JP3982221B2 - Lithium ion polymer secondary battery and method for synthesizing binder used for adhesion layer of battery - Google Patents

Description

【００２４】
【化２】

【００２５】
化学式（１）に示すように、ＰＶｄＦに放射線としてγ線を照射することによりＰＶｄＦの片末端にラジカルを形成する。化学式（２）に示すように、この片末端にラジカルを有するＰＶｄＦにアクリル酸を接触させて、ＰＶｄＦのラジカルにアクリル酸の二重結合部分がグラフト重合される。
【００２６】
また別の例として化学式（３）及び化学式（４）にＰＶｄＦとメタクリル酸のグラフト重合を示す。
【００２７】
【化３】

【００２８】
【化４】

【００２９】
化学式（３）に示すように、ＰＶｄＦが放射線としてγ線を照射することによりＰＶｄＦの片末端にラジカルを形成し、化学式（４）で片末端にラジカルを有するＰＶｄＦにメタクリル酸を接触させて、ＰＶｄＦのラジカルにメタクリル酸の二重結合部分がグラフト重合される。
【００３０】
グラフト重合は活性化した主基がグラフト化材料と接触している時間の長さ、放射線による主基の予備活性の程度、グラフト化材料が主基を透過できるまでの程度、主基及びグラフト化材料が接触しているときの温度等によりそれぞれ重合生成が異なる。グラフト化材料が酸である場合、グラフト化材料である化合物を含有する溶液をサンプリングして、アルカリにより滴定し、残留する酸化合物濃度を測定することにより、グラフト化の程度を観測することができる。得られた組成物中のグラフト化の割合は、最終質量の１０〜３０％が望ましい。
【００３１】
このようにして得られたグラフト重合された変性高分子化合物を密着層の第３結着剤とし、この第３結着剤を溶媒に溶解してポリマー溶液を作製し、ポリマー溶液中に導電性物質を分散させて第１及び第２密着層スラリーを調製する。導電性物質には粒径０．５〜３０μｍ、黒鉛化度５０％以上の炭素材が用いられる。第３結着剤と導電性物質との質量比（第３結着剤／導電性物質）が１３／８７〜５０／５０になるように混合して密着層のスラリーを調製する。溶媒にはジメチルアセトアミド（DiMethylAcetamide、以下、ＤＭＡという。）、アセトン、ジメチルフォルムアミド、Ｎ-メチルピロリドンが用いられる。
【００３２】
次いで、シート状の正極及び負極集電体をそれぞれ用意し、この正極及び負極集電体に調製した第１及び第２密着層スラリーをドクターブレード法によりそれぞれ塗工及び乾燥し、乾燥後の密着層厚さが０．５〜３０μｍの第１及び第２密着層を有する正極又は負極集電体を形成する。乾燥後の正極及び負極の密着層厚さは１〜１５μｍが好ましい。シート状の正極集電体としてはＡｌ箔が、負極集電体としてはＣｕ箔がそれぞれ挙げられる。ここでドクターブレード法とは、セラミックスをシート状に成型する方法の１つであり、キャリアフィルムやエンドレスベルト等のキャリア上に載せて運ばれるスリップの厚さをドクターブレードと呼ばれるナイフエッジとキャリアとの間隔を調整することによってシートの厚さを精密に制御する方法である。
【００３３】
次に、正極活物質層、負極活物質層及び電解質層に必要な成分をそれぞれ混合して正極活物質層塗工用スラリー、負極活物質層塗工用スラリー及び電解質層塗工用スラリーをそれぞれ調製する。
得られた正極活物質層塗工用スラリーを第１密着層を有する正極集電体上にドクターブレード法により塗布して乾燥し、圧延することにより正極を形成する。また負極も同様にして、得られた負極活物質層塗工用スラリーを第２密着層を有する負極集電体上にドクターブレード法により塗布して乾燥し、圧延することにより負極を形成する。正極又は負極活物質層は乾燥後の厚さが、２０〜２５０μｍとなるように形成する。電解質層は得られた電解質層塗工用スラリーを剥離紙上に電解質層の乾燥厚さが１０〜１５０μｍとなるようにドクターブレード法により塗工及び乾燥し、剥離紙より剥がして形成する。また、電解質層塗工用スラリーを正極表面や負極表面に塗工及び乾燥して電解質層を形成してもよい。それぞれ形成した正極と電解質層と負極を順に積層し、積層物を熱圧着することにより、図１に示すように、シート状の電極体が形成される。
【００３４】
最後に、この電極体にＮｉからなる正極リード及び負極リードをそれぞれ正極集電体及び負極集電体に溶接し、開口部を有する袋状に加工したラミネートパッケージ材に収納し、減圧条件下で熱圧着により開口部を封止して、シート状のリチウムイオンポリマー二次電池が作製できる。
【００３５】
【実施例】
次に本発明の実施例を比較例とともに説明する。
＜実施例１＞
先ず、第１及び第２結着剤としてＰＶｄＦ粉末５０ｇを、変性物質として１５質量％アクリル酸水溶液２６０ｇをそれぞれ用意した。次いで、ＰＶｄＦ粉末をポリエチレン製パックに入れて真空パックし、ＰＶｄＦへの吸収線量が５０ｋＧｙとなるようにコバルト６０をγ線源としてγ線を照射した。次に、γ線照射したＰＶｄＦ粉末をポリエチレン製パックより取出して窒素雰囲気に移し、１５質量％アクリル酸水溶液２６０ｇ中にＰＶｄＦを供給して８０℃に保持し、アクリル酸水溶液と反応させて上記化学式（２）に示すグラフト重合により生成したアクリル酸グラフト化ＰＶｄＦ（Acrylic Acid grafting PolyVinylidene Fluoride、以下、ＡＡ-ｇ-ＰＶｄＦという。）を合成した。
反応溶液のサンプルを採取し、ＰＶｄＦにグラフト重合反応したアクリル酸の減少量を滴定により逐次測定し、ＡＡ-ｇ-ＰＶｄＦ中のグラフト化されたアクリル酸基の含有割合が１７質量％になったら、反応を止めて得られた固体状生成物を純水で洗浄して乾燥させ、これを第３結着剤とした。
【００３６】
＜実施例２＞
変性物質を１５質量％メタクリル酸水溶液２６０ｇにした以外は実施例１と同様にして第３結着剤を得た。
＜実施例３＞
変性物質を１５質量％アクリル酸メチル水溶液２６０ｇにした以外は実施例１と同様にして第３結着剤を得た。
＜実施例４＞
変性物質を１５質量％メタクリル酸メチル水溶液２６０ｇにした以外は実施例１と同様にして第３結着剤を得た。
【００３７】
＜比較例１＞
第３結着剤として市販されているアクリル酸エステル-メタクリル酸エステル共重合体を用意した。
＜比較例２＞
第３結着剤として市販されているＰＶｄＦのホモポリマーを用意した。
＜比較例３＞
第３結着剤として市販されているＰＶｄＦのコポリマーを用意した。
＜比較例４＞
変性物質を１質量％クロトン酸を含む水溶液２６００ｇにした以外は実施例１と同様にして第３結着剤を得た。
【００３８】
＜比較評価１＞
実施例１〜４及び比較例１〜４で得られた第３結着剤を用いて以下の評価試験を行った。
(1) ジメチルアセトアミドに対する溶解性試験
実施例１〜４及び比較例１〜４で得られた第３結着剤をそれぞれ４ｇづつ採取し、このサンプルにＤＭＡ５６ｇを添加して６０℃まで加熱しながら撹拌し、ポリマー溶液とした。この溶液をガラスビンに保存し、一日放置した後の溶液中の沈殿状況を確認した。
【００３９】
(2) 銅箔及びアルミ箔に対する接着性試験
先ず、実施例１〜４及び比較例１〜４で得られた第３結着剤を用いて前述した評価試験(1)のポリマー溶液と同様のポリマー溶液をそれぞれ調製した。次いで、これらの溶液をそれぞれ幅３０ｍｍ、長さ２００ｍｍ、厚さ１４μｍの表面を脱脂したＣｕ箔に均一に塗布し、その上に、幅１０ｍｍ、長さ１００ｍｍ、厚さ２０μｍの表面を脱脂したＡｌ箔を貼り付けて接着性試験用ピール試料を作製した。作製した試料を乾燥機により大気中で８０℃、５日間の乾燥を行った。次に、乾燥した試料を剥離試験器によりＣｕ箔及びＡｌ箔に対する結着剤の評価を行った。剥離試験方法は、測定する際に試料のＣｕ箔側を試験台に固定し、Ｃｕ箔に接着しているＡｌ箔を垂直上方に１００ｍｍ／分の速度で引っ張り上げて、Ａｌ箔がＣｕ箔から引き剥がすのにかかる力を測定した。
【００４０】
(3) 電池の密着層に用いられる場合の電池のサイクル容量維持特性試験
先ず、実施例１〜４及び比較例１〜４で得られた第３結着剤をそれぞれ２ｇづつ採取し、このサンプルにＤＭＡ２００ｇを添加して６０℃まで加熱しながら撹拌し、ポリマー溶液とした。この溶液に比表面積１５０ｍ²／ｇの黒鉛粉末８ｇ及びこの黒鉛粉末を分散させるための分散剤１．２ｇをそれぞれ添加し、密着層スラリーを調製した。次いで、正極集電体として厚さ２０μｍ、幅２５０μｍのＡｌ箔を用意し、このＡｌ箔に調製した密着層スラリーをドクターブレード法により塗工及び乾燥し、乾燥後の密着層厚さを１０±１μｍの範囲内に制御した。また負極集電体として厚さ１４μｍ、幅２５０μｍのＣｕ箔を用意し、このＣｕ箔表面に調製した密着層スラリーをドクターブレード法により塗工及び乾燥し、乾燥後の密着層厚さを１０±１μｍの範囲内に制御した。次に、下記表１に示される各成分をボールミルで２時間混合することにより、正極活物質層塗工用スラリー、負極活物質層塗工用スラリー及び電解質層塗工用スラリーをそれぞれ調製した。
【００４１】
【表１】

【００４２】
得られた正極活物質塗工用スラリーを密着層を有するＡｌ箔表面に正極活物質層の乾燥厚さが８０μｍとなるようにドクターブレード法により塗工及び乾燥し、圧延することにより正極を形成した。同様に、負極活物質塗工用スラリーを密着層を有するＣｕ箔表面に負極活物質層の乾燥厚さが８０μｍとなるようにドクターブレード法により塗工及び乾燥し、圧延することにより負極を形成した。更に電解質層塗工用スラリーを乾燥厚さが５０μｍとなるように正極及び負極にそれぞれドクターブレード法により塗工し、これらの電解質層を有する正極及び負極を積層して熱圧着することにより、シート状の電極体を作製した。作製した電極体にＮｉからなる正極リード及び負極リードをそれぞれ正極集電体、負極集電体に溶接し、開口部を有する袋状に加工したラミネートパッケージ材に収納し、減圧条件下で開口部を熱圧着して封止し、シート状電池を作製した。
次に、得られたシート状電池を最大充電電圧４Ｖ、充電電流０．５Ａの条件で２．５時間の充電を行う充電工程と、０．５Ａの定電流放電で放電電圧が最低放電電圧となる２．７５Ｖとなるまで放電を行う放電工程とを１サイクルとして充放電サイクルを繰り返し、各サイクルの充放電容量をそれぞれ測定して初期放電容量の８０％迄低下するサイクル数を測定した。
【００４３】
(4) 電池の密着層に用いられる場合の密着層の集電体に対する密着性試験
先ず、実施例１〜４及び比較例１〜４で得られた第３結着剤を用いて前述した評価試験(3)のシート状電池と同様のシート状電池をそれぞれ作製した。次いで、この電池を７０℃環境下で、上記評価試験(3)と同様の条件での充放電サイクルを１００サイクル行った。その後、１００サイクルの充放電を終えたシート状電池の収納パッケージを除去し、電池の正極と負極を引き剥がしてそれぞれを分離し、分離した正極の密着層及び負極の密着層をピンセットでつまんで引っ張ったときに、密着層が集電体から剥離するか否かを確認した。
【００４４】
上記評価試験(1)〜(4)における評価結果を表２にそれぞれ示す。なお、表２中の評価試験(1)欄における記号は、次の意味である。
◎：均一な無沈殿溶液。
【００４５】
また、表２中の評価試験(4)欄における記号は、次の意味である。
◎：密着層が集電体への密着が極めて良好であり、剥離しない。
○：密着層が集電体から部分的に剥離する。
△：密着層が集電体から広い面積にわたって剥離する。
×：密着層が集電体から完全に剥離する。
【００４６】
【表２】

【００４７】
表２から明らかなように、評価試験(1)のＤＭＡに対する溶解特性は実施例１〜４及び比較例１〜４で得られた第３結着剤はそれぞれＤＭＡに完全に溶解することができ、更にこの溶液を一日放置しても沈殿は発生せず、塗工用スラリーとして適していることが判った。
評価試験(2)のＣｕ箔及びＡｌ箔に対する接着性試験では、比較例２〜４で得られた第３結着剤を用いた試験では、２Ｎ／ｃｍ以下となり、密着層材料として接着効果が不十分であることが判る。これに対して、実施例１〜４で得られた第３結着剤を用いてＣｕ箔に接着したＡｌ箔は、Ｃｕ箔からの剥離強度が全て１０Ｎ／ｃｍ以上となり、電池の活物質と集電体を接着するのに十分な強度を示した。
【００４８】
評価試験(3)のサイクル容量維持特性試験では、比較例１〜４の第３結着剤を用いた電池の８０％容量サイクル数に比べて実施例１〜４の第３結着剤を用いた電池の８０％容量サイクル数はそれぞれ高いサイクル数を示している。これは、実施例１〜４の第３結着剤が接着特性が優れており、電解液への耐久性が高いため、サイクル容量維持特性が向上されたと考えられる。
評価試験(4)の密着層の集電体に対する密着性試験では、実施例１〜４の第３結着剤を用いた密着層は、比較例１〜４の第３結着剤を用いた密着層に比べて集電体から剥離しにくく、集電体との接着が優れていることを示した。フッ素を含まない共重合体を第３結着剤とした比較例１はＣｕ箔及びＡｌ箔に対する密着特性が高いものの、耐電解液特性が不十分であり、充放電サイクルを繰り返した後では密着層が電池の集電体から剥離する現象が発生した。
【００４９】
以上の評価試験より、変性物質、特にアクリル酸、アクリル酸メチル、メタクリル酸、メタクリル酸メチルがＰＶｄＦにグラフト化した変性高分子化合物が第１及び第２密着層の第３結着剤に適していることが判った。
【００５０】
＜実施例５〜１１及び比較例５，６＞
先ず、第１及び第２結着剤としてＰＶｄＦ粉末５０ｇを、変性物質として１５質量％アクリル酸水溶液２６０ｇをそれぞれ用意した。次いで、ＰＶｄＦ粉末をポリエチレン製パックに入れて真空パックし、ＰＶｄＦへの吸収線量が５０ｋＧｙとなるようにコバルト６０をγ線源としてγ線を照射した。次に、γ線照射したＰＶｄＦ粉末をポリエチレン製パックより取出して窒素雰囲気に移し、１５質量％アクリル酸水溶液２６０ｇ中にＰＶｄＦを供給して８０℃に保持し、アクリル酸水溶液と反応させてＡＡ-ｇ-ＰＶｄＦを合成した。
反応溶液のサンプルを採取し、ＰＶｄＦにグラフト重合反応したアクリル酸の減少量を滴定により逐次測定し、ＡＡ-ｇ-ＰＶｄＦ中のグラフト化されたアクリル酸基の含有割合が２質量％（実施例５）、７質量％（実施例６）、１０質量％（実施例７）、１３質量％（実施例８）、１７質量％（実施例９）、２５質量％（実施例１０）、４０質量％（実施例１１）、１質量％（比較例５）及び５５質量％（比較例６）になったら、反応を止めて得られた固体状生成物を純水で洗浄して乾燥させ、これらをそれぞれ実施例５〜１１及び比較例５，６の第３結着剤とした。
【００５１】
＜比較評価２＞
実施例５〜１１及び比較例５，６で得られた第３結着剤を用いて比較評価１の評価試験(1)〜評価試験(4)と同様の試験をそれぞれ行い、９種類のＡＡ-ｇ-ＰＶｄＦにおけるアクリル酸基の含有割合による接着特性や電池の電気特性の影響について調査した。評価試験(1)及び評価試験(4)の結果を表３に、評価試験(2)の結果を図２に、評価試験(3)の結果を図３にそれぞれ示す。なお、表３中の評価試験(1)欄における記号は、次の意味である。
◎：均一な無沈殿溶液。
○：ＤＭＡへ溶解するが、溶液に沈殿が少量発生する。
×：ＤＭＡへ溶解できない。
【００５２】
また、表３中の評価試験(4)欄における記号は、次の意味である。
◎：密着層が集電体への密着が極めて良好であり、剥離しない。
○：密着層が集電体から部分的に剥離する。
×：密着層が集電体から完全に剥離する。
【００５３】
【表３】

【００５４】
表３より明らかなように、評価試験(1)のＤＭＡに対する溶解特性では、アクリル酸基の含有割合が２５質量％以下である実施例５〜９の第３結着剤は、ＤＭＡに完全に溶解し、放置しても沈殿が発生しなかった。アクリル酸基の含有割合が２５質量％の実施例１０の第３結着剤は、ＤＭＡへの溶解が困難になり、溶解した溶液を一日放置すると少量の沈殿が現れた。この少量の沈殿は溶液を更にホモジナイザで長時間撹拌することにより再び溶解する程度であり、銅箔やアルミ箔に接着するには問題ないレベルである。これに対してアクリル酸基の含有割合が５５質量％の比較例６ではＤＭＡに殆ど溶解できず、銅箔やアルミ箔に接着するのには適していないことが判る。なお、アクリル酸基の含有割合が１質量％の比較例５はＤＭＡに問題なく溶解した。
評価試験(2)のＣｕ箔及びＡｌ箔に対する接着性試験では、図２に示すように、ＡＡ-ｇ-ＰＶｄＦで接着したＣｕ箔及びＡｌ箔の接着強度は、ＡＡ-ｇ-ＰＶｄＦ中に含まれるアクリル酸基の含有割合と相関する。比較例６の結果では含有割合が５５質量％以上になると、接着効果が下がることが判る。これは評価試験(1)の結果からも明らかなように、ＡＡ-ｇ-ＰＶｄＦがＤＭＡへの溶解が不十分であったためと考えられる。また、アクリル酸基の含有割合が１質量％の比較例５でも、接着強度が減少した。実施例５〜１１の結果から十分な接着特性を得るためには、ＡＡ-ｇ-ＰＶｄＦ中のアクリル酸基の含有割合は２〜５０質量％が必要であり、１０〜３０質量％が好ましいことが判る。
【００５５】
評価試験(3)のサイクル容量維持特性試験では、図３に示したように、評価試験(2)の接着強度の試験結果と同様な傾向を示していた。
評価試験(4)の密着層の集電体に対する密着性試験では、表３より明らかなように、充放電サイクルを行った後の電池密着層を解析した結果、密着層の密着特性が評価試験(2)及び評価試験(3)と同様に、ＡＡ-ｇ-ＰＶｄＦ中のアクリル酸基の含有割合が２〜５０質量％であるとき、電池の結着剤として適しており、１０〜３０質量％が好ましいことが判る。
【００５６】
＜実施例１２〜１６及び比較例７，８＞
先ず、第１及び第２結着剤としてＰＶｄＦ粉末５０ｇを、変性物質として１５質量％アクリル酸水溶液２６０ｇをそれぞれ用意した。次いで、ＰＶｄＦ粉末をポリエチレン製パックに入れて真空パックし、ＰＶｄＦへの吸収線量がそれぞれ９０ｋＧｙ（実施例１２）、７０ｋＧｙ（実施例１３）、５０ｋＧｙ（実施例１４）、２０ｋＧｙ（実施例１５）、１０ｋＧｙ（実施例１６）、１３０ｋＧｙ（比較例７）及び０．５ｋＧｙ（比較例８）となるようにコバルト６０をγ線源としてγ線を照射した。次に、γ線照射したＰＶｄＦ粉末をポリエチレン製パックより取出して窒素雰囲気に移し、１５質量％アクリル酸水溶液２６０ｇ中にＰＶｄＦを供給して８０℃に保持し、アクリル酸水溶液と反応させてＡＡ-ｇ-ＰＶｄＦを合成した。
反応溶液のサンプルを採取し、ＰＶｄＦにグラフト重合反応したアクリル酸の減少量を滴定により逐次測定し、ＡＡ-ｇ-ＰＶｄＦ中のアクリル酸基の含有割合が１７質量％になったら、反応を止めて得られた固体状生成物を純水で洗浄して乾燥させ、これらをそれぞれ実施例１２〜１６及び比較例７，８の第３結着剤とした。
【００５７】
＜比較評価３＞
実施例１２〜１６及び比較例７，８で得られた第３結着剤を用いて比較評価１の評価試験(1)〜評価試験(4)と同様の試験をそれぞれ行った。評価試験(1)及び評価試験(4)の結果を表４に、評価試験(2)の結果を図４に、評価試験(3)の結果を図５にそれぞれ示す。なお、表４中の評価試験(1)及び評価試験(4)欄における記号は、比較評価２で用いた記号と同様の意味を有する記号である。
【００５８】
【表４】

【００５９】
表４より明らかなように、評価試験(1)のＤＭＡに対する溶解特性では、吸収線量が７０ｋＧｙ未満の実施例１３〜１６では合成したＡＡ-ｇ-ＰＶｄＦは室温でもＤＭＡに溶解することができた。吸収線量が９０ｋＧｙの実施例１２では、合成したＡＡ-ｇ-ＰＶｄＦは高温（８５℃）状態に維持したＤＭＡに溶解した。これに対して、吸収線量が１３０ｋＧｙの比較例７では、撹拌を加えてもＤＭＡへの溶解はほぼ不可能となることが判った。
評価試験(2)のＣｕ箔及びＡｌ箔に対する接着性試験では、図４に示すように、ＡＡ-ｇ-ＰＶｄＦで接着したＣｕ箔及びＡｌ箔の接着強度は、ＡＡ-ｇ-ＰＶｄＦ中に含まれるアクリル酸基の含有割合と相関する。比較例７及び８の結果では吸収線量が１ｋＧｙ以下、１２０ｋＧｙ以上になると、ＡＡ-ｇ-ＰＶｄＦの接着強度が低く、結着剤として適さないことが判る。この理由として、吸収線量が１ｋＧｙ以下の場合、グラフトされるアクリル酸基が少なく、１２０ｋＧｙ以上の場合は、ＡＡ-ｇ-ＰＶｄＦの溶解状況が悪いことが原因であると考えられる。
【００６０】
評価試験(3)のサイクル容量維持特性試験では、図５に示したように、評価試験(2)の接着強度の試験結果と同様な傾向を示していた。この結果から、４００サイクル以上で８０％容量を維持できる電池を作製するために、吸収線量が１ｋＧｙ〜１２０ｋＧｙの範囲内であることが好ましいことが判った。
評価試験(4)の密着層の集電体に対する密着性試験では、表４より明らかなように、充放電サイクルを行った後の電池密着層を解析した結果、吸収線量が１ｋＧｙ〜１２０ｋＧｙのＰＶｄＦを用いて合成したＡＡ-ｇ-ＰＶｄＦは電池の密着層結着剤として適していることが判る。安定した密着特性を得るために、γ線吸収線量が２０〜１００ｋＧｙのＰＶｄＦを原料として用いることが好ましい。
【００６１】
＜実施例１７＞
先ず、第３結着剤として１７質量％のアクリル酸をＰＶｄＦにグラフト重合したＡＡ-ｇ-ＰＶｄＦを２ｇ用意した。このＡＡ-ｇ-ＰＶｄＦ２ｇに溶媒としてＤＭＡ９８ｇを添加し、ホモジナイザにより溶解してポリマー溶液とした。導電性物質として比表面積１５０ｍ²／ｇの黒鉛粉末８ｇを用意し、この黒鉛粉末をＤＭＡ８０ｇに分散させて分散液を調製した。この分散液を上記ポリマー溶液に加えて密着層スラリーを調製した。
正極集電体として厚さ２０μｍ、幅２５０ｍｍのＡｌ箔を用意し、このＡｌ箔に調製した密着層スラリーをドクターブレード法により塗工及び乾燥し、乾燥後の密着層厚さが５μｍの密着層を有するＡｌ箔を得た。一方、負極集電体として厚さ１０μｍ、幅２５０ｍｍのＣｕ箔を用意し、このＣｕ箔にドクターブレード法により塗工及び乾燥し、乾燥後の密着層厚さが５μｍの密着層を有するＣｕ箔を得た。
次に、上記表１に示される各成分をボールミルで２時間混合することによりそれぞれ正極活物質層塗工用スラリー、負極活物質層塗工用スラリー及び電解質層塗工用スラリーを調製した。
【００６２】
得られた正極活物質層塗工用スラリーを密着層を有するＡｌ箔上に正極活物質層の乾燥厚さが８０μｍとなるようにドクターブレード法により塗工及び乾燥し、圧延することにより正極を形成した。得られた負極活物質層塗工用スラリーを密着層を有するＣｕ箔上に負極活物質層の乾燥厚さが８０μｍとなるようにドクターブレード法により塗工及び乾燥し、圧延することにより負極を形成した。得られた電解質層塗工用スラリーを厚さ２５μｍ、幅２５０ｍｍの剥離紙上に電解質層の乾燥厚さが５０μｍとなるようにドクターブレード法により塗工及び乾燥し、剥離紙より剥がして電解質層シートを形成した。それぞれ形成した正極と電解質シートと負極を順に積層し、積層物を熱圧着することによりシート状の電極体を作製した。
次に、この電極体にＮｉからなる正極リード及び負極リードをそれぞれ正極集電体及び負極集電体に溶接し、開口部を有する袋状に加工したラミネートパッケージ材に収納し、減圧条件下で熱圧着により開口部を封止し、シート状の電池を作製した。
【００６３】
＜実施例１８＞
密着層に用いる変性高分子を１７質量％のメタクリル酸をポリフッ化ビニリデンにグラフト重合した上記化学式（２）に示す変性高分子（Methacrylic Acid grafting PolyVinylidene Fluoride、ＭＡ-ｇ-ＰＶｄＦ）とした以外は実施例１７と同様に電池を作製した。
＜実施例１９＞
密着層スラリーの調製において、導電性物質を溶媒に分散させるときに、分散剤を１．２ｇ加えて酸性高分子系分散剤含有量を固形物質量中で１０．７質量％とした以外は実施例１７と同様に電池を作製した。
＜実施例２０＞
密着層スラリーの調製において、導電性物質を溶媒に分散させるときに、分散剤を１．２ｇ加えて酸性高分子系分散剤含有量を固形物質量中で１０．７質量％とした以外は実施例１８と同様に電池を作製した。
【００６４】
＜実施例２１＞
正極集電体及び負極集電体上に設けた密着層の乾燥厚さをそれぞれ０．５μｍとした以外は実施例１７と同様に電池を作製した。
＜実施例２２＞
正極集電体及び負極集電体上に設けた密着層の乾燥厚さをそれぞれ１μｍとした以外は実施例１７と同様に電池を作製した。
＜実施例２３＞
正極集電体及び負極集電体上に設けた密着層の乾燥厚さをそれぞれ１０μｍとした以外は実施例１７と同様に電池を作製した。
＜実施例２４＞
正極集電体及び負極集電体上に設けた密着層の乾燥厚さをそれぞれ１５μｍとした以外は実施例１７と同様に電池を作製した。
【００６５】
＜実施例２５＞
密着層塗工用スラリーの導電性物質である黒鉛粉末を２ｇとしてバインダと導電性物質との質量比を５０／５０とした以外は実施例１７と同様に電池を作製した。
＜実施例２６＞
密着層塗工用スラリーの導電性物質である黒鉛粉末を４ｇとしてバインダと導電性物質との質量比を３３／６７とした以外は実施例１７と同様に電池を作製した。
＜実施例２７＞
密着層塗工用スラリーの導電性物質である黒鉛粉末を１２ｇとしてバインダと導電性物質との質量比を１４／８６とした以外は実施例１７と同様に電池を作製した。
＜実施例２８＞
密着層塗工用スラリーの導電性物質である黒鉛粉末を１４ｇとしてバインダと導電性物質との質量比を１３／８７とした以外は実施例１７と同様に電池を作製した。
【００６６】
＜比較例９＞
密着層を正極集電体及び負極集電体上に設けない以外は実施例１７と同様にして電池を作製した。
＜比較例１０＞
密着層塗工用スラリーのバインダをＡＡ-ｇ-ＰＶｄＦからブチルゴムに、溶媒をＤＭＡからトルエンにした以外は実施例１７と同様に電池を作製した。
＜比較例１１＞
密着層塗工用スラリーのバインダをＡＡ-ｇ-ＰＶｄＦからアクリル酸エステル−メタクリル酸エステル共重合体に、溶媒をＤＭＡから水にした以外は実施例１７と同様に電池を作製した。
＜比較例１２＞
密着層塗工用スラリーのバインダをＡＡ-ｇ-ＰＶｄＦからポリウレタン樹脂に、溶媒をＤＭＡからメチルエチルケトン１０８ｇとメチルイソブチルケトン７２ｇの混合溶媒にした以外は実施例１７と同様に電池を作製した。
＜比較例１３＞
密着層塗工用スラリーのバインダをＡＡ-ｇ-ＰＶｄＦからエポキシ樹脂に、溶媒をＤＭＡからメチルエチルケトン１０８ｇとメチルイソブチルケトン７２ｇの混合溶媒にした以外は実施例１７と同様に電池を作製した。
【００６７】
＜比較例１４＞
密着層スラリーの調製において、導電性物質を溶媒に分散させるときに、分散剤を３．５ｇ加えて分散剤含有量を２６質量％とした以外は実施例１７と同様に電池を作製した。
＜比較例１５＞
正極集電体及び負極集電体上に設けた密着層の乾燥厚さをそれぞれ４０μｍとした以外は実施例１７と同様に電池を作製した。
＜比較例１６＞
密着層塗工用スラリーの導電性物質である黒鉛粉末を２０ｇとしてバインダと導電性物質との質量比を９／９１とした以外は実施例１７と同様に電池を作製した。
【００６８】
＜比較評価＞
実施例１７〜２８及び比較例９〜１６で得られた電池について以下の評価試験を行った。
(5) 密着層の電解液に対する耐性試験
実施例１７〜２８及び比較例９〜１６で得られた密着層を有する負極集電体を炭酸プロピレン２０質量部、炭酸エチレン４０質量部及び炭酸ジエチル４０質量部からなる電解液に１週間浸漬して、密着層を有する負極集電体の質量増加量を測定し、密着層の第３結着剤である変性高分子の電解液による膨潤の有無を確かめた。また、負極集電体Ｃｕ箔を指で擦り、密着層が剥離するか否かを確認した。
(6) 密着層のフッ化水素（ＨＦ）に対する集電体保護性能試験
実施例１７〜２８及び比較例９〜１６において得られた密着層を有する負極集電体の表面に濃度５ｐｐｍのフッ化水素酸水溶液２ｍｌを滴下し、２４時間放置した後の集電体の状態を確認した。
【００６９】
(7) 密着層の活物質層に対する密着性試験
実施例１７〜２８及び比較例９〜１６において得られた正極集電体及び負極集電体の表面にそれぞれ粘着テープを貼付け、ゴムローラで押しつけた。この粘着テープを貼付けた正極集電体及び負極集電体をそれぞれ１０ｍｍ幅に切取り、１０ｍｍ幅の集電体を垂直上方に引っ張りあげて活物質層を引き剥がすのにかかる力を測定した。また、その剥がれ方を目視により確認した。
(8) サイクル容量維持特性試験
実施例１７〜２８及び比較例９〜１６において得られたシート状の電池を充放電サイクル試験にかけ、最大充電電圧４．２Ｖ、充電０．５Ａの条件で２．５時間の充電と、０．５Ａの定電流で放電電圧が２．７５Ｖ（最低放電電圧）となるまで放電を行う充放電サイクルを繰返し、各サイクルの放電容量を測定して初期放電容量の８０％まで低下するサイクル数を測定した。
【００７０】
上記評価試験(5)〜評価試験(8)における結果を表５に示す。なお表５中の評価試験(5)欄における記号は、次の意味である。
◎：極めて良好であり、剥離しない。
○：良好であり、剥離しない。
△：一部剥離する、
×：完全に剥離する。
【００７１】
また、表５中の評価試験(6)欄における記号は、次の意味である。
◎：極めて良好であり、腐食しない。
○：良好であり、腐食しない。
△：一部腐食する。
×：腐食する。
【００７２】
【表５】

【００７３】
(5) 密着層の電解液に対する耐性試験
比較例１０〜１３では密着層を有する負極集電体の増加量が大きく、電解液によって密着層を形成しているバインダにより膨潤していることが判る。これに対して実施例１７〜２８では、電解液に１週間浸漬したにもかかわらず密着層を有する負極集電体の増加量は僅かであり、電解液に対する耐性が示されている。
(6) 密着層のフッ化水素（ＨＦ）に対する集電体保護性能試験
比較例９及び１１の集電体はＨＦにより腐食されていた。また、比較例１０，１２及び１３では一部分が腐食されていた。これに対して実施例１７〜２８の集電体はＨＦによる腐食されておらず、密着層による保護機能が働いていることが判る。
【００７４】
(7) 密着層の活物質層に対する密着性試験
比較例９〜１３の密着力に比べ、実施例１７〜２８では活物質層を引き剥がすのにかかる力が大きい。また、剥がれ方は比較例９〜１３は面内にむらがあり、剥がれた部分と剥がれない部分がそれぞれできていた。これに対して実施例１７〜２８は面内が均一で全面で剥がれていた。
(8) サイクル容量維持特性試験
比較例９〜１３の８０％容量サイクル数に比べると実施例１７〜２８ではそれぞれ高いサイクル数を示しており、充放電によるサイクル維持特性が優れることが判る。
【００７５】
【発明の効果】
以上述べたように、本発明によれば、正極集電体と正極活物質層との間に第１密着層を有し、及び負極集電体と負極活物質層との間に第２密着層を有し、第１及び第２密着層が第３結着剤と導電性物質の双方をそれぞれ含み、この第３結着剤が第１結着剤又は第２結着剤を変性物質により変性させた高分子化合物であるため、第１結着剤又は第２結着剤を基にした変性高分子は、正極活物質層又は負極活物質層に対する密着力が高く、変性したことにより集電体との密着性も従来の結着剤を用いるより大幅に向上する。その結果、活物質層の集電体からの剥がれを抑制でき、集電体と活物質層との導電性が大幅に向上するため、サイクル容量維持特性も向上させることができる。また、電解液が変性高分子化合物中に浸漬しにくいため、密着層が電解液中の有機溶媒に対して安定で長期保存性に優れる。電池内にフッ酸等の強酸が発生する場合でも変性高分子化合物が保護層となるため、集電体の腐食を抑制できる。
【図面の簡単な説明】
【図１】 本発明のリチウムイオンポリマー二次電池の電極体を示す部分断面構成図。
【図２】 実施例５〜１１及び比較例５，６で得られた第３結着剤の評価試験(2)の結果を示す図。
【図３】 実施例５〜１１及び比較例５，６で得られた第３結着剤の評価試験(4)の結果を示す図。
【図４】 実施例１２〜１６及び比較例７，８で得られた第３結着剤の評価試験(2)の結果を示す図。
【図５】 実施例１２〜１６及び比較例７，８で得られた第３結着剤の評価試験(4)の結果を示す図。
【符号の説明】
１１ 正極
１２ 正極集電体
１３ 正極活物質層
１４ 負極
１６ 負極集電体
１７ 負極活物質層
１８ ポリマー電解質層
１９ 第１密着層
２１ 第２密着層[0001]
BACKGROUND OF THE INVENTION
  The present invention relates to a lithium ion polymer secondary battery having an adhesion layer and a method for synthesizing a binder used for the adhesion layer of the battery.
[0002]
[Prior art]
  Due to the spread of portable devices such as video cameras and notebook computers in recent years, the demand for thin batteries has increased. As this thin battery, a lithium ion polymer secondary battery formed by laminating a positive electrode and a negative electrode is known. The positive electrode is made by forming an active material layer on the surface of a sheet-like positive electrode current collector, and the negative electrode is made by forming an active material layer on the surface of a sheet-like negative electrode current collector. An electrolyte layer is interposed between the positive electrode active material layer and the negative electrode active material layer. In this battery, a positive electrode terminal and a negative electrode terminal for taking out a potential difference in each active material as an electric current are provided in the positive electrode current collector and the negative electrode current collector, and the stacked ones are sealed by a package. An ion polymer secondary battery is formed. In this lithium ion polymer secondary battery, desired electricity can be obtained by using a positive electrode terminal and a negative electrode terminal drawn out of the package as terminals of the battery.
[0003]
  Lithium ion polymer secondary batteries having such a structure have received much attention because of their high battery voltage and high energy density. In order to further increase the discharge capacity of the lithium ion polymer secondary battery, it is necessary to increase the area of the sheet-like positive electrode or negative electrode. If the area of the positive electrode or the negative electrode is simply enlarged, there is a problem that the handling becomes difficult due to the large area. In order to eliminate this point, it is also conceivable to fold or wind the expanded sheet-like positive electrode or negative electrode to a desired size. However, if folding or winding is performed with the sheet-like positive electrode or negative electrode laminated, the positive electrode or negative electrode at the crease part will be bent, and the sheet at that part will peel off from the electrolyte layer, and the electrode and electrolyte interface will be effective. There is a problem in that the surface area is reduced and the discharge capacity is reduced, and resistance is caused inside the battery to deteriorate the cycle characteristics of the discharge capacity. Similarly, there is also a problem that the active material layer forming the positive electrode or the negative electrode is peeled off from the current collector due to bending at the fold. Further, in this battery, during the charging and discharging process, the positive electrode and the negative electrode active material layer are expanded and contracted by occlusion and release of lithium ions into the positive electrode and the negative electrode active material, and the stress generated thereby causes the active material layer to be There was also a problem of peeling from the current collector.
[0004]
  Therefore, as techniques for solving the above problems, as shown below, techniques for preventing the active material layer from peeling from the current collector and lowering the adhesion have been proposed.(1)Japanese Patent Publication No. 7-70328 proposes a current collector coated with a conductive coating film composed of a binder and a conductive filler. In this invention, examples of the binder material include phenol resin, melamine resin, urea resin, vinyl resin, alkyd resin, and synthetic rubber.(2)In JP-A-9-35707, a negative electrode material layer containing a binder composed of carbon powder and polyvinylidene fluoride (hereinafter referred to as PVdF) is formed on a negative electrode current collector, and the negative electrode current collector is formed. It describes that an adhesive layer made of an acrylic copolymer mixed with a conductive agent is formed thereon. In the present invention, a high adhesion effect can be obtained by using an acrylic copolymer having high adhesion to copper for the negative electrode plate in which the negative electrode current collector is formed of copper foil.(3)In JP-A-10-149810, an undercoat layer in which a polyurethane resin or an epoxy resin is applied is formed between an active material layer and a current collector. In this invention, the adhesion between the active material coating layer and the current collector in the electrode is improved by forming an undercoat layer coated with polyurethane resin or epoxy resin, and the cycle capacity maintenance characteristics of the battery are improved. be able to.
[0005]
  (Four)In JP 10-144298 A, an adhesive layer made of graphite and a binder is provided between a negative electrode current collector and a negative electrode active material layer. In this invention, the graphite contained in the adhesive layer functions to increase the current collection efficiency of the negative electrode.(Five)JP-A-9-213370 uses grafted PVdF as the electrolyte part of the battery active material layer and the binder of the electrolyte layer. In this invention, the contact efficiency with the current collector is improved by using the graft polymerized PVdF as the electrolyte part of the battery active material layer or the binder of the electrolyte layer.
[0006]
[Problems to be solved by the invention]
  Properties required for the adhesion layer include adhesion to the current collector material, binding force with the binder contained in the active material layer, stability against organic solvents in the electrolyte, and excellent long-term storage, thermal For example, it is stable and is not peeled off when exposed to high temperatures, is electrochemically stable and can withstand repeated charge and discharge, and the like.
  But above(1)In the technique shown in (2), since butyl rubber, phenol resin, and the like used as a binder are attacked by the electrolytic solution, there is a problem of peeling. Also(2)Even in the technique shown in FIG. 4, since the acrylic copolymer has a strong binding force with PVdF and the negative electrode current collector contained in the negative electrode material layer, an acrylic material in which a conductive material is mixed between the negative electrode current collector and the negative electrode material layer. The binding force between the negative electrode current collector and the negative electrode material layer can be increased by forming a binding layer containing a main copolymer as a main component, but the acrylic copolymer is affected by the electrolytic solution. Therefore, there was a problem of peeling. More(3)Even when the polyurethane resin is used as the undercoat layer, the peel strength and the 80% capacity cycle number are improved as compared with the battery without the undercoat layer, but it is practically sufficient. I could not say it. Further, when an epoxy resin is used, it may be peeled off because it is attacked by the electrolytic solution.
[0007]
  (Four)In the technique shown in Fig. 4, the adhesive layer uses the same material as the binder contained in the active material, so that the adhesion to the active material is good, but the adhesion to the current collector is the same as that of the active material layer. It was not much different from that formed directly on the current collector, and could not be said to be sufficient. Further, since the electrolyte solution penetrates into the binder, there is a problem that the adhesive strength with the current collector is weak.(Five)In the technique shown in FIG. 3, since the graft-polymerized polymer having high adhesion to the current collector is used for the binder of the active material layer, the active material layer can be directly formed on the current collector without providing an adhesion layer. Since such a polymer is hardly soluble, there is a drawback that a solvent to be used is limited. Further, it is difficult to completely remove the solvent from the inside of the battery, and if the solvent remains inside the battery, the battery performance may be adversely affected.
[0008]
  A first object of the present invention is to provide a lithium ion polymer battery that is excellent in adhesion and electrical conductivity between a current collector and an active material layer and can improve cycle capacity maintenance characteristics.
  The second object of the present invention is to provide a lithium ion polymer battery in which the adhesion layer is stable with respect to the organic solvent in the electrolytic solution and has excellent long-term storage stability.
  A third object of the present invention is to provide a lithium ion polymer battery capable of suppressing the corrosion of the current collector by a strong acid such as hydrofluoric acid generated in the battery.
  A fourth object of the present invention is to provide a method for synthesizing a binder used for an adhesion layer of a lithium ion polymer secondary battery excellent in adhesion and conductivity between a current collector and an active material layer.
[0009]
[Means for Solving the Problems]
  As shown in FIG. 1, the invention according to claim 1 includes a positive electrode 11 in which a positive electrode active material layer 13 in which a first binder is contained in an active material is formed on the surface of a positive electrode current collector 12, and A negative electrode 14 in which a negative electrode active material layer 17 in which a second binder that is the same as or different from the first binder is contained in the active material is formed on the surface of the negative electrode current collector 16, and an electrolyte 18 are provided. This is an improvement of a lithium ion polymer secondary battery.
  The characteristic configuration includes a first adhesion layer 19 between the positive electrode current collector 12 and the positive electrode active material layer 13, and a second adhesion layer 21 between the negative electrode current collector 16 and the negative electrode active material layer 17. The first and second adhesion layers 19 and 21 include both the third binder and the conductive material, respectively, and the third binder modifies the first binder or the second binder. It is a polymer compound modified with a substance.
  In the invention which concerns on Claim 1, the 3rd binder contained in a 1st and 2nd contact | adherence layer contains the 1st binder or the 2nd binder which each contains in a positive electrode active material layer or a negative electrode active material layer. Since it is a high molecular compound modified by a modifying substance, adhesion to the positive electrode active material layer or the negative electrode active material layer is high. In addition, by using a polymer compound obtained by modifying the first binder or the second binder as the third binder, the adhesion with the positive electrode current collector or the negative electrode current collector is also improved from the conventional binder. Greatly improved over use.
[0010]
  The invention according to claim 2 is the invention according to claim 1, wherein either one or both of the first and second binders are polytetrafluoroethylene, polychlorotrifluoroethylene, PVdF, vinylidene fluoride- It is a lithium ion polymer secondary battery which is a fluorine-containing polymer compound selected from a hexafluoropropylene copolymer or polyvinyl fluoride.
  In the invention according to claim 2, polytetrafluoroethylene and PVdF are preferable because the binder has high durability to the electrolytic solution.
[0011]
  The invention according to claim 3 is the invention according to claim 1, wherein the modifying substance is ethylene, styrene, butadiene, vinyl chloride, vinyl acetate, acrylic acid, methyl acrylate, methyl vinyl ketone, acrylamide, acrylonitrile, vinylidene chloride. , A lithium ion polymer secondary battery which is a compound selected from methacrylic acid, methyl methacrylate or isoprene.
  In the invention according to claim 3, the modifying substance is preferable because acrylic acid, methyl acrylate, methacrylic acid, and methyl methacrylate can be used to obtain good adhesion to the current collector.
[0012]
  The invention according to claim 4 is the lithium ion polymer secondary battery according to claim 1, wherein the first and second adhesion layers have a thickness of 0.5 to 30 μm.
  In the invention which concerns on Claim 4, the thickness of the 1st and 2nd contact | adherence layer is 0.5-30 micrometers. When the thickness is less than 0.5 μm, the function of protecting the current collector from corrosion is deteriorated, and the cycle characteristics of the discharge capacity are deteriorated. Moreover, since it becomes difficult to disperse | distribute electroconductive powder uniformly at the time of 1st and 2nd contact | adherence layer formation, it raises an internal impedance. If it exceeds 30 μm, the volume of the portion that does not contribute to the battery reaction andmassBecause the volume andmassEnergy density is reduced. The thickness of the adhesion layer is preferably 1 to 15 μm.
[0013]
  The invention according to a fifth aspect is the invention according to the first or fourth aspect, wherein a dispersant is further added in the first and second adhesion layers in an amount of 0.1-20.mass% Lithium ion polymer secondary battery.
  In the invention which concerns on Claim 5, 0.1-20 in a dispersing agent in the 1st and 2nd contact | adherence layer.massThe conductive substance can be uniformly dispersed in the first and second adhesion layers by containing the content of 1%. Examples of the dispersant include acidic polymer dispersants, basic polymer dispersants, and neutral polymer dispersants. 0.1massIf it is less than%, there is no difference in the dispersion of the conductive powder from the case where no dispersant is added, and the added effect cannot be obtained. 20massEven if it exceeds%, the dispersion state of the conductive powder does not change and does not contribute to the battery reaction, so there is no need to add excessively. Dispersant content is 2-15mass% Is preferred.
[0014]
  The invention according to claim 6 is the invention according to claim 1, wherein the conductive material is a carbon material having a particle size of 0.5 to 30 μm and a graphitization degree of 50% or more. Between the third binder contained and the conductive materialmassThe lithium ion polymer secondary battery has a ratio (third binder / conductive substance) of 13/87 to 50/50.
  In the invention according to claim 6, the third binder and the conductive materialmassThe ratio is 13/87 to 50/50.massWhen the ratio is less than 13/87, the polymer ratio is small and sufficient adhesion cannot be obtained.massWhen the ratio exceeds 50/50, the conductive material is small, the electron transfer between the current collector and the active material layer cannot be sufficiently performed, and the internal impedance increases. Between the third binder and the conductive material.massThe ratio is preferably 14/86 to 33/67.
[0015]
  The invention according to claim 7 is a method for synthesizing the third binder contained in the adhesion layer of the lithium ion polymer secondary battery according to any one of claims 1 to 6, wherein the third binder is the first binder. One or both of the binder and the second binder is synthesized by modifying with a modifying substance, and the synthesized third binder is 100.mass%, The ratio of the modifying substance contained in the third binder is 2-50.mass% Of the binder.
  In the invention according to claim 7, the synthesized third binder is 100mass%, The third binder having excellent adhesion and conductivity can be obtained by setting the ratio of the modifying substance contained in the third binder to the above ratio. When the ratio of the modifying substance contained in the binder is less than the lower limit value, it becomes difficult to dissolve in the solvent, and when the ratio exceeds the upper limit value, the adhesive strength to the current collector decreases. The ratio of the modified substance contained in the binder is 70 to 90.mass% Is preferred.
[0016]
  The invention according to claim 8 is the invention according to claim 7, wherein the modification with the denaturing substance is performed on the irradiated object after irradiating one or both of the first and second binders with radiation. This is a synthesis method carried out by mixing a modifying substance and graft polymerization.
  The invention according to claim 9 is the invention according to claim 7, wherein the modification with the modifying substance is performed by mixing the modifying substance with one or both of the first and second binders and applying radiation to the mixture. Is a synthetic method carried out by irradiation and graft polymerization.
[0017]
  The invention according to claim 10 is the invention according to claim 8 or 9, wherein either one or both of the first and second binders are irradiated with either the first or second binder. This is a synthesis method performed by irradiating γ rays so that the absorbed dose to one or both is 1 to 120 kGy.
  In the invention which concerns on Claim 10, a gamma ray is irradiated so that absorbed dose may be 1-120 kGy. If the absorbed dose is less than the lower limit and greater than the upper limit, there is a problem that the adhesive strength of the resulting binder is lowered.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
  Next, an embodiment of the present invention will be described.
  In the lithium ion polymer secondary battery of the present invention, the first and second adhesion layers each include both the third binder and the conductive material, and the third binder is the first binder or the second binder. It is a polymer compound in which the agent is modified with a modifying substance.
  “Modification” means that the property is changed. In this specification, by modifying a polymer compound with a modifying substance, not only the property of a conventional polymer compound but also the property of a modifying substance may be combined. , It means to give a new property that both do not have.
[0019]
  Since this modified polymer compound is mainly based on the first binder or the second binder in the active material layer, it has high adhesion to the active material layer. On the other hand, the modification with a denaturing substance having high adhesion to the current collector improves the adhesion to the current collector much more than when using the same binder as that for the active material layer. For this reason, peeling of the active material layer from the current collector is suppressed, and cycle characteristics are improved.
  In addition, the modified polymer compound becomes chemically stable by being modified as compared with the binder used for the active material layer, and the active material layer is not separated from the current collector without being dissolved in the electrolytic solution. It is suppressed. For the same reason, since the conductive material dispersed in the adhesion layer is maintained without collapsing, good electron conduction is maintained, and long-term storage and cycle characteristics are excellent. In addition, since the current collector is coated on a chemically stable layer, even when hydrofluoric acid or the like is generated inside the battery, the adhesion layer becomes a protective layer and corrosion of the current collector can be suppressed.
  Furthermore, the modified polymer compound becomes thermally stable by being modified as compared with the binder used for the active material layer, and even if the battery is placed at a high temperature, it does not dissolve in the solvent in the battery and deteriorates the battery. Can be suppressed. The modified polymer compound is electrochemically stable by being modified compared to the binder used in the active material layer, and it does not deteriorate even when the positive electrode is placed at a high potential when fully charged. Keep power and conductivity. In addition, since it is difficult for the electrolytic solution to penetrate into the modified polymer compound, the electrolytic solution hardly adheres to the current collector, and elution of the positive electrode current collector during full charge can be suppressed.
[0020]
  Next, the manufacturing procedure of the lithium ion polymer secondary battery of the present invention will be described.
  First, the binder contained in each of the positive electrode active material layer or the negative electrode active material layer is modified with a modifying material, and this modified polymer compound is used as the third binder of the first and second adhesion layers.
  Since the first and second adhesion layers are required to be chemically, electrochemically, and thermally stable, they serve as a base for the first or second binder and modified polymer compound used in the active material. The polymer compound is preferably a polymer compound containing fluorine in the molecule. Examples of the fluorine-containing polymer compound include polytetrafluoroethylene, polychlorotrifluoroethylene, PVdF, vinylidene fluoride-hexafluoropropylene copolymer, and polyvinyl fluoride.
[0021]
  Examples of a technique for modifying the fluorine-containing polymer compound include graft polymerization and crosslinking. Examples of modifying substances used for graft polymerization include compounds such as ethylene, styrene, butadiene, vinyl chloride, vinyl acetate, acrylic acid, methyl acrylate, methyl vinyl ketone, acrylamide, acrylonitrile, vinylidene chloride, methacrylic acid, and methyl methacrylate. Can be mentioned. Particularly when acrylic acid, methyl acrylate, methacrylic acid, or methyl methacrylate is used, good adhesion to the current collector can be obtained.
  Examples of the modifying substance used for crosslinking include compounds having two or more unsaturated bonds, such as butadiene and isoprene. Crosslinking may be performed by vulcanization.
[0022]
  In this embodiment, graft polymerization will be described. Examples of the graft polymerization method include a catalyst method, a chain transfer method, a radiation method, a photopolymerization method, and a mechanical cutting method. For example, in the radiation method, a polymer compound and a compound to be a grafting material can be combined and polymerized by continuously or intermittently radiating radiation, and before the grafting material and the polymer compound are brought into contact with each other, It is preferable to preliminarily radiate a polymer compound as a group. Specifically, after irradiating the polymer compound with radiation, a modified substance that becomes a grafting material is mixed into the irradiated object, thereby modifying the polymer compound as a main chain and a modified substance as a side chain. Molecular compounds can be obtained. Examples of the radiation used for graft polymerization include an electron beam, X-rays, and γ rays. Gamma rays are irradiated so that the absorbed dose to the polymer compound is 1 to 120 kGy. By irradiating the polymer compound as the main group with radiation, a radical is formed at one end, and the grafted material is easily polymerized. The following chemical formula (1) and chemical formula (2) show graft polymerization of PVdF and acrylic acid by the radiation method.
[0023]
[Chemical 1]

[0024]
[Chemical 2]

[0025]
  As shown in chemical formula (1), a radical is formed at one end of PVdF by irradiating PVdF with γ rays as radiation. As shown in chemical formula (2), acrylic acid is brought into contact with PVdF having a radical at one end, and a double bond portion of acrylic acid is graft-polymerized to the PVdF radical.
[0026]
  As another example, graft polymerization of PVdF and methacrylic acid is shown in chemical formula (3) and chemical formula (4).
[0027]
[Chemical 3]

[0028]
[Formula 4]

[0029]
  As shown in chemical formula (3), PVdF forms a radical at one end of PVdF by irradiating gamma rays as radiation, and PVdF having a radical at one end in chemical formula (4) is contacted with methacrylic acid, The double bond part of methacrylic acid is graft-polymerized to the radical of PVdF.
[0030]
  Graft polymerization is the length of time the activated main group is in contact with the grafted material, the degree of pre-activation of the main group by radiation, the extent to which the grafted material can penetrate the main group, the main group and the grafting The polymerization formation differs depending on the temperature when the materials are in contact with each other. When the grafting material is an acid, the degree of grafting can be observed by sampling a solution containing the compound that is the grafting material, titrating with an alkali, and measuring the concentration of the remaining acid compound. . The proportion of grafting in the resulting composition is the finalmass10-30% of is desirable.
[0031]
  The graft polymer-modified polymer compound thus obtained is used as the third binder of the adhesion layer, and the third binder is dissolved in a solvent to prepare a polymer solution. The materials are dispersed to prepare first and second adhesion layer slurries. A carbon material having a particle size of 0.5 to 30 μm and a graphitization degree of 50% or more is used as the conductive material. Between the third binder and the conductive material.massA slurry of the adhesion layer is prepared by mixing so that the ratio (third binder / conductive substance) is 13/87 to 50/50. Dimethylacetamide (hereinafter referred to as DMA), acetone, dimethylformamide, and N-methylpyrrolidone are used as the solvent.
[0032]
  Next, a sheet-like positive electrode and negative electrode current collector are prepared, and the first and second adhesion layer slurries prepared on the positive electrode and negative electrode current collector are coated and dried by the doctor blade method, respectively. A positive electrode or negative electrode current collector having first and second adhesion layers having a layer thickness of 0.5 to 30 μm is formed. The adhesion layer thickness of the positive electrode and the negative electrode after drying is preferably 1 to 15 μm. Examples of the sheet-like positive electrode current collector include Al foil, and examples of the negative electrode current collector include Cu foil. Here, the doctor blade method is one of the methods for molding ceramics into a sheet, and the thickness of the slip carried on the carrier such as a carrier film or an endless belt is determined by means of a knife edge called a doctor blade and a carrier. This is a method for precisely controlling the thickness of the sheet by adjusting the interval of the sheet.
[0033]
  Next, components necessary for the positive electrode active material layer, the negative electrode active material layer, and the electrolyte layer are mixed to prepare a positive electrode active material layer coating slurry, a negative electrode active material layer coating slurry, and an electrolyte layer coating slurry, respectively. Prepare.
  The obtained positive electrode active material layer coating slurry is applied onto a positive electrode current collector having a first adhesion layer by a doctor blade method, dried, and rolled to form a positive electrode. Similarly, the negative electrode active material layer coating slurry is applied to the negative electrode current collector having the second adhesion layer by the doctor blade method, dried, and rolled to form the negative electrode. The positive electrode or negative electrode active material layer is formed so that the thickness after drying is 20 to 250 μm. The electrolyte layer is formed by coating and drying the obtained slurry for coating the electrolyte layer on the release paper by a doctor blade method so that the dry thickness of the electrolyte layer is 10 to 150 μm, and peeling it off the release paper. Alternatively, the electrolyte layer may be formed by coating and drying the slurry for coating the electrolyte layer on the positive electrode surface or the negative electrode surface. Each of the formed positive electrode, electrolyte layer, and negative electrode is laminated in order, and the laminate is thermocompression bonded to form a sheet-like electrode body as shown in FIG.
[0034]
  Finally, a positive electrode lead and a negative electrode lead made of Ni are welded to the positive electrode current collector and the negative electrode current collector, respectively, on this electrode body, and housed in a laminate package material processed into a bag shape having an opening. A sheet-like lithium ion polymer secondary battery can be produced by sealing the opening by thermocompression bonding.
[0035]
【Example】
  Next, examples of the present invention will be described together with comparative examples.
  <Example 1>
  First, 50 g of PVdF powder as the first and second binders and 15massA 260% acrylic acid aqueous solution was prepared. Next, PVdF powder was put in a polyethylene pack and vacuum-packed, and γ-rays were irradiated using cobalt 60 as a γ-ray source so that the absorbed dose to PVdF was 50 kGy. Next, the PVdF powder irradiated with γ-rays is taken out from the polyethylene pack and transferred to a nitrogen atmosphere.massAcrylic acid grafting PolyVinylidene Fluoride (hereinafter referred to as “Acrylic acid grafting polyvinylidene fluoride”) produced by graft polymerization represented by the above chemical formula (2) by supplying PVdF to 260 g of an acrylic acid aqueous solution and maintaining it at 80 ° C. , AA-g-PVdF).
  A sample of the reaction solution was collected, and the amount of acrylic acid graft-reacted on PVdF was sequentially measured by titration. The content ratio of grafted acrylic acid groups in AA-g-PVdF was 17mass%, The solid product obtained by stopping the reaction was washed with pure water and dried to obtain a third binder.
[0036]
  <Example 2>
  15 denaturing substancesmassA third binder was obtained in the same manner as in Example 1 except that the amount was 260 g of a methacrylic acid aqueous solution.
  <Example 3>
  15 denaturing substancesmassA third binder was obtained in the same manner as in Example 1 except that 260% aqueous methyl acrylate solution was used.
  <Example 4>
  15 denaturing substancesmassA third binder was obtained in the same manner as in Example 1 except that 260% of a methyl methacrylate aqueous solution was used.
[0037]
  <Comparative Example 1>
  A commercially available acrylic ester-methacrylic ester copolymer was prepared as the third binder.
  <Comparative example 2>
  A commercially available homopolymer of PVdF was prepared as the third binder.
  <Comparative Example 3>
  A commercially available PVdF copolymer was prepared as the third binder.
  <Comparative example 4>
  1 denaturing substancemassA third binder was obtained in the same manner as in Example 1 except that 2600 g of an aqueous solution containing% crotonic acid was used.
[0038]
  <Comparison evaluation 1>
  The following evaluation tests were performed using the third binders obtained in Examples 1 to 4 and Comparative Examples 1 to 4.
(1) Solubility test for dimethylacetamide
  4 g of the third binder obtained in each of Examples 1 to 4 and Comparative Examples 1 to 4 was sampled, and 56 g of DMA was added to this sample and stirred while heating to 60 ° C. to obtain a polymer solution. This solution was stored in a glass bottle, and the state of precipitation in the solution after being allowed to stand for one day was confirmed.
[0039]
(2) Adhesion test for copper foil and aluminum foil
  First, the evaluation test described above using the third binder obtained in Examples 1 to 4 and Comparative Examples 1 to 4(1)A polymer solution similar to the polymer solution was prepared. Next, these solutions were applied uniformly to a degreased Cu foil having a surface of 30 mm in width, 200 mm in length, and 14 μm in thickness, respectively, and an Al in which the surface of 10 mm in width, 100 mm in length and 20 μm in thickness was degreased thereon A foil sample was attached to produce a peel sample for adhesion test. The prepared sample was dried at 80 ° C. for 5 days in the air using a dryer. Next, the binder was evaluated with respect to Cu foil and Al foil with the peeling tester for the dried sample. In the peeling test method, the Cu foil side of the sample is fixed to a test stand when measuring, and the Al foil adhered to the Cu foil is pulled vertically upward at a rate of 100 mm / min. The force required to peel off was measured.
[0040]
(3) Battery cycle capacity maintenance characteristics test when used in battery adhesion layer
  First, 2 g of each of the third binders obtained in Examples 1 to 4 and Comparative Examples 1 to 4 was sampled, and 200 g of DMA was added to this sample and stirred while heating to 60 ° C. to obtain a polymer solution. . This solution has a specific surface area of 150m²/ G of graphite powder 8 g and a dispersant 1.2 g for dispersing the graphite powder were added to prepare an adhesion layer slurry. Next, an Al foil having a thickness of 20 μm and a width of 250 μm was prepared as a positive electrode current collector, and the adhesion layer slurry prepared on the Al foil was applied and dried by a doctor blade method. The thickness of the adhesion layer after drying was 10 ±. It controlled within the range of 1 micrometer. Further, a Cu foil having a thickness of 14 μm and a width of 250 μm was prepared as a negative electrode current collector, and the adhesion layer slurry prepared on the surface of the Cu foil was applied and dried by a doctor blade method. The thickness of the adhesion layer after drying was 10 ±. It controlled within the range of 1 micrometer. Next, each component shown in the following Table 1 was mixed for 2 hours by a ball mill to prepare a positive electrode active material layer coating slurry, a negative electrode active material layer coating slurry, and an electrolyte layer coating slurry.
[0041]
[Table 1]

[0042]
  The positive electrode active material coating slurry is applied to the surface of an Al foil having an adhesion layer, dried by a doctor blade method so that the dry thickness of the positive electrode active material layer is 80 μm, and rolled to form a positive electrode. did. Similarly, a negative electrode is formed by coating and drying a negative electrode active material coating slurry on a Cu foil surface having an adhesion layer by a doctor blade method so that the dry thickness of the negative electrode active material layer is 80 μm and rolling. did. Further, the electrolyte layer coating slurry is applied to the positive electrode and the negative electrode by a doctor blade method so that the dry thickness is 50 μm, and the positive electrode and the negative electrode having these electrolyte layers are laminated and thermocompression bonded to form a sheet. A shaped electrode body was produced. The positive electrode lead and the negative electrode lead made of Ni are welded to the positive electrode current collector and the negative electrode current collector, respectively, in the produced electrode body, and are housed in a laminate package material processed into a bag shape having an opening portion. Was heat-pressed and sealed to prepare a sheet-like battery.
  Next, a charging process in which the obtained sheet-shaped battery is charged for 2.5 hours under the conditions of a maximum charging voltage of 4 V and a charging current of 0.5 A, The charge / discharge cycle was repeated with one discharge cycle for discharging until 2.75 V, and the charge / discharge capacity of each cycle was measured, and the number of cycles that decreased to 80% of the initial discharge capacity was measured.
[0043]
(Four) Adhesion test for current collector of adhesive layer when used for adhesive layer of battery
  First, the evaluation test described above using the third binder obtained in Examples 1 to 4 and Comparative Examples 1 to 4(3)Each of the sheet batteries similar to the sheet battery was prepared. Next, the battery was subjected to the above evaluation test in an environment of 70 ° C.(3)100 charge / discharge cycles under the same conditions as described above were performed. Thereafter, the storage package of the sheet battery after 100 cycles of charge / discharge is removed, the positive electrode and the negative electrode of the battery are peeled off to separate each other, and the separated positive electrode adhesion layer and negative electrode adhesion layer are pinched with tweezers. It was confirmed whether or not the adhesion layer was peeled from the current collector when pulled.
[0044]
  Above evaluation test(1)~(Four)The evaluation results are shown in Table 2. In addition, the evaluation test in Table 2(1)The symbols in the columns have the following meanings.
  (Double-circle): Uniform precipitation-free solution.
[0045]
  In addition, the evaluation test in Table 2(Four)The symbols in the columns have the following meanings.
  A: The adhesion layer has very good adhesion to the current collector and does not peel off.
  ○: The adhesion layer partially peels from the current collector.
  Δ: The adhesion layer peels from the current collector over a wide area.
  X: The adhesion layer completely peels from the current collector.
[0046]
[Table 2]

[0047]
  As is clear from Table 2, the evaluation test(1)The third binder obtained in Examples 1 to 4 and Comparative Examples 1 to 4 can be completely dissolved in DMA, and the precipitate does not precipitate even if this solution is left for one day. It did not occur and was found to be suitable as a slurry for coating.
  Evaluation test(2)In the adhesion test for Cu foil and Al foil, the test using the third binder obtained in Comparative Examples 2 to 4 was 2 N / cm or less, and the adhesion effect as an adhesion layer material was insufficient. I understand. On the other hand, the Al foil bonded to the Cu foil using the third binder obtained in Examples 1 to 4 has a peel strength from the Cu foil of 10 N / cm or more, and the active material of the battery. It was strong enough to bond the current collector.
[0048]
  Evaluation test(3)In the cycle capacity maintenance characteristic test, 80% of the battery using the third binder of Examples 1 to 4 compared to the 80% capacity cycle number of the battery using the third binder of Comparative Examples 1 to 4. Each capacity cycle number indicates a high cycle number. This is considered that the cycle capacity maintenance characteristics were improved because the third binders of Examples 1 to 4 had excellent adhesion characteristics and high durability to the electrolytic solution.
  Evaluation test(Four)In the adhesion test of the adhesion layer to the current collector, the adhesion layer using the third binder of Examples 1 to 4 was compared with the adhesion layer using the third binder of Comparative Examples 1 to 4. It was difficult to peel from the current collector, indicating that the adhesion with the current collector was excellent. Comparative Example 1 using a copolymer containing no fluorine as a third binder has high adhesion characteristics to Cu foil and Al foil, but has insufficient electrolytic solution resistance and adheres after repeated charge / discharge cycles. A phenomenon occurred in which the layer peeled from the battery current collector.
[0049]
  From the above evaluation tests, a modified polymer compound in which a modified substance, particularly acrylic acid, methyl acrylate, methacrylic acid, and methyl methacrylate is grafted to PVdF, is suitable for the third binder of the first and second adhesion layers. I found out.
[0050]
  <Examples 5 to 11 and Comparative Examples 5 and 6>
  First, 50 g of PVdF powder as the first and second binders and 15massA 260% acrylic acid aqueous solution was prepared. Next, PVdF powder was put in a polyethylene pack and vacuum-packed, and γ-rays were irradiated using cobalt 60 as a γ-ray source so that the absorbed dose to PVdF was 50 kGy. Next, the PVdF powder irradiated with γ-rays is taken out from the polyethylene pack and transferred to a nitrogen atmosphere.massPVdF was supplied to 260 g of a% acrylic acid aqueous solution and kept at 80 ° C., and reacted with an acrylic acid aqueous solution to synthesize AA-g-PVdF.
  A sample of the reaction solution was taken, and the amount of acrylic acid graft-reacted on PVdF was sequentially measured by titration. The content of grafted acrylic acid groups in AA-g-PVdF was 2mass% (Example 5), 7mass% (Example 6), 10mass% (Example 7), 13mass% (Example 8), 17mass% (Example 9), 25mass% (Example 10), 40mass% (Example 11), 1mass% (Comparative Example 5) and 55mass% (Comparative Example 6), the solid product obtained by stopping the reaction was washed with pure water and dried, and these were the third binders of Examples 5 to 11 and Comparative Examples 5 and 6, respectively. An agent was used.
[0051]
  <Comparison evaluation 2>
  Evaluation test of comparative evaluation 1 using the third binder obtained in Examples 5 to 11 and Comparative Examples 5 and 6(1)~Evaluation test(Four)Each of the same tests was conducted, and the influence of the adhesive properties and the electrical properties of the battery on the content of acrylic acid groups in nine types of AA-g-PVdF was investigated. Evaluation test(1)And evaluation test(Four)Table 3 shows the evaluation test results(2)Figure 2 shows the evaluation test results(3)The results are shown in FIG. In addition, the evaluation test in Table 3(1)The symbols in the columns have the following meanings.
  (Double-circle): Uniform precipitation-free solution.
  ○: Although dissolved in DMA, a small amount of precipitate is generated in the solution.
  X: Insoluble in DMA.
[0052]
  In addition, the evaluation tests in Table 3(Four)The symbols in the columns have the following meanings.
  A: The adhesion layer has very good adhesion to the current collector and does not peel off.
  ○: The adhesion layer partially peels from the current collector.
  X: The adhesion layer completely peels from the current collector.
[0053]
[Table 3]

[0054]
  As is clear from Table 3, the evaluation test(1)As for the solubility characteristics of DMA, the content ratio of acrylic acid groups is 25mass% Of the third binders of Examples 5 to 9 were completely dissolved in DMA, and no precipitation occurred even when allowed to stand. The content of acrylic acid groups is 25mass% Of the third binder of Example 10 was difficult to dissolve in DMA, and a small amount of precipitate appeared when the dissolved solution was allowed to stand for one day. The small amount of precipitation is such that the solution is dissolved again by further stirring with a homogenizer for a long time, and is at a level that does not pose any problem for adhesion to copper foil or aluminum foil. In contrast, the acrylic acid group content is 55mass% Comparative Example 6 is hardly soluble in DMA and is not suitable for bonding to copper foil or aluminum foil. In addition, the content rate of an acrylic acid group is 1mass% Comparative Example 5 dissolved in DMA without problems.
  Evaluation test(2)In the adhesion test for Cu foil and Al foil, as shown in FIG. 2, the adhesion strength of Cu foil and Al foil adhered with AA-g-PVdF is the same as that of the acrylic acid group contained in AA-g-PVdF. Correlate with content. In the result of Comparative Example 6, the content ratio is 55.massIt can be seen that the adhesion effect is lowered when the ratio is more than%. This is an evaluation test(1)As is apparent from the results, it is considered that AA-g-PVdF was not sufficiently dissolved in DMA. Moreover, the content rate of an acrylic acid group is 1mass% Comparative Example 5 also decreased the adhesive strength. In order to obtain sufficient adhesive properties from the results of Examples 5 to 11, the content ratio of acrylic acid groups in AA-g-PVdF is 2 to 50.mass% Is required, 10-30mass% Is preferred.
[0055]
  Evaluation test(3)In the cycle capacity maintenance characteristic test, as shown in FIG.(2)The same tendency as the test result of adhesive strength was shown.
  Evaluation test(Four)In the adhesion test of the adhesion layer to the current collector, as is clear from Table 3, as a result of analyzing the battery adhesion layer after performing the charge / discharge cycle, the adhesion characteristics of the adhesion layer were evaluated.(2)And evaluation test(3)Similarly, the content ratio of acrylic acid group in AA-g-PVdF is 2-50.mass%, It is suitable as a battery binder, and 10-30mass% Is preferred.
[0056]
  <Examples 12 to 16 and Comparative Examples 7 and 8>
  First, 50 g of PVdF powder as the first and second binders and 15massA 260% acrylic acid aqueous solution was prepared. Next, the PVdF powder is put in a polyethylene pack and vacuum packed, and the absorbed dose to the PVdF is 90 kGy (Example 12), 70 kGy (Example 13), 50 kGy (Example 14), 20 kGy (Example 15), respectively. Gamma rays were irradiated using cobalt 60 as a gamma ray source so as to be 10 kGy (Example 16), 130 kGy (Comparative Example 7), and 0.5 kGy (Comparative Example 8). Next, the PVdF powder irradiated with γ-rays is taken out from the polyethylene pack and transferred to a nitrogen atmosphere.massPVdF was supplied to 260 g of a% acrylic acid aqueous solution and kept at 80 ° C., and reacted with an acrylic acid aqueous solution to synthesize AA-g-PVdF.
  A sample of the reaction solution was collected, and the amount of acrylic acid graft-reacted on PVdF was measured sequentially by titration. The content of acrylic acid groups in AA-g-PVdF was 17mass%, The solid product obtained by stopping the reaction was washed with pure water and dried, and these were used as the third binders of Examples 12 to 16 and Comparative Examples 7 and 8, respectively.
[0057]
  <Comparison evaluation 3>
  Evaluation test of comparative evaluation 1 using the third binder obtained in Examples 12 to 16 and Comparative Examples 7 and 8(1)~Evaluation test(Four)The same test was conducted. Evaluation test(1)And evaluation test(Four)Table 4 shows the evaluation test results.(2)Figure 4 shows the results of the evaluation test(3)The results are shown in FIG. In addition, the evaluation test in Table 4(1)And evaluation test(Four)The symbols in the column are symbols having the same meaning as the symbols used in Comparative Evaluation 2.
[0058]
[Table 4]

[0059]
  As is clear from Table 4, the evaluation test(1)With respect to the dissolution properties of DMA, in Examples 13 to 16 where the absorbed dose was less than 70 kGy, the synthesized AA-g-PVdF could be dissolved in DMA even at room temperature. In Example 12 where the absorbed dose was 90 kGy, the synthesized AA-g-PVdF was dissolved in DMA maintained at a high temperature (85 ° C.). In contrast, in Comparative Example 7 where the absorbed dose was 130 kGy, it was found that dissolution in DMA was almost impossible even when stirring was added.
  Evaluation test(2)In the adhesion test for Cu foil and Al foil, the adhesion strength of Cu foil and Al foil adhered with AA-g-PVdF is the same as that of acrylic acid group contained in AA-g-PVdF, as shown in FIG. Correlate with content. From the results of Comparative Examples 7 and 8, it can be seen that when the absorbed dose is 1 kGy or less and 120 kGy or more, the adhesive strength of AA-g-PVdF is low and it is not suitable as a binder. The reason for this is considered to be that when the absorbed dose is 1 kGy or less, there are few grafted acrylic acid groups, and when it is 120 kGy or more, the dissolution state of AA-g-PVdF is poor.
[0060]
  Evaluation test(3)In the cycle capacity maintenance characteristic test, as shown in FIG.(2)The same tendency as the test result of adhesive strength was shown. From this result, it was found that the absorbed dose is preferably in the range of 1 kGy to 120 kGy in order to produce a battery capable of maintaining 80% capacity at 400 cycles or more.
  Evaluation test(Four)As is apparent from Table 4, in the adhesion test of the adhesion layer to the current collector, the battery adhesion layer after the charge / discharge cycle was analyzed, and as a result, the absorbed dose was synthesized using PVdF having 1 kGy to 120 kGy. It can be seen that AA-g-PVdF is suitable as a binder for the adhesion layer of the battery. In order to obtain stable adhesion characteristics, it is preferable to use PVdF having a gamma ray absorbed dose of 20 to 100 kGy as a raw material.
[0061]
  <Example 17>
  First, as the third binder, 17mass2 g of AA-g-PVdF obtained by graft polymerization of% acrylic acid on PVdF was prepared. As a solvent, 98 g of DMA was added to 2 g of this AA-g-PVdF and dissolved with a homogenizer to obtain a polymer solution. Specific surface area of 150m as conductive material²/ G of graphite powder was prepared, and this graphite powder was dispersed in 80 g of DMA to prepare a dispersion. This dispersion was added to the polymer solution to prepare an adhesion layer slurry.
  An Al foil having a thickness of 20 μm and a width of 250 mm is prepared as a positive electrode current collector, and the adhesion layer slurry prepared on the Al foil is applied and dried by a doctor blade method, and the adhesion layer thickness after drying is 5 μm. An Al foil having On the other hand, a Cu foil having a thickness of 10 μm and a width of 250 mm was prepared as a negative electrode current collector, and this Cu foil was coated and dried by a doctor blade method, and a Cu foil having an adhesion layer having a thickness of 5 μm after drying. Got.
  Next, each component shown in Table 1 was mixed for 2 hours by a ball mill to prepare a positive electrode active material layer coating slurry, a negative electrode active material layer coating slurry, and an electrolyte layer coating slurry.
[0062]
  The obtained positive electrode active material layer coating slurry is coated on an Al foil having an adhesion layer, dried by a doctor blade method so that the dry thickness of the positive electrode active material layer is 80 μm, and rolled to obtain a positive electrode. Formed. The obtained slurry for coating the negative electrode active material layer is coated on a Cu foil having an adhesion layer, dried by a doctor blade method so that the dry thickness of the negative electrode active material layer is 80 μm, and rolled to form a negative electrode. Formed. The electrolyte layer coating slurry thus obtained is coated and dried by a doctor blade method on a release paper having a thickness of 25 μm and a width of 250 mm so that the dry thickness of the electrolyte layer is 50 μm, and then peeled off from the release paper and the electrolyte layer sheet Formed. Each formed positive electrode, electrolyte sheet, and negative electrode were laminated in order, and the laminate was thermocompression bonded to produce a sheet-like electrode body.
  Next, a positive electrode lead and a negative electrode lead made of Ni are welded to the positive electrode current collector and the negative electrode current collector, respectively, on this electrode body, and housed in a laminate package material processed into a bag shape having an opening, and under reduced pressure conditions The opening was sealed by thermocompression bonding to produce a sheet-like battery.
[0063]
  <Example 18>
  17 modified polymers used for the adhesion layermassA battery was prepared in the same manner as in Example 17 except that the modified polymer (Methacrylic Acid grafting PolyVinylidene Fluoride, MA-g-PVdF) represented by the chemical formula (2) obtained by graft polymerization of 1% of methacrylic acid to polyvinylidene fluoride was used.
  <Example 19>
  In the preparation of the adhesion layer slurry, when dispersing the conductive material in the solvent, 1.2 g of the dispersant is added to reduce the content of the acidic polymer dispersant to the solid matter.mass10.7massA battery was produced in the same manner as in Example 17 except that the percentage was changed to%.
  <Example 20>
  In the preparation of the adhesion layer slurry, when dispersing the conductive material in the solvent, 1.2 g of the dispersant is added to reduce the content of the acidic polymer dispersant to the solid matter.mass10.7massA battery was produced in the same manner as in Example 18 except that the percentage was changed to%.
[0064]
  <Example 21>
  A battery was fabricated in the same manner as in Example 17, except that the dry thickness of the adhesion layer provided on the positive electrode current collector and the negative electrode current collector was 0.5 μm.
  <Example 22>
  A battery was fabricated in the same manner as in Example 17 except that the dry thickness of the adhesion layer provided on the positive electrode current collector and the negative electrode current collector was 1 μm.
  <Example 23>
  A battery was fabricated in the same manner as in Example 17 except that the dry thickness of the adhesion layer provided on the positive electrode current collector and the negative electrode current collector was 10 μm.
  <Example 24>
  A battery was produced in the same manner as in Example 17 except that the dry thickness of the adhesion layer provided on the positive electrode current collector and the negative electrode current collector was 15 μm.
[0065]
  <Example 25>
  2 g of graphite powder, which is the conductive material of the slurry for adhesion layer coating, is used for the binder and the conductive material.massA battery was fabricated in the same manner as in Example 17 except that the ratio was 50/50.
  <Example 26>
  4 g of graphite powder, which is the conductive material of the slurry for adhesion layer coating, is used for the binder and the conductive material.massA battery was fabricated in the same manner as in Example 17 except that the ratio was 33/67.
  <Example 27>
  12 g of graphite powder, which is a conductive material of the slurry for adhesion layer coating, is used to form a binder and a conductive material.massA battery was fabricated in the same manner as in Example 17 except that the ratio was 14/86.
  <Example 28>
  14 g of graphite powder, which is a conductive material of the slurry for adhesion layer coating, is used to form a binder and a conductive material.massA battery was fabricated in the same manner as in Example 17 except that the ratio was 13/87.
[0066]
  <Comparative Example 9>
  A battery was fabricated in the same manner as in Example 17 except that the adhesion layer was not provided on the positive electrode current collector and the negative electrode current collector.
  <Comparative Example 10>
  A battery was prepared in the same manner as in Example 17 except that the binder of the adhesion layer coating slurry was changed from AA-g-PVdF to butyl rubber and the solvent was changed from DMA to toluene.
  <Comparative Example 11>
  A battery was prepared in the same manner as in Example 17, except that the binder of the adhesion layer coating slurry was changed from AA-g-PVdF to an acrylate-methacrylate ester copolymer, and the solvent was changed from DMA to water.
  <Comparative Example 12>
  A battery was fabricated in the same manner as in Example 17, except that the binder for the adhesion layer coating slurry was changed from AA-g-PVdF to polyurethane resin, and the solvent was changed from DMA to a mixed solvent of 108 g of methyl ethyl ketone and 72 g of methyl isobutyl ketone.
  <Comparative Example 13>
  A battery was fabricated in the same manner as in Example 17, except that the binder for the adhesion layer coating slurry was changed from AA-g-PVdF to an epoxy resin, and the solvent was changed from DMA to a mixed solvent of 108 g of methyl ethyl ketone and 72 g of methyl isobutyl ketone.
[0067]
  <Comparative example 14>
  In the preparation of the adhesion layer slurry, when dispersing the conductive material in the solvent, 3.5 g of the dispersant was added to reduce the dispersant content to 26.massA battery was produced in the same manner as in Example 17 except that the percentage was changed to%.
  <Comparative Example 15>
  A battery was fabricated in the same manner as in Example 17, except that the dry thickness of the adhesion layer provided on the positive electrode current collector and the negative electrode current collector was 40 μm.
  <Comparative Example 16>
  20 g of graphite powder, which is a conductive material of the slurry for adhesion layer coating, is used to form a binder and a conductive material.massA battery was fabricated in the same manner as in Example 17 except that the ratio was 9/91.
[0068]
  <Comparison evaluation>
  The batteries obtained in Examples 17 to 28 and Comparative Examples 9 to 16 were subjected to the following evaluation tests.
(Five) Tolerance test of adhesive layer to electrolyte
  The negative electrode current collector having the adhesion layers obtained in Examples 17 to 28 and Comparative Examples 9 to 16 was used as propylene carbonate 20massPart, ethylene carbonate 40massParts and diethyl carbonate 40massOf a negative electrode current collector having an adhesion layer by immersing in an electrolyte solution comprising a partmassThe amount of increase was measured, and the presence or absence of swelling of the modified polymer, which is the third binder of the adhesion layer, by the electrolytic solution was confirmed. Further, the negative electrode current collector Cu foil was rubbed with a finger to confirm whether or not the adhesion layer was peeled off.
(6) Current collector protection performance test for hydrogen fluoride (HF) in adhesion layer
  The state of the current collector after dropping 2 ml of a 5 ppm hydrofluoric acid aqueous solution onto the surface of the negative electrode current collector having the adhesion layers obtained in Examples 17 to 28 and Comparative Examples 9 to 16 and leaving it for 24 hours It was confirmed.
[0069]
(7) Adhesion test of the adhesive layer to the active material layer
  Adhesive tapes were applied to the surfaces of the positive electrode current collector and the negative electrode current collector obtained in Examples 17 to 28 and Comparative Examples 9 to 16, respectively, and pressed with a rubber roller. The positive electrode current collector and the negative electrode current collector to which the adhesive tape was attached were each cut to a width of 10 mm, and the force required to pull off the active material layer by pulling the 10 mm width current collector vertically upward was measured. Moreover, the peeling method was confirmed visually.
(8) Cycle capacity maintenance characteristics test
  The sheet-like batteries obtained in Examples 17 to 28 and Comparative Examples 9 to 16 were subjected to a charge / discharge cycle test, charged for 2.5 hours under the conditions of a maximum charge voltage of 4.2 V and a charge of 0.5 A; The charge / discharge cycle is repeated until the discharge voltage reaches 2.75 V (minimum discharge voltage) at a constant current of 5 A, the discharge capacity of each cycle is measured, and the number of cycles that decrease to 80% of the initial discharge capacity is measured. did.
[0070]
  Above evaluation test(Five)~Evaluation test(8)Table 5 shows the results. The evaluation tests in Table 5(Five)The symbols in the columns have the following meanings.
  (Double-circle): It is very favorable and does not peel.
  ○: Good and does not peel off.
  Δ: Partially peeled off
  X: Completely peeled off.
[0071]
  In addition, the evaluation test in Table 5(6)The symbols in the columns have the following meanings.
  A: Extremely good and does not corrode.
  ○: Good and does not corrode.
  Δ: Partially corroded.
  X: Corrosion occurs.
[0072]
[Table 5]

[0073]
(Five) Tolerance test of adhesive layer to electrolyte
  In Comparative Examples 10 to 13, it can be seen that the amount of increase in the negative electrode current collector having the adhesion layer is large, and it is swollen by the binder that forms the adhesion layer with the electrolytic solution. On the other hand, in Examples 17 to 28, although the amount of increase in the negative electrode current collector having the adhesion layer was small despite being immersed in the electrolytic solution for 1 week, resistance to the electrolytic solution is shown.
(6) Current collector protection performance test for hydrogen fluoride (HF) in adhesion layer
  The current collectors of Comparative Examples 9 and 11 were corroded by HF. In Comparative Examples 10, 12, and 13, a part was corroded. On the other hand, it can be seen that the current collectors of Examples 17 to 28 are not corroded by HF and the protective function by the adhesion layer is working.
[0074]
(7) Adhesion test of the adhesive layer to the active material layer
  Compared to the adhesion of Comparative Examples 9 to 13, in Examples 17 to 28, the force required to peel off the active material layer is large. Moreover, as for how to peel, Comparative Examples 9-13 had in-plane unevenness, and the part which peeled and the part which did not peel were each formed. On the other hand, in Examples 17 to 28, the in-plane was uniform and the entire surface was peeled off.
(8) Cycle capacity maintenance characteristics test
  Compared to the 80% capacity cycle number of Comparative Examples 9 to 13, Examples 17 to 28 each show a higher cycle number, and it can be seen that the cycle maintaining characteristics by charge and discharge are excellent.
[0075]
【The invention's effect】
  As described above, according to the present invention, the first adhesion layer is provided between the positive electrode current collector and the positive electrode active material layer, and the second adhesion is provided between the negative electrode current collector and the negative electrode active material layer. Each of the first and second adhesive layers includes both the third binder and the conductive material, and the third binder includes the first binder or the second binder by the modifying substance. Since it is a modified polymer compound, the modified polymer based on the first binder or the second binder has high adhesion to the positive electrode active material layer or the negative electrode active material layer, and is collected due to modification. Adhesiveness with the electric body is also greatly improved as compared with the conventional binder. As a result, peeling of the active material layer from the current collector can be suppressed, and the electrical conductivity between the current collector and the active material layer is greatly improved, so that the cycle capacity maintenance characteristics can also be improved. In addition, since the electrolytic solution is difficult to be immersed in the modified polymer compound, the adhesion layer is stable with respect to the organic solvent in the electrolytic solution and excellent in long-term storage. Even when strong acid such as hydrofluoric acid is generated in the battery, the modified polymer compound serves as a protective layer, so that corrosion of the current collector can be suppressed.
[Brief description of the drawings]
FIG. 1 is a partial cross-sectional configuration diagram showing an electrode body of a lithium ion polymer secondary battery of the present invention.
FIG. 2 is an evaluation test of the third binder obtained in Examples 5 to 11 and Comparative Examples 5 and 6.(2)FIG.
FIG. 3 is an evaluation test of the third binder obtained in Examples 5 to 11 and Comparative Examples 5 and 6.(Four)FIG.
4 is an evaluation test of a third binder obtained in Examples 12 to 16 and Comparative Examples 7 and 8. FIG.(2)FIG.
FIG. 5: Evaluation test of the third binder obtained in Examples 12 to 16 and Comparative Examples 7 and 8(Four)FIG.
[Explanation of symbols]
  11 Positive electrode
  12 Positive current collector
  13 Positive electrode active material layer
  14 Negative electrode
  16 Negative electrode current collector
  17 Negative electrode active material layer
  18 Polymer electrolyte layer
  19 First adhesion layer
  21 Second adhesion layer

Claims (10)

A positive electrode (11) in which a positive electrode active material layer (13) in which a first binder is contained in an active material is formed on the surface of a positive electrode current collector (12);
A negative electrode (14) having a negative electrode active material layer (17) in which a second binder that is the same as or different from the first binder is contained in the active material on the surface of the negative electrode current collector (16); ,
In a lithium ion polymer secondary battery comprising an electrolyte (18),
A first adhesion layer (19) is provided between the positive electrode current collector (12) and the positive electrode active material layer (13), and the negative electrode current collector (16) and the negative electrode active material layer (17) Having a second adhesion layer (21) between
The first and second adhesion layers (19, 21) each include both a third binder and a conductive material;
The lithium ion polymer secondary battery, wherein the third binder is a polymer compound obtained by modifying the first binder or the second binder with a modifying substance.   Either or both of the first and second binders contain fluorine selected from polytetrafluoroethylene, polychlorotrifluoroethylene, polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, or polyvinyl fluoride. The lithium ion polymer secondary battery according to claim 1, which is a polymer compound.   The modifying substance is a compound selected from ethylene, styrene, butadiene, vinyl chloride, vinyl acetate, acrylic acid, methyl acrylate, methyl vinyl ketone, acrylamide, acrylonitrile, vinylidene chloride, methacrylic acid, methyl methacrylate or isoprene. 2. The lithium ion polymer secondary battery according to 1.   2. The lithium ion polymer secondary battery according to claim 1, wherein each of the first and second adhesion layers has a thickness of 0.5 to 30 μm. The lithium ion polymer secondary battery according to claim 1 or 4, further comprising 0.1 to 20% by mass of a dispersant in the first and second adhesion layers. A carbon material having a particle size of 0.5 to 30 μm and a graphitization degree of 50% or more is used as a conductive material, and a mass ratio of the third binder contained in the first and second adhesion layers and the conductive material (first The lithium ion polymer secondary battery according to claim 1, wherein (3 binder / conductive substance) is 13/87 to 50/50. A method for synthesizing a third binder contained in the adhesion layer of the lithium ion polymer secondary battery according to claim 1,
The third binder is synthesized by modifying either one or both of the first binder and the second binder with a modifying substance,
When 100% by mass of the third binder is the synthesis, the synthesis methods of the binder, wherein the proportion of the modified material contained in the third binder is from 2 to 50 mass%.   The modification with the modifying substance is performed by irradiating one or both of the first and second binders with radiation, and then mixing the modifying substance with the irradiated material and graft polymerization. Synthesis method.   8. The synthesis according to claim 7, wherein the modification with the modifying substance is performed by mixing the modifying substance with one or both of the first and second binders and irradiating the mixture with radiation to perform graft polymerization. Method.   Irradiation to either one or both of the first or second binder is performed by applying gamma rays so that the absorbed dose to either or both of the first or second binder is 1 to 120 kGy. The synthesis method according to claim 8 or 9, which is carried out by irradiation.

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