JP2004079370A - Battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize high capacity and an excellent load characteristic with a small amount of binder. <P>SOLUTION: This battery is provided with a pair of electrodes and an electrolyte. At least one of the pair of electrodes is equipped with a first layer 21 containing a binder, and a second layer 22 containing an active material on a collector 20 in that order. The first layer 21 shows strong binding force as compared with the second layer 22. Since the first layer 21 showing the strong binding force is interlaid between the collector 20 and the second layer 22 containing the active material in at least one of electrodes, the second layer 22 can provide strong binding force even if the binder content is small. Since the binder content of the second layer 22 can be small, the capacity can be increased. Even if the thickness of the second layer 22 is increased for the purpose of high capacity, the load capacity is never degraded. <P>COPYRIGHT: (C)2004,JPO

Description

【０１１４】
表１から明らかなように、正極、負極のうち少なくとも一方において、第１の層と第２の層との膜厚比が５：９５〜８０：２０の範囲内であるサンプル１〜サンプル７は、電極の剥離強度及び柔軟性、負荷特性、放電容量のいずれにおいても優れた結果であった。
【０１１５】
＜実験２＞
実験２では、結着力の大きな第１の層が活物質を含有するとともに結着剤としてポリフッ化ビニリデンを含有する構成の電極を有する電池において、正極の第１の層の結着剤（ポリフッ化ビニリデン）含有量の最適範囲を検討した。
【０１１６】
サンプル１６
第１の層用塗料として、正極活物質としてＬｉＣｏＯ_２を９３重量部と、導電剤を５重量部と、結着剤としてポリフッ化ビニリデンを２重量部とを混合し、この混合物を溶剤に分散させて調製したものを用いたこと以外は、サンプル１と同様にして非水電解液二次電池を作製した。
【０１１７】
サンプル１７
正極における第１の層と第２の層との膜厚比を５０％：５０％となるように設定したこと、及び負極における第１の層と第２の層との膜厚比を５０％：５０％となるように設定したこと以外は、サンプル１６と同様にして非水電解液二次電池を作製した。
【０１１８】
サンプル１８
正極における第１の層と第２の層との膜厚比を８０％：２０％となるように設定したこと、及び負極における第１の層と第２の層との膜厚比を８０％：２０％となるように設定したこと以外は、サンプル１６と同様にして非水電解液二次電池を作製した。
【０１１９】
サンプル１９
正極における第１の層と第２の層との膜厚比を１００％：０％となるように設定したこと、及び負極における第１の層と第２の層との膜厚比を５％：９５％となるように設定したこと以外は、サンプル１６と同様にして非水電解液二次電池を作製した。
【０１２０】
サンプル２０
正極における第１の層と第２の層との膜厚比を１００％：０％となるように設定したこと、及び負極における第１の層と第２の層との膜厚比を８０％：２０％となるように設定したこと以外は、サンプル１６と同様にして非水電解液二次電池を作製した。
【０１２１】
サンプル２１
正極における第１の層と第２の層との膜厚比を５％：９５％となるように設定したこと、及び負極における第１の層と第２の層との膜厚比を１００％：０％となるように設定したこと以外は、サンプル１６と同様にして非水電解液二次電池を作製した。
【０１２２】
サンプル２２
正極における第１の層と第２の層との膜厚比を８０％：２０％となるように設定したこと、及び負極における第１の層と第２の層との膜厚比を１００％：０％となるように設定したこと以外は、サンプル１６と同様にして非水電解液二次電池を作製した。
【０１２３】
サンプル２３
第１の層用塗料として、正極活物質としてＬｉＣｏＯ_２を９０重量部と、導電剤を５重量部と、結着剤としてポリフッ化ビニリデンを５重量部とを混合し、この混合物を溶剤に分散させて調製したものを用いたこと、正極における第１の層と第２の層との膜厚比を５％：９５％となるように設定したこと、及び負極における第１の層と第２の層との膜厚比を５％：９５％となるように設定したこと以外は、サンプル１６と同様にして非水電解液二次電池を作製した。
【０１２４】
サンプル２４
正極における第１の層と第２の層との膜厚比を５０％：５０％となるように設定したこと、及び負極における第１の層と第２の層との膜厚比を５０％：５０％となるように設定したこと以外は、サンプル２３と同様にして非水電解液二次電池を作製した。
【０１２５】
サンプル２５
正極における第１の層と第２の層との膜厚比を３％：９７％となるように設定したこと、及び負極における第１の層と第２の層との膜厚比を３％：９７％となるように設定したこと以外は、サンプル１６と同様にして非水電解液二次電池を作製した。
【０１２６】
サンプル２６
正極における第１の層と第２の層との膜厚比を９０％：１０％となるように設定したこと、及び負極における第１の層と第２の層との膜厚比を９０％：１０％となるように設定したこと以外は、サンプル１６と同様にして非水電解液二次電池を作製した。
【０１２７】
サンプル２７
第１の層用塗料として、正極活物質としてＬｉＣｏＯ_２を９４重量部と、導電剤を５重量部と、結着剤としてポリフッ化ビニリデンを１重量部とを混合し、この混合物を溶剤に分散させて調製したものを用いたこと、正極における第１の層と第２の層との膜厚比を３％：９７％となるように設定したこと、及び負極における第１の層と第２の層との膜厚比を３％：９７％となるように設定したこと以外は、サンプル１６と同様にして非水電解液二次電池を作製した。
【０１２８】
サンプル２８
正極における第１の層と第２の層との膜厚比を５％：９５％となるように設定したこと、及び負極における第１の層と第２の層との膜厚比を５％：９５％となるように設定したこと以外は、サンプル２７と同様にして非水電解液二次電池を作製した。
【０１２９】
サンプル２９
正極における第１の層と第２の層との膜厚比を５０％：５０％となるように設定したこと、及び負極における第１の層と第２の層との膜厚比を５０％：５０％となるように設定したこと以外は、サンプル２７と同様にして非水電解液二次電池を作製した。
【０１３０】
サンプル３０
正極における第１の層と第２の層との膜厚比を８０％：２０％となるように設定したこと、及び負極における第１の層と第２の層との膜厚比を８０％：２０％となるように設定したこと以外は、サンプル２７と同様にして非水電解液二次電池を作製した。
【０１３１】
サンプル３１
正極における第１の層と第２の層との膜厚比を９０％：１０％となるように設定したこと、及び負極における第１の層と第２の層との膜厚比を９０％：１０％となるように設定したこと以外は、サンプル２７と同様にして非水電解液二次電池を作製した。
【０１３２】
以上のサンプル１６〜サンプル３１について、実験１と同様の手法により電極の剥離強度及び柔軟性、並びに負荷特性及び放電容量を測定した。
【０１３３】
これらの結果について、正極の第１の層中のポリフッ化ビニリデン含有量及び電極の膜厚比を併せて下記の表２に示す。なお、以下の表では、ポリフッ化ビニリデンをＰＶｄＦと略記する。
【０１３４】
【表２】

【０１３５】
表２から明らかなように、サンプル１６〜サンプル２４がサンプル２７〜サンプル３１に比べて優れた結果を示すことから、第１の層のポリフッ化ビニリデン含有量は２重量％以上必要であることがわかった。ただし、ポリフッ化ビニリデン含有量が２重量％以上であるものの第１の層と第２の層との膜厚比が５：９５〜８０：２０の範囲を外れるサンプル２５及びサンプル２６は、電極の剥離強度及び柔軟性、負荷特性、放電容量のいずれに劣ることから、第１の層のポリフッ化ビニリデン含有量と、電極の膜厚比との両方の条件を満足することが重要であると判明した。
【０１３６】
＜実験３＞
実験３では、結着力の大きな第１の層が活物質を含有するとともに結着剤としてポリフッ化ビニリデンを含有する構成の電極を有する電池において、第２の層が結着剤として軟質性結着剤の代わりにポリフッ化ビニリデンのみを含有する場合について検討した。
【０１３７】
サンプル３２
正極の第１の層用塗料として、正極活物質としてＬｉＣｏＯ_２を９３重量部と、導電剤を５重量部と、結着剤としてポリフッ化ビニリデンを２重量部とを混合し、この混合物を溶剤に分散させて調製したものを用いた。また、正極の第２の層用塗料として、正極活物質としてＬｉＣｏＯ_２を９４重量部と、導電剤を５重量部と、軟質性結着剤の代わりにポリフッ化ビニリデンを１重量部とを混合し、この混合物を溶剤に分散させて調製したものを用いた。また、負極の第２の層用塗料として、負極活物質として人造黒鉛を９８重量部と、軟質性結着剤の代わりにポリフッ化ビニリデンを２重量部とを混合し、この混合物を溶剤に分散させて調製したものを用いた。これらの変更以外は、サンプル１と同様にして非水電解液二次電池を作製した。
【０１３８】
サンプル３３
正極における第１の層と第２の層との膜厚比を５０％：５０％となるように設定したこと、及び負極における第１の層と第２の層との膜厚比を５０％：５０％となるように設定したこと以外は、サンプル３２と同様にして非水電解液二次電池を作製した。
【０１３９】
サンプル３４
正極における第１の層と第２の層との膜厚比を８０％：２０％となるように設定したこと、及び負極における第１の層と第２の層との膜厚比を８０％：２０％となるように設定したこと以外は、サンプル３２と同様にして非水電解液二次電池を作製した。
【０１４０】
サンプル３５
正極における第１の層と第２の層との膜厚比を９５％：５％となるように設定したこと、及び負極における第１の層と第２の層との膜厚比を９５％：５％となるように設定したこと以外は、サンプル３２と同様にして非水電解液二次電池を作製した。
【０１４１】
以上のサンプル３２〜サンプル３５について、実験１と同様の手法により電極の剥離強度及び柔軟性、並びに負荷特性及び放電容量を測定した。
【０１４２】
これらの結果について、正極の第１の層中のポリフッ化ビニリデン含有量及び電極の膜厚比を併せて下記の表３に示す。
【０１４３】
【表３】

【０１４４】
以上の表３から明らかなように、第２の層が軟質性結着剤を含有しないサンプル３２〜サンプル３５では電極の柔軟性が著しく損なわれていた。このことから、電極の第２の層は軟質性結着剤を含有することが必要であるとわかった。
【０１４５】
＜実験４＞
実験４では、結着力の大きな第１の層が活物質を含有するとともに結着剤としてポリフッ化ビニリデンを含有する構成の電極を有する電池において、第２の層の軟質性結着剤の組成について検討した。
【０１４６】
サンプル３６
正極の第２の層の軟質性結着剤としてポリフッ化ビニリデン９５重量％とヘキサフルオロプロピレン５重量％とを混合したものを用い、負極の第２の層の軟質性結着剤としてポリフッ化ビニリデン９５重量％とヘキサフルオロプロピレン５重量％とを混合したものを用いたこと以外は、サンプル１と同様にして非水電解液二次電池を作製した。
【０１４７】
サンプル３７
正極の第２の層の軟質性結着剤としてポリフッ化ビニリデン５０重量％とヘキサフルオロプロピレン５０重量％とを混合したものを用い、負極の第２の層の軟質性結着剤としてポリフッ化ビニリデン５０重量％とヘキサフルオロプロピレン５０重量％とを混合したものを用いたこと以外は、サンプル１と同様にして非水電解液二次電池を作製した。
【０１４８】
サンプル３８
正極の第２の層の軟質性結着剤としてヘキサフルオロプロピレン１００重量％を用い、負極の第２の層の軟質性結着剤としてポリフッ化ビニリデン９５重量％とヘキサフルオロプロピレン５重量％とを混合したものを用いたこと以外は、サンプル１と同様にして非水電解液二次電池を作製した。
【０１４９】
サンプル３９
正極の第２の層の軟質性結着剤としてポリフッ化ビニリデン９５重量％とスチレンブタジエン系ラテックス５重量％とを混合したものを用い、負極の第２の層の軟質性結着剤としてポリフッ化ビニリデン９５重量％とヘキサフルオロプロピレン５重量％とを混合したものを用いたこと以外は、サンプル１と同様にして非水電解液二次電池を作製した。
【０１５０】
サンプル４０
正極の第２の層の軟質性結着剤としてポリフッ化ビニリデン５０重量％とスチレンブタジエン系ラテックス５０重量％とを混合したものを用い、負極の第２の層の軟質性結着剤としてポリフッ化ビニリデン９５重量％とヘキサフルオロプロピレン５重量％とを混合したものを用いたこと以外は、サンプル１と同様にして非水電解液二次電池を作製した。
【０１５１】
サンプル４１
正極の第２の層の軟質性結着剤としてスチレンブタジエン系ラテックス１００重量％を用い、負極の第２の層の軟質性結着剤としてポリフッ化ビニリデン９５重量％とヘキサフルオロプロピレン５重量％とを混合したものを用いたこと以外は、サンプル１と同様にして非水電解液二次電池を作製した。
【０１５２】
サンプル４２
正極の第２の層の軟質性結着剤としてポリフッ化ビニリデン９５重量％とヘキサフルオロプロピレン５重量％とを混合したものを用い、負極の第２の層の軟質性結着剤としてポリフッ化ビニリデン５０重量％とヘキサフルオロプロピレン５０重量％とを混合したものを用いたこと以外は、サンプル１と同様にして非水電解液二次電池を作製した。
【０１５３】
サンプル４３
正極の第２の層の軟質性結着剤としてポリフッ化ビニリデン９５重量％とヘキサフルオロプロピレン５重量％とを混合したものを用い、負極の第２の層の軟質性結着剤としてヘキサフルオロプロピレン１００重量％を用いたこと以外は、サンプル１と同様にして非水電解液二次電池を作製した。
【０１５４】
サンプル４４
正極の第２の層の軟質性結着剤としてポリフッ化ビニリデン９５重量％とヘキサフルオロプロピレン５重量％とを混合したものを用い、負極の第２の層の軟質性結着剤としてポリフッ化ビニリデン９５重量％とスチレンブタジエン系ラテックス５重量％とを混合したものを用いたこと以外は、サンプル１と同様にして非水電解液二次電池を作製した。
【０１５５】
サンプル４５
正極の第２の層の軟質性結着剤としてポリフッ化ビニリデン９５重量％とヘキサフルオロプロピレン５重量％とを混合したものを用い、負極の第２の層の軟質性結着剤としてポリフッ化ビニリデン５０重量％とスチレンブタジエン系ラテックス５０重量％とを混合したものを用いたこと以外は、サンプル１と同様にして非水電解液二次電池を作製した。
【０１５６】
サンプル４６
正極の第２の層の軟質性結着剤としてポリフッ化ビニリデン９５重量％とヘキサフルオロプロピレン５重量％とを混合したものを用い、負極の第２の層の軟質性結着剤としてスチレンブタジエン系ラテックス１００重量％を用いたこと以外は、サンプル１と同様にして非水電解液二次電池を作製した。
【０１５７】
サンプル４７
正極の第２の層の軟質性結着剤としてポリフッ化ビニリデン１００重量％を用い、負極の第２の層の軟質性結着剤としてポリフッ化ビニリデン１００重量％を用いたこと以外は、サンプル１と同様にして非水電解液二次電池を作製した。
【０１５８】
以上のサンプル３６〜サンプル４７について、実験１と同様の手法により電極の剥離強度及び柔軟性、並びに放電容量を測定した。
【０１５９】
また、電極の柔軟性は、電極の膜厚構成が第１の層：第２の層＝５％：９５％であり、且つ第２の層が含有する軟質性結着剤がヘキサフルオロプロピレン又はスチレンブタジエン系ラテックスのみからなる場合の柔軟性を１０．０としたときの相対値で表した。
【０１６０】
これらの結果について、正極及び負極の第２の層中の軟質性結着剤組成を併せて下記の表４に示す。なお、表４中、ヘキサフルオロプロピレンをＨＦＰと略記し、スチレンブタジエン系ラテックスをＳＢＲと略記した。
【０１６１】
【表４】

【０１６２】
以上の表４から、正極、負極のうち少なくとも一方が、第２の層の軟質性結着剤としてポリフッ化ビニリデンとヘキサフルオロプロピレンとの混合物又はポリフッ化ビニリデンとスチレンブタジエン系ラテックスとの混合物を含有することで、剥離強度と柔軟性とを両立する電極を実現できることがわかった。
【０１６３】
＜実験５＞
実験５では、第２の層のみが活物質を含有し、第１の層がプライマー層として機能する正極の各層の膜厚及び組成の最適範囲について検討した。
【０１６４】
サンプル４８
先ず、以下のようにして正極を作製した。厚さ２０μｍの帯状アルミニウム箔からなる正極集電体の両面に、第１の層用塗料を均一に塗布し、乾燥させて第１の層を形成した。第１の層の平均膜厚は、０．５μｍであった。また、第１の層上に、第２の層用塗料を均一に塗布し、乾燥させ、ローラープレスにより一定圧力で圧縮成型して第２の層を形成し、これをスリットすることで正極を得た。なお、第２の層を形成する際、第２の層のプレス後膜厚が１６０μｍ、体積密度が３．５ｇ／ｃｍ^３となるように塗布量を調整した。
【０１６５】
ここで用いた第１の層用塗料は、結着剤としてポリフッ化ビニリデンを９０重量％と、導電剤である炭素粉末としてアセチレンブラックを１０重量％とを混合し、この混合物を溶剤としてＮ−メチル−２−ピロリドン中に分散させて調製したものである。
【０１６６】
また、第２の層用塗料は、正極活物質としてＬｉＣｏＯ_２を９８重量％と、導電剤としてケッチェンブラックを１重量％と、結着剤としてポリフッ化ビニリデンを１重量％とを混合し、この混合物を溶剤としてＮ−メチル−２−ピロリドン中に分散させて調製したものである。
【０１６７】
次に、以下のようにして負極を作製した。厚さ１５μｍの帯状銅箔からなる負極集電体に、負極合剤用塗料を均一に塗布し、乾燥させ、ローラープレスにより一定圧力で圧縮成型して負極合剤層を形成し、これをスリットすることで負極を得た。なお、負極合剤層を形成する際、負極合剤層のプレス後膜厚が１６０μｍ、体積密度が１．６６ｇ／ｃｍ^３となるように塗布量を調整した。
【０１６８】
ここで用いた負極合剤用塗料は、負極活物質としてグラファイトを９４重量％と、結着剤としてポリフッ化ビニリデンを６重量％とを混合し、この混合物を溶剤に分散させて調製したものである。
【０１６９】
以上のようにして得られた正極と、負極と、厚さ２０μｍの微孔性ポリエチレンフィルムからなるセパレータとを、負極、セパレータ、正極、セパレータの順に積層して密着させ、渦巻型に多数回巻回することにより巻回体を作製した。
【０１７０】
次に、その内側にニッケルメッキを施した鉄製の電池缶の底部に絶縁板を挿入し、さらに巻回体を収納した。そして負極の集電をとるために、ニッケル製の負極リードの一端を負極に圧着させ、他端を電池缶に溶接した。また、正極の集電をとるために、アルミニウム製の正極リードの一端を正極に取り付け、他端を電池蓋と電気的に接続した。
【０１７１】
そして、この電池缶の中に非水電解液を注入した。この非水電解液は、エチレンカーボネートとジメチルカーボネートとを１：１の体積比で混合した混合溶媒中に、電解質としてＬｉＰＦ_６を１モル／ｌの濃度で溶解させて調製したものである。
【０１７２】
最後に、アスファルトを塗布した絶縁封口ガスケットを介して電池缶をかしめることにより、電流遮断用薄板、ＰＴＣ素子及び電池蓋を固定して、直径が約１８ｍｍ、高さが約６５ｍｍの円筒型の非水電解液二次電池を作製した。
【０１７３】
サンプル４９
正極の第２の層のＬｉＣｏＯ_２含有量を９４重量％とし、ポリフッ化ビニリデン含有量を５重量％としたこと以外は、サンプル４８と同様にして非水電解液二次電池を作製した。
【０１７４】
サンプル５０
正極の第１の層の膜厚を５μｍとし、アセチレンブラック含有量を７５重量％としたこと以外は、サンプル４８と同様にして非水電解液二次電池を作製した。
【０１７５】
サンプル５１
正極の第１の層の膜厚を５μｍとし、アセチレンブラック含有量を７５重量％とし、第２の層のＬｉＣｏＯ_２含有量を９４重量％とし、ポリフッ化ビニリデン含有量を５重量％としたこと以外は、サンプル４８と同様にして非水電解液二次電池を作製した。
【０１７６】
サンプル５２
正極の第１の層のアセチレンブラック含有量を７５重量％としたこと以外は、サンプル４８と同様にして非水電解液二次電池を作製した。
【０１７７】
サンプル５３
正極の第１の層の膜厚を５μｍとし、第２の層のＬｉＣｏＯ_２含有量を９４重量％とし、ポリフッ化ビニリデン含有量を５重量％としたこと以外は、サンプル４８と同様にして非水電解液二次電池を作製した。
【０１７８】
サンプル５４
正極の第２の層の膜厚を３００μｍとし、負極合剤層の膜厚を３００μｍとしたこと以外は、サンプル４８と同様にして非水電解液二次電池を作製した。
【０１７９】
サンプル５５
正極の第２の層のＬｉＣｏＯ_２含有量を９４重量％とし、ポリフッ化ビニリデン含有量を５重量％とし、負極合剤層の膜厚を３００μｍとしたこと以外は、サンプル５４と同様にして非水電解液二次電池を作製した。
【０１８０】
サンプル５６
正極の第１の層の膜厚を５μｍとし、アセチレンブラック含有量を７５重量％とし、負極合剤層の膜厚を３００μｍとしたこと以外は、サンプル５４と同様にして非水電解液二次電池を作製した。
【０１８１】
サンプル５７
正極の第１の層の膜厚を５μｍとし、アセチレンブラック含有量を７５重量％とし、第２の層のＬｉＣｏＯ_２含有量を９４重量％とし、ポリフッ化ビニリデン含有量を５重量％とし、負極合剤層の膜厚を３００μｍとしたこと以外は、サンプル５４と同様にして非水電解液二次電池を作製した。
【０１８２】
サンプル５８
正極の第１の層のアセチレンブラック含有量を７５重量％とし、負極合剤層の膜厚を３００μｍとしたこと以外は、サンプル５４と同様にして非水電解液二次電池を作製した。
【０１８３】
サンプル５９
正極の第１の層の膜厚を５μｍとし、第２の層のＬｉＣｏＯ_２含有量を９４重量％とし、ポリフッ化ビニリデン含有量を５重量％とし、負極合剤層の膜厚を３００μｍとしたこと以外は、サンプル５４と同様にして非水電解液二次電池を作製した。
【０１８４】
サンプル６０
正極の第１の層を形成せず、第２の層の膜厚を１５０μｍとし、ＬｉＣｏＯ_２含有量を９３重量％とし、ポリフッ化ビニリデン含有量を６重量％とし、負極合剤層の膜厚を１５０μｍとしたこと以外は、サンプル４８と同様にして非水電解液二次電池を作製した。
【０１８５】
サンプル６１
正極の第１の層を形成せず、第２の層のＬｉＣｏＯ_２含有量を９３重量％とし、ポリフッ化ビニリデン含有量を６重量％としたこと以外は、サンプル４８と同様にして非水電解液二次電池を作製した。
【０１８６】
サンプル６２
正極の第１の層の膜厚を５μｍとし、アセチレンブラック含有量を７５重量％とし、ＬｉＣｏＯ_２含有量を９３重量％とし、第２の層のポリフッ化ビニリデン含有量を６重量％としたこと以外は、サンプル４８と同様にして非水電解液二次電池を作製した。
【０１８７】
サンプル６３
正極の第１の層を形成せず、第２の層のＬｉＣｏＯ_２含有量を９４重量％とし、ポリフッ化ビニリデン含有量を５重量％としたこと以外は、サンプル４８と同様にして非水電解液二次電池を作製した。
【０１８８】
サンプル６４
正極の第１の層を形成しなかったこと以外は、サンプル４８と同様にして非水電解液二次電池を作製した。
【０１８９】
サンプル６５
正極の第１の層を形成せず、第２の層の膜厚を３００μｍとし、ＬｉＣｏＯ_２含有量を９４重量％とし、ポリフッ化ビニリデン含有量を５重量％とし、負極合剤層の膜厚を３００μｍとしたこと以外は、サンプル４８と同様にして非水電解液二次電池を作製した。
【０１９０】
サンプル６６
正極の第１の層の膜厚を５μｍとし、アセチレンブラック含有量を７５重量％とし、第２の層のＬｉＣｏＯ_２含有量を９８．５重量％とし、ポリフッ化ビニリデン含有量を０．５重量％としたこと以外は、サンプル４８と同様にして非水電解液二次電池を作製した。
【０１９１】
サンプル６７
正極の第１の層の膜厚を５μｍとし、アセチレンブラック含有量を７５重量％とし、第２の層の膜厚を３１０μｍとし、ＬｉＣｏＯ_２含有量を９４重量％とし、ポリフッ化ビニリデン含有量を５重量％とし、負極合剤層の膜厚を３１０μｍとしたこと以外は、サンプル４８と同様にして非水電解液二次電池を作製した。
【０１９２】
サンプル６８
正極の第１の層のアセチレンブラック含有量を５重量％とし、第２の層の膜厚を３００μｍとし、負極合剤層の膜厚を３００μｍとしたこと以外は、サンプル４８と同様にして非水電解液二次電池を作製した。
【０１９３】
サンプル６９
正極の第１の層のアセチレンブラック含有量を８０重量％とし、第２の層の膜厚を３００μｍとし、負極合剤層の膜厚を３００μｍとしたこと以外は、サンプル４８と同様にして非水電解液二次電池を作製した。
【０１９４】
以上のように作製されたサンプル４８〜サンプル６９について、正極の剥離の様子及び割れを観察し、結果を下記の表５に示した。剥離については、正極に剥離が全く観察されなかったものを○とし、微小な剥離が観察されたものを△とし、大きな剥離が観察されたものを×として表記した。また、割れについては、正極に割れが全く観察されなかったものを○とし、微小な割れが観察されたものを△とし、大きな割れが観察されたものを×として表記した。
【０１９５】
また、サンプル４８〜サンプル６９について、以下のようにして０．２Ｃでの放電容量及び１Ｃ、０℃での低温負荷特性を測定し、結果を併せて下記の表５に示した。
【０１９６】
放電容量は、作製された非水電解液二次電池について、環境温度２３℃、充電電圧４．２０Ｖ、充電電流１０００ｍＡ、充電時間３時間の条件で充電を行った後、放電電流４００ｍＡ、終止電圧２．７５Ｖで放電を行ったときの初期容量として求めた。
【０１９７】
低温負荷特性は、上記の放電容量測定後の非水電解液二次電池について、充電電圧４．２０Ｖ、充電電流１０００ｍＡ、充電時間３時間の条件で充電を行った後、環境温度０℃、放電電流２０００ｍＡ、終止電圧２．７５Ｖで放電を行ったときの容量を求め、初期容量に対する割合を百分率で表した。
【０１９８】
【表５】

【０１９９】
表５から明らかなように、サンプル４８〜サンプル５９は、放電容量、低温負荷特性、電極の剥離及び割れのいずれについても良好な結果であった。これに対してサンプル６０〜サンプル６９は、上記の特性のうちいずれかに劣るものであった。
【０２００】
なお、表５には示していないが、正極の第１の層の膜厚が０．５μｍ以下となるように塗布を行った場合、塗膜が薄すぎて均一な塗布が不可能であった。また、正極の第１の層の膜厚が５μｍを上回るように塗布を行った場合、放電容量の低下を引き起こした。
【０２０１】
以上の実験５の結果から、第１の層の炭素粉末含有量が１０重量％〜７５重量％であり、第１の層の膜厚が０．５μｍ〜５μｍであり、第２の層の結着剤含有量が１重量％〜５重量％であり、且つ第２の層の膜厚が１６０μｍ〜３００μｍであることが好ましいことがわかった。
【０２０２】
＜実験６＞
実験６では、ＣｕＫα線によるＸ線回折測定を行ったときの、Ｘ線回折パターンにおける回折角（２θ、θ：ブラッグ角）２０．０°付近のピーク比（集電体側／第２の層側）の最適範囲について検討した。また、負極活物質として用いる合金についても検討した。
【０２０３】
サンプル７０
先ず、以下のようにして負極を作製した。厚さ１５μｍの帯状銅箔からなる負極集電体の両面に、第１の層用塗料を均一に塗布し、乾燥させて第１の層を形成した。乾燥後の第１の層の膜厚は、０．５μｍであった。また、第１の層上に、第２の層用塗料を均一に塗布し、乾燥させ、ローラープレスにより一定圧力で圧縮成型して第２の層を形成し、これをスリットすることで負極を得た。
【０２０４】
ここで用いた第１の層用塗料は、結着剤としてポリフッ化ビニリデンを９０重量％と、導電剤である炭素粉末としてアセチレンブラックを１０重量％とを混合し、この混合物を溶剤としてＮ−メチル−２−ピロリドン中に分散させて調製したものである。
【０２０５】
また、第２の層用塗料は、負極活物質としてＣｕＳｎ粉体を６０重量％と、鱗片状黒鉛を３５重量％と、結着剤としてポリフッ化ビニリデンを５重量％とを混合し、この混合物を溶剤としてＮ−メチル−２−ピロリドンに分散させて調製したものである。ＣｕＳｎ粉体は、Ｃｕを５０重量部とＳｎを５０重量部とを溶融し、ガスアトマイズ法により合成したものである。得られたＣｕＳｎ粉体を６３μｍのふるいでメッシュパスしたところ、平均粒径は２５μｍであった。
【０２０６】
なお、得られた負極について、Ｘ線回折による回折角（２θ、θ：ブラッグ角）２０．０°付近のピーク比（集電体側／第２の層側）を測定した。具体的には、負極集電体の一主面側にのみ第１の層及び第２の層が形成された状態で、集電体側及び第２の層側についてＸ線回折測定を行った。測定によって得られたＸ線回折パターンにおいて、回折角（２θ、θ：ブラッグ角）２０．０°付近のピーク比（集電体側／第２の層側）を求めた。Ｘ線回折による回折角（２θ、θ：ブラッグ角）２０．０°付近のピーク比（集電体側／第２の層側）は、１．１であった。
【０２０７】
Ｘ線回折測定に用いたＸ線回折装置は理学電機製ＲＡＤ−ＩＩＣであり、Ｘ線源はＣｕ対陰極を用い、グラファイトモノクロメーターを使用した。また、スリットはＤＳ（発散スリット）＝１°、ＲＳ（受光スリット）＝０．６°、ＳＳ（散乱スリット）＝１°とした。走査速度は０．５°／分とし、管電圧は４０ｋＶ、管電流は３０ｍＡとした。
【０２０８】
また、Ｘ線回折による回折角（２θ、θ：ブラッグ角）２０．０°付近のピーク比（集電体側／第２の層側）を測定する状態の負極に対して、日本電子製走査型電子顕微鏡ＪＳＭ−５６００によりフッ素原子マッピングを行い、フッ素密度比を求めた。求められたフッ素密度比は、１．１であった。
【０２０９】
次に、以下のようにして正極を作製した。厚さ２０μｍの帯状アルミニウム箔からなる正極集電体の両面に、正極合剤層用塗料を均一に塗布し、乾燥させ、ローラープレスにより一定圧力で圧縮成型して正極合剤層を形成し、これをスリットすることで正極を得た。
【０２１０】
ここで用いた正極合剤層用塗料は、正極活物質としてＬｉＣｏＯ_２粉末を９５重量％と炭酸リチウム粉末５重量％とを混合した混合物を９１重量％と、導電剤として鱗片状黒鉛を６重量％と、結着剤としてポリフッ化ビニリデンを３重量％とを混合し、この混合物を溶剤としてＮ−メチル−２−ピロリドン中に分散させて調製したものである。
【０２１１】
正極活物質として用いたＬｉＣｏＯ_２粉末は、次のように作製した。すなわち、炭酸リチウム０．５ｍｏｌと炭酸コバルト１ｍｏｌとを混合し、この混合物を空気中、９００℃５時間焼成した。得られた材料についてＸ線回折測定を行った結果、ピーク位置がＪＣＰＤＳファイルに登録されたＬｉＣｏＯ_２のデータとよく一致していた。この得られた材料を粉砕し、レーザー回折法で得られる累積５０％粒径を１５μｍとして、正極活物質とした。
【０２１２】
以上のようにして得られた正極と、負極と、厚さ２５μｍの微孔性ポリプロピレンフィルムからなるセパレータとを、負極、セパレータ、正極、セパレータの順に積層して密着させ、渦巻型に多数回巻回して最外周のセパレータの最終端部をテープで固定することにより巻回体を作製した。
【０２１３】
次に、その内側にニッケルメッキを施した鉄製の電池缶の底部に絶縁板を挿入し、さらに巻回体を収納した。そして負極の集電をとるために、ニッケル製の負極リードの一端を負極に圧着させ、他端を電池缶に溶接した。また、正極の集電をとるために、アルミニウム製の正極リードの一端を正極に取り付け、他端を電池蓋と電気的に接続した。
【０２１４】
そして、この電池缶の中に非水電解液を注入した。この非水電解液は、エチレンカーボネートとジメチルカーボネートとを１：１の体積比で混合した混合溶媒中に、電解質としてＬｉＰＦ_６を１モル／ｌの濃度で溶解させて調製したものである。
【０２１５】
最後に、アスファルトを塗布した絶縁封口ガスケットを介して電池缶をかしめることにより、電流遮断用薄板、ＰＴＣ素子及び電池蓋を固定して、直径が約１８ｍｍ、高さが約６５ｍｍの円筒型の非水電解液二次電池を作製した。
【０２１６】
サンプル７１
負極の第１の層の膜厚を１．０μｍとしたこと以外は、サンプル７０と同様にして非水電解液二次電池を作製した。
【０２１７】
サンプル７２
負極の第１の層の膜厚を１．０μｍとしたこと以外は、サンプル７０と同様にして非水電解液二次電池を作製した。なお、Ｘ線回折による回折角（２θ、θ：ブラッグ角）２０．０°付近のピーク比（集電体側／第２の層側）は１．２であり、フッ素密度比は１．３であった。
【０２１８】
サンプル７３
負極の第１の層の膜厚を１．５μｍとしたこと以外は、サンプル７０と同様にして非水電解液二次電池を作製した。なお、Ｘ線回折による回折角（２θ、θ：ブラッグ角）２０．０°付近のピーク比（集電体側／第２の層側）は１．４であり、フッ素密度比は１．４であった。
【０２１９】
サンプル７４
負極の第１の層の膜厚を３．０μｍとしたこと以外は、サンプル７０と同様にして非水電解液二次電池を作製した。なお、Ｘ線回折による回折角（２θ、θ：ブラッグ角）２０．０°付近のピーク比（集電体側／第２の層側）は１．８であり、フッ素密度比は１．７であった。
【０２２０】
サンプル７５
負極活物質としてＦｅＳｎ粉末を用いたこと以外は、サンプル７０と同様にして非水電解液二次電池を作製した。なお、Ｘ線回折による回折角（２θ、θ：ブラッグ角）２０．０°付近のピーク比（集電体側／第２の層側）は１．１であり、フッ素密度比は１．１であった。
【０２２１】
サンプル７６
負極の第１の層を形成しなかったこと以外は、サンプル７０と同様にして非水電解液二次電池を作製した。なお、Ｘ線回折による回折角（２θ、θ：ブラッグ角）２０．０°付近のピーク比（集電体側／第２の層側）は０．９であり、フッ素密度比は０．９であった。
【０２２２】
以上のように作製されたサンプル７１〜サンプル７６について、充放電サイクル特性及び電極強度比を測定した。
【０２２３】
充放電サイクル特性は、先ず、作製された非水電解液二次電池に対して環境温度２３℃、定電流０．５Ａ、最大電圧４．２Ｖ、充電時間４時間の条件で定電流定電圧充電を行い、次に、環境温度２３℃、定電流０．３Ａ、終止電圧２．７５Ｖの条件で放電を行い、このときの容量を初期容量として求めた。次に、環境温度２３℃、定電流２．０Ａ、最大電圧４．２Ｖ、充電時間２．５時間の条件で定電流定電圧充電を行い、この後で環境温度２３℃、定電流０．３Ａ、終止電圧２．７５Ｖの条件で放電を行い、これを１サイクルとした。この充放電を１００サイクル繰り返したときの容量を測定し、初期容量を１００％としたときの比率を容量維持率として表した。
【０２２４】
また、電極強度比は、以下のようにして測定した。負極を３０ｍｍ×２００ｍｍに切断し、粘着テープを用いて１ｍ／分の速度で引っ張り強度試験を行い、このときの強度を測定した。そして、測定した強度を、サンプル７１の電極強度を１００％としたときの比率で表した。
【０２２５】
以上のサンプル７１〜サンプル７６に関するＸ線回折による回折角（２θ、θ：ブラッグ角）２０．０°付近のピーク比（集電体側／第２の層側）、フッ素密度比、１００サイクル後の容量維持率、及び電極強度比を下記の表６に示す。
【０２２６】
【表６】

【０２２７】
以上の表６から、サンプル７１〜サンプル７５は、Ｘ線回折による回折角（２θ、θ：ブラッグ角）２０．０°付近のピーク比が０．９であるサンプル７６に比べて容量維持率及び電極強度比のいずれにおいても優れた結果であることがわかる。
【０２２８】
したがって、実験６の結果から、Ｘ線回折による回折角（２θ、θ：ブラッグ角）２０．０°付近のピーク比（集電体側／第２の層側）が１以上であることが好ましいことが判明した。また、負極活物質として合金材料を用いた場合であっても本発明は有効であることが明らかとなった。
【０２２９】
【発明の効果】
以上の説明からも明らかなように、本発明に係る電池は、少なくとも一方の電極において集電体と活物質を含む第２の層との間に強い結着力を示す第１の層を介在させるので、第２の層は結着剤含有量が少量であっても強い結着力を得られる。そして、第２の層の結着剤含有量が少量で済むので、高容量化が可能となる。また、さらなる高容量化を目的として電極の厚みを増した場合でも、負荷特性の低下を招くことがない。したがって本発明によれば、少量の結着剤でも電極の剥離強度を向上させることができ、高容量及び優れた負荷特性を実現した電池を提供することができる。
【図面の簡単な説明】
【図１】本発明を適用した非水電解液二次電池の断面図である。
【図２】集電体上に第１の層及び第２の層を備える電極の要部概略断面図である。
【符号の説明】
１　　非水電解液二次電池
２　　正極
３　　負極
４　　セパレータ
５　　電池缶
６　　絶縁板
７　　絶縁板
８　　負極リード
９　　正極リード
１０　　電池蓋
１１　　絶縁封口ガスケット
１２　　安全弁装置
１３　　ＰＴＣ素子
２０　　集電体
２１　　第１の層
２２　　第２の層[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention includes a pair of electrodes and an electrolyte, and at least one of the pair of electrodes includes a first layer containing a binder on a current collector, and a second layer containing an active material. In this order.
[0002]
[Prior art]
2. Description of the Related Art In recent years, remarkable progress in electronic technology has realized a reduction in size and weight of electronic devices one after another. Along with this, a demand for a smaller and lighter secondary battery as a driving power source is further increasing. Under such demands, non-aqueous electrolyte batteries using a non-aqueous electrolyte as an electrolyte have been actively researched and developed, and have already been put to practical use. Among non-aqueous electrolyte batteries, a so-called lithium ion secondary battery that uses doping and undoping of lithium ions has a higher capacity than conventional aqueous batteries such as a lead battery and a nickel cadmium battery. This battery is of particular interest because it can be designed.
[0003]
In general, a non-aqueous electrolyte battery has a positive electrode and a negative electrode capable of doping and undoping lithium ions, and a non-aqueous electrolyte as a non-aqueous electrolyte in which, for example, a lithium salt is dissolved in an aprotic organic solvent. Each of the positive electrode and the negative electrode includes a current collector, and a mixture layer containing an active material, a conductive agent, and a binder for binding the active material and the current collector to the current collector. In ordinary nonaqueous electrolyte batteries, polyvinylidene fluoride is widely used as a binder.
[0004]
Even in such non-aqueous electrolyte batteries, demands for higher energy density and longer discharge time, that is, higher capacity are increasing year by year. There are many methods for realizing these high energy densities and high capacities, but the following two methods are considered as methods that do not involve changing the active material.
[0005]
(1) The ratio of the active material occupying in the electrode is increased by reducing the amount of a member other than the active material, particularly, a binder not involved in charge and discharge.
(2) To increase the thickness of the mixture layer and increase the density of the active material.
[0006]
[Problems to be solved by the invention]
However, when the method (1) is employed using existing polyvinylidene fluoride as the binder, the amount of the binder that can be reduced is limited due to the balance of the binding force between the mixture layer and the current collector. . That is, simply decreasing the amount of polyvinylidene fluoride as a binder lowers the bonding strength and peel strength between the mixture layer and the current collector, causing an increase in the defective rate during manufacturing.
[0007]
In addition, when the method (2) is employed, the internal resistance increases due to the binder contained in the mixture layer, and the load characteristics deteriorate. Furthermore, if polyvinylidene fluoride is used as the binder and the method (2) is adopted, the flexibility of the electrode is impaired. Therefore, a step of winding the electrode after applying the mixture layer on the current collector , Defects such as peeling of the mixture layer and cracking of the mixture layer are likely to occur.
[0008]
Therefore, the present invention has been proposed to solve such a conventional problem, and it is an object of the present invention to provide a battery capable of realizing high capacity and excellent load characteristics with a small amount of a binder. Aim.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, a battery according to the present invention includes a pair of electrodes and an electrolyte, and at least one of the pair of electrodes has a first layer containing a binder on a current collector. And a second layer containing an active material, in this order, wherein the first layer has a stronger binding force than the second layer.
[0010]
In the battery having the above structure, the first layer having a strong binding force is interposed between the current collector and the second layer containing the active material in at least one of the electrodes. Even if the content of the adhesive is small, a strong binding force can be obtained. And since the binder content of the second layer is small, the capacity can be increased. Further, even when the thickness of the second layer is increased for the purpose of further increasing the capacity, the load characteristics do not deteriorate.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, a battery to which the present invention is applied will be described in detail with reference to the drawings. Here, a non-aqueous electrolyte secondary battery called a so-called lithium ion secondary battery will be described with reference to FIG.
[0012]
As shown in FIG. 1, a non-aqueous electrolyte secondary battery 1 has a wound body in which a film-shaped positive electrode 2 and a film-shaped negative electrode 3 are laminated in close contact with a separator 4 and wound. , And is loaded inside the battery can 5. In the battery can 5, a non-aqueous electrolyte is injected as an electrolyte.
[0013]
In the present invention, at least one of the positive electrode 2 and the negative electrode 3 has, as shown in FIG. 2, a first layer 21 having at least a binder on a current collector 20 and a second layer 21 having at least an active material. Are provided in this order. Here, the first layer 21 has a stronger binding force than the second layer 22. In the following, the positive electrode 2 and / or the negative electrode 3 having a two-layer structure on such a current collector may be collectively referred to as an electrode.
[0014]
In this electrode, since the first layer 21 having a strong binding force is interposed between the current collector 20 and the second layer 22, the binder of the second layer 22 formed thereon is formed. Even if the content is small, a strong binding force can be obtained. As a result, the content of the binder in the second layer 22 can be reduced, that is, the content of the active material can be increased, so that the capacity can be increased. As described above, the battery of the present invention achieves high capacity without causing a decrease in the peel strength of the electrode due to a decrease in the binder content. In addition, since the amount of the binder in the second layer 22 is reduced, the load characteristics are not impaired even when the thickness of the second layer 22 is increased in order to further increase the capacity. Therefore, the battery of the present invention can achieve both high capacity and excellent load characteristics.
[0015]
Further, the electrode having the above configuration has a peak ratio (current collector side / second side) near the diffraction angle (2θ, θ: Bragg angle) of 20.0 ° in the X-ray diffraction pattern when X-ray diffraction measurement using CuKα ray is performed. (2 layer side) is preferably 1 or more. When the peak ratio is 1 or more, the effect of the present invention of realizing high peel strength with a small amount of the binder can be reliably obtained. If the peak ratio is less than 1, the peel strength may be insufficient.
[0016]
By the way, the first layer 21 and the second layer 22 containing at least the active material are provided in this order on the current collector 20 as described above, and the binding force of the first layer 21 is relatively large. The electrode having the structure described above can realize higher battery characteristics by satisfying the conditions of the following film thickness and composition.
[0017]
The details of the configuration of such an electrode include the case where the first layer having a large binding force contains an active material and also contains polyvinylidene fluoride as a binder, and the case where the first layer having a large binding force has a binding agent And a powder containing a fluororesin and a carbon powder and not containing an active material.
[0018]
First, the case where the first layer having a large binding force contains an active material and also contains polyvinylidene fluoride as a binder will be described.
[0019]
In the electrode in this case, the above-described first layer contains 2% by weight or more of polyvinylidene fluoride, and the second layer contains 1% by weight or more of the soft binder. Further, the thickness ratio of the first layer to the second layer is in the range of 5:95 to 80:20.
[0020]
Here, the soft binder is, for example, a rubber compound having a diene structure such as butadiene latex such as styrene butadiene latex, or a rubber binder such as fluorine rubber such as acrylic rubber or hexafluoropropylene. , A mixture of a rubber-based binder and polyvinylidene fluoride, a polymer of a rubber-based binder and polyvinylidene fluoride, etc. Refers to an adhesive. Among them, a mixture of polyvinylidene fluoride and hexafluoropropylene or a mixture of polyvinylidene fluoride and styrene-butadiene-based latex is a suitable material as a soft binder.
[0021]
In the battery using the electrode of this example, for the same reason as the battery having the basic electrode structure described above, without causing a decrease in peel strength due to a decrease in the amount of the binder, a high capacity and excellent load characteristics are obtained. Can be realized.
[0022]
Further, in addition to the above-described binding force, since the first layer contains polyvinylidene fluoride as a binder at 2% by weight or more, a higher effect of improving peel strength can be obtained. As a result, in the battery of the first example, a higher capacity can be realized without causing an increase in the defective rate due to insufficient peel strength. Further, since the amount of the binder in the entire electrode can be reduced, the electronic conductivity of the electrode is improved, and the load characteristics are further improved. If the polyvinylidene fluoride content of the first layer is less than 2% by weight, the peel strength may be insufficient.
[0023]
Further, since the second layer contains the above-mentioned soft binder in an amount of 1% by weight or more, a highly flexible electrode can be realized. As a result, for example, the electrodes are not damaged even in the step of manufacturing a wound electrode body as shown in FIG. In addition, for example, when polyvinylidene fluoride is used alone as a binder of the second layer, a crack occurs in the second layer in a step of manufacturing a wound body of the electrode due to insufficient flexibility of the electrode, Defective products may occur frequently. When the content of the soft binder in the second layer is less than 1% by weight, the binding strength of the second layer may be insufficient.
[0024]
Further, by defining the thicknesses of the first layer and the second layer within the above-described ranges, both the peel strength of the electrode and the flexibility of the electrode can be achieved.
[0025]
Next, a case where the first layer having a large binding force contains a fluorine-based resin and a carbon powder as a binder and does not contain an active material will be described.
[0026]
In the electrode in this case, the first layer contains a fluorine-based resin as a binder. Further, the first layer contains 10 to 75% by weight of carbon powder. The thickness of the first layer is 0.5 μm to 5 μm. Further, the second layer contains a binder in an amount of 1% by weight to 5% by weight, and has a thickness of 160 μm to 300 μm.
[0027]
In the battery using the electrode of this example, for the same reason as the battery having the basic electrode structure described above, without causing a decrease in peel strength due to a decrease in the amount of the binder, a high capacity and excellent load characteristics are obtained. Can be realized.
[0028]
Further, the second layer has a thickness of 160 μm to 300 μm, which is extremely large as compared with the conventional one for the purpose of further increasing the capacity, but the content of the binder is 1% to 5% by weight as compared with the conventional one. Since it is reduced, load characteristics do not deteriorate. When the thickness of the second layer is less than 160 μm, the battery capacity becomes a value equal to or lower than that of the existing battery, and when the thickness exceeds 300 μm, the load characteristics are reduced, and when the battery is formed, Cracks may occur. When the content of the binder in the second layer is less than 1% by weight, the second layer is peeled off. There is a possibility that the characteristics are deteriorated.
[0029]
Further, since the first layer using a fluorine-based resin as a binder is interposed between the second layer and the current collector, the peel strength due to the reduction in the binder content of the second layer is obtained. To suppress the decrease. The first layer contains carbon powder in the fluororesin in an amount of 10% by weight to 75% by weight to secure the conductivity and the binding force required for the electrode. When the thickness of the first layer is 0.5 μm to 5 μm, a sufficient binding force can be secured while suppressing a decrease in the capacity of the electrode. When the content of the carbon powder in the first layer is less than 10% by weight, the conductivity becomes insufficient, and when it exceeds 75% by weight, the binding force may be insufficient. On the other hand, when the thickness of the first layer is less than 0.5 μm, it becomes difficult to form the first layer by coating, so that uniformity cannot be secured. Conversely, when the thickness exceeds 5 μm, The capacity may be reduced.
[0030]
As described above, the battery using the electrode of the second example can achieve both higher capacity and excellent load characteristics without causing a decrease in peel strength due to a decrease in the amount of the binder. .
[0031]
Further, since the first layer does not contain an active material, a flat electrode surface can be obtained. When the first layer contains the active material, the active material is particles having a certain width of particle size distribution. When the coating is extremely thin (approximately 5 μm), irregularities due to the shape of coarse particles may appear on the surface of the first layer, and the surface properties of the electrode may be impaired.
[0032]
Examples of the carbon powder contained in the first layer include graphite and carbon black, and these can be used alone or in combination. Among carbon blacks, oil furnace black (Ketjen black) and acetylene black are particularly preferably used.
[0033]
Examples of the fluorine-based resin contained in the first layer include polyvinyl fluoride, polyvinylidene fluoride, and polytetrafluoroethylene, and these can be used alone or in combination.
[0034]
As the binder contained in the second layer, any of the known binders usually used for this type of battery can be used, but the same type as the fluorine-based resin used in the first layer can be used. Preferably, there is.
[0035]
Next, materials constituting the electrodes having the above-described various structures will be described. When the electrode is, for example, a positive electrode, a known positive electrode material such as a transition metal oxide capable of doping / dedoping lithium ions can be used as the active material without limitation. For example, a chalcogen compound with a transition metal containing an alkali metal, in particular, an oxide of an alkali metal and a transition metal can be used. As the crystal structure of the compound used for the positive electrode active material, a layered compound, a spinel type compound, and the like are generally used. A preferred positive electrode active material has the general formula A_xM_yO₂(Where A is a kind selected from Li, Na and K. In the formula, M is Fe, Co, Ni, Mn, Cu, Zn, Cr, V, Ti, Al, Sn, B, Ga , Mg, Ca, and Sr. Also, 0.5 ≦ x ≦ 1.1 and 0.5 ≦ y ≦ 1). Particularly preferred is Li_xNi_1-yM_yO_2-δ, Li_xCo_1-yM_yO_2-δ, Li_xMn_1-yM_yO_2-δ, Li_xFe_1-yM_yO_2-δ(Where 0 ≦ x ≦ 1.5, 0 ≦ y ≦ 1, 0 ≦ δ ≦ 0.5. M is Al, Fe, Cu, Co, Cr, Mg, Ca, V, Ni , Ag, Sn, B, Ga, and at least one element selected from the group consisting of second transition metal elements.)₂O₄, Li₄Mn₅O₁₂, LiMn_xFe_1-xPO₄(Where 0 ≦ x ≦ 1), Li_xMn_2-yM_yO_4-δ(Where 0 ≦ x ≦ 1.5, 0 ≦ y ≦ 1.5, 0 ≦ δ ≦ 2, and M is Al, Fe, Cu, Co, Cr, Mg, Ca, V, Ni , Ag, Sn, B, Ga, and at least one element selected from the group consisting of second transition metal elements).
[0036]
Further, the positive electrode may contain a conductive material, an additive exhibiting various functions, and the like, as necessary. The conductive material is not particularly limited as long as it can impart conductivity by being mixed with an active material in an appropriate amount. Usually, a carbon material such as graphite and carbon black can be used.
[0037]
Further, as the current collector of the positive electrode, a metal foil such as aluminum can be used.
[0038]
For example, in the case of a negative electrode, examples of the active material include metallic lithium, a material capable of doping and undoping lithium, a metal capable of forming an alloy with lithium, and an alloy compound of a metal capable of forming an alloy with lithium. .
[0039]
Examples of the material capable of doping / dedoping lithium include carbon materials capable of doping / dedoping lithium. Specific carbon materials that can be doped / dedoped with lithium include, for example, non-graphitizable carbon materials, pyrolytic carbons, cokes, graphites, glassy carbons, fired bodies of organic polymer compounds, mesocarbons Examples include microbeads, carbon fibers, activated carbon, and the like.
[0040]
As the non-graphitizable carbon material, the (002) plane spacing is 0.37 nm or more, and the true density is 1.70 g / cm.³It is preferable to use a material that exhibits a physical parameter of not having an exothermic peak at 700 ° C. or higher in differential thermal analysis (DTA) in air.
[0041]
As a typical example of the non-graphitizable carbon material, there is a material obtained by firing and carbonizing a furan resin made of a homopolymer or copolymer of furfuryl alcohol or furfural, or a copolymer with another resin. Examples of the organic material serving as a starting material include phenolic resins, acrylic resins, vinyl halide resins, polyimide resins, polyamideimide resins, polyamide resins, polyacetylenes, conjugated resins such as poly (p-phenylene), cellulose and derivatives thereof, Any organic polymer compound or the like can be used.
[0042]
In addition, a petroleum pitch having a specific H / C atomic ratio into which a functional group containing oxygen is introduced (so-called oxygen cross-linking) is not melted in the carbonization process (400 ° C. or higher), similarly to the above-mentioned furan resin. It becomes the final non-graphitizable carbon material in the solid state. The above petroleum pitch is distilled (vacuum distillation, atmospheric distillation, steam distillation) from coal tar, ethylene bottom oil, tar obtained from high-temperature pyrolysis of crude oil, asphalt, etc., thermal polycondensation, extraction, chemical polycondensation, etc. Obtained by the following operation. At this time, the H / C atomic ratio of the petroleum pitch is important, and the H / C atomic ratio needs to be 0.6 to 0.8 in order to obtain a non-graphitizable carbon material.
[0043]
When a carbon material is obtained using the above organic materials, for example, after carbonizing at 300 ° C. to 700 ° C., the temperature is raised at a rate of 1 ° C. to 100 ° C. per minute, a temperature reached 900 ° C. to 1300 ° C., and a holding time at the temperature reached 0 What is necessary is just to bake on conditions of about 30 hours. Of course, in some cases, the carbonization operation may be omitted.
[0044]
The graphite that can be used as an active material has a true density of 2.1 g / cm.³More preferably, 2.18 g / cm³The above is more preferred. In order to obtain such a true density, the (002) plane spacing obtained by the X-ray diffraction method is less than 0.340 nm, preferably 0.335 nm or more and less than 0.337 nm, and the (002) plane C-axis crystal It is necessary that the element thickness be 14.0 nm or more.
[0045]
Examples of coke include pitch coke, needle coke, petroleum coke, and the like.
[0046]
Coal, pitch, and the like are typical examples of the organic material used as a starting material when producing artificial graphite. Examples of pitch include distillation (vacuum distillation, normal pressure distillation, steam distillation) from tar, asphalt, etc. obtained by high-temperature pyrolysis of coal tar, ethylene bottom oil, crude oil, etc., hot polycondensation, extraction, chemical polycondensation, etc. Examples thereof include those obtained by the operation and other pitches generated during wood carbonization. Further, starting materials for forming pitch include polyvinyl chloride resin, polyvinyl acetate, polyvinyl butyrate, 3,5-dimethylphenol resin and the like.
[0047]
During the carbonization, these coals and pitches exist in a liquid state at a maximum of about 400 ° C., and aromatic rings are condensed and polycyclized to be in a laminated orientation by holding at that temperature, and thereafter, a state of about 500 ° C. or more is obtained. At temperature, a solid carbon precursor, ie, semi-coke, is formed. Such a process is called a liquid phase carbonization process, and is a typical production process of graphitizable carbon.
[0048]
In order to produce a desired artificial graphite using the above organic material as a starting material, for example, the organic material is heated at 300 ° C. to 700 ° C. in an inert gas stream such as nitrogen at a rate of 1 ° C. to 100 ° C./min. Calcination is carried out under the conditions of an ultimate temperature of 900 ° C. to 1500 ° C. and a holding time at the ultimate temperature of about 0 to 30 hours (the material which has been passed through this process is an easily graphitizable carbon material), and more than 2000 ° C., preferably It is obtained by heat treatment at 2500 ° C. or more. Of course, in some cases, the carbonization or calcination operation may be omitted.
[0049]
The graphite material to be produced is classified or pulverized / classified and supplied to the negative electrode material.The pulverization may be performed in any of carbonization, before and after calcining, or in a heating process before graphitization. In this case, heat treatment for graphitization is finally performed in a powder state.
[0050]
Examples of the material capable of doping and undoping lithium include metal oxides and intermetallic compounds capable of doping and undoping lithium, and polymers such as polyacetylene and polypyrrole.
[0051]
As the metal oxide capable of doping and undoping lithium, an oxide containing a transition metal is preferable, and a crystalline compound mainly composed of iron oxide, ruthenium oxide, molybdenum oxide, tungsten oxide, titanium oxide, tin oxide, or the like. Alternatively, an amorphous compound can be used as a negative electrode. Among them, compounds having a charge / discharge potential relatively close to lithium metal are particularly preferable.
[0052]
Further, as the negative electrode active material, a metal capable of forming an alloy with lithium or an alloy compound of the metal can be used.
[0053]
The alloy compound referred to here is a chemical formula M, where M is a metal element capable of forming an alloy with lithium._xM '_yLi_z(However, in the formula, M ′ is one or more metal elements other than the Li element and the M element. Further, x is a numerical value larger than 0, and y and z are numerical values of 0 or more.) Compound. Further, in the present invention, semiconductor elements such as B, Si, and As are included in the metal elements. Further, the alloy compound includes a lithium compound such as a lithium alloy.
[0054]
As a metal or an alloy compound of the metal capable of forming an alloy with lithium, specifically, Mg, B, Al, Ga, In, Si, Ge, Sn, Pb, Sb, Bi, Cd, Ag, Zn, Each metal such as Hf and Y and alloy compounds thereof, that is, for example, Li-Al, Li-Al-M (wherein, M is at least one or more of a 2A group, 3B group, and 4B group transition metal element) ), AlSb, CuMgSb, and the like.
[0055]
Among the elements described above, it is preferable to use an element such as Si or Sn or an alloy thereof in addition to the 3B group typical element. Among them, Si or Si alloy is particularly preferable. As Si or Si alloy, M_xSi, M_xA compound represented by Sn (wherein, M is one or more metal elements other than Si or Sn), and specifically, SiB₄, SiB₆, Mg₂Si, Mg₂Sn, Ni₂Si, TiSi₂, MoSi₂, CoSi₂, NiSi₂, CaSi₂, CrSi₂, Cu₅Si, FeSi₂, MnSi₂, NbSi₂, TaSi₂, VSi₂, WSi₂, ZnSi₂Etc. can be used.
[0056]
Further, a group 4B element other than carbon containing one or more nonmetallic elements can also be used as the negative electrode active material. The material may contain one or more group 4B elements. Further, a metal element other than Group 4B including Li may be contained. For example, SiC, Si₃N₄, Si₂N₂O, Ge₂N₂O, SiO_x(Where 0 <x ≦ 2), LiSiO, LiSnO and the like.
[0057]
As the negative electrode active material, any of the above-described materials and the like can be used, but from the viewpoint of more remarkably exhibiting the effects of the present invention, a metal capable of forming an alloy with lithium or an alloy of the metal. Preferably, a compound is used.
[0058]
In addition, the electrode as described above may be applied to both the positive electrode and the negative electrode, either of the positive electrode or the negative electrode, but from the viewpoint of reliably obtaining the effect of the present invention, both the positive electrode and the negative electrode may be used. It is preferred to apply. In the case where the above-described structure is applied to one of the pair of electrodes and not to the other, the other electrode may include an arbitrary electrode material such as the above-described electrode material and have a conventionally known structure. It is possible.
[0059]
The non-aqueous electrolyte is obtained by dissolving an electrolyte salt in a non-aqueous solvent. Specific non-aqueous solvents include propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, 1,2-dimethoxyethane, 1,2-diethoxyethane, γ-butyrolactone, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3 -Dioxolan, 4-methyl-1,3-dioxolan, diethyl ether, sulfolane, methylsulfolane, acetonitrile, propionitrile, anisole, acetate, butyrate, propionate and the like.
[0060]
As the electrolyte salt, specifically, LiPF₆Is preferred, but LiClO₄, LiAsF₆, LiBF₄, LiB (C₆H₅)₄, CH₃SO₃Li, CF₃SO₃Li, LiN (CF₃SO₂)₂, LiC (CF₃SO₂)₃, LiCl, and lithium salts such as LiBr. One of these electrolyte salts may be used alone, or a plurality of them may be used as a mixture.
[0061]
Examples of the material of the battery can 5 include iron, nickel, stainless steel, and aluminum. Further, in order to prevent electrochemical corrosion in the non-aqueous electrolyte during charging and discharging of the battery, the battery can 5 may be subjected to a surface treatment such as plating.
[0062]
As described above, in the nonaqueous electrolyte secondary battery 1 to which the present invention is applied, at least one of the positive electrode 2 and the negative electrode 3 has the first layer and the second layer on the current collector in this order. The first layer basically has a feature of exhibiting a stronger binding force than the second layer. As described above, the first layer having a strong binding force is thinly interposed between the current collector and the second layer containing the active material, so that the binder does not decrease in peel strength of the electrode. The content can be reduced. Therefore, the nonaqueous electrolyte secondary battery 1 achieves high capacity without causing an increase in the defective rate due to insufficient peel strength. Further, in the nonaqueous electrolyte secondary battery 1, even if the second layer is thickened, a decrease in load characteristics is suppressed, so that a higher capacity can be achieved while securing load characteristics.
[0063]
In addition, the nonaqueous electrolyte secondary battery 1 has, in addition to the above basic features, that the first layer contains an active material and polyvinylidene fluoride, and further contains polyvinylidene fluoride in the first layer. It is preferable to satisfy the conditions regarding the amount, the content and type of the soft binder in the second layer, the thickness ratio of the first layer and the second layer, and the like. Thereby, the non-aqueous electrolyte secondary battery 1 can reliably obtain the effect of realizing high capacity and excellent load characteristics while maintaining the high peel strength as described above, and also have high flexibility. can get.
[0064]
In addition, the nonaqueous electrolyte secondary battery 1 has, in addition to the above basic features, that the first layer contains a fluorocarbon resin and a carbon powder as a binder and does not contain an active material. It is preferable to satisfy the conditions regarding the provisions such as the content of the carbon powder, the thickness of the first layer, the content of the binder in the second layer, and the thickness of the second layer. Thereby, the nonaqueous electrolyte secondary battery 1 can reliably obtain the effect of achieving high capacity and excellent load characteristics while maintaining the above-described high peel strength. In particular, with this structure, the thickness of the second layer can be made extremely thick as specified above without impairing the load characteristics, and further higher capacity can be achieved.
[0065]
Next, a method of manufacturing the nonaqueous electrolyte secondary battery 1 as shown in FIG. 1 will be described.
[0066]
First, the positive electrode 2 and / or the negative electrode 3 satisfying the above-described conditions are manufactured. First, a first layer is formed on one main surface of a belt-shaped current collector. When forming the first layer, each component constituting the first layer is dispersed and coated using a solvent such as N-methyl-2-pyrrolidone, and the coating is applied on a current collector. ,dry. For the formation of the dispersion paint, a ball mill, a sand mill, a twin-screw kneader, or the like, which is a commonly used disperser, can be used. There is no particular limitation on the coating device for applying the coating material on the current collector, such as slide coating or extrusion type die coating, reverse roll, gravure, knife coater, kiss coater, microgravure, rod coater, blade coater, and the like. A known coating device can be used. The drying method is not particularly limited. For example, besides drying, a blower dryer, a warm air dryer, an infrared heater, a far infrared heater, or the like can be used.
[0067]
Next, a second layer is formed over the first layer. As a method of forming the second layer, the components constituting the second layer are mixed together with a solvent, and if necessary, are dispersed and coated using a dispersing machine such as a ball mill, a sand mill, or a twin-screw kneader. , And a method of applying it on the first layer and drying it. Thereby, the strip-shaped positive electrode 2 and / or negative electrode 3 in which the first layer and the second layer are formed on the current collector are obtained. The solvent used here is not particularly limited as long as it is inert to the first layer and can dissolve the binder as a component of the second layer. For example, N-methyl-2 Any known inorganic and organic solvents such as pyrrolidone can be used. There is no particular limitation on the coating apparatus for applying the coating material on the first layer, and slide coating or extrusion type die coating, reverse roll, gravure, knife coater, kiss coater, microgravure, rod coater, blade coater, etc. Can be used. The drying method is not particularly limited. For example, besides drying, a blower dryer, a warm air dryer, an infrared heater, a far infrared heater, or the like can be used.
[0068]
In addition, the positive electrode 2 or the negative electrode 3 that does not satisfy the above-described conditions can be manufactured by a known manufacturing method.
[0069]
The strip-shaped positive electrode 2 and the negative electrode 3 obtained as described above are laminated via a separator 4 made of, for example, a microporous polypropylene film, and wound a number of times in the longitudinal direction to produce a spiral wound body. I do.
[0070]
Next, the insulating plate 6 is inserted into the bottom of the battery can 5 having nickel plating on the inside, the wound body is housed, and the insulating plate 7 is disposed on the top of the wound body. In order to collect the current of the negative electrode 3, one end of a negative electrode lead 8 made of, for example, nickel is pressed against the negative electrode 3 and the other end is welded to the battery can 5. As a result, the battery can 5 has conductivity with the negative electrode 3 and serves as an external negative electrode of the nonaqueous electrolyte secondary battery 1. In order to collect the current of the positive electrode 2, one end of a positive electrode lead 9 made of, for example, aluminum is attached to the positive electrode 2, and the other end is electrically connected to the battery lid 10 via a current interrupting thin plate. The current interrupting thin plate interrupts the current in accordance with the internal pressure of the battery. As a result, the battery lid 10 has conduction with the positive electrode 2 and serves as an external positive electrode of the nonaqueous electrolyte secondary battery 1.
[0071]
Next, a non-aqueous electrolyte is injected into the battery can 5. This non-aqueous electrolyte is prepared by dissolving an electrolyte in a non-aqueous solvent.
[0072]
Next, the battery lid 5 is fixed by caulking the battery can 5 through the insulating sealing gasket 11 coated with asphalt, and the cylindrical nonaqueous electrolyte secondary battery 1 is manufactured.
[0073]
The non-aqueous electrolyte secondary battery 1 has a safety valve device 12 for bleeding out gas when the pressure inside the battery becomes higher than a predetermined value, and a PTC for preventing temperature rise inside the battery. (Positive \ Temperature \ Coefficient) element 13.
[0074]
By the way, in the above description, a non-aqueous electrolyte secondary battery using a non-aqueous electrolyte obtained by dissolving an electrolyte salt in a non-aqueous solvent was taken as an example of an electrolyte, but the electrolyte contained an electrolyte salt. Any known electrolyte such as a solid electrolyte, a gel electrolyte in which an organic polymer is impregnated with a non-aqueous solvent and an electrolyte salt, or the like can be used.
[0075]
As the solid electrolyte, any of an inorganic solid electrolyte, a polymer solid electrolyte, and the like can be used as long as the material has lithium ion conductivity. Examples of the inorganic solid electrolyte include lithium nitride and lithium iodide. The polymer solid electrolyte includes an electrolyte salt and a polymer compound that dissolves the electrolyte salt. Specific examples of the polymer compound include ether polymers such as poly (ethylene oxide) and the same crosslinked product, poly (methacrylate) esters, acrylates, and the like, which may be used alone or copolymerized or mixed in the molecule. Can be.
[0076]
As the organic polymer used for the gel electrolyte, various polymers can be used as long as they absorb the above-mentioned non-aqueous electrolyte and gel. For example, fluorine-based polymers such as poly (vinylidene fluoride) and poly (vinylidene fluoride-co-hexafluoropropylene), ether polymers such as poly (ethylene oxide) and crosslinked products thereof, and poly (acrylonitrile) are exemplified. Can be Among these, it is preferable to use a fluoropolymer from the viewpoint of oxidation-reduction stability. These organic polymers are provided with ionic conductivity by containing an electrolyte salt.
[0077]
Further, the shape of the battery of the present invention is not particularly limited, such as a cylindrical shape, a square shape, a coin shape, a button shape and the like, and can be various sizes such as a thin shape and a large size.
[0078]
Further, the battery of the present invention is not limited to a secondary battery, and may be applied to a primary battery.
[0079]
The present invention is not limited to the above description, and can be appropriately modified without departing from the gist of the present invention.
[0080]
【Example】
Hereinafter, specific examples to which the present invention is applied will be described based on experimental results.
[0081]
<Experiment 1>
In Experiment 1, in a battery having an electrode in which the first layer having a large binding force contains an active material and also contains polyvinylidene fluoride as a binder, the optimum layer between the first layer and the second layer is used. The thickness ratio was examined.
[0082]
Sample 1
First, a positive electrode was produced as follows. The first layer paint was uniformly applied to both surfaces of a positive electrode current collector made of a 20-μm-thick strip-shaped aluminum foil, and dried to form a first layer. Further, a second layer coating material was uniformly applied on the first layer and dried to form a second layer, thereby obtaining a positive electrode. The thickness ratio between the first layer and the second layer in the positive electrode was set to be 5%: 95%.
[0083]
The coating material for the first layer used here was LiCoO 2 as a positive electrode active material.₂Was mixed with 92 parts by weight, 5 parts by weight of a conductive agent, and 3 parts by weight of polyvinylidene fluoride as a binder, and this mixture was dispersed in a solvent.
[0084]
The coating material for the second layer is LiCoO 2 as a positive electrode active material.₂Was mixed with 94 parts by weight, 5 parts by weight of a conductive agent, and 1 part by weight of a soft binder as a binder, and the mixture was dispersed in a solvent. The soft binder used here is obtained by copolymerizing 70% of polyvinylidene fluoride with 30% of hexafluoropropylene.
[0085]
Next, a negative electrode was produced as follows. The first layer paint was uniformly applied to both surfaces of a negative electrode current collector made of a strip-shaped copper foil having a thickness of 15 μm, and dried to form a first layer. Further, a second layer coating material was uniformly applied on the first layer and dried to form a second layer, thereby obtaining a negative electrode.
[0086]
The first layer coating material used here was prepared by mixing 94 parts by weight of artificial graphite as a negative electrode active material and 6 parts by weight of polyvinylidene fluoride as a binder, and dispersing this mixture in a solvent. Things.
[0087]
The second layer paint was prepared by mixing 98 parts by weight of artificial graphite as a negative electrode active material and 2 parts by weight of a soft binder as a binder, and dispersing this mixture in a solvent. Things. The soft binder used here is the same as the soft binder used in the above-described positive electrode.
[0088]
The thickness ratio between the first layer and the second layer in the negative electrode was set to be 5%: 95%.
[0089]
The positive electrode obtained as described above, the negative electrode, and a separator made of a microporous polyethylene film having a thickness of 20 μm are laminated and adhered in the order of a negative electrode, a separator, a positive electrode, and a separator, and spirally wound many times. By turning, a wound body was produced.
[0090]
Next, an insulating plate was inserted into the bottom of an iron battery can with nickel plating on the inside, and the wound body was further housed. Then, in order to collect the current of the negative electrode, one end of a nickel negative electrode lead was pressed against the negative electrode, and the other end was welded to the battery can. Further, in order to collect the current of the positive electrode, one end of an aluminum positive electrode lead was attached to the positive electrode, and the other end was electrically connected to the battery lid.
[0091]
Then, a non-aqueous electrolyte was injected into the battery can. This non-aqueous electrolyte is prepared by mixing LiPF as an electrolyte in a mixed solvent obtained by mixing ethylene carbonate and dimethyl carbonate at a volume ratio of 1: 1.₆Was dissolved at a concentration of 1 mol / l.
[0092]
Finally, by caulking the battery can through an insulating sealing gasket coated with asphalt, the thin plate for current interruption, the PTC element and the battery lid are fixed, and a cylindrical type having a diameter of about 18 mm and a height of about 65 mm is formed. A non-aqueous electrolyte secondary battery was manufactured.
[0093]
Sample 2
The thickness ratio between the first layer and the second layer in the positive electrode was set to be 50%: 50%, and the thickness ratio between the first layer and the second layer in the negative electrode was 50%. : A non-aqueous electrolyte secondary battery was prepared in the same manner as in Sample 1, except that the setting was made to be 50%.
[0094]
Sample 3
The thickness ratio of the first layer and the second layer in the positive electrode was set to be 80%: 20%, and the thickness ratio of the first layer and the second layer in the negative electrode was 80%. : A non-aqueous electrolyte secondary battery was prepared in the same manner as in Sample 1, except that the setting was made to be 20%.
[0095]
Sample 4
The thickness ratio between the first layer and the second layer in the positive electrode was set to be 100%: 0%, and the thickness ratio between the first layer and the second layer in the negative electrode was 5%. : A non-aqueous electrolyte secondary battery was fabricated in the same manner as in Sample 1, except that the setting was made to be 95%.
[0096]
Sample 5
The thickness ratio between the first layer and the second layer in the positive electrode was set to be 100%: 0%, and the thickness ratio between the first layer and the second layer in the negative electrode was 80%. : A non-aqueous electrolyte secondary battery was prepared in the same manner as in Sample 1, except that the setting was made to be 20%.
[0097]
Sample 6
The thickness ratio between the first layer and the second layer in the positive electrode was set to be 5%: 95%, and the thickness ratio between the first layer and the second layer in the negative electrode was 100%. A non-aqueous electrolyte secondary battery was produced in the same manner as in Sample 1, except that the content was set to be 0%.
[0098]
Sample 7
The thickness ratio between the first layer and the second layer in the positive electrode was set to be 80%: 20%, and the thickness ratio between the first layer and the second layer in the negative electrode was 100%. A non-aqueous electrolyte secondary battery was produced in the same manner as in Sample 1, except that the content was set to be 0%.
[0099]
Sample 8
The thickness ratio of the first layer to the second layer in the positive electrode was set to be 3%: 97%, and the thickness ratio of the first layer to the second layer in the negative electrode was 3%. : A non-aqueous electrolyte secondary battery was prepared in the same manner as in Sample 1, except that the setting was made to be 97%.
[0100]
Sample 9
The thickness ratio between the first layer and the second layer in the positive electrode was set to be 90%: 10%, and the thickness ratio between the first layer and the second layer in the negative electrode was 90%. : A non-aqueous electrolyte secondary battery was produced in the same manner as in Sample 1, except that it was set to be 10%.
[0101]
Sample 10
The thickness ratio of the first layer and the second layer in the positive electrode was set to be 100%: 0%, and the thickness ratio of the first layer and the second layer in the negative electrode was 4%. : A non-aqueous electrolyte secondary battery was produced in the same manner as in Sample 1, except that the setting was made to be 96%.
[0102]
Sample 11
The thickness ratio between the first layer and the second layer in the positive electrode was set to be 100%: 0%, and the thickness ratio between the first layer and the second layer in the negative electrode was 81%. : A non-aqueous electrolyte secondary battery was manufactured in the same manner as in Sample 1, except that the setting was made to be 19%.
[0103]
Sample 12
The thickness ratio between the first layer and the second layer in the positive electrode was set to be 4%: 96%, and the thickness ratio between the first layer and the second layer in the negative electrode was 100%. A non-aqueous electrolyte secondary battery was produced in the same manner as in Sample 1, except that the content was set to be 0%.
[0104]
Sample 13
The thickness ratio between the first layer and the second layer in the positive electrode was set to be 81%: 19%, and the thickness ratio between the first layer and the second layer in the negative electrode was 100%. A non-aqueous electrolyte secondary battery was produced in the same manner as in Sample 1, except that the content was set to be 0%.
[0105]
Sample 14
The thickness ratio between the first layer and the second layer in the positive electrode was set to be 100%: 0%, and the thickness ratio between the first layer and the second layer in the negative electrode was 100%. A non-aqueous electrolyte secondary battery was produced in the same manner as in Sample 1, except that the content was set to be 0%.
[0106]
Sample 15
The thickness ratio of the first layer and the second layer in the positive electrode was set to be 0%: 100%, and the thickness ratio of the first layer and the second layer in the negative electrode was 0%. : A non-aqueous electrolyte secondary battery was produced in the same manner as in Sample 1, except that the setting was made to be 100%.
[0107]
The peel strength and flexibility of the electrodes constituting the nonaqueous electrolyte secondary batteries of Samples 1 to 15 prepared as described above were measured as follows. The load characteristics and discharge capacity of the non-aqueous electrolyte secondary batteries of Sample 1 to Sample 15 were measured.
[0108]
Regarding the peel strength of the electrode, a tape having a size of 25 mm × 60 mm was adhered to the application surface of the electrode to be measured, the tape was pulled in a direction parallel to the application surface, and the tensile strength when peeled was measured. .
[0109]
The flexibility of the electrode was evaluated by measuring the displacement and stress until a crack was formed in the electrode when the electrode to be measured had a ring shape and a load was applied at a constant speed in the diameter direction. Then, the flexibility when the thickness configuration of the electrode was 1st layer: 2nd layer = 0%: 100% was represented by 10.0 as a relative value.
[0110]
With respect to the discharge capacity of the nonaqueous electrolyte secondary battery, the prepared battery was fully charged up to 4.2 V, and then the discharge capacity was measured when constant current discharge was performed at 1 C.
[0111]
The load characteristic is a ratio of the discharge capacity at 3 C to the discharge capacity at 0.5 C, and was expressed as a relative value when the load characteristic of Sample 1 was 10.0.
[0112]
Table 1 below shows the electrode thickness ratio, peel strength and flexibility, load characteristics, and discharge capacity of Samples 1 to 15 described above.
[0113]
[Table 1]

[0114]
As is clear from Table 1, in at least one of the positive electrode and the negative electrode, Sample 1 to Sample 7 in which the thickness ratio of the first layer to the second layer is in the range of 5:95 to 80:20 are The results were excellent in all of the peel strength and flexibility of the electrode, the load characteristics, and the discharge capacity.
[0115]
<Experiment 2>
In Experiment 2, in a battery having an electrode in which the first layer having a large binding force contains an active material and also contains polyvinylidene fluoride as a binder, the binder (polyfluoride) of the first layer of the positive electrode was used. The optimum range of vinylidene) content was studied.
[0116]
Sample 16
LiCoO as a positive electrode active material as a first layer coating material₂Sample 1 was prepared by mixing 93 parts by weight, 5 parts by weight of a conductive agent, and 2 parts by weight of polyvinylidene fluoride as a binder, and dispersing the mixture in a solvent. In the same manner as in the above, a non-aqueous electrolyte secondary battery was produced.
[0117]
Sample 17
The thickness ratio between the first layer and the second layer in the positive electrode was set to be 50%: 50%, and the thickness ratio between the first layer and the second layer in the negative electrode was 50%. : A non-aqueous electrolyte secondary battery was manufactured in the same manner as in Sample 16, except that the setting was made to be 50%.
[0118]
Sample 18
The thickness ratio of the first layer and the second layer in the positive electrode was set to be 80%: 20%, and the thickness ratio of the first layer and the second layer in the negative electrode was 80%. : A non-aqueous electrolyte secondary battery was produced in the same manner as in Sample 16, except that the setting was made to be 20%.
[0119]
Sample 19
The thickness ratio between the first layer and the second layer in the positive electrode was set to be 100%: 0%, and the thickness ratio between the first layer and the second layer in the negative electrode was 5%. : A non-aqueous electrolyte secondary battery was fabricated in the same manner as in Sample 16, except that the setting was made to be 95%.
[0120]
Sample 20
The thickness ratio between the first layer and the second layer in the positive electrode was set to be 100%: 0%, and the thickness ratio between the first layer and the second layer in the negative electrode was 80%. : A non-aqueous electrolyte secondary battery was produced in the same manner as in Sample 16, except that the setting was made to be 20%.
[0121]
Sample 21
The thickness ratio between the first layer and the second layer in the positive electrode was set to be 5%: 95%, and the thickness ratio between the first layer and the second layer in the negative electrode was 100%. A non-aqueous electrolyte secondary battery was produced in the same manner as in Sample 16, except that the content was set to be 0%.
[0122]
Sample 22
The thickness ratio between the first layer and the second layer in the positive electrode was set to be 80%: 20%, and the thickness ratio between the first layer and the second layer in the negative electrode was 100%. A non-aqueous electrolyte secondary battery was produced in the same manner as in Sample 16, except that the content was set to be 0%.
[0123]
Sample 23
LiCoO as a positive electrode active material as a first layer coating material₂, 90 parts by weight of a conductive agent, 5 parts by weight of a conductive agent, and 5 parts by weight of polyvinylidene fluoride as a binder, and a mixture prepared by dispersing the mixture in a solvent. The thickness ratio between the first layer and the second layer was set to be 5%: 95%, and the thickness ratio between the first layer and the second layer in the negative electrode was set to 5%: 95%. A non-aqueous electrolyte secondary battery was fabricated in the same manner as in Sample 16, except that the settings were made as follows.
[0124]
Sample 24
The thickness ratio between the first layer and the second layer in the positive electrode was set to be 50%: 50%, and the thickness ratio between the first layer and the second layer in the negative electrode was 50%. : A non-aqueous electrolyte secondary battery was produced in the same manner as in Sample 23 except that the setting was made to be 50%.
[0125]
Sample 25
The thickness ratio of the first layer to the second layer in the positive electrode was set to be 3%: 97%, and the thickness ratio of the first layer to the second layer in the negative electrode was 3%. : A non-aqueous electrolyte secondary battery was manufactured in the same manner as in Sample 16, except that the setting was made to be 97%.
[0126]
Sample 26
The thickness ratio between the first layer and the second layer in the positive electrode was set to be 90%: 10%, and the thickness ratio between the first layer and the second layer in the negative electrode was 90%. : A non-aqueous electrolyte secondary battery was produced in the same manner as in Sample 16, except that it was set to be 10%.
[0127]
Sample 27
LiCoO as a positive electrode active material as a first layer coating material₂Was mixed with 94 parts by weight, 5 parts by weight of a conductive agent, and 1 part by weight of polyvinylidene fluoride as a binder, and the mixture was dispersed in a solvent. The thickness ratio between the first layer and the second layer was set to be 3%: 97%, and the thickness ratio between the first layer and the second layer in the negative electrode was 3%: 97%. A non-aqueous electrolyte secondary battery was fabricated in the same manner as in Sample 16, except that the settings were made as follows.
[0128]
Sample 28
The thickness ratio of the first layer to the second layer in the positive electrode was set to be 5%: 95%, and the thickness ratio of the first layer to the second layer in the negative electrode was 5%. : A non-aqueous electrolyte secondary battery was prepared in the same manner as in Sample 27 except that the setting was made to be 95%.
[0129]
Sample 29
The thickness ratio between the first layer and the second layer in the positive electrode was set to be 50%: 50%, and the thickness ratio between the first layer and the second layer in the negative electrode was 50%. : A non-aqueous electrolyte secondary battery was prepared in the same manner as in Sample 27 except that the setting was made to be 50%.
[0130]
Sample 30
The thickness ratio of the first layer and the second layer in the positive electrode was set to be 80%: 20%, and the thickness ratio of the first layer and the second layer in the negative electrode was 80%. : A non-aqueous electrolyte secondary battery was produced in the same manner as in Sample 27 except that the setting was made to be 20%.
[0131]
Sample 31
The thickness ratio between the first layer and the second layer in the positive electrode was set to be 90%: 10%, and the thickness ratio between the first layer and the second layer in the negative electrode was 90%. : A non-aqueous electrolyte secondary battery was produced in the same manner as in Sample 27 except that it was set to be 10%.
[0132]
With respect to Samples 16 to 31 described above, the peel strength and flexibility of the electrode, the load characteristics, and the discharge capacity were measured in the same manner as in Experiment 1.
[0133]
Table 2 below shows these results together with the polyvinylidene fluoride content in the first layer of the positive electrode and the film thickness ratio of the electrode. In the following table, polyvinylidene fluoride is abbreviated as PVdF.
[0134]
[Table 2]

[0135]
As is clear from Table 2, since Samples 16 to 24 show superior results as compared to Samples 27 to 31, the polyvinylidene fluoride content of the first layer is required to be 2% by weight or more. all right. However, although the polyvinylidene fluoride content was 2% by weight or more, the thickness ratio of the first layer to the second layer was out of the range of 5:95 to 80:20. It is found that it is important to satisfy both conditions of the polyvinylidene fluoride content of the first layer and the film thickness ratio of the electrode because the peel strength and the flexibility, the load characteristics, and the discharge capacity are inferior. did.
[0136]
<Experiment 3>
In Experiment 3, in a battery having an electrode in which the first layer having a large binding force contains the active material and also contains polyvinylidene fluoride as the binder, the second layer has a soft binder as the binder. The case of containing only polyvinylidene fluoride instead of the agent was studied.
[0137]
Sample 32
LiCoO as a positive electrode active material as a coating for the first layer of the positive electrode₂Was mixed with 93 parts by weight, 5 parts by weight of a conductive agent, and 2 parts by weight of polyvinylidene fluoride as a binder, and this mixture was prepared by dispersing the mixture in a solvent. LiCoO as a positive electrode active material is used as a coating for the second layer of the positive electrode.₂Was mixed with 94 parts by weight, 5 parts by weight of a conductive agent, and 1 part by weight of polyvinylidene fluoride in place of the soft binder, and this mixture was prepared by dispersing the mixture in a solvent. In addition, as a coating for the second layer of the negative electrode, 98 parts by weight of artificial graphite as the negative electrode active material and 2 parts by weight of polyvinylidene fluoride instead of the soft binder were mixed, and this mixture was dispersed in a solvent. What was prepared by making it used was used. A non-aqueous electrolyte secondary battery was fabricated in the same manner as in Sample 1, except for these changes.
[0138]
Sample 33
The thickness ratio between the first layer and the second layer in the positive electrode was set to be 50%: 50%, and the thickness ratio between the first layer and the second layer in the negative electrode was 50%. : A non-aqueous electrolyte secondary battery was manufactured in the same manner as in Sample 32 except that the setting was made to be 50%.
[0139]
Sample 34
The thickness ratio of the first layer and the second layer in the positive electrode was set to be 80%: 20%, and the thickness ratio of the first layer and the second layer in the negative electrode was 80%. : A non-aqueous electrolyte secondary battery was prepared in the same manner as in Sample 32 except that the setting was made to be 20%.
[0140]
Sample 35
The thickness ratio between the first layer and the second layer in the positive electrode was set to be 95%: 5%, and the thickness ratio between the first layer and the second layer in the negative electrode was 95%. : A non-aqueous electrolyte secondary battery was produced in the same manner as in Sample 32 except that the setting was made to be 5%.
[0141]
With respect to Samples 32 to 35 described above, the peel strength and flexibility of the electrode, the load characteristics, and the discharge capacity were measured in the same manner as in Experiment 1.
[0142]
These results are shown in Table 3 below together with the polyvinylidene fluoride content in the first layer of the positive electrode and the film thickness ratio of the electrode.
[0143]
[Table 3]

[0144]
As is clear from Table 3 above, in Samples 32 to 35 in which the second layer did not contain a soft binder, the flexibility of the electrode was significantly impaired. This proved that the second layer of the electrode needed to contain a soft binder.
[0145]
<Experiment 4>
In Experiment 4, in a battery having an electrode in which the first layer having a large binding force contains an active material and also contains polyvinylidene fluoride as a binder, the composition of the soft binder in the second layer was determined. investigated.
[0146]
Sample 36
A mixture of 95% by weight of polyvinylidene fluoride and 5% by weight of hexafluoropropylene is used as a soft binder of the second layer of the positive electrode, and a polyvinylidene fluoride is used as a soft binder of the second layer of the negative electrode. A non-aqueous electrolyte secondary battery was produced in the same manner as in Sample 1, except that a mixture of 95% by weight and 5% by weight of hexafluoropropylene was used.
[0147]
Sample 37
A mixture of 50% by weight of polyvinylidene fluoride and 50% by weight of hexafluoropropylene is used as a soft binder of the second layer of the positive electrode, and polyvinylidene fluoride is used as a soft binder of the second layer of the negative electrode. A non-aqueous electrolyte secondary battery was fabricated in the same manner as in Sample 1, except that a mixture of 50% by weight and 50% by weight of hexafluoropropylene was used.
[0148]
Sample 38
100% by weight of hexafluoropropylene is used as a soft binder of the second layer of the positive electrode, and 95% by weight of polyvinylidene fluoride and 5% by weight of hexafluoropropylene are used as the soft binder of the second layer of the negative electrode. A non-aqueous electrolyte secondary battery was produced in the same manner as in Sample 1, except that the mixture was used.
[0149]
Sample 39
A mixture of 95% by weight of polyvinylidene fluoride and 5% by weight of styrene-butadiene-based latex is used as a soft binder of the second layer of the positive electrode, and a polyfluoride is used as a soft binder of the second layer of the negative electrode. A non-aqueous electrolyte secondary battery was produced in the same manner as in Sample 1, except that a mixture of 95% by weight of vinylidene and 5% by weight of hexafluoropropylene was used.
[0150]
Sample 40
A mixture of 50% by weight of polyvinylidene fluoride and 50% by weight of styrene-butadiene-based latex is used as a soft binder for the second layer of the positive electrode, and a polyfluoride is used as a soft binder for the second layer of the negative electrode. A non-aqueous electrolyte secondary battery was produced in the same manner as in Sample 1, except that a mixture of 95% by weight of vinylidene and 5% by weight of hexafluoropropylene was used.
[0151]
Sample 41
100% by weight of styrene butadiene latex is used as a soft binder of the second layer of the positive electrode, and 95% by weight of polyvinylidene fluoride and 5% by weight of hexafluoropropylene are used as the soft binder of the second layer of the negative electrode. A non-aqueous electrolyte secondary battery was produced in the same manner as in Sample 1, except that a mixture of the above was used.
[0152]
Sample 42
A mixture of 95% by weight of polyvinylidene fluoride and 5% by weight of hexafluoropropylene is used as a soft binder of the second layer of the positive electrode, and a polyvinylidene fluoride is used as a soft binder of the second layer of the negative electrode. A non-aqueous electrolyte secondary battery was fabricated in the same manner as in Sample 1, except that a mixture of 50% by weight and 50% by weight of hexafluoropropylene was used.
[0153]
Sample 43
A mixture of 95% by weight of polyvinylidene fluoride and 5% by weight of hexafluoropropylene is used as a soft binder of the second layer of the positive electrode, and hexafluoropropylene is used as a soft binder of the second layer of the negative electrode. A non-aqueous electrolyte secondary battery was produced in the same manner as in Sample 1, except that 100% by weight was used.
[0154]
Sample 44
A mixture of 95% by weight of polyvinylidene fluoride and 5% by weight of hexafluoropropylene is used as a soft binder of the second layer of the positive electrode, and a polyvinylidene fluoride is used as a soft binder of the second layer of the negative electrode. A non-aqueous electrolyte secondary battery was produced in the same manner as in Sample 1, except that a mixture of 95% by weight and 5% by weight of a styrene-butadiene-based latex was used.
[0155]
Sample 45
A mixture of 95% by weight of polyvinylidene fluoride and 5% by weight of hexafluoropropylene is used as a soft binder of the second layer of the positive electrode, and a polyvinylidene fluoride is used as a soft binder of the second layer of the negative electrode. A non-aqueous electrolyte secondary battery was fabricated in the same manner as in Sample 1, except that a mixture of 50% by weight and 50% by weight of a styrene-butadiene-based latex was used.
[0156]
Sample 46
A mixture of 95% by weight of polyvinylidene fluoride and 5% by weight of hexafluoropropylene is used as a soft binder for the second layer of the positive electrode, and a styrene-butadiene-based soft binder for the second layer of the negative electrode is used. A non-aqueous electrolyte secondary battery was produced in the same manner as in Sample 1, except that 100% by weight of latex was used.
[0157]
Sample 47
Sample 1 was obtained except that 100% by weight of polyvinylidene fluoride was used as the soft binder of the second layer of the positive electrode and 100% by weight of polyvinylidene fluoride was used as the soft binder of the second layer of the negative electrode. In the same manner as in the above, a non-aqueous electrolyte secondary battery was produced.
[0158]
With respect to the above Samples 36 to 47, the peel strength and flexibility of the electrode and the discharge capacity were measured in the same manner as in Experiment 1.
[0159]
The flexibility of the electrode is such that the thickness of the electrode is 1st layer: 2nd layer = 5%: 95%, and the soft binder contained in the second layer is hexafluoropropylene or The flexibility when only styrene-butadiene-based latex was used was represented by a relative value when 10.0 was set.
[0160]
Table 4 below shows these results together with the composition of the soft binder in the second layers of the positive electrode and the negative electrode. In Table 4, hexafluoropropylene is abbreviated as HFP, and styrene-butadiene-based latex is abbreviated as SBR.
[0161]
[Table 4]

[0162]
From the above Table 4, at least one of the positive electrode and the negative electrode contains a mixture of polyvinylidene fluoride and hexafluoropropylene or a mixture of polyvinylidene fluoride and styrene-butadiene-based latex as the soft binder of the second layer. Thus, it was found that an electrode having both peel strength and flexibility can be realized.
[0163]
<Experiment 5>
In Experiment 5, the optimum range of the thickness and composition of each layer of the positive electrode in which only the second layer contains the active material and the first layer functions as a primer layer was examined.
[0164]
Sample 48
First, a positive electrode was produced as follows. The first layer paint was uniformly applied to both surfaces of a positive electrode current collector made of a 20-μm-thick strip-shaped aluminum foil, and dried to form a first layer. The average thickness of the first layer was 0.5 μm. In addition, the second layer paint is uniformly applied on the first layer, dried, and compression-molded at a constant pressure by a roller press to form a second layer, which is slit to form a positive electrode. Obtained. When forming the second layer, the thickness of the second layer after pressing was 160 μm, and the volume density was 3.5 g / cm.³The coating amount was adjusted so that
[0165]
The coating material for the first layer used here is a mixture of 90% by weight of polyvinylidene fluoride as a binder and 10% by weight of acetylene black as a carbon powder as a conductive agent. It was prepared by dispersing in methyl-2-pyrrolidone.
[0166]
The coating material for the second layer is LiCoO 2 as a positive electrode active material.₂98% by weight, 1% by weight of ketjen black as a conductive agent, and 1% by weight of polyvinylidene fluoride as a binder, and dispersing this mixture in N-methyl-2-pyrrolidone as a solvent. It was prepared by
[0167]
Next, a negative electrode was produced as follows. A negative electrode current collector made of a strip-shaped copper foil having a thickness of 15 μm is uniformly coated with a negative electrode mixture paint, dried, and compression-molded at a constant pressure by a roller press to form a negative electrode mixture layer. Thus, a negative electrode was obtained. When forming the negative electrode mixture layer, the thickness of the negative electrode mixture layer after pressing was 160 μm, and the volume density was 1.66 g / cm.³The coating amount was adjusted so that
[0168]
The paint for negative electrode mixture used here was prepared by mixing 94% by weight of graphite as a negative electrode active material and 6% by weight of polyvinylidene fluoride as a binder, and dispersing this mixture in a solvent. is there.
[0169]
The positive electrode obtained as described above, the negative electrode, and a separator made of a microporous polyethylene film having a thickness of 20 μm are laminated and adhered in the order of a negative electrode, a separator, a positive electrode, and a separator, and spirally wound many times. By turning, a wound body was produced.
[0170]
Next, an insulating plate was inserted into the bottom of an iron battery can with nickel plating on the inside, and the wound body was further housed. Then, in order to collect the current of the negative electrode, one end of a nickel negative electrode lead was pressed against the negative electrode, and the other end was welded to the battery can. Further, in order to collect the current of the positive electrode, one end of an aluminum positive electrode lead was attached to the positive electrode, and the other end was electrically connected to the battery lid.
[0171]
Then, a non-aqueous electrolyte was injected into the battery can. This non-aqueous electrolyte is prepared by mixing LiPF as an electrolyte in a mixed solvent obtained by mixing ethylene carbonate and dimethyl carbonate at a volume ratio of 1: 1.₆Was dissolved at a concentration of 1 mol / l.
[0172]
Finally, by caulking the battery can through an insulating sealing gasket coated with asphalt, the thin plate for current interruption, the PTC element and the battery lid are fixed, and a cylindrical type having a diameter of about 18 mm and a height of about 65 mm is formed. A non-aqueous electrolyte secondary battery was manufactured.
[0173]
Sample 49
LiCoO of the second layer of the positive electrode₂A non-aqueous electrolyte secondary battery was produced in the same manner as in Sample 48, except that the content was 94% by weight and the polyvinylidene fluoride content was 5% by weight.
[0174]
Sample 50
A non-aqueous electrolyte secondary battery was fabricated in the same manner as in Sample 48, except that the thickness of the first layer of the positive electrode was 5 μm and the acetylene black content was 75% by weight.
[0175]
Sample 51
The first layer of the positive electrode has a thickness of 5 μm, the acetylene black content is 75% by weight, and the LiCoO 2 of the second layer is₂A non-aqueous electrolyte secondary battery was produced in the same manner as in Sample 48, except that the content was 94% by weight and the polyvinylidene fluoride content was 5% by weight.
[0176]
Sample 52
A non-aqueous electrolyte secondary battery was fabricated in the same manner as in Sample 48, except that the acetylene black content of the first layer of the positive electrode was 75% by weight.
[0177]
Sample 53
The thickness of the first layer of the positive electrode is 5 μm, and the thickness of the second layer is LiCoO 2.₂A non-aqueous electrolyte secondary battery was produced in the same manner as in Sample 48, except that the content was 94% by weight and the polyvinylidene fluoride content was 5% by weight.
[0178]
Sample 54
A non-aqueous electrolyte secondary battery was fabricated in the same manner as in Sample 48, except that the thickness of the second layer of the positive electrode was 300 μm, and the thickness of the negative electrode mixture layer was 300 μm.
[0179]
Sample 55
LiCoO of the second layer of the positive electrode₂A non-aqueous electrolyte secondary battery was produced in the same manner as in Sample 54, except that the content was 94% by weight, the polyvinylidene fluoride content was 5% by weight, and the thickness of the negative electrode mixture layer was 300 μm. .
[0180]
Sample 56
A nonaqueous electrolyte secondary solution was prepared in the same manner as in Sample 54, except that the thickness of the first layer of the positive electrode was 5 μm, the acetylene black content was 75% by weight, and the thickness of the negative electrode mixture layer was 300 μm. A battery was manufactured.
[0181]
Sample 57
The first layer of the positive electrode has a thickness of 5 μm, the acetylene black content is 75% by weight, and the LiCoO 2 of the second layer is₂A non-aqueous electrolyte secondary battery was produced in the same manner as in Sample 54, except that the content was 94% by weight, the polyvinylidene fluoride content was 5% by weight, and the thickness of the negative electrode mixture layer was 300 μm. .
[0182]
Sample 58
A non-aqueous electrolyte secondary battery was produced in the same manner as in Sample 54, except that the acetylene black content of the first layer of the positive electrode was 75% by weight and the thickness of the negative electrode mixture layer was 300 μm.
[0183]
Sample 59
The thickness of the first layer of the positive electrode is 5 μm, and the thickness of the second layer is LiCoO 2.₂A non-aqueous electrolyte secondary battery was produced in the same manner as in Sample 54, except that the content was 94% by weight, the polyvinylidene fluoride content was 5% by weight, and the thickness of the negative electrode mixture layer was 300 μm. .
[0184]
Sample 60
The first layer of the positive electrode was not formed, and the thickness of the second layer was set to 150 μm.₂A non-aqueous electrolyte secondary battery was produced in the same manner as in Sample 48, except that the content was 93% by weight, the polyvinylidene fluoride content was 6% by weight, and the thickness of the negative electrode mixture layer was 150 μm. .
[0185]
Sample 61
The first layer of the positive electrode is not formed, and the second layer of LiCoO₂A non-aqueous electrolyte secondary battery was produced in the same manner as in Sample 48, except that the content was 93% by weight and the polyvinylidene fluoride content was 6% by weight.
[0186]
Sample 62
The thickness of the first layer of the positive electrode was set to 5 μm, the acetylene black content was set to 75% by weight, and LiCoO 2 was used.₂A non-aqueous electrolyte secondary battery was produced in the same manner as in Sample 48, except that the content was 93% by weight and the polyvinylidene fluoride content of the second layer was 6% by weight.
[0187]
Sample 63
The first layer of the positive electrode is not formed, and the second layer of LiCoO₂A non-aqueous electrolyte secondary battery was produced in the same manner as in Sample 48, except that the content was 94% by weight and the polyvinylidene fluoride content was 5% by weight.
[0188]
Sample 64
A non-aqueous electrolyte secondary battery was fabricated in the same manner as in Sample 48, except that the first layer of the positive electrode was not formed.
[0189]
Sample 65
The first layer of the positive electrode was not formed, and the thickness of the second layer was set to 300 μm.₂A non-aqueous electrolyte secondary battery was produced in the same manner as in Sample 48, except that the content was 94% by weight, the polyvinylidene fluoride content was 5% by weight, and the thickness of the negative electrode mixture layer was 300 μm. .
[0190]
Sample 66
The first layer of the positive electrode has a thickness of 5 μm, the acetylene black content is 75% by weight, and the LiCoO 2 of the second layer is₂A non-aqueous electrolyte secondary battery was produced in the same manner as in Sample 48, except that the content was 98.5% by weight and the polyvinylidene fluoride content was 0.5% by weight.
[0191]
Sample 67
The thickness of the first layer of the positive electrode was 5 μm, the content of acetylene black was 75% by weight, the thickness of the second layer was 310 μm, and LiCoO₂A non-aqueous electrolyte secondary battery was produced in the same manner as in Sample 48, except that the content was 94% by weight, the polyvinylidene fluoride content was 5% by weight, and the thickness of the negative electrode mixture layer was 310 μm. .
[0192]
Sample 68
Except that the acetylene black content of the first layer of the positive electrode was 5% by weight, the thickness of the second layer was 300 μm, and the thickness of the negative electrode mixture layer was 300 μm, A water electrolyte secondary battery was produced.
[0193]
Sample 69
The same procedure as in Sample 48 was carried out except that the acetylene black content of the first layer of the positive electrode was 80% by weight, the thickness of the second layer was 300 μm, and the thickness of the negative electrode mixture layer was 300 μm. A water electrolyte secondary battery was produced.
[0194]
With respect to Samples 48 to 69 produced as described above, the state of peeling of the positive electrode and cracks were observed, and the results are shown in Table 5 below. Regarding the peeling, the case where no peeling was observed on the positive electrode was indicated by ○, the case where minute peeling was observed was indicated by Δ, and the case where large peeling was observed was indicated by ×. Regarding the cracks, those in which no cracks were observed in the positive electrode were indicated by ○, those in which minute cracks were observed were indicated by Δ, and those in which large cracks were observed were indicated by ×.
[0195]
For Samples 48 to 69, the discharge capacity at 0.2 C and the low-temperature load characteristics at 1 C and 0 ° C. were measured as follows, and the results are shown in Table 5 below.
[0196]
The discharge capacity of the produced non-aqueous electrolyte secondary battery was determined by charging the battery under the conditions of an ambient temperature of 23 ° C., a charging voltage of 4.20 V, a charging current of 1000 mA, and a charging time of 3 hours, followed by a discharging current of 400 mA and a termination voltage. It was determined as the initial capacity when discharging at 2.75V.
[0197]
The low-temperature load characteristics are as follows. The non-aqueous electrolyte secondary battery after the above-mentioned discharge capacity measurement was charged at a charging voltage of 4.20 V, a charging current of 1000 mA, a charging time of 3 hours, and then discharged at an environmental temperature of 0 ° C. The capacity when discharging was performed at a current of 2000 mA and a final voltage of 2.75 V was determined, and the ratio to the initial capacity was expressed as a percentage.
[0198]
[Table 5]

[0199]
As is clear from Table 5, Samples 48 to 59 had favorable results in all of the discharge capacity, low-temperature load characteristics, and peeling and cracking of the electrodes. On the other hand, Samples 60 to 69 were inferior to any of the above characteristics.
[0200]
Although not shown in Table 5, when the coating was performed so that the thickness of the first layer of the positive electrode was 0.5 μm or less, the coating was too thin to achieve uniform coating. . In addition, when the coating was performed so that the thickness of the first layer of the positive electrode exceeded 5 μm, the discharge capacity was reduced.
[0201]
From the results of Experiment 5 above, the carbon powder content of the first layer was 10% by weight to 75% by weight, the film thickness of the first layer was 0.5 μm to 5 μm, and the It has been found that the content of the adhesive is preferably 1% by weight to 5% by weight, and the thickness of the second layer is preferably 160 μm to 300 μm.
[0202]
<Experiment 6>
In Experiment 6, the peak ratio (current collector side / second layer side) near the diffraction angle (2θ, θ: Bragg angle) of 20.0 ° in the X-ray diffraction pattern when X-ray diffraction measurement using CuKα ray was performed. ) Was examined for the optimal range. Further, an alloy used as a negative electrode active material was also studied.
[0203]
Sample 70
First, a negative electrode was manufactured as follows. The first layer paint was uniformly applied to both surfaces of a negative electrode current collector made of a strip-shaped copper foil having a thickness of 15 μm, and dried to form a first layer. The thickness of the first layer after drying was 0.5 μm. In addition, the second layer coating material is uniformly applied on the first layer, dried, compression-molded at a constant pressure by a roller press to form a second layer, and the negative electrode is formed by slitting the second layer. Obtained.
[0204]
The coating material for the first layer used here is a mixture of 90% by weight of polyvinylidene fluoride as a binder and 10% by weight of acetylene black as a carbon powder as a conductive agent. It was prepared by dispersing in methyl-2-pyrrolidone.
[0205]
Further, the second layer paint is prepared by mixing 60% by weight of CuSn powder, 35% by weight of flaky graphite as a negative electrode active material, and 5% by weight of polyvinylidene fluoride as a binder. Was dispersed in N-methyl-2-pyrrolidone as a solvent. The CuSn powder is obtained by melting 50 parts by weight of Cu and 50 parts by weight of Sn and synthesizing them by a gas atomizing method. When the obtained CuSn powder was mesh-passed with a sieve of 63 μm, the average particle size was 25 μm.
[0206]
For the obtained negative electrode, the peak ratio (current collector side / second layer side) near the diffraction angle (2θ, θ: Bragg angle) of 20.0 ° by X-ray diffraction was measured. Specifically, in a state where the first layer and the second layer were formed only on one main surface side of the negative electrode current collector, X-ray diffraction measurement was performed on the current collector side and the second layer side. In an X-ray diffraction pattern obtained by the measurement, a peak ratio (current collector side / second layer side) around diffraction angle (2θ, θ: Bragg angle) of 20.0 ° was determined. The peak ratio (current collector side / second layer side) of the diffraction angle (2θ, θ: Bragg angle) around 20.0 ° by X-ray diffraction was 1.1.
[0207]
The X-ray diffractometer used for the X-ray diffraction measurement was RAD-IIC manufactured by Rigaku Denki, and the X-ray source used was a Cu-cathode and a graphite monochromator. The slits were DS (divergence slit) = 1 °, RS (light receiving slit) = 0.6 °, and SS (scattering slit) = 1 °. The scanning speed was 0.5 ° / min, the tube voltage was 40 kV, and the tube current was 30 mA.
[0208]
In addition, a scanning type manufactured by JEOL Ltd. was applied to the negative electrode whose peak ratio (current collector side / second layer side) near the diffraction angle (2θ, θ: Bragg angle) of 20.0 ° by X-ray diffraction was measured. Fluorine atom mapping was performed using an electron microscope JSM-5600 to determine a fluorine density ratio. The determined fluorine density ratio was 1.1.
[0209]
Next, a positive electrode was produced as follows. On both surfaces of a positive electrode current collector made of a 20-μm-thick strip-shaped aluminum foil, a coating for a positive electrode mixture layer is uniformly applied, dried, and compression-molded at a constant pressure by a roller press to form a positive electrode mixture layer, This was slit to obtain a positive electrode.
[0210]
The coating material for the positive electrode mixture layer used here was LiCoO 2 as a positive electrode active material.₂A mixture of 95% by weight of powder and 5% by weight of lithium carbonate powder was mixed with 91% by weight, 6% by weight of flake graphite as a conductive agent, and 3% by weight of polyvinylidene fluoride as a binder. This mixture was prepared by dispersing this mixture in N-methyl-2-pyrrolidone as a solvent.
[0211]
LiCoO used as positive electrode active material₂The powder was prepared as follows. That is, 0.5 mol of lithium carbonate and 1 mol of cobalt carbonate were mixed, and this mixture was fired in air at 900 ° C. for 5 hours. An X-ray diffraction measurement was performed on the obtained material, and as a result, the LiCoO whose peak position was registered in the JCPDS file was used.₂Well matched the data. The obtained material was pulverized, and the cumulative 50% particle size obtained by a laser diffraction method was set to 15 μm, to obtain a positive electrode active material.
[0212]
The positive electrode obtained as described above, the negative electrode, and a separator made of a microporous polypropylene film having a thickness of 25 μm are laminated and adhered in the order of the negative electrode, the separator, the positive electrode, and the separator, and spirally wound many times. The wound body was produced by turning and fixing the final end of the outermost separator with a tape.
[0213]
Next, an insulating plate was inserted into the bottom of an iron battery can with nickel plating on the inside, and the wound body was further housed. Then, in order to collect the current of the negative electrode, one end of a nickel negative electrode lead was pressed against the negative electrode, and the other end was welded to the battery can. Further, in order to collect the current of the positive electrode, one end of an aluminum positive electrode lead was attached to the positive electrode, and the other end was electrically connected to the battery lid.
[0214]
Then, a non-aqueous electrolyte was injected into the battery can. This non-aqueous electrolyte is prepared by mixing LiPF as an electrolyte in a mixed solvent obtained by mixing ethylene carbonate and dimethyl carbonate at a volume ratio of 1: 1.₆Was dissolved at a concentration of 1 mol / l.
[0215]
Finally, by caulking the battery can through an insulating sealing gasket coated with asphalt, the thin plate for current interruption, the PTC element and the battery lid are fixed, and a cylindrical type having a diameter of about 18 mm and a height of about 65 mm is formed. A non-aqueous electrolyte secondary battery was manufactured.
[0216]
Sample 71
A non-aqueous electrolyte secondary battery was fabricated in the same manner as in Sample 70, except that the thickness of the first layer of the negative electrode was 1.0 μm.
[0219]
Sample 72
A non-aqueous electrolyte secondary battery was fabricated in the same manner as in Sample 70, except that the thickness of the first layer of the negative electrode was 1.0 μm. The peak ratio (current collector side / second layer side) near 20.0 ° of the diffraction angle (2θ, θ: Bragg angle) by X-ray diffraction was 1.2, and the fluorine density ratio was 1.3. there were.
[0218]
Sample 73
A nonaqueous electrolyte secondary battery was fabricated in the same manner as in Sample 70, except that the thickness of the first layer of the negative electrode was 1.5 μm. The peak ratio (current collector side / second layer side) near the diffraction angle (2θ, θ: Bragg angle) of 20.0 ° by X-ray diffraction was 1.4, and the fluorine density ratio was 1.4. there were.
[0219]
Sample 74
A non-aqueous electrolyte secondary battery was fabricated in the same manner as in Sample 70, except that the thickness of the first layer of the negative electrode was 3.0 μm. Incidentally, the peak ratio (current collector side / second layer side) near the diffraction angle (2θ, θ: Bragg angle) of 20.0 ° by X-ray diffraction is 1.8, and the fluorine density ratio is 1.7. there were.
[0220]
Sample 75
A non-aqueous electrolyte secondary battery was fabricated in the same manner as in Sample 70 except that FeSn powder was used as the negative electrode active material. The peak ratio (current collector side / second layer side) near 20.0 ° of the diffraction angle (2θ, θ: Bragg angle) by X-ray diffraction is 1.1, and the fluorine density ratio is 1.1. there were.
[0221]
Sample 76
A non-aqueous electrolyte secondary battery was manufactured in the same manner as in Sample 70 except that the first layer of the negative electrode was not formed. The peak ratio (current collector side / second layer side) near 20.0 ° of the diffraction angle (2θ, θ: Bragg angle) by X-ray diffraction was 0.9, and the fluorine density ratio was 0.9. there were.
[0222]
The charge / discharge cycle characteristics and the electrode strength ratio of the samples 71 to 76 manufactured as described above were measured.
[0223]
The charge / discharge cycle characteristics were as follows. First, the prepared nonaqueous electrolyte secondary battery was charged at a constant current and a constant voltage under the conditions of an ambient temperature of 23 ° C., a constant current of 0.5 A, a maximum voltage of 4.2 V, and a charging time of 4 hours. Then, discharging was performed under the conditions of an environmental temperature of 23 ° C., a constant current of 0.3 A, and a final voltage of 2.75 V, and the capacity at this time was determined as an initial capacity. Next, constant-current constant-voltage charging is performed under the conditions of an environmental temperature of 23 ° C., a constant current of 2.0 A, a maximum voltage of 4.2 V, and a charging time of 2.5 hours. The discharge was performed under the condition of a final voltage of 2.75 V, which was defined as one cycle. The capacity when this charge and discharge was repeated 100 cycles was measured, and the ratio when the initial capacity was set to 100% was expressed as a capacity retention rate.
[0224]
The electrode strength ratio was measured as follows. The negative electrode was cut into 30 mm x 200 mm, and a tensile strength test was performed at a speed of 1 m / min using an adhesive tape, and the strength at this time was measured. The measured strength was represented by a ratio when the electrode strength of the sample 71 was set to 100%.
[0225]
Peak ratio (current collector side / second layer side) near 20.0 ° diffraction angle (2θ, θ: Bragg angle) by X-ray diffraction for Samples 71 to 76 above, fluorine density ratio, after 100 cycles Table 6 below shows the capacity retention ratio and the electrode strength ratio.
[0226]
[Table 6]

[0227]
From Table 6 above, Samples 71 to 75 have a higher capacity retention ratio and a higher capacity retention ratio than Sample 76 having a peak ratio of 0.9 near the diffraction angle (2θ, θ: Bragg angle) of 20.0 ° by X-ray diffraction. It can be seen that the results were excellent in any of the electrode strength ratios.
[0228]
Therefore, from the results of Experiment 6, it is preferable that the peak ratio (current collector side / second layer side) near the diffraction angle (2θ, θ: Bragg angle) 20.0 ° by X-ray diffraction is 1 or more. There was found. Further, it has been found that the present invention is effective even when an alloy material is used as the negative electrode active material.
[0229]
【The invention's effect】
As is clear from the above description, in the battery according to the present invention, the first layer having a strong binding force is interposed between the current collector and the second layer containing the active material in at least one electrode. Therefore, the second layer can obtain a strong binding force even if the binder content is small. And since the binder content of the second layer is small, the capacity can be increased. Further, even when the thickness of the electrode is increased for the purpose of further increasing the capacity, the load characteristics do not deteriorate. Therefore, according to the present invention, it is possible to improve the peel strength of the electrode even with a small amount of the binder, and to provide a battery having high capacity and excellent load characteristics.
[Brief description of the drawings]
FIG. 1 is a sectional view of a nonaqueous electrolyte secondary battery to which the present invention is applied.
FIG. 2 is a schematic cross-sectional view of a main part of an electrode including a first layer and a second layer on a current collector.
[Explanation of symbols]
1. Non-aqueous electrolyte secondary battery
2 positive electrode
3 negative electrode
4 separator
5 battery can
6 insulation board
7 insulation board
8mm negative electrode lead
9mm positive electrode lead
10 Battery cover
11 Insulation sealing gasket
12 Safety valve device
13 PTC element
20cm current collector
21 First layer
22 Second layer

Claims (24)

Comprising a pair of electrodes and an electrolyte,
At least one of the pair of electrodes includes, in this order, a first layer containing a binder on a current collector, and a second layer containing an active material.
The battery according to claim 1, wherein the first layer has a stronger binding force than the second layer. The battery according to claim 1, wherein the first layer contains the active material and contains polyvinylidene fluoride as the binder. The battery according to claim 2, wherein the first layer contains the polyvinylidene fluoride in an amount of 2% by weight or more. 3. The battery according to claim 2, wherein the second layer contains a soft binder. 5. The battery according to claim 4, wherein the soft binder is a polymer or a mixture of a rubber binder and polyvinylidene fluoride or a rubber binder. The battery according to claim 5, wherein the rubber-based binder is a rubber-based compound having a diene structure, acrylic rubber, or fluororubber. 7. The battery according to claim 6, wherein the rubber compound having a diene structure is a styrene butadiene latex. 7. The battery according to claim 6, wherein the fluoro rubber is hexafluoropropylene. The battery according to claim 4, wherein the second layer contains the soft binder in an amount of 1% by weight or more. The battery according to claim 2, wherein a thickness ratio of the first layer to the second layer is in a range of 5:95 to 80:20. 3. The battery according to claim 2, wherein the pair of electrodes are stacked in close contact with a separator interposed therebetween, and the wound body is housed in a battery can. The battery according to claim 1, wherein the first layer contains a fluorine-based resin and carbon powder as the binder, and does not contain the active material. 13. The battery according to claim 12, wherein the fluororesin is at least one of polyvinyl fluoride, polyvinylidene fluoride, and polytetrafluoroethylene. 13. The battery according to claim 12, wherein the first layer contains the carbon powder in an amount of 10% by weight to 75% by weight. 13. The battery according to claim 12, wherein the carbon powder is graphite and / or carbon black. The battery according to claim 12, wherein the first layer has a thickness of 0.5 m to 5 m. The battery according to claim 12, wherein the second layer contains 1 to 5% by weight of a binder. The battery according to claim 12, wherein the second layer has a thickness of 160 m to 300 m. 18. The battery according to claim 17, wherein the binder contained in the first layer is the same as the binder contained in the second layer. When an X-ray diffraction measurement using CuKα ray is performed on at least one of the electrodes, a peak ratio (current collector side / second side) around 20.0 ° in the X-ray diffraction pattern (2θ, θ: Bragg angle) The battery according to claim 1, wherein the number of layers is 1 or more. The battery according to claim 1, wherein the active material is a lithium transition metal composite oxide. 2. The active material according to claim 1, wherein the active material is at least one of a material capable of doping and undoping lithium, a metal capable of forming an alloy with lithium, and an alloy compound of a metal capable of forming an alloy with lithium. The battery as described. The battery according to claim 1, wherein the electrolyte is a non-aqueous electrolyte. The battery according to claim 1, wherein the battery is a secondary battery.

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