる工程と、を含む製造方法により、簡便で安定的に製造される。
【００２３】
【発明の実施の形態】
本発明に係る二次電池用電解液は、非プロトン性溶媒と、下記一般式（１）で示されるスルホニウム塩とを含む。
【００２４】
【化３】

【００２５】
（ただし、上記一般式（１）において、Ｒ₁、Ｒ_２、およびＲ₃は、置換もしくは未置換のフェニル基、置換もしくは未置換の直鎖状乃至分岐状のアルキル基、置換もしくは未置換のシクロアルキル基を示す。また、Ｒ_１及びＲ_２が互いに縮合した環構造であってもよい。Ｘ⁻は、陰イオンを示す。）
【００２６】
Ｒ₁、Ｒ_２、またはＲ₃を置換フェニル基とする場合、置換基を、たとえば炭素数１以上６以下のアルキル基、フッ素、塩素、臭素などのハロゲン原子、炭素数１以上３以下のパーフルオロアルキル基、炭素数１以上３以下のアルキルオキシ基などの中から選択することができる。
【００２７】
また、Ｒ₁、Ｒ_２、またはＲ₃を置換アルキル基とする場合、置換基を、たとえばフッ素、塩素、臭素などのハロゲン原子、炭素数１以上３以下のアルキルオキシ基などの中から選択することができる。
【００２８】
また、Ｒ₁、Ｒ_２、またはＲ₃をシクロアルキル基とする場合、たとえば炭素数５以上７以下とすることができる。置換シクロアルキル基とする場合、置換基を、たとえば炭素数１以上６以下のアルキル基、フッ素、塩素、臭素などのハロゲン原子、炭素数１以上３以下のパーフルオロアルキル基、炭素数１以上３以下のアルキルオキシ基、炭素数１以上３以下のパーフルオロアルキルオキシ基などの中から選択することができる。
【００２９】
また、Ｒ_１及びＲ_２が互いに縮合した環構造である場合、たとえば下記一般式（２）で示される化合物を用いることができる。
【００３０】
【化４】

【００３１】
上記一般式（２）において、Ｒ_４は炭素数４以上７以下のα，ω−アルキレン基とすることができる。また、Ｒ_３、Ｘ⁻は一般式（１）の場合と同様の構造の中から選択することができる。
【００３２】
一般式（１）の化合物の代表例を、式（３）〜式（１０）に具体的に例示するが、本発明において用いることができるスルホニウム塩はこれらに限定されるものではない。
【００３３】
【化５】

【００３４】
【化６】

【００３５】
【化７】

【００３６】
【化８】

【００３７】
【化９】

【００３８】
【化１０】

【００３９】
【化１１】

【００４０】
【化１２】

【００４１】
また、上記一般式（１）において、Ｘ⁻で表される陰イオンは、ＰＦ_６ ⁻、ＢＦ_４ ⁻、Ｂｒ⁻、Ｉ⁻、ＡｓＦ_６ ⁻、ＳｂＦ_６ ⁻、イミドアニオン、アルキルスルホナートイオン、置換あるいは未置換のベンゼンスルホナートイオン、パーフルオロアルキルスルホナートイオン、またはカンファースルホナートイオンを含むことができる。
【００４２】
Ｘ⁻をアルキルスルホナートイオンから選択する場合、たとえば炭素数を１以上６以下とすることができる。
【００４３】
また、Ｘ⁻をパーフルオロアルキルスルホナートイオンから選択する場合、たとえば炭素数を１以上６以下とすることができる。
【００４４】
また、Ｘ⁻をイミドアニオンから選択する場合、たとえば、⁻Ｎ（Ｃ_ｎＦ_２ｎ＋１ＳＯ_２）(Ｃ_ｍＦ_２ｍ＋１ＳＯ_２)（ｎ、ｍは独立した１以上６以下の自然数）で示される化合物とすることができる。こうすることにより、負極表面の皮膜は、良好なイオン伝導性を確保しつつ、物理的、化学的安定性を備えることが可能となる。
【００４５】
さらに、Ｘ⁻をカンファースルホナートイオンから選択する場合、たとえば、ｄ−ショウノウ−１０−スルホン酸イオンなどを用いることができる。
【００４６】
一般式（１）で示されるスルホニウム塩は、たとえば、Ｊ．Ｃ．Ｃｒｉｖｅｌｌｏら、Ｊｏｕｒｎａｌ ｏｆ Ｐｏｌｙｍｅｒ Ｓｃｉｅｎｃｅ、Ｐｏｌｙｍｅｒ Ｃｈｅｍｉｓｔｒｙ Ｅｄｉｔｉｏｎ、１７、９７７〜９９９(１９７９)などに記載の方法で合成することができる。
【００４７】
一般式（１）で示されるスルホニウム塩の電解液に占める割合は特に制限されないが、好ましくは、電解液全体の０．０１質量％以上１０質量％以下含む構成とすることができる。０．０１質量％以上とすることにより、電池特性向上に対し十分に効果を発揮させることができる。より好ましくは０．１質量％以上添加することができ、こうすることにより、電池特性をさらに向上させることができる。また、１０質量％以下とすることにより、電解液の抵抗値を小さくすることができる。より好ましくは５質量％以下添加することができ、こうすることにより、電池特性をさらに向上させることができる。
【００４８】
本発明における二次電池用電解液は、非プロトン溶媒として、たとえば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、またはこれらのフッ素誘導体を含む構成とすることができる。
【００４９】
具体的には、たとえばプロピレンカーボネート（ＰＣ）、エチレンカーボネート（ＥＣ）、ブチレンカーボネート（ＢＣ）、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、ジオキソラン、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、Ｎ−メチルピロリドン、フッ素化カルボン酸エステル、メチル−2,2,2−トリフルオロエチルカーボネート、メチル−2,2,3,3,3−ペンタフルオロプロピルカーボネート、トリフルオロメチルエチレンカーボネート、モノフルオロメチルエチレンカーボネート、ジフルオロメチルエチレンカーボネート、4,5−ジフルオロ−1,3−ジオキソラン−2−オン、モノフルオロエチレンカーボネートなどのうち、一種または二種以上を混合して使用することができる。
【００５０】
本発明の二次電池用電解液において、さらに電解質としてリチウム塩を含む構成とすることができる。こうすることにより、リチウムイオンを移動物質とすることができるため、電池特性を向上させることができる。リチウム塩として、たとえばリチウムイミド塩、ＬｉＰＦ_６、ＬｉＡｓＦ_６、ＬｉＡｌＣｌ_４、ＬｉＣｌＯ_４、ＬｉＢＦ_４、ＬｉＳｂＦ_６、ＬｉＮ（Ｃ_ｎＦ_２ｎ＋１ＳＯ_２）(Ｃ_ｍＦ_２ｍ＋１ＳＯ_２)（ｎ、ｍは独立した１以上６以下の自然数）の中から選択された一以上物質を含む構成とすることができる。また、特にＬｉＰＦ₆、ＬｉＢＦ₄、ＬｉＮ（Ｃ_ｎＦ_２ｎ＋１ＳＯ_２）(Ｃ_ｍＦ_２ｍ＋１ＳＯ_２)（ｎ、ｍは独立した１以上６以下の自然数）を用いることが好ましい。これらを用いることにより、リチウム塩の電気伝導率を高めることができ、二次電池のサイクル特性をさらに向上させることができる。
【００５１】
本発明の二次電池用電解液において、⁻Ｎ（Ｃ_ｎＦ_２ｎ＋１ＳＯ_２）（Ｃ_ｍＦ_２ｍ＋１ＳＯ_２）（ｎ、ｍは独立した１以上６以下の自然数）で示されるイミドアニオンを含む構成とすることができる。イミドアニオンは、たとえば上記一般式（１）で示されるスルホニウム塩の陰イオンとして含むことができる。また、リチウム塩のカウンターイオンとして含まれてもよい。本発明に係る二次電池用電解液の溶媒である非プロトン性溶媒に溶解させることにより、イミドアニオンが生じる。こうすることにより、二次電池のサイクル特性をより一層向上させることができる。
【００５２】
また、本発明に係る二次電池用電解液に、ビニレンカーボネート（以下ＶＣと略す）またはその誘導体、１，３−プロパンスルトン（以下ＰＳと略す）またはその誘導体を添加することにより、サイクル特性をさらに向上させることができる。
【００５３】
ＶＣまたはその誘導体は、たとえば特開平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などを用いることができる。ＶＣまたはその誘導体の添加量は、電解液全体の０．０１質量％以上１０質量％以下であることが好ましい。０．０１質量％以上とすることにより、サイクル特性向上効果を好適に発揮させることができ、また、１０質量％以下とすることにより、電解液の抵抗値を低くすることができる。
【００５４】
また、ＰＳまたはその誘導体として、たとえば特開２０００−３７２４号公報、特開２０００−３７２５号公報に示された化合物などを用いることができる。ＰＳまたはその誘導体を、たとえば電解液全体の０．０１質量％以上１０質量％以下含ませることができる。こうすることにより、サイクル特性向上効果が好適に発揮される。
【００５５】
次に、本発明に係る二次電池用電解液を用いた二次電池について説明する。本発明に係る二次電池は、たとえば図１のような構造を有する。図１は、本発明に係る二次電池の負極集電体の厚さ方向の概略拡大断面図である。正極は、正極活物質を含有する層１２が正極集電体１１上に成膜して成る。負極は、負極活物質を含有する層１３が負極集電体１４上に成膜して成る。これらの正極と負極は、電解質水溶液の電解液１５、及び前記電解液１５の中の多孔質セパレーター１６を介して対向配置してある。多孔質セパレーター１６は、負極活物質を含有する層１３に対して略平行に配置されている。
【００５６】
電解液１５には、スルホニウム塩を含む上述の二次電池用電解液を用いる。二次電池用電解液は、非プロトン性溶媒にスルホニウム塩、および必要に応じてリチウム塩や他の添加物を溶解または分散させることにより得られる。
【００５７】
図１の二次電池において、負極集電体１４としては、たとえばＡｌ、Ｃｕなどを主体とする金属薄膜を用いることができる。また、負極活物質を含有する層１３に用いる負極活物質には、たとえばリチウム金属、リチウム合金、およびリチウムを吸蔵、放出できる材料、からなる群から選択される一または二以上の物質を用いることができる。リチウムイオンを吸蔵、放出する材料としては、炭素材料または酸化物を用いることができる。
【００５８】
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。このうち、特に黒鉛材料または非晶質炭素であることが好ましい。とくに黒鉛材料は、電子伝導性が高く、銅などの金属からなる集電体との接着性と電圧平坦性が優れており、高い処理温度によって形成されるため含有不純物が少なく、負極性能の向上に有利に働くため、好ましい。
【００５９】
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。
【００６０】
リチウム合金は、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。たとえば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。リチウム金属乃至リチウム合金としては、特にアモルファス状合金が好ましい。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。
【００６１】
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。
【００６２】
図１の二次電池において、正極活物質を含有する層１２に用いる正極活物質としては、リチウムイオンを吸蔵、放出し得る酸化物、Ｌｉ_ｘＭＯ_２（ただしＭは、少なくとも１つの遷移金属を表す。０＜ｘ＜１．２）で示される複合酸化物、たとえば、Ｌｉ_ｘＣｏＯ_２、Ｌｉ_ｘＮｉＯ_２など、Ｌｉ_ｘＭｎ_２Ｏ_４、Ｌｉ_ｘＭｎＯ_３、Ｌｉ_ｘＮｉ_ｙＣ_１−ｙＯ_２（０＜ｘ＜１．２、０＜ｙ＜１）、または有機イオウ化合物、導電性高分子、安定化ラジカル化合物などのいずれかまたはこれらの混合物を用いることができる。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、たとえば下記一般式(１１)で表される化合物とすることができる。
Ｌｉ_ａ（Ｍ_ｘＭｎ_２−ｂ）Ｏ_４ （１１）
（式中、０＜ｂ＜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。）
【００６３】
図１の二次電池における正極は、これらの正極活物質を、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（以下ＮＭＰと略す。）等の溶剤中に分散、混練し、これをアルミニウム箔等の正極集電体１１上に塗布することにより得ることができる。
【００６４】
図１の二次電池は、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、多孔質セパレーター１６を介して積層、あるいは積層したものを捲回した後に、電池缶や、合成樹脂と金属箔との積層体からなる可撓性フィルム等の外装体に収容し、スルホニウム塩を含む電解液を含浸させる。そして、外装体を封止することによって電池を製造することができる。電池外装体を封止または封止後に、二次電池の充電を行うことにより、負極上に皮膜を形成させることができる。なお、多孔質セパレーター１６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。
【００６５】
本発明に係る二次電池の形状に特に制限はないが、たとえば、円筒型、角型、コイン型、ラミネート外装型などがあげられる。
【００６６】
【実施例】
（参考例１）
（電池の作製）
本実施例および参考例の電池の作製について説明する。正極集電体に２０μｍのアルミニウム箔、正極中の正極活物質にＬｉＭｎ_２Ｏ_４、負極中の負極活物質に、負極集電体の１０μｍの銅箔上に蒸着した２０μｍのリチウム金属、電解液は、溶媒としてＥＣとＤＥＣの混合溶媒（体積比：３０／７０）を用い、電解質として１ｍｏｌＬ^−１のＬｉＰＦ_６を用いた。
【００６７】
次に、添加剤として、上記式（３）で示されるスルホニウム塩を、電解液中に１質量％含まれるように加え、本実施例および参考例の電解液を作製した。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ーを介して積層し、二次電池を作製した。
【００６８】
（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３００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１に示す。
【００６９】
【表１】

【００７０】
（参考例２〜５）
電解液に上記式（３）で示されるスルホニウム塩を加える代わりに、表２に示すスルホンニウム化合物を加えた電解液を用い、参考例１と同様にして電池を作製し評価した。サイクル特性の結果を表１に示す。
【００７１】
（比較例１）
電解液中にスルホニウム塩を添加せずに、参考例１と同様の電池を作製し、参考例１と同様にサイクル特性を調べた。結果を表１に示す。
【００７２】
参考例１〜５に示した電池は、比較例１と比較して、サイクル試験後の容量維持率が大きく増加していること、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。容量維持率の向上は、負極表面に安定な被膜が形成され、かつ被膜が高いイオン伝導性を有しているためであると考えられる。
【００７３】
（参考例６）
本参考例においては、負極活物質として黒鉛を用い、電解質として１ｍｏｌＬ^−１のＬｉＮ（Ｃ_２Ｆ_５ＳＯ_２）_２を用いた。黒鉛からなる負極は、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、乾燥させたものである。得られた負極を用いて、参考例１と同様に二次電池を作製し、サイクル特性の評価を行った。サイクル試験で得られた結果を表２に示す。
【００７４】
【表２】

【００７５】
（参考例７〜９）
表２に示すスルホニウム塩を用いて、参考例６と同様に二次電池を作製し、サイクル特性の評価を行った。
【００７６】
（比較例２）
スルホニウム塩を添加せずに、参考例６と同様の二次電池を作製し、サイクル特性の評価を行った。サイクル試験の結果を表２に示す。
【００７７】
参考例６〜９に示した電池は、比較例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。したがって、負極活物質を黒鉛とした場合においても、電解液にスルホニウム塩を添加することにより、サイクル特性が改善されることがわかる。
【００７８】
（参考例１０）
負極活物質として非晶質炭素を用い、参考例１と同様に二次電池を作製し、サイクル特性の評価を行った。本参考例においては、電解液の溶媒をＰＣ（２０）／ＥＣ（２０）／ＤＥＣ（６０）（体積比）とした。サイクル試験の結果を表３に示す。
【００７９】
【表３】

【００８０】
（参考例１１）
参考例１０と同様に二次電池を作製し、サイクル特性の評価を行った。ただし、スルホニウム塩として、上記式（７）に示す化合物を用いた。サイクル試験の結果を表３に示す。
【００８１】
（比較例３）
スルホニウム塩を添加せずに、参考例７と同様の二次電池を作製し、サイクル特性の評価を行った。サイクル試験の結果を表３に示す。
【００８２】
参考例１０、１１の電池は、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。
【００８３】
（実施例１２）
（電池の作製）
電解液に加える添加剤として、上記式（３）で示されるスルホニウム塩および１，３−プロパンスルトン（ＰＳ）を用い、それぞれ電解液中に１質量％含まれるよう添加した。これを用い、参考例１と同様にして電解液および二次電池を作製した。
【００８４】
（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３００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。サイクル試験の結果を表４に示す。
【００８５】
【表４】

【００８６】
実施例１２に示した電池は、参考例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スルホニウム塩とＰＳとの複合効果によるものである。
【００８７】
（実施例１３）
本実施例においては、スルホニウム塩に加え、ビニレンカーボネート（ＶＣ）を更に含有させた電解液を用いた二次電池を作製した。電解液の溶媒はＰＣ（２０）／ＥＣ（２０）／ＤＥＣ（６０）（体積比）とし、電解質として１ｍｏｌＬ^−１のＬｉＰＦ_６を用いた。次に添加剤として、上記式（３）で示されるスルホニウム塩を電解液中に１質量％加え、さらにビニレンカーボネート（ＶＣ）を１質量％となるよう加えた。そして、非晶質炭素からなる負極とＬｉＭｎ_２Ｏ_４からなる正極とをポリエチレンからなるセパレーターを介して積層し、二次電池を作製した。得られた二次電池のサイクル特性を表５に示す。
【００８８】
【表５】

【００８９】
実施例１３は比較例３及び参考例７と比較してサイクル特性が改善された。これは、添加剤として使用したスルホニウム塩とＶＣとの複合効果によるものである。
【００９０】
（参考例１４〜１７）
参考例１０の二次電池において、上記式（３）で示されるスルホニウム塩の濃度を変化させ、サイクル特性を測定した。結果を表６に示す。
【００９１】
【表６】

【００９２】
表６よりスルホニウム塩濃度が０．１〜１０質量％でサイクル特性が改善されていることがわかる。したがって、本参考例においては、スルホニウム塩を０．１質量％以上１０質量％以下添加することにより、サイクル特性の改善効果が発揮され、特に１質量％以上５質量％以下添加することにより、より一層好ましい効果が発揮されることがわかった。
【００９３】
【発明の効果】
以上説明したように、本発明によれば、非プロトン性溶媒と、上記一般式（１）に示すスルホニウム塩とを含む電解液を用いることにより、二次電池のサイクル寿命を安定で優れたものとする二次電池用電解液が実現される。また、本発明によれば、安定かつ優れたサイクル寿命と高い充放電効率を発揮する二次電池が実現される。
【図面の簡単な説明】
【図１】本発明に係る二次電池の一例を示す概略構成図である。
【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 電解液
１６ 多孔質セパレーター[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electrolyte for a secondary battery 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 metals for the negative electrode are attracting attention as power sources for mobile phones and laptop computers because they can achieve high energy density. Yes. In this secondary battery, it is known that a film called a surface film, a protective film, a surface electrolyte interface (SEI) or a film is formed on the surface of the negative electrode. Since this surface film has a great influence on charge / discharge efficiency, cycle life and safety, it is known that control of the surface film is indispensable for improving the performance of the negative electrode. It is necessary to reduce the irreversible capacity of carbon materials and oxide materials, and it is necessary to solve the safety problem due to the formation of dendrites in the case of lithium metal and alloy negative electrodes.
[0003]
Various methods for solving these problems have been proposed. For example, it has been proposed to suppress the formation of dendrite by providing a film layer made of lithium fluoride or the like on the surface of lithium metal or lithium alloy using a chemical reaction.
[0004]
For example, 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. It is disclosed. Hydrofluoric acid is LiPF₆And produced by reaction of trace amounts 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 negative electrode surface. However, this lithium fluoride film is formed by utilizing the reaction between the electrode interface and the liquid, and side reaction components are easily mixed into the surface film, making it difficult to obtain a uniform film. Also, there may be cases where the surface film of lithium hydroxide or lithium oxide is not uniformly formed or there is a part where lithium is exposed. In these cases, a uniform thin film cannot be formed. In addition, there is a safety problem due to the reaction of lithium with water or hydrogen fluoride. Moreover, when reaction is inadequate, unnecessary compound components other than a fluoride remain, and bad influences, such as causing the fall of ion conductivity, are considered. Furthermore, in the method of forming a fluoride layer using such a chemical reaction at the interface, the selection range of the available fluoride and electrolyte is limited, and it is difficult to form a stable surface film with a high yield. there were.
[0005]
Japanese Laid-Open Patent Publication No. 8-250108 discloses a technique for obtaining a lithium fluoride surface film on the negative electrode surface by reacting a mixed gas of argon and hydrogen fluoride with an aluminum-lithium alloy. However, when a surface film is present on the lithium metal surface in advance, particularly when a plurality of types of compounds are present, the reaction tends to be non-uniform, and it is difficult to form a lithium fluoride film uniformly. For this reason, it becomes difficult to obtain a lithium secondary battery having sufficient cycle characteristics.
[0006]
Japanese Patent Laid-Open No. 11-288706 discloses a surface film mainly composed of a substance having a rock salt type crystal structure on the surface of a lithium sheet having a uniform crystal structure, that is, a (100) crystal plane preferentially oriented. Techniques for forming the structure are disclosed. By carrying out like this, it is said that uniform precipitation dissolution reaction, ie, charge / discharge of a battery, can be performed, dendrite precipitation of lithium metal can be suppressed, and the cycle life of the battery can be improved. It is stated that the substance used for the surface film preferably has a halide of lithium, and it is preferable to use a solid solution of LiF with at least one selected from LiCl, LiBr, and LiI. Specifically, in order to form a solid solution film of at least one of LiCl, LiBr, and LiI and LiF, a lithium sheet with a (100) crystal plane preferentially oriented formed by pressing (rolling) is used. A negative electrode for a non-aqueous electrolyte battery is created 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. . In the case of this technology, a rolled lithium metal sheet is used, and since the lithium sheet is easily exposed to the atmosphere, a film derived from moisture and the like is easily formed on the surface, and the presence of active sites becomes uneven, which is the purpose. It became difficult to produce a stable surface film, and the effect of suppressing dentlite was not always sufficiently obtained.
[0007]
Naoi et al. Also held conferences at the 68th Electrochemical Society (September 2000, Chiba Institute of Technology, lecture number 2A24) and the 41st Battery Conference (November 2000, Nagoya International Conference Center, lecture number 1E03). In the presentation, we report the effect of lanthanoid transition metals such as europium and imide anions on the lithium metal anode. Here, LiN (C as a lithium salt in a mixed solvent of propylene carbonate or ethylene carbonate and 1,2-dimethoxyethane is used.₂F₅SO₂)₂In addition to Eu [(C₂F₅SO₂)₂]_ThreeOn the Li metal immersed in the electrolyte, Eu [(C₂F₅SO₂)₂]_ThreeA surface film made of a complex is formed. Although this method has a certain effect in improving the cycle life, it is not sufficient. In addition, LiN (CF₃SO₂)₂It is essential to use a relatively expensive lithium imide salt such as Lithium salt other than this (for example, commonly used LiPF₆), Transition metals and CF₃SO₃ ⁻Even if a complex composed of ions is added, a complex composed of a transition metal and an imide anion is not generated, and thus the cycle characteristics are not improved. Furthermore, when using a lithium imide salt as an electrolyte, LiPF₆Since the resistance of the electrolytic solution is higher than when using the above, there is a problem that the internal resistance of the battery is increased.
[0008]
On the other hand, when a carbon material such as graphite or hard carbon that can occlude and release lithium ions is used as the negative electrode, the following method is proposed as a technique for improving the battery capacity and charge / discharge efficiency by forming a coating layer on the negative electrode Has been.
[0009]
For example, Japanese Patent Application Laid-Open No. 5-234583 proposes a negative electrode in which a carbon material is coated with aluminum. Thereby, reductive decomposition on the carbon surface of solvent molecules solvated with lithium ions is suppressed, and deterioration of cycle life is suppressed. However, since aluminum reacts with a small amount of water, there is a problem that the capacity rapidly decreases when the cycle is repeated.
[0010]
JP-A-5-275077 discloses a negative electrode in which the surface of a carbon material is covered with a thin film of a lithium ion conductive solid electrolyte. Thereby, it is said that the decomposition | disassembly of the solvent which arises when using a carbon material can be suppressed, and especially the lithium ion secondary battery which can use a propylene carbonate can be provided. However, cracks generated in the solid electrolyte due to changes in stress during insertion and desorption of lithium ions lead to deterioration of characteristics. In addition, due to non-uniformity such as crystal defects in the solid electrolyte, a uniform reaction cannot be obtained on the negative electrode surface, leading to deterioration of cycle life.
[0011]
Further, in Japanese Patent Application Laid-Open No. 2000-3724, the negative electrode is made of a material containing graphite, the non-aqueous electrolyte is mainly composed of a cyclic carbonate and a chain carbonate, and the non-aqueous electrolyte contains 0.1 wt% or more and 4 wt%. A secondary battery containing the following 1,3-propane sultone and / or 1,4-butane sultone is disclosed. 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 a highly crystallized carbon material having an activity such as natural graphite or artificial graphite. It is considered to have an effect of suppressing the decomposition of the electrolytic solution without impairing the normal reaction of the battery by covering with a film. However, this method has a problem that a sufficient film effect cannot be obtained, and charges due to decomposition of solvent molecules or anions appear as irreversible capacity components, leading to a decrease in initial charge / discharge efficiency.
[0012]
[Problems to be solved by the invention]
As described above, the conventional technique has not obtained a sufficient effect for improving the battery characteristics, and has the following problems.
[0013]
The surface film formed on the surface of the negative electrode is deeply related to charge / discharge efficiency, cycle life, and safety depending on its properties, but there is still no method for controlling the film for a long time. For example, when a surface film made of lithium halide or glassy oxide is formed on a layer made of lithium or an alloy thereof, although a certain degree of dentite suppression effect can be obtained during initial use, The surface film is deteriorated and the function as a protective film is lowered. This is because a layer made of lithium or an alloy thereof changes in volume by occlusion / release of lithium, whereas a film made of lithium halide or the like located on the upper side hardly changes in volume. This is thought to be due to the generation of internal stress at the interface. By generating such internal stress, it is considered that a part of the surface film made of lithium halide or the like is particularly damaged, and the dendrite suppressing function is lowered.
[0014]
In addition, for carbon materials such as graphite, charges due to decomposition of solvent molecules or anions appear as irreversible capacity components, leading to a reduction in the initial charge / discharge efficiency. Further, the composition, crystal state, stability, etc. of the film produced at this time have a great influence on the subsequent efficiency and cycle life. Furthermore, 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 is promoted, and it was necessary to remove water molecules.
[0015]
Thus, the surface film generated on the negative electrode surface is deeply related to charge and discharge efficiency, cycle life, safety, etc. depending on its properties, but there is no method for controlling the film over a long period of time, There has been a demand for the development of an electrolyte solution that forms a film that leads to stable and sufficient charge / discharge efficiency on the negative electrode.
[0016]
In view of the above circumstances, an object of the present invention is to provide an electrolytic solution for a secondary battery that makes the cycle life of the secondary battery stable and excellent. Another object of the present invention is to provide a secondary battery that exhibits stable and excellent cycle life and high charge / discharge efficiency.
[0017]
[Means for Solving the Problems]
  According to the present invention, an aprotic solvent and a sulfonium salt represented by the following general formula (1):, Vinylene carbonate or 1,3-propane sultone, and the content of the sulfonium salt is 0.01% by mass or more and 10% by mass or less of the total electrolyte for a secondary battery, the vinylene carbonate or the 1,3 -Propane sultone content is 0.01 mass% or more and 10 mass% or less of the entire electrolyte for secondary batteries.An electrolyte for a secondary battery is provided.
[0018]
[Chemical formula 2]

[0019]
(However, in the above general formula (1), R₁, R₂, And R_ThreeRepresents a substituted or unsubstituted phenyl group, a substituted or unsubstituted linear or branched alkyl group, or a substituted or unsubstituted cycloalkyl group. R₁And R₂The ring structures may be condensed with each other. X⁻Indicates an anion. )
[0020]
The electrolyte solution for a secondary battery of the present invention uses an aprotic solvent as a solvent, and a sulfonium salt represented by the above formula (1) is dissolved or dispersed therein. Therefore, the cycle characteristics can be improved when used in a secondary battery.
[0021]
According to the present invention, there is provided a secondary battery comprising at least a positive electrode and a negative electrode, the secondary battery including the secondary battery electrolyte. Since the secondary battery of the present invention includes an electrolyte solution for a secondary battery containing the sulfonium salt represented by the above formula (1) as the electrolyte solution, the cycle characteristics are improved and improved.
[0022]
In addition, the electrolytic solution for a secondary battery according to the present invention is simple by a production method including a step of dissolving the sulfonium salt represented by the general formula (1) in a solvent and a step of dissolving a lithium salt. Manufactured stably.
[0023]
DETAILED DESCRIPTION OF THE INVENTION
The electrolyte solution for secondary batteries according to the present invention includes an aprotic solvent and a sulfonium salt represented by the following general formula (1).
[0024]
[Chemical 3]

[0025]
(However, in the above general formula (1), R₁, R₂, And R_ThreeRepresents a substituted or unsubstituted phenyl group, a substituted or unsubstituted linear or branched alkyl group, or a substituted or unsubstituted cycloalkyl group. R₁And R₂The ring structures may be condensed with each other. X⁻Indicates an anion. )
[0026]
R₁, R₂Or R_ThreeIs a substituted phenyl group, the substituent is, for example, an alkyl group having 1 to 6 carbon atoms, a halogen atom such as fluorine, chlorine or bromine, a perfluoroalkyl group having 1 to 3 carbon atoms, or 1 to 3 carbon atoms. The following alkyloxy groups can be selected.
[0027]
R₁, R₂Or R_ThreeIs a substituted alkyl group, the substituent can be selected from halogen atoms such as fluorine, chlorine and bromine, alkyloxy groups having 1 to 3 carbon atoms, and the like.
[0028]
R₁, R₂Or R_ThreeCan be, for example, 5 to 7 carbon atoms. In the case of a substituted cycloalkyl group, the substituent is, for example, an alkyl group having 1 to 6 carbon atoms, a halogen atom such as fluorine, chlorine or bromine, a perfluoroalkyl group having 1 to 3 carbon atoms, or 1 to 3 carbon atoms. It can be selected from the following alkyloxy groups, perfluoroalkyloxy groups having 1 to 3 carbon atoms, and the like.
[0029]
R₁And R₂Can be used, for example, a compound represented by the following general formula (2) can be used.
[0030]
[Formula 4]

[0031]
In the general formula (2), R₄Can be an α, ω-alkylene group having 4 to 7 carbon atoms. R₃, X⁻Can be selected from structures similar to those in the general formula (1).
[0032]
Representative examples of the compound of the general formula (1) are specifically exemplified by the formulas (3) to (10), but the sulfonium salts that can be used in the present invention are not limited to these.
[0033]
[Chemical formula 5]

[0034]
[Chemical 6]

[0035]
[Chemical 7]

[0036]
[Chemical 8]

[0037]
[Chemical 9]

[0038]
[Chemical Formula 10]

[0039]
Embedded image

[0040]
Embedded image

[0041]
In the general formula (1), X⁻The anion represented by PF₆ ⁻, BF₄ ⁻, Br⁻, I⁻, AsF₆ ⁻, SbF₆ ⁻, An imide anion, an alkyl sulfonate ion, a substituted or unsubstituted benzene sulfonate ion, a perfluoroalkyl sulfonate ion, or a camphor sulfonate ion.
[0042]
X⁻Is selected from alkyl sulfonate ions, for example, the carbon number can be 1 or more and 6 or less.
[0043]
X⁻Is selected from perfluoroalkylsulfonate ions, for example, the number of carbon atoms can be 1 or more and 6 or less.
[0044]
X⁻Is selected from imide anions, for example,⁻N (C_nF_{2n + 1}SO₂(C_mF_{2m + 1}SO₂) (N and m are independent natural numbers of 1 or more and 6 or less). By doing so, the coating on the negative electrode surface can be provided with physical and chemical stability while ensuring good ionic conductivity.
[0045]
In addition, X⁻Can be selected from camphorsulfonate ions, for example, d-camphor-10-sulfonate ion or the like can be used.
[0046]
The sulfonium salt represented by the general formula (1) is, for example, J.I. C. It can be synthesized by the method described in Crivello et al., Journal of Polymer Science, Polymer Chemistry Edition, 17, 977-999 (1979).
[0047]
  The proportion of the sulfonium salt represented by the general formula (1) in the electrolytic solution is not particularly limited, but preferably 0.01% of the total electrolytic solution.mass% Or more 10mass% Or less. 0.01massBy setting it as% or more, the effect can be sufficiently exhibited for improving battery characteristics. More preferably 0.1mass% Or more can be added, and by doing so, the battery characteristics can be further improved. 10massBy setting the ratio to not more than%, the resistance value of the electrolytic solution can be reduced. More preferably 5mass% Or less can be added, and by doing so, the battery characteristics can be further improved.
[0048]
The electrolyte solution for a secondary battery in the present invention includes, for example, cyclic carbonates, chain carbonates, aliphatic carboxylic acid esters, γ-lactones, cyclic ethers, chain ethers, or these as aprotic solvents. It can be set as the structure containing a fluorine derivative.
[0049]
Specifically, for example, cyclic carbonates such as propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate (BC), vinylene carbonate (VC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), chain carbonates such as dipropyl carbonate (DPC), aliphatic carboxylic acid esters such as methyl formate, methyl acetate and ethyl propionate, γ-lactones such as γ-butyrolactone, 1,2-ethoxy Chain ethers such as ethane (DEE) and ethoxymethoxyethane (EME), cyclic ethers such as tetrahydrofuran and 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, acetamide, dimethylphenol Lumamide, dioxolane, acetonitrile, propylnitrile, nitromethane, ethyl monoglyme, phosphoric acid triester, trimethoxymethane, dioxolane derivative, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, 3-methyl-2- Oxazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, ethyl ether, N-methylpyrrolidone, fluorinated carboxylic acid ester, methyl-2,2,2-trifluoroethyl carbonate, methyl-2,2,3,3,3-pentafluoro Propyl carbonate, trifluoromethyl ethylene carbonate, monofluoromethyl ethylene carbonate, difluoromethyl ethylene carbonate, 4,5-difluoro-1,3-dioxolan-2-one, monofluoroethylene carbonate Among such bets may be used by mixing one or two or more.
[0050]
The electrolyte solution for a secondary battery of the present invention can further include a lithium salt as an electrolyte. In this way, since lithium ions can be used as a mobile substance, battery characteristics can be improved. Examples of lithium salts include lithium imide salts and LiPF.₆, LiAsF₆LiAlCl₄LiClO₄, LiBF₄, LiSbF₆, LiN (C_nF_{2n + 1}SO₂(C_mF_{2m + 1}SO₂) (N and m are independent natural numbers of 1 or more and 6 or less). In particular, LiPF₆, LiBF_Four, LiN (C_nF_{2n + 1}SO₂(C_mF_{2m + 1}SO₂) (N and m are independent natural numbers of 1 to 6) are preferably used. By using these, the electrical conductivity of the lithium salt can be increased, and the cycle characteristics of the secondary battery can be further improved.
[0051]
In the secondary battery electrolyte of the present invention,⁻N (C_nF_{2n + 1}SO₂) (C_mF_{2m + 1}SO₂) (N and m are independent natural numbers of 1 or more and 6 or less). The imide anion can be contained, for example, as an anion of a sulfonium salt represented by the general formula (1). Further, it may be contained as a counter ion of a lithium salt. An imide anion is generated by dissolving in an aprotic solvent that is a solvent for the electrolyte solution for a secondary battery according to the present invention. By doing so, the cycle characteristics of the secondary battery can be further improved.
[0052]
In addition, by adding vinylene carbonate (hereinafter abbreviated as VC) or a derivative thereof, 1,3-propane sultone (hereinafter abbreviated as PS) or a derivative thereof to the electrolytic solution for a secondary battery according to the present invention, cycle characteristics are improved. Further improvement can be achieved.
[0053]
  VC or its derivatives are disclosed in, for example, JP-A-4-16975, JP-A-7-122296, JP-A-8-45545, JP-A-5-82138, JP-A-5-74486, JP-A-6 The compounds disclosed in JP-A No. -52887, JP-A No. 11-260401, JP-A No. 2000-208169, JP-A No. 2001-35530, JP-A No. 2000-138071 can be used. The amount of VC or its derivative added is 0.01% of the total electrolyte.mass% Or more 10mass% Or less is preferable. 0.01mass% Or more, the effect of improving the cycle characteristics can be suitably exhibited.massBy setting the ratio to not more than%, the resistance value of the electrolytic solution can be lowered.
[0054]
  Further, as PS or a derivative thereof, for example, compounds disclosed in Japanese Patent Application Laid-Open Nos. 2000-3724 and 2000-3725 can be used. PS or a derivative thereof, for example, 0.01% of the total electrolytemass% Or more 10mass% Or less can be included. By doing so, the effect of improving the cycle characteristics is suitably exhibited.
[0055]
Next, a secondary battery using the secondary battery electrolyte solution according to the present invention will be described. The secondary battery according to the present invention has a structure as shown in FIG. FIG. 1 is a schematic enlarged cross-sectional view in the thickness direction of a negative electrode current collector of a secondary battery according to the present invention. The positive electrode is formed by forming a layer 12 containing a positive electrode active material on the positive electrode current collector 11. The negative electrode is formed by forming a layer 13 containing a negative electrode active material on a negative electrode current collector 14. The positive electrode and the negative electrode are disposed to face each other with an electrolyte solution 15 of an electrolyte aqueous solution and a porous separator 16 in the electrolyte solution 15 interposed therebetween. The porous separator 16 is disposed substantially parallel to the layer 13 containing the negative electrode active material.
[0056]
As the electrolytic solution 15, the above-described secondary battery electrolytic solution containing a sulfonium salt is used. The electrolyte solution for a secondary battery can be obtained by dissolving or dispersing a sulfonium salt and, if necessary, a lithium salt and other additives in an aprotic solvent.
[0057]
In the secondary battery of FIG. 1, as the negative electrode current collector 14, for example, a metal thin film mainly composed of Al, Cu or the like can be used. In addition, as the negative electrode active material used for the layer 13 containing the negative electrode active material, for example, one or more substances selected from the group consisting of lithium metal, lithium alloy, and a material capable of inserting and extracting lithium are used. Can do. As a material for inserting and extracting lithium ions, a carbon material or an oxide can be used.
[0058]
As the carbon material, graphite storing lithium, amorphous carbon, diamond-like carbon, carbon nanotube, or the like, or a composite thereof can be used. Of these, graphite material or amorphous carbon is particularly preferable. In particular, graphite materials have high electron conductivity, excellent adhesion to current collectors made of metals such as copper and voltage flatness, and are formed at high processing temperatures, so they contain fewer impurities and improve negative electrode performance. It is preferable because it works advantageously.
[0059]
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 other compounds, and the amorphous structure does not lead to deterioration due to nonuniformity such as crystal grain boundaries and defects. As a film formation method, a vapor deposition method, a CVD method, a sputtering method, or the like can be used.
[0060]
The lithium alloy is composed of lithium and a metal capable of forming an alloy with lithium. For example, it is made of a binary or ternary alloy of a metal such as Al, Si, Pb, Sn, In, Bi, Ag, Ba, Ca, Hg, Pd, Pt, Te, Zn, La, and lithium. As the lithium metal or lithium alloy, an amorphous alloy is particularly preferable. This is because the amorphous structure hardly causes deterioration due to non-uniformity such as crystal grain boundaries and defects.
[0061]
Lithium metal or lithium alloy is formed by an appropriate method such as a melt cooling method, a liquid quenching method, an atomizing method, a vacuum deposition method, a sputtering method, a plasma CVD method, a photo CVD method, a thermal CVD method, a sol-gel method, etc. Can do.
[0062]
In the secondary battery of FIG. 1, as the positive electrode active material used for the layer 12 containing the positive electrode active material, an oxide that can occlude and release lithium ions, Li_xMO₂(Where M represents at least one transition metal, 0 <x <1.2), for example, a complex oxide such as Li_xCoO₂, Li_xNiO₂Li_xMn₂O₄, Li_xMnO₃, Li_xNi_yC_1-yO₂(0 <x <1.2, 0 <y <1), or any of organic sulfur compounds, conductive polymers, stabilized radical compounds, or a mixture thereof can be used. Alternatively, a lithium-containing composite oxide having a plateau at 4.5 V or more at the metal lithium counter electrode potential can be used. Examples of the lithium-containing composite oxide include spinel-type lithium manganese composite oxide, olivine-type lithium-containing composite oxide, and reverse spinel-type lithium-containing composite oxide. The lithium-containing composite oxide can be, for example, a compound represented by the following general formula (11).
Li_a(M_xMn_2-b) O₄      (11)
(In the formula, 0 <b <2, 0 <a <1.2. M is at least one selected from the group consisting of Ni, Co, Fe, Cr, and Cu.)
[0063]
The positive electrode in the secondary battery of FIG. 1 includes these positive electrode active materials, N-methyl-2-pyrrolidone (hereinafter abbreviated as NMP) together with a conductive material such as carbon black and a binder such as polyvinylidene fluoride (PVDF). Or the like, and is applied onto the positive electrode current collector 11 such as an aluminum foil.
[0064]
The secondary battery shown in FIG. 1 has a negative electrode and a positive electrode laminated in a dry air or inert gas atmosphere via a porous separator 16, or a laminated product, and then a battery can, a synthetic resin and a metal foil. And is impregnated with an electrolyte solution containing a sulfonium salt. And a battery can be manufactured by sealing an exterior body. A film can be formed on the negative electrode by charging the secondary battery after sealing or sealing the battery outer package. In addition, as the porous separator 16, porous films, such as polyolefin, such as a polypropylene and polyethylene, a fluororesin, are used.
[0065]
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, a coin shape, and a laminate outer shape.
[0066]
【Example】
  (Reference example1)
  (Production of battery)
  ExampleAnd reference examplesThe production of the battery will be described. 20 μm aluminum foil for the positive electrode current collector and LiMn for the positive electrode active material in the positive electrode₂O₄The negative electrode active material in the negative electrode, 20 μm lithium metal deposited on the 10 μm copper foil of the negative electrode current collector, and the electrolyte used a mixed solvent of EC and DEC (volume ratio: 30/70) as a solvent, 1 molL as electrolyte^-1LiPF₆Was used.
[0067]
  Next, as an additive, a sulfonium salt represented by the above formula (3) is added to the electrolyte solution as 1mass% To be included, this exampleAnd reference examplesAn electrolyte solution was prepared. And the negative electrode and the positive electrode were laminated | stacked through the separator which consists of polyethylene, and the secondary battery was produced.
[0068]
(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 factor (discharge depth) of the lithium metal negative electrode was 33%. The capacity retention rate (%) is a value obtained by dividing the discharge capacity (mAh) after 300 cycles by the discharge capacity (mAh) at the 10th cycle. The results obtained in the cycle test are shown in Table 1 below.
[0069]
[Table 1]

[0070]
  (Reference example2-5)
  Instead of adding the sulfonium salt represented by the above formula (3) to the electrolytic solution, an electrolytic solution added with the sulfonium compound shown in Table 2 was used.Reference exampleA battery was prepared and evaluated in the same manner as in Example 1. The results of the cycle characteristics are shown in Table 1.
[0071]
  (Comparative Example 1)
  Without adding a sulfonium salt to the electrolyte,Reference example1 is manufactured,Reference exampleThe cycle characteristics were examined in the same manner as in 1. The results are shown in Table 1.
[0072]
  Reference exampleIn the batteries shown in 1 to 5, it was confirmed that the capacity retention rate after the cycle test was greatly increased, that is, the cycle characteristics were improved, as compared with Comparative Example 1. The improvement of the capacity retention rate is considered to be because a stable coating is formed on the negative electrode surface and the coating has high ionic conductivity.
[0073]
  (Reference example6)
  This reference example, Graphite is used as the negative electrode active material, and 1 molL as the electrolyte.^-1LiN (C₂F₅SO₂)₂Was used. A negative electrode made of graphite is obtained by applying a paste obtained by mixing polyvinylidene fluoride dissolved in N-methyl-2-pyrrolidone as a binder to graphite powder and a conductive material, and applying it to a copper foil, followed by drying. is there. Using the negative electrode obtained,Reference exampleA secondary battery was produced in the same manner as in Example 1, and the cycle characteristics were evaluated. Table 2 shows the results obtained in the cycle test.
[0074]
[Table 2]

[0075]
  (Reference example7-9)
  Using the sulfonium salt shown in Table 2,Reference exampleA secondary battery was prepared in the same manner as in Example 6, and the cycle characteristics were evaluated.
[0076]
  (Comparative Example 2)
  Without adding sulfonium salt,Reference exampleA secondary battery similar to that of No. 6 was produced, and the cycle characteristics were evaluated. The results of the cycle test are shown in Table 2.
[0077]
  Reference exampleIn the batteries shown in 6 to 9, 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 Example 2. Therefore, it can be seen that even when the negative electrode active material is graphite, the cycle characteristics are improved by adding a sulfonium salt to the electrolytic solution.
[0078]
  (Reference example10)
  Negative electrode active materialAsUsing amorphous carbon,Reference exampleA secondary battery was produced in the same manner as in Example 1, and the cycle characteristics were evaluated.This reference exampleThe solvent of the electrolytic solution was PC (20) / EC (20) / DEC (60) (volume ratio). The results of the cycle test are shown in Table 3.
[0079]
[Table 3]

[0080]
  (Reference example11)
  Reference exampleSecondary batteries were produced in the same manner as in Example 10, and the cycle characteristics were evaluated. However, the compound represented by the above formula (7) was used as the sulfonium salt. The results of the cycle test are shown in Table 3.
[0081]
  (Comparative Example 3)
  Without adding sulfonium salt,Reference exampleA secondary battery similar to that of No. 7 was produced and the cycle characteristics were evaluated. The results of the cycle test are shown in Table 3.
[0082]
  Reference exampleAs compared with Comparative Example 3, it was confirmed that the batteries of Nos. 10 and 11 had an improved capacity retention rate after the cycle test, that is, improved cycle characteristics.
[0083]
  Example 12
  (Production of battery)
  As an additive to be added to the electrolytic solution, a sulfonium salt represented by the above formula (3) and 1,3-propane sultone (PS) were used, and each was added so as to be contained by 1% by mass in the electrolytic solution. Using this,Reference exampleIn the same manner as in Example 1, an electrolytic solution and a secondary battery were produced.
[0084]
(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 factor (discharge depth) of the lithium metal negative electrode was 33%. The capacity retention rate (%) is a value obtained by dividing the discharge capacity (mAh) after 300 cycles by the discharge capacity (mAh) at the 10th cycle. The results of the cycle test are shown in Table 4.
[0085]
[Table 4]

[0086]
  The battery shown in Example 12 isReference exampleCompared to 1, it was confirmed that the capacity retention rate after the cycle test was improved, that is, the cycle characteristics were improved. This is because the sulfonium salt used as an additivePSThis is due to the combined effect.
[0087]
  (Example 13)
  In this example, a secondary battery using an electrolytic solution further containing vinylene carbonate (VC) in addition to a sulfonium salt was produced. The solvent of the electrolytic solution is PC (20) / EC (20) / DEC (60) (volume ratio), and 1 molL as an electrolyte.^-1LiPF₆Was used. Next, as an additive, a sulfonium salt represented by the above formula (3) is added to the electrolyte 1mass% And vinylene carbonate (VC) 1mass% Was added. A negative electrode made of amorphous carbon and LiMn₂O₄A secondary battery was fabricated by laminating a positive electrode made of the above with a separator made of polyethylene. Table 5 shows the cycle characteristics of the obtained secondary battery.
[0088]
[Table 5]

[0089]
  Example 13 is Comparative Example 3 andReference exampleCompared to 7, the cycle characteristics were improved. This is due to the combined effect of the sulfonium salt used as an additive and VC.
[0090]
  (Reference example14-17)
  Reference exampleIn 10 secondary batteries, the concentration of the sulfonium salt represented by the above formula (3) was changed, and the cycle characteristics were measured. The results are shown in Table 6.
[0091]
[Table 6]

[0092]
  From Table 6, the sulfonium salt concentration is 0.1-10.massIt can be seen that the cycle characteristics are improved at%. So bookReference exampleIn, the sulfonium salt is 0.1mass% Or more 10mass% Or less, the effect of improving the cycle characteristics is exhibited.mass% Or more 5massIt has been found that a more preferable effect is exhibited by adding at most%.
[0093]
【The invention's effect】
As described above, according to the present invention, by using an electrolytic solution containing an aprotic solvent and the sulfonium salt represented by the general formula (1), the cycle life of the secondary battery is stable and excellent. The electrolyte solution for secondary batteries is realized. Further, according to the present invention, a secondary battery that exhibits a stable and excellent cycle life and high charge / discharge efficiency is realized.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram showing an example of a secondary battery according to the present invention.
[Explanation of symbols]
11 Positive current collector
12 Layer containing positive electrode active material
13 Layer containing negative electrode active material
14 Negative electrode current collector
15 Electrolyte
16 Porous separator

Claims (12)

An aprotic solvent, a sulfonium salt represented by the following general formula (1) , vinylene carbonate or 1,3-propane sultone,
The content of the sulfonium salt is 0.01% by mass or more and 10% by mass or less of the entire electrolyte for a secondary battery,
Content of the said vinylene carbonate or the said 1, 3- propane sultone is 0.01 mass% or more and 10 mass% or less of the whole electrolyte solution for secondary batteries.
Electrolytic solution for a secondary battery is.

(In the general formula (1), R ₁ , R ₂ and R ₃ are substituted or unsubstituted phenyl groups, substituted or unsubstituted linear or branched alkyl groups, substituted or unsubstituted A cycloalkyl group, or a ring structure in which R ₁ and R ₂ are condensed with each other, X ⁻ represents an anion.) 2. The electrolyte for a secondary battery according to claim 1, wherein X ⁻ in the general formula (1) is PF ₆ ⁻ , BF ₄ ⁻ , Br ⁻ , I ⁻ , AsF ₆ ⁻ , SbF ₆ ⁻ , an imide anion. An electrolyte solution for a secondary battery comprising one selected from alkylsulfonate ions, substituted or unsubstituted benzenesulfonate ions, perfluoroalkylsulfonate ions, or camphorsulfonate ions.   3. The secondary battery electrolyte according to claim 1, further comprising a lithium salt as an electrolyte. In the electrolytic solution for a secondary battery according to claim 3, as the lithium _{salt, LiPF 6, LiAsF 6, LiAlCl} 4, LiClO 4, LiBF 4, LiSbF 6, and _{LiN (C n F 2n + 1} SO 2) (C m F _{2m + 1} SO ₂ ) (n and m are independent natural numbers of 1 or more and 6 or less), and one or more substances selected from the group consisting of: The electrolyte solution for a secondary battery according to any one of claims 1 to 4,
^{_{- N (C n F 2n +}} 1 SO 2) (C m F 2m + 1 SO 2) (n, m 1 to 6 natural number which is independent)
The electrolyte solution for secondary batteries characterized by including the imide anion shown by these.   The electrolyte solution for a secondary battery according to any one of claims 1 to 5, wherein the aprotic solvent is a cyclic carbonate, a chain carbonate, an aliphatic carboxylic acid ester, a γ-lactone, a cyclic ether, An electrolyte solution for a secondary battery, comprising one or more solvents selected from the group consisting of chain ethers and a fluorine derivative of any one of the above compounds. A secondary battery comprising at least a positive electrode and the negative electrode, a secondary battery comprising the electrolyte solution for a secondary battery according to any one of claims 1 to 6. The secondary battery according to claim 7 , comprising a lithium-containing composite oxide as a positive electrode active material. In the secondary battery according to claim 7 or 8, as a negative electrode active material, selected absorbs lithium, release can material, lithium metal, metal materials capable of forming an alloy with lithium, and oxide materials, from the group consisting of A secondary battery comprising one or more substances. The secondary battery according to claim 9 , wherein the negative electrode active material includes a carbon material. The secondary battery according to claim 10 , wherein the carbon material is graphite. The secondary battery according to claim 10 , wherein the carbon material is amorphous carbon.

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