JP2004281325A - Electrolyte for secondary battery and the secondary battery using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress decomposition of electrolyte solvent for a secondary battery, to increase cycle life of the secondary battery, to suppress resistance increase of the secondary battery, and to increase capacity maintenance rate of the secondary battery. <P>SOLUTION: An electrolyte 15 containing an aprotic organic solvent and a compound represented by formula 1 is used. In formula 1, R<SB>1</SB>-R<SB>4</SB>each represents hydrogen atom, a methyl group, an ethyl group or halogen atom, and n represents an integer of 0-2. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

（但し、上記一般式（１）において、Ｒ_１〜Ｒ_４は、水素原子、メチル基、エチル基またはハロゲン原子であり、ｎは０以上２以下の整数である。）
【００２２】
本発明に係る二次電池用電解液は、上記一般式（１）で示される環式ジスルホン酸エステルを含む。上記一般式（１）で示される化合物は、電池の電極界面における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、正極がマンガンを含む酸化物の場合、マンガンの溶出を抑え、また溶出したマンガンが負極に付着することを防ぐ。よって本発明に係る二次電池用電解液を二次電池に用いることにより、負極に皮膜を形成し、またマンガンなどの溶出に対する影響を緩和できるなどの効果より、二次電池のサイクル特性を向上することができ、且つ抵抗上昇を抑制できる。
【００２３】
本発明の二次電池用電解液において、イミドアニオンおよび遷移金属イオンを含む構成とすることができる。こうすることにより、イミドアニオンと遷移金属イオンとの金属錯体が負極表面に形成される。また、イミドアニオンと遷移金属とからなる金属錯体を本発明の電解液に添加することもできる。添加した金属錯体自体あるいはその反応物が電極表面に形成される。これらの皮膜形成は、二次電池のサイクル特性を向上させることができる。また、二次電池中のガス発生または抵抗の上昇を抑制することができる。
【００２４】
本発明によれば、少なくとも正極と負極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、電解液として上記一般式（１）で示される化合物を含む二次電池用電解液を含むため、充放電効率、サイクル特性、または抵抗上昇率などの電池特性のいずれかが改善されるものである。
【００２５】
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）で示される化合物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。
【００２６】
【発明の実施の形態】
以下、本発明の具体的構成について図面を参照しながら説明する。本発明に係る電池はたとえば図１のような構造を有する。図１は、本実施形態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、電解液１５、および電解液１５の中の多孔質セパレータ１６を介して対向配置されている。多孔質セパレータ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。
【００２７】
電解液１５は、非プロトン性溶媒と、下記一般式（１）で示される環式ジスルホン酸エステルとを含む。
【００２８】
【化１０】

【００２９】
（但し、上記一般式（１）において、Ｒ_１〜Ｒ_４は、水素原子、メチル基、エチル基またはハロゲン原子であり、ｎは０以上２以下の整数である。）
【００３０】
上記一般式（１）で示される化合物は、たとえば下記一般式（２）で示される化合物とすることができる。
【００３１】
【化１１】

【００３２】
（但し、上記一般式（２）において、Ｒ_１〜Ｒ_２は、水素原子、メチル基、エチル基またはハロゲン原子であり、ｎは０以上２以下の整数である。）
【００３３】
さらに具体的には、一般式（２）で示される化合物が下記化学式（３）で示される化合物であってもよい。また、前記一般式（２）で示される化合物は、下記化学式（４）で示される化合物であってもよい。
【００３４】
【化１２】

【００３５】
【化１３】

【００３６】
また、上記一般式（１）で示される化合物は下記一般式（５）で示される化合物とすることもできる。
【００３７】
【化１４】

【００３８】
（但し、上記一般式（５）において、Ｒ_１〜Ｒ_２は、水素原子、メチル基、エチル基またはハロゲン原子であり、ｎは０以上２以下の整数である。）
【００３９】
さらに、上記一般式（１）で示される化合物の代表例を表１に具体的に例示するが、本発明はこれらに限定されるものではない。なお、上記化学式（３）で示される化合物は表１における化合物Ｎｏ．１であり、上記化学式（４）で示される化合物は表１中の化合物Ｎｏ．２である。また、表１において、化合物Ｎｏ．１、４、７、１０、１３および１６の主骨格は７員環であり、化合物Ｎｏ．２、５、８、１１、１２、１４および１７の主骨格は９員環であり、化合物Ｎｏ．３、６、９および１５の主骨格は１１員環である。
【００４０】
【表１】

【００４１】
上記一般式（１）に示す化合物は、例えば米国特許第４９５０７６８号または特公平５−４４９４６号公報に記載される製造方法を用いて得ることができる。
【００４２】
一般式（１）で示される化合物の電解液１５に占める割合は特に限定されないが、電解液１５全体の０．００５〜１０ｗｔ％で含まれることが好ましい。一般式（１）で示される化合物の濃度を０．００５ｗｔ％以上とすることにより、十分な皮膜効果を得ることができる。より好ましくは０．０１ｗｔ％以上添加され、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、１０ｗｔ％以下とすることにより、電解液１５の粘性の上昇、およびそれに伴う抵抗の増加を抑制することができる。より好ましくは５ｗｔ％以下添加され、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。
【００４３】
電解液１５は、上記一般式（１）で示される化合物に加え、さらにスルホニル基を有する一以上の化合物を含む構成とすることができる。たとえば、下記一般式（６）で示される化合物を含んでもよい。
【００４４】
【化１５】

【００４５】
（ただし、上記一般式（６）において、Ａは、置換もしくは無置換の炭素数１〜５のアルキレン基、カルボニル基、スルフィニル基、置換もしくは無置換の炭素数１〜５のフルオロアルキレン基、エーテル結合を介してアルキレン単位またはフルオロアルキレン単位が結合した炭素数２〜６の２価の基を示し、Ｂは置換もしくは無置換のアルキレン基を示す。）
【００４６】
電解液１５は、上記一般式（６）で示される化合物を含む。上記一般式（６）で示される化合物は、溶媒分子の分解をより一層抑制する。また、正極がマンガンを含む酸化物の場合、マンガンなどの溶出に対する影響をさらに確実に緩和できる。このため、二次電池のサイクル特性をさらに向上することができる。また、二次電池の抵抗上昇を抑制することができる。
【００４７】
なお、上記一般式（６）において、Ａの炭素数は、環を構成する炭素の数を指し、側鎖に含まれる炭素の数は含まれない。Ａが置換もしくは無置換の炭素数２〜５のフルオロアルキレン基である場合、Ａはメチレン単位とフルオロメチレン単位とを有していてもよいし、フルオロメチレン単位のみを有していてもよい。また、エーテル結合を介してアルキレン単位またはフルオロアルキレン単位が結合している場合、アルキレン単位同士が結合していてもよいし、フルオロアルキレン単位同士が結合していてもよいし、また、アルキレン単位とフルオロアルキレン単位とが結合していてもよい。
【００４８】
また、スルホニル基を有する化合物としてたとえば下記一般式（７）で示される化合物を含んでもよい。
【００４９】
【化１６】

【００５０】
（ただし、上記一般式（７）において、Ｚは、炭素数２以上４以下の置換または無置換のアルキレン基、炭素数２以上４以下の置換または無置換のアルケニレン基、置換または無置換の芳香族環、置換または無置換の複素環を示す。）
【００５１】
また、スルホニル基を有する化合物としてたとえば下記一般式（８）で示されるスルトン化合物を含むことができる。
【００５２】
【化１７】

【００５３】
（ただし、上記一般式（８）において、ｎは０以上２以下の整数である。また、Ｒ_１〜Ｒ_６は、水素原子、炭素数１以上１２以下のアルキル基、炭素数３以上６以下のシクロアルキル基、炭素数６以上１２以下のアリール基から独立に選択される。）
【００５４】
一般式（１）に示す化合物に加え、一般式（７）または（８）で示されるスルホニル基を有する化合物を加えることにより、電解液１５の粘度の調整が容易になる。また、スルホニル基を有する化合物を組み合わせて用いることにより相乗効果により、皮膜の安定性が向上する。また、溶媒分子の分解抑制を抑制することができる。また、電解液１５中の水分の除去効果が大きくなる。
【００５５】
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）、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。
【００５６】
前記一般式（１）に加え、さらにスルホニル化合物を電解液１５中に添加する場合、たとえば電解液１５中に０．００５ｗｔ％以上１０ｗｔ％以下となるよう添加することができる。０．００５ｗｔ％以上とすることにより、負極表面において効果的に皮膜を形成することができる。より好ましくは０．０１ｗｔ％以上とすることができる。また、１０ｗｔ％以下とすることにより、スルホニル化合物の溶解性が維持され、また電解液１５の粘性上昇を抑制することができる。より好ましくは、５ｗｔ％以下とすることができる。
【００５７】
電解液１５は、非プロトン性溶媒に一般式（１）で示される化合物、および必要に応じてスルホニル基を有する化合物、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。性質の異なる添加剤を混合させることにより、負極表面に性質の異なる皮膜を形成させるため、電池特性の向上に有効である。
【００５８】
他の添加物として、電解液１５は一般式（１）の化合物に加え、さらにイミドアニオンおよび遷移金属イオンを含むことができる。イミドアニオンと遷移金属とからなる金属錯体およびリチウム塩を含んでもよい。具体的には、イミド化合物と遷移金属化合物を溶解させ、さらに一般式（１）に示される化合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、さらに一般式（１）に示される化合物を溶解させる場合の二つの方法により作製される。
【００５９】
電解液１５がイミドアニオンと遷移金属イオンを含む場合、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））。また、イミドアニオンと遷移金属イオンとの金属錯体が含まれる場合、金属錯体をあらかじめ合成し、これを電解液１５に溶解することで充放電に関係なく金属錯体が負極表面に吸着される。このイミドアニオンを含んだ金属錯体は、電解液１５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。
【００６０】
また、このとき、イミドアニオンと遷移金属イオンとの金属錯体と、上記一般式（１）で示される二つの化合物が負極表面に存在するようになる。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、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。
【００６１】
この場合にも、本発明で重要な添加物である上記一般式（１）で示される化合物は、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、一般式（１）で示される化合物では負極や電解液１５に存在する微量の水分と反応し水分除去に有効である。
【００６２】
電解液１５に含まれるイミドアニオンは、たとえば、
⁻Ｎ（Ｃ_ｎＦ_２ｎ＋１ＳＯ_２）（Ｃ_ｍＦ_２ｍ＋１ＳＯ_２）（ただし、ｎ、ｍは独立した１以上６以下の自然数である。）
で示される化合物とすることができる。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）］とすることが好ましい。
【００６３】
また、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）のいずれかもしくはこれらの混合物とすることが好ましい。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。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、上述の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１５との界面により一層安定に存在することができる。
【００６４】
イミド化合物と遷移化合物を溶解させ、さらに上記一般式（１）で示される化合物を溶解させる場合、電解液１５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、好ましくは電解液１５全体に対して、０．００５ｗｔ％以上１０ｗｔ％以下の濃度とすることが好ましい。０．００５ｗｔ％以上とすることにより、電極表面全体に添加剤の効果が行き渡り、負極表面での皮膜形成に十分な効果が発揮される。好ましくは、０．０５ｗｔ％以上とすることができる。また、１０ｗｔ％以下とすることにより、電解液１５の粘性の増大が抑えられるため、電解液１５の抵抗を小さくすることができる。好ましくは、５ｗｔ％以下とすることができる。
【００６５】
このとき、電解液１５全体に含まれる環状ジスルホン酸エステルは０．０１ｗｔ％以上１０ｗｔ％以下であることが好ましい。０．０１ｗｔ％以上とすることにより、電極全体に添加剤の効果が行き渡らせることができる。また、１０ｗｔ％以下とすることにより、電解液１５の粘性の増大が抑えられるため、電解液１５の抵抗を小さくすることができる。
【００６６】
また、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、さらに上記一般式（１）で示される化合物を溶解させる場合、電解液１５に含まれる金属錯体は、特に限定されないが、同様の理由から、電界液１５全体に対して、０．００５ｗｔ％以上１０ｗｔ％以下の濃度とすることが好ましい。また、このとき、電解液１５全体に占める環状ジスルホン酸エステルは、同様の理由から、０．０１ｗｔ％以上１０ｗｔ％以下の濃度とすることが好ましい。
【００６７】
また、電解液１５に、ビニレンカーボネート（ＶＣ）またはその誘導体を添加することにより、二次電池のサイクル特性や抵抗上昇抑制効果の改善を図ることができる。ビニレンカボネートまたはその誘導体は、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。
【００６８】
ＶＣまたはその誘導体の添加量は、電解液１５全体の０．０１ｗｔ％以上１０ｗｔ％以下であることが好ましい。０．０１ｗｔ％以上とすることにより、サイクル特性を好適に発揮させることができ、さらに高温化での保存時の抵抗上昇を抑制することも可能となる。１０ｗｔ％以下とすることにより、電解液１５の抵抗値を低くすることができる。
【００６９】
電解液１５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、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）の中から選択された一以上の物質を含む構成とすることができる。また、特にＬｉＰＦ_６またはＬｉＢＦ_４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。
【００７０】
電解液１５は、非プロトン性溶媒として、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これらのいずれかのフッ素誘導体、からなる群から選択された一または２以上の溶媒を含むことができる。
【００７１】
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、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。
【００７２】
図１の二次電池において、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。
【００７３】
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酸化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。特に、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であり、好ましい。
【００７４】
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。
【００７５】
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。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。
【００７６】
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。
【００７７】
図１の二次電池の負極において、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液１５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。
【００７８】
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、充放電効率を高く維持することができる。
【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イミドアニオンとの反応性生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】
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、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る。また、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。
【００８１】
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（９）で表される化合物とすることができる。
Ｌｉ_ａ（Ｍ_ｘＭｎ_２−ｘ）Ｏ_４ （９）
（ただし、上記一般式（９）において、０＜ｘ＜２であり、また、０＜ａ＜１．２である。また、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。）
【００８２】
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。
【００８３】
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とう性フィルム等の外装体に収容し、上記一般式（１）で示される化合物を含む電解液１５を含浸させる。そして、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。
【００８４】
本実施形態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、ラミネート外装型、コイン型などがあげられる。
【００８５】
【実施例】
（実施例１）
（電池の作製）
本実施例の電池の作製について説明する。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。また、負極集電体として厚み１０μｍの銅箔を用い、こ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負極として用いた。また、電解液の溶媒として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と略記する。）を１ｍｏｌＬ^−１溶解し、さらに、上記表１に記載の化合物Ｎｏ．１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。
【００８６】
（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表２に示す。
【００８７】
（実施例２〜４）
実施例１において、化合物Ｎｏ．１の代わりに、表２に示す化合物を用いる他は、実施例１と同様にして二次電池を作製した。そして、実施例１と同様に電池の特性を調べた。結果を表２に示す。
【００８８】
（比較例１）
実施例１において、化合物Ｎｏ．１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。そして、実施例１と同様に電池の特性を調べた。結果を表２に示す。
【００８９】
（比較例２）
実施例１において、化合物Ｎｏ．１に代えて１，３−プロパンスルトン（１，３−ＰＳ）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。そして、実施例１と同様に電池の特性を調べた。結果を表２に示す。
【００９０】
【表２】

【００９１】
表２より、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。
【００９２】
（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、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。そして、実施例１と同様に電池の特性を調べた。結果を表３に示す。
【００９３】
（実施例６〜８）
実施例５において、化合物Ｎｏ．１に代えて表３に示す化合物を用いる他は、実施例５と同様にして二次電池を作製した。そして、実施例５と同様に電池の特性を調べた。結果を表３に示す。
【００９４】
（比較例３）
実施例５において、化合物Ｎｏ．１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。そして、実施例５と同様に電池の特性を調べた。結果を表３に示す。
【００９５】
【表３】

【００９６】
表３より、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。
【００９７】
（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。そして、実施例５と同様に電池の特性を調べた。結果を表４に示す。
【００９８】
（実施例１０〜１２）
実施例９において、化合物Ｎｏ．１に代えて表４に示す化合物を用いる他は、実施例９と同様にして二次電池を作製した。そして、実施例９と同様に電池の特性を調べた。結果を表４に示す。
【００９９】
（比較例４）
実施例９において、化合物Ｎｏ．１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。そして、実施例９と同様に電池の特性を調べた。結果を表４に示す。
【０１００】
【表４】

【０１０１】
表４より、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。
【０１０２】
（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とも表す。）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。そして、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。
【０１０３】
（実施例１４〜１６）
実施例１３において、化合物Ｎｏ．１に代えて表５に示す化合物を用いる他は、実施例１３と同様にして二次電池を作製した。そして、実施例１３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】
表５より、実施例１３〜１６に示した電池は、実施例１〜４および比較例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）で示される化合物と１，３−ＰＳとの複合効果によるものである。
【０１０６】
（実施例１７）
実施例５において、電解液にさらに１，３−ＰＳ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。そして、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１８〜２０）
実施例１７において、化合物Ｎｏ．１に代えて表６に示す化合物を用いる他は、実施例１７と同様にして二次電池を作製した。そして、実施例１７と同様に電池の特性を調べた。結果を表６に示す。
【０１０８】
【表６】

【０１０９】
表６より、実施例１７〜２０に示した電池は、実施例５〜８および比較例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）で示される化合物と１，３−ＰＳとの複合効果によるものである。
【０１１０】
（実施例２１）
実施例９において、電解液にさらに１，３−ＰＳ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。そして、実施例９と同様に電池の特性を調べた。結果を表７に示す。
【０１１１】
（実施例２２〜２４）
実施例２１において、化合物Ｎｏ．１に代えて表７に示す化合物を用いる他は、実施例２１と同様にして二次電池を作製した。そして、実施例２１と同様に電池の特性を調べた。結果を表７に示す。
【０１１２】
【表７】

【０１１３】
表７より、実施例２１〜２４に示した電池は、実施例９〜１２および比較例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）で示される化合物と１，３−ＰＳとの複合効果によるものである。
【０１１４】
（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８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。そして、実施例９と同様に電池の特性を調べた。結果を表８に示す。
【０１１５】
【表８】

【０１１６】
表８より、実施例２５〜２８の電池は、いずれも比較例４および実施例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。
【０１１７】
（実施例２９〜３２）
実施例９において、電解液にさらに表９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。そして、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。
【０１１８】
【表９】

【０１１９】
表９より、実施例２９〜３２の電池は、いずれも比較例４および実施例９と比べ、サイクル特性が改善されたことが確認された。
【０１２０】
（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とも表す。）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。そして、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。
【０１２１】
（実施例３４〜３６）
実施例３３において、化合物Ｎｏ．１に代えて表１０に示す化合物を用いる他は、実施例３３と同様にして二次電池を作製した。そして、実施例３３と同様に電池の特性を調べた。結果を表１０に示す。
【０１２２】
【表１０】

【０１２３】
表１０より、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。
【０１２４】
（実施例３７）
実施例９において、電解液にさらにＶＣと１，３−ＰＳがそれぞれ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。そして、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。
【０１２５】
（実施例３８〜４０）
実施例３７において、化合物Ｎｏ．１に代えて表１１に示す化合物を用いる他は、実施例３７と同様にして二次電池を作製した。そして、実施例３７と同様に電池の特性を調べた。結果を表１１に示す。
【０１２６】
【表１１】

【０１２７】
表１１より、実施例３７〜４０に示した電池は、比較例４や実施例９〜１２および実施例３３〜３６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、一般式（１）で示す化合物とＶＣと１，３−ＰＳとの複合効果によるものである。
【０１２８】
（実施例４１）
電解液の添加剤として化合物Ｎｏ．１に示す化合物を用いて、実施例９と同様な二次電池を作製した。本実施例では、保存放置における二次電池の抵抗値を測定した。まず作製した二次電池について、２０℃において充電および放電を１回ずつ行った。この時の充電電流および放電電流は一定であり、この際の放電容量を初期容量としその際の抵抗を初期抵抗とした。その後、定電流定電圧で所定の電圧まで２．５時間の放電後、４５℃または６０℃の条件下で９０日間放置した。放置後の室温において再度定電流で放電操作を行い、続いて同じく定電流で充電、放電をもう一度繰り返し、充電時の抵抗を測定した。
【０１２９】
初期抵抗を１とし、９０日保存後の抵抗値を相対値（４５℃または６０℃保存）で示した結果と、６０℃保存後の容量維持率（９０日後の放電容量／初期放電容量）の結果を表１２に示す。
【０１３０】
（実施例４２〜４５）
電解液に含まれる添加物として表１２に示す化合物を用いて、実施例９と同様な二次電池を作製し、実施例４１と同様の評価を行った。
【０１３１】
（比較例５）
電解液に含まれる添加物として、１，３−ＰＳを用いる以外は、実施例４１と同様に二次電池を作製し、同様な評価を行った。結果を表１２に示す。
【０１３２】
【表１２】

【０１３３】
表１２に示されるように、実施例４１〜４５の電池はいずれも従来の１，３−ＰＳを添加した比較例５と比べ、各温度での抵抗上昇率が抑制されていることが判明した。特に、６０℃下での抵抗上昇の抑制が顕著であった。また、容量維持率は比較例５と比較して顕著に向上している。
【０１３４】
（実施例４６）
本実施例は電解液の添加物として化合物Ｎｏ．１を用いて、実施例３３と同じ二次電池を作製し、実施例４１と同様の評価を行った。初期抵抗を１とし、９０日保存後の抵抗値を相対値（４５℃または６０℃保存）で示した結果と、６０℃保存後の容量維持率（９０日後の放電容量／初期放電容量）の結果を表１３に示す。
【０１３５】
（実施例４７〜５０）
添加物としてとして表１３に示す化合物を用いて、実施例３３と同様に二次電池を作製し、同様に評価を行った。
【０１３６】
（比較例６）
電解液に含まれる添加物として、１，３−ＰＳを用いる以外は、実施例４６と同様に二次電池を作製し、同様に評価を行った。結果を表１３に示す。
【０１３７】
【表１３】

【０１３８】
表１３に示されるように、実施例４６〜５０の電池はいずれも従来の１，３−ＰＳを添加した比較例６と比べ、各温度での抵抗上昇率が抑制されていることが判明した。特に、６０℃下での抵抗上昇の抑制が顕著であった。また、容量維持率は比較例６と比較して顕著に向上している。
【０１３９】
【発明の効果】
以上説明したように本発明によれば、非プロトン性有機溶媒と、上記一般式（１）で示される化合物とを含む電解質を用いることにより、二次電池の電解液の溶媒の分解を抑制することができる。また、本発明によれば、二次電池のサイクル寿命を向上させることができる。また、本発明によれば、二次電池の抵抗上昇を抑制することができる。また、本発明によれば、二次電池の容量維持率を向上させることができる。
【図面の簡単な説明】
【図１】本実施形態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 電解液
１６ 多孔質セパレータ[0001]
TECHNICAL FIELD 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 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 called a surface film, a protective film, a SEI (Solid Electrolyte Interface: solid electrolyte interface) or a film (hereinafter, also referred to as a “surface film”) is formed on the surface of the negative electrode. ing. 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. 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.
[0004]
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.
[0005]
Patent Literature 1 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. 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. These react to form a surface film of lithium fluoride on the negative electrode surface. 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. Further, there may be a case where the surface film of lithium hydroxide or lithium oxide is not formed uniformly, or a case where there is a part where lithium is exposed. In these cases, a uniform thin film cannot be formed, or a problem arises due to reaction of lithium with water, hydrogen fluoride, or the like. In addition, when the reaction was insufficient, unnecessary compound components other than the fluoride remained, which sometimes caused a decrease in ionic conductivity. 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 high yield. there were.
[0006]
In Patent Document 2, 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. 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.
[0007]
Patent Literature 3 discloses a technique for forming a surface film structure mainly composed of a material having a rock salt type crystal structure on the surface of a lithium sheet in which a uniform crystal structure, that is, a (100) crystal plane is preferentially oriented. It has been 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. 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. Specifically, in order to form a solid solution film of at least one of LiCl, LiBr, and LiI and LiF, a lithium sheet having a (100) crystal plane preferentially oriented by pressing treatment (rolling) produced by pressing (rolling) is used. A negative electrode for a non-aqueous electrolyte battery is manufactured by immersing in an electrolytic solution 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. . However, in Patent Document 3, 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 nonuniform. Thus, it was difficult to form a stable surface film, and the effect of suppressing dendrite was not always sufficiently obtained.
[0008]
Naoi et al. Reported the 68th Electrochemical Society (September 2000, Chiba Institute of Technology, lecture number: 2A24) and the 41st Battery Symposium (November 2000, Nagoya International Convention Center, lecture number 1E03). In a conference presentation, we reported on the effect of complexes of lanthanoid transition metals such as europium and imide anions on lithium metal anodes. 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. Although this method has a certain effect on improving the cycle life, it has not been sufficient. In addition, LiN (C₂F₅SO₂)₂It is essential to use a relatively expensive lithium imide salt such as₆) Transition metals and CF₃SO₃ ⁻F₃Even when a complex composed of S ions is added, a complex composed of a transition metal and an imide anion is not formed, so that the cycle characteristics are not improved. Further, when a lithium imide salt is used as the electrolyte, LiPF₆Therefore, there is a problem that the internal resistance of the battery increases because the resistance of the electrolytic solution is higher than in the case of using such a method.
[0009]
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.
[0010]
Patent Literature 4 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, the capacity may decrease rapidly when the cycle is repeated.
[0011]
Patent Literature 5 discloses a negative electrode in which a surface of a carbon material is coated with a thin film of a lithium ion conductive solid electrolyte. It is said that this makes it possible to suppress the decomposition of the solvent that occurs when a carbon material is used, and to provide a lithium ion secondary battery that can use propylene carbonate, in particular. 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, which may lead to deterioration of cycle life.
[0012]
Further, in Patent Document 6, in a nonaqueous electrolyte secondary battery including a carbon material having a d value of 3.37 ° or less on a lattice plane (002) plane as a negative electrode and containing a carbonate ester, A secondary battery including a vinylene carbonate derivative is disclosed. It is stated that the decomposition of the non-aqueous electrolyte on the carbon anode can be suppressed, and the cycle characteristics of the non-aqueous secondary battery can be improved. However, there is still room for improvement in the performance of secondary batteries using vinylene carbonate and vinylene carbonate derivatives, and further improvements in high-temperature characteristics and cycle characteristics are required.
[0013]
Further, in Patent Document 7, the negative electrode is made of a material containing graphite, and a cyclic carbonate and a chain carbonate are mainly used as an electrolytic solution, and 0.1 to 4 wt% of 1,3-propane is contained in the electrolytic solution. A secondary battery containing 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 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. However, this method has a problem that a sufficient film effect cannot be obtained, and charges due to the decomposition of solvent molecules or anions appear as irreversible capacity components, leading to a decrease in initial charge / discharge efficiency. In addition, there has been a problem that the resistance of the formed film component is high, and particularly at high temperatures, the rate of increase of the resistance over time is large.
[0014]
[Patent Document 1]
JP-A-7-302617
[Patent Document 2]
JP-A-8-250108
[Patent Document 3]
JP-A-11-288706
[Patent Document 4]
JP-A-5-234585
[Patent Document 5]
JP-A-5-275077
[Patent Document 6]
JP-A-7-122296
[Patent Document 7]
JP-A-2000-3724
[0015]
[Problems to be solved by the invention]
As described above, the conventional technology cannot obtain a sufficient film effect for improving the battery characteristics, and has the following problems.
[0016]
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. 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. 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. 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.
[0017]
In addition, for a carbon material such as graphite, a sufficient film effect cannot be obtained, and charges due to the decomposition of solvent molecules or anions appear as irreversible capacity components, leading to a decrease in 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. 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.
[0018]
The nature of the film formed on the negative electrode surface in this way is deeply related to its charge / discharge efficiency, cycle life, safety, etc., but there is no method that can control the film over a long period of time. It has been desired to develop an electrolytic solution that forms a film that leads to stable and sufficient charge / discharge efficiency.
[0019]
The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a technique for suppressing the decomposition of a solvent in an electrolytic solution of a secondary battery. Another object of the present invention is to provide a technique for improving the cycle life of a secondary battery. Another object of the present invention is to provide a technique for suppressing an increase in resistance of a secondary battery. Another object of the present invention is to provide a technique for improving the capacity retention of a secondary battery.
[0020]
[Means for Solving the Problems]
According to the present invention, there is provided an electrolyte for a secondary battery, comprising: an aprotic solvent; and a cyclic disulfonic acid ester having an unsaturated bond represented by the following general formula (1). .
[0021]
Embedded image

(However, in the above general formula (1), R₁~ R₄Is a hydrogen atom, a methyl group, an ethyl group or a halogen atom, and n is an integer of 0 or more and 2 or less. )
[0022]
The electrolytic solution for a secondary battery according to the present invention contains the cyclic disulfonic acid ester represented by the general formula (1). The compound represented by the general formula (1) contributes to the formation of a passive film at the electrode interface of the battery, and as a result, suppresses the decomposition of solvent molecules. In addition, when the positive electrode is an oxide containing manganese, elution of manganese is suppressed, and the eluted manganese is prevented from adhering to the negative electrode. Therefore, by using the electrolyte solution for a secondary battery according to the present invention in a secondary battery, a film is formed on the negative electrode, and the effect on elution of manganese and the like can be reduced, thereby improving the cycle characteristics of the secondary battery. And an increase in resistance can be suppressed.
[0023]
The electrolytic solution for a secondary battery of the present invention may be configured to include an imide anion and a transition metal ion. By doing so, a metal complex of the imide anion and the transition metal ion is formed on the negative electrode surface. In addition, a metal complex composed of an imide anion and a transition metal can be added to the electrolytic solution of the present invention. The added metal complex itself or its reactant is formed on the electrode surface. The formation of these films can improve the cycle characteristics of the secondary battery. Further, generation of gas or an increase in resistance in the secondary battery can be suppressed.
[0024]
According to the present invention, there is provided a secondary battery including 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 contains an electrolyte for a secondary battery containing the compound represented by the general formula (1) as an electrolyte, any one of the battery characteristics such as charge / discharge efficiency, cycle characteristics, and resistance increase rate. Is improved.
[0025]
The electrolyte solution for a secondary battery according to the present invention is simple and stable by a production method including a step of dissolving the compound represented by the general formula (1) in a solvent and a step of dissolving a lithium salt. Manufactured.
[0026]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, a specific configuration of the present invention will be described with reference to the drawings. The battery according to the present invention has, for example, 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 embodiment. The positive electrode is formed by forming a layer 12 containing a positive electrode active material on a 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 opposed to each other with an electrolyte 15 and a porous separator 16 in the electrolyte 15 interposed therebetween. The porous separator 16 is disposed substantially parallel to the layer 13 containing the negative electrode active material.
[0027]
The electrolytic solution 15 includes an aprotic solvent and a cyclic disulfonic acid ester represented by the following general formula (1).
[0028]
Embedded image

[0029]
(However, in the above general formula (1), R₁~ R₄Is a hydrogen atom, a methyl group, an ethyl group or a halogen atom, and n is an integer of 0 or more and 2 or less. )
[0030]
The compound represented by the general formula (1) can be, for example, a compound represented by the following general formula (2).
[0031]
Embedded image

[0032]
(However, in the above general formula (2), R₁~ R₂Is a hydrogen atom, a methyl group, an ethyl group or a halogen atom, and n is an integer of 0 or more and 2 or less. )
[0033]
More specifically, the compound represented by the general formula (2) may be a compound represented by the following chemical formula (3). Further, the compound represented by the general formula (2) may be a compound represented by the following chemical formula (4).
[0034]
Embedded image

[0035]
Embedded image

[0036]
Further, the compound represented by the general formula (1) may be a compound represented by the following general formula (5).
[0037]
Embedded image

[0038]
(However, in the above general formula (5), R₁~ R₂Is a hydrogen atom, a methyl group, an ethyl group or a halogen atom, and n is an integer of 0 or more and 2 or less. )
[0039]
Furthermore, typical examples of the compound represented by the general formula (1) are specifically shown in Table 1, but the present invention is not limited thereto. The compound represented by the above chemical formula (3) is the compound No. in Table 1. 1, and the compound represented by the above chemical formula (4) is Compound No. 1 in Table 1. 2. In Table 1, Compound No. The main skeleton of 1, 4, 7, 10, 13 and 16 is a 7-membered ring, and Compound No. The main skeleton of 2, 5, 8, 11, 12, 14 and 17 is a 9-membered ring. The main skeleton of 3, 6, 9 and 15 is an 11-membered ring.
[0040]
[Table 1]

[0041]
The compound represented by the above general formula (1) can be obtained, for example, by using a production method described in US Pat. No. 4,950,768 or Japanese Patent Publication No. 5-44946.
[0042]
The proportion of the compound represented by the general formula (1) in the electrolytic solution 15 is not particularly limited, but is preferably contained at 0.005 to 10 wt% of the entire electrolytic solution 15. By setting the concentration of the compound represented by the general formula (1) to 0.005 wt% or more, a sufficient film effect can be obtained. More preferably, it is added in an amount of 0.01 wt% or more, whereby the battery characteristics can be further improved. Further, by setting the content to 10 wt% or less, it is possible to suppress an increase in the viscosity of the electrolytic solution 15 and an accompanying increase in resistance. More preferably, it is added in an amount of 5 wt% or less, whereby the battery characteristics can be further improved.
[0043]
The electrolytic solution 15 can be configured to include one or more compounds having a sulfonyl group in addition to the compound represented by the general formula (1). For example, it may contain a compound represented by the following general formula (6).
[0044]
Embedded image

[0045]
(However, in the general formula (6), A represents a substituted or unsubstituted alkylene group having 1 to 5 carbon atoms, a carbonyl group, a sulfinyl group, a substituted or unsubstituted fluoroalkylene group having 1 to 5 carbon atoms, an ether A divalent group having 2 to 6 carbon atoms to which an alkylene unit or a fluoroalkylene unit is bonded via a bond, and B is a substituted or unsubstituted alkylene group.)
[0046]
The electrolytic solution 15 contains the compound represented by the general formula (6). The compound represented by the general formula (6) further suppresses the decomposition of the solvent molecule. In addition, when the positive electrode is an oxide containing manganese, the influence on elution of manganese and the like can be more reliably reduced. For this reason, the cycle characteristics of the secondary battery can be further improved. Further, an increase in resistance of the secondary battery can be suppressed.
[0047]
In the general formula (6), the number of carbon atoms of A indicates the number of carbon atoms constituting the ring, and does not include the number of carbon atoms contained in the side chain. When A is a substituted or unsubstituted fluoroalkylene group having 2 to 5 carbon atoms, A may have a methylene unit and a fluoromethylene unit, or may have only a fluoromethylene unit. When an alkylene unit or a fluoroalkylene unit is bonded via an ether bond, the alkylene units may be bonded to each other, or the fluoroalkylene units may be bonded to each other, or A fluoroalkylene unit may be bonded.
[0048]
Further, the compound having a sulfonyl group may include, for example, a compound represented by the following general formula (7).
[0049]
Embedded image

[0050]
(In the above general formula (7), Z is a substituted or unsubstituted alkylene group having 2 to 4 carbon atoms, a substituted or unsubstituted alkenylene group having 2 to 4 carbon atoms, a substituted or unsubstituted aromatic group. Represents an aromatic ring, a substituted or unsubstituted heterocyclic ring.)
[0051]
Further, as the compound having a sulfonyl group, for example, a sultone compound represented by the following general formula (8) can be included.
[0052]
Embedded image

[0053]
(In the above general formula (8), n is an integer of 0 or more and 2 or less.₁~ R₆Is independently selected from a hydrogen atom, an alkyl group having 1 to 12 carbon atoms, a cycloalkyl group having 3 to 6 carbon atoms, and an aryl group having 6 to 12 carbon atoms. )
[0054]
By adding a compound having a sulfonyl group represented by the general formula (7) or (8) in addition to the compound represented by the general formula (1), the viscosity of the electrolytic solution 15 can be easily adjusted. Further, by using a compound having a sulfonyl group in combination, the stability of the film is improved due to a synergistic effect. Further, the suppression of the decomposition of the solvent molecules can be suppressed. Further, the effect of removing water in the electrolytic solution 15 increases.
[0055]
Specific examples of the compound having a sulfonyl group 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), γ-sultone compound (JP-A-2000-235866) ), Sulfolene derivatives (JP-A-2000-294278), and the like, but are not limited thereto.
[0056]
When a sulfonyl compound is further added to the electrolytic solution 15 in addition to the general formula (1), for example, the sulfonyl compound can be added to the electrolytic solution 15 so as to be 0.005% by weight or more and 10% by weight or less. When the content is 0.005 wt% or more, a film can be effectively formed on the negative electrode surface. More preferably, it can be 0.01 wt% or more. When the content is 10 wt% or less, the solubility of the sulfonyl compound is maintained, and the increase in the viscosity of the electrolytic solution 15 can be suppressed. More preferably, it can be 5 wt% or less.
[0057]
The electrolytic solution 15 is obtained by dissolving or dispersing the compound represented by the general formula (1) and, if necessary, a compound having a sulfonyl group, a lithium salt and other additives in an aprotic solvent. By mixing additives having different properties to form films having different properties on the surface of the negative electrode, it is effective for improving battery characteristics.
[0058]
As another additive, the electrolyte solution 15 may further contain an imide anion and a transition metal ion in addition to the compound of the general formula (1). A metal complex comprising an imide anion and a transition metal and a lithium salt may be included. Specifically, the case where the imide compound and the transition metal compound are dissolved and the compound represented by the general formula (1) is further dissolved, and the case where the metal complex composed of the transition metal cation and the imide anion is dissolved in advance and the general formula ( It is prepared by two methods for dissolving the compound shown in 1).
[0059]
When the electrolyte solution 15 contains an imide anion and a transition metal ion, a metal complex of the imide anion and the transition metal is formed on the surface of the negative electrode by charging and discharging (the 2000 Autumn Meeting of Electrochemistry (September 2000, Chiba Institute of Technology, (Lecture number: 2A24), 41st Battery Symposium (November 2000, Nagoya International Congress Center, lecture number: 1E03)). When a metal complex of an imide anion and a transition metal ion is contained, the metal complex is synthesized in advance and dissolved in the electrolytic solution 15, whereby the metal complex is adsorbed on the negative electrode surface regardless of charge and discharge. The metal complex containing the imide anion forms a uniform film on the surface of the negative electrode in the electrolytic solution 15, thereby arranging 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.
[0060]
At this time, the metal complex of the imide anion and the transition metal ion and the two compounds represented by the general formula (1) are present on the negative electrode surface. The metal complex formed by the imide salt to be added or the metal complex formed by the imide salt and the transition metal forms a stabilized film by adsorbing to a non-reactive site, thereby performing lithium ion conduction.
[0061]
Also in this case, the compound represented by the general formula (1), which is an important additive in the present invention, contributes to the formation of a passive film on the negative electrode surface, and as a result, suppresses the decomposition of solvent molecules. In addition, the compound represented by the general formula (1) reacts with a small amount of water present in the negative electrode and the electrolytic solution 15 and is effective in removing water.
[0062]
The imide anion contained in the electrolytic solution 15 is, for example,
⁻N (C_nF_{2n + 1}SO₂) (C_mF_{2m + 1}SO₂(However, n and m are independent natural numbers of 1 or more and 6 or less.)
Can be obtained. In particular, a perfluoroethylsulfonylimide anion [⁻N (C₂F₅SO₂)].
[0063]
In addition, the transition metal is preferably a lanthanoid transition metal, and in particular, any one of europium (Eu), neodymium (Nd), erbium (Er), and holmium (Ho) or a mixture thereof. . 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. 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-based transition metal cation and the imide anion can be more stably present at the interface between the negative electrode and the electrolyte 15.
[0064]
When dissolving the imide compound and the transition compound, and further dissolving the compound represented by the general formula (1), the imide compound and the transition metal contained in the electrolytic solution 15 are not particularly limited. On the other hand, it is preferable that the concentration is not less than 0.005 wt% and not more than 10 wt%. When the content is 0.005% by weight or more, the effect of the additive spreads over the entire electrode surface, and a sufficient effect for forming a film on the negative electrode surface is exhibited. Preferably, it can be 0.05% by weight or more. Further, by setting the content to 10 wt% or less, an increase in the viscosity of the electrolytic solution 15 is suppressed, so that the resistance of the electrolytic solution 15 can be reduced. Preferably, it can be 5 wt% or less.
[0065]
At this time, the content of the cyclic disulfonic acid ester contained in the entire electrolytic solution 15 is preferably 0.01 wt% or more and 10 wt% or less. By making the content 0.01% by weight or more, the effect of the additive can be spread over the entire electrode. Further, by setting the content to 10 wt% or less, an increase in the viscosity of the electrolytic solution 15 is suppressed, so that the resistance of the electrolytic solution 15 can be reduced.
[0066]
When a metal complex composed of a transition metal cation and an imide anion is dissolved in advance and the compound represented by the general formula (1) is further dissolved, the metal complex contained in the electrolytic solution 15 is not particularly limited. For this reason, it is preferable that the concentration is 0.005 wt% or more and 10 wt% or less with respect to the entire electrolytic solution 15. At this time, the cyclic disulfonic acid ester occupying in the entire electrolytic solution 15 is preferably set to a concentration of 0.01 wt% or more and 10 wt% or less for the same reason.
[0067]
In addition, by adding vinylene carbonate (VC) or a derivative thereof to the electrolytic solution 15, the cycle characteristics of the secondary battery and the effect of suppressing a rise in resistance can be improved. Vinylene carbonate or a derivative thereof is disclosed 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. .
[0068]
It is preferable that the addition amount of VC or its derivative is 0.01 wt% or more and 10 wt% or less of the entire electrolytic solution 15. When the content is 0.01 wt% or more, the cycle characteristics can be suitably exhibited, and the resistance increase during storage at high temperatures can be suppressed. By setting the content to 10 wt% or less, the resistance value of the electrolytic solution 15 can be reduced.
[0069]
The electrolyte solution 15 may be configured to further include a lithium salt as an electrolyte. By doing so, lithium ions can be used as the mobile substance, so that battery characteristics can be improved. As a lithium salt, for example, lithium imide salt, LiPF₆, LiBF₄, LiAsF₆, LiSbF₆, LiClO₄, LiAlCl₄, LiN (C_nF_{2n + 1}SO₂) (C_mF_{2m + 1}SO₂) (N and m are natural numbers). In particular, LiPF₆Or LiBF₄It is preferable to use 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.
[0070]
The electrolytic solution 15 may include, as an aprotic solvent, cyclic carbonates, chain carbonates, aliphatic carboxylic esters, γ-lactones, cyclic ethers, chain ethers, and fluorine derivatives of any of these. It may include one or more solvents selected from the group consisting of:
[0071]
Specifically, for example, 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 methyl carbonate (EMC), chain carbonates such as dipropyl carbonate (DPC), aliphatic carboxylic acid esters such as methyl formate, methyl acetate, 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-dioxolan, formamide, acetamide, dimethylpho Lumamide, acetonitrile, propyl nitrile, nitromethane, ethyl monoglyme, phosphate 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-pentafluoropropyl carbonate , Trifluoromethylethylene carbonate, monofluoromethylethylene carbonate, difluoromethylethylene carbonate, 4,5-difluoro-1,3-dioxolan-2-one, monofluoroethylene Of such alkylene carbonate, it can be used by mixing one or two or more.
[0072]
In the secondary battery of FIG. 1, the negative electrode active material used for the layer 13 containing the negative electrode active material is, for example, one or two selected from the group consisting of lithium metal, lithium alloy, and a material capable of inserting and extracting lithium. The above substances can be used. As a material for inserting and extracting lithium ions, a carbon material or an oxide can be used.
[0073]
As the carbon material, graphite that absorbs lithium, amorphous carbon, diamond-like carbon, carbon nanotube, or the like, or a composite oxide thereof can be used. Among them, graphite or amorphous carbon is particularly preferable. In particular, graphite material has high electron conductivity, excellent adhesion to a current collector made of metal such as copper, and excellent voltage flatness. It is advantageous for improvement and is preferable.
[0074]
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.
[0075]
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 is unlikely to occur due to the amorphous structure.
[0076]
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.
[0077]
In the negative electrode of the secondary battery of FIG. 1, when a complex composed of a transition metal cation and an imide anion is present at the interface with the electrolytic solution 15, the negative electrode has flexibility with respect to volume changes of the metal and alloy phases and uniformity of ion distribution. It is preferable because it has excellent physical and chemical stability. As a result, generation of dendrite and pulverization of lithium can be effectively prevented, and cycle efficiency and life are improved.
[0078]
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 composed of 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 can be kept high.
[0079]
Furthermore, when the film is mechanically broken, lithium fluoride, which is a reaction product of lithium on the negative electrode surface and imide anion adsorbed on the negative electrode surface, has a function of repairing the film at the broken point. This has the effect of leading to the generation of a stable surface compound even after the film is broken.
[0080]
In the secondary battery of FIG. 1, the positive electrode active material used for the layer 12 containing the positive electrode active material is, for example, LiCoO 2₂, LiNiO₂, LiMn₂O₄And other lithium-containing composite oxides. Further, the transition metal portion of these lithium-containing composite oxides may be replaced with another element.
[0081]
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 (9).
Li_a(M_xMn_2-x) O₄                (9)
(However, in the above general formula (9), 0 <x <2 and 0 <a <1.2. M is selected from the group consisting of Ni, Co, Fe, Cr and Cu. Is at least one kind.)
[0082]
The positive electrode is prepared by dispersing and kneading these active materials together with a conductive material such as carbon black and a binder such as polyvinylidene fluoride (PVDF) in a solvent such as N-methyl-2-pyrrolidone (NMP). On a substrate such as an aluminum foil.
[0083]
The secondary battery of FIG. 1 is obtained by laminating a negative electrode and a positive electrode through a porous separator 16 in a dry air or inert gas atmosphere, or winding the laminated product, and then forming a battery can, a synthetic resin and a metal foil. And is accommodated in an exterior body such as a flexible film made of a laminate of the above, and is impregnated with the electrolytic solution 15 containing the compound represented by the general formula (1). Then, by charging the secondary battery after sealing or sealing the exterior body, a film can be formed on the negative electrode. As the porous separator 16, a porous film such as a polyolefin such as polypropylene or polyethylene, or a fluororesin is used.
[0084]
The shape of the secondary battery according to the present embodiment is not particularly limited, and examples thereof include a cylindrical type, a square type, a laminate exterior type, and a coin type.
[0085]
【Example】
(Example 1)
(Production of battery)
The fabrication of the battery of this example will be described. An aluminum foil having a thickness of 20 μm was used as a positive electrode current collector, and LiMn was used as a positive electrode active material.₂O₄Was used. A 10 μm thick copper foil was used as the negative electrode current collector, and a 20 μm thick lithium metal was deposited as a negative electrode active material on the copper foil to be used as the negative electrode. Also, a mixed solvent of EC and DEC (volume ratio: 30/70) was used as a solvent for the electrolyte, and LiN (C₂F₅SO₂)₂(Hereinafter abbreviated as LiBETI) in an amount of 1 molL.^-1And dissolved in Compound No. 1 shown in Table 1 above. 1 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.
[0086]
(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 2 shows the results obtained in the cycle test.
[0087]
(Examples 2 to 4)
In Example 1, Compound No. A secondary battery was fabricated in the same manner as in Example 1, except that the compounds shown in Table 2 were used instead of 1. Then, the characteristics of the battery were examined in the same manner as in Example 1. Table 2 shows the results.
[0088]
(Comparative Example 1)
In Example 1, Compound No. A secondary battery was fabricated in the same manner as in Example 1 except that No. 1 was not added. Then, the characteristics of the battery were examined in the same manner as in Example 1. Table 2 shows the results.
[0089]
(Comparative Example 2)
In Example 1, Compound No. A secondary battery was fabricated in the same manner as in Example 1, except that 1,3-propane sultone (1,3-PS) was used instead of 1. Then, the characteristics of the battery were examined in the same manner as in Example 1. Table 2 shows the results.
[0090]
[Table 2]

[0091]
From Table 2, it was confirmed that the batteries shown in Examples 1 to 4 had improved capacity retention after the cycle test, that is, improved cycle characteristics, as compared with Comparative Examples 1 and 2. Was done.
[0092]
(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, a paste-like material was applied to a copper foil, and the resultant was dried. A secondary battery was fabricated in the same manner as in Example 1 except that the secondary battery was used. Then, the characteristics of the battery were examined in the same manner as in Example 1. Table 3 shows the results.
[0093]
(Examples 6 to 8)
In Example 5, Compound No. A secondary battery was fabricated in the same manner as in Example 5, except that the compounds shown in Table 3 were used instead of 1. Then, the characteristics of the battery were examined in the same manner as in Example 5. Table 3 shows the results.
[0094]
(Comparative Example 3)
In Example 5, Compound No. A secondary battery was fabricated in the same manner as in Example 5, except that 1 was not added. Then, the characteristics of the battery were examined in the same manner as in Example 5. Table 3 shows the results.
[0095]
[Table 3]

[0096]
From Table 3, it was confirmed that the batteries shown in Examples 5 to 8 had improved capacity retention after the cycle test, that is, improved cycle characteristics, as compared with Comparative Example 3. .
[0097]
(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. Then, the characteristics of the battery were examined in the same manner as in Example 5. Table 4 shows the results.
[0098]
(Examples 10 to 12)
In Example 9, Compound No. A secondary battery was fabricated in the same manner as in Example 9, except that the compounds shown in Table 4 were used instead of 1. Then, the characteristics of the battery were examined in the same manner as in Example 9. Table 4 shows the results.
[0099]
(Comparative Example 4)
In Example 9, Compound No. A secondary battery was fabricated in the same manner as in Example 9, except that 1 was not added. Then, the characteristics of the battery were examined in the same manner as in Example 9. Table 4 shows the results.
[0100]
[Table 4]

[0101]
From Table 4, 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. .
[0102]
(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, also referred to as 1,3-PS). did. Then, the characteristics of the battery were examined in the same manner as in Example 1. Table 5 shows the results.
[0103]
(Examples 14 to 16)
In Example 13, Compound No. A secondary battery was fabricated in the same manner as in Example 13, except that the compounds shown in Table 5 were used instead of 1. Then, the characteristics of the battery were examined in the same manner as in Example 13. Table 5 shows the results.
[0104]
[Table 5]

[0105]
From Table 5, the batteries shown in Examples 13 to 16 have improved capacity retention rates after the cycle test as compared with Examples 1 to 4 and Comparative Example 1, that is, the cycle characteristics have been improved. Was confirmed. This is due to the combined effect of the compound represented by the general formula (1) used as an additive and 1,3-PS.
[0106]
(Example 17)
A secondary battery was fabricated in the same manner as in Example 5, except that 1 wt% of 1,3-PS was further contained in the electrolytic solution. Then, the characteristics of the battery were examined in the same manner as in Example 5. Table 6 shows the results.
[0107]
(Examples 18 to 20)
In Example 17, Compound No. A secondary battery was fabricated in the same manner as in Example 17, except that the compounds shown in Table 6 were used instead of 1. Then, the characteristics of the battery were examined in the same manner as in Example 17. Table 6 shows the results.
[0108]
[Table 6]

[0109]
From Table 6, the batteries shown in Examples 17 to 20 have improved capacity retention rates after the cycle test as compared with Examples 5 to 8 and Comparative Example 3, that is, the cycle characteristics have been improved. Was confirmed. This is due to the combined effect of the compound represented by the general formula (1) used as an additive and 1,3-PS.
[0110]
(Example 21)
A secondary battery was fabricated in the same manner as in Example 9, except that the electrolyte further contained 1 wt% of 1,3-PS. Then, the characteristics of the battery were examined in the same manner as in Example 9. Table 7 shows the results.
[0111]
(Examples 22 to 24)
In Example 21, Compound No. A secondary battery was fabricated in the same manner as in Example 21, except that the compounds shown in Table 7 were used instead of 1. Then, the characteristics of the battery were examined in the same manner as in Example 21. Table 7 shows the results.
[0112]
[Table 7]

[0113]
From Table 7, the batteries shown in Examples 21 to 24 have improved capacity retention after the cycle test as compared with Examples 9 to 12 and Comparative Example 4, that is, the cycle characteristics have been improved. Was confirmed. This is due to the combined effect of the compound represented by the general formula (1) used as an additive and 1,3-PS.
[0114]
(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 8 having an anion was contained at 0.3 wt%. Then, the characteristics of the battery were examined in the same manner as in Example 9. Table 8 shows the results.
[0115]
[Table 8]

[0116]
From Table 8, it is found that the batteries of Examples 25 to 28 have improved capacity retention after the cycle test, that is, improved cycle characteristics, as compared with Comparative Example 4 and Example 9. Was confirmed.
[0117]
(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 9. Then, the characteristics of the battery were examined in the same manner as in Example 9. Table 9 shows the results.
[0118]
[Table 9]

[0119]
From Table 9, 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.
[0120]
(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, also referred to as VC). Then, the characteristics of the battery were examined in the same manner as in Example 9. Table 10 shows the results.
[0121]
(Examples 34 to 36)
In Example 33, Compound No. A secondary battery was fabricated in the same manner as in Example 33 except that the compounds shown in Table 10 were used instead of 1. Then, the characteristics of the battery were examined in the same manner as in Example 33. Table 10 shows the results.
[0122]
[Table 10]

[0123]
From Table 10, the batteries shown in Examples 33 to 36 have improved capacity retention after the cycle test as compared with Comparative Example 4 and Examples 9 to 12, that is, the cycle characteristics have been improved. Was confirmed.
[0124]
(Example 37)
A secondary battery was fabricated in the same manner as in Example 9, except that the electrolyte further contained 1 wt% of VC and 1,3-PS, respectively. Then, the characteristics of the battery were examined in the same manner as in Example 9. Table 11 shows the results.
[0125]
(Examples 38 to 40)
In Example 37, Compound No. A secondary battery was fabricated in the same manner as in Example 37, except that the compounds shown in Table 11 were used instead of 1. Then, the characteristics of the battery were examined as in Example 37. Table 11 shows the results.
[0126]
[Table 11]

[0127]
From Table 11, the batteries shown in Examples 37 to 40 have improved capacity retention rates after the cycle test as compared with Comparative Example 4, Examples 9 to 12, and Examples 33 to 36, that is, It was confirmed that the cycle characteristics were improved. This is due to the combined effect of the compound represented by the general formula (1), VC and 1,3-PS.
[0128]
(Example 41)
Compound No. as an additive for the electrolyte solution. Using the compound shown in No. 1, a secondary battery similar to that in Example 9 was produced. In this example, the resistance value of the secondary battery during storage was measured. First, the fabricated secondary battery was charged and discharged once at 20 ° C. The charge current and discharge current at this time were constant, and the discharge capacity at this time was defined as the initial capacity, and the resistance at that time was defined as the initial resistance. Thereafter, the battery was discharged at a constant current and constant voltage to a predetermined voltage for 2.5 hours, and then left at 45 ° C. or 60 ° C. for 90 days. After the standing, the discharging operation was performed again at a constant current at room temperature, and then the charging and discharging were repeated once again at a constant current, and the resistance during charging was measured.
[0129]
With the initial resistance as 1, the resistance value after storage for 90 days as a relative value (45 ° C. or 60 ° C. storage) and the capacity retention rate after 60 ° C. storage (discharge capacity after 90 days / initial discharge capacity) Table 12 shows the results.
[0130]
(Examples 42 to 45)
Using the compounds shown in Table 12 as additives contained in the electrolytic solution, a secondary battery similar to that of Example 9 was manufactured, and the same evaluation as that of Example 41 was performed.
[0131]
(Comparative Example 5)
A secondary battery was fabricated in the same manner as in Example 41, except that 1,3-PS was used as an additive contained in the electrolytic solution, and the same evaluation was performed. Table 12 shows the results.
[0132]
[Table 12]

[0133]
As shown in Table 12, all of the batteries of Examples 41 to 45 were found to have a reduced rate of resistance increase at each temperature as compared with Comparative Example 5 in which conventional 1,3-PS was added. . Particularly, the suppression of the increase in resistance at 60 ° C. was remarkable. Further, the capacity retention ratio is significantly improved as compared with Comparative Example 5.
[0134]
(Example 46)
In this example, Compound No. 1 was used to fabricate the same secondary battery as in Example 33, and the same evaluation as in Example 41 was performed. With the initial resistance as 1, the resistance value after storage for 90 days as a relative value (45 ° C. or 60 ° C. storage) and the capacity retention rate after 60 ° C. storage (discharge capacity after 90 days / initial discharge capacity) Table 13 shows the results.
[0135]
(Examples 47 to 50)
Using a compound shown in Table 13 as an additive, a secondary battery was produced in the same manner as in Example 33, and was similarly evaluated.
[0136]
(Comparative Example 6)
A secondary battery was fabricated in the same manner as in Example 46, except that 1,3-PS was used as an additive contained in the electrolytic solution, and was similarly evaluated. Table 13 shows the results.
[0137]
[Table 13]

[0138]
As shown in Table 13, it was found that the batteries of Examples 46 to 50 all had a reduced resistance increase rate at each temperature, as compared with Comparative Example 6 to which conventional 1,3-PS was added. . Particularly, the suppression of the increase in resistance at 60 ° C. was remarkable. Further, the capacity retention ratio is significantly improved as compared with Comparative Example 6.
[0139]
【The invention's effect】
As described above, according to the present invention, by using an electrolyte containing an aprotic organic solvent and the compound represented by the general formula (1), the decomposition of the solvent in the electrolytic solution of the secondary battery is suppressed. be able to. Further, according to the present invention, the cycle life of the secondary battery can be improved. Further, according to the present invention, an increase in resistance of the secondary battery can be suppressed. Further, according to the present invention, the capacity retention of the secondary battery can be improved.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of a secondary battery according to an embodiment.
[Explanation of symbols]
11 positive electrode 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 (25)

An electrolyte solution for a secondary battery, comprising: an aprotic solvent; and a cyclic disulfonic acid ester having an unsaturated bond represented by the following general formula (1).

(However, in the general formula (1), R _{1 to} R ₄ are a hydrogen atom, a methyl group, an ethyl group, or a halogen atom, and n is an integer of 0 or more and 2 or less.) The electrolyte for a secondary battery according to claim 1, wherein the compound represented by the general formula (1) is a compound represented by the following general formula (2).

(However, in the general formula (2), R _{1 to} R ₂ are a hydrogen atom, a methyl group, an ethyl group or a halogen atom, and n is an integer of 0 or more and 2 or less.) 3. The electrolyte for a secondary battery according to claim 2, wherein the compound represented by the general formula (2) is a compound represented by the following chemical formula (3).

The electrolyte for a secondary battery according to claim 2, wherein the compound represented by the general formula (2) is a compound represented by the following chemical formula (4).

The electrolyte for a secondary battery according to claim 1, wherein the compound represented by the general formula (1) is a compound represented by the following general formula (5).

(However, in the general formula (5), R _{1 to} R ₂ are a hydrogen atom, a methyl group, an ethyl group, or a halogen atom, and n is an integer of 0 or more and 2 or less.) The secondary battery electrolyte according to claim 1, further comprising one or more compounds having a sulfonyl group in addition to the compound represented by the general formula (1). Electrolyte. The electrolyte for a secondary battery according to claim 6, wherein the one or more compounds having a sulfonyl group include a compound represented by the following general formula (6).

(However, in the general formula (6), A represents a substituted or unsubstituted alkylene group having 1 to 5 carbon atoms, a carbonyl group, a sulfinyl group, a substituted or unsubstituted fluoroalkylene group having 1 to 5 carbon atoms, an ether A divalent group having 2 to 6 carbon atoms to which an alkylene unit or a fluoroalkylene unit is bonded via a bond, and B is a substituted or unsubstituted alkylene group.) The electrolyte for a secondary battery according to claim 6, wherein the one or more compounds having a sulfonyl group include a compound represented by the following general formula (7).

(In the above general formula (7), Z is a substituted or unsubstituted alkylene group having 2 to 4 carbon atoms, a substituted or unsubstituted alkenylene group having 2 to 4 carbon atoms, a substituted or unsubstituted aromatic group. Represents an aromatic ring, a substituted or unsubstituted heterocyclic ring.) The electrolyte solution for a secondary battery according to claim 6, wherein the one or more compounds having a sulfonyl group include a sultone compound represented by the following general formula (8).

(However, in the general formula (8), n is an integer of 0 or more and 2 or less. Further, R _{1 to} R ₆ are a hydrogen atom, an alkyl group having 1 to 12 carbon atoms, and a carbon number of 3 to 6 Are independently selected from cycloalkyl groups of the above formulas and aryl groups having 6 to 12 carbon atoms.) The electrolyte for a secondary battery according to any one of claims 1 to 9, further comprising an imide anion and a transition metal ion. The electrolyte for a secondary battery according to any one of claims 1 to 9, further comprising a metal complex comprising an imide anion and a transition metal ion. The electrolyte for a secondary battery according to claim 10, wherein the transition metal ion is a lanthanoid-based transition metal ion. 13. The electrolyte for a secondary battery according to claim 12, wherein the lanthanoid-based transition metal ion contains one of europium ion, neodymium ion, erbium ion and holmium ion. In the electrolytic solution for a secondary battery according to any one claims 10 to 13, wherein the anion is ^{_{- N (C n F 2n +}} 1 SO 2) (C m F 2m + 1 SO 2) ( provided that, n, m are independent 1 And a natural number of 6 or less.) 15. The electrolytic solution for a secondary battery according to claim 10, wherein the imide anion or a metal complex thereof is contained in an amount of 0.005 wt% to 10 wt% of the entire electrolytic solution. liquid. The electrolyte for a secondary battery according to any one of claims 1 to 15, wherein the compound represented by the general formula (1) is contained in an amount of 0.005 wt% to 10 wt% of the entire electrolyte. Electrolyte for secondary battery. 17. The electrolyte for a secondary battery according to claim 1, further comprising vinylene carbonate or a derivative thereof. The electrolyte solution for a secondary battery according to any one of claims 1 to 17, wherein the aprotic solvent is a cyclic carbonate, a chain carbonate, an aliphatic carboxylic acid ester, a γ-lactone, a cyclic ether, An electrolyte for a secondary battery, comprising one or more solvents selected from the group consisting of chain ethers and any of these fluorine derivatives. In the electrolytic solution for a secondary battery according to any of claims 1 to 18, as a lithium _{salt, LiPF 6, LiBF 4, LiAsF} 6, LiSbF 6, LiClO 4, LiAlCl 4, and _{LiN (C n F 2n + 1} SO 2) _{(C m F 2m + 1 SO} 2) (n, m are natural numbers), the electrolyte solution for a secondary battery, which comprises one or more substances selected from the group consisting of. A secondary battery comprising at least a positive electrode and a negative electrode, comprising the electrolyte for a secondary battery according to claim 1. 21. The secondary battery according to claim 20, further comprising a lithium-containing composite oxide as a positive electrode active material. 22. The secondary battery according to claim 20, wherein the negative electrode active material comprises a material capable of inserting and extracting lithium, lithium metal, a metal material capable of forming an alloy with lithium, and an oxide material. A secondary battery comprising one or more substances selected from the group. 23. The secondary battery according to claim 22, wherein the negative electrode active material includes a carbon material. 24. The secondary battery according to claim 23, wherein the carbon material is graphite. 24. The secondary battery according to claim 23, wherein the carbon material is amorphous carbon.

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