JP4081569B2 - Voltage control method for non-aqueous electrolyte secondary battery - Google Patents

Description

（但し、式中、Ｒ⁶〜Ｒ⁸は、水素原子、またはメチル基、エチル基、ｎ−プロピル基、ｉ−プロピル基、ｎ−ブチル基、ｉ−ブチル基、ｓ−ブチル基、ｔ−ブチル基等の炭素数１〜６、特に１〜４のアルキル基を示し、Ｘ≧１かつＹ≧０の条件を満足するものか、またはＸ≧０かつＹ≧１の条件を満足するものであり、好ましくはＲ⁶〜Ｒ⁸は、メチル基、エチル基、ｎ−プロピル基、ｉ−プロピル基、ｎ−ブチル基、ｉ−ブチル基、ｓ−ブチル基、ｔ−ブチル基である。）
【００４７】
【化２】

（但し、式中、Ｒ⁹〜Ｒ¹¹は、水素原子、またはメチル基、エチル基、ｎ−プロピル基、ｉ−プロピル基、ｎ−ブチル基、ｉ−ブチル基、ｓ−ブチル基、ｔ−ブチル基等の炭素数１〜６、特に１〜４のアルキル基を示し、Ａ≧１かつＢ≧０の条件を満足するものか、またはＡ≧０かつＢ≧１の条件を満足するものであり、好ましくはＲ⁹〜Ｒ¹¹は、メチル基、エチル基、ｎ−プロピル基、ｉ−プロピル基、ｎ−ブチル基、ｉ−ブチル基、ｓ−ブチル基、ｔ−ブチル基である。）
【００４８】
上記式（３）において、例えば、Ｘ＝９、Ｙ＝０、Ｒ⁶＝Ｒ⁸＝ＣＨ₃が好ましく用いられる。一方。上記式（４）において、例えばＡ＝２または９、Ｂ＝０、Ｒ⁹＝Ｒ¹¹＝ＣＨ₃が好ましく用いられる。
また、トリエステル化合物としては、トリメチロールプロパントリメタクリレートが好適である。
【００４９】
上記ポリオキシアルキレン成分を含有するジエステル化合物とポリオキシアルキレン成分を含有するモノエステル化合物は、イオン導電性塩と有機溶媒との混合物中で紫外線、電子線、Ｘ線、γ線、マイクロ波、高周波などを照射することにより、または混合物を加熱することにより、ポリマー三次元架橋ネットワーク構造を形成する。
この場合、一般にはポリオキシアルキレン成分を含有するジエステル化合物は、これ単独で重合を行い、ポリマー三次元架橋ネットワークを形成することができるが、上述したように、このポリオキシアルキレン成分を含有するジエステル化合物に、さらに一官能性モノマーであるポリオキシアルキレン成分を含有するモノエステル化合物を添加することによって、三次元網目上にポリオキシアルキレン分岐鎖を導入することができる。
【００５０】
ここで、ポリオキシアルキレン成分を含有するジエステル化合物およびモノエステル化合物と、トリエステル化合物との組成比は、ポリオキシアルキレン成分の長さによって適宜設定されるものであり、特に限定されるものではないが、モル比で、
〔ジエステル化合物／モノエステル化合物〕＝０．１〜２、特に０．３〜１．５
〔ジエステル化合物／トリエステル化合物〕＝２〜１５、特に３〜１０
の範囲内がゲル強度向上という点から見て好ましい。
【００５１】
上記反応性二重結合を有する化合物に、直鎖または分岐線状高分子化合物を添加してＳｅｍｉ−ＩＰＮ構造を形成させることもできる。
この場合、必要な直鎖または分岐線状高分子化合物としては、線状高分子化合物であれば、特に限定されるものではないが、例えば、（ａ）ヒドロキシアルキル多糖誘導体、（ｂ）オキシアルキレン分岐型ポリビニルアルコール誘導体、（ｃ）ポリグリシドール誘導体、（ｄ）シアノ基置換一価炭化水素基含有ポリビニルアルコール誘導体、等が挙げられる。
【００５２】
上記（ａ）ヒドロキシアルキル多糖類誘導体としては、▲１▼セルロース、デンプン、プルランなどの天然に産出される多糖類にエチレンオキシドを反応させることによって得られるヒドロキシエチル多糖類、▲２▼上記多糖類にプロピレンオキシドを反応させることによって得られるヒドロキシプロピル多糖類、▲３▼上記多糖類にグリシドールまたは３−クロロ−１，２−プロパンジオールを反応させることによって得られるジヒドロキシプロピル多糖類等が挙げられ、これらヒドロキシアルキル多糖類の水酸基の一部または全てがエステル結合もしくはエーテル結合を介した置換基で封鎖されたものである。
なお、上記ヒドロキシアルキル多糖類は、モル置換度が２〜３０、好ましくは２〜２０のものである。モル置換度が２より小さい場合、イオン導電性塩類を溶解する能力が低すぎて使用に適さない。
【００５３】
上記（ｂ）オキシアルキレン分岐型のポリビニルアルコール誘導体としては、分子中に下記一般式（５）で示されるポリビニルアルコール単位を有する平均重合度２０以上の高分子化合物における上記ポリビニルアルコール単位中の水酸基の一部または全部が、平均モル置換度０．３以上のオキシアルキレン含有基で置換されてなる高分子化合物を好適に用いることができる。
【００５４】
【化３】

（式中、ｎは２０〜１０，０００であることが好ましい。）
【００５５】
すなわち、上記高分子化合物は、オキシアルキレン分率が高いために、多くのイオン導電性塩を溶解できる能力を有するとともに、分子中にイオンが移動するオキシアルキレン部分が多くなるので、イオンが移動し易くなる。その結果、高いイオン導電性を発現できる。また、上記高分子化合物は高い粘着性を備えているから、バインダー成分としての役割および正負極を強固に接着する機能を十分発揮でき、該高分子化合物からなる高分子電解質用ポリマーにイオン導電性塩を高濃度に溶解させた組成物を、フィルム電池等の高分子ゲル電解質として好適に用いることができる。
【００５６】
このような高分子化合物としては、▲１▼ポリビニルアルコール単位を有する高分子化合物と、エチレンオキシド、プロピレンオキシド、グリシドール等のオキシラン化合物とを反応させて得られる高分子化合物（ジヒドロキシプロピル化ポリエチレンビニルアルコール、プロピレンオキシド化ポリビニルアルコール等）、
▲２▼ポリビニルアルコール単位を有する高分子化合物と、水酸基に対して反応性を有する置換基を末端に有するポリオキシアルキレン化合物とを反応させて得られる高分子化合物が挙げられる。
なお、ポリビニルアルコール単位を有する高分子化合物とオキシラン化合物、またはオキシアルキレン化合物との反応は、水酸化ナトリウム、水酸化カリウム、種々のアミン化合物などの塩基性触媒を用いて行うことができる。
【００５７】
ここで、ポリビニルアルコール単位を有する高分子化合物は、分子中にポリビニルアルコール単位を有する数平均重合度２０以上、好ましくは３０以上、さらに好ましくは５０以上の高分子化合物において、上記ポリビニルアルコール単位中の水酸基の一部または全部がオキシアルキレン含有基によって置換されたものである。この場合、数平均重合度の上限は、取り扱い性等を考慮すると、２，０００以下、より好ましくは５００以下、特に２００以下であることが好ましい。
【００５８】
上記ポリビニルアルコール単位を有する高分子化合物は、上記数平均重合度範囲を満たし、かつ、分子中のポリビニルアルコール単位の分率が９８モル％以上のホモポリマーが最適であるが、これに限定されるものではなく、上記数平均重合度範囲を満たし、かつ、ポリビニルアルコール分率が好ましくは６０モル％以上、より好ましくは７０モル％以上のポリビニルアルコール単位を有する高分子化合物、例えば、ポリビニルアルコールの水酸基の一部がホルマール化されたポリビニルホルマール、ポリビニルアルコールの水酸基の一部がアルキル化された変性ポリビニルアルコール、ポリ（エチレンビニルアルコール）、部分ケン化ポリ酢酸ビニル、その他の変性ポリビニルアルコール等を用いることができる。
【００５９】
この高分子化合物は、上記ポリビニルアルコール単位中の水酸基の一部または全部が平均モル置換度０．３以上のオキシアルキレン含有基（なお、このオキシアルキレン基は、その水素原子の一部が水酸基によって置換されていてもよい）で置換されているものであり、好ましくは３０モル％以上、より好ましくは５０モル％以上置換されているものである。ここで、平均のモル置換度（ＭＳ）は、仕込み質量と反応生成物の質量を正確に測定することで算出できる。
【００６０】
上記（ｃ）ポリグリシドール誘導体は、下記式（６）で示される単位（以下、Ａ単位という）と、下記式（７）で示される単位（以下、Ｂ単位という）とを有し、分子鎖の各末端が分子鎖の末端が所定の置換基により封鎖されたものである。
【００６１】
【化４】

【００６２】
ここで、上記ポリグリシドールは、グリシドールまたは３−クロロ−１，２−プロパンジオールを重合させることにより得ることができるが、一般的には、グリシドールを原料とし、塩基性触媒またはルイス酸触媒を用いて重合を行うことが好ましい。
【００６３】
上記ポリグリシドールは、分子中にＡ，Ｂ二つの単位を両者合わせて２個以上、好ましくは６個以上、より好ましくは１０個以上有するものである。この場合、上限は特に制限されないが、通常１０，０００個以下程度である。これら各単位の合計数は、必要とするポリグリシドールの流動性および粘性等を考慮して適宜設定すればよい。また、分子中のＡ単位とＢ単位との比率は、モル比でＡ：Ｂ＝１／９〜９／１、好ましくは３／７〜７／３である。なお、Ａ，Ｂ単位の出現には規則性はなく、任意の組み合わせが可能である。
【００６４】
さらに、上記ポリグリシドールにおけるゲル濾過クロマトグラフィー（ＧＰＣ）を用いたポリエチレングリコール換算の重量平均分子量（Ｍｗ）が好ましくは２００〜７３０，０００、より好ましくは２００〜１００，０００、さらに好ましくは６００〜２０，０００のものである。また、平均分子量比（Ｍｗ／Ｍｎ）が１．１〜２０、より好ましくは１．１〜１０である。
【００６５】
これら上記線状高分子化合物（ａ）〜（ｃ）は、分子中の水酸基の一部または全部、好ましくは１０モル％以上をハロゲン原子、炭素数１〜１０の非置換または置換一価炭化水素基、Ｒ¹²ＣＯ−基（Ｒ¹²は炭素数１〜１０の非置換または置換一価炭化水素基）、Ｒ¹² ₃Ｓｉ−基（Ｒ¹²は上記と同じ）、アミノ基、アルキルアミノ基およびリン原子を有する基から選ばれる１種または２種以上の一価の置換基により封鎖し、水酸基封鎖ポリマー誘導体を得ることができる。
【００６６】
ここで、炭素数１〜１０の非置換または置換の一価炭化水素基としては、例えば、メチル基、エチル基、プロピル基、イソプロピル基、ｔ−ブチル基、ペンチル基等のアルキル基、フェニル基、トリル基等のアリール基、ベンジル基等のアラルキル基、ビニル基等のアルケニル基、これらの基の水素原子の一部または全部をハロゲン原子、シアノ基、水酸基、アミノ基等で置換したもの等が挙げられ、これらの１種を単独でまたは２種以上を組み合わせて用いることができる。
【００６７】
この場合、上記置換基によるオキシアルキレン鎖を持つ線状高分子化合物（ａ）〜（ｃ）の水酸基の封鎖には、▲１▼高濃度にイオン導電性塩を含むポリマーにおいて、低誘電率の高分子マトリックス中では解離したカチオンと対アニオンとの再結合が生じやすく、導電性の低下が生じるが、高分子マトリックスの極性を上げるとイオンの会合が起こりにくくなるので、オキシアルキレン基を持つ線状高分子化合物（ａ）〜（ｃ）の水酸基に極性基を導入することにより、マトリックス高分子の誘電率を上げる目的と、▲２▼線状高分子化合物（ａ）〜（ｃ）に疎水性、難燃性などの優れた特性を付与する目的とがある。
【００６８】
ここで、▲１▼線状高分子化合物（ａ）〜（ｃ）の誘電率を上げるためには、オキシアルキレン鎖を持つ線状高分子化合物（ａ）〜（ｃ）と、水酸基に対する反応性を有する化合物とを反応させることにより、この線状高分子化合物の水酸基の高極性の置換基で封鎖する。
このような高極性の置換基としては、特に制限されるものではないが、イオン性の置換基より中性の置換基の方が好ましく、例えば、炭素数１〜１０の非置換または置換一価炭化水素基、Ｒ¹²ＣＯ−基（Ｒ¹²は上記と同じ）等が挙げられる。また、必要に応じてアミノ基、アルキルアミノ基などで封鎖することもできる。
【００６９】
一方、▲２▼線状高分子化合物（ａ）〜（ｃ）に疎水性、難燃性を付与する場合には、上記線状高分子化合物の水酸基をハロゲン原子、Ｒ¹² ₃Ｓｉ−基（Ｒ¹²は上記と同じ）、リン原子を有する基などで封鎖する。
ここで、上記置換基について具体的に説明すると、ハロゲン原子としてはフッ素、臭素、塩素等が挙げられ、炭素数１〜１０（好ましくは１〜８）の非置換または置換一価炭化水素基としては上記と同様のものを例示することができる。
【００７０】
Ｒ¹² ₃Ｓｉ−基としては、Ｒ¹²が炭素数１〜１０（好ましくは１〜６）の上記と同様の非置換または置換一価炭化水素基であるものが挙げられ、好ましくはＲ¹²はアルキル基であり、トリアルキルシリル基、中でもトリメチルシリル基が好ましい。また、上記置換基は、アミノ基、アルキルアミノ基、リン原子を有する基などであってもよい。
ここで、上記置換基による末端封鎖率は１０モル％以上であることが好ましく、より好ましくは５０モル％以上、さらに好ましくは９０モル％以上であり、実質的に全ての末端を上記置換基にて封鎖する（封鎖率約１００モル％）こともできる。
【００７１】
なお、ポリマー分子鎖の総ての末端水酸基をハロゲン原子、Ｒ¹² ₃Ｓｉ−基、リン原子を有する基で封鎖すると、ポリマー自体のイオン導電性塩溶解能力が低下する場合があるので、溶解性の程度を考慮しつつ、適当量の置換基を導入する必要がある。具体的には全末端（水酸基）に対して１０〜９５モル％、好ましくは５０〜９５モル％、さらに好ましくは５０〜９０モル％である。
本発明においては、上記置換基の中でも、特にシアノ基置換一価炭化水素基が好ましく、具体的にはシアノエチル基、シアノベンジル基、シアノベンゾイル基、その他のアルキル基にシアノ基が結合した置換基などが挙げられる。
【００７２】
上記（ｄ）シアノ基置換一価炭化水素基置換ポリビニルアルコール誘導体として、上述の一般式（５）で示される分子中にポリビニルアルコール単位を有する平均重合度２０以上の高分子化合物における上記ポリビニルアルコール単位中の水酸基の一部または全部が、シアノ基置換一価炭化水素基で置換された高分子化合物も好適に用いることができる。
すなわち、当該高分子化合物は、側鎖が比較的短いものであるため、電解質用組成物の粘度を低く抑えることができ、該組成物の電池構造体等への浸透を速やかに行え、電池等の生産性向上および性能向上を図ることができる。
【００７３】
このような高分子化合物としては、シアノエチル基、シアノベンジル基、シアノベンゾイル基等で水酸基の一部または全部が置換されたポリビニルアルコールが挙げられ、側鎖が短いという点を考慮すると、特にシアノエチルポリビニルアルコールが好適である。
なお、ポリビニルアルコールの水酸基をシアノ基置換一価炭化水素基で置換する手法としては、公知の種々の方法を採用できる。
【００７４】
上記分子中に反応性二重結合を２つ以上有する化合物の配合量は、電解質用組成物全体に対して１重量％以上、好ましくは５〜４０重量％である。分子中に反応性二重結合を２つ以上有する化合物が少なすぎると膜強度が上がらなくなる場合がある。一方、多すぎると電解質用組成物中のイオン導電性金属塩溶解能力が低下し、塩が析出したり、強度が低下し、脆くなる等の不都合が生じる場合がある。
【００７５】
上述した電解質用組成物をゲル化させて高分子ゲル電解質を得る方法としては、特に限定されるものではなく、例えば、以下に示したものが挙げられる。
すなわち、上記電解質溶液、分子中に反応性二重結合を２個以上有する化合物に、紫外線、電子線、Ｘ線、γ線、マイクロ波、高周波などを照射することにより、または加熱することにより、三次元網目構造を形成し、電解質溶液を含んだ高分子ゲル電解質を得ることができる。
また、上記電解質溶液、分子中に反応性二重結合を有する化合物、線状高分子化合物を配合してなる組成物に、上記と同様に紫外線等の照射、加熱等を行うことで、分子中に反応性二重結合を２個以上有する化合物を反応または重合させて生成した三次元網目構造と、線状高分子化合物の分子鎖とが相互に絡み合った三次元架橋ネットワーク（ｓｅｍｉ−ＩＰＮ）構造を有する高分子ゲル電解質を得ることができる。
【００７６】
上記重合反応としては、ラジカル重合反応を行うことが好適であり、重合反応を行う場合は、通常、重合開始剤を添加する。
このような重合開始剤（触媒）としては、特に限定はなく、以下に示すような公知の種々の重合開始剤を用いることができる。
【００７７】
例えば、アセトフェノン，トリクロロアセトフェノン，２−ヒドロキシ−２−メチルプロピオフェノン，２−ヒドロキシ−２−メチルイソプロピオフェノン，１−ヒドロキシシクロヘキシルケトン，ベンゾインエーテル，２，２−ジエトキシアセトフェノン，ベンジルジメチルケタール等の光重合開始剤、クメンヒドロペルオキシド，ｔ−ブチルヒドロペルオキシド，ジクミルペルオキシド，ジ−ｔ−ブチルペルオキシド等の高温熱重合開始剤、過酸化ベンゾイル，過酸化ラウロイル，過硫酸塩，２，２′−アゾビス（２，４−ジメチルバレロニトリル），２，２′−アゾビス（４−メトキシ−２，４−ジメチルバレロニトリル），２，２′−アゾビスイソブチロニトリル等の熱重合開始剤、過酸化水素・第１鉄塩，過硫酸塩・酸性亜硫酸ナトリウム，クメンヒドロペルオキシド・第１鉄塩，過酸化ベンゾイル・ジメチルアニリン等の低温熱重合開始剤（レドックス開始剤）、過酸化物・有機金属アルキル、トリエチルホウ素、ジエチル亜鉛、酸素・有機金属アルキル等を用いることができる。
【００７８】
これらの重合開始剤の１種を単独でまたは２種以上を混合して用いることができ、その添加量は、電解質用組成物１００重量部に対して０．１〜１重量部、好ましくは０．１〜０．５重量部の範囲である。触媒の添加量が０．１重量部未満では重合速度が著しく低下する場合がある。一方、１重量部を超えても反応性に影響はなく、試薬の無駄となるだけである。
【００７９】
上記高分子ゲル電解質は、分子内に反応性二重結合を２個以上有する化合物を反応させた三次元網目構造を有するものであり、優れた強度を有し、形状保持能力の高いものである。さらに、線状高分子化合物を用い、三次元網目構造中に高分子化合物が絡みついた強固な半相互侵入高分子網目構造を形成した場合には、異種高分子鎖間の相溶性を向上することができるとともに、相間結合力を高めることができ、結果として、形状保持能力を飛躍的に向上させることができる。
【００８０】
しかも、半相互侵入高分子網目構造を有する場合、分子構造はアモルファスであり、結晶化していないため、分子内をイオン導電体がスムーズに移動することができ、室温で１０^-3〜１０^-4Ｓ／ｃｍ程度の高導電性および高粘着性を有する上に、蒸発、液漏れの心配がなく、リチウムイオン二次電池等をはじめとする各種二次電池の高分子ゲル電解質として好適に使用することができるものである。
【００８１】
なお、高分子ゲル電解質を薄膜化する方法としては、例えば、アプリケータロールなどのローラコーティング、スクリーンコーティング、ドクターブレード法、スピンコーティング、バーコーダーなどの手段を用いて、均一な厚みの電解質膜に形成することができる。
【００８２】
上記非水電解質二次電池の正極としては、正極集電体の表裏両面または片面に、バインダーポリマーと正極活物質とを主成分として含む正極用バインダー組成物を塗布してなるものを用いることができる。
なお、バインダーポリマーと正極活物質とを主成分として含む正極用バインダー組成物を溶融混練した後、押出し、フィルム成形することにより正極を形成することもできる。
【００８３】
上記バインダーポリマーとしては、当該用途に使用できるポリマーであれば特に限定はないが、例えば、（Ｉ）下記式から求めた膨潤率が１５０〜８００重量％の範囲である熱可塑性樹脂、（ＩＩ）フッ素系高分子材料等を一種単独で、または（Ｉ），（ＩＩ）の二種以上を組み合わせて用いることが好ましい。
また、上記（Ｉ）の熱可塑性樹脂は、下記式から求めた膨潤率が１５０〜８００重量％の範囲であり、より好ましくは２５０〜５００重量％、さらに好ましくは２５０〜４００重量％である。
【００８４】
【数１】

【００８５】
このような熱可塑性樹脂としては、（Ｄ）ポリオール化合物と、（Ｅ）ポリイソシアネート化合物と、必要に応じて（Ｆ）鎖伸長剤とを反応させてなる熱可塑性ポリウレタン系樹脂を用いることが好ましい。
なお、熱可塑性ポリウレタン系樹脂には、ウレタン結合を有するポリウレタン樹脂以外にも、ウレタン結合とウレア結合とを有するポリウレタンウレア樹脂も含まれる。
【００８６】
（Ｄ）成分のポリオール化合物としては、ポリエステルポリオール，ポリエステルポリエーテルポリオール，ポリエステルポリカーボネートポリオール，ポリカプロラクトンポリオール、またはこれらの混合物を用いることが好ましい。
このような（Ｄ）成分のポリオール化合物の数平均分子量は１，０００〜５，０００であることが好ましく、より好ましくは１，５００〜３，０００である。ポリオール化合物の数平均分子量が小さすぎると、得られる熱可塑性ポリウレタン系樹脂フィルムの耐熱性、引張り伸び率などの物理特性が低下する場合がある。一方、大きすぎると、合成時の粘度が上昇し、得られる熱可塑性ポリウレタン系樹脂の製造安定性が低下する場合がある。なお、ここでいうポリオール化合物の数平均分子量は、いずれもＪＩＳ Ｋ１５７７に準拠して測定した水酸基価に基づいて算出した数平均分子量を意味する。
【００８７】
（Ｅ）成分のポリイソシアネート化合物としては、例えば、トリレンジイソシアネート，４，４′−ジフェニルメタンジイソシアネート，ｐ−フェニレンジイソシアネート，１，５−ナフチレンジイソシアネート，キシリレンジイソシアネート等の芳香族ジイソシアネート類、ヘキサメチレンジイソシアネート，イソホロンジイソシアネート，４，４′−ジシクロヘキシルメタンジイソシアネート，水添化キシリレンジイソシアネート等の脂肪族または脂環式ジイソシアネート類等が挙げられる。
【００８８】
（Ｆ）成分の鎖伸長剤としては、イソシアネート基および反応性の活性水素原子を分子中に２個有し、かつ分子量が３００以下である低分子量化合物を用いることが好ましい。
このような低分子量化合物としては、公知の種々の化合物を使用でき、例えば、エチレングリコール，プロピレングリコール，１，３−プロパンジオール等の脂肪族ジオール、１，４−ビス（β−ヒドロキシエトキシ）ベンゼン，１，４−シクロヘキサンジオール，ビス（β−ヒドロキシエチル）テレフタレート等の芳香族ジオールまたは脂環式ジオール、ヒドラジン，エチレンジアミン，ヘキサメチレンジアミン，キシリレンジアミン等のジアミン、アジピン酸ヒドラジド等のアミノアルコール等が挙げられ、これらの１種を単独でまたは２種以上を組合わせて用いることができる。
【００８９】
なお、上記熱可塑性ポリウレタン系樹脂においては、（Ｄ）成分のポリオール化合物１００重量部に対して（Ｅ）成分のポリイソシアネート化合物を５〜２００重量部、好ましくは２０〜１００重量部添加し、（Ｆ）成分の鎖伸長剤を１〜２００重量部、好ましくは５〜１００重量部添加する。
【００９０】
また、上記（Ｉ）のバインダーポリマーとしては、下記一般式（８）で表わされる単位を含む熱可塑性樹脂を用いることもできる。
【００９１】
【化５】

（式中、ｒは３〜５、ｓは５以上の整数を示す。）
【００９２】
次に、上記（ＩＩ）のバインダーポリマーであるフッ素系高分子材料としては、例えば、ポリフッ化ビニリデン（ＰＶＤＦ）、フッ化ビニリデンとヘキサフルオロプロピレンとの共重合体〔Ｐ（ＶＤＦ−ＨＦＰ）〕、フッ化ビニリデンと塩化３フッ化エチレンとの共重合体〔Ｐ（ＶＤＦ−ＣＴＦＥ）〕等が好ましく用いられる。これらの内でも、フッ化ビニリデンが５０重量％以上、特に７０重量％以上（上限値は９７重量％程度である）であるものが好適である。
この場合、フッ素系ポリマーの重量平均分子量は、特に限定はないが、５００，０００〜２，０００，０００が好ましく、より好ましくは５００，０００〜１，５００，０００である。重量平均分子量が小さすぎると物理的強度が著しく低下する場合がある。
【００９３】
上記正極集電体としては、ステンレス鋼、アルミニウム、チタン、タンタル、ニッケル等を用いることができる。これらの中でも、アルミニウム箔または酸化アルミニウム箔が性能と価格との両面から見て好ましい。この正極集電体は、箔状、エキスパンドメタル状、板状、発泡状、ウール状、ネット状等の三次元構造などの種々の形態のものを採用することができる。
【００９４】
上記正極活物質は、電池の種類などに応じて適宜選定されるが、リチウム二次電池の正極とする場合には、例えば、ＣｕＯ，Ｃｕ₂Ｏ，Ａｇ₂Ｏ，ＣｕＳ，ＣｕＳＯ₂等のＩ族金属化合物、ＴｉＳ，ＳｉＯ₂，ＳｎＯ等のＩＶ族金属化合物、Ｖ₂Ｏ₅，Ｖ₆Ｏ₁₃，ＶＯ_x，Ｎｂ₂Ｏ₅，Ｂｉ₂Ｏ₃，Ｓｂ₂Ｏ₃等のＶ族金属化合物、ＣｒＯ₃，Ｃｒ₂Ｏ₃，ＭｏＯ₃，ＭｏＳ₂，ＷＯ₃，ＳｅＯ₂等のＶＩ族金属化合物、ＭｎＯ₂，Ｍｎ₂Ｏ₄等のＶＩＩ族金属化合物、Ｆｅ₂Ｏ₃，ＦｅＯ，Ｆｅ₃Ｏ₄，Ｎｉ₂Ｏ₃，ＮｉＯ，ＣｏＯ₂等のＶＩＩＩ族金属化合物、ポリピロール，ポリアニリン，ポリパラフェニレン，ポリアセチレン，ポリアセン系材料等の導電性高分子化合物などが挙げられる。
【００９５】
また、リチウムイオン二次電池の場合には、リチウムイオンを吸着離脱可能なカルコゲン化合物、またはリチウムイオン含有カルコゲン化合物（リチウム含有複合酸化物）等が用いられる。
ここで、リチウムイオンを吸着離脱可能なカルコゲン化合物としては、例えば、ＦｅＳ₂、ＴｉＳ₂、ＭｏＳ₂、Ｖ₂Ｏ₅、Ｖ₆Ｏ₁₃、ＭｎＯ₂等が挙げられる。
一方、リチウムイオン含有カルコゲン化合物（リチウム含有複合酸化物）としては、例えば、ＬｉＣｏＯ₂、ＬｉＭｎＯ₂、ＬｉＭｎ₂Ｏ₄、ＬｉＭｏ₂Ｏ₄、ＬｉＶ₃Ｏ₈、ＬｉＮｉＯ₂、Ｌｉ_xＮｉ_yＭ_1-yＯ₂（但し、Ｍは、Ｃｏ，Ｍｎ，Ｔｉ，Ｃｒ，Ｖ，Ａｌ，Ｓｎ，Ｐｂ，Ｚｎから選ばれる少なくとも１種以上の金属元素を表し、０．０５≦ｘ≦１．１０、０．５≦ｙ≦１．０）等が挙げられる。
【００９６】
なお、正極用バインダー組成物には、上述のバインダー樹脂および正極活物質以外にも、必要に応じて導電材を添加することができる。導電材としては、カーボンブラック、ケッチェンブラック、アセチレンブラック、カーボンウイスカー、炭素繊維、天然黒鉛、人造黒鉛などが挙げられる。
【００９７】
上記正極用バインダー組成物において、バインダー樹脂１００重量部に対して正極活物質の添加量は１，０００〜５，０００重量部、好ましくは１，２００〜３，５００重量部であり、導電材の添加量は２０〜５００重量部、好ましくは５０〜４００重量部である。
【００９８】
本発明の非水電解質二次電池に用いられる負極は、負極集電体の表裏両面または片面に、バインダーポリマーと負極活物質とを主成分として含む負極用バインダー組成物を塗布してなるものである。ここで、バインダーポリマーとしては、正極と同じものを用いることができる。
なお、バインダーポリマーと負極活物質とを主成分として含む負極用バインダー組成物を溶融混練した後、押出し、フィルム成形することにより負極を形成してもよい。
【００９９】
負極集電体としては、銅、ステンレス鋼、チタン、ニッケルなどが挙げられ、これらの中でも、銅箔または表面が銅メッキ膜にて被覆された金属箔が性能と価格との両面から見て好ましい。この集電体は、箔状、エキスパンドメタル状、板状、発泡状、ウール状、ネット状等の三次元構造などの種々の形態のものを採用することができる。
【０１００】
上記負極活物質としては、アルカリ金属、アルカリ合金、炭素質材料、上記正極活物質と同じ材料等を用いることができる。
この場合、アルカリ金属としては、Ｌｉ、Ｎａ、Ｋ等が挙げられ、アルカリ金属合金としては、例えば、金属Ｌｉ、Ｌｉ−Ａｌ、Ｌｉ−Ｍｇ、Ｌｉ−Ａｌ−Ｎｉ、Ｎａ、Ｎａ−Ｈｇ、Ｎａ−Ｚｎ等が挙げられる。
また、炭素質材料としては、グラファイト，カーボンブラック，コークス，ガラス状炭素，炭素繊維、またはこれらの焼結体等が挙げられる。
【０１０１】
なお、リチウムイオン二次電池の場合には、リチウムイオンを可逆的に吸蔵、放出する材料を用いることとなる。
かかる材料としては、難黒鉛化炭素系材料や黒鉛系材料等の炭素質材料を使用することができる。より具体的には、熱分解炭素類、コークス類（ピッチコークス、ニートルコークス、石油コークス)、黒鉛類、ガラス状炭素類、有機高分子化合物焼成体(フェノール樹脂、フラン樹脂等を適当な温度で焼成し炭素化したもの)、炭素繊維、活性炭等の炭素質材料を使用することができる。このほか、リチウムイオンを可逆的に吸蔵、放出し得る材料としては、ポリアセチレン、ポリピロール等の高分子やＳｎＯ₂等の酸化物を使用することもできる。
なお、負極用バインダー組成物にも、必要に応じて導電材を添加することができる。導電材としては、前述の正極用バインダーと同様のものが挙げられる。
【０１０２】
上記負極用バインダー組成物において、バインダーポリマー１００重量部に対して負極活物質の添加量は５００〜１，７００重量部、好ましくは７００〜１，３００重量部であり、導電材の添加量は０〜７０重量部、好ましくは０〜４０重量部である。
【０１０３】
上記負極用バインダー組成物および正極用バインダー組成物は、通常、分散媒を加えてペースト状で用いられる。分散媒としては、例えば、Ｎ−メチル−２−ピロリドン（ＮＭＰ）、ジメチルホルムアミド、ジメチルアセトアミド、ジメチルスルホアミド等の極性溶媒が挙げられる。この場合、分散媒の添加量は、正極用または負極用バインダー組成物１００重量部に対して３０〜３００重量部程度である。
【０１０４】
なお、正極および負極を薄膜化する方法としては、特に制限されないが、例えば、アプリケータロール等のローラーコーティング、スクリーンコーティング、ドクターブレード法、スピンコーティング、バーコーター等の手段を用いて、乾燥後における活物質層の厚さを１０〜２００μｍ、特に５０〜１５０μｍの均一な厚みに形成することが好ましい。
【０１０５】
上記非水電解質二次電池は、上述した正極と負極との間にセパレータを介在させてなる電池構造体を、積層、折畳、または捲回させて、さらにラミネート型やコイン型に形成し、これを電池缶またはラミネートパック等の電池容器に収容し、電池缶であれば封缶、ラミネートパックであればヒートシールすることで、組み立てられる。この場合、セパレータを正極と負極との間に介在させ、電池容器に収容した後、非水系電解質，電解質用組成物を充填し、電極間、セパレータと電極間の空隙に十分に浸透させ、さらに電解質用組成物の場合は加熱等により反応硬化させることとなる。
【０１０６】
以上説明したように、本発明の電圧制御方法を適用した非水電解質二次電池は、過充電特性に優れており、保護回路を設けずに過充電した場合でも危険性がないことから、電池の製造工程の簡略化および製造コストの低減化を図ることができる。
また、空孔率の高いセパレータと高分子ゲル電解質とを組み合わせて用いた場合には、二次電池の大電流放電特性を維持しつつ、内部短絡の発生率を一層低くすることが可能となる。
【０１０７】
したがって、上記非水電解質二次電池は、ビデオカメラ、ノート型パソコン、携帯電話，ＰＨＳ等の携帯端末などの主電源、メモリのバックアップ電源用途をはじめとしたパソコン等の瞬時停電対策用電源、電気自動車またはハイブリッド自動車への応用、太陽電池と併用したソーラー発電エネルギー貯蔵システム等の様々な用途に好適に用いることができるものである。
【０１０８】
【実施例】
以下、合成例、実施例および比較例を挙げて、本発明をより具体的に説明するが、本発明は下記の実施例に制限されるものではない。
【０１０９】
［合成例１］ ポリビニルアルコール誘導体の合成
撹拌羽根を装着した反応容器にポリビニルアルコール（平均重合度５００，ビニルアルコール分率＝９８％以上）３重量部と、１，４−ジオキサン２０重量部と、アクリロニトリル１４重量部とを仕込み、撹拌下で水酸化ナトリウム０．１６重量部を水１重量部に溶解した水溶液を徐々に加え、２５℃で１０時間撹拌した。
次に、イオン交換樹脂（商品名；アンバーライト ＩＲＣ−７６，オルガノ株式会社製）を用いて中和した。イオン交換樹脂を濾別した後、溶液に５０重量部のアセトンを加えて不溶物を濾別した。アセトン溶液を透析膜チューブに入れ、流水で透析した。透析膜チューブ内に沈殿するポリマーを集めて、再びアセトンに溶解して濾過し、アセトンを蒸発させてシアノエチル化された合成例１のＰＶＡ誘導体を得た。
得られたポリマー誘導体は、赤外吸収スペクトルにおける水酸基の吸収は確認できず、水酸基が完全にシアノエチル基で封鎖されている（封鎖率１００％）ことが確認できた。
【０１１０】
得られたＰＶＡポリマー３重量部をジオキサン２０重量部とアクリロニトリル１４重量部に混合した。この混合溶液に水酸化ナトリウム０．１６重量部を１重量部の水に溶解した水酸化ナトリウム水溶液を加えて、２５℃で１０時間撹拌した。
次に、イオン交換樹脂（商品名；アンバーライト ＩＲＣ−７６，オルガノ（株）製）を用いて中和した。イオン交換樹脂を濾別した後、溶液に５０重量部のアセトンを加えて不溶物を濾別した。濾過後のアセトン溶液を透析膜チューブに入れ、流水で透析し、透析膜チューブ内に沈殿するポリマーを集めて、再びアセトンに溶解して濾過し、アセトンを蒸発させてシアノエチル化されたＰＶＡポリマー誘導体を得た。
得られたポリマー誘導体は、赤外吸収スペクトルにおける水酸基の吸収は確認できず、水酸基が完全にシアノエチル基で封鎖されている（封鎖率１００％）ことが確認できた。
【０１１１】
［合成例２］ 熱可塑性ポリウレタン系樹脂の合成
撹拌機、温度計および冷却管を備えた反応器に、予め加熱脱水したポリカプロラクトンジオール（プラクセル２２０Ｎ、ダイセル化学工業（株）製）６４．３４重量部と、４，４′−ジフェニルメタンジイソシアネート２８．５７重量部とを仕込み、窒素気流下、１２０℃で２時間撹拌・混合した後、１，４−ブタンジオール７．０９重量部を加えて、同様に窒素気流下、１２０℃にて反応させた。反応が進行し、反応物がゴム状になった時点で反応を停止した。その後、反応物を反応器から取り出し、１００℃で１２時間加熱し、赤外線吸収スペクトルでイソシアネート基の吸収ピークが消滅したのを確認した後加熱を止め、固体状のポリウレタン樹脂を得た。
【０１１２】
得られたポリウレタン樹脂の重量平均分子量（Ｍｗ）は１．７１×１０⁵であった。このポリウレタン樹脂８重量部をＮ−メチル−２−ピロリドン９２重量部に溶解することによって、ポリウレタン樹脂溶液を得た。
【０１１３】
［実施例１］ 二次電池１
〈正極の作製〉
正極活物質であるＬｉＣｏＯ₂（正同化学（株）製）、導電材であるケッチェンブラックＥＣ（ライオン（株）製）、ポリフッ化ビニリデン（ＰＶＤＦ１３００、呉羽化学（株）製）、合成例２のポリウレタン（ＰＵ）を、それぞれ質量配合比１００．０：４．３５：４．１３：２．７２の比率で混合し、さらに１−メチル−２−ピロリドン（ＮＭＰ、ＬｉＣｏＯ₂１００に対して質量比５６．７４）（和光純薬工業（株）製）に溶解し、分散・混合させてスラリーを作製した。
このスラリーをアルミシート（厚さ０．０２０ｍｍ、日本製箔（株）製）に塗布した後、乾燥、圧延して５０．０ｍｍ（内、塗布部：４０．０ｍｍ）×２０．０ｍｍおよび５０．０×２７０．０ｍｍに裁断し、正極を得た。
【０１１４】
〈負極の作製〉
負極活物質であるＭＣＭＢ（ＭＣＭＢ６−２８、大阪ガスケミカル（株）製）、ポリフッ化ビニリデン（ＰＶＤＦ９００、呉羽化学（株）製）を、それぞれ質量配合比１００．０：８．７０の比率で混合し、さらにＮＭＰ（ＭＣＭＢ１００に対して質量比１２１．７）に溶解し、分散・混合させてスラリーを作製した。
このスラリーを銅箔（厚さ０．０１０ｍｍ、日本製箔（株）製）に塗布した後、乾燥、圧延して５０．０ｍｍ（内、塗布部：４０．０ｍｍ）×２０．０ｍｍおよび５０．０×２７０．０ｍｍに裁断し、負極を得た。
【０１１５】
〈電極群の作製〉
セルロースセパレータ（厚さ０．０３５ｍｍ、ＦＴ４０−３５、日本高度紙工業（株）製）を５４．０×２６０．０ｍｍに裁断して２枚に折り曲げたものに、上述のようにして作製した正極２枚、負極２枚を対向させて組み、３０ＣＢ（ｔ＝３０μｍ、５０．０ｍｍ×２０．０ｍｍ）にＡｌテープを溶接したものをＡｌ／ＡｌＯｘ参照電極としてセパレータに介して電極群を得た。
【０１１６】
〈電解質溶液の作製〉
エチレンカーボネート（ＥＣ）、ジエチルカーボネート（ＤＥＣ）、プロピレンカーボネート（ＰＣ）、およびビニレンカーボネート（ＶＣ）を質量比１００．０：１１５．９：２６．１５：２．４７９の割合で混合し、これにＬｉＰＦ₆を１Ｍの濃度となるように溶解して電解質溶液を作製した。
【０１１７】
〈プレゲル組成物の作製〉
上記電解質溶液中のＥＣの質量１００に対して合成例１のポリビニルアルコール誘導体を０．１０７６、ＮＫエステル Ｍ−２０Ｇ（モノメタクリレート），ＮＫエステル ９Ｇ（ジメタクリレート），ＮＫエステル Ａ−ＴＭＰＴ（トリメタクリレート）（いずれも、新中村化学工業（株）製）をそれぞれ８．４７５，１２．０５，１．０１４、２，２′−アゾビス（２，４−ジメチルバレロニトリル）を１．５５０添加し、撹拌・混合してプレゲル組成物を得た。
【０１１８】
〈電池の作製〉
上記のように作製した電極群の外径長を測定し、計算による体積に対して等しい容量（１００．０ｖｏｌ％）の上記プレゲル組成物を注液した後、約７６Ｔｏｒｒに減圧し、ラミネートパッキングした。
その後、５５℃で２時間、８０℃で３０分間加熱し、プレゲル組成物をゲル化させ、非水電解質二次電池を得た。
【０１１９】
［実施例２］
実施例１で得られた正極および負極に、セルロースセパレータ（厚さ０．０３５ｍｍ、ＦＴ４０−３５、日本高度紙工業（株）製）を５４．０×６７０．０ｍｍを介して捲回し、電極群を作製した以外は、実施例１と同様にして非水電解質二次電池を得た。
【０１２０】
［比較例１］
プレゲル組成物作製時に、ＮＫエステル Ｍ−２０Ｇ（モノメタクリレート），ＮＫエステル ９Ｇ（ジメタクリレート），ＮＫエステル Ａ−ＴＭＰＴ（トリメタクリレート）、２，２′−アゾビス（２，４−ジメチルバレロニトリル）を用いなかった以外は、実施例１と同様にして、非水電解質二次電池を作製した。
【０１２１】
［比較例２］
プレゲル組成物作製時に、ＮＫエステル Ｍ−２０Ｇ（モノメタクリレート），ＮＫエステル ９Ｇ（ジメタクリレート），ＮＫエステル Ａ−ＴＭＰＴ（トリメタクリレート）、２，２′−アゾビス（２，４−ジメチルバレロニトリル）を用いなかった以外は、実施例２と同様にして、非水電解質二次電池を作製した。
【０１２２】
上記実施例１および比較例１で得られた非水電解質二次電池について、充電容量と電池電圧の関係、充電容量と正極および負極の電圧との関係を測定し、結果を図３〜６に示した。
なお、正極活物質のファラデー反応
ＬｉＣｏＯ₂ → Ｌｉ_xＣｏＯ₂ ＋ （１−ｘ）Ｌｉ⁺ ＋ （１−ｘ）ｅ^-
におけるｘ＝０．５に対応する電気容量の理論値１３７ｍＡｈ／ｇより算出した正極活物質の容量を電池容量とし、それを充電状態１００％とした。
【０１２３】
この二次電池サンプルに対して、初期充電として０．０１Ｃの電流率で１．５Ｖまで充電した後、さらに０．０５Ｃの充電率で３．２Ｖまで充電し、その後、５５℃で２時間、さらに８０℃で３０分間エージングを行った。
次に、設定電流０．５Ｃ、設定電圧４．２Ｖ、０．１Ｃ電流終止で定電流−定電圧充電、休止１時間、１．０Ｃで３．０Ｖ終止の定電流放電、休止１時間を１サイクルとして、３サイクル行い、この時点を電池サンプルの初期状態とした。その後、充電量に対する可逆性を評価する試験として、０．５Ｃの電流率で充電量Ｘ％だけ充電し、休止１時間の後、電流率１．０Ｃ、３．０Ｖ終止で定電流放電を行った。このとき、Ｘ＝５０．０、７５．０、１００．０、１５０．０、２００．０および２５０．０として順に充電量Ｘを増加させながら充放電させた。
【０１２４】
図３には、実施例１で得られた二次電池の充電容量と電池電圧の関係が示されている。ここからわかるように、実施例１の二次電池では、充電量が増加しても充電電圧は上昇せず安全性に優れているだけでなく、放電電圧が顕著に低下することもないことがわかる。特に、充電量１５０％以降は、放電電圧の変化が小さいと言える。
【０１２５】
一方、図４には、比較例１で得られた二次電池の充電容量と電池電圧の関係が示されている。ここからわかるように、比較例１の二次電池では、充電量が増加すると充電電圧が急激に上昇して安全性に問題があるだけでなく、放電電圧も顕著に低下している。２５０％を超えて充電した場合には、充電時に破裂、発火の虞があるとともに、正極が可逆性を失って本来の放電容量を得ることができなくなる。
【０１２６】
図５には、実施例１で得られた二次電池の充電容量と正極および負極の電圧の関係が示され、図６には、比較例１で得られた二次電池の充電容量と正極および負極の電圧の関係が示されている。ここからわかるように、実施例１の二次電池では、１５０，２００，２５０％と過充電領域の充電を経験しても、正極および負極の放電電位は変化の少ない挙動を示している。これに対して、比較例１の二次電池では、充電量１５０％を超えて充電した場合、正極に顕著な電位変化が見られ、活物質の可逆性が失われており、本来の放電容量が得られないことがわかる。
【０１２７】
図７には、実施例２および比較例２で得られた二次電池の充電量と電圧の関係、並びに充電量と電池温度の関係が示されている。ここからわかるように、比較例２の二次電池では、充電量１６０％付近で温度上昇を起こし、充電量１９０％で急激な電圧上昇と温度上昇を引き起こすのに対し、実施例２の二次電池では、充電量１００％から温度上昇を始めるが、その後、急激な電圧上昇および温度上昇が生じていないことがわかる。
【０１２８】
実施例１および比較例１で得られた二次電池に関して、正極で起こる反応は、図８に示されるボルタモグラムで説明することができる。
すなわち、比較例１では１．０５Ｖ ｖｓ． Ａｇ／ＡｇＯ_x付近および１．４５Ｖ ｖｓ． Ａｇ／ＡｇＯ_x付近にそれぞれ、
▲１▼ ＬｉＣｏＯ₂ → Ｌｉ_0.5ＣｏＯ₂
▲２▼ Ｌｉ_0.5ＣｏＯ₂ → Ｌｉ_0.3ＣｏＯ₂
の反応に起因する酸化波を観察することができる。さらに、１．６０Ｖ ｖｓ．Ａｇ／ＡｇＯ_x付近に▲３▼の酸化波を観察することができ、▲３▼以降の酸化で活物質は可逆性を失うこととなる。
【０１２９】
これに対して、実施例１では、１．１０Ｖ ｖｓ． Ａｇ／ＡｇＯ_x付近で、
▲１▼ ＬｉＣｏＯ₂ → Ｌｉ_0.5ＣｏＯ₂に対応する酸化波を観察することができる。さらに、１．４０Ｖ ｖｓ． Ａｇ／ＡｇＯ_x付近に、▲１▼〜▲３▼とは異なる酸化波▲４▼を観察することができる。
この▲４▼の酸化反応により、充電の電気エネルギーが消費され、その結果、
▲２▼ Ｌｉ_0.5ＣｏＯ₂ → Ｌｉ_0.3ＣｏＯ₂
の変化が起こらないため、活物質の可逆性が失われず、しかも、不安定なＬｉ_0.3ＣｏＯ₂が生成しないので、二次電池の安全性が確保されることとなる。
【０１３０】
［実施例３〜７］
〈電解質溶液の作製〉
ジエチルカーボネート（ＤＥＣ）、エチレンカーボネート（ＥＣ）、プロピレンカーボネート（ＰＣ）、およびビニレンカーボネート（ＶＣ）を重量比５０：３５：１３：２の割合で混合し、これにＬｉＰＦ₆を１Ｍの濃度となるように溶解して電解質溶液を作製した。
【０１３１】
〈電解質用組成物の作製〉
予め脱水処理されたポリエチレングリコールジメタクリレート（オキシレンユニット数＝９）１００重量部と、メトキシポリエチレングリコールモノメタクリレート（オキシレンユニット数＝２）７０．１５重量部と、トリメチロールプロパントリメタクリレート８．４１重量部とを混合し、この混合組成物１００重量部に対し、合成例１で得られたポリビニルアルコール誘導体０．５重量部を加え、プレゲル組成物を得た。
得られたプレゲル組成物７重量部と、上記電解質溶液９３重量部との混合物に、アゾビスイソブチロニトリル０．５重量部を加えて電解質用組成物を得た。
【０１３２】
〈正極の作製〉
正極活物質としてＬｉＣｏＯ₂９２重量部、導電材としてケッチェンブラック４重量部、合成例２で得られたポリウレタン樹脂溶液２．５重量部、およびポリフッ化ビニリデン１０重量部を、Ｎ−メチル−２−ピロリドン９０重量部に溶解した溶液３８重量部と、Ｎ−メチル−２−ピロリドン１８重量部とを撹拌、混合し、ペースト状の正極用バインダー組成物を得た。この正極用バインダー組成物をアルミ箔上に乾燥膜厚１００μｍとなるようにドクターブレードにより塗布した後、８０℃で２時間乾燥し、厚みが８０μｍとなるようにロールプレスして正極を作製した。
【０１３３】
〈負極の作製〉
負極活物質としてＭＣＭＢ（ＭＣＭＢ６−２８、大阪ガスケミカル（株）製）９２重量部、およびポリフッ化ビニリデン１０重量部をＮ−メチル−２−ピロリドン９０重量部に溶解した溶液８０重量部と、Ｎ−メチル−２−ピロリドン４０重量部とを撹拌、混合し、ペースト状の負極用バインダー組成物を得た。この負極用バインダー組成物を銅箔上に、乾燥膜厚１００μｍとなるようにドクターブレードにより塗布した後、８０℃で２時間乾燥し、厚みが８０μｍとなるようにロールプレスして負極を作製した。
【０１３４】
〈電池の作製〉
上記のように作製した正極、負極について、正極は正極活物質層の塗工部が５ｃｍ×４８ｃｍの大きさになるように、負極は負極活物質の塗工部が５．２ｃｍ×４８．２ｃｍの大きさになるように、それぞれカットした。但し、この際、正極には正極活物質の未塗工部分を、負極には負極活物質の未塗工部分を、それぞれ設けた。
次に、正極の正極活物質層の未塗工部分にアルミの端子リードを、負極の負極活物質層の未塗工部分にニッケルの端子リードを、それぞれ抵抗溶接して取り付けた後、端子リードを取り付けた正極、負極を１４０℃で１２時間真空乾燥させ、乾燥後の正極、負極と、下記表１に示される所定のセパレータとを積層したものを捲回して、扁平状電極体を作製した。
続いて、正極、負極より正極端子、負極端子を取り出し、アルミラミネートケースへ収納して端子部を熱融着したものを電池構造体とし、上記で作製した電解質用組成物を注液して真空含浸させた後、アルミラミネートケースを熱融着により封止した。その後、５５℃で２時間、８０℃で０．５時間加熱してゲル化させ、非水電解質二次電池を得た。
【０１３５】
【表１】

【０１３６】
［１］電池容量、エネルギー密度の測定
上記実施例３〜７で得られた非水電解質二次電池について、２５℃で１２０ｍＡ（０．５ｍＡ／ｃｍ²：０．２Ｃ相当）の定電流で４．２Ｖまで充電し、その後、２時間定電圧充電を行った。次に、５分間の休止を置き、終止電圧を２．７Ｖとして１２０ｍＡの定電流で放電を行い、放電容量およびエネルギー密度を測定した。
【０１３７】
［２］過充電特性試験
［２−１］過充電試験（２５℃）
▲１▼実施例３，５，６，７の二次電池について、２５℃で６００ｍＡ（２．５ｍＡ／ｃｍ²：１Ｃ相当）の定電流で２．５時間を上限として過充電試験を行った。２．５時間の過充電試験中（充電率２５０％）、実施例の二次電池の電池電圧の最大値は４．８Ｖであり、電池表面温度は、いずれも４０℃を超えなかった。
▲２▼一方、比較例の電池は、全て２５０％過充電ポイントに至る前に５．５Ｖの電圧の急上昇、電池温度１００℃以上への温度の急上昇が見られ、２００％過充電付近で発火した。
▲３▼実施例４の二次電池について、２５℃で１８００ｍＡ（７．５ｍＡ／ｃｍ²：３Ｃ相当）の定電流で５０分間を上限として過充電試験を行った。５０分間の過充電試験中（充電率２５０％）、実施例１の二次電池の電池電圧の最大値は４．９５Ｖであり、電池表面の最高温度は５２．８℃であった。
▲３▼実施例４の二次電池について、２５℃で３００ｍＡ（１．２５ｍＡ／ｃｍ²：０．５Ｃ相当）の定電流で４時間を上限として過充電試験を行った。４時間の過充電試験中（充電率４００％）、実施例４の二次電池は、最大電圧４．５８Ｖであり、電池の表面温度は４０℃を超えなかった。
【０１３８】
［２−２］過充電試験（６０℃）
▲４▼実施例３の二次電池について、６０℃で６００ｍＡ（２．５ｍＡ／ｃｍ²：１Ｃ相当）の定電流で２時間を上限として過充電試験を行った。２時間の過充電試験中（充電率２００％）、実施例３の二次電池は、最大電圧４．８Ｖであり、電池の表面温度は９０℃を超えず、発火、爆発しなかった。
なお、上記試験結果を表２にまとめて示す。
【０１３９】
【表２】

【０１４０】
【発明の効果】
以上説明したように、本発明の非水電解質二次電池の電圧制御方法によれば、過充電時に電極で酸化される物質を非水電解質に加えているから、正極で生じる過充電反応で消費される電気エネルギーが、正極活物質からのリチウムの放出反応ではなく、該物質の電極酸化反応の消費されることとなり、非水電解質二次電池の過充電時の電池電圧の上昇が抑制されることとなる。また、この電極酸化反応が起こるために、極めて酸化性が高く、熱的に不安定なＬｉ_<0.3ＣｏＯ₂が生じなくなり、電池の暴走反応を起こす危険性も低くなり、安全性に優れた非水電解質二次電池を提供することができる。
【図面の簡単な説明】
【図１】従来のリチウム系二次電池の過充電時電圧と電池温度を示すグラフである。
【図２】本発明のリチウム系二次電池の過充電時電圧と電池温度を示すグラフである。
【図３】実施例１の二次電池における各充電量に対する充放電時の電圧曲線を示すグラフである。
【図４】比較例１の二次電池における各充電量に対する充放電時の電圧曲線を示すグラフである。
【図５】実施例１の二次電池における各充電量に対する充放電時の電位変化を示すグラフである。
【図６】比較例１の二次電池における各充電量に対する充放電時の電位変化を示すグラフである。
【図７】実施例２および比較例２の二次電池における充電時の電圧および電池表面温度の変化を示すグラフである。
【図８】実施例１および比較例１の二次電池における正極のサイクリックボルタモグラム示すグラフである。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a voltage control method for a nonaqueous electrolyte secondary battery that can prevent an increase in voltage of the nonaqueous electrolyte secondary battery during overcharging.
[0002]
[Background Art and Problems to be Solved by the Invention]
In recent years, a demand for a high-capacity secondary battery is increasing as a power source for portable devices such as a video camera and a laptop computer, and a power source for an electric vehicle, a hybrid vehicle, and a power storage.
Secondary batteries that are widely used at present include nickel-cadmium batteries and nickel metal hydride batteries using aqueous electrolytes, but these aqueous batteries are subject to electrolysis of water, so the battery voltage is low. In addition to being as low as about 1.2 V, it is difficult to improve the energy density.
[0003]
For this reason, a lithium secondary battery having a high battery voltage of 3 V or more and a large energy density per weight has recently attracted attention.
This lithium secondary battery is generally made of an aprotic organic solvent as an electrolyte and LiBF._Four, LiPF₆A solution in which an ion conductive salt such as is dissolved is used as an electrolyte solution, and is classified as a non-aqueous electrolyte battery.
The lithium secondary battery is classified into a lithium metal secondary battery using lithium metal or a lithium alloy as a negative electrode, and a lithium ion secondary battery using a carbon material or transition metal capable of doping lithium ions as an electrode active material. The
[0004]
The former lithium ion secondary battery often uses highly active lithium or a lithium alloy as a negative electrode active material, and special consideration is necessary for ensuring safety. On the other hand, the latter lithium ion secondary battery uses a carbon material capable of inserting and extracting lithium ions as a negative electrode active material, and LiCoO as a positive electrode active material.₂, LiNiO₂, LiMn₂O_FourLiFeO₂After assembling as a battery using a lithium-containing metal oxide such as an electrolyte solution in which a solute lithium salt is dissolved in an organic solvent, lithium ions released from the positive electrode active material by the first charge enter the carbon particles. In general, it is considered to be safe because it does not use metallic lithium as a raw material.
[0005]
However, in actuality, when overcharge is performed beyond the rated capacity, as the overcharge state increases, excessive extraction of lithium ions occurs from the positive electrode, and excessive insertion of lithium ions occurs at the negative electrode. Precipitate.
As a result, on the positive electrode side that has lost lithium ions, not only highly unstable high oxides are generated, but the voltage continues to rise due to overcharging, and organic substances in the electrolyte undergo a decomposition reaction and are flammable. A large amount of gas is generated, and a sudden exothermic reaction occurs to cause abnormal heat generation of the battery, eventually resulting in fire. This causes a problem that the safety of the battery cannot be sufficiently secured. Such a situation becomes more important as the energy density of the lithium ion secondary battery increases.
[0006]
In order to prevent the battery runaway reaction described above, a battery having a function of short-circuiting the positive and negative electrodes when the battery temperature is 60 ° C. or higher (Japanese Patent Laid-Open No. 10-255757), a self-incombustible fluorine-based organic compound in the electrolyte Has been developed (Japanese Patent Laid-Open No. 9-2559925), but these measures are not necessarily sufficient, and generally, a protection circuit for preventing overcharge described later is used. The current situation is.
[0007]
By the way, in a nickel-cadmium storage battery or the like, a gas absorption mechanism in which oxygen generated on the positive electrode side during overcharge is reacted with hydrogen on the negative electrode side and returned to water is skillfully used. For this reason, the overcharge state is prevented, and the internal pressure rise, voltage rise, and electrolyte concentration rise do not occur.
On the other hand, in a lithium secondary battery using an organic solvent, it is considered that it is almost impossible in principle to use such a gas absorption mechanism. In a lithium ion secondary battery using an organic solvent, an overcharge is performed. It is considered necessary to incorporate a protection circuit to prevent this.
[0008]
However, since the protection circuit for preventing overcharge requires a complicated control technique, the total cost of the battery increases. In addition, since lithium ion secondary batteries that are actually used have a protective circuit disposed in the battery pack, the occupied volume and mass of the lithium ion secondary battery are substantially equal to the energy density of the battery, particularly the volume energy density (Wh / m^Three).
[0009]
On the other hand, recently, it has been reported that a lithium ion secondary battery in which a polyvinylidene fluoride resin is interposed between positive and negative electrodes does not cause a runaway reaction when the battery voltage does not increase even when overcharged ( JP-A-9-2559925).
In this publication, by inserting a polyvinylidene fluoride resin between positive and negative electrodes, such as filling a polyvinylidene fluoride resin in a separator disposed between positive and negative electrodes, forming a polyvinylidene fluoride resin film between positive and negative electrodes, It has been reported that voltage rise due to overcharge can be prevented.
[0010]
However, since the polyvinylidene fluoride resin itself has poor ionic conductivity, there is a concern that the internal resistance of the battery is increased by interposing the resin between the positive and negative electrodes, and the battery performance such as rate characteristics is lowered. Is done.
In addition, polyvinylidene fluoride resin is known to be a resin having a large thermal deformation property. In particular, it is a fluoride of polyvinylidene fluoride component and ethylene trifluoride chloride, ethylene tetrafluoride, hexafluoropropylene, ethylene and the like. The vinylidene fluoride copolymer is known to be more susceptible to thermal deformation. When the battery reaches a high temperature of 60 ° C. or higher, the polyvinylidene fluoride resin is deformed or melted, which adversely affects the performance of the battery. Is expected to give
Furthermore, there is no guarantee that the overcharge prevention function will work in a high temperature range of 60 ° C or higher.
.
[0011]
The present invention has been made in view of the above circumstances. Even when the battery is overcharged to a charging rate of 100% or more of the battery capacity, the battery voltage is maintained within a predetermined range, and the non-aqueous electrolyte secondary battery can be used without using a protection circuit. An object of the present invention is to provide a voltage control method for a non-aqueous electrolyte secondary battery capable of improving safety.
[0012]
Means for Solving the Problem and Embodiment of the Invention
In order to achieve the above object, the present inventors have made extensive studies based on the following knowledge.
That is, as described above, in a non-aqueous electrolyte secondary battery such as a lithium ion secondary battery, when overcharging beyond the rated capacity, excessive lithium ions are extracted from the positive electrode as it enters an overcharged state. In the negative electrode, excessive insertion of lithium ions occurs, and lithium metal is deposited. On the positive electrode side that has lost the lithium ions, a very unstable high oxide is generated.
[0013]
The voltage continues to rise due to overcharge, and organic substances such as the electrolyte present in the battery undergo a decomposition reaction, generating a large amount of flammable gas and causing a sudden exothermic reaction, resulting in abnormal battery operation. It generates heat and eventually ignites.
Specifically, as shown in FIG. 1, when the battery is charged to about 170%, the battery voltage and the battery temperature rapidly increase, and eventually the battery bursts and ignites. In this case, LiCoO₂For example, a lithium ion battery having a positive electrode active material as the positive electrode active material is LiCoO.₂To Li⁺Is pulled out and the following reaction proceeds.
LiCoO₂  → 0.5Li⁺+ Li_0.5CoO₂+ 0.5e^-
[0014]
At this time, LiCoO₂Li is extracted from all LiCoO₂Li_0.5CoO₂The electric capacity at the time of changing to is a theoretical capacity of 137 mAh / g, and the battery is designed with this time as 100% charge rate (full charge). Continue to charge, LiCoO₂If the reaction for extracting Li from the reaction proceeds, Li_<0.5CoO₂And gradually Li₀CoO₂Li is approaching_<0.3CoO₂Is extremely oxidative and thermally unstable, so it self-heats and triggers battery runaway. The generated Li_<0.3CoO₂Has very low reversibility and LiCoO₂Will not play.
[0015]
Therefore, the present inventors have made Li_0.5CoO₂From this, the electric energy provided to the reaction for further extracting Li is used for another reaction, whereby Li_<0.3CoO₂As a result of intensive investigations on the method of suppressing the generation of runaway and suppressing the runaway reaction of the non-aqueous electrolyte secondary battery, by adding a predetermined substance to the electrolyte, the electrical energy during overcharge can be oxidized by the electrode. In addition, a circulation reaction mechanism in which a substance generated by oxidation is reduced at the negative electrode functions efficiently, and Li_<0.3CoO₂It was found that the formation of can be suppressed, and the present invention was completed.
[0016]
  That is, the present invention
1. A non-aqueous solution comprising a positive electrode and a negative electrode comprising a material that absorbs and releases lithium and a binder polymer, at least one separator that separates both the positive and negative electrodes, and a non-aqueous electrolyte containing a lithium salt A voltage control method when an electrolyte secondary battery is overcharged to a charge rate of 100% or more of a rated capacity, wherein a substance that is oxidized at the positive electrode by electrical energy supplied during the overcharge is added to the nonaqueous electrolyte The battery voltage during overcharging is controlled to 4.1 to 5.2 V by electrode oxidation of the substance.The substance oxidized at the positive electrode is an acrylic ester and / or a methacrylic esterA voltage control method for a non-aqueous electrolyte secondary battery,
2. SaidThe substance oxidized at the positive electrode is at least one selected from glycidyl methacrylate, glycidyl acrylate, methoxydiethylene glycol methacrylate, and methoxypolyethylene glycol methacrylate.A voltage control method for the non-aqueous electrolyte secondary battery according to claim 1;
3.The separator has a porosity of 40% or more, and oxygen and / or carbon dioxide is generated by the electrode oxidation, and the oxygen and / or carbon dioxide is produced in a small amount on the negative electrode as lithium metal. ₂ O and / or Li ₂ CO _Three 1 to oxidizeNon-aqueous electrolyte secondary battery voltage control method,
4).The non-aqueous electrolyte secondary battery includes a battery structure in which a separator is interposed between the positive electrode and the negative electrode, and a battery container that accommodates the battery structure, and the battery container is sealed 3Non-aqueous electrolyte secondary battery voltage control method,
5. SaidThe thickness of the separator is 20 to 50 μm 3Non-aqueous electrolyte secondary battery voltage control method,
6).Due to the electrical energy supplied during charging, the Li ₂ CO _Three And / or Li ₂ O is electrode reduced to metallic lithium and / or lithium ions at the negative electrode 3Non-aqueous electrolyte secondary battery voltage control method,
7. SaidThe separator comprises at least one of cellulose, polypropylene, polyethylene and polyester, and the porosity is 60% or more 3Non-aqueous electrolyte secondary battery voltage control method,
8). SaidElectrode oxidation is the reference electrode AlO _x Occurs in the range of 1.40 to 1.60V with respect to 1Voltage control method for non-aqueous electrolyte secondary battery
I will provide a.
[0017]
Hereinafter, the present invention will be described in more detail.
In the present invention, as described above, a positive electrode and a negative electrode comprising a material that absorbs and releases lithium ions and a binder polymer, at least one separator that separates both the positive and negative electrodes, and a non-aqueous solution that contains a lithium salt When a non-aqueous electrolyte secondary battery comprising an electrolyte is overcharged to a charge rate of 100% or more of its rated capacity, a substance that is oxidized at the positive electrode by electrical energy supplied during overcharge is converted to a non-aqueous electrolyte. In addition, by subjecting this substance to electrode oxidation, the battery voltage during overcharge is controlled to 4.1 to 5.2V.
[0018]
In the present invention, the rated capacity is a constant-current constant-voltage charge of a nonaqueous electrolyte secondary battery up to a predetermined charging voltage at 0.2 C, and then a constant-current discharge at 0.2 C up to a predetermined discharge end voltage. For example, LiCoO on the positive electrode₂In the case of a lithium ion battery using graphite made of an easily graphitized carbon material as a negative electrode, the charging voltage is 4.2V and the discharge end voltage is 2.7V.
The electrode oxidation reaction may occur at a charging rate of 100% or more of the rated capacity. However, the electrode oxidation reaction is generated so that the rated capacity of the battery is ensured and the reversibility of the active material is not affected. In consideration, it is particularly preferable that the electrode oxidation reaction occurs at a charging rate of 150% or more.
[0019]
More specifically, the electrode oxidation is performed as a reference electrode AlO._xPreferably, it occurs in the range of 1.40 to 1.60 V, and at less than 1.40 V, the electrode oxidation reaction is LiCoO.₂→ Li_0.5CoO₂The rated capacity may not be obtained at the same time or before the charging reaction of Li, and if it exceeds 1.60 V, before the electrode oxidation reaction occurs, Li_0.5CoO₂→ Li_<0.3CoO₂As a result, the reversibility of the positive electrode active material is lost, an unstable high oxide is generated, and the battery may run away.
[0020]
Further, when the standard hydrogen potential (SHE) is used as a reference, a normal temperature of 298.15 K and 101.325 Pa in one or more organic solvents selected from ethylene carbonate, propylene carbonate, vinylene carbonate and diethyl carbonate. Electrode oxidation preferably occurs in the range of 1.05 to 1.61 V with respect to the standard hydrogen potential (SHE) under pressure conditions.
Also in this case, at less than 1.05 V, the electrode oxidation reaction is LiCoO.₂→ Li_0.5CoO₂The rated capacity may not be obtained at the same time or before the charging reaction of Li, and if it exceeds 1.61 V, before the electrode oxidation reaction occurs, Li_0.5CoO₂→ Li_<0.3CoO₂As a result, the reversibility of the positive electrode active material is lost, an unstable high oxide is generated, and the battery may run away. Considering these points, it is preferable that electrode oxidation occurs in the range of 1.40 to 1.60V.
[0021]
Note that the battery voltage during overcharge is 4.1 to 5.2 V as described above, but if it exceeds 5.2 V, the battery may explode or generate heat. From the viewpoint of avoiding this, the battery voltage is preferably controlled to about 4.2 to 4.8V. The surface temperature of the battery is not limited as long as the above problem does not occur. However, if the surface temperature is 120 ° C. or higher, the battery is likely to run out of heat, so the battery temperature during overcharging is The surface temperature is preferably less than 120 ° C, more preferably less than 90 ° C, and even more preferably less than 70 ° C.
[0022]
In the present invention, oxygen and / or carbon dioxide is generated by the electrode oxidation, and the oxygen and / or carbon dioxide is produced in a small amount on the negative electrode by using Li metal.₂O and / or Li₂CO_ThreeIt is preferable to oxidize.
In addition, the Li₂CO_ThreeAnd / or Li₂It is preferred that O be electrode reduced to metallic lithium and / or lithium ions at the negative electrode.
Thus, after oxidizing lithium in a reaction that does not involve charge transfer with oxygen and carbon dioxide generated by electrode oxidation, this is subjected to electrode reduction, and a cyclic reaction system in which the substance generated by this electrode reduction is further electrode oxidized. By establishing, the electric energy supplied at the time of overcharge is consumed by this circulation reaction, and a raise of a battery voltage etc. can be prevented efficiently.
[0023]
On the other hand, even if it is possible to prevent an increase in battery voltage during overcharging, if the electrode deteriorates due to an irreversible reaction during this time, there is a high possibility that it will not function as a battery. For this reason, when charging is performed at a charging current rate with respect to the theoretical capacity of the positive electrode at 25 ° C. and a current of 1.00 C or less, it is preferable that the positive electrode and the negative electrode do not deteriorate up to a charging rate L% of the following formula.
Charging rate L (%) = (theoretical capacity) × 5 × (charging current rate C)^-0.5× 100
The theoretical capacity is LiCoO.₂Is used as the positive electrode active material,
LiCoO₂  → 0.5Li⁺+ Li_0.5CoO₂+ 0.5e^-
The electric capacity corresponding to is shown.
[0024]
In the present invention, the substance that is subjected to electrode oxidation with electric energy supplied during overcharge is not particularly limited as long as the battery voltage can be controlled to 4.1 to 5.2 V by electrode oxidation. The material oxidized at the positive electrode is represented by the general formula R-CO-R, general formula R-CO-OR, general formula R-CO-NR'R, general formula RO-CO-OR, general formula RO-CO-X. —CO—OR and general formula RR′N—CO—NR′R (wherein R is the same or different substituted or unsubstituted monovalent hydrocarbon group, R ′ is hydrogen atom or the same as each other) Or it is preferable that it is 1 type, or 2 or more types chosen from the compound shown by a different substituted or unsubstituted monovalent | monohydric hydrocarbon group, X shows a bivalent organic group.
[0025]
Here, the monovalent hydrocarbon group may have a chain, branched or cyclic structure, and may be either a saturated hydrocarbon group or an unsaturated hydrocarbon group.
The chain or branched hydrocarbon group is preferably a saturated or unsaturated hydrocarbon group having 1 to 10 carbon atoms, such as methyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl, t-butyl, n-pentyl, i-pentyl, neo-pentyl, n-hexyl, i-hexyl group, vinyl, allyl, isopropenyl, 1-propenyl, 3-butenyl, 2-butenyl, 1-butenyl, 1- Examples thereof include methyl-2-propenyl, 1-methyl-2-propenyl, 1-methyl-1-propenyl, and the like. In particular, methyl group, ethyl group, n-propyl are particularly preferable because they are easily subjected to electrode oxidation under the above-described conditions. I-propyl group is preferable, and ethyl group and i-propyl group are particularly preferable.
As the cyclic hydrocarbon group, C_nH_2nCan be used, and examples thereof include cyclopentyl, cyclohexyl, phenyl, tolyl, xylyl, cumenyl, mesityl, and styryl groups.
[0026]
A chain hydrocarbon group having an oxyalkylene structure can also be used, and in particular, — (CH₂CHR^aO)_n-, Wherein n = 1 to 30, R^a= A hydrogen atom or a methyl group is preferably used.
X represents a divalent organic group, for example, — (CH₂)_mAn alkylene group represented by-(m = 1 to 30),-(CR₂)_mA group represented by-(R is the same as above, m = 1 to 30) and the like.
In the compounds represented by the above general formulas, the two terminal R groups may be bonded to form a cyclic structure to form a lactone, lactide, lactam structure, or the like.
[0027]
Specific examples of the substance include acrylic acid or methacrylic acid ester such as glycidyl methacrylate, glycidyl acrylate, methoxydiethylene glycol methacrylate, methoxypolyethylene glycol methacrylate (average molecular weight 200 to 1,200), methacryloyl isocyanate, 2-hydroxymethylmethacrylate. An acid etc. are mentioned.
[0028]
Thus, by adding a substance that is oxidized at the electrode during overcharge to the non-aqueous electrolyte, the electrical energy consumed in the overcharge reaction that occurs at the positive electrode is not the lithium release reaction from the positive electrode active material, The electrode oxidation reaction is consumed, and as a result, as shown in FIG. 2, an increase in battery voltage during overcharging of the nonaqueous electrolyte secondary battery is suppressed. In addition, since this electrode oxidation reaction occurs, it is extremely oxidizable and thermally unstable Li_<0.3CoO₂Will not occur, and the risk of battery runaway reaction is reduced.
[0029]
The separator used in the non-aqueous electrolyte secondary battery of the present invention is not particularly limited as long as the battery voltage can be controlled to 4.1 to 5.2 V by the electrode reaction described above. It is preferable to use 40% or more.
Here, if the porosity is less than 40%, the substance in the electrolyte cannot smoothly move between the positive and negative electrodes, and the progress of the above-described circulation reaction may be hindered. Accordingly, the porosity is preferably as high as possible as long as the positive and negative electrodes can be separated, and particularly preferably 60% or more.
[0030]
The material of the separator is not particularly limited, but preferably includes one or more of cellulose, polypropylene, polyethylene, and polyester. In this case as well, the porosity is preferably 60% or more.
Further, the thickness of the separator is usually 20 to 50 μm, more preferably 25 to 40 μm, and particularly 25 to 35 μm. By setting the thickness within this range, the rate of occurrence of internal short circuit of the battery is reduced. The deterioration of the discharge load characteristics can be prevented.
The separator structure is not particularly limited, and may be a single layer structure or a multilayer structure in which a plurality of films or sheets are laminated. In addition, a non-woven separator using one or more fibers of cellulose, polypropylene, polyethylene, and polyester can also be suitably used.
[0031]
The non-aqueous electrolyte of the non-aqueous electrolyte secondary battery is a non-aqueous electrolyte composed of a lithium salt and an organic solvent, or an electrolyte mainly composed of a lithium salt, a compound having a reactive double bond in the molecule, and an organic solvent. Any of those obtained by gelling the composition can be used. Among them, an electrolyte containing one or more methacrylic acid esters and / or one or more acrylic acid esters and a polymerization initiator is gelled by radical polymerization. It is preferable that the gel electrolyte is obtained by crystallization.
[0032]
Examples of the organic solvent include, for example, cyclic or chain carbonate ester, chain carboxylate ester, cyclic or chain ether, phosphate ester, lactone compound, nitrile compound, amide compound, etc. alone or in combination. Can be used.
[0033]
Examples of the cyclic carbonate include alkylene carbonates such as propylene carbonate (PC), ethylene carbonate (EC), and butylene carbonate, vinylene carbonate (VC), and the like. Examples of the chain carbonate include dialkyl carbonates such as dimethyl carbonate (DMC), methyl ethyl carbonate (MEC), and diethyl carbonate (DEC). Examples of chain carboxylic acid esters include methyl acetate and methyl propionate. Examples of the cyclic or chain ether include tetrahydrofuran, 1,3-dioxolane, 1,2-dimethoxyethane, and the like. Examples of phosphate esters include trimethyl phosphate, triethyl phosphate, ethyl dimethyl phosphate, diethyl methyl phosphate, tripropyl phosphate, tributyl phosphate, tri (trifluoromethyl) phosphate, and tri (trichloromethyl) phosphate. , Tri (trifluoroethyl) phosphate, tri (triperfluoroethyl) phosphate, 2-ethoxy-1,3,2-dioxaphospholan-2-one, 2-trifluoroethoxy-1,3,2 -Dioxaphospholan-2-one, 2-methoxyethoxy-1,3,2-dioxaphosphoran-2-one and the like can be mentioned. Examples of the lactone compound include γ-butyrolactone. Examples of the nitrile compound include acetonitrile. Examples of the amide compound include dimethylformamide.
[0034]
Among these, it is particularly preferable to use one or more selected from ethylene carbonate, propylene carbonate, vinylene carbonate, and diethyl carbonate as the organic solvent.
[0035]
The lithium salt is not particularly limited as long as it can be used for non-aqueous electrolyte secondary batteries such as lithium secondary batteries and lithium ion secondary batteries. For example, lithium tetrafluoroborate, hexafluorophosphoric acid Lithium, lithium perchlorate, lithium trifluoromethanesulfonate, lithium salt of sulfonylimide represented by the following general formula (1), lithium salt of sulfonylmethide represented by the following general formula (2), lithium acetate, trifluoroacetic acid Examples thereof include lithium salts such as lithium, lithium benzoate, lithium p-toluenesulfonate, lithium nitrate, lithium bromide, lithium iodide, and lithium 4-phenylborate.
(R¹-SO₂) (R²-SO₂) NLi (1)
(R^Three-SO₂) (R^Four-SO₂) (R^Five-SO₂) CLi (2)
[In the formulas (1) and (2), R¹~ R^FiveRepresents a C 1-4 perfluoroalkyl group which may contain one or two ether groups. ]
[0036]
Specific examples of the sulfonylimide lithium salt represented by the general formula (1) include those represented by the following formula.
(CF_ThreeSO₂)₂NLi, (C₂F_FiveSO₂)₂NLi, (C_ThreeF₇SO₂)₂NLi, (C_FourF₉SO₂)₂NLi, (CF_ThreeSO₂) (C₂F_FiveSO₂) NLi, (CF_ThreeSO₂) (C_ThreeF₇SO₂) NLi, (CF_ThreeSO₂) (C_FourF₉SO₂) NLi, (C₂F_FiveSO₂) (C_ThreeF₇SO₂) NLi, (C₂F_FiveSO₂) (C_FourF₉SO₂) NLi, (CF_ThreeOCF₂SO₂)₂NLi
[0037]
Specific examples of the lithium salt of a sulfonylmethide represented by the general formula (2) include those represented by the following formula.
(CF_ThreeSO₂)_ThreeCLi, (C₂F_FiveSO₂)_ThreeCLi, (C_ThreeF₇SO₂)_ThreeCLi, (C_FourF₉SO₂)_ThreeCLi, (CF_ThreeSO₂)₂(C₂F_FiveSO₂) CLi, (CF_ThreeSO₂)₂(C_ThreeF₇SO₂) CLi, (CF_ThreeSO₂)₂(C_FourF₉SO₂) CLi, (CF_ThreeSO₂) (C₂F_FiveSO₂)₂CLi, (CF_ThreeSO₂) (C_ThreeF₇SO₂)₂CLi, (CF_ThreeSO₂) (C_FourF₉SO₂)₂CLi, (C₂F_FiveSO₂)₂(C_ThreeF₇SO₂) CLi, (C₂F_FiveSO₂)₂(C_FourF₉SO₂) CLi, (CF_ThreeOCF₂SO₂)_ThreeCLi
[0038]
Among these, lithium tetrafluoroborate, lithium hexafluorophosphate, the lithium salt of sulfonylmethide represented by the above general formula (1) and the above general formula (2) exhibits particularly high ionic conductivity, and Since it is an ion conductive salt excellent in thermal stability, it is preferable. In addition, these ion conductive salts can be used individually by 1 type or in combination of 2 or more types.
[0039]
Moreover, the density | concentration of the lithium salt in the electrolyte solution which dissolved the lithium salt in the organic solvent is 0.05-3 mol / L normally, Preferably it is 0.1-2 mol / L. If the concentration of the lithium salt is too low, sufficient ionic conductivity may not be obtained. On the other hand, if it is too high, it may not be completely dissolved in the organic solvent.
[0040]
In the case of the above-described gel electrolyte, the electrolyte composition contains a compound having two or more reactive double bonds in the molecule in addition to the lithium salt and the organic solvent, and preferably further linear or branched It contains a linear polymer compound.
That is, when a polymer gel electrolyte obtained by gelling the electrolyte composition is used in the form of a thin film, 2 reactive double bonds are added to the molecule from the viewpoint of increasing physical strength such as shape retention. A compound having at least one compound is added, and a three-dimensional network structure is formed by the reaction of the compound, thereby enhancing the electrolyte shape retention ability.
[0041]
In addition, when a linear polymer compound is also included, the molecular chain of the linear polymer compound is entangled with the three-dimensional network structure of the polymer formed by crosslinking the compound having a reactive double bond. A gel having an interpenetrating polymer network ((sem-IPN)) structure can be obtained, and the shape retention ability and strength of the electrolyte can be further enhanced, and the adhesiveness can also be enhanced. It is.
[0042]
Examples of the compound having a reactive double bond include divinylbenzene, divinylsulfone, allyl methacrylate, ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, polyethylene glycol dimethacrylate (average molecular weight 200 to 200). 1,000), 1,3-butylene glycol dimethacrylate, 1,6-hexanediol dimethacrylate, neopentyl glycol dimethacrylate, polypropylene glycol dimethacrylate (average molecular weight 400), 2-hydroxy-1,3 -Dimethacryloxypropane, 2,2-bis- [4- (methacryloxyethoxy) phenyl] propane, 2,2-bis- [4- (methacryloxyethoxy diethoxy) phenyl] propane, 2,2-bis- [ -(Methacryloxyethoxy / polyethoxy) phenyl] propane, ethylene glycol diacrylate, diethylene glycol diacrylate, triethylene glycol diacrylate, polyethylene glycol diacrylate (average molecular weight 200 to 1,000), 1,3-butylene glycol diacrylate, 1,6-hexanediol diacrylate, neopentyl glycol diacrylate, polypropylene glycol diacrylate (average molecular weight 400), 2-hydroxy-1,3-diaacryloxypropane, 2,2-bis- [4- (acryloxy) Ethoxy) phenyl] propane, 2,2-bis- [4- (acryloxyethoxy diethoxy) phenyl] propane, 2,2-bis- [4- (acryloxyethoxy polyethoxy) phenyl] pro , Trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, tetramethylolmethane triacrylate, tetramethylolmethane tetraacrylate, water-soluble urethane diacrylate, water-soluble urethane dimethacrylate, tricyclodecane dimethanol acrylate, hydrogenated dicyclopentadiene Examples thereof include compounds having two or more reactive double bonds in the molecule such as diacrylate, polyester diacrylate, and polyester dimethacrylate.
[0043]
If necessary, for example, glycidyl methacrylate, glycidyl acrylate, methoxydiethylene glycol methacrylate, methoxytriethylene glycol methacrylate, methoxypolyethylene glycol methacrylate (average molecular weight 200 to 1,200) or other acrylic acid or methacrylate ester, methacryloyl A compound having one acrylic acid group or one methacrylic acid group in a molecule such as isocyanate, 2-hydroxymethyl methacrylic acid, N, N-dimethylaminoethyl methacrylic acid or the like can be added. Furthermore, acrylamide compounds such as N-methylolacrylamide, methylenebisacrylamide and diacetone acrylamide, vinyl compounds such as vinyloxazolines and vinylene carbonate, and other compounds having a reactive double bond can be added.
[0044]
In order to form a polymer three-dimensional network structure, it is necessary to add a compound having two or more reactive double bonds in the molecule. That is, a compound having only one reactive double bond such as methyl methacrylate cannot form a three-dimensional network structure of a polymer, and therefore has at least two reactive double bonds in part. It is necessary to add a compound.
[0045]
Among the compounds containing a reactive double bond, a particularly preferable reactive monomer includes a diester compound containing a polyoxyalkylene component represented by the following general formula (3), and this and the following general formula (4). It is recommended to use a combination of a monoester compound containing a polyoxyalkylene component represented by the formula (1) and a triester compound.
[0046]
[Chemical 1]

(However, in the formula, R⁶~ R⁸Has 1 to 6 carbon atoms such as a hydrogen atom or a methyl group, ethyl group, n-propyl group, i-propyl group, n-butyl group, i-butyl group, s-butyl group, t-butyl group, etc. 1 to 4 alkyl groups satisfying the condition of X ≧ 1 and Y ≧ 0, or satisfying the condition of X ≧ 0 and Y ≧ 1, preferably R⁶~ R⁸Are methyl group, ethyl group, n-propyl group, i-propyl group, n-butyl group, i-butyl group, s-butyl group and t-butyl group. )
[0047]
[Chemical formula 2]

(However, in the formula, R⁹~ R¹¹Has 1 to 6 carbon atoms such as a hydrogen atom or a methyl group, ethyl group, n-propyl group, i-propyl group, n-butyl group, i-butyl group, s-butyl group, t-butyl group, etc. 1 to 4 alkyl groups satisfying the conditions of A ≧ 1 and B ≧ 0, or satisfying the conditions of A ≧ 0 and B ≧ 1, preferably R⁹~ R¹¹Are methyl group, ethyl group, n-propyl group, i-propyl group, n-butyl group, i-butyl group, s-butyl group and t-butyl group. )
[0048]
In the above formula (3), for example, X = 9, Y = 0, R⁶= R⁸= CH_ThreeIs preferably used. on the other hand. In the above formula (4), for example, A = 2 or 9, B = 0, R⁹= R¹¹= CH_ThreeIs preferably used.
As the triester compound, trimethylolpropane trimethacrylate is suitable.
[0049]
The diester compound containing the polyoxyalkylene component and the monoester compound containing the polyoxyalkylene component are ultraviolet, electron beam, X-ray, γ-ray, microwave, high frequency in a mixture of an ion conductive salt and an organic solvent. The polymer three-dimensional cross-linked network structure is formed by irradiating, etc., or by heating the mixture.
In this case, in general, a diester compound containing a polyoxyalkylene component can be polymerized alone to form a polymer three-dimensional crosslinked network. As described above, the diester compound containing this polyoxyalkylene component is used. By adding a monoester compound containing a polyoxyalkylene component, which is a monofunctional monomer, to the compound, a polyoxyalkylene branched chain can be introduced onto the three-dimensional network.
[0050]
Here, the composition ratio of the diester compound and monoester compound containing the polyoxyalkylene component and the triester compound is appropriately set depending on the length of the polyoxyalkylene component, and is not particularly limited. But in molar ratio
[Diester compound / monoester compound] = 0.1 to 2, especially 0.3 to 1.5
[Diester compound / Triester compound] = 2-15, especially 3-10
This range is preferable from the viewpoint of improving the gel strength.
[0051]
A semi-IPN structure can also be formed by adding a linear or branched linear polymer compound to the compound having a reactive double bond.
In this case, the necessary linear or branched linear polymer compound is not particularly limited as long as it is a linear polymer compound. For example, (a) a hydroxyalkyl polysaccharide derivative, (b) oxyalkylene Examples thereof include branched polyvinyl alcohol derivatives, (c) polyglycidol derivatives, (d) cyano group-substituted monovalent hydrocarbon group-containing polyvinyl alcohol derivatives, and the like.
[0052]
Examples of (a) hydroxyalkyl polysaccharide derivatives include (1) hydroxyethyl polysaccharides obtained by reacting naturally occurring polysaccharides such as cellulose, starch, and pullulan with ethylene oxide, and (2) the polysaccharides described above. Hydroxypropyl polysaccharides obtained by reacting propylene oxide, (3) dihydroxypropyl polysaccharides obtained by reacting the above polysaccharides with glycidol or 3-chloro-1,2-propanediol, and the like. Some or all of the hydroxyl groups of the hydroxyalkyl polysaccharide are blocked with a substituent via an ester bond or an ether bond.
The hydroxyalkyl polysaccharide has a molar substitution degree of 2 to 30, preferably 2 to 20. When the degree of molar substitution is less than 2, the ability to dissolve ion conductive salts is too low to be suitable for use.
[0053]
As the (b) oxyalkylene branched polyvinyl alcohol derivative, the hydroxyl group in the polyvinyl alcohol unit in the polymer compound having an average degree of polymerization of 20 or more having a polyvinyl alcohol unit represented by the following general formula (5) in the molecule: A polymer compound partially or wholly substituted with an oxyalkylene-containing group having an average molar substitution degree of 0.3 or more can be suitably used.
[0054]
[Chemical Formula 3]

(In the formula, n is preferably 20 to 10,000.)
[0055]
That is, since the above polymer compound has a high oxyalkylene fraction, it has the ability to dissolve many ion conductive salts, and the number of oxyalkylene moieties in which ions move in the molecule increases, so that ions move. It becomes easy. As a result, high ionic conductivity can be expressed. In addition, since the polymer compound has high adhesiveness, it can sufficiently exert its role as a binder component and a function of firmly bonding the positive and negative electrodes, and the polymer electrolyte polymer comprising the polymer compound has ionic conductivity. A composition in which a salt is dissolved at a high concentration can be suitably used as a polymer gel electrolyte such as a film battery.
[0056]
As such a polymer compound, (1) a polymer compound obtained by reacting a polymer compound having a polyvinyl alcohol unit with an oxirane compound such as ethylene oxide, propylene oxide, or glycidol (dihydroxypropylated polyethylene vinyl alcohol, Propylene oxide polyvinyl alcohol, etc.),
(2) A polymer compound obtained by reacting a polymer compound having a polyvinyl alcohol unit with a polyoxyalkylene compound having a substituent having a reactivity with a hydroxyl group at the terminal can be mentioned.
The reaction between the polymer compound having a polyvinyl alcohol unit and the oxirane compound or oxyalkylene compound can be carried out using a basic catalyst such as sodium hydroxide, potassium hydroxide, or various amine compounds.
[0057]
Here, the polymer compound having a polyvinyl alcohol unit is a polymer compound having a polyvinyl alcohol unit in the molecule and having a number average polymerization degree of 20 or more, preferably 30 or more, more preferably 50 or more. A part or all of the hydroxyl group is substituted with an oxyalkylene-containing group. In this case, the upper limit of the number average degree of polymerization is preferably 2,000 or less, more preferably 500 or less, and particularly preferably 200 or less in consideration of handling properties.
[0058]
The polymer compound having the polyvinyl alcohol unit is optimally a homopolymer satisfying the number average polymerization degree range and having a polyvinyl alcohol unit fraction in the molecule of 98 mol% or more, but is not limited thereto. And a polymer compound satisfying the above-mentioned number average polymerization degree range and having a polyvinyl alcohol fraction of preferably 60 mol% or more, more preferably 70 mol% or more, such as a hydroxyl group of polyvinyl alcohol. Use of polyvinyl formal partially formalized, modified polyvinyl alcohol partially alkylated with polyvinyl alcohol, poly (ethylene vinyl alcohol), partially saponified polyvinyl acetate, other modified polyvinyl alcohol, etc. Can do.
[0059]
This polymer compound has an oxyalkylene-containing group in which a part or all of the hydroxyl groups in the polyvinyl alcohol unit have an average molar substitution degree of 0.3 or more. Which may be substituted), preferably 30 mol% or more, more preferably 50 mol% or more. Here, the average molar substitution degree (MS) can be calculated by accurately measuring the charged mass and the mass of the reaction product.
[0060]
The (c) polyglycidol derivative has a unit represented by the following formula (6) (hereinafter referred to as A unit) and a unit represented by the following formula (7) (hereinafter referred to as B unit), and has a molecular chain. Each of the ends of the molecular chain is blocked with a predetermined substituent at the end of the molecular chain.
[0061]
[Formula 4]

[0062]
Here, the polyglycidol can be obtained by polymerizing glycidol or 3-chloro-1,2-propanediol. Generally, glycidol is used as a raw material and a basic catalyst or Lewis acid catalyst is used. It is preferable to perform polymerization.
[0063]
The polyglycidol has 2 or more, preferably 6 or more, more preferably 10 or more of two units of A and B in the molecule. In this case, the upper limit is not particularly limited, but is usually about 10,000 or less. The total number of these units may be appropriately set in consideration of the fluidity and viscosity of the required polyglycidol. Moreover, the ratio of A unit to B unit in the molecule is A: B = 1/9 to 9/1, preferably 3/7 to 7/3 in terms of molar ratio. Note that there is no regularity in the appearance of the A and B units, and arbitrary combinations are possible.
[0064]
Furthermore, the weight average molecular weight (Mw) in terms of polyethylene glycol using gel filtration chromatography (GPC) in the polyglycidol is preferably 200 to 730,000, more preferably 200 to 100,000, and still more preferably 600 to 20 , 000. Moreover, average molecular weight ratio (Mw / Mn) is 1.1-20, More preferably, it is 1.1-10.
[0065]
These linear polymer compounds (a) to (c) are a part of or all of the hydroxyl groups in the molecule, preferably 10 mol% or more of halogen atoms and unsubstituted or substituted monovalent hydrocarbons having 1 to 10 carbon atoms. Group, R¹²CO-group (R¹²Is an unsubstituted or substituted monovalent hydrocarbon group having 1 to 10 carbon atoms), R¹² _ThreeSi-group (R¹²Can be blocked with one or more monovalent substituents selected from an amino group, an alkylamino group and a group having a phosphorus atom to obtain a hydroxyl-blocked polymer derivative.
[0066]
Here, examples of the unsubstituted or substituted monovalent hydrocarbon group having 1 to 10 carbon atoms include alkyl groups such as methyl, ethyl, propyl, isopropyl, t-butyl, and pentyl groups, and phenyl groups. An aryl group such as a tolyl group, an aralkyl group such as a benzyl group, an alkenyl group such as a vinyl group, a hydrogen atom of these groups partially or entirely substituted with a halogen atom, a cyano group, a hydroxyl group, an amino group, etc. These can be used alone or in combination of two or more.
[0067]
In this case, for blocking the hydroxyl groups of the linear polymer compounds (a) to (c) having an oxyalkylene chain by the substituent, (1) a polymer containing an ion conductive salt at a high concentration has a low dielectric constant. In the polymer matrix, recombination between dissociated cations and counter anions is likely to occur, resulting in a decrease in conductivity. However, if the polarity of the polymer matrix is increased, ion association is less likely to occur. The purpose of increasing the dielectric constant of the matrix polymer by introducing a polar group into the hydroxyl groups of the linear polymer compounds (a) to (c) and (2) the linear polymer compounds (a) to (c) are hydrophobic It has the purpose of imparting excellent properties such as heat resistance and flame retardancy.
[0068]
Here, (1) In order to increase the dielectric constant of the linear polymer compounds (a) to (c), the linear polymer compounds (a) to (c) having an oxyalkylene chain and the reactivity with respect to a hydroxyl group. By reacting with a compound having a hydroxyl group, the linear polymer compound is blocked with a highly polar substituent of the hydroxyl group.
Such a highly polar substituent is not particularly limited, but is preferably a neutral substituent rather than an ionic substituent, for example, an unsubstituted or substituted monovalent having 1 to 10 carbon atoms. Hydrocarbon group, R¹²CO-group (R¹²Is the same as above). Moreover, it can also block with an amino group, an alkylamino group, etc. as needed.
[0069]
On the other hand, (2) when imparting hydrophobicity and flame retardancy to the linear polymer compounds (a) to (c), the hydroxyl group of the linear polymer compound is a halogen atom, R¹² _ThreeSi-group (R¹²Is blocked with a group having a phosphorus atom or the like.
Here, the substituent will be specifically described. Examples of the halogen atom include fluorine, bromine, chlorine and the like. As an unsubstituted or substituted monovalent hydrocarbon group having 1 to 10 carbon atoms (preferably 1 to 8 carbon atoms). The same thing as the above can be illustrated.
[0070]
R¹² _ThreeAs Si-group, R¹²Is an unsubstituted or substituted monovalent hydrocarbon group as described above having 1 to 10 carbon atoms (preferably 1 to 6 carbon atoms), preferably R¹²Is an alkyl group, and a trialkylsilyl group, particularly a trimethylsilyl group is preferred. Further, the substituent may be an amino group, an alkylamino group, a group having a phosphorus atom, or the like.
Here, the terminal blocking ratio by the substituent is preferably 10 mol% or more, more preferably 50 mol% or more, and still more preferably 90 mol% or more. And can be blocked (blocking rate is about 100 mol%).
[0071]
In addition, all terminal hydroxyl groups of the polymer molecular chain are halogen atoms, R¹² _ThreeBlocking with a Si-group or a group having a phosphorus atom may lower the ability of the polymer itself to dissolve the ionic conductive salt, so it is necessary to introduce an appropriate amount of substituents while considering the degree of solubility. . Specifically, it is 10 to 95 mol%, preferably 50 to 95 mol%, more preferably 50 to 90 mol% with respect to all terminals (hydroxyl groups).
In the present invention, among the above substituents, a cyano group-substituted monovalent hydrocarbon group is particularly preferable, and specifically, a cyano group, a cyanobenzyl group, a cyanobenzoyl group, a substituent in which a cyano group is bonded to another alkyl group. Etc.
[0072]
As the (d) cyano group-substituted monovalent hydrocarbon group-substituted polyvinyl alcohol derivative, the polyvinyl alcohol unit in the polymer compound having an average polymerization degree of 20 or more having a polyvinyl alcohol unit in the molecule represented by the general formula (5). A polymer compound in which part or all of the hydroxyl groups therein are substituted with a cyano group-substituted monovalent hydrocarbon group can also be suitably used.
That is, since the polymer compound has a relatively short side chain, the viscosity of the electrolyte composition can be kept low, and the penetration of the composition into a battery structure or the like can be performed quickly, such as a battery. Productivity and performance can be improved.
[0073]
Examples of such a polymer compound include polyvinyl alcohol in which part or all of the hydroxyl group is substituted with a cyanoethyl group, a cyanobenzyl group, a cyanobenzoyl group, and the like, and in view of the short side chain, particularly cyanoethyl polyvinyl Alcohol is preferred.
In addition, as a method of substituting the hydroxyl group of polyvinyl alcohol with a cyano group-substituted monovalent hydrocarbon group, various known methods can be employed.
[0074]
The compounding quantity of the compound which has two or more reactive double bonds in the said molecule | numerator is 1 weight% or more with respect to the whole composition for electrolytes, Preferably it is 5 to 40 weight%. If there are too few compounds having two or more reactive double bonds in the molecule, the film strength may not increase. On the other hand, if the amount is too large, the ability to dissolve the ionic conductive metal salt in the electrolyte composition may be reduced, and there may be inconveniences such as precipitation of salt, reduced strength, and brittleness.
[0075]
The method for obtaining the polymer gel electrolyte by gelling the above-described electrolyte composition is not particularly limited, and examples thereof include the following.
That is, by irradiating the electrolyte solution, the compound having two or more reactive double bonds in the molecule with ultraviolet rays, electron beams, X-rays, γ-rays, microwaves, high-frequency waves, etc., or by heating, A three-dimensional network structure is formed, and a polymer gel electrolyte containing an electrolyte solution can be obtained.
In addition, the composition obtained by blending the electrolyte solution, the compound having a reactive double bond in the molecule, and the linear polymer compound is irradiated with ultraviolet rays or the like in the same manner as described above, and heated. Three-dimensional cross-linked network (semi-IPN) structure in which a three-dimensional network structure formed by reacting or polymerizing a compound having two or more reactive double bonds with each other and a molecular chain of a linear polymer compound are entangled with each other It is possible to obtain a polymer gel electrolyte having
[0076]
As the polymerization reaction, a radical polymerization reaction is preferably performed. When the polymerization reaction is performed, a polymerization initiator is usually added.
Such a polymerization initiator (catalyst) is not particularly limited, and various known polymerization initiators as shown below can be used.
[0077]
For example, acetophenone, trichloroacetophenone, 2-hydroxy-2-methylpropiophenone, 2-hydroxy-2-methylisopropiophenone, 1-hydroxycyclohexyl ketone, benzoin ether, 2,2-diethoxyacetophenone, benzyldimethyl ketal, etc. Photopolymerization initiators, high temperature thermal polymerization initiators such as cumene hydroperoxide, t-butyl hydroperoxide, dicumyl peroxide, di-t-butyl peroxide, benzoyl peroxide, lauroyl peroxide, persulfate, 2,2 ' -Thermal polymerization initiators such as azobis (2,4-dimethylvaleronitrile), 2,2'-azobis (4-methoxy-2,4-dimethylvaleronitrile), 2,2'-azobisisobutyronitrile, Hydrogen peroxide, ferrous salt, persulfate, acidic sodium sulfite Low temperature thermal polymerization initiators (redox initiators) such as lithium, cumene hydroperoxide, ferrous salt, benzoyl peroxide, dimethylaniline, peroxides, organometallic alkyls, triethyl boron, diethyl zinc, oxygen, organometallic alkyls, etc. Can be used.
[0078]
One of these polymerization initiators can be used alone or in admixture of two or more, and the addition amount is 0.1 to 1 part by weight, preferably 0 with respect to 100 parts by weight of the electrolyte composition. .1 to 0.5 parts by weight. If the addition amount of the catalyst is less than 0.1 parts by weight, the polymerization rate may be significantly reduced. On the other hand, if the amount exceeds 1 part by weight, the reactivity is not affected and only the reagent is wasted.
[0079]
The polymer gel electrolyte has a three-dimensional network structure obtained by reacting a compound having two or more reactive double bonds in the molecule, has excellent strength, and has high shape retention ability. . Furthermore, when a linear polymer compound is used to form a strong semi-interpenetrating polymer network structure in which the polymer compound is entangled in the three-dimensional network structure, the compatibility between different polymer chains should be improved. In addition, the interphase coupling force can be increased, and as a result, the shape retention ability can be dramatically improved.
[0080]
In addition, in the case of having a semi-interpenetrating polymer network structure, the molecular structure is amorphous and not crystallized, so that the ionic conductor can move smoothly in the molecule, and the molecular structure is 10 at room temperature.^-3-10^-FourIn addition to having high conductivity of about S / cm and high adhesiveness, there is no fear of evaporation and liquid leakage, and it is suitably used as a polymer gel electrolyte for various secondary batteries such as lithium ion secondary batteries. It is something that can be done.
[0081]
In addition, as a method of thinning the polymer gel electrolyte, for example, by using means such as roller coating such as applicator roll, screen coating, doctor blade method, spin coating, bar coder, etc., an electrolyte film having a uniform thickness is formed. Can be formed.
[0082]
As the positive electrode of the non-aqueous electrolyte secondary battery, one obtained by applying a positive electrode binder composition containing a binder polymer and a positive electrode active material as main components on both the front and back surfaces or one surface of a positive electrode current collector is used. it can.
In addition, after melt-kneading the binder composition for positive electrodes which contains a binder polymer and a positive electrode active material as a main component, a positive electrode can also be formed by extrusion and film forming.
[0083]
The binder polymer is not particularly limited as long as it is a polymer that can be used in the application. For example, (I) a thermoplastic resin having a swelling ratio in the range of 150 to 800% by weight obtained from the following formula, (II) It is preferable to use a fluorine polymer material or the like alone or in combination of two or more of (I) and (II).
In the thermoplastic resin (I), the swelling ratio obtained from the following formula is in the range of 150 to 800% by weight, more preferably 250 to 500% by weight, and still more preferably 250 to 400% by weight.
[0084]
[Expression 1]

[0085]
As such a thermoplastic resin, it is preferable to use a thermoplastic polyurethane-based resin obtained by reacting (D) a polyol compound, (E) a polyisocyanate compound, and (F) a chain extender as necessary. .
The thermoplastic polyurethane resin includes a polyurethane urea resin having a urethane bond and a urea bond in addition to the polyurethane resin having a urethane bond.
[0086]
As the polyol compound of component (D), it is preferable to use polyester polyol, polyester polyether polyol, polyester polycarbonate polyol, polycaprolactone polyol, or a mixture thereof.
The number average molecular weight of the polyol compound as the component (D) is preferably 1,000 to 5,000, more preferably 1,500 to 3,000. If the number average molecular weight of the polyol compound is too small, physical properties such as heat resistance and tensile elongation of the resulting thermoplastic polyurethane resin film may be lowered. On the other hand, when too large, the viscosity at the time of synthesis may increase, and the production stability of the resulting thermoplastic polyurethane resin may decrease. In addition, all the number average molecular weights of a polyol compound here mean the number average molecular weight computed based on the hydroxyl value measured based on JISK1577.
[0087]
Examples of the polyisocyanate compound of component (E) include aromatic diisocyanates such as tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, p-phenylene diisocyanate, 1,5-naphthylene diisocyanate, xylylene diisocyanate, and hexamethylene. Aliphatic or alicyclic diisocyanates such as diisocyanate, isophorone diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, hydrogenated xylylene diisocyanate and the like.
[0088]
As the chain extender of the component (F), it is preferable to use a low molecular weight compound having two isocyanate groups and reactive active hydrogen atoms in the molecule and having a molecular weight of 300 or less.
As such a low molecular weight compound, various known compounds can be used, for example, aliphatic diols such as ethylene glycol, propylene glycol and 1,3-propanediol, and 1,4-bis (β-hydroxyethoxy) benzene. , 1,4-cyclohexanediol, aromatic diols such as bis (β-hydroxyethyl) terephthalate or alicyclic diols, diamines such as hydrazine, ethylenediamine, hexamethylenediamine, xylylenediamine, amino alcohols such as adipic acid hydrazide, etc. These can be used alone or in combination of two or more.
[0089]
In the thermoplastic polyurethane-based resin, 5 to 200 parts by weight, preferably 20 to 100 parts by weight of the polyisocyanate compound (E) is added to 100 parts by weight of the polyol compound (D). Add 1 to 200 parts by weight, preferably 5 to 100 parts by weight, of the chain extender of component F).
[0090]
Further, as the binder polymer (I), a thermoplastic resin containing a unit represented by the following general formula (8) can also be used.
[0091]
[Chemical formula 5]

(In the formula, r represents 3 to 5, and s represents an integer of 5 or more.)
[0092]
Next, as the fluorine-based polymer material that is the binder polymer of (II), for example, polyvinylidene fluoride (PVDF), a copolymer of vinylidene fluoride and hexafluoropropylene [P (VDF-HFP)], A copolymer of vinylidene fluoride and chloroethylene trifluoride [P (VDF-CTFE)] or the like is preferably used. Among these, those having a vinylidene fluoride content of 50% by weight or more, particularly 70% by weight or more (the upper limit is about 97% by weight) are suitable.
In this case, the weight average molecular weight of the fluoropolymer is not particularly limited, but is preferably 500,000 to 2,000,000, and more preferably 500,000 to 1,500,000. If the weight average molecular weight is too small, the physical strength may be significantly reduced.
[0093]
As the positive electrode current collector, stainless steel, aluminum, titanium, tantalum, nickel, or the like can be used. Among these, aluminum foil or aluminum oxide foil is preferable in terms of both performance and price. As this positive electrode current collector, various forms such as a three-dimensional structure such as a foil shape, an expanded metal shape, a plate shape, a foam shape, a wool shape, and a net shape can be adopted.
[0094]
The positive electrode active material is appropriately selected according to the type of the battery, and when the positive electrode of the lithium secondary battery is used, for example, CuO, Cu₂O, Ag₂O, CuS, CuSO₂Group I metal compounds such as TiS, SiO₂, SnO group IV metal compounds, V₂O_Five, V₆O₁₃, VO_x, Nb₂O_Five, Bi₂O_Three, Sb₂O_ThreeGroup V metal compounds such as CrO_Three, Cr₂O_Three, MoO_Three, MoS₂, WO_Three, SeO₂Group VI metal compounds such as MnO₂, Mn₂O_FourGroup VII metal compounds such as Fe₂O_Three, FeO, Fe_ThreeO_Four, Ni₂O_Three, NiO, CoO₂Group VIII metal compounds such as polypyrrole, polyaniline, polyparaphenylene, polyacetylene, and polyacenic materials.
[0095]
In the case of a lithium ion secondary battery, a chalcogen compound capable of adsorbing and releasing lithium ions, a lithium ion-containing chalcogen compound (lithium-containing composite oxide), or the like is used.
Here, as a chalcogen compound capable of adsorbing and desorbing lithium ions, for example, FeS₂TiS₂, MoS₂, V₂O_Five, V₆O₁₃, MnO₂Etc.
On the other hand, as the lithium ion-containing chalcogen compound (lithium-containing composite oxide), for example, LiCoO₂LiMnO₂, LiMn₂O_FourLiMo₂O_Four, LiV_ThreeO₈LiNiO₂, Li_xNi_yM_1-yO₂(However, M represents at least one metal element selected from Co, Mn, Ti, Cr, V, Al, Sn, Pb, and Zn, and 0.05 ≦ x ≦ 1.10, 0.5 ≦ y ≦ 1.0).
[0096]
In addition to the above-described binder resin and positive electrode active material, a conductive material can be added to the positive electrode binder composition as necessary. Examples of the conductive material include carbon black, ketjen black, acetylene black, carbon whisker, carbon fiber, natural graphite, and artificial graphite.
[0097]
In the positive electrode binder composition, the amount of the positive electrode active material added is 1,000 to 5,000 parts by weight, preferably 1,200 to 3,500 parts by weight, based on 100 parts by weight of the binder resin. The addition amount is 20 to 500 parts by weight, preferably 50 to 400 parts by weight.
[0098]
The negative electrode used in the non-aqueous electrolyte secondary battery of the present invention is formed by applying a negative electrode binder composition containing a binder polymer and a negative electrode active material as main components to both front and back surfaces or one surface of a negative electrode current collector. is there. Here, as a binder polymer, the same thing as a positive electrode can be used.
In addition, after melt-kneading the binder composition for negative electrodes which contains a binder polymer and a negative electrode active material as a main component, you may form an anode by extruding and film-forming.
[0099]
Examples of the negative electrode current collector include copper, stainless steel, titanium, and nickel. Among these, a copper foil or a metal foil whose surface is coated with a copper plating film is preferable in terms of both performance and price. . As this current collector, various forms such as a three-dimensional structure such as a foil shape, an expanded metal shape, a plate shape, a foam shape, a wool shape, and a net shape can be adopted.
[0100]
As the negative electrode active material, an alkali metal, an alkali alloy, a carbonaceous material, the same material as the positive electrode active material, or the like can be used.
In this case, examples of the alkali metal include Li, Na, and K. Examples of the alkali metal alloy include metals Li, Li—Al, Li—Mg, Li—Al—Ni, Na, Na—Hg, and Na. -Zn etc. are mentioned.
Examples of the carbonaceous material include graphite, carbon black, coke, glassy carbon, carbon fiber, or a sintered body thereof.
[0101]
In the case of a lithium ion secondary battery, a material that reversibly occludes and releases lithium ions is used.
As such materials, carbonaceous materials such as non-graphitizable carbon materials and graphite materials can be used. More specifically, pyrolytic carbons, cokes (pitch coke, knee coke, petroleum coke), graphites, glassy carbons, organic polymer compound fired bodies (phenol resin, furan resin, etc.) at an appropriate temperature. Carbonaceous materials such as carbon fiber and activated carbon can be used. In addition, as materials capable of reversibly occluding and releasing lithium ions, polymers such as polyacetylene and polypyrrole, SnO, and the like can be used.₂Oxides such as these can also be used.
In addition, a conductive material can be added to the negative electrode binder composition as necessary. Examples of the conductive material include the same materials as the positive electrode binder described above.
[0102]
In the above binder composition for a negative electrode, the addition amount of the negative electrode active material is 500 to 1,700 parts by weight, preferably 700 to 1,300 parts by weight with respect to 100 parts by weight of the binder polymer, and the addition amount of the conductive material is 0. -70 weight part, Preferably it is 0-40 weight part.
[0103]
The negative electrode binder composition and the positive electrode binder composition are usually used in the form of a paste by adding a dispersion medium. Examples of the dispersion medium include polar solvents such as N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, and dimethylsulfoamide. In this case, the addition amount of the dispersion medium is about 30 to 300 parts by weight with respect to 100 parts by weight of the positive electrode or negative electrode binder composition.
[0104]
The method of thinning the positive electrode and the negative electrode is not particularly limited, but for example, using means such as applicator roll roller coating, screen coating, doctor blade method, spin coating, bar coater, etc., after drying The active material layer is preferably formed to a uniform thickness of 10 to 200 μm, particularly 50 to 150 μm.
[0105]
The non-aqueous electrolyte secondary battery is formed by laminating, folding, or winding a battery structure in which a separator is interposed between the positive electrode and the negative electrode, and further forming a laminate type or a coin type. This can be assembled by storing it in a battery container such as a battery can or a laminate pack, and sealing it if it is a battery can, or heat sealing if it is a laminate pack. In this case, after the separator is interposed between the positive electrode and the negative electrode and accommodated in the battery container, it is filled with the nonaqueous electrolyte and the composition for electrolyte, and sufficiently penetrates between the electrodes and between the separator and the electrodes, In the case of an electrolyte composition, it is cured by heating or the like.
[0106]
As described above, the non-aqueous electrolyte secondary battery to which the voltage control method of the present invention is applied has excellent overcharge characteristics, and there is no danger even when overcharged without providing a protection circuit. The manufacturing process can be simplified and the manufacturing cost can be reduced.
In addition, when a separator with a high porosity and a polymer gel electrolyte are used in combination, it is possible to further reduce the occurrence rate of internal short circuit while maintaining the large current discharge characteristics of the secondary battery. .
[0107]
Therefore, the non-aqueous electrolyte secondary battery is a main power source for video cameras, laptop computers, mobile phones, PHS and other portable terminals, a power source for instantaneous power failure such as a personal computer including a memory backup power source, It can be suitably used for various applications such as application to automobiles or hybrid automobiles, and solar power generation energy storage systems used in combination with solar cells.
[0108]
【Example】
Hereinafter, although a synthesis example, an Example, and a comparative example are given and this invention is demonstrated more concretely, this invention is not restrict | limited to the following Example.
[0109]
[Synthesis Example 1] Synthesis of polyvinyl alcohol derivative
In a reaction vessel equipped with a stirring blade, 3 parts by weight of polyvinyl alcohol (average polymerization degree 500, vinyl alcohol fraction = 98% or more), 20 parts by weight of 1,4-dioxane, and 14 parts by weight of acrylonitrile are charged and stirred. Then, an aqueous solution in which 0.16 parts by weight of sodium hydroxide was dissolved in 1 part by weight of water was gradually added and stirred at 25 ° C. for 10 hours.
Next, neutralization was performed using an ion exchange resin (trade name; Amberlite IRC-76, manufactured by Organo Corporation). After the ion exchange resin was filtered off, 50 parts by weight of acetone was added to the solution to separate insoluble matters. The acetone solution was placed in a dialysis membrane tube and dialyzed against running water. The polymer precipitated in the dialysis membrane tube was collected, dissolved again in acetone and filtered, and acetone was evaporated to obtain cyanoethylated PVA derivative of Synthesis Example 1.
The obtained polymer derivative was not able to confirm the absorption of the hydroxyl group in the infrared absorption spectrum, and it was confirmed that the hydroxyl group was completely blocked with a cyanoethyl group (blocking rate: 100%).
[0110]
3 parts by weight of the obtained PVA polymer was mixed with 20 parts by weight of dioxane and 14 parts by weight of acrylonitrile. To this mixed solution was added an aqueous sodium hydroxide solution in which 0.16 parts by weight of sodium hydroxide was dissolved in 1 part by weight of water, and the mixture was stirred at 25 ° C. for 10 hours.
Next, it neutralized using the ion exchange resin (Brand name; Amberlite IRC-76, Organo Co., Ltd. product). After the ion exchange resin was filtered off, 50 parts by weight of acetone was added to the solution to separate insoluble matters. The filtered acetone solution is put into a dialysis membrane tube, dialyzed against running water, the polymer precipitated in the dialysis membrane tube is collected, dissolved again in acetone, filtered, and acetone is evaporated to cyanoethylated PVA polymer derivative Got.
The obtained polymer derivative was not able to confirm the absorption of the hydroxyl group in the infrared absorption spectrum, and it was confirmed that the hydroxyl group was completely blocked with a cyanoethyl group (blocking rate: 100%).
[0111]
[Synthesis Example 2] Synthesis of thermoplastic polyurethane resin
In a reactor equipped with a stirrer, a thermometer and a condenser tube, 64.34 parts by weight of polycaprolactone diol (Placcel 220N, manufactured by Daicel Chemical Industries, Ltd.) previously dehydrated and 4,4′-diphenylmethane diisocyanate 28. After adding 57 parts by weight and stirring and mixing at 120 ° C. for 2 hours under a nitrogen stream, 7.09 parts by weight of 1,4-butanediol was added and reacted at 120 ° C. under a nitrogen stream in the same manner. . The reaction was stopped when the reaction proceeded and the reaction product became rubbery. Thereafter, the reaction product was taken out from the reactor and heated at 100 ° C. for 12 hours. After confirming that the absorption peak of the isocyanate group had disappeared in the infrared absorption spectrum, the heating was stopped to obtain a solid polyurethane resin.
[0112]
The weight average molecular weight (Mw) of the obtained polyurethane resin was 1.71 × 10.^FiveMet. A polyurethane resin solution was obtained by dissolving 8 parts by weight of this polyurethane resin in 92 parts by weight of N-methyl-2-pyrrolidone.
[0113]
[Example 1] Secondary battery 1
<Preparation of positive electrode>
LiCoO as positive electrode active material₂(Manufactured by Shodo Chemical Co., Ltd.), Ketjen Black EC (manufactured by Lion Corporation) which is a conductive material, polyvinylidene fluoride (PVDF1300, manufactured by Kureha Chemical Co., Ltd.), and polyurethane (PU) of Synthesis Example 2 Each was mixed at a mass blending ratio of 100.0: 4.35: 4.13: 2.72, and further 1-methyl-2-pyrrolidone (NMP, LiCoO₂The slurry was dissolved in 100. mass ratio 56.74 (manufactured by Wako Pure Chemical Industries, Ltd.), and dispersed and mixed to prepare a slurry.
This slurry was applied to an aluminum sheet (thickness 0.020 mm, manufactured by Nihon Foil Co., Ltd.), dried and rolled, and 50.0 mm (inside, applied portion: 40.0 mm) × 20.0 mm and 50.mm. Cut to 0 × 270.0 mm to obtain a positive electrode.
[0114]
<Preparation of negative electrode>
MCMB (MCMB6-28, manufactured by Osaka Gas Chemical Co., Ltd.) and polyvinylidene fluoride (PVDF900, manufactured by Kureha Chemical Co., Ltd.), which are negative electrode active materials, are mixed at a mass mixing ratio of 100.0: 8.70, respectively. Furthermore, it was dissolved in NMP (mass ratio 121.7 with respect to MCMB100), and dispersed and mixed to prepare a slurry.
This slurry was applied to a copper foil (thickness 0.010 mm, manufactured by Nippon Foil Co., Ltd.), then dried and rolled, and 50.0 mm (inside, applied portion: 40.0 mm) × 20.0 mm and 50.mm. Cut to 0 × 270.0 mm to obtain a negative electrode.
[0115]
<Production of electrode group>
A positive electrode produced as described above in which a cellulose separator (thickness: 0.035 mm, FT40-35, manufactured by Nippon Advanced Paper Industries Co., Ltd.) was cut into 54.0 × 260.0 mm and folded into two. Two electrodes and two negative electrodes were assembled facing each other, and 30 CB (t = 30 μm, 50.0 mm × 20.0 mm) welded with Al tape was used as an Al / AlOx reference electrode to obtain an electrode group through a separator.
[0116]
<Preparation of electrolyte solution>
Ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), and vinylene carbonate (VC) were mixed at a mass ratio of 100.0: 115.9: 26.15: 2.479. LiPF₆Was dissolved to a concentration of 1M to prepare an electrolyte solution.
[0117]
<Preparation of pregel composition>
0.1076, NK ester M-20G (monomethacrylate), NK ester 9G (dimethacrylate), NK ester A-TMPT (trimethacrylate) with respect to 100 mass of EC in the electrolyte solution ) (Both manufactured by Shin-Nakamura Chemical Co., Ltd.), 8.475, 12.05, 1.014 and 1.550 of 2,2′-azobis (2,4-dimethylvaleronitrile) were added, The pregel composition was obtained by stirring and mixing.
[0118]
<Production of battery>
After measuring the outer diameter length of the electrode group produced as described above and injecting the pregel composition having the same capacity (100.0 vol%) with respect to the calculated volume, the pressure was reduced to about 76 Torr and laminate packing was performed. .
Then, it heated at 55 degreeC for 2 hours and 80 degreeC for 30 minutes, the pregel composition was gelatinized, and the nonaqueous electrolyte secondary battery was obtained.
[0119]
[Example 2]
A cellulose separator (thickness: 0.035 mm, FT40-35, manufactured by Nippon Advanced Paper Industries Co., Ltd.) is wound on the positive electrode and the negative electrode obtained in Example 1 through 54.0 × 670.0 mm, and an electrode group A nonaqueous electrolyte secondary battery was obtained in the same manner as in Example 1 except that was manufactured.
[0120]
[Comparative Example 1]
NK ester M-20G (monomethacrylate), NK ester 9G (dimethacrylate), NK ester A-TMPT (trimethacrylate), 2,2'-azobis (2,4-dimethylvaleronitrile) at the time of preparing the pregel composition A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that it was not used.
[0121]
[Comparative Example 2]
NK ester M-20G (monomethacrylate), NK ester 9G (dimethacrylate), NK ester A-TMPT (trimethacrylate), 2,2'-azobis (2,4-dimethylvaleronitrile) at the time of preparing the pregel composition A nonaqueous electrolyte secondary battery was produced in the same manner as Example 2 except that it was not used.
[0122]
For the nonaqueous electrolyte secondary batteries obtained in Example 1 and Comparative Example 1, the relationship between the charge capacity and the battery voltage and the relationship between the charge capacity and the positive electrode and negative electrode voltages were measured, and the results are shown in FIGS. Indicated.
The Faraday reaction of the positive electrode active material
LiCoO₂  → Li_xCoO₂  + (1-x) Li⁺  + (1-x) e^-
The capacity of the positive electrode active material calculated from the theoretical value 137 mAh / g of the electric capacity corresponding to x = 0.5 in the battery was defined as the battery capacity, and the charged state was defined as 100%.
[0123]
This secondary battery sample was charged to 1.5 V at a current rate of 0.01 C as an initial charge, then charged to 3.2 V at a charge rate of 0.05 C, and then at 55 ° C. for 2 hours. Further, aging was performed at 80 ° C. for 30 minutes.
Next, set current 0.5C, set voltage 4.2V, constant current-constant voltage charge at the end of 0.1C current, pause 1 hour, constant current discharge 3.0V end at 1.0C, pause 1 hour 1 As a cycle, three cycles were performed, and this time point was set as an initial state of the battery sample. After that, as a test for evaluating reversibility with respect to the charge amount, a charge amount of X% was charged at a current rate of 0.5 C, and after a pause of 1 hour, a constant current discharge was performed at a current rate of 1.0 C and 3.0 V termination. It was. At this time, charging / discharging was performed while increasing the charge amount X in order as X = 50.0, 75.0, 100.0, 150.0, 200.0 and 250.0.
[0124]
FIG. 3 shows the relationship between the charge capacity of the secondary battery obtained in Example 1 and the battery voltage. As can be seen from the above, in the secondary battery of Example 1, not only the charge voltage does not increase and the safety is excellent even when the charge amount increases, but also the discharge voltage does not significantly decrease. Recognize. In particular, it can be said that the change in the discharge voltage is small after the charge amount of 150%.
[0125]
On the other hand, FIG. 4 shows the relationship between the charge capacity of the secondary battery obtained in Comparative Example 1 and the battery voltage. As can be seen from this, in the secondary battery of Comparative Example 1, when the amount of charge increases, not only does the charge voltage increase rapidly, causing a problem in safety, but also the discharge voltage is significantly reduced. When charging exceeds 250%, there is a risk of rupture and ignition during charging, and the positive electrode loses reversibility and cannot obtain the original discharge capacity.
[0126]
FIG. 5 shows the relationship between the charge capacity of the secondary battery obtained in Example 1 and the voltages of the positive electrode and the negative electrode. FIG. 6 shows the charge capacity of the secondary battery obtained in Comparative Example 1 and the positive electrode. The relationship between the negative electrode voltage and the negative electrode voltage is shown. As can be seen from this, in the secondary battery of Example 1, the discharge potentials of the positive electrode and the negative electrode show a behavior with little change even if the overcharge region is experienced as 150, 200, 250%. On the other hand, in the secondary battery of Comparative Example 1, when the charge amount exceeds 150%, a significant potential change is seen in the positive electrode, the reversibility of the active material is lost, and the original discharge capacity It can be seen that cannot be obtained.
[0127]
FIG. 7 shows the relationship between the charge amount and voltage of the secondary batteries obtained in Example 2 and Comparative Example 2, and the relationship between the charge amount and battery temperature. As can be seen from the above, in the secondary battery of Comparative Example 2, the temperature rises near the charge amount of 160%, while the voltage rises and the temperature rises suddenly at the charge amount of 190%. In the battery, the temperature starts to increase from the charged amount of 100%, but it can be seen that no rapid voltage increase or temperature increase has occurred thereafter.
[0128]
Regarding the secondary batteries obtained in Example 1 and Comparative Example 1, the reaction occurring at the positive electrode can be explained by the voltammogram shown in FIG.
That is, in Comparative Example 1, 1.05 V vs. Ag / AgO_xNear and 1.45V vs. Ag / AgO_xIn the vicinity,
(1) LiCoO₂  → Li_0.5CoO₂
▲ 2 ▼ Li_0.5CoO₂  → Li_0.3CoO₂
Oxidation waves resulting from this reaction can be observed. In addition, 1.60 V vs. Ag / AgO_xAn oxidation wave of (3) can be observed in the vicinity, and the active material loses reversibility by oxidation after (3).
[0129]
On the other hand, in Example 1, 1.10V vs.. Ag / AgO_xIn the vicinity,
(1) LiCoO₂  → Li_0.5CoO₂Oxidation waves corresponding to can be observed. Furthermore, 1.40V vs. Ag / AgO_xIn the vicinity, an oxidation wave (4) different from (1) to (3) can be observed.
Due to the oxidation reaction (4), electric energy for charging is consumed, and as a result,
▲ 2 ▼ Li_0.5CoO₂  → Li_0.3CoO₂
Therefore, the reversibility of the active material is not lost, and unstable Li_0.3CoO₂Therefore, the safety of the secondary battery is ensured.
[0130]
[Examples 3 to 7]
<Preparation of electrolyte solution>
Diethyl carbonate (DEC), ethylene carbonate (EC), propylene carbonate (PC), and vinylene carbonate (VC) were mixed at a weight ratio of 50: 35: 13: 2, and this was mixed with LiPF.₆Was dissolved to a concentration of 1M to prepare an electrolyte solution.
[0131]
<Preparation of electrolyte composition>
100 parts by weight of pre-dehydrated polyethylene glycol dimethacrylate (number of oxylene units = 9), 70.15 parts by weight of methoxypolyethylene glycol monomethacrylate (number of oxylene units = 2), and 8.41 of trimethylolpropane trimethacrylate Part by weight was mixed, and 0.5 parts by weight of the polyvinyl alcohol derivative obtained in Synthesis Example 1 was added to 100 parts by weight of this mixed composition to obtain a pregel composition.
An electrolyte composition was obtained by adding 0.5 parts by weight of azobisisobutyronitrile to a mixture of 7 parts by weight of the resulting pregel composition and 93 parts by weight of the electrolyte solution.
[0132]
<Preparation of positive electrode>
LiCoO as positive electrode active material₂92 parts by weight, 4 parts by weight of ketjen black as a conductive material, 2.5 parts by weight of the polyurethane resin solution obtained in Synthesis Example 2, and 10 parts by weight of polyvinylidene fluoride in 90 parts by weight of N-methyl-2-pyrrolidone 38 parts by weight of the dissolved solution and 18 parts by weight of N-methyl-2-pyrrolidone were stirred and mixed to obtain a paste-like positive electrode binder composition. This positive electrode binder composition was applied onto an aluminum foil with a doctor blade so as to have a dry film thickness of 100 μm, dried at 80 ° C. for 2 hours, and roll-pressed so as to have a thickness of 80 μm to produce a positive electrode.
[0133]
<Preparation of negative electrode>
As a negative electrode active material, 92 parts by weight of MCMB (MCMB6-28, manufactured by Osaka Gas Chemical Co., Ltd.) and 80 parts by weight of a solution prepared by dissolving 10 parts by weight of polyvinylidene fluoride in 90 parts by weight of N-methyl-2-pyrrolidone; -40 parts by weight of methyl-2-pyrrolidone was stirred and mixed to obtain a paste-like negative electrode binder composition. This negative electrode binder composition was applied onto a copper foil with a doctor blade so as to have a dry film thickness of 100 μm, then dried at 80 ° C. for 2 hours, and roll-pressed to a thickness of 80 μm to produce a negative electrode. .
[0134]
<Production of battery>
Regarding the positive electrode and negative electrode produced as described above, the negative electrode has a negative electrode active material coating portion of 5.2 cm × 48.2 cm so that the positive electrode has a positive electrode active material layer coating portion size of 5 cm × 48 cm. Each was cut to a size of. However, at this time, an uncoated portion of the positive electrode active material was provided on the positive electrode, and an uncoated portion of the negative electrode active material was provided on the negative electrode.
Next, the aluminum terminal lead is attached to the uncoated part of the positive electrode active material layer of the positive electrode, and the nickel terminal lead is attached to the uncoated part of the negative electrode active material layer of the negative electrode by resistance welding. The positive electrode and the negative electrode to which the electrode was attached were vacuum-dried at 140 ° C. for 12 hours, and the dried positive electrode and negative electrode were laminated with a predetermined separator shown in Table 1 to prepare a flat electrode body. .
Subsequently, the positive electrode terminal and the negative electrode terminal are taken out from the positive electrode and the negative electrode, housed in an aluminum laminate case, and the terminal part is heat-sealed to form a battery structure, and the electrolyte composition prepared above is injected and vacuumed After impregnation, the aluminum laminate case was sealed by heat sealing. Thereafter, the mixture was heated and gelled at 55 ° C. for 2 hours and at 80 ° C. for 0.5 hour to obtain a nonaqueous electrolyte secondary battery.
[0135]
[Table 1]

[0136]
[1] Measurement of battery capacity and energy density
About the nonaqueous electrolyte secondary battery obtained in the above Examples 3-7, 120 mA (0.5 mA / cm at 25 ° C.)²: Equivalent to 0.2C), and charged to 4.2V, followed by constant voltage charging for 2 hours. Next, after resting for 5 minutes, the discharge voltage and energy density were measured by discharging at a constant current of 120 mA with a final voltage of 2.7V.
[0137]
[2] Overcharge characteristics test
[2-1] Overcharge test (25 ° C)
(1) About the secondary batteries of Examples 3, 5, 6 and 7 at 25 ° C., 600 mA (2.5 mA / cm²The overcharge test was performed with a constant current of 1 C (corresponding to 1 C) for an upper limit of 2.5 hours. During the 2.5 hour overcharge test (charging rate 250%), the maximum value of the battery voltage of the secondary battery of the example was 4.8 V, and the battery surface temperature did not exceed 40 ° C.
(2) On the other hand, the batteries of the comparative examples all showed a sudden rise in voltage of 5.5V before reaching the 250% overcharge point, and a sudden rise in temperature to a battery temperature of 100 ° C or higher. did.
(3) About the secondary battery of Example 4, 1800 mA (7.5 mA / cm at 25 ° C.²: 3C equivalent), and an overcharge test was conducted for 50 minutes as the upper limit. During the 50-minute overcharge test (charging rate 250%), the maximum value of the battery voltage of the secondary battery of Example 1 was 4.95 V, and the maximum temperature on the battery surface was 52.8 ° C.
(3) About the secondary battery of Example 4, 300 mA (1.25 mA / cm at 25 ° C.²: Equivalent to 0.5 C), and an overcharge test was performed with the upper limit of 4 hours. During the 4-hour overcharge test (charging rate 400%), the secondary battery of Example 4 had a maximum voltage of 4.58 V, and the surface temperature of the battery did not exceed 40 ° C.
[0138]
[2-2] Overcharge test (60 ° C)
(4) About the secondary battery of Example 3, 600 mA (2.5 mA / cm at 60 ° C.²: 1C equivalent) and an overcharge test was conducted with the upper limit being 2 hours. During the two-hour overcharge test (charging rate 200%), the secondary battery of Example 3 had a maximum voltage of 4.8 V, the surface temperature of the battery did not exceed 90 ° C., and it did not ignite or explode.
The test results are summarized in Table 2.
[0139]
[Table 2]

[0140]
【The invention's effect】
As described above, according to the voltage control method for a non-aqueous electrolyte secondary battery of the present invention, a substance that is oxidized at the electrode during overcharge is added to the non-aqueous electrolyte. The consumed electric energy is consumed not by the lithium release reaction from the positive electrode active material but by the electrode oxidation reaction of the material, and the rise of the battery voltage when the non-aqueous electrolyte secondary battery is overcharged is suppressed. It will be. In addition, since this electrode oxidation reaction occurs, it is extremely oxidizable and thermally unstable Li_<0.3CoO₂The risk of causing a runaway reaction of the battery is reduced, and a non-aqueous electrolyte secondary battery excellent in safety can be provided.
[Brief description of the drawings]
FIG. 1 is a graph showing the overcharge voltage and battery temperature of a conventional lithium secondary battery.
FIG. 2 is a graph showing the overcharge voltage and battery temperature of the lithium secondary battery of the present invention.
3 is a graph showing a voltage curve during charging / discharging for each charge amount in the secondary battery of Example 1. FIG.
4 is a graph showing voltage curves during charging / discharging for each charge amount in the secondary battery of Comparative Example 1. FIG.
5 is a graph showing potential changes during charging / discharging with respect to respective charge amounts in the secondary battery of Example 1. FIG.
6 is a graph showing potential changes during charging / discharging with respect to respective charge amounts in the secondary battery of Comparative Example 1. FIG.
7 is a graph showing changes in voltage and battery surface temperature during charging in the secondary batteries of Example 2 and Comparative Example 2. FIG.
8 is a graph showing a cyclic voltammogram of a positive electrode in the secondary batteries of Example 1 and Comparative Example 1. FIG.

Claims (8)

A non-aqueous solution comprising a positive electrode and a negative electrode comprising a material that absorbs and releases lithium and a binder polymer, at least one separator that separates both the positive and negative electrodes, and a non-aqueous electrolyte containing a lithium salt A voltage control method in the case where an electrolyte secondary battery is overcharged to a charge rate of 100% or more of the rated capacity,
A substance that is oxidized at the positive electrode by the electrical energy supplied during the overcharge is added to the non-aqueous electrolyte, and the substance is electrode oxidized to control the battery voltage during the overcharge to 4.1 to 5.2V. Is,
The voltage control method for a non-aqueous electrolyte secondary battery, wherein the substance oxidized at the positive electrode is an acrylic ester and / or a methacrylic ester . 2. The voltage control method for a nonaqueous electrolyte secondary battery according to claim 1, wherein the substance oxidized at the positive electrode is at least one selected from glycidyl methacrylate, glycidyl acrylate, methoxydiethylene glycol methacrylate, and methoxypolyethylene glycol methacrylate . The separator has a porosity of 40% or more, and oxygen and / or carbon dioxide is generated by the electrode oxidation, and the oxygen and / or carbon dioxide is produced in a small amount on the negative electrode by using Li ₂ O and lithium metal. The voltage control method for a nonaqueous electrolyte secondary battery according to claim 1, wherein the voltage is oxidized to Li ₂ CO ₃ . The non-aqueous electrolyte secondary battery, wherein the battery structure comprising by interposing a separator between the positive electrode and the negative electrode, and a battery container for housing them, according to claim 3, the battery container is sealed The voltage control method of the nonaqueous electrolyte secondary battery as described. The voltage control method for a non-aqueous electrolyte secondary battery according to claim 3 , wherein the separator has a thickness of 20 to 50 μm . The voltage of the nonaqueous electrolyte secondary battery according to claim 3 , wherein the Li ₂ CO ₃ and / or Li ₂ O are electrode-reduced to metallic lithium and / or lithium ions at the negative electrode by electric energy supplied during charging. Control method. The voltage control method for a non-aqueous electrolyte secondary battery according to claim 3 , wherein the separator comprises at least one of cellulose, polypropylene, polyethylene, and polyester and has a porosity of 60% or more . The electrode oxidation, reference electrode AlO _x claim 1 nonaqueous voltage control method of electrolyte secondary battery according to occur in the range of 1.40~1.60V respect.

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