JP4822603B2 - Method for producing non-aqueous electrolyte secondary battery - Google Patents

Description

【００２２】
（３）正極の作製
一方、正極活物質としての平均粒径が５μｍのＬｉＣｏＯ₂粉末と、導電剤としての人造黒鉛粉末とを、質量比で９：１となるように混合して正極合剤を調製した。この正極合剤と、ポリビニリデンフルオライド（ＰＶｄＦ）よりなる結着剤をＮ−メチル−２−ピロリドン（ＮＭＰ）からなる有機溶剤に５質量％溶解した結着剤溶液とを、固形分の質量比で９５：５になるように混合、混練して正極活物質スラリー２７を調製した。
【００２３】
この正極活物質スラリー２７をスラリー塗布装置２０のスラリー充填槽２１に充填した後、一対の送りローラ２３，２４により送り出された正極集電体（例えば、アルミニウム箔あるいはアルミニウム合金箔）２８の片面に、スラリー充填槽２１に充填された正極活物質スラリー２７を塗布し、塗布量調整治具２２を通過させて所定量のスラリーを塗布した。ついで、スラリー層を乾燥させた後、このスラリー塗布装置２０の前方に配設された別のスラリー塗布装置（図示せず）を通過させて、スラリーが塗布されていない正極集電体２８の他面にも同様にスラリーを塗布し、乾燥させた。その後、乾燥正極板をロールプレス機により圧延して、片面当たりの活物質層の厚みが５０μｍ、充填密度が３．４ｇ／ｃｍ³の正極板を作製した後、所定寸法に切断して正極とした。
【００２４】
（４）非水電解液二次電池の作製
ついで、上述のようにして作製した負極ａ１，ａ２，ａ３，ｘ１，ｘ２，ｘ３と正極とを、有機溶媒との反応性が低く、かつ微多孔のポリオレフィン系樹脂からなるセパレータを間にして重ね合わせた後、巻き取り機により渦巻状に卷回して電極群とした。この後、この電極群を外装缶の開口部より挿入し、電極群の負極より延出する負極集電タブを外装缶の内底部に抵抗溶接した後、電極群の正極より延出する正極集電タブを封口体の底部に溶接した。ついで、外装缶内に非水電解液（エチレンカーボネート（ＥＣ）とジエチルカーボネート（ＤＥＣ）を等体積比で混合した溶媒に、六フッ化リン酸リチウム（ＬｉＰＦ₆）を１モル／リットル溶解した溶液）をそれぞれ注入した。
【００２５】
この後、外装缶の開口部を封口体で液密に封口して、非水電解質二次電池Ａ１，Ａ２，Ａ３，Ｘ１，Ｘ２，Ｘ３をそれぞれ作製した。なお、このようにして作製した各非水電解質二次電池Ａ１（負極ａ１を用いたもの）、Ａ２（負極ａ２を用いたもの）、Ａ３（負極ａ３を用いたもの）、Ｘ１（負極ｘ１を用いたもの）、Ｘ２（負極ｘ２を用いたもの）、Ｘ３（負極ｘ３を用いたもの）の容量は６００ｍＡｈであった。
【００２６】
（５）非水電解液二次電池の負荷特性試験
ついで、上述のように作製した各電池Ａ１，Ａ２，Ａ３，Ｘ１，Ｘ２，Ｘ３をそれぞれ、室温（約２５℃）で、６００ｍＡ（１ＩｔｍＡ）の定電流で電池電圧が４．１０Ｖになるまで充電し、ついで、４．１０Ｖの定電圧で電流値が１０ｍＡになるまで充電した。この後、６００ｍＡ（１ＩｔｍＡ）の放電電流で電池電圧が２．７５Ｖになるまで放電させて、放電時間から１Ｉｔ放電時の放電容量を求めると、下記の表２に示すような結果となった。
また、これらの各電池Ａ１，Ａ２，Ａ３，Ｘ１，Ｘ２，Ｘ３を上記と同様な条件で充電した後、１２００ｍＡ（２ＩｔｍＡ）の放電電流で電池電圧が２．７５Ｖになるまで放電させて、放電時間から２Ｉｔ放電時の放電容量を求めた。
ついで、求めた１Ｉｔ放電時の放電容量に対する２Ｉｔ放電時の放電容量の比率を放電容量比（放電容量比＝２Ｉｔ放電時の放電容量／１Ｉｔ放電時の放電容量）として求めると、下記の表２に示すような結果となった。
【００２７】
【表２】

【００２８】
上記表２の結果から明らかなように、気泡を送り込まないスラリーを使用して気泡痕３２が生じなかった負極板ｘ１を用いた電池Ｘ１および気泡痕３２の面積割合が０．５％の負極板ｘ２を用いた電池Ｘ２においては、１Ｉｔ放電時容量は６００（ｍＡｈ）で良好であるが放電容量比が７５％、８５％と低下していることが分かる。一方、気泡痕３２の面積割合が７％の負極板ｘ３を用いた電池Ｘ３においては、放電容量比は９９で良好であるが１Ｉｔ放電時容量は５１０（ｍＡｈ）と低下していることが分かる。これらに対して、気泡痕３２の面積割合を１．０〜５．０％にした負極板ａ１〜ａ３を用いた電池Ａ１〜Ａ３においては、１Ｉｔ放電時容量および放電容量比が共に良好であることが分かる。
【００２９】
ここで、各電池を充電状態で分解したところ、気泡痕３２の面積割合が７％の負極板ｘ３を用いた電池Ｘ３においては、気泡痕３２を中心にしてリチウムの析出が多く見られ、他の電池にリチウムの析出は見あたらなかった。これにより電池Ｘ３においては放電容量が極端に低下したと考えられる。
また、気泡痕３２の面積割合が０％および０．５％と気泡痕３２の発生を少なくした負極板ｘ１，ｘ２においては、気泡痕３２の面積割合が少なすぎるために電解液の浸透性（含液性）が低下して放電容量比が低下したと考えられる。
これらに対して、気泡痕３２の面積割合を１．０〜５．０％にした負極板ａ１〜ａ３においては、電解液の浸透性（含液性）が向上したために、１Ｉｔ放電時容量および放電容量比が共に向上したと考えられる。
以上のことから、負極板の全表面積に対する気泡痕（低充填密度部）３２の面積割合は１．０％以上で５．０％以下にする必要がある。
【００３０】
（６）気泡痕の直径の検討
上述と同様に、負極活物質スラリー１５を調製し、これをスラリー撹拌装置１０のスラリー撹拌槽１１に充填した後、空気ノズル１４から空気を吐出（この場合、得られた負極の全表面積に対して、気泡痕の全表面積が３．０％になるよう空気の吐出量を調整している）させて、スラリー１５中に空気を送り込むとともに、撹拌軸１２を所定の回転速度で１０分間だけ回転させた。ここで、撹拌速度を２０００ｒｐｍにして撹拌したものをスラリーａ４とし、１５００ｒｐｍにして撹拌したものをスラリーａ５とし、１０００ｒｐｍにして撹拌したものをスラリーａ６とし、５００ｒｐｍにして撹拌したものをスラリーａ７とし、３００ｒｐｍにして撹拌したものをスラリーａ８とし、２００ｒｐｍにして撹拌したものをスラリーａ９とした。
【００３１】
これらの各負極活物質スラリー１５（ａ４，ａ５，ａ６，ａ７，ａ８，ａ９）をスラリー塗布装置２０のスラリー充填槽２１に充填した後、上述と同様に負極集電体１６の両面にスラリーをそれぞれ塗布し、乾燥させた後、所定の厚みに圧延し、活物質の充填密度が１．７ｇ／ｃｍ³の負極板をそれぞれ作製した後、所定寸法に切断して負極３０（ａ４，ａ５，ａ６，ａ７，ａ８，ａ９）とした。
ここで、気泡痕３２の部分の活物質層を欠き落として充填密度を測定すると、その充填密度は１．２ｇ／ｃｍ³で低密度であった。また、上述と同様に、負極３０（ａ４，ａ５，ａ６，ａ７，ａ８，ａ９）を観察して、気泡痕３２の直径を測定すると、下記の表３に示すような結果となった。
【００３２】
【表３】

【００３３】
ついで、上述のようにして作製した負極３０（ａ４，ａ５，ａ６，ａ７，ａ８，ａ９）と正極とを用いて、上述と同様に非水電解質二次電池Ａ４（負極ａ４を用いたもの），Ａ５（負極ａ５を用いたもの），Ａ６（負極ａ６を用いたもの），Ａ７（負極ａ７を用いたもの），Ａ８（負極ａ８を用いたもの），Ａ９（負極ａ９を用いたもの）をそれぞれ作製した後、上述と同様に負荷特性試験を行って、１Ｉｔ放電時の放電容量を求めるとともに、２Ｉｔ放電時の放電容量を求め、Ｉｔ放電時の放電容量に対する２Ｉｔ放電時の放電容量の比率を放電容量比（放電容量比＝２Ｉｔ放電時の放電容量／１Ｉｔ放電時の放電容量）として求めると、下記の表４に示すような結果となった。
【００３４】
【表４】

【００３５】
上記表４の結果から明らかなように、気泡痕３２の直径の大きさによらず放電容量比は無気泡痕のものに比べて高い値を示していることが分かる。また、気泡痕３２が存在しても、負極ａ４のように直径が小さすぎても、負極ａ８，ａ９のように直径が大きすぎても放電容量比は低下することが分かる。
これは、気泡痕３２の面積割合が同じであっても、気泡痕３２の直径が小さすぎると、負極板表面全体に微少な凹凸が形成されて負極板の表面状態が粗くなり、これにより内部抵抗が上昇して放電容量比が低下したと考えられる。
一方、気泡痕３２の直径が大きくなりすぎると、負極板表面全体に凹凸が形成されにくくなって連続して平滑な部分が多くなるが、反面、電解液の含液性（浸透性）の向上に寄与する気泡痕３２が偏在するため、負極板表面全体での反応性が低下して放電容量比が低下したと考えられる。
これらに対して、気泡痕３２の直径を０．５〜２．０ｍｍにした負極板ａ４〜ａ７においては、電解液の浸透性（含液性）と負極板表面全体の粗さが適度に調和して、放電容量比が向上したと考えられる。
以上のことから、負極の気泡痕（低充填密度部）３２の直径は０．５ｍｍ以上で２．０ｍｍ以下にするのが望ましいということができる。
【００３６】
２．第２実施形態
上述した第１実施形態においては、負極活物質スラリーに気泡を導入して、負極に低密度部分を形成させた場合の特性の変化について検討したが、以下では、正極活物質スラリーに気泡を導入して、正極に低密度部分を形成させた場合の特性の変化について検討する。
【００３７】
（１）正極の作製
まず、正極活物質としての平均粒径が５μｍのＬｉＣｏＯ₂粉末と、導電剤としての人造黒鉛粉末とを、質量比で９：１となるように混合して正極合剤を調製した。この正極合剤と、ポリビニリデンフルオライド（ＰＶｄＦ）よりなる結着剤をＮ−メチル−２−ピロリドン（ＮＭＰ）からなる有機溶剤に５質量％溶解した結着剤溶液とを、固形分の質量比で９５：５になるように混合、混練して正極活物質スラリー２７を調製した。ついで、得られた正極活物質スラリー２７をスラリー撹拌装置１０のスラリー撹拌槽１１に充填した後、空気ノズル１４からスラリー１ｋｇに対して毎分５０ｍｌの空気を吐出させて、スラリー２７中に空気を送り込むとともに、撹拌軸１２を１０００ｒｐｍの回転速度で所定の時間だけ回転させた。
【００３８】
これにより、撹拌羽根１３は回転し、スラリー撹拌槽１１に充填された正極活物質スラリー２７は送り込まれた空気とともに撹拌されて、正極活物質スラリー２７に多数の気泡が発生することとなる。ここで、撹拌時間を５分間にして撹拌したものをスラリーｂ１とし、１０分間にして撹拌したものをスラリーｂ２とし、２０分間にして撹拌したものをスラリーｂ３とした。また、気泡を送り込まないものをスラリーｙ１とし、撹拌時間を１分間にして撹拌したものをスラリーｙ２とし、４０分間にして撹拌したものをスラリーｙ３とした。
【００３９】
このようにして作製した各正極活物質スラリー２７（ｂ１，ｂ２，ｂ３，ｙ１，ｙ２，ｙ３）をスラリー塗布装置２０のスラリー充填槽２１に充填した後、一対の送りローラ２３，２４により送り出された正極集電体（例えば、アルミニウム箔あるいはアルミニウム合金箔）２８の片面に、スラリー充填槽２１に充填された正極活物質スラリー２７（ｂ１，ｂ２，ｂ３，ｙ１，ｙ２，ｙ３）をそれぞれ塗布し、塗布量調整治具２２を通過させて所定量のスラリーを塗布した。
【００４０】
ついで、スラリー層を乾燥させた後、このスラリー塗布装置２０の前方に配設された別のスラリー塗布装置（図示せず）を通過させて、スラリーが塗布されていない正極集電体２８の他面にも同様にスラリーを塗布し、乾燥させた。その後、乾燥正極板をロールプレス機により圧延して、片面当たりの活物質層の厚みが５０μｍ、充填密度が３．４ｇ／ｃｍ³の正極板をそれぞれ作製した後、所定寸法に切断して正極４０（ｂ１，ｂ２，ｂ３，ｙ１，ｙ２，ｙ３）とした。
【００４１】
ここで、正極４０（ｂ１，ｂ２，ｂ３，ｙ１，ｙ２，ｙ３）を観察すると、図３（ｂ）に示すように、ロールプレス機による圧延で気泡が弾けて形成されたクレータ状の気泡痕４２が高密度充填部（充填密度が３．４ｇ／ｃｍ³）４１のあちこちに点在していた。この場合、気泡痕４２は高密度充填部４１よりも薄い色合となるので、高密度充填部４１と気泡痕４２との識別は目視により可能である。この気泡痕４２の直径を測定してその平均直径を求めると、０．５ｍｍ以上で２．０ｍｍ以下であることが明らかとなった。
【００４２】
そして、気泡痕４２の部分の活物質層を欠き落として質量を測定し、気泡痕４２の直径と活物質層の厚さから充填密度を求めると、その充填密度は３．０ｇ／ｃｍ³で低密度であった。また、各気泡痕４２の表面積を測定し、この測定結果に基づいて気泡痕４２の全表面積を算出した後、各正極ｂ１，ｂ２，ｂ３，ｙ１，ｙ２，ｙ３の全表面積に対する割合（面積割合：面積率）を求めると下記の表５に示すような結果となった。なお、正極ｙ１は気泡を送り込まないスラリーを使用したため、気泡痕４２はなかった。
【００４３】
【表５】

【００４４】
（２）負極の作製
一方、天然黒鉛（Ｌｃ値が１０００Åで、ｄ₀₀₂値が３．３５６Åで、平均粒径が２０μｍのもの）よりなる負極活物質と、スチレン−ブタジエンゴム（ＳＢＲ）のディスパージョン（固形分が４８質量％）を水に分散させた後、増粘剤であるカルボキシメチルセルロース（ＣＭＣ）を添加して負極活物質スラリー１５を調製した。この場合、乾燥後の固形分質量組成比が、黒鉛：ＳＢＲ：ＣＭＣ＝１００：３：２となるように調製した。
【００４５】
このようにして作製した負極活物質スラリー１５をスラリー塗布装置２０のスラリー充填槽２１に充填した後、一対の送りローラ２３，２４により送り出された負極集電体（例えば、銅箔）１６の片面に、スラリー充填槽２１に充填された負極活物質スラリー１５をそれぞれ塗布し、塗布量調整治具２２を通過させて所定量のスラリーを塗布した。ついで、スラリー層を乾燥させた後、このスラリー塗布装置２０の前方に配設された別のスラリー塗布装置（図示せず）を通過させて、スラリーが塗布されていない負極集電体１６の他面にも同様にスラリーを塗布し、乾燥させた。その後、乾燥負極板をロールプレス機により圧延して、片面当たりの活物質層の厚みが５０μｍ、充填密度が１．７ｇ／ｃｍ³の負極板をそれぞれ作製した後、所定寸法に切断して負極とした。
【００４６】
（３）非水電解液二次電池の作製
ついで、上述のようにして作製した正極ｂ１，ｂ２，ｂ３，ｙ１，ｙ２，ｙ３と負極とを用いて、上述と同様に非水電解質二次電池Ｂ１，Ｂ２，Ｂ３，Ｙ１，Ｙ２，Ｙ３をそれぞれ作製した。なお、このようにして作製した各非水電解質二次電池Ｂ１（正極ｂ１を用いたもの）、Ｂ２（正極ｂ２を用いたもの）、Ｂ３（正極ｂ３を用いたもの）、Ｙ１（正極ｙ１を用いたもの）、Ｙ２（正極ｙ２を用いたもの）、Ｙ３（正極ｙ３を用いたもの）の容量は６００ｍＡｈであった。この後、上述と同様に負荷特性試験を行って、１Ｉｔ放電時の放電容量を求めるとともに、２Ｉｔ放電時の放電容量を求め、Ｉｔ放電時の放電容量に対する２Ｉｔ放電時の放電容量の比率を放電容量比（放電容量比＝２Ｉｔ放電時の放電容量／１Ｉｔ放電時の放電容量）として求めると、下記の表６に示すような結果となった。
【００４７】
【表６】

【００４８】
上記表６の結果から明らかなように、気泡を送り込まないスラリーを使用して気泡痕４２が生じなかった正極板ｙ１を用いた電池Ｙ１および気泡痕４２の面積割合が０．５％の負極板ｙ２を用いた電池Ｙ２においては、１Ｉｔ放電時容量は６００（ｍＡｈ）で良好であるが放電容量比が７５％、８５％と低下していることが分かる。一方、気泡痕４２の面積割合が７％の負極板ｙ３を用いた電池Ｙ３においては、放電容量比は９９で良好であるが１Ｉｔ放電時容量は５１０（ｍＡｈ）と低下していることが分かる。これらに対して、気泡痕４２の面積割合を１．０〜５．０％にした負極板ｂ１〜ｂ３を用いた電池Ｂ１〜Ｂ３においては、１Ｉｔ放電時容量および放電容量比が共に良好であることが分かる。
【００４９】
これは、気泡痕４２の面積割合が７％の負極板ｙ３を用いた電池Ｙ３においては、気泡痕４２の面積割合が大きいために活物質の充填量が低下して放電容量が極端に低下したと考えられる。
また、気泡痕４２の面積割合が０％および０．５％と気泡痕４２の発生を少なくした負極板ｙ１，ｙ２においては、気泡痕４２の面積割合が少なすぎるために電解液の浸透性（含液性）が低下して放電容量比が低下したと考えられる。
これらに対して、気泡痕４２の面積割合を１．０〜５．０％にした負極板ｂ１〜ｂ３においては、電解液の浸透性（含液性）が向上したために、１Ｉｔ放電時容量および放電容量比が共に向上したと考えられる。
以上のことから、正極板の全表面積に対する気泡痕（低充填密度部）４２の面積割合は１．０％以上で５．０％以下にする必要がある。
【００５０】
（４）気泡痕の直径の検討
上述と同様に、正極活物質スラリー２７を調製し、これをスラリー撹拌装置１０のスラリー撹拌槽１１に充填した後、空気ノズル１４から空気を吐出（この場合、得られた負極の全表面積に対して、気泡痕の全表面積が３．０％になるよう空気の吐出量を調整している）させて、スラリー１５中に空気を送り込むとともに、撹拌軸１２を所定の回転速度で１０分間だけ回転させた。ここで、撹拌速度を２０００ｒｐｍにして撹拌したものをスラリーｂ４とし、１５００ｒｐｍにして撹拌したものをスラリーｂ５とし、１０００ｒｐｍにして撹拌したものをスラリーｂ６とし、５００ｒｐｍにして撹拌したものをスラリーｂ７とし、３００ｒｐｍにして撹拌したものをスラリーｂ８とし、２００ｒｐｍにして撹拌したものをスラリーｂ９とした。
【００５１】
これらの各正極活物質スラリー２７（ｂ４，ｂ５，ｂ６，ｂ７，ｂ８，ｂ９）をスラリー塗布装置２０のスラリー充填槽２１に充填した後、上述と同様に正極集電体２８の両面にスラリー層をそれぞれ塗布し、乾燥させた後、所定の厚みに圧延し、活物質の充填密度が３．４ｇ／ｃｍ³の正極板をそれぞれ作製した後、所定寸法に切断して正極４０（ｂ４，ｂ５，ｂ６，ｂ７，ｂ８，ｂ９）とした。
ここで、気泡痕４２の部分の活物質層を欠き落として充填密度を測定すると、その充填密度は３．０ｇ／ｃｍ³で低密度であった。また、上述と同様に、正極４０（ｂ４，ｂ５，ｂ６，ｂ７，ｂ８，ｂ９）を観察して、気泡痕４２の直径を測定すると、下記の表７に示すような結果となった。
【００５２】
【表７】

【００５３】
ついで、上述のようにして作製した正極４０（ｂ４，ｂ５，ｂ６，ｂ７，ｂ８，ｂ９）と負極とを用いて、上述と同様に非水電解質二次電池Ｂ４（正極ｂ４を用いたもの），Ｂ５（正極ｂ５を用いたもの），Ｂ６（正極ｂ６を用いたもの），Ｂ７（正極ｂ７を用いたもの），Ｂ８（正極ｂ８を用いたもの），Ｂ９（正極ｂ９を用いたもの）をそれぞれ作製した後、上述と同様に負荷特性試験を行って、１Ｉｔ放電時の放電容量を求めるとともに、２Ｉｔ放電時の放電容量を求め、Ｉｔ放電時の放電容量に対する２Ｉｔ放電時の放電容量の比率を放電容量比（放電容量比＝２Ｉｔ放電時の放電容量／１Ｉｔ放電時の放電容量）として求めると、下記の表８に示すような結果となった。
【００５４】
【表８】

【００５５】
上記表８の結果から明らかなように、気泡痕４２の直径の大きさによらず放電容量比は無気泡痕のものに比べて高い値を示していることが分かる。また、気泡痕４２が存在しても、正極ｂ４のように直径が小さすぎても、正極ｂ８，ｂ９のように直径が大きすぎても放電容量比は低下することが分かる。
これは、気泡痕４２の面積割合が同じであっても、気泡痕４２の直径が小さすぎると、正極板表面全体に微少な凹凸が形成されて正極板の表面状態が粗くなり、これにより内部抵抗が上昇して放電容量比が低下する。
一方、気泡痕４２の直径が大きくなりすぎると、正極板表面全体に凹凸が形成されにくくなって連続して平滑な部分が多くなるが、反面、電解液の含液性（浸透性）の向上に寄与する気泡痕４２が偏在するため、正極板表面全体での反応性が低下して放電容量比が低下する。
これらに対して、気泡痕４２の直径を０．５〜２．０ｍｍにした正極板ｂ４〜ｂ７においては、電解液の浸透性（含液性）と正極板表面全体の粗さが適度に調和して、放電容量比が向上したと考えられる。
以上のことから、正極の気泡痕（低充填密度部）４２の平均直径は０．５ｍｍ以上で２．０ｍｍ以下にするのが望ましいということができる。
【００５６】
上述したように、本発明においては、負極と正極の少なくとも一方に活物質の充填密度が低い低密度部分（気泡痕）が点在するとともに、この低密度部分の表面積率は正極あるいは負極の全表面積に対して１％以上で５％以下になるようにして、活物質の充填密度が低い低密度部分を点在させているので、活物質が高密度に充填されていても、低密度部分を通して電解液が活物質中に浸透するようになるため、活物質の利用率が向上して放電容量および高率放電特性が向上する。
【００５７】
なお、上述した実施の形態においては、気泡痕３２を形成させた負極３０と、気泡痕を形成させない正極とを用いて非水電解質二次電池を作製する例、あるいは気泡痕４２を形成させた正極４０と、気泡痕を形成させない負極とを用いて非水電解質二次電池を作製する例について説明したが、本発明はこれに限らず、気泡痕３２を形成させた負極３０と気泡痕４２を形成させた正極４０とを用いて非水電解質二次電池を作製するようにしても良い。この場合、負極および正極を共に高充填密度にすることが可能となるので、さらに、高容量で負荷特性に優れた非水電解質二次電池が得られるようになる。
【００５８】
なお、上述した実施の形態においては、電解液に用いる混合溶媒としてエチレンカーボネート（ＥＣ）にジエチルカーボネート（ＤＥＣ）を混合したものを用いた例について説明したが、上述したエチレンカーボネート（ＥＣ）にジエチルカーボネート（ＤＥＣ）を混合したもの以外に、プロピレンカーボネート（ＰＣ）、ビニレンカーボネート（ＶＣ）、ブチレンカーボネート（ＢＣ）、シクロペンタノン、スルホラン、３−メチルスルホラン、２，４−ジメチルスルホラン、３−メチル−１、３−オキサゾリジン−２−オン、γ−ブチロラクトン（ＧＢＬ）ジメチルカーボネート、エチルメチルカーボネート、メチルプロピルカーボネート、ブチルメチルカーボネート、エチルプロピルカーボネート、ブチルエチルカーボネート、ジプロピルカーボネート、１，２−ジエトキシエタン（ＤＥＥ）、１，２−ジメトキシ工タン（ＤＭＥ）、テトラヒドロフラン、２−メチルテトラヒドロフラン、１，３−ジオキソラン、酢酸メチル、酢酸エチル等の単体、２成分および３成分などの混合溶媒を用いてもよい。
【００５９】
また、これらの溶媒に溶解される溶質としては、ＬｉＰＦ₆以外に、ＬｉＢＦ₄、ＬｉＣＦ₃ＳＯ₃、ＬｉＡｓＦ₆、ＬｉＮ（ＣＦ₃ＳＯ₂）₂、ＬｉＯＳＯ₂（ＣＦ₂）₃ＣＦ₃、ＬｉＣｌＯ₄等を用いてもよい。さらに、ポリマー電解質、ポリマーに非水電解液を含浸させたようなゲル状電解質、固体電解質なども使用できる。
また、上述した実施の形態においては、正極活物質にコバルト酸リチウムを用いた例について説明したが、コバルト酸リチウム以外に、ニッケル酸リチウム、マンガン酸リチウム等のリチウム含有遷移金属複合酸化物あるいは二酸化マンガン（ＭｎＯ₂）、五酸化バナジウム、五酸化ニオブなどの金属酸化物、二硫化チタン、二硫化モリブデンなどの金属カルコゲン化物等も使用できる。
【００６０】
また、上述した実施の形態においては、負極活物質として天然黒鉛を用いた例について説明したが、天然黒鉛以外に、リチウムイオンを吸蔵・放出し得るカーボン系材料、例えば、カーボンブラック、コークス、ガラス状炭素、炭素繊維、またはこれらの焼成体、非晶質酸化物等の公知のものを用いてもよい。また、リチウム、リチウムを主体とする合金を負極に用いるときには、正極に本発明を適用できるのは勿論である。
また、負極に添加される増粘剤としては、上述した実施の形態においては、カルボキシメチルセルロース（ＣＭＣ）を用いる例について説明したが、ＣＭＣ以外の増粘剤としては、メチルセルロース、ヒドロキシメチルセルロース、エチルセルロース、ポリビニルアルコール、ポリアクリル酸（塩）、酸化スターチ、リン酸化スターチ、カゼイン等を使用することができる。
【００６１】
また、正、負極に添加される結着剤としては、上述した実施の形態においては、正極にポリフッ化ビニリデン（ＰＶｄＦ）、負極にスチレン−ブタジエンゴム（共重合体）を用いる例について説明したが、正極にスチレン−ブタジエンゴム（共重合体）、負極にポリフッ化ビニリデン（ＰＶｄＦ）を用いてもよい。さらに、それら以外の結着剤としては、メチル（メタ）アクリレート、エチル（メタ）アクリレート、ブチル（メタ）アクリレート、（メタ）アクリレート、ヒドロキシエチル（メタ）アクリレート、等のエチレン性不飽和カルボン酸エステル、さらに、アクリル酸、メタクリル酸、イタコン酸、フマル酸、マレイン酸等のエチレン性不飽和カルボン酸を使用することができる。
【図面の簡単な説明】
【図１】 本発明の電池の製造に用いられるスラリー撹拌装置の一例を模式的に示す図である。
【図２】 本発明の電池の製造に用いられるスラリー塗布装置の一例を模式的に示す図である。
【図３】 本発明により製造された極板を模式的に示す図であり、図３（ａ）は負極板の一例を示し、図３（ｂ）は正極板の一例を示している。
【符号の説明】
１０…スラリー撹拌装置、１１…撹拌槽、１２…撹拌軸、１３…撹拌羽根、１４…空気ノズル、１５…スラリー、２０…スラリー塗布装置、２１…スラリー充填槽、２２…塗布量調整治具、２３，２４…送りローラ、２５，２６…保持ローラ３０…負極板、３１…高密度充填部、３２…気泡痕（低密度充填部）、４０…正極板、４１…高密度充填部、４２…気泡痕（低密度充填部）[0001]
BACKGROUND OF THE INVENTION
The present invention includes a negative electrode containing a negative electrode active material capable of occluding and releasing lithium ions, a positive electrode containing a positive electrode active material capable of occluding and releasing lithium ions, and a non-aqueous electrolyte. Non-aqueous electrolyte secondary battery Manufacturing method About.
[0002]
[Prior art]
In recent years, lithium-cobalt composite oxide (LiCoO) has been used as a battery for portable electronic / communication equipment such as small video cameras, mobile phones, and notebook computers. ₂ ), Lithium-nickel composite oxide (LiNiO) ₂ ), Lithium-manganese composite oxide (LiMn) ₂ O _Four Lithium-containing transition metal composite oxide or manganese dioxide (MnO) capable of occluding and releasing lithium ions such as ₂ ) And the like as a positive electrode active material, and a non-aqueous electrolyte secondary battery using a lithium metal, a lithium alloy, or a carbon material capable of occluding and releasing lithium ions as a negative electrode active material has attracted attention. A non-aqueous electrolyte using a carbon material as a negative electrode active material Electrolyte secondary batteries have come into practical use.
[0003]
By the way, in the positive electrode plate or the negative electrode plate used in this type of non-aqueous electrolyte secondary battery, a fluid active material slurry is applied to a metal foil serving as a current collector, and then dried. It is compressed and manufactured so as to have a density. In this case, the active material slurry is generally manufactured by applying the active material slurry so that the surface state is made as uniform as possible and the packing density of the active material does not vary.
[0004]
[Problems to be solved by the invention]
However, when manufacturing each electrode plate by applying an active material slurry so that the packing density of the active material does not vary, if the packing density of the active material is increased to increase the capacity of the electrode plate, the load characteristics As a result, the battery characteristics deteriorated. This is because when the packing density of the active material is increased, the permeability of the electrolytic solution is reduced, so that it is difficult for lithium ions to enter and exit, and battery characteristics such as load characteristics are reduced.
[0005]
By the way, the active material has a packing density that is greater on the surface than on the inside and a part of the surface is cut off to form irregularities on the surface of the electrode plate, which has excellent liquid absorption. Japanese Unexamined Patent Publication No. 59-23460 proposes a plate.
However, the electrode plate proposed in Japanese Patent Application Laid-Open No. 59-23460 has a problem that a high-capacity electrode plate cannot be obtained because the packing density of the active material in the entire electrode plate is not high.
[0006]
Therefore, the present invention has been made to solve the above-described problems, and an electrode plate that does not deteriorate the battery characteristics even when the packing density of the active material is increased is obtained, and the battery characteristics such as the high rate discharge characteristics are obtained. Improved non-aqueous electrolyte secondary battery Manufacturing method Is intended to provide.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, the non-aqueous electrolyte secondary battery manufacturing method of the present invention is applied to a negative electrode active material or an active material slurry containing a positive electrode active material. The active material slurry is stirred while introducing air, and the active material slurry is stirred. A bubble introduction step for introducing bubbles, and a slurry application step for applying an active material slurry with bubbles introduced to a current collector And a drying step of drying the active material slurry layer applied by the slurry application step, a rolling step of rolling the active material slurry layer dried by the drying step to repel bubbles and causing bubble marks to appear. With air bubbles Scar The packing density of the active material where there is a bubble Scar Lower density than the packing density of the active material where there is no The low density part which is is characterized by being formed. here, The bubble scar is a low-density portion in which the amount of active material is small as much as air is present. As a result, it is possible to easily obtain an electrode plate dotted with low density portions having a low active material packing density. in this case Alive When the stirring time of the material slurry is changed, the surface area ratio of the low density portion can be easily changed. Further, by changing the stirring speed of the active material slurry, the diameter of the low density portion can be easily changed.
[0008]
In this case, if the surface area ratio of the low density portion is less than 1.0% and too small, the permeability (liquid content) of the electrolyte into the active material is lowered, and the surface area ratio of the low density portion is 5.0%. If the amount is larger than that, the amount of the active material to be filled is decreased, and lithium is deposited in the low density portion, so that the discharge capacity is extremely decreased. For this reason, the surface area ratio of the low density part with respect to the total surface area of an electrode plate needs to be 1.0% or more and 5.0% or less. In addition, by interspersing the low density portion, the permeability (liquid containing property) of the electrolytic solution into the active material is improved, so that the active material can be filled with high density. For this reason, 1.7 g / cm in the negative electrode ^Three The negative electrode plate having the above high packing density can be used, and in the positive electrode, 3.4 g / cm. ^Three The positive electrode plate having the above high packing density can be used. As a result, a high-capacity nonaqueous electrolyte secondary battery can be obtained.
[0009]
And since such a low density part is formed when the bubble which existed in the active material slurry repels, the planar shape becomes a substantially circular shape. And even if the surface area ratio of the low density portion is the same, if the average diameter of the substantially circular shape becomes too smaller than 0.2 mm, the internal resistance rises and the high rate discharge characteristic deteriorates, and is larger than 8.0 mm. When it becomes too much, the reactivity in the whole electrode plate will fall and a high rate discharge characteristic will fall. For this reason, it is desirable that the average diameter of the low density portion is 0.2 mm or more and 8.0 mm or less.
[0010]
In this case, if the average diameter is smaller than 0.5 mm, a minute unevenness is formed on the entire surface of the electrode plate, and the electrode plate surface becomes rough, the internal resistance increases and the high rate discharge characteristic decreases. To do. On the other hand, when the average diameter is larger than 2.0 mm, unevenness is hardly formed on the entire surface of the electrode plate, and the number of continuously smooth portions increases, but on the other hand, the liquid content (permeability) of the electrolyte is improved. Therefore, the low density portion contributing to the above becomes unevenly distributed, so that the reactivity of the whole electrode plate is lowered and the high rate discharge characteristic is lowered. From this, it can be said that the average diameter of the low density portion is more preferably 0.5 mm or more and 2.0 mm or less.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Next, embodiments of the present invention will be described below.
1. First embodiment
(1) Electrode plate manufacturing equipment
The main electrode plate manufacturing apparatus for manufacturing the electrode plate of the present invention is composed of a slurry stirring device 10 shown in FIG. 1 and a slurry applying device 20 shown in FIG.
The slurry agitating device 10 includes a stirring tank 11 that contains the filled slurry 15 and a stirring blade 13 that stirs the slurry 15 filled in the stirring tank 11 at the lower end, and rotates with respect to the stirring tank 11. The stirring shaft 12 is mounted at the center of the stirring tank 11 and the air nozzle 14 is disposed below the stirring tank 11 and discharges air to the slurry 15 filled in the stirring tank 11. The
[0014]
On the other hand, the slurry application device 20 applies a slurry filling tank 21 for applying the slurry 15 (27) to the current collector 16 (28), and an application for adjusting the applied slurry 15 (27) to a predetermined application amount. An amount adjusting jig 22, a pair of feed rollers 23 and 24 for moving the current collector 16 (28) coated with the slurry 15 (27) at a predetermined speed, and a holder for holding the current collector 16 (28). And rollers 25 and 26. The application amount of the applied slurry 15 (27) is adjusted by adjusting the gap between the current collector 16 (28) and the application amount adjustment jig 22.
[0015]
(2) Production of negative electrode
First, natural graphite (Lc value is 1000%, d ₀₀₂ A negative active material comprising a value of 3.356 mm and an average particle size of 20 μm) and a dispersion of styrene-butadiene rubber (SBR) (solid content of 48% by mass) are dispersed in water and then thickened. The negative electrode active material slurry 15 was prepared by adding carboxymethylcellulose (CMC) as an agent. In this case, the solid mass composition ratio after drying was adjusted to be graphite: SBR: CMC = 100: 3: 2. Next, after the obtained negative electrode active material slurry 15 is filled in the slurry agitation tank 11 of the slurry agitation device 10, 50 ml of air is discharged from the air nozzle 14 to 1 kg of the slurry to make air into the slurry 15. At the same time, the stirring shaft 12 was rotated at a rotational speed of 1000 rpm for a predetermined time.
[0016]
As a result, the stirring blade 13 rotates, and the negative electrode active material slurry 15 filled in the slurry stirring tank 11 is stirred together with the fed air, and a large number of bubbles are generated in the negative electrode active material slurry 15. Here, what was stirred for 5 minutes was the slurry a1, what was stirred for 10 minutes was slurry a2, and what was stirred for 20 minutes was slurry a3. Further, a slurry that did not feed bubbles was designated as slurry x1, a slurry that was stirred for 1 minute was stirred as slurry x2, and a slurry that was stirred for 40 minutes was designated as slurry x3.
[0017]
Each negative electrode active material slurry 15 (a1, a2, a3, x1, x2, x3) produced in this way is filled in the slurry filling tank 21 of the slurry coating device 20, and then fed out by a pair of feed rollers 23, 24. The negative electrode active material slurry 15 (a1, a2, a3, x1, x2, x3) filled in the slurry filling tank 21 is applied to one side of the negative electrode current collector (for example, copper foil) 16 to adjust the coating amount. A predetermined amount of slurry was applied through the jig 22.
[0018]
Next, after the slurry layer is dried, the slurry layer is passed through another slurry coating device (not shown) disposed in front of the slurry coating device 20, and the other of the negative electrode current collector 16 to which the slurry is not coated. Similarly, the slurry was applied to the surface and dried. Thereafter, the dried negative electrode plate is rolled by a roll press, and the thickness of the active material layer per side is 50 μm and the packing density is 1.7 g / cm. ^Three Each of the negative electrode plates was prepared, and then cut into predetermined dimensions to form negative electrodes 30 (a1, a2, a3, x1, x2, x3).
[0019]
Here, when observing the negative electrode 30 (a1, a2, a3, x1, x2, x3), as shown in FIG. 3A, crater-like bubble traces formed by blowing bubbles by rolling with a roll press machine 32 is a high-density filling part (filling density is 1.7 g / cm ^Three ) It was scattered all over 31. In this case, since the bubble scar 32 has a lighter hue than the high-density filling portion 31, the high-density filling portion 31 and the bubble scar 32 can be visually identified. When the diameter of the bubble scar 32 was measured and the average diameter was determined, it was revealed that it was 0.5 mm or more and 2.0 mm or less.
[0020]
Then, the mass is measured by removing the active material layer at the bubble scar 32, and the packing density is determined from the diameter of the bubble scar 32 and the thickness of the active material layer. The packing density is 1.2 g / cm. ^Three It was low density. Moreover, after measuring the surface area of each bubble trace 32 and calculating the total surface area of the bubble trace 32 based on this measurement result, the ratio (area ratio) of each negative electrode a1, a2, a3, x1, x2, x3 to the total surface area : Area ratio) was obtained as shown in Table 1 below. In addition, since the negative electrode x1 used the slurry which does not send a bubble, there was no bubble trace 32. FIG.
[0021]
[Table 1]

[0022]
(3) Fabrication of positive electrode
On the other hand, LiCoO having an average particle size of 5 μm as a positive electrode active material ₂ The positive electrode mixture was prepared by mixing the powder and artificial graphite powder as a conductive agent so that the mass ratio was 9: 1. The positive electrode material mixture and a binder solution obtained by dissolving 5% by mass of a binder made of polyvinylidene fluoride (PVdF) in an organic solvent made of N-methyl-2-pyrrolidone (NMP) are used as a solid mass. The positive electrode active material slurry 27 was prepared by mixing and kneading so that the ratio was 95: 5.
[0023]
After the positive electrode active material slurry 27 is filled in the slurry filling tank 21 of the slurry application device 20, the positive electrode current collector (for example, aluminum foil or aluminum alloy foil) 28 fed out by the pair of feed rollers 23 and 24 is disposed on one side. Then, the positive electrode active material slurry 27 filled in the slurry filling tank 21 was applied, and a predetermined amount of slurry was applied through the coating amount adjusting jig 22. Next, after the slurry layer is dried, the slurry layer is passed through another slurry coating device (not shown) disposed in front of the slurry coating device 20, and the positive electrode current collector 28 to which no slurry is coated is applied. Similarly, the slurry was applied to the surface and dried. Thereafter, the dried positive electrode plate is rolled by a roll press, and the thickness of the active material layer per side is 50 μm, and the packing density is 3.4 g / cm. ^Three After producing a positive electrode plate, the positive electrode plate was cut to a predetermined size to obtain a positive electrode.
[0024]
(4) Production of non-aqueous electrolyte secondary battery
Next, the negative electrodes a1, a2, a3, x1, x2, and x3 prepared as described above and the positive electrode are stacked with a separator made of a microporous polyolefin resin having low reactivity with an organic solvent. After combining, it was wound in a spiral shape by a winder to form an electrode group. After that, this electrode group is inserted from the opening of the outer can, and a negative electrode current collecting tab extending from the negative electrode of the electrode group is resistance-welded to the inner bottom of the outer can, and then the positive electrode collector extending from the positive electrode of the electrode group. The electric tab was welded to the bottom of the sealing body. Next, a non-aqueous electrolyte (ethylene carbonate (EC) and diethyl carbonate (DEC) mixed in an equal volume ratio in the outer can is mixed with lithium hexafluorophosphate (LiPF). ₆ ) Was dissolved in 1 mol / liter.
[0025]
Then, the opening part of the exterior can was sealed liquid-tightly with the sealing body, and nonaqueous electrolyte secondary battery A1, A2, A3, X1, X2, X3 was produced, respectively. Each non-aqueous electrolyte secondary battery A1 (using the negative electrode a1), A2 (using the negative electrode a2), A3 (using the negative electrode a3), X1 (using the negative electrode x1) Used), X2 (using negative electrode x2), and X3 (using negative electrode x3) had a capacity of 600 mAh.
[0026]
(5) Non-aqueous electrolyte secondary battery load characteristics test
Next, the batteries A1, A2, A3, X1, X2, and X3 produced as described above were charged at room temperature (about 25 ° C.) with a constant current of 600 mA (1 ItmA) until the battery voltage reached 4.10 V, respectively. Then, the battery was charged at a constant voltage of 4.10 V until the current value reached 10 mA. Thereafter, the battery was discharged at a discharge current of 600 mA (1 ItmA) until the battery voltage reached 2.75 V, and the discharge capacity at the time of 1 It discharge was determined from the discharge time. The results shown in Table 2 below were obtained.
In addition, after charging each of these batteries A1, A2, A3, X1, X2, and X3 under the same conditions as described above, the batteries were discharged at a discharge current of 1200 mA (2 ItmA) until the battery voltage reached 2.75 V, and discharged. The discharge capacity at the time of 2 It discharge was calculated | required from time.
Next, the ratio of the discharge capacity at the time of 2 It discharge to the discharge capacity at the time of 1 It discharge was calculated as a discharge capacity ratio (discharge capacity ratio = 2 discharge capacity at the time of 1 It discharge / discharge capacity at the time of 1 It discharge). The result was as shown in.
[0027]
[Table 2]

[0028]
As is clear from the results of Table 2 above, the negative electrode plate 1 using the negative electrode plate x1 in which the bubble marks 32 were not generated using the slurry that did not send the bubbles and the area ratio of the bubble marks 32 was 0.5%. In the battery X2 using x2, the 1It discharge capacity is good at 600 (mAh), but the discharge capacity ratio is reduced to 75% and 85%. On the other hand, in the battery X3 using the negative electrode plate x3 in which the area ratio of the bubble scar 32 is 7%, the discharge capacity ratio is good at 99, but the capacity at 1 It discharge is reduced to 510 (mAh). . On the other hand, in the batteries A1 to A3 using the negative plates a1 to a3 in which the area ratio of the bubble marks 32 is 1.0 to 5.0%, both the 1 It discharge capacity and the discharge capacity ratio are good. I understand that.
[0029]
Here, when each battery was disassembled in a charged state, in the battery X3 using the negative electrode plate x3 in which the area ratio of the bubble trace 32 was 7%, a large amount of lithium deposition was observed around the bubble trace 32. No lithium deposition was found in the batteries. As a result, it is considered that the discharge capacity of the battery X3 was extremely reduced.
In addition, in the negative electrode plates x1 and x2, in which the area ratio of the bubble marks 32 is 0% and 0.5% and the generation of the bubble marks 32 is reduced, the area ratio of the bubble marks 32 is too small, so that the electrolyte permeability ( It is considered that the discharge capacity ratio was reduced due to a decrease in liquid content.
On the other hand, in the negative electrode plates a1 to a3 in which the area ratio of the bubble marks 32 was 1.0 to 5.0%, the permeability (liquid containing property) of the electrolyte was improved. Both discharge capacity ratios are considered to have improved.
From the above, the area ratio of the bubble trace (low filling density part) 32 to the total surface area of the negative electrode plate needs to be 1.0% or more and 5.0% or less.
[0030]
(6) Examination of diameter of bubble mark
Similarly to the above, after preparing the negative electrode active material slurry 15 and filling it in the slurry agitation tank 11 of the slurry agitator 10, air is discharged from the air nozzle 14 (in this case, relative to the total surface area of the obtained negative electrode). The air discharge amount is adjusted so that the total surface area of the bubble marks is 3.0%), and air is fed into the slurry 15 and the stirring shaft 12 is rotated at a predetermined rotational speed for 10 minutes. I let you. Here, what was stirred at a stirring speed of 2000 rpm was slurry a4, what was stirred at 1500 rpm was slurry a5, what was stirred at 1000 rpm was slurry a6, what was stirred at 500 rpm was slurry a7, What was stirred at 300 rpm was designated as slurry a8, and what was stirred at 200 rpm was designated as slurry a9.
[0031]
After each of these negative electrode active material slurries 15 (a4, a5, a6, a7, a8, a9) is filled in the slurry filling tank 21 of the slurry coating device 20, the slurry is applied to both surfaces of the negative electrode current collector 16 in the same manner as described above. Each is coated and dried, then rolled to a predetermined thickness, and the packing density of the active material is 1.7 g / cm. ^Three Each negative electrode plate was prepared, and then cut into predetermined dimensions to form negative electrodes 30 (a4, a5, a6, a7, a8, a9).
Here, when the packing density is measured by cutting off the active material layer of the bubble scar 32, the packing density is 1.2 g / cm. ^Three It was low density. Similarly to the above, when the negative electrode 30 (a4, a5, a6, a7, a8, a9) was observed and the diameter of the bubble scar 32 was measured, the results shown in Table 3 below were obtained.
[0032]
[Table 3]

[0033]
Then, using the negative electrode 30 (a4, a5, a6, a7, a8, a9) produced as described above and the positive electrode, the nonaqueous electrolyte secondary battery A4 (using the negative electrode a4) was used in the same manner as described above. , A5 (using negative electrode a5), A6 (using negative electrode a6), A7 (using negative electrode a7), A8 (using negative electrode a8), A9 (using negative electrode a9) Then, the load characteristic test is performed in the same manner as described above to determine the discharge capacity at the time of 1 It discharge, the discharge capacity at the time of 2 It discharge, and the discharge capacity at the time of 2 It discharge relative to the discharge capacity at the time of It discharge. When the ratio was determined as the discharge capacity ratio (discharge capacity ratio = 2 discharge capacity at the time of 1 It discharge / discharge capacity at the time of 1 It discharge), the results shown in Table 4 below were obtained.
[0034]
[Table 4]

[0035]
As is clear from the results in Table 4 above, it can be seen that the discharge capacity ratio shows a higher value than that of the bubble-free trace regardless of the diameter of the bubble trace 32. It can also be seen that the discharge capacity ratio decreases even if the bubble scar 32 is present, the diameter is too small as in the negative electrode a4, or the diameter is too large as in the negative electrodes a8 and a9.
This is because even if the area ratio of the bubble trace 32 is the same, if the diameter of the bubble trace 32 is too small, fine irregularities are formed on the entire surface of the negative electrode plate, and the surface state of the negative electrode plate becomes rough. It is considered that the resistance increased and the discharge capacity ratio decreased.
On the other hand, if the diameter of the bubble scar 32 becomes too large, irregularities are hardly formed on the entire surface of the negative electrode plate, and the number of continuously smooth portions increases, but on the other hand, the liquid content (permeability) of the electrolyte is improved. It is considered that the bubble scar 32 contributing to the uneven distribution is uneven, so that the reactivity on the entire surface of the negative electrode plate is lowered and the discharge capacity ratio is lowered.
On the other hand, in the negative electrode plates a4 to a7 in which the diameter of the bubble scar 32 is 0.5 to 2.0 mm, the permeability of the electrolytic solution (liquid content) and the roughness of the entire surface of the negative electrode plate are moderately matched. Thus, the discharge capacity ratio is considered to have improved.
From the above, it can be said that the diameter of the bubble scar (low filling density part) 32 of the negative electrode is desirably 0.5 mm or more and 2.0 mm or less.
[0036]
2. Second embodiment
In the first embodiment described above, changes in characteristics were examined when air bubbles were introduced into the negative electrode active material slurry to form a low density portion in the negative electrode, but in the following, air bubbles were introduced into the positive electrode active material slurry. Thus, a change in characteristics when a low density portion is formed on the positive electrode will be examined.
[0037]
(1) Fabrication of positive electrode
First, LiCoO having an average particle size of 5 μm as a positive electrode active material ₂ The positive electrode mixture was prepared by mixing the powder and artificial graphite powder as a conductive agent so that the mass ratio was 9: 1. The positive electrode material mixture and a binder solution obtained by dissolving 5% by mass of a binder made of polyvinylidene fluoride (PVdF) in an organic solvent made of N-methyl-2-pyrrolidone (NMP) are used as a solid mass. The positive electrode active material slurry 27 was prepared by mixing and kneading so that the ratio was 95: 5. Next, after the obtained positive electrode active material slurry 27 is filled in the slurry agitation tank 11 of the slurry agitation apparatus 10, 50 ml of air is discharged from the air nozzle 14 to 1 kg of the slurry to make air into the slurry 27. At the same time, the stirring shaft 12 was rotated at a rotational speed of 1000 rpm for a predetermined time.
[0038]
As a result, the stirring blade 13 rotates, and the positive electrode active material slurry 27 filled in the slurry agitation tank 11 is stirred together with the fed air, and a large number of bubbles are generated in the positive electrode active material slurry 27. Here, what was stirred for 5 minutes was the slurry b1, what was stirred for 10 minutes was slurry b2, and what was stirred for 20 minutes was slurry b3. Further, the slurry y1 was not fed with bubbles, the slurry agitated for 1 minute and the slurry y2, and the slurry stirred for 40 minutes as the slurry y3.
[0039]
Each positive electrode active material slurry 27 (b1, b2, b3, y1, y2, y3) produced in this way is filled in the slurry filling tank 21 of the slurry coating device 20, and then sent out by a pair of feed rollers 23, 24. The positive electrode active material slurry 27 (b1, b2, b3, y1, y2, y3) filled in the slurry filling tank 21 was applied to one side of the positive electrode current collector (for example, aluminum foil or aluminum alloy foil) 28, respectively. Then, a predetermined amount of slurry was applied through the coating amount adjusting jig 22.
[0040]
Next, after the slurry layer is dried, the slurry layer is passed through another slurry coating device (not shown) disposed in front of the slurry coating device 20, and the positive electrode current collector 28 to which no slurry is coated is applied. Similarly, the slurry was applied to the surface and dried. Thereafter, the dried positive electrode plate is rolled by a roll press, and the thickness of the active material layer per side is 50 μm, and the packing density is 3.4 g / cm. ^Three Each positive electrode plate was prepared, and then cut into predetermined dimensions to form positive electrodes 40 (b1, b2, b3, y1, y2, y3).
[0041]
Here, when observing the positive electrode 40 (b1, b2, b3, y1, y2, y3), as shown in FIG. 3 (b), crater-like bubble traces formed by blowing bubbles by rolling with a roll press machine 42 is a high density filling portion (filling density is 3.4 g / cm ^Three ) It was scattered all over 41. In this case, since the bubble scar 42 has a lighter color than the high-density filling portion 41, the high-density filling portion 41 and the bubble scar 42 can be visually identified. When the diameter of the bubble scar 42 was measured and the average diameter was determined, it was revealed that it was 0.5 mm or more and 2.0 mm or less.
[0042]
Then, the mass of the active material layer is measured by removing the active material layer in the portion of the bubble scar 42, and when the filling density is determined from the diameter of the bubble scar 42 and the thickness of the active material layer, the packing density is 3.0 g / cm. ^Three It was low density. Further, after measuring the surface area of each bubble mark 42 and calculating the total surface area of the bubble mark 42 based on the measurement result, the ratio (area ratio) of each positive electrode b1, b2, b3, y1, y2, y3 to the total surface area : Area ratio) was obtained as shown in Table 5 below. In addition, since the positive electrode y1 used the slurry which does not send a bubble, there was no bubble trace 42. FIG.
[0043]
[Table 5]

[0044]
(2) Production of negative electrode
On the other hand, natural graphite (Lc value is 1000%, d ₀₀₂ A negative active material comprising a value of 3.356 mm and an average particle size of 20 μm) and a dispersion of styrene-butadiene rubber (SBR) (solid content of 48% by mass) are dispersed in water and then thickened. The negative electrode active material slurry 15 was prepared by adding carboxymethylcellulose (CMC) as an agent. In this case, the solid mass composition ratio after drying was adjusted to be graphite: SBR: CMC = 100: 3: 2.
[0045]
After filling the thus prepared negative electrode active material slurry 15 into the slurry filling tank 21 of the slurry application device 20, one side of the negative electrode current collector (for example, copper foil) 16 fed out by the pair of feed rollers 23, 24. Each of the negative electrode active material slurries 15 filled in the slurry filling tank 21 was applied, and the slurry was applied through a coating amount adjusting jig 22 to apply a predetermined amount of slurry. Next, after the slurry layer is dried, the slurry layer is passed through another slurry coating device (not shown) disposed in front of the slurry coating device 20, and the other of the negative electrode current collector 16 to which the slurry is not coated. Similarly, the slurry was applied to the surface and dried. Thereafter, the dried negative electrode plate is rolled by a roll press, and the thickness of the active material layer per side is 50 μm and the packing density is 1.7 g / cm. ^Three Each negative electrode plate was prepared, and then cut into a predetermined size to obtain a negative electrode.
[0046]
(3) Production of non-aqueous electrolyte secondary battery
Next, using the positive electrodes b1, b2, b3, y1, y2, y3 and the negative electrode produced as described above, the nonaqueous electrolyte secondary batteries B1, B2, B3, Y1, Y2, Y3 are formed in the same manner as described above. Each was produced. Each non-aqueous electrolyte secondary battery B1 (using positive electrode b1), B2 (using positive electrode b2), B3 (using positive electrode b3), Y1 (positive electrode y1) was prepared as described above. Used), Y2 (using positive electrode y2), and Y3 (using positive electrode y3) had a capacity of 600 mAh. Thereafter, a load characteristic test is performed in the same manner as described above to determine the discharge capacity at the time of 1 It discharge, the discharge capacity at the time of 2 It discharge, and the ratio of the discharge capacity at the time of 2 It discharge to the discharge capacity at the time of It discharge. When calculated as a capacity ratio (discharge capacity ratio = 2 discharge capacity at the time of 1 It discharge / discharge capacity at the time of 1 It discharge), the results shown in Table 6 below were obtained.
[0047]
[Table 6]

[0048]
As is clear from the results of Table 6 above, the battery Y1 using the positive electrode plate y1 in which the bubble marks 42 were not generated using the slurry that did not send the bubbles, and the negative electrode plate having the area ratio of the bubble marks 42 of 0.5% In the battery Y2 using y2, the capacity during 1 It discharge is good at 600 (mAh), but the discharge capacity ratio is reduced to 75% and 85%. On the other hand, in the battery Y3 using the negative electrode plate y3 in which the area ratio of the bubble marks 42 is 7%, the discharge capacity ratio is 99, which is good, but the 1It discharge capacity is reduced to 510 (mAh). . On the other hand, in the batteries B1 to B3 using the negative plates b1 to b3 in which the area ratio of the bubble marks 42 is 1.0 to 5.0%, both the 1 It discharge capacity and the discharge capacity ratio are good. I understand that.
[0049]
This is because in the battery Y3 using the negative electrode plate y3 in which the area ratio of the bubble marks 42 is 7%, the area ratio of the bubble marks 42 is large, so the filling amount of the active material is decreased and the discharge capacity is extremely decreased. it is conceivable that.
In addition, in the negative electrode plates y1 and y2 in which the area ratio of the bubble marks 42 is 0% and 0.5% and the generation of the bubble marks 42 is reduced, the area ratio of the bubble marks 42 is too small, so that the electrolyte permeability ( It is considered that the discharge capacity ratio was reduced due to a decrease in liquid content.
On the other hand, in the negative electrode plates b1 to b3 in which the area ratio of the bubble marks 42 was 1.0 to 5.0%, the permeability of the electrolytic solution (liquid content) was improved. Both discharge capacity ratios are considered to have improved.
From the above, it is necessary that the area ratio of the bubble trace (low filling density portion) 42 to the total surface area of the positive electrode plate is 1.0% or more and 5.0% or less.
[0050]
(4) Examination of bubble mark diameter
Similarly to the above, after preparing the positive electrode active material slurry 27 and filling it in the slurry agitation tank 11 of the slurry agitator 10, air is discharged from the air nozzle 14 (in this case, relative to the total surface area of the obtained negative electrode). The air discharge amount is adjusted so that the total surface area of the bubble marks is 3.0%), and air is fed into the slurry 15 and the stirring shaft 12 is rotated at a predetermined rotational speed for 10 minutes. I let you. Here, what was stirred at a stirring speed of 2000 rpm was slurry b4, what was stirred at 1500 rpm was slurry b5, what was stirred at 1000 rpm was slurry b6, what was stirred at 500 rpm was slurry b7, What was stirred at 300 rpm was slurry b8, and what was stirred at 200 rpm was slurry b9.
[0051]
After filling each of these positive electrode active material slurries 27 (b4, b5, b6, b7, b8, b9) into the slurry filling tank 21 of the slurry coating device 20, the slurry layers are formed on both surfaces of the positive electrode current collector 28 as described above. Each is coated and dried, and then rolled to a predetermined thickness, so that the packing density of the active material is 3.4 g / cm. ^Three Each positive electrode plate was prepared, and then cut into predetermined dimensions to form positive electrodes 40 (b4, b5, b6, b7, b8, b9).
Here, when the packing density is measured by cutting off the active material layer in the bubble scar 42, the packing density is 3.0 g / cm. ^Three It was low density. Similarly to the above, when the positive electrode 40 (b4, b5, b6, b7, b8, b9) was observed and the diameter of the bubble mark 42 was measured, the results shown in Table 7 below were obtained.
[0052]
[Table 7]

[0053]
Next, using the positive electrode 40 (b4, b5, b6, b7, b8, b9) and the negative electrode produced as described above, the nonaqueous electrolyte secondary battery B4 (using the positive electrode b4) was used in the same manner as described above. , B5 (using positive electrode b5), B6 (using positive electrode b6), B7 (using positive electrode b7), B8 (using positive electrode b8), B9 (using positive electrode b9) Then, the load characteristic test is performed in the same manner as described above to determine the discharge capacity at the time of 1 It discharge, the discharge capacity at the time of 2 It discharge, and the discharge capacity at the time of 2 It discharge relative to the discharge capacity at the time of It discharge. When the ratio was determined as the discharge capacity ratio (discharge capacity ratio = 2 discharge capacity at the time of 1 It discharge / discharge capacity at the time of 1 It discharge), the results shown in Table 8 below were obtained.
[0054]
[Table 8]

[0055]
As is apparent from the results of Table 8 above, it can be seen that the discharge capacity ratio shows a higher value than that of the bubble-free trace regardless of the diameter of the bubble trace 42. It can also be seen that the discharge capacity ratio decreases even if the bubble scar 42 is present, the diameter is too small as in the positive electrode b4, or the diameter is too large as in the positive electrodes b8 and b9.
This is because even if the area ratio of the bubble trace 42 is the same, if the diameter of the bubble trace 42 is too small, minute irregularities are formed on the entire surface of the positive electrode plate, and the surface state of the positive electrode plate becomes rough. The resistance increases and the discharge capacity ratio decreases.
On the other hand, if the diameter of the bubble mark 42 becomes too large, irregularities are hardly formed on the entire surface of the positive electrode plate, and the number of continuously smooth portions increases, but on the other hand, the liquid content (permeability) of the electrolyte is improved. Since the bubble traces 42 that contribute to the uneven distribution are present, the reactivity on the entire surface of the positive electrode plate is lowered and the discharge capacity ratio is lowered.
On the other hand, in the positive electrode plates b4 to b7 in which the diameter of the bubble mark 42 is 0.5 to 2.0 mm, the permeability of the electrolytic solution (liquid content) and the roughness of the entire surface of the positive electrode plate are appropriately matched. Thus, the discharge capacity ratio is considered to have improved.
From the above, it can be said that it is desirable that the average diameter of the bubble scar (low filling density portion) 42 of the positive electrode is 0.5 mm or more and 2.0 mm or less.
[0056]
As described above, in the present invention, at least one of the negative electrode and the positive electrode is dotted with low density portions (bubble marks) having a low packing density of the active material, and the surface area ratio of the low density portion is the total area of the positive electrode or the negative electrode. Since the surface area is 1% or more and 5% or less, the low density portion having a low active material filling density is scattered, so even if the active material is filled with a high density, the low density portion Since the electrolyte solution penetrates into the active material through the active material, the utilization factor of the active material is improved, and the discharge capacity and the high rate discharge characteristics are improved.
[0057]
In the above-described embodiment, an example in which a nonaqueous electrolyte secondary battery is manufactured using the negative electrode 30 in which the bubble mark 32 is formed and the positive electrode in which the bubble mark is not formed, or the bubble mark 42 is formed. Although the example which produces a nonaqueous electrolyte secondary battery using the positive electrode 40 and the negative electrode which does not form a bubble trace was demonstrated, this invention is not limited to this, The negative electrode 30 in which the bubble trace 32 was formed, and the bubble trace 42 A non-aqueous electrolyte secondary battery may be manufactured using the positive electrode 40 on which is formed. In this case, since both the negative electrode and the positive electrode can have a high packing density, a non-aqueous electrolyte secondary battery having a high capacity and excellent load characteristics can be obtained.
[0058]
In the above-described embodiment, an example in which ethylene carbonate (EC) is mixed with diethyl carbonate (DEC) as the mixed solvent used in the electrolytic solution has been described. However, the above-described ethylene carbonate (EC) is mixed with diethyl. In addition to carbonate (DEC) mixed, propylene carbonate (PC), vinylene carbonate (VC), butylene carbonate (BC), cyclopentanone, sulfolane, 3-methylsulfolane, 2,4-dimethylsulfolane, 3-methyl -1,3-oxazolidine-2-one, γ-butyrolactone (GBL) dimethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, butyl methyl carbonate, ethyl propyl carbonate, butyl ethyl carbonate, dipro Simple substances such as dicarbonate, 1,2-diethoxyethane (DEE), 1,2-dimethoxytechtane (DME), tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, methyl acetate, ethyl acetate, and the like; A mixed solvent such as a three component may be used.
[0059]
Moreover, as a solute dissolved in these solvents, LiPF ₆ In addition to LiBF _Four , LiCF _Three SO _Three , LiAsF ₆ , LiN (CF _Three SO ₂ ) ₂ , LiOSO ₂ (CF ₂ ) _Three CF _Three LiClO _Four Etc. may be used. Furthermore, a polymer electrolyte, a gel electrolyte in which a polymer is impregnated with a non-aqueous electrolyte, a solid electrolyte, and the like can also be used.
In the above-described embodiment, the example in which lithium cobaltate is used as the positive electrode active material has been described. In addition to lithium cobaltate, lithium-containing transition metal composite oxides such as lithium nickelate and lithium manganate, or dioxide dioxide Manganese (MnO ₂ ), Metal oxides such as vanadium pentoxide and niobium pentoxide, metal chalcogenides such as titanium disulfide and molybdenum disulfide, and the like can also be used.
[0060]
In the embodiment described above, an example in which natural graphite is used as the negative electrode active material has been described. However, in addition to natural graphite, a carbon-based material capable of occluding and releasing lithium ions, such as carbon black, coke, and glass. Known carbon or carbon fiber, or a fired body or amorphous oxide thereof may be used. In addition, when lithium or a lithium-based alloy is used for the negative electrode, the present invention can of course be applied to the positive electrode.
In addition, as the thickener added to the negative electrode, in the above-described embodiment, the example using carboxymethylcellulose (CMC) has been described, but as the thickener other than CMC, methylcellulose, hydroxymethylcellulose, ethylcellulose, Polyvinyl alcohol, polyacrylic acid (salt), oxidized starch, phosphorylated starch, casein, and the like can be used.
[0061]
In addition, as the binder added to the positive and negative electrodes, in the above-described embodiment, an example in which polyvinylidene fluoride (PVdF) is used for the positive electrode and styrene-butadiene rubber (copolymer) is used for the negative electrode has been described. Further, styrene-butadiene rubber (copolymer) may be used for the positive electrode, and polyvinylidene fluoride (PVdF) may be used for the negative electrode. Furthermore, as other binders, ethylenically unsaturated carboxylic acid esters such as methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, (meth) acrylate, hydroxyethyl (meth) acrylate, etc. Furthermore, ethylenically unsaturated carboxylic acids such as acrylic acid, methacrylic acid, itaconic acid, fumaric acid and maleic acid can be used.
[Brief description of the drawings]
FIG. 1 is a diagram schematically showing an example of a slurry agitation apparatus used for manufacturing a battery of the present invention.
FIG. 2 is a diagram schematically showing an example of a slurry coating apparatus used for manufacturing the battery of the present invention.
3A and 3B are diagrams schematically showing an electrode plate manufactured according to the present invention. FIG. 3A shows an example of a negative electrode plate, and FIG. 3B shows an example of a positive electrode plate.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... Slurry stirring apparatus, 11 ... Stirring tank, 12 ... Stirring shaft, 13 ... Stirring blade, 14 ... Air nozzle, 15 ... Slurry, 20 ... Slurry coating apparatus, 21 ... Slurry filling tank, 22 ... Coating amount adjusting jig, 23, 24 ... feed roller, 25,26 ... holding roller 30 ... negative electrode plate, 31 ... high density filling portion, 32 ... bubble scar (low density filling portion), 40 ... positive electrode plate, 41 ... high density filling portion, 42 ... Bubble trace (low density filling part)

Claims (6)

A non-aqueous electrolyte comprising a negative electrode containing a negative electrode active material capable of occluding and releasing lithium ions, a positive electrode containing a positive electrode active material capable of occluding and releasing lithium ions, and a non-aqueous electrolyte A method for manufacturing a secondary battery, comprising:
A bubble introducing step of introducing bubbles into the active material slurry by stirring the active material slurry while introducing air into the negative electrode active material or the active material slurry containing the positive electrode active material;
A slurry application step of applying the active material slurry into which the bubbles have been introduced to a current collector ;
A drying step of drying the active material slurry layer applied by the slurry application step;
Rolling the active material slurry layer dried by the drying step to repel the bubbles and causing bubble marks to appear , and
Packing density non-aqueous electrolyte secondary battery characterized in that so as to form a low-density portion which is a lower density than the packing density of the active material in no bubble marks portions of the active material of a portion of said bubble marks Manufacturing method.   2. The nonaqueous electrolyte secondary battery according to claim 1, wherein in the bubble introduction step, the surface area ratio of the low density portion is changed by changing a stirring time of the active material slurry. Production method.   2. The nonaqueous electrolyte secondary battery according to claim 1, wherein, in the bubble introduction step, an average diameter of the low density portion is changed by changing a stirring speed of the active material slurry. Production method. The packing density excluding the low density portion of the negative electrode is 1.7 g / cm ³ or more, or the packing density of the positive electrode excluding the low density portion is 3.4 g / cm ³ or more. The manufacturing method of the nonaqueous electrolyte secondary battery of Claim 1 characterized by these. The planar shape of the low density portion scattered in at least one of the positive electrode and the negative electrode is substantially circular, and the average diameter of the substantially circular low density portion is 0.2 mm or more and 8.0 mm or less. The manufacturing method of the nonaqueous electrolyte secondary battery of Claim 1 characterized by the above-mentioned. The planar shape of the low density portion scattered in at least one of the positive electrode and the negative electrode is substantially circular, and the average diameter of the substantially circular low density portion is 0.5 mm or more and 2.0 mm or less. The manufacturing method of the nonaqueous electrolyte secondary battery of Claim 1 characterized by the above-mentioned.

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