JP3961597B2 - Nonaqueous electrolyte and nonaqueous electrolyte secondary battery - Google Patents

Description

（Ｒ ¹ 、Ｒ ² 、Ｒ ³ は同一であっても異なっていてもよく、アルキル基、アリール基、ジア
ルキルアミド基、アルキル基を末端に持つポリアルキレンオキシド基、およびこれらをハロゲン置換した基を示す。）
ハロゲンを含有する環状炭酸エステルが、一般式（ II ）で表される化合物から選ばれる
【化２】

（Ｒ⁴、Ｒ⁵、Ｒ⁶、Ｒ⁷は互いに同一であっても異なっていてもよく、水素原子、アルキル基、ハロゲン原子、ハロゲン化アルキル基、またはエーテル基,カルボニル基,エステル基,炭酸ジエステル基を含むアルキル基またはハロゲン化アルキル基であり、Ｒ⁴〜Ｒ⁷のうち少なくとも一つが、ハロゲン原子、ハロゲン化アルキル基、またはエーテル基,カルボニル基,エステル基,炭酸ジエステル基を含むハロゲン化アルキル基を示す。）
ことを特徴とする。
溶解してなることを特徴とする。
【００１５】
前記ハロゲンを含有する環状炭酸エステルのハロゲンは、フッ素、塩素、または臭素であることが好ましい。
また、前記ハロゲンを含有する環状炭酸エステルは、フルオロエチレンカーボネート、１,１−ジフルオロエチレンカーボネート、１,２−ジフルオロエチレンカーボネート、１,１,２,２−テトラフルオロエチレンカーボネート、３−フルオロ−１，２−プロピレンカーボネート、３,３−ジフルオロ−１,２−プロピレンカーボネート、１,１,２,３,３,３−ヘキサフルオロ−１,２−プロピレンカーボネート、２−フルオロ−１,３−プロピレンカーボネート、２,２−ジフルオロ−１,３−プロピレンカーボネート、ブチレンカーボネートまたはペンテンカーボネートの水素をフッ素で置換した化合物であることが好ましい。
【００１８】
非水電解液中のハロゲンを含む環状炭酸エステルとリン酸エステルの混合比率は体積比で１０：１〜１：１の範囲であることが好ましい。
ハロゲンを含有する環状炭酸エステルとリン酸エステルの量は溶媒全体に対し１０〜１００体積％の範囲であることが好ましい。
【００１９】
本発明にかかる非水電解液二次電池は、
負極活物質として、金属リチウム、リチウム含有合金、リチウムイオンのドープ・アンドープが可能な化合物、リチウムイオンのドープ・脱ドープが可能な炭素材料のいずれか１種を含む負極と、
正極活物質としてリチウムと遷移金属の複合酸化物を含む正極と、
上記のような非水電解液とを、
有することを特徴とする。
【００２０】
【発明の具体的な説明】
以下本発明に係る非水電解液およびこの非水電解液を用いた非水電解液二次電池について具体的に説明する。
【００２１】
非水電解液
本発明に係る非水電解液は、
リン酸エステル化合物とハロゲンを含有する環状炭酸エステルとを含む非水溶媒に、
リチウム塩を溶解してなることを特徴としている。
【００２２】
リン酸エステル化合物
非水溶媒中に含まれるリン酸エステル化合物としては、下記一般式（Ｉ）で表される化合物であることが好ましい。
【００２３】
【化５】

【００２４】
式中Ｒ¹、Ｒ²、Ｒ³は同一であっても異なっていてもよく、炭素数が１〜４個のアルキル基または炭素数が１〜４個のハロゲン化アルキル基を示す。
このようなリン酸エステル化合物として、具体的には、
リン酸トリメチル、リン酸エチルジメチル、リン酸ジエチルメチル、リン酸トリエチル、リン酸トリプロピル、リン酸トリブチル、リン酸トリ（ジメチルアミド）などのリン酸エステル、リン酸トリアミド、リン酸トリ（トリフルオロエチル）、リン酸トリ（トリクロロエチル）、リン酸トリ（トリブロモエチル）、リン酸トリ（ジ（トリフルオロエチル）アミド）などのハロゲン置換リン酸エステル、ハロゲン置換リン酸トリアミドなどが挙げられる。
【００２５】
ハロゲンを含有する環状炭酸エステル
非水溶媒中に含まれるハロゲンを含有する環状炭酸エステルとしては、下記一般式（II）で表される化合物であることが好ましい。
【００２６】
ハロゲンを含有する環状炭酸エステルのハロゲンは、フッ素、塩素または臭素であることが好ましい。
【００２７】
【化６】

【００２８】
式中Ｒ⁴、Ｒ⁵、Ｒ⁶、Ｒ⁷は互いに同一であっても異なっていてもよく、水素原子、アルキル基、ハロゲン原子、ハロゲン化アルキル基、またはエーテル基、カルボニル基、エステル基、炭酸ジエステル基を含むアルキル基またはハロゲン化アルキル基であり、Ｒ⁴〜Ｒ⁷のうち少なくとも一つが、ハロゲン原子、ハロゲン化アルキル基、またはエーテル基,カルボニル基,エステル基,炭酸ジエステル基を含むハロゲン化アルキル基である。
【００２９】
前記アルキル基、ハロゲン化アルキル基（エーテル基,カルボニル基,エステル基,炭酸ジエステル基を含むハロゲン化アルキル基のアルキル基部分も含む）の炭素数は、１〜４であることが好ましい。
【００３０】
このようなハロゲンを含有する環状炭酸エステルとしては、具体的に、
フルオロエチレンカーボネート、１,１−ジフルオロエチレンカーボネート、１,２−ジフルオロエチレンカーボネート、１,１,２,２−テトラフルオロエチレンカーボネート、３−フルオロ−１，２−プロピレンカーボネート、３,３−ジフルオロ−１,２−プロピレンカーボネート、３,３,３−トリフルオロ−１,２−プロピレンカーボネート、１,１,２,３,３,３−ヘキサフルオロ−１,２−プロピレンカーボネート、２−フルオロ−１,３−プロピレンカーボネート、２,２−ジフルオロ−１,３−プロピレンカーボネート等のエチレンカーボネートやプロピレンカーボネートの水素をフッ素で置換した化合物、
ブチレンカーボネートやペンテンカーボネートの水素をフッ素で置換した化合物、
以上の化合物をフッ素の代わりに、塩素または臭素で置換した化合物等が挙げられる。
【００３１】
非水溶媒
非水溶媒中における、以上のようなハロゲンを含有する環状炭酸エステルとリン酸エステルとの比率は、体積比で２０：１〜１：１０、好ましくは１０：１〜１：２の範囲であるのが望ましい。このような体積比の範囲内であると、充分な難燃性を有し、高い電池性能を保つことができる。
【００３２】
以上のようなハロゲンを含有する環状炭酸エステルとリン酸エステルを合わせた合計量の非水溶媒全体に占める割合は、１０〜１００体積％、好ましくは２０〜９０体積％の範囲であることが望ましい。このような範囲であると、充分な難燃性を有し、高い電池性能を保つことができる。
【００３３】
本発明に係る非水電解液中には、上記ハロゲンを含有する環状炭酸エステルとリン酸エステル以外に、必要に応じて他の非水溶媒が含まれていてもよい。
非水溶媒としては、リチウム塩を溶解させるためにリチウムイオンと適度な溶媒和能力をもった非水溶媒や、溶解したリチウムイオンの移動を妨げないような非水溶媒が好ましく使用される。
【００３４】
リチウムイオンと適度な溶媒和能力をもつような非水溶媒としては、高誘電率の非水溶媒が使用され、具体的には、
エチレンカーボネート、プロピレンカーボネート、ブチレンカーボネートなどの環状炭酸エステル類、
γ−ブチロラクトンなどの環状エステル類、
スルホランなどの環状スルホン類、
Ｎ−メチルオキサゾリジノンなどの環状カーバメート、
Ｎ−メチルピロリドンなどの環状アミド等の環状の極性基を有する非水溶媒が挙げられる。
【００３５】
リチウムイオンの移動を妨げないような非水溶媒としては、粘度の低い非水溶媒が使用され、具体的には、
ジメチルカーボネート、メチルエチルカーボネート、ジエチルカーボネート、メチルプロピルカーボネート、メチルイソプロピルカーボネートなどの鎖状炭酸エステル類、
酢酸エチル、プロピオン酸メチルなどの鎖状エステル、
ジメトキシエタン、テトラヒドロフランなどのエーテル類、
Ｎ,Ｎ−ジメチルアセトアミドなどの鎖状アミド、
メチル−Ｎ,Ｎ−ジメチルカーバメートなどの鎖状カーバメート等の鎖状の非水溶媒が挙げられる。
【００３６】
以上の非水溶媒は、単一で使用してもよいが、誘電率の高い非水溶媒と、粘度の低い非水溶媒とを組み合わせて使用することが好ましく、特に環状炭酸エステルと鎖状炭酸エステルを組み合わせて使用することがより好ましい。これらの溶媒は電解液中の非水溶媒全体に対し、１０〜９０体積％、好ましくは３０〜７０体積％の範囲で含まれていることが望ましい。
【００３７】
リチウム塩
非水電解液中に溶解しているリチウム塩としては、具体的には、ＬｉＰＦ₆、ＬｉＢＦ₄、ＬｉＣｌＯ₄、ＬｉＡｓＦ₆、ＬｉＣＦ₃ＳＯ₃、ＬｉＮ(ＳＯ₂ＣＦ₃)₂、ＬｉＡｌＣｌ₃、ＬｉＳｉＦ₆などが挙げられる。これらのリチウム塩は単独で使用してもよく、２種以上のリチウム塩を混合して使用してもよい。これらリチウム塩のうち、ＬｉＰＦ₆はリン酸エステルとの相乗作用で難燃性が高くなるため好ましい。このようなリチウム塩は、通常、０．３〜２モル／リットル、好ましくは０．５〜１．５モル／リットルの量で非水電解液中に含まれていることが望ましい。
【００３８】
非水電解液二次電池
本発明に係る非水電解液二次電池は、
負極活物質として金属リチウム、リチウム含有合金、リチウムイオンをドープ・アンドープが可能な化合物、リチウムイオンのドープ・脱ドープが可能な炭素材料のいずれかを含む負極と、
正極活物質としてリチウムと遷移金属の複合酸化物を含む正極と、
前記の非水電解液とを有することを特徴としている。
【００３９】
このような非水電解液二次電池は、たとえば円筒型非水電解液二次電池に適用できる。円筒型非水電解液二次電池は、図１に示すように負極集電体９に負極活物質を塗布してなる負極１と、正極集電体１０に正極活物質を塗布してなる正極２とを、非水電解液を注入されたセパレータ３を介して巻回し、巻回体の上下に絶縁板４を載置した状態で電池缶５に収納してなるものである。電池缶５には電池蓋７が封口ガスケット６を介してかしめることにより取り付けられ、それぞれ負極リード１１および正極リード１２を介して負極１あるいは正極２と電気的に接続され、電池の負極あるいは正極として機能するように構成されている。なおセパレータは多孔性の膜である。
【００４０】
この電池では、正極リード１２は、電流遮断用薄板８を介して電池蓋７との電気的接続がはかられていてもよい。このような電池では、電池内部の圧力が上昇すると、電流遮断用薄板８が押し上げられ変形し、正極リード１２が上記薄板８と溶接された部分を残して切断され、電流が遮断されるようなっている。
【００４１】
このような負極１を構成する負極活物質としては、金属リチウム、リチウム合金、リチウムイオンをドープ・アンドープが可能な化合物、リチウムイオンをドープ・脱ドープすることが可能な炭素材料のいずれを用いることができる。これらのうちで、リチウムイオンをドープ・脱ドープすることが可能な炭素材料を用いることが好ましい。このような炭素材料としてはグラファイトでも非晶質炭素でもよく、活性炭、炭素繊維、カーボンブラック、メソカーボンマイクロビーズ等あらゆる炭素材料が用いられる。
【００４２】
また正極２を構成する正極活物質としては、ＬｉＣｏＯ₂、ＬｉＭｎＯ₂、ＬｉＭｎ₂Ｏ₄、ＬｉＮｉＯ₂等のリチウムと遷移金属とからなる複合酸化物が用いられる。
【００４３】
なお本発明に係る非水電解液二次電池は、電解液として以上説明した非水電解液を含むものであり、電池の形状などは図１に示したものに限定されず、図２に示すようなコイン型、あるいは角型などであってもよい。
【００４４】
【発明の効果】
本発明に係る非水電解液は、難燃性であり充放電性能に優れ、このような非水電解液を用いた非水電解液二次電池は、安全で、高電圧を発生でき、充放電特性に優れる。
【００４５】
【実施例】
以下に実施例を挙げて本発明を具体的に説明するが、本発明はこれら実施例により何ら限定されるものではない。
【００４６】
【実施例１】
非水電解液の調製
六フッ化リン酸リチウム（ＬｉＰＦ₄）１５２ｇ（１モル）を、3,3,3-トリフルオロプロピレンカーボネート（ＴＦＰＣ）と、リン酸トリメチル（ＴＭＰＡ）と、メチルエチルカーボネート（ＭＥＣ）との混合溶媒(体積比TFPC:TMPA:MEC=4:2:4)に溶解して１リットルの非水電解液を調製した（電解質濃度１．０モル／リットル）。
非水電解液の燃焼性評価
前記非水電解液の入ったビーカー中に、１５ｍｍ、長さ３２０ｍｍの短冊状に切断した厚さ０．０４ｍｍのセパレーター用マニラ紙を１分以上浸した。マニラ紙から滴り落ちる過剰の非水電解液をビーカー壁で拭い、マニラ紙を２５ｍｍ間隔で支持針を有するサンプル台の支持針に刺して水平に固定した。マニラ紙を固定したサンプル台を２５ｃｍ×２５ｃｍ×５０ｃｍの金属製の箱に入れ、一端をライターで着火し、セパレーター紙の燃えた長さを測定した。
【００４７】
結果を表１に示す。
【００４８】
【実施例２】
実施例１において、3,3,3-トリフルオロプロピレンカーボネート（ＴＦＰＣ）の代わりにクロロエチレンカーボネート（ＣｌＥＣ）を使用した以外は実施例１と同様にした。
【００４９】
結果を表１に示す。
【００５０】
【比較例１】
実施例１において、3,3,3-トリフルオロプロピレンカーボネート（ＴＦＰＣ）の代わりにエチレンカーボネート（ＥＣ）を使用した以外は実施例１と同様にした。
【００５１】
結果を表１に示す。
【００５２】
【比較例２】
実施例１において、3,3,3-トリフルオロプロピレンカーボネート（ＴＦＰＣ）の代わりにエチレンカーボネート（ＥＣ）を使用し、リン酸トリメチル（ＴＭＰＡ）を使用しない以外は実施例１と同様にした。
【００５３】
結果を表１に示す。
【００５４】
【表１】

【００５５】
【実施例３】
電池の作成
ポリビニリデンフルオライド０.２５ｇを溶解したＮ−メチルピロリドン溶液５ｍｌに、人造黒鉛（面間隔０.３３７ｎｍ、Ｌｃ４０ｎｍ、Ｌａ６０ｎｍ）の粉末４.７５ｇを加えよく混合しペースト状にした。このペーストを銅箔上に塗布し、乾燥した後、コイン（直径１０ｍｍ）状に打ち抜いた。コイン状に打ち抜いたものを２００kg／cm²でプレスし、１５０℃で真空乾燥して炭素電極を作成した。
【００５６】
この炭素電極を使用して図２に示すように、負極１３に金属リチウム、正極１４に炭素電極を、セパレーター１５（セルガード３５０１）を介して対向させて、実施例１に示した3,3,3-トリフルオロプロピレンカーボネート（ＴＦＰＣ）とリン酸トリメチル（ＴＭＰＡ）とメチルエチルカーボネート（ＭＥＣ）の混合溶媒（体積比TFPC:TMPA:MEC=4:2:4）にＬｉＰＦ₄を１モル／リットルの濃度で溶解した非水電解液を０.０４ミリリットル加えて、ＣＲ２０３０コイン電池を作製した。
充放電特性
上記のコイン電池を使用して、０.１２５ｍＡの定電流で、０Ｖまで放電し、１.５Ｖまで充電するサイクルを行った。１サイクル目の黒鉛電極重量当たりの不可逆容量、および４サイクル目の黒鉛電極重量当たりの放電容量を測定した。
【００５７】
結果を表２に示す。
【００５８】
【実施例４】
実施例３において非水電解液の混合溶媒として、3,3,3-トリフルオロプロピレンカーボネート（ＴＦＰＣ）とリン酸トリメチル（ＴＭＰＡ）とメチルエチルカーボネート（ＭＥＣ）とエチレンカーボネート（ＥＣ）との混合溶媒（体積比TFPC:TMPA:MEC:EC=3:2:4:1）を使用した以外は、実施例３と同様にしてコイン電池を作製し、充放電特性を測定した。
【００５９】
結果を表２に示す。
【００６０】
【実施例５】
実施例３において非水電解液の混合溶媒として、3,3,3-トリフルオロプロピレンカーボネート（ＴＦＰＣ）とリン酸トリメチル（ＴＭＰＡ）とメチルエチルカーボネート（ＭＥＣ）とエチレンカーボネート（ＥＣ）との混合溶媒（体積比TFPC:TMPA:MEC:EC=2:2:4:2）を使用した以外は、実施例３と同様にしコイン電池を作製し、充放電特性を測定した。
【００６１】
結果を表２に示す。
【００６２】
【実施例６】
実施例３において非水電解液の混合溶媒として、3,3,3-トリフルオロプロピレンカーボネート（ＴＦＰＣ）とリン酸トリメチル（ＴＭＰＡ）とメチルエチルカーボネート（ＭＥＣ）とエチレンカーボネート（ＥＣ）との混合溶媒（体積比TFPC:TMPA:MEC:EC=1:3:4:2）を使用した以外は、実施例３と同様にしコイン電池を作製し、充放電特性を測定した。
【００６３】
結果を表２に示す。
【００６４】
【実施例７】
実施例３において非水電解液の混合溶媒として、実施例２に示したクロロエチレンカーボネート（ＣｌＥＣ）とリン酸トリメチル（ＴＭＰＡ）とメチルエチルカーボネート（ＭＥＣ）との混合溶媒（体積比ClEC:TMPA:MEC=4:2:4）を使用した以外は、実施例３と同様にしコイン電池を作製し、充放電特性を測定した。
【００６５】
結果を表２に示す。
【００６６】
【比較例３】
実施例３において非水電解液の混合溶媒として、比較例１に示したリン酸トリメチル（ＴＭＰＡ）とメチルエチルカーボネート（ＭＥＣ）とエチレンカーボネート（ＥＣ）との混合溶媒（体積比TMPA:MEC:EC=2:4:4）を使用した以外は、実施例３と同様にしコイン電池を作製し、充放電特性を測定した。
【００６７】
結果を表２に示す。
【００６８】
【比較例４】
実施例３において非水電解液の混合溶媒として、比較例２に示したメチルエチルカーボネート（ＭＥＣ）とエチレンカーボネート（ＥＣ）との混合溶媒（体積比MEC:EC=1:1）を使用した以外は、実施例３と同様にしコイン電池を作製し、充放電特性を測定した。
【００６９】
結果を表２に示す。
【００７０】
【表２】

【図面の簡単な説明】
【図１】 本発明の非水電解液二次電池の一実施例を示す概略断面図である。
【図２】 本発明の実施例３〜６、比較例３、４で使用するコイン型電池の概略断面図である。
【符号の説明】
１,１３・・・・負極
２,１４・・・・正極
３,１５・・・・セパレータ
４・・・・絶縁板
５・・・・電池缶
６・・・・封口ガスケット
７・・・・電池蓋
８・・・・電流遮断用薄板
９・・・・負極集電体
１０・・・・正極集電体
１１・・・・負極リード
１２・・・・正極リード
１６・・・・封口板
１７・・・・ケース
１８・・・・ガスケット[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a non-aqueous electrolyte and a non-aqueous electrolyte secondary battery, and more specifically, a non-aqueous electrolyte that is highly flame retardant, safe, capable of generating a high voltage, and has excellent battery charge / discharge performance, and its The present invention relates to a non-aqueous electrolyte secondary battery containing an electrolyte.
[0002]
TECHNICAL BACKGROUND OF THE INVENTION
A battery using a non-aqueous electrolyte has a high voltage, an energy density, and is excellent in reliability such as storability. Therefore, the battery is widely used as a power source for consumer electronic devices.
[0003]
Such a battery is used as a non-aqueous electrolyte solution in an aprotic non-aqueous solvent that is not easily electrolyzed, and lithium such as LiBF ₄ , LiPF ₆ , LiClO ₄ , LiAsF ₆ , LiCF ₃ SO ₃ , LiAlCl ₄ , and LiSiF _6. What dissolved the salt is used. The non-aqueous solvent used in the non-aqueous electrolyte should have a high dielectric constant and low viscosity so as to dissolve lithium salt, have an appropriate solvating ability with lithium ions, and do not hinder the movement of ions. Is required. Moreover, the non-aqueous solvent is liquid at the operating temperature of the battery, has a low freezing point, a high boiling point, is chemically stable with respect to the active material of the positive electrode and the negative electrode, and is intense due to a charge / discharge reaction in the battery. It must also be durable to a redox atmosphere. However, since it is difficult to satisfy all of these properties with a single non-aqueous solvent, propylene carbonate, γ-butyrolactone, sulfolane, etc., which are high dielectric constant solvents, and dimethoxyethane, tetrahydrofuran, which are low viscosity solvents, A mixed solvent with 1,3-dioxolane or the like is generally used.
[0004]
Some of the non-aqueous solvents have a low withstand voltage, and when charging and discharging are repeated using these low withstand voltage solvents, the solvent is electrolyzed, and the internal pressure of the battery increases due to the gas generated by the decomposition, The product may cause a polymerization reaction and adhere to the electrode. For this reason, there existed problems, such as battery charging / discharging efficiency falling, battery energy density falling, or the lifetime of a battery becoming short.
[0005]
As an attempt to improve the durability of the electrolytic solution, high withstand voltage such as esters such as γ-butyrolactone and ethyl acetate, and ethers such as dimethoxyethane, tetrahydrofuran and 1,3-dioxolane, which have been conventionally used, are used. Reduction of battery energy density after repeated charging and discharging using carbonate is performed (for example, JP-A-2-10666).
[0006]
On the other hand, in a battery using a non-aqueous electrolyte, lithium metal or lithium alloy having high reducing ability is used as a negative electrode material. However, when these batteries are repeatedly charged and discharged, lithium ions in the electrolytic solution may be deposited on the electrode, and a needle-like highly reactive metal called dendrite may be generated on the electrode. This dendrite electrolyzes the electrolytic solution to accelerate the decrease in current efficiency, and since it has a needle shape, it may break through the separator and cause a short circuit between the positive electrode and the negative electrode. In such a state, there are problems such as an increase in self-discharge.
[0007]
In recent years, in order to solve the generation of dendrites, which has been a problem in using alkali metals and alkaline earth metals as negative electrode materials, a carbon material is used for the negative electrode of the battery, and a composite of lithium and transition metal is used for the positive electrode. A secondary battery called a rocking chair type using LiCoO ₂ which is an oxide has been developed. In this battery, the battery voltage can be generated at 4 V or more, and the lithium of the negative electrode material only goes back and forth between the carbon negative electrode and the metal oxide positive electrode in the ionic state at the time of charge / discharge, so the dendrite is not in the metal state. There is no generation. For this reason, the safety of the battery has been dramatically improved, and the safety has been confirmed by experiments such as overcharge, external short-circuiting, nail stab, and crushing, and batteries using non-aqueous electrolytes have become popular as high-energy batteries. It is becoming popular. However, in the future, when the energy density and size are significantly increased, it is necessary to further improve the safety such as flame retardancy.
[0008]
Many of the currently used electrolyte solvents do not necessarily have a high flash point and are not self-extinguishing. For this reason, it has been proposed to add phosphate esters known as self-extinguishing compounds to the electrolytic solution (Japanese Patent Laid-Open No. 4-184870). However, an electrolyte solution containing 15% by weight or more of such a compound is flame retardant and improves safety, but has problems in terms of battery charge / discharge efficiency, battery energy density, and battery life. . In addition, one using trimethyl phosphate as a solvent for an electrolytic solution has been proposed (Japanese Patent Laid-Open No. 1-102862). However, since trimethyl phosphate is relatively easy to react with metallic lithium and the like, the charge / discharge efficiency is lowered. As a constituent material of the electrolyte solution, the performance was not necessarily satisfactory.
[0009]
OBJECT OF THE INVENTION
The present invention has been made in view of the above problems, and is a non-aqueous electrolyte solution that is highly flame retardant, safe, capable of generating a high voltage, and excellent in battery charge / discharge performance, and a non-aqueous electrolyte solution using the electrolyte solution. It aims at providing a water electrolyte secondary battery.
[0010]
More specifically, non-aqueous electrolyte that exhibits good battery characteristics even when phosphoric acid esters are added and exhibits flame retardancy and the use of the electrolyte improves safety and exhibits good characteristics. An object of the present invention is to provide an electrolyte secondary battery.
[0011]
SUMMARY OF THE INVENTION
The non-aqueous electrolytic solution according to the present invention is obtained by dissolving a lithium salt in a non-aqueous solvent containing a phosphate ester compound, a cyclic carbonate containing a halogen, and a chain carbonate ,
The phosphate ester compound is a compound represented by the following general formula (I):
[Chemical 1]

(R ¹ , R ² and R ³ may be the same or different, and may be an alkyl group, an aryl group,
A rualkylamide group, a polyalkylene oxide group having an alkyl group at its end, and a group obtained by halogen-substituting them are shown. )
The halogen-containing cyclic carbonate is selected from the compounds represented by the general formula ( II )

(R ⁴ , R ⁵ , R ⁶ and R ⁷ may be the same as or different from each other, and may be a hydrogen atom, alkyl group, halogen atom, halogenated alkyl group, or ether group, carbonyl group, ester group, carbonic acid group. An alkyl group or a halogenated alkyl group containing a diester group, wherein at least one of R ^{4 to} R ⁷ is a halogen atom, a halogenated alkyl group, or an ether group, a carbonyl group, an ester group, or a carbonic acid diester group. Represents an alkyl group.)
It is characterized by that.
It is characterized by being dissolved.
[0015]
The halogen of the cyclic carbonate containing halogen is preferably fluorine, chlorine or bromine.
The cyclic carbonate containing halogen is fluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,2-difluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 3-fluoro-1 , 2-propylene carbonate, 3,3-difluoro-1,2-propylene carbonate, 1,1,2,3,3,3-hexafluoro-1,2-propylene carbonate, 2-fluoro-1,3-propylene A compound in which hydrogen of carbonate, 2,2-difluoro-1,3-propylene carbonate, butylene carbonate or pentene carbonate is substituted with fluorine is preferable.
[0018]
The mixing ratio of the cyclic carbonate containing halogen and the phosphate ester in the non-aqueous electrolyte is preferably in the range of 10: 1 to 1: 1 by volume ratio.
The amount of the halogenated cyclic carbonate and phosphate is preferably in the range of 10 to 100% by volume based on the entire solvent.
[0019]
Nonaqueous electrolyte secondary battery according to the present invention,
As a negative electrode active material, a negative electrode containing any one of metallic lithium, a lithium-containing alloy, a compound that can be doped / undoped with lithium ions, and a carbon material that can be doped / undoped with lithium ions,
A positive electrode containing a composite oxide of lithium and a transition metal as a positive electrode active material;
A non-aqueous electrolyte as described above,
It is characterized by having.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the nonaqueous electrolyte solution according to the present invention and the nonaqueous electrolyte secondary battery using the nonaqueous electrolyte solution will be described in detail.
[0021]
Non-aqueous electrolyte The non-aqueous electrolyte according to the present invention is:
In a non-aqueous solvent containing a phosphate compound and a cyclic carbonate containing a halogen,
It is characterized by dissolving a lithium salt.
[0022]
Phosphate ester compound The phosphate ester compound contained in the non-aqueous solvent is preferably a compound represented by the following general formula (I).
[0023]
[Chemical formula 5]

[0024]
In the formula, R ¹ , R ² and R ³ may be the same or different and each represents an alkyl group having 1 to 4 carbon atoms or a halogenated alkyl group having 1 to 4 carbon atoms.
As such a phosphoric ester compound, specifically,
Phosphoric esters such as trimethyl phosphate, ethyl dimethyl phosphate, diethyl methyl phosphate, triethyl phosphate, tripropyl phosphate, tributyl phosphate, tri (dimethylamide) phosphate, triamide phosphate, tri (phosphate trifluoro) Ethyl), tri (trichloroethyl) phosphate, tri (tribromoethyl) phosphate, tri (di (trifluoroethyl) amide) phosphate and the like, halogen-substituted phosphate triamide, and the like.
[0025]
Cyclic carbonate containing halogen The cyclic carbonate containing halogen contained in the non-aqueous solvent is preferably a compound represented by the following general formula (II).
[0026]
The halogen of the cyclic carbonate containing halogen is preferably fluorine, chlorine or bromine.
[0027]
[Chemical 6]

[0028]
In the formula, R ⁴ , R ⁵ , R ⁶ and R ⁷ may be the same or different from each other, and are a hydrogen atom, an alkyl group, a halogen atom, a halogenated alkyl group, or an ether group, a carbonyl group, an ester group, An alkyl group or a halogenated alkyl group containing a carbonic acid diester group, and at least one of R ^{4 to} R ⁷ is a halogen atom, a halogenated alkyl group, or an ether group, a carbonyl group, an ester group, a halogen containing a carbonic acid diester group Alkyl group.
[0029]
The alkyl group and the halogenated alkyl group (including the alkyl group portion of the halogenated alkyl group including an ether group, a carbonyl group, an ester group, and a carbonic acid diester group) preferably have 1 to 4 carbon atoms.
[0030]
As such a cyclic carbonate containing halogen, specifically,
Fluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,2-difluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 3-fluoro-1,2-propylene carbonate, 3,3-difluoro- 1,2-propylene carbonate, 3,3,3-trifluoro-1,2-propylene carbonate, 1,1,2,3,3,3-hexafluoro-1,2-propylene carbonate, 2-fluoro-1 , 3-propylene carbonate, 2,2-difluoro-1,3-propylene carbonate, etc., ethylene carbonate or a compound obtained by substituting hydrogen of propylene carbonate with fluorine,
A compound in which hydrogen of butylene carbonate or pentene carbonate is substituted with fluorine,
Examples include compounds in which the above compounds are substituted with chlorine or bromine instead of fluorine.
[0031]
Non-aqueous solvent The ratio of the above-mentioned halogen-containing cyclic carbonate and phosphate in a non-aqueous solvent is 20: 1 to 1:10, preferably 10: 1 to 1 by volume. A range of 1: 2 is desirable. When the volume ratio is within such a range, it has sufficient flame retardancy and high battery performance can be maintained.
[0032]
The ratio of the total amount of the non-aqueous solvent in the total amount of the halogenated cyclic carbonate and phosphate is 10 to 100% by volume, preferably 20 to 90% by volume. . Within such a range, it has sufficient flame retardancy and high battery performance can be maintained.
[0033]
In the non-aqueous electrolyte according to the present invention, other non-aqueous solvents may be contained as necessary in addition to the halogen-containing cyclic carbonate and phosphate.
As the non-aqueous solvent, a non-aqueous solvent having an appropriate solvating ability with lithium ions in order to dissolve the lithium salt, or a non-aqueous solvent that does not hinder the movement of the dissolved lithium ions is preferably used.
[0034]
As a non-aqueous solvent having an appropriate solvating ability with lithium ions, a non-aqueous solvent having a high dielectric constant is used. Specifically,
Cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate,
cyclic esters such as γ-butyrolactone,
Cyclic sulfones such as sulfolane,
Cyclic carbamates such as N-methyloxazolidinone,
Nonaqueous solvents having a cyclic polar group such as a cyclic amide such as N-methylpyrrolidone can be mentioned.
[0035]
As a non-aqueous solvent that does not hinder the movement of lithium ions, a non-aqueous solvent having a low viscosity is used. Specifically,
Chain carbonates such as dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, methyl propyl carbonate, methyl isopropyl carbonate,
Chain esters such as ethyl acetate and methyl propionate,
Ethers such as dimethoxyethane and tetrahydrofuran;
Chain amides such as N, N-dimethylacetamide,
Examples thereof include chain non-aqueous solvents such as chain carbamates such as methyl-N, N-dimethylcarbamate.
[0036]
The above non-aqueous solvents may be used alone, but it is preferable to use a combination of a non-aqueous solvent having a high dielectric constant and a non-aqueous solvent having a low viscosity, and in particular, a cyclic carbonate and a chain carbonate. It is more preferable to use a combination of esters. These solvents are contained in an amount of 10 to 90% by volume, preferably 30 to 70% by volume, based on the entire nonaqueous solvent in the electrolytic solution.
[0037]
Examples of the lithium salt dissolved in a lithium salt <br/> nonaqueous electrolytic solution, _{specifically, LiPF 6, LiBF 4, LiClO} 4, LiAsF 6, LiCF 3 SO 3, LiN (SO 2 CF 3) ₂ , LiAlCl ₃ , LiSiF _{6 and the} like. These lithium salts may be used alone or as a mixture of two or more lithium salts. Of these lithium salts, LiPF ₆ is preferable because it has high flame retardancy due to synergistic action with the phosphate ester. Such a lithium salt is usually contained in the non-aqueous electrolyte in an amount of 0.3 to 2 mol / liter, preferably 0.5 to 1.5 mol / liter.
[0038]
Non-aqueous electrolyte secondary battery The non-aqueous electrolyte secondary battery according to the present invention is:
A negative electrode including any one of metallic lithium, a lithium-containing alloy, a compound capable of doping / undoping lithium ions, and a carbon material capable of doping / undoping lithium ions as a negative electrode active material;
A positive electrode containing a composite oxide of lithium and a transition metal as a positive electrode active material;
It has the said nonaqueous electrolyte solution, It is characterized by the above-mentioned.
[0039]
Such a non-aqueous electrolyte secondary battery can be applied to, for example, a cylindrical non-aqueous electrolyte secondary battery. As shown in FIG. 1, the cylindrical non-aqueous electrolyte secondary battery includes a negative electrode 1 obtained by applying a negative electrode active material to a negative electrode current collector 9 and a positive electrode obtained by applying a positive electrode active material to a positive electrode current collector 10. 2 is wound through a separator 3 into which a non-aqueous electrolyte is injected, and is housed in a battery can 5 in a state where insulating plates 4 are placed above and below the wound body. A battery lid 7 is attached to the battery can 5 by caulking through a sealing gasket 6 and is electrically connected to the negative electrode 1 or the positive electrode 2 via a negative electrode lead 11 and a positive electrode lead 12, respectively. Is configured to function as The separator is a porous film.
[0040]
In this battery, the positive electrode lead 12 may be electrically connected to the battery lid 7 through the current interrupting thin plate 8. In such a battery, when the pressure inside the battery rises, the current interrupting thin plate 8 is pushed up and deformed, and the positive electrode lead 12 is cut leaving a portion welded to the thin plate 8 to interrupt the current. ing.
[0041]
As the negative electrode active material constituting such a negative electrode 1, any of metallic lithium, lithium alloy, a compound capable of doping / undoping lithium ions, and a carbon material capable of doping / dedoping lithium ions should be used. Can do. Among these, it is preferable to use a carbon material that can be doped / undoped with lithium ions. Such a carbon material may be graphite or amorphous carbon, and any carbon material such as activated carbon, carbon fiber, carbon black, and mesocarbon microbeads is used.
[0042]
As the positive electrode active material constituting the positive electrode 2, a composite oxide composed of lithium and a transition metal such as LiCoO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , LiNiO ₂ is used.
[0043]
The non-aqueous electrolyte secondary battery according to the present invention includes the non-aqueous electrolyte described above as the electrolyte, and the shape of the battery is not limited to that shown in FIG. 1, but is shown in FIG. Such a coin shape or a square shape may be used.
[0044]
【The invention's effect】
The non-aqueous electrolyte according to the present invention is flame retardant and has excellent charge / discharge performance, and a non-aqueous electrolyte secondary battery using such a non-aqueous electrolyte is safe, can generate a high voltage, Excellent discharge characteristics.
[0045]
【Example】
EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.
[0046]
[Example 1]
Preparation of non-aqueous electrolyte Lithium hexafluorophosphate (LiPF ₄ ) 152 g (1 mol), 3,3,3-trifluoropropylene carbonate (TFPC), trimethyl phosphate (TMPA), 1 liter of non-aqueous electrolyte was prepared by dissolving in a mixed solvent (volume ratio TFPC: TMPA: MEC = 4: 2: 4) with methyl ethyl carbonate (MEC) (electrolyte concentration 1.0 mol / liter).
Evaluation of flammability of non-aqueous electrolyte In a beaker containing the non-aqueous electrolyte, a Manila paper for a separator having a thickness of 0.04 mm cut into strips having a length of 15 mm and a length of 320 mm is immersed for 1 minute or longer. did. Excess non-aqueous electrolyte dripping from the Manila paper was wiped with a beaker wall, and the Manila paper was fixed horizontally by piercing the support needles of the sample stage having support needles at intervals of 25 mm. The sample table on which the Manila paper was fixed was placed in a metal box of 25 cm × 25 cm × 50 cm, one end was ignited with a lighter, and the burned length of the separator paper was measured.
[0047]
The results are shown in Table 1.
[0048]
[Example 2]
Example 1 was the same as Example 1 except that chloroethylene carbonate (ClEC) was used instead of 3,3,3-trifluoropropylene carbonate (TFPC).
[0049]
The results are shown in Table 1.
[0050]
[Comparative Example 1]
Example 1 was the same as Example 1 except that ethylene carbonate (EC) was used instead of 3,3,3-trifluoropropylene carbonate (TFPC).
[0051]
The results are shown in Table 1.
[0052]
[Comparative Example 2]
In Example 1, it was carried out similarly to Example 1 except having used ethylene carbonate (EC) instead of 3,3,3-trifluoropropylene carbonate (TFPC) and not using trimethyl phosphate (TMPA).
[0053]
The results are shown in Table 1.
[0054]
[Table 1]

[0055]
[Example 3]
Preparation of battery 4.75 g of artificial graphite (plane spacing 0.337 nm, Lc 40 nm, La 60 nm) powder was added to 5 ml of an N-methylpyrrolidone solution in which 0.25 g of polyvinylidene fluoride was dissolved, and the resulting mixture was mixed well. I made it. This paste was applied onto a copper foil, dried, and then punched into a coin (diameter 10 mm). A coin punched out was pressed at 200 kg / cm ² and vacuum dried at 150 ° C. to prepare a carbon electrode.
[0056]
Using this carbon electrode, as shown in FIG. 2, metallic lithium is opposed to the negative electrode 13, and the carbon electrode is opposed to the positive electrode 14 via the separator 15 (Celguard 3501). 1 mol / liter of LiPF ₄ in a mixed solvent of 3-trifluoropropylene carbonate (TFPC), trimethyl phosphate (TMPA) and methyl ethyl carbonate (MEC) (volume ratio TFPC: TMPA: MEC = 4: 2: 4) A CR2030 coin battery was prepared by adding 0.04 ml of the non-aqueous electrolyte dissolved at a concentration.
Charging / discharging characteristics Using the above coin battery, a cycle of discharging to 0 V and charging to 1.5 V at a constant current of 0.125 mA was performed. The irreversible capacity per graphite electrode weight at the first cycle and the discharge capacity per graphite electrode weight at the fourth cycle were measured.
[0057]
The results are shown in Table 2.
[0058]
[Example 4]
In Example 3, a mixed solvent of 3,3,3-trifluoropropylene carbonate (TFPC), trimethyl phosphate (TMPA), methyl ethyl carbonate (MEC), and ethylene carbonate (EC) was used as the mixed solvent of the nonaqueous electrolytic solution. A coin battery was produced in the same manner as in Example 3 except that (volume ratio TFPC: TMPA: MEC: EC = 3: 2: 4: 1) was used, and charge / discharge characteristics were measured.
[0059]
The results are shown in Table 2.
[0060]
[Example 5]
In Example 3, a mixed solvent of 3,3,3-trifluoropropylene carbonate (TFPC), trimethyl phosphate (TMPA), methyl ethyl carbonate (MEC), and ethylene carbonate (EC) was used as the mixed solvent of the nonaqueous electrolytic solution. A coin battery was produced in the same manner as in Example 3 except that (volume ratio TFPC: TMPA: MEC: EC = 2: 2: 4: 2) was used, and charge / discharge characteristics were measured.
[0061]
The results are shown in Table 2.
[0062]
[Example 6]
In Example 3, a mixed solvent of 3,3,3-trifluoropropylene carbonate (TFPC), trimethyl phosphate (TMPA), methyl ethyl carbonate (MEC), and ethylene carbonate (EC) was used as the mixed solvent of the nonaqueous electrolytic solution. A coin battery was produced in the same manner as in Example 3 except that (volume ratio TFPC: TMPA: MEC: EC = 1: 3: 4: 2) was used, and charge / discharge characteristics were measured.
[0063]
The results are shown in Table 2.
[0064]
[Example 7]
In Example 3, a mixed solvent of chloroethylene carbonate (ClEC), trimethyl phosphate (TMPA) and methyl ethyl carbonate (MEC) shown in Example 2 (volume ratio ClEC: TMPA: A coin battery was produced in the same manner as in Example 3 except that MEC = 4: 2: 4) was used, and charge / discharge characteristics were measured.
[0065]
The results are shown in Table 2.
[0066]
[Comparative Example 3]
In Example 3, the mixed solvent of trimethyl phosphate (TMPA), methyl ethyl carbonate (MEC), and ethylene carbonate (EC) shown in Comparative Example 1 (volume ratio TMPA: MEC: EC) was used as the mixed solvent of the nonaqueous electrolytic solution. = 2: 4: 4) A coin battery was produced in the same manner as in Example 3 except that the charge / discharge characteristics were measured.
[0067]
The results are shown in Table 2.
[0068]
[Comparative Example 4]
In Example 3, the mixed solvent of methyl ethyl carbonate (MEC) and ethylene carbonate (EC) shown in Comparative Example 2 (volume ratio MEC: EC = 1: 1) was used as the mixed solvent of the nonaqueous electrolytic solution. Produced a coin battery in the same manner as in Example 3 and measured the charge / discharge characteristics.
[0069]
The results are shown in Table 2.
[0070]
[Table 2]

[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view showing one embodiment of a non-aqueous electrolyte secondary battery of the present invention.
FIG. 2 is a schematic cross-sectional view of a coin-type battery used in Examples 3 to 6 and Comparative Examples 3 and 4 of the present invention.
[Explanation of symbols]
1, 13 ... Negative electrode 2, 14 ... Positive electrode 3, 15 ... Separator 4 ... Insulating plate 5 ... Battery can 6 ... Sealing gasket 7 ... Battery lid 8 ... Thin plate 9 for current interruption ... Negative electrode current collector 10 ... Positive electrode current collector 11 ... Negative electrode lead 12 ... Positive electrode lead 16 ... Sealing plate 17 ··· Case 18 ··· Gasket

Claims (6)

A lithium salt is dissolved in a non-aqueous solvent containing a phosphate ester compound, a cyclic carbonate containing a halogen, and a chain carbonate ,
The phosphate ester compound is a compound represented by the following general formula (I):

(R ¹ , R ² and R ³ may be the same or different, and may be an alkyl group, an aryl group,
A rualkylamide group, a polyalkylene oxide group having an alkyl group at its end, and a group obtained by halogen-substituting them are shown. )
The cyclic carbonate containing a halogen is selected from the compounds represented by the general formula ( II )

(R ⁴ , R ⁵ , R ⁶ and R ⁷ may be the same as or different from each other, and may be a hydrogen atom, alkyl group, halogen atom, halogenated alkyl group, or ether group, carbonyl group, ester group, carbonic acid group. An alkyl group or a halogenated alkyl group containing a diester group, wherein at least one of R ^{4 to} R ⁷ is a halogen atom, a halogenated alkyl group, or an ether group, a carbonyl group, an ester group, or a carbonic acid diester group. Represents an alkyl group.)
A non-aqueous electrolyte characterized by that.   The nonaqueous electrolytic solution according to claim 1, wherein the halogen atom of the cyclic carbonate containing halogen is fluorine, chlorine, or bromine.   Cyclic carbonate is fluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,2-difluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 3-fluoro-1,2-propylene carbonate, 3 , 3-Difluoro-1,2-propylene carbonate, 1,1,2,3,3,3-hexafluoro-1,2-propylene carbonate, 2-fluoro-1,3-propylene carbonate, 2,2-difluoro The nonaqueous electrolytic solution according to claim 2, which is a compound in which hydrogen of 1,3-propylene carbonate, butylene carbonate, or pentene carbonate is substituted with fluorine.   The non-aqueous electrolyte according to any one of claims 1 to 3, wherein a mixing ratio of the halogenated cyclic carbonate and phosphate is in a range of 10: 1 to 1: 1 by volume ratio.   The nonaqueous electrolytic solution according to claim 1, wherein the amount of the halogen-containing carbonate ester and phosphate ester is in the range of 10 to 100% by volume with respect to the entire solvent.   A negative electrode including any one of metallic lithium, a lithium-containing alloy, and a carbon material capable of doping and dedoping lithium ions as a negative electrode active material, a positive electrode including a composite oxide of lithium and a transition metal as a positive electrode active material, and an electrolytic solution A non-aqueous electrolyte secondary battery comprising: the non-aqueous electrolyte solution according to claim 1.

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