JP4075416B2 - Nonaqueous electrolyte and lithium secondary battery using the same - Google Patents
Nonaqueous electrolyte and lithium secondary battery using the same Download PDFInfo
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Description
【０００１】
【発明の属する技術分野】
本発明は、電池のサイクル特性や電気容量、保存特性などの電池特性にも優れたリチウム二次電池を提供することができる非水電解液、およびそれを用いたリチウム二次電池に関する。
【０００２】
【従来の技術】
近年、リチウム二次電池は小型電子機器などの駆動用電源として広く使用されている。リチウム二次電池は、主に正極、非水電解液および負極から構成されており、特に、ＬｉＣｏＯ2などのリチウム複合酸化物を正極とし、炭素材料又はリチウム金属を負極としたリチウム二次電池が好適に使用されている。そして、そのリチウム二次電池用の非水電解液としては、エチレンカーボネート（ＥＣ）、プロピレンカーボネート（ＰＣ）などのカーボネート類が好適に使用されている。
【０００３】
【発明が解決しようとする課題】
しかしながら、電池のサイクル特性および電気容量などの電池特性について、さらに優れた特性を有する二次電池が求められている。
正極として、例えばＬｉＣｏＯ2、ＬｉＭｎ2Ｏ4、ＬｉＮｉＯ2などを用いたリチウム二次電池は、非水電解液中の溶媒が充電時に局部的に一部酸化分解することにより、該分解物が電池の望ましい電気化学的反応を阻害するために電池性能の低下を生じる。これは正極材料と非水電解液との界面における溶媒の電気化学的酸化に起因するものと思われる。
また、負極として例えば天然黒鉛や人造黒鉛などの高結晶化した炭素材料を用いたリチウム二次電池は、非水電解液中の溶媒が充電時に負極表面で還元分解し、非水電解液溶媒として一般に広く使用されているＥＣにおいても充放電を繰り返す間に一部還元分解が起こり、電池性能の低下が起こる。
このため、電池のサイクル特性および電気容量などの電池特性は必ずしも満足なものではないのが現状である。
【０００４】
本発明は、前記のようなリチウム二次電池用非水電解液に関する課題を解決し、電池のサイクル特性に優れ、さらに電気容量や充電状態での保存特性などの電池特性にも優れたリチウム二次電池を構成することができるリチウム二次電池に使用できる非水電解液、およびそれを用いたリチウム二次電池を提供することを目的とする。
【０００５】
【課題を解決するための手段】
本発明は、非水溶媒に電解質塩が溶解されている非水電解液において、該非水電解液中に、少なくとも１種のペンタフルオロフェニルアルカン化合物が非水電解液の重量に対して０．０１以上３重量％未満含有されていることを特徴とするリチウム二次電池用非水電解液に関する。また、本発明は、正極、負極および非水溶媒に電解質塩が溶解されている非水電解液からなるリチウム二次電池において、該非水電解液中に、少なくとも１種のペンタフルオロフェニルアルカン化合物が０．０１以上３重量％未満含有されていることを特徴とするリチウム二次電池に関する。
【０００６】
【発明の実施の形態】
本発明において、前記ペンタフルオロフェニルアルカン化合物が、下記一般式（III）、
【化３】
【０００７】
本発明において、非水電解液中に含有される前記一般式（ III ）で表わされる化合物の具体例について以下に詳述する。
【０００９】
本発明において、１種または２種以上のペンタフルオロフェニルアルカン化合物が非水電解液中に含有される。非水電解液中に含有される前記ペンタフルオロフェニルアルカン化合物の含有量は、過度に多いと電池性能が低下することがあり、また、過度に少ないと期待した十分な電池性能が得られない。したがって、その含有量は非水電解液の重量に対して０．０１以上３重量％未満、好ましくは０．０５以上３重量％未満、特に好ましくは０．１以上３重量％未満の範囲がサイクル特性が向上するのでよい。
【００１０】
前記一般式（III）において、Ｒ７が炭素数１〜１２のアルキル基としては、メチル基、エチル基、プロピル基、ブチル基、ペンチル基、ヘキシル基、ヘプチル基、オクチル基、ノニル基、デシル基、ドデシル基のような置換基が挙げられる。また、イソプロピル基、tert−ブチル基、２−エチルヘキシル基のような分枝したアルキル基が挙げられる。また、ベンジル基のような前記置換基が有する水素原子のうち少なくとも１つが芳香族基で置換されたアルキル基、あるいは、アリル基（ＣＨ２＝ＣＨ−ＣＨ２−）の如きメチレン基（ＣＨ２＝）のような不飽和結合を有する置換基からなるアルキル基が挙げられる。具体的なペンタフルオロフェニルアルカン化合物としては、２，３，４，５，６−ペンタフルオロトルエンが好適に挙げられる。
【００１１】
本発明において、１種または２種以上のペンタフルオロフェニルアルカン化合物が非水電解液中に含有される。非水電解液中に含有される前記ペンタフルオロフェニルアルカン化合物の含有量は、過度に多いと電池性能が低下することがあり、また、過度に少ないと期待した十分な電池性能が得られない。したがって、その含有量は非水電解液の重量に対して０．０１〜２０重量％、好ましくは０．０５〜１０重量％、特に好ましくは０．１〜５重量％の範囲がサイクル特性が向上するのでよい。
【００１２】
本発明で使用される非水溶媒としては、例えば、エチレンカーボネート（ＥＣ）、プロピレンカーボネート（ＰＣ）、ブチレンカーボネート（ＢＣ）、ビニレンカーボネート（ＶＣ）などの環状カーボネート類や、γ−ブチロラクトンなどのラクトン類、ジメチルカーボネート（ＤＭＣ）、メチルエチルカーボネート（ＭＥＣ）、ジエチルカーボネート（ＤＥＣ）などの鎖状カーボネート類、テトラヒドロフラン、２−メチルテトラヒドロフラン、１，４−ジオキサン、１，２−ジメトキシエタン、１，２−ジエトキシエタン、１，２−ジブトキシエタンなどのエーテル類、アセトニトリルなどのニトリル類、プロピオン酸メチル、ピバリン酸メチル、ピバリン酸オクチルなどのエステル類、ジメチルホルムアミドなどのアミド類が挙げられる。
【００１３】
これらの非水溶媒は、１種類で使用してもよく、また２種類以上を組み合わせて使用してもよい。非水溶媒の組み合わせは特に限定されないが、例えば、環状カーボネート類と鎖状カーボネート類との組み合わせ、環状カーボネート類とラクトン類との組み合わせ、環状カーボネート類３種類と鎖状カーボネート類との組み合わせなど種々の組み合わせが挙げられる。
【００１４】
本発明で使用される電解質塩としては、例えば、ＬｉＰＦ6、ＬｉＢＦ4、ＬｉＣｌＯ4、ＬｉＮ（ＳＯ2ＣＦ3）2、ＬｉＮ（ＳＯ2Ｃ2Ｆ5）2、ＬｉＣ（ＳＯ2ＣＦ3）3、ＬｉＰＦ4（ＣＦ3）2、ＬｉＰＦ3（Ｃ2Ｆ5）3、ＬｉＰＦ3（ＣＦ3）3、ＬｉＰＦ3（ｉｓｏ−Ｃ3Ｆ7）3、ＬｉＰＦ5（ｉｓｏ−Ｃ3Ｆ7）などが挙げられる。これらの電解質塩は、１種類で使用してもよく、２種類以上組み合わせて使用してもよい。これら電解質塩は、前記の非水溶媒に通常０．１〜３Ｍ、好ましくは０．５〜１．５Ｍの濃度で溶解されて使用される。
【００１５】
本発明の電解液は、例えば、前記の非水溶媒を混合し、これに前記の電解質塩を溶解し、前記ペンタフルオロフェニル化合物のうち少なくとも１種を溶解することにより得られる。
【００１６】
本発明の非水電解液は、二次電池、特にリチウム二次電池の構成部材として使用される。二次電池を構成する非水電解液以外の構成部材については特に限定されず、従来使用されている種々の構成部材を使用できる。
【００１７】
例えば、正極活物質としてはコバルトまたはニッケルを含有するリチウムとの複合金属酸化物が使用される。これらの正極活物質は、１種類だけを選択して使用しても良いし、２種類以上を組み合わせて用いても良い。このような複合金属酸化物としては、例えば、ＬｉＣｏＯ2、ＬｉＮｉＯ2、ＬｉＣｏ1-xＮｉxＯ2（０．０１＜ｘ＜１）などが挙げられる。また、ＬｉＣｏＯ2とＬｉＭｎ2Ｏ4、ＬｉＣｏＯ2とＬｉＮｉＯ2、ＬｉＭｎ2Ｏ4とＬｉＮｉＯ2のように適当に混ぜ合わせて使用しても良い。
【００１８】
正極は、前記の正極活物質をアセチレンブラック、カーボンブラックなどの導電剤およびポリテトラフルオロエチレン（ＰＴＦＥ）、ポリフッ化ビニリデン（ＰＶＤＦ）、スチレンとブタジエンの共重合体（ＳＢＲ）、アクリロニトリルとブタジエンの共重合体（ＮＢＲ）、カルボキシメチルセルロース（ＣＭＣ）などの結着剤と混練して正極合剤とした後、この正極材料を集電体としてのアルミニウム箔やステンレス製のラス板に圧延して、５０℃〜２５０℃程度の温度で２時間程度真空下に加熱処理することにより作製される。
【００１９】
負極（負極活物質）としては、リチウム金属やリチウム合金、およびリチウムを吸蔵・放出可能な炭素材料〔熱分解炭素類、コークス類、グラファイト類（人造黒鉛、天然黒鉛など）、有機高分子化合物燃焼体、炭素繊維〕、または複合スズ酸化物などの物質が使用される。特に、格子面（００２）の面間隔（ｄ002）が０．３３５〜０．３４０ｎｍである黒鉛型結晶構造を有する炭素材料を使用することが好ましい。これらの負極活物質は、１種類だけを選択して使用しても良いし、２種類以上を組み合わせて用いても良い。なお、炭素材料のような粉末材料はエチレンプロピレンジエンターポリマー（ＥＰＤＭ）、ポリテトラフルオロエチレン（ＰＴＦＥ）、ポリフッ化ビニリデン（ＰＶＤＦ）、スチレンとブタジエンの共重合体（ＳＢＲ）、アクリロニトリルとブタジエンの共重合体（ＮＢＲ）、カルボキシメチルセルロース（ＣＭＣ）などの結着剤と混練して負極合剤として使用される。負極の製造方法は、特に限定されず、上記の正極の製造方法と同様な方法により製造することができる。
【００２０】
リチウム二次電池の構造は特に限定されるものではなく、正極、負極および単層又は複層のセパレータを有するコイン型電池、さらに、正極、負極およびロール状のセパレータを有する円筒型電池や角型電池などが一例として挙げられる。なお、セパレータとしては公知のポリオレフィンの微多孔膜、織布、不織布などが使用される。
【００２１】
〔実施例〕次に、実施例および比較例を挙げて、本発明を具体的に説明する。（ただし、実施例１〜４、６、７、９〜１１は、それぞれ参考例１〜４、６、７、９〜１１とし、〔表１〕についても同様の扱いとする。）
実施例１
〔非水電解液の調製〕ＰＣ：ＤＭＣ（容量比）＝１：２の非水溶媒を調製し、これに電解質塩としてＬｉＰＦ6を１Ｍの濃度になるように溶解して非水電解液を調製した後、さらに２，３，４，５，６−ペンタフルオロアニソールを非水電解液に対して０．５重量％となるように加えた。
【００２２】
〔リチウム二次電池の作製および電池特性の測定〕
ＬｉＣｏＯ2（正極活物質）を９０重量％、アセチレンブラック（導電剤）を５重量％、ポリフッ化ビニリデン（結着剤）を５重量％の割合で混合し、これに１−メチル−２−ピロリドン溶剤を加えて混合したものをアルミニウム箔上に塗布し、乾燥、加圧成型、加熱処理して正極を調製した。人造黒鉛（負極活物質）を９０重量％、ポリフッ化ビニリデン（結着剤）を１０重量％の割合で混合し、これに１−メチル−２−ピロリドン溶剤を加え、混合したものを銅箔上に塗布し、乾燥、加圧成型、加熱処理して負極を調製した。そして、ポリプロピレン微多孔性フィルムのセパレータを用い、上記の非水電解液を注入させてコイン電池（直径２０ｍｍ、厚さ３．２ｍｍ）を作製した。
このコイン電池を用いて、室温（２０℃）下、１．１ｍＡの定電流および定電圧で、終止電圧４．２Ｖまで５時間充電し、次に１．１ｍＡの定電流下、終止電圧２．７Ｖまで放電し、この充放電を繰り返した。初期充放電容量は、ペンタフルオロフェニル化合物を添加しない１Ｍ ＬｉＰＦ６−ＥＣ／ＤＥＣ（容量比３／７）を非水電解液として用いた場合（比較例２の初期充放電容量を１とする）と比べて０．９９であり、５０サイクル後の電池特性を測定したところ、初期放電容量を１００％としたときの放電容量維持率は９０．１％であった。コイン電池の作製条件および電池特性を表１に示す。
【００２３】
実施例２
添加剤として、２，３，４，５，６−ペンタフルオロアニソールを非水電解液に対して１重量％使用したほかは実施例１と同様に非水電解液を調製してコイン電池を作製し、５０サイクル後の電池特性を測定したところ、放電容量維持率は９０．５％であった。コイン電池の作製条件および電池特性を表１に示す。
【００２４】
実施例３
添加剤として、２，３，４，５，６−ペンタフルオロアニソールを非水電解液に対して２重量％使用したほかは実施例１と同様に非水電解液を調製してコイン電池を作製し、５０サイクル後の電池特性を測定したところ、放電容量維持率は８９．５％であった。コイン電池の作製条件および電池特性を表１に示す。
【００２５】
実施例４
添加剤として、デカフルオロビフェニルを非水電解液に対して１重量％使用したほかは実施例１と同様に非水電解液を調製してコイン電池を作製し、５０サイクル後の電池特性を測定したところ、放電容量維持率は９０．３％であった。コイン電池の作製条件および電池特性を表１に示す。
【００２６】
実施例５
添加剤として、２，３，４，５，６−ペンタフルオロトルエンを非水電解液に対して１重量％使用したほかは実施例１と同様に非水電解液を調製してコイン電池を作製し、５０サイクル後の電池特性を測定したところ、放電容量維持率は８９．９％であった。コイン電池の作製条件および電池特性を表１に示す。
【００２７】
実施例６
非水溶媒として、ＥＣ／ＭＥＣ（容量比３／７）を使用し、添加剤として、２，３，４，５，６−ペンタフルオロアニソールを非水電解液に対して１重量％使用したほかは実施例１と同様に非水電解液を調製してコイン電池を作製し、５０サイクル後の電池特性を測定したところ、放電容量維持率は９１．７％であった。コイン電池の作製条件および電池特性を表１に示す。
【００２８】
実施例７
非水溶媒として、ＥＣ／ＭＥＣ（容量比３／７）を使用し、添加剤として、デカフルオロビフェニルを非水電解液に対して１重量％使用したほかは実施例１と同様に非水電解液を調製してコイン電池を作製し、５０サイクル後の電池特性を測定したところ、放電容量維持率は８９．１％であった。コイン電池の作製条件および電池特性を表１に示す。
【００２９】
実施例８
非水溶媒として、ＥＣ／ＭＥＣ（容量比３／７）を使用し、添加剤として、２，３，４，５，６−ペンタフルオロトルエンを非水電解液に対して１重量％使用したほかは実施例１と同様に非水電解液を調製してコイン電池を作製し、５０サイクル後の電池特性を測定したところ、放電容量維持率は９０．７％であった。コイン電池の作製条件および電池特性を表１に示す。
【００３０】
実施例９
非水溶媒として、ＥＣ／ＤＥＣ（容量比１／２）を使用し、添加剤として、２，３，４，５，６−ペンタフルオロアニソールを非水電解液に対して１重量％使用したほかは実施例１と同様に非水電解液を調製してコイン電池を作製し、５０サイクル後の電池特性を測定したところ、放電容量維持率は９０．４％であった。コイン電池の作製条件および電池特性を表１に示す。
【００３１】
実施例１０
正極活物質として、ＬｉＣｏＯ２に代えてＬｉＭｎ２Ｏ４を使用し、添加剤として、２，３，４，５，６−ペンタフルオロアニソールを非水電解液に対して１重量％使用したほかは実施例１と同様に非水電解液を調製してコイン電池を作製し、５０サイクル後の電池特性を測定したところ、放電容量維持率は８９．２％であった。コイン電池の作製条件および電池特性を表１に示す。
【００３２】
実施例１１
負極活物質として、人造黒鉛に代えて天然黒鉛を使用し、添加剤として、２，３，４，５，６−ペンタフルオロアニソールを非水電解液に対して１重量％使用したほかは実施例１と同様に非水電解液を調製してコイン電池を作製し、５０サイクル後の電池特性を測定したところ、放電容量維持率は８９．８％であった。コイン電池の作製条件および電池特性を表１に示す。
【００３３】
比較例１
ＰＣ：ＤＭＣ（容量比）＝１：２の非水溶媒を調製し、これにＬｉＰＦ6を１Ｍの濃度になるように溶解した。このときペンタフルオロフェニル化合物は全く添加しなかった。この非水電解液を使用して実施例１と同様にコイン電池を作製し、電池特性を測定したが、全く充放電しなかった。
【００３４】
比較例２
ＥＣ：ＤＥＣ（容量比）＝３：７の非水溶媒を調製し、これにＬｉＰＦ6を１Ｍの濃度になるように溶解した。このときペンタフルオロフェニル化合物は全く添加しなかった。この非水電解液を使用して実施例１と同様にコイン電池を作製し、電池特性を測定した。初期放電容量に対し、５０サイクル後の放電容量維持率は８２．１％であった。コイン電池の作製条件および電池特性を表１に示す。
【００３５】
比較例３
添加剤として、４−フルオロアニソールを非水電解液に対して１重量％使用したほかは実施例１と同様に非水電解液を調製してコイン電池を作製し、５０サイクル後の電池特性を測定したが、全く充放電しなかった。コイン電池の作製条件および電池特性を表１に示す。
【００３６】
比較例４
添加剤として、２，４−ジフルオロアニソールを非水電解液に対して１重量％使用したほかは実施例１と同様に非水電解液を調製してコイン電池を作製し、５０サイクル後の電池特性を測定したが、全く充放電しなかった。コイン電池の作製条件および電池特性を表１に示す。
【００３７】
比較例５
添加剤として、２，４，５−トリフルオロアニソールを非水電解液に対して１重量％使用したほかは実施例１と同様に非水電解液を調製してコイン電池を作製し、５０サイクル後の電池特性を測定したが、全く充放電しなかった。コイン電池の作製条件および電池特性を表１に示す。
【００３８】
【表１】
なお、本発明は記載の実施例に限定されず、発明の趣旨から容易に類推可能な様々な組み合わせが可能である。特に、上記実施例の溶媒の組み合わせは限定されるものではない。更には、上記実施例はコイン電池に関するものであるが、本発明は円筒形、角柱形の電池にも適用される。
【００４０】
【発明の効果】
本発明によれば、電池のサイクル特性、電気容量、保存特性などの電池特性に優れたリチウム二次電池を提供することができる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a non-aqueous electrolyte that can provide a lithium secondary battery excellent in battery characteristics such as battery cycle characteristics, electric capacity, and storage characteristics, and a lithium secondary battery using the same.
[0002]
[Prior art]
In recent years, lithium secondary batteries have been widely used as driving power sources for small electronic devices and the like. A lithium secondary battery is mainly composed of a positive electrode, a non-aqueous electrolyte, and a negative electrode. In particular, a lithium secondary battery using a lithium composite oxide such as LiCoO 2 as a positive electrode and a carbon material or lithium metal as a negative electrode is used. It is preferably used. As the non-aqueous electrolyte for the lithium secondary battery, carbonates such as ethylene carbonate (EC) and propylene carbonate (PC) are preferably used.
[0003]
[Problems to be solved by the invention]
However, there is a demand for a secondary battery having more excellent battery characteristics such as battery cycle characteristics and electric capacity.
A lithium secondary battery using, for example, LiCoO 2 , LiMn 2 O 4 , LiNiO 2 or the like as a positive electrode is partially decomposed by oxidation when a solvent in a non-aqueous electrolyte is locally charged. In order to inhibit the desired electrochemical reaction, the battery performance is degraded. This seems to be due to the electrochemical oxidation of the solvent at the interface between the positive electrode material and the non-aqueous electrolyte.
In addition, a lithium secondary battery using a highly crystallized carbon material such as natural graphite or artificial graphite as the negative electrode is reduced and decomposed on the negative electrode surface when the solvent in the non-aqueous electrolyte is charged. Even in EC that is generally widely used, reductive decomposition occurs partly during repeated charging and discharging, resulting in a decrease in battery performance.
For this reason, at present, battery characteristics such as battery cycle characteristics and electric capacity are not always satisfactory.
[0004]
The present invention solves the above-mentioned problems related to the non-aqueous electrolyte for a lithium secondary battery, has excellent battery cycle characteristics, and has excellent battery characteristics such as electric capacity and storage characteristics in a charged state. It aims at providing the nonaqueous electrolyte which can be used for the lithium secondary battery which can comprise a secondary battery, and a lithium secondary battery using the same.
[0005]
[Means for Solving the Problems]
The present invention relates to a non-aqueous electrolyte solution in which an electrolyte salt is dissolved in a non-aqueous solvent, and at least one pentafluorophenylalkane compound is 0.01% in the non-aqueous electrolyte solution with respect to the weight of the non-aqueous electrolyte solution. The present invention relates to a non-aqueous electrolyte for a lithium secondary battery , characterized by containing less than 3% by weight . The present invention also provides a lithium secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte in which an electrolyte salt is dissolved in a non-aqueous solvent, wherein at least one pentafluorophenylalkane compound is contained in the non-aqueous electrolyte. The present invention relates to a lithium secondary battery characterized by containing 0.01 to 3% by weight .
[0006]
DETAILED DESCRIPTION OF THE INVENTION
In the present invention, before Symbol pentafluorophenyl alkane compound is represented by the following formula (III),
[Chemical Formula 3]
[0007]
In the present invention, specific examples of the compound represented by the general formula ( III ) contained in the non-aqueous electrolyte will be described in detail below.
[0009]
In the present invention, one or more pentafluorophenylalkane compounds are contained in the nonaqueous electrolytic solution. If the content of the pentafluorophenylalkane compound contained in the nonaqueous electrolytic solution is excessively large, battery performance may be deteriorated, and sufficient battery performance expected to be excessively small cannot be obtained. Therefore, the content is within the range of 0.01 to 3% by weight , preferably 0.05 to 3% by weight , particularly preferably 0.1 to 3% by weight, based on the weight of the nonaqueous electrolyte. It is good because the characteristics are improved.
[0010]
Prior following general formula (III), R7 is an alkyl group having 1 to 12 carbon atoms, a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, heptyl group, octyl group, nonyl group, decyl And substituents such as a dodecyl group. In addition, branched alkyl groups such as isopropyl group, tert-butyl group, and 2-ethylhexyl group are exemplified. In addition, an alkyl group in which at least one of the hydrogen atoms of the substituent such as a benzyl group is substituted with an aromatic group, or a methylene group (CH 2 such as an allyl group (CH 2 ═CH—CH 2 —)). And an alkyl group composed of a substituent having an unsaturated bond such as =). As a specific pentafluorophenylalkane compound, 2,3,4,5,6-pentafluorotoluene is preferably exemplified.
[0011]
In the present invention, one or more pentafluorophenyl alkane compound is contained in the nonaqueous electrolytic solution. The content of the pentafluorophenyl alkane compound contained in the nonaqueous electrolytic solution may be excessively large, the battery performance decreases, also sufficient battery performance can not be obtained as expected and too small. Therefore, the cycle characteristics are improved when the content is in the range of 0.01 to 20% by weight, preferably 0.05 to 10% by weight, particularly preferably 0.1 to 5% by weight, based on the weight of the non-aqueous electrolyte. It is good to do.
[0012]
Examples of the non-aqueous solvent used in the present invention include cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), and vinylene carbonate (VC), and lactones such as γ-butyrolactone. , Chain carbonates such as dimethyl carbonate (DMC), methyl ethyl carbonate (MEC), diethyl carbonate (DEC), tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, 1,2-dimethoxyethane, 1,2 -Ethers such as diethoxyethane and 1,2-dibutoxyethane; nitriles such as acetonitrile; esters such as methyl propionate, methyl pivalate and octyl pivalate; and amides such as dimethylformamide .
[0013]
These nonaqueous solvents may be used alone or in combination of two or more. The combination of non-aqueous solvents is not particularly limited. For example, various combinations such as a combination of cyclic carbonates and chain carbonates, a combination of cyclic carbonates and lactones, a combination of three types of cyclic carbonates and chain carbonates, and the like. The combination of is mentioned.
[0014]
Examples of the electrolyte salt used in the present invention include LiPF 6 , LiBF 4 , LiClO 4 , LiN (SO 2 CF 3 ) 2 , LiN (SO 2 C 2 F 5 ) 2 , LiC (SO 2 CF 3 ) 3. LiPF 4 (CF 3 ) 2 , LiPF 3 (C 2 F 5 ) 3 , LiPF 3 (CF 3 ) 3 , LiPF 3 (iso-C 3 F 7 ) 3 , LiPF 5 (iso-C 3 F 7 ), etc. Is mentioned. These electrolyte salts may be used alone or in combination of two or more. These electrolyte salts are used by being dissolved in the non-aqueous solvent at a concentration of usually 0.1 to 3M, preferably 0.5 to 1.5M.
[0015]
The electrolytic solution of the present invention can be obtained, for example, by mixing the non-aqueous solvent, dissolving the electrolyte salt therein, and dissolving at least one of the pentafluorophenyl compounds.
[0016]
The nonaqueous electrolytic solution of the present invention is used as a constituent member of a secondary battery, particularly a lithium secondary battery. The constituent members other than the non-aqueous electrolyte constituting the secondary battery are not particularly limited, and various conventionally used constituent members can be used.
[0017]
For example, a composite metal oxide with lithium containing cobalt or nickel is used as the positive electrode active material. Only one type of these positive electrode active materials may be selected and used, or two or more types may be used in combination. Examples of such composite metal oxides include LiCoO 2 , LiNiO 2 , LiCo 1-x Ni x O 2 (0.01 <x <1). Further, LiCoO 2 and LiMn 2 O 4 , LiCoO 2 and LiNiO 2 , LiMn 2 O 4 and LiNiO 2 may be appropriately mixed and used.
[0018]
The positive electrode is composed of a conductive agent such as acetylene black and carbon black, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), a copolymer of styrene and butadiene (SBR), a copolymer of acrylonitrile and butadiene. After kneading with a binder such as a polymer (NBR) or carboxymethyl cellulose (CMC) to form a positive electrode mixture, this positive electrode material was rolled into an aluminum foil or stainless steel lath plate as a current collector, and 50 It is produced by heat-treating under vacuum at a temperature of from about 0 to 250 ° C. for about 2 hours.
[0019]
Negative electrodes (negative electrode active materials) include lithium metals and lithium alloys, and carbon materials that can occlude and release lithium (pyrolytic carbons, cokes, graphites (artificial graphite, natural graphite, etc.), organic polymer compound combustion Body, carbon fiber], or composite tin oxide. In particular, it is preferable to use a carbon material having a graphite-type crystal structure in which a lattice spacing ( 002 ) (d 002 ) is 0.335 to 0.340 nm. Only one kind of these negative electrode active materials may be selected and used, or two or more kinds may be used in combination. Powder materials such as carbon materials are ethylene propylene diene terpolymer (EPDM), polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), a copolymer of styrene and butadiene (SBR), and a copolymer of acrylonitrile and butadiene. Kneaded with a binder such as a polymer (NBR) or carboxymethylcellulose (CMC) and used as a negative electrode mixture. The manufacturing method of a negative electrode is not specifically limited, It can manufacture with the method similar to the manufacturing method of said positive electrode.
[0020]
The structure of the lithium secondary battery is not particularly limited, and a coin-type battery having a positive electrode, a negative electrode, and a single-layer or multi-layer separator, and a cylindrical battery or a square type having a positive electrode, a negative electrode, and a roll separator. An example is a battery. A known polyolefin microporous film, woven fabric, non-woven fabric or the like is used as the separator.
[0021]
[Examples] Next, the present invention will be specifically described with reference to Examples and Comparative Examples. (However, Examples 1-4, 6, 7, 9-11 are referred to as Reference Examples 1-4, 6, 7, 9-11, respectively, and the same applies to [Table 1].)
Example 1
[Preparation of Nonaqueous Electrolyte] A nonaqueous solvent of PC: DMC (volume ratio) = 1: 2 is prepared, and LiPF 6 is dissolved in the electrolyte salt to a concentration of 1M to obtain a nonaqueous electrolyte. After the preparation, 2,3,4,5,6-pentafluoroanisole was further added to 0.5 wt% with respect to the non-aqueous electrolyte.
[0022]
[Production of lithium secondary battery and measurement of battery characteristics]
90% by weight of LiCoO 2 (positive electrode active material), 5% by weight of acetylene black (conductive agent), and 5% by weight of polyvinylidene fluoride (binder) are mixed, and this is mixed with 1-methyl-2-pyrrolidone. What mixed and added the solvent was apply | coated on the aluminum foil, and it dried, press-molded, and heat-processed, and prepared the positive electrode. 90% by weight of artificial graphite (negative electrode active material) and 10% by weight of polyvinylidene fluoride (binder) were mixed, and 1-methyl-2-pyrrolidone solvent was added to this, and the resulting mixture was added to the copper foil. The negative electrode was prepared by drying, pressure molding, and heat treatment. And using the separator of a polypropylene microporous film, said nonaqueous electrolyte solution was inject | poured and the coin battery (diameter 20mm, thickness 3.2mm) was produced.
Using this coin battery, it was charged at a constant current and a constant voltage of 1.1 mA at room temperature (20 ° C.) for 5 hours to a final voltage of 4.2 V, and then at a constant current of 1.1 mA and a final voltage of 2. The battery was discharged to 7 V, and this charge / discharge was repeated. The initial charge / discharge capacity is 1 M LiPF 6 -EC / DEC (capacity ratio 3/7) to which no pentafluorophenyl compound is added as a non-aqueous electrolyte (the initial charge / discharge capacity of Comparative Example 2 is 1). When the battery characteristics after 50 cycles were measured, the discharge capacity retention rate when the initial discharge capacity was 100% was 90.1%. The production conditions and battery characteristics of the coin battery are shown in Table 1.
[0023]
Example 2
A coin battery was prepared by preparing a non-aqueous electrolyte in the same manner as in Example 1 except that 2,3,4,5,6-pentafluoroanisole was used as an additive in an amount of 1% by weight based on the non-aqueous electrolyte. When the battery characteristics after 50 cycles were measured, the discharge capacity retention rate was 90.5%. The production conditions and battery characteristics of the coin battery are shown in Table 1.
[0024]
Example 3
A coin battery was prepared by preparing a non-aqueous electrolyte in the same manner as in Example 1 except that 2,3,4,5,6-pentafluoroanisole was used as an additive in an amount of 2% by weight based on the non-aqueous electrolyte. When the battery characteristics after 50 cycles were measured, the discharge capacity retention rate was 89.5%. The production conditions and battery characteristics of the coin battery are shown in Table 1.
[0025]
Example 4
A coin battery was prepared by preparing a non-aqueous electrolyte in the same manner as in Example 1 except that 1% by weight of decafluorobiphenyl was used as an additive with respect to the non-aqueous electrolyte, and the battery characteristics after 50 cycles were measured. As a result, the discharge capacity retention rate was 90.3%. The production conditions and battery characteristics of the coin battery are shown in Table 1.
[0026]
Example 5
A coin battery was prepared by preparing a nonaqueous electrolyte in the same manner as in Example 1 except that 2,3,4,5,6-pentafluorotoluene was used as an additive in an amount of 1% by weight based on the nonaqueous electrolyte. Then, when the battery characteristics after 50 cycles were measured, the discharge capacity retention rate was 89.9%. The production conditions and battery characteristics of the coin battery are shown in Table 1.
[0027]
Example 6
EC / MEC (capacity ratio 3/7) was used as a non-aqueous solvent, and 2,3,4,5,6-pentafluoroanisole was used as an additive in an amount of 1% by weight based on the non-aqueous electrolyte. Prepared a coin battery by preparing a nonaqueous electrolytic solution in the same manner as in Example 1, and measured the battery characteristics after 50 cycles. As a result, the discharge capacity retention rate was 91.7%. The production conditions and battery characteristics of the coin battery are shown in Table 1.
[0028]
Example 7
Nonaqueous electrolysis as in Example 1 except that EC / MEC (capacity ratio 3/7) was used as the nonaqueous solvent and decafluorobiphenyl was used as an additive in an amount of 1% by weight based on the nonaqueous electrolyte. A coin battery was prepared by preparing a liquid, and the battery characteristics after 50 cycles were measured. As a result, the discharge capacity retention rate was 89.1%. The production conditions and battery characteristics of the coin battery are shown in Table 1.
[0029]
Example 8
EC / MEC (capacity ratio 3/7) was used as a non-aqueous solvent, and 2,3,4,5,6-pentafluorotoluene was used as an additive in an amount of 1% by weight based on the non-aqueous electrolyte. Prepared a coin battery by preparing a nonaqueous electrolytic solution in the same manner as in Example 1, and measured the battery characteristics after 50 cycles. As a result, the discharge capacity retention rate was 90.7%. The production conditions and battery characteristics of the coin battery are shown in Table 1.
[0030]
Example 9
EC / DEC (volume ratio 1/2) was used as a non-aqueous solvent, and 2,3,4,5,6-pentafluoroanisole was used as an additive in an amount of 1% by weight based on the non-aqueous electrolyte. Prepared a coin battery by preparing a nonaqueous electrolytic solution in the same manner as in Example 1, and measured the battery characteristics after 50 cycles. As a result, the discharge capacity retention rate was 90.4%. The production conditions and battery characteristics of the coin battery are shown in Table 1.
[0031]
Example 10
Other than using LiMn 2 O 4 instead of LiCoO 2 as the positive electrode active material and 1% by weight of 2,3,4,5,6-pentafluoroanisole as the additive with respect to the non-aqueous electrolyte A coin battery was prepared by preparing a non-aqueous electrolyte in the same manner as in Example 1, and the battery characteristics after 50 cycles were measured. The discharge capacity retention rate was 89.2%. The production conditions and battery characteristics of the coin battery are shown in Table 1.
[0032]
Example 11
Example except that natural graphite was used instead of artificial graphite as the negative electrode active material, and 1% by weight of 2,3,4,5,6-pentafluoroanisole was used as an additive with respect to the non-aqueous electrolyte. A coin battery was prepared by preparing a non-aqueous electrolyte in the same manner as in Example 1, and the battery characteristics after 50 cycles were measured. The discharge capacity retention rate was 89.8%. The production conditions and battery characteristics of the coin battery are shown in Table 1.
[0033]
Comparative Example 1
A non-aqueous solvent of PC: DMC (volume ratio) = 1: 2 was prepared, and LiPF 6 was dissolved therein to a concentration of 1M. At this time, no pentafluorophenyl compound was added. Using this non-aqueous electrolyte, a coin battery was produced in the same manner as in Example 1, and the battery characteristics were measured.
[0034]
Comparative Example 2
A non-aqueous solvent of EC: DEC (volume ratio) = 3: 7 was prepared, and LiPF 6 was dissolved therein to a concentration of 1M. At this time, no pentafluorophenyl compound was added. Using this non-aqueous electrolyte, a coin battery was produced in the same manner as in Example 1, and the battery characteristics were measured. With respect to the initial discharge capacity, the discharge capacity retention ratio after 50 cycles was 82.1%. The production conditions and battery characteristics of the coin battery are shown in Table 1.
[0035]
Comparative Example 3
A non-aqueous electrolyte was prepared in the same manner as in Example 1 except that 4-fluoroanisole was used as an additive in an amount of 1% by weight based on the non-aqueous electrolyte, and the battery characteristics after 50 cycles were obtained. Although measured, it was not charged or discharged at all. The production conditions and battery characteristics of the coin battery are shown in Table 1.
[0036]
Comparative Example 4
A non-aqueous electrolyte was prepared in the same manner as in Example 1 except that 1% by weight of 2,4-difluoroanisole was used as an additive with respect to the non-aqueous electrolyte. Although the characteristics were measured, the battery was not charged or discharged at all. The production conditions and battery characteristics of the coin battery are shown in Table 1.
[0037]
Comparative Example 5
A non-aqueous electrolyte was prepared in the same manner as in Example 1 except that 1% by weight of 2,4,5-trifluoroanisole was used as an additive with respect to the non-aqueous electrolyte. The later battery characteristics were measured, but the battery was not charged or discharged at all. The production conditions and battery characteristics of the coin battery are shown in Table 1.
[0038]
[Table 1]
Note that the present invention is not limited to the described embodiments, and various combinations that can be easily inferred from the gist of the invention are possible. In particular, the combination of solvents in the above examples is not limited. Furthermore, although the said Example is related with a coin battery, this invention is applied also to a cylindrical and prismatic battery.
[0040]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to this invention, the lithium secondary battery excellent in battery characteristics, such as a cycling characteristic of a battery, an electrical capacity, and a storage characteristic, can be provided.
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| WO2007083975A1 (en) * | 2006-01-23 | 2007-07-26 | Lg Chem, Ltd. | Non-aqueous-electrolyte and lithium secondary battery using the same |
| KR100760763B1 (en) | 2006-10-17 | 2007-10-04 | 삼성에스디아이 주식회사 | Electrolyte for high voltage lithium rechargeable battery and high voltage lithium rechargeable rechargeable battery employing the same |
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| US8795904B2 (en) | 2010-05-13 | 2014-08-05 | The United States Of America As Represented By The Secretary Of The Army | Nonaqueous electrolyte solvents and additives |
| US10438753B2 (en) | 2010-07-06 | 2019-10-08 | The United States Of America As Represented By The Secretary Of The Army | Electrolytes in support of 5V Li ion chemistry |
| CN107531830B (en) | 2015-08-26 | 2019-06-28 | 赢创德固赛有限公司 | Purposes of certain polymer as charge accumulator |
| KR102007112B1 (en) | 2015-08-26 | 2019-08-02 | 에보니크 데구사 게엠베하 | Use of Specific Polymers as Charge Storage |
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