JP5070657B2 - Nonaqueous electrolyte secondary battery and method for producing negative electrode of nonaqueous electrolyte secondary battery - Google Patents

Description

【００９７】
表１から明らかなように、サンプル１−１，１−３，１−５，１−７のセルは、初期電池効率が非常に高く、何れも８０％を越えている。
【００９８】
これに対して、サンプル１−２，１−４，１−６，１−８のセルは、非水電解液の還元分解に使用されるロス容量が多いため、初期電池効率が何れも８０％未満であり、実用上好ましくない。
【００９９】
したがって、表面が水溶性ポリマーで被覆されている炭素粒子を負極活物質として用いることにより、初期電池効率に優れる非水電解液電池を実現できることがわかる。
【０１００】
また、炭素粒子の真密度が２．０ｇ／ｃｃであるサンプル１−１，１−３のセルは、炭素粒子の真密度が２．０ｇ／ｃｃ未満であるサンプル１−５，１−７のセルと比較すると、初期電池効率の改善幅がより大きい。したがって、結晶性の高い炭素粒子の表面を水溶性ポリマーで被覆してなる負極活物質を用いることにより、初期電池効率に非常に優れる非水電解質電池を実現できることがわかる。
【０１０１】
＜実験２＞
負極活物質として水溶性ポリマーの被覆量を変えたポリマー被覆炭素粒子を調製し、これを含有する非水電解液電池を作製した。
【０１０２】
サンプル２−１〜２−９
負極活物質を調製する際に、炭素粒子と水溶性ポリマーとの混合条件を適宜調整することで、活物質あたりの水溶性ポリマーの被覆量を下記表２に示すとおりにしたこと以外はサンプル１−１と同様にしてセルを作製した。
【０１０３】
以上のようにして作製したサンプル２−１〜２−９のセルに対して、実験１にて行った充放電試験を同様にして行い、初期電池効率を求めた。さらに、サンプル２−１〜２−９のセル、およびサンプル１−１，１−２のセルに対して、下記に示す充放電試験を行い、大電流特性を評価した。
【０１０４】
まず、初期充電と同一条件で０Ｖまで充電し、６ｍＡの定電流で放電し、ついで、初期充電と同一の条件で０Ｖまで充電し、１２ｍＡの定電流で放電した。そそして、先に測定した０．５ｍＡ放電容量に対する６ｍＡ放電容量、および、先に測定した０．５ｍＡ放電容量に対する１２ｍＡ放電容量の割合を求め、この割合を６ｍＡ放電持容量維持率（単位：％）、１２ｍＡ放電持容量維持率（単位：％）とした。
【０１０５】
以上の測定結果を、負極活物質における炭素粒子の重量比、および水溶性ポリマーの被覆量とあわせて表２に示す。
【０１０６】
【表２】

【０１０７】
負極活物質における水溶性ポリマーの被覆量が０．０２重量％であるサンプル２−２のセルは、負極活物質における水溶性ポリマーの被覆量が０．０２重量％未満であるサンプル２−１のセルと比較して、初期電池効率の改善幅が大きいことがわかる。
【０１０８】
また、負極活物質における水溶性ポリマーの被覆量が１０重量％であるサンプル２−７のセルは、負極活物質における水溶性ポリマーの被覆量が１０重量％を越えるサンプル２−８のセルと比較して、初期電池効率の改善幅には差がみられないが、６ｍＡ放電時容量維持率および１２ｍＡ放電時容量維持率が良好であることがわかる。
【０１０９】
したがって、炭素粒子の表面を水溶性ポリマーで被覆する際、水溶性ポリマーの被覆量を、負極活物質あたり０．０２重量％以上、１０重量％以下の範囲として負極活物質を調製することにより、初期電池効率に優れ、且つ、大電流特性に優れる非水電解液電池を実現できることがわかる。
【０１１０】
＜実験３＞
負極合剤を調製する際に用いる溶剤を変えて負極を作製し、この負極を備える非水電解液電池を作製した。
【０１１１】
サンプル３−１
負極を作製する際に、負極活物質を９５重量％と、ポリビニルアルコールを３重量％と、スチレン−ブタジエンゴムを２重量％とを、水中に分散させてスラリー状の負極合剤を調製した。そして、この負極合剤を負極集電体となる厚み１５μｍである銅箔上に塗布した後、乾燥してプレスし、２０１６型コインセル用の大きさに打ち抜いて負極を得ること以外はサンプル１−３と同様にして、セルを作製した。なお、負極活物質としては、サンプル１−３と同様に、ＭＣＭＢを２８００℃で焼成してなる黒鉛質炭素の表面を水溶性ポリマーで被覆してなり、水溶性ポリマーの被覆量が１重量％である活物質を使用した。
【０１１２】
サンプル３−２
負極を作製する際に、負極活物質を９５重量％と、カルボキシメチルセルロース（Ｎａ塩）を３重量％と、スチレン−ブタジエンゴムを２重量％とを、水中に分散させてスラリー状の負極合剤を調製した。そして、この負極合剤を負極集電体となる厚み１５μｍである銅箔上に塗布した後、乾燥してプレスし、２０１６型コインセル用の大きさに打ち抜いて負極を得ること以外はサンプル１−３と同様にして、セルを作製した。なお、負極活物質としては、サンプル１−３と同様に、ＭＣＭＢを２８００℃で焼成してなる黒鉛質炭素の表面を水溶性ポリマーで被覆してなり、水溶性ポリマーの被覆量が１重量％であるものを使用した。
【０１１３】
以上のようにして作製したサンプル３−１，３−２のセル、およびサンプル１−３のセルに対し、下記に示す充放電試験を行い、サイクル特性を評価した。
【０１１４】
まず、開放電圧から１ｍＡで０Ｖまで定電流充電し、ついで、０Ｖで電流値が０．０１ｍＡになるまで定電圧充電を行った。ついで、０．５ｍＡの定電流でセル電圧が１．５Ｖになるまで放電した。このときの充電容量に対する放電容量の割合を求め、これを初期電池効率（単位：％）とした。ついで、同一条件で充放電サイクルを行い、各サイクルにおける電池効率を求めた。
【０１１５】
以上の、各サイクルにおける電池効率の測定結果を、図２に示す。
【０１１６】
図２から、非水溶媒であるＮ−メチル−２−ピロリドン中に負極活物質を分散してなる負極合剤を用いて作製された負極を備えるサンプル１−３のセルでは、初期電池効率が非常に高く、電池の初期容量として高い値を与えることがわかる。また、サイクル中の電池効率の変化も１００％に近い値を推移しており、サイクル性がよいことがわかる。
【０１１７】
これに対して、水中に負極活物質を分散してなる負極合剤を用いて作製された負極を備えるサンプル３−１，３−２のセルでは、初期電池効率が低く、サイクル中の電池効率の変化も、サンプル１−３のセルの電池効率の変化を下回っている。この原因とし、サンプル３−１，３−２のセルでは、継続的な非水電解液の分解が生じていることが考えられる。これより、サンプル３−１，３−２の負極と、コバルト酸リチウム等のようなリチウム吸蔵放出型の正極と組み合わせたリチウムイオン二次電池を試作した場合、充放電サイクルに伴う容量低下がより激しいと考えられる。
【０１１８】
したがって、水溶性ポリマーを炭素粒子の表面に選択的に担持し、この選択制が破壊されないように、ポリマー被覆炭素粒子を非水溶媒中に分散させて負極合剤を調製し、この負極合剤を用いてセルを作製することで、初期効率が高くて高容量であり、且つサイクル特性に優れる非水電解液電池を実現できることがわかる。
【０１１９】
＜実験４＞
ポリマー被覆炭素粒子を含有する負極を備える非水電解液電池と、ポリマー被覆炭素粒子および導電剤として機能する炭素粒子又は金属粒子を含有する負極を備える非水電解液電池とを作製した。
【０１２０】
サンプル４−１
負極を作製する際に、負極活物質を９４重量％と、ポリフッ化ビニリデンを５重量％と、黒鉛化気相成長炭素繊維を１重量％とを、Ｎ−メチル−２−ピロリドン中に分散させてスラリー状の負極合剤を調製した。そして、この負極合剤を負極集電体となる厚み１５μｍである銅箔上に塗布した後、乾燥してプレスし、２０１６型コインセル用の大きさに打ち抜いて負極を得ること以外はサンプル１−３と同様にして、セルを作製した。なお、負極活物質としては、サンプル１−３と同様に、ＭＣＭＢを２８００℃で焼成してなる黒鉛質炭素の表面を水溶性ポリマーで被覆してなり、水溶性ポリマーの被覆量が１重量％である活物質を使用した。
【０１２１】
サンプル４−２
負極を作製する際に、負極活物質を９４重量％と、ポリフッ化ビニリデンを５重量％と、アセチレンブラックを１重量％とを、Ｎ−メチル−２−ピロリドン中に分散させてスラリー状の負極合剤を調製した。そして、この負極合剤を負極集電体となる厚み１５μｍである銅箔上に塗布した後、乾燥してプレスし、２０１６型コインセル用の大きさに打ち抜いて負極を得ること以外はサンプル１−３と同様にして、セルを作製した。なお、負極活物質としては、サンプル１−３と同様に、ＭＣＭＢを２８００℃で焼成してなる黒鉛質炭素の表面を水溶性ポリマーで被覆してなり、水溶性ポリマーの被覆量が１重量％である活物質を使用した。
【０１２２】
サンプル４−３
負極を作製する際に、負極活物質を９４重量％と、ポリフッ化ビニリデンを５重量％と、ニッケル微粒子を１重量％とを、Ｎ−メチル−２−ピロリドン中に分散させてスラリー状の負極合剤を調製した。そして、この負極合剤を負極集電体となる厚み１５μｍである銅箔上に塗布した後、乾燥してプレスし、２０１６型コインセル用の大きさに打ち抜いて負極を得ること以外はサンプル１−３と同様にして、セルを作製した。なお、負極活物質としては、サンプル１−３と同様に、ＭＣＭＢを２８００℃で焼成してなる黒鉛質炭素の表面を水溶性ポリマーで被覆してなり、水溶性ポリマーの被覆量が１重量％である活物質を使用した。
【０１２３】
以上のようにして作製したサンプル４−１〜４−３のセル、およびサンプル１−３のセルに対して、上述した実験１および実験２において行った充放電試験を同様にして行い、初期電池効率、６ｍＡ放電時の容量維持率、および１２ｍＡ放電時の容量維持率を求めた。
【０１２４】
以上の測定結果を表３に示す。
【０１２５】
【表３】

【０１２６】
導電剤を含有しない負極を備えるサンプル１−３のセルと、導電剤として機能する炭素粒子又は金属粒子を含有する負極を備えるサンプル４−１〜４−３のセルとを比較すると初期電池効率に大きな変化はみられないが、サンプル４−１〜４−３のセルでは、負荷特性が大幅に向上していることがわかる。
【０１２７】
ポリマー被覆炭素粒子は、表面を絶縁性の水溶性ポリマーで広く被覆されているため、電極プレス時等の負極活物質粒子間の微少な電気的接触では、大電流放電用途の場合に負荷特性の低下が見られることがある。
【０１２８】
したがって、負極に導電剤として機能する炭素粒子又は金属粒子を添加することにより、活物質炭素表面の安定性と活物質間の集電性を同時に満たす負極となり、初期効率が高くて高容量であり、且つサイクル特性及び大電流特性に非常に優れる非水電解液電池を実現できることがわかる。
【０１２９】
＜実験５＞
負極活物質として炭素粒子またはポリマー被覆炭素粒子を含有し、且つ、分解性の高い非水溶媒を含有する非水電解液を併用してなる非水電解液電池を作製した。
【０１３０】
サンプル５−１
非水電解液を調製する際に、エチレンカーボネートと、γ−ブチロラクトンとを、重量比で３：７の割合で混合した溶液に、電解質塩としてＬｉＰＦ_６を１ｍｏｌ／ｋｇの濃度で溶解させたこと以外はサンプル１−１と同様にしてセルを作製した。
【０１３１】
サンプル５−２
非水電解液を調製する際に、エチレンカーボネートと、γ−ブチロラクトンとを、重量比で３：７の割合で混合した溶液に、電解質塩としてＬｉＰＦ_６を１ｍｏｌ／ｋｇの濃度で溶解させたこと以外はサンプル１−２と同様にしてセルを作製した。
【０１３２】
以上のようにして作製したサンプル５−１，５−２のセルに対して、以下に示す充放電試験を行い、サイクル特性を評価した。
【０１３３】
まず、開放電圧から１ｍＡで０Ｖまで定電流充電し、ついで、０Ｖで電流値が０．０１ｍＡになるまで定電圧充電を行った。ついで、３ｍＡの定電流でセル電圧が１．５Ｖになるまで放電した。この充放電サイクルをくり返し行い、初期放電容量に対する各サイクル時点での放電容量の割合を求め、この割合を容量維持率（％）とした。
【０１３４】
以上の測定結果を、図３に示す。
【０１３５】
図３から、ポリマー被覆炭素粒子を負極活物質として含有するサンプル５−１のセルでは、γ−ブチロラクトンの含有率が高い非水電解液を用いているにもかかわらず、容量維持率の急激な低下はみられず、安定したサイクル特性を示していることがわかる。
【０１３６】
これに対し、表面を水溶性ポリマーで被覆されてない炭素粒子を負極活物質として含有するサンプル５−２のセルでは、急激に容量維持率が減少していることがわかる。
【０１３７】
したがって、ポリマー被覆炭素粒子を負極活物質として含有することにより、分解性の高い非水溶媒を含有する非水電解液を用いた場合であっても、安定したサイクル特性を有する非水電解液電池を実現できることがわかる。
【０１３８】
＜実験６＞
負極活物質として炭素粒子またはポリマー被覆炭素粒子を含有し、且つ、分解性の高い非水溶媒を含有する非水電解液を併用してなる非水電解液電池を作製した。
【０１３９】
サンプル６−１
非水電解液を調製する際に、エチレンカーボネートと、プロピレンカーボネートとを、重量比で３：７の割合で混合した溶液に、電解質塩としてＬｉＰＦ_６を１ｍｏｌ／ｋｇの濃度で溶解させたこと以外はサンプル１−１と同様にしてセルを作製した。
【０１４０】
サンプル６−２
非水電解液を調製する際に、エチレンカーボネートと、プロピレンカーボネートとを、重量比で３：７の割合で混合した溶液に、電解質塩としてＬｉＰＦ_６を１ｍｏｌ／ｋｇの濃度で溶解させたこと以外はサンプル１−３と同様にしてセルを作製した。
【０１４１】
サンプル６−３
非水電解液を調製する際に、エチレンカーボネートと、プロピレンカーボネートとを、重量比で３：７の割合で混合した溶液に、電解質塩としてＬｉＰＦ_６を１ｍｏｌ／ｋｇの濃度で溶解させたこと以外はサンプル１−２と同様にしてセルを作製した。
【０１４２】
サンプル６−４
非水電解液を調製する際に、エチレンカーボネートと、プロピレンカーボネートとを、重量比で３：７の割合で混合した溶液に、電解質塩としてＬｉＰＦ_６を１ｍｏｌ／ｋｇの濃度で溶解させたこと以外はサンプル１−４と同様にしてセルを作製した。
【０１４３】
以上のようにして作製したサンプル６−１〜６−４のセルに対して、実験１にて行った充放電試験を同様にして行い、初期電池効率を求めた。
【０１４４】
以上の測定結果を、表４に示す。
【０１４５】
【表４】

【０１４６】
ポリマー被覆炭素粒子を負極活物質として含有するサンプル６−１，６−２のセルでは、プロピレンカーボネートの含有率が高い非水電解液を用いているにもかかわらず、初期電池効率が非常に高い。
【０１４７】
これに対し、表面を水溶性ポリマーで被覆されてない炭素粒子を負極活物質として含有するサンプル６−３，６−４のセルでは、非水電解液の分解に使用されるロス容量が非常に大きいため、初期電池効率が低い。
【０１４８】
したがって、ポリマー被覆炭素粒子を負極活物質として含有することにより、分解性の高い非水溶媒を含有する非水電解液を用いた場合であっても、初期電池効率に優れた非水電解液電池を実現できることがわかる。
【０１４９】
＜実験７＞
ゲル状電解質を用いた電池を作製した。
【０１５０】
サンプル７−１
まず、正極を以下に示すようにして作製した。まず、正極活物質としてコバルト酸リチウムを９１重量％と、導電剤として黒鉛を６重量％と、結着剤としてポリフッ化ビニリデンを１０重量％とを混合した後、Ｎ−メチル−２−ピロリドン中に分散させてスラリー状の正極合剤を調製した。ついで、このスラリー状の正極合剤を、厚み２０μｍのアルミ箔の片面に均一に塗布して乾燥し、アルミ箔上に正極合剤層を形成した。さらにロールプレス機を用いて圧縮成形した後、セルの径に準じて円形に打ち抜くことで、正極を得た。
【０１５１】
ついで、負極を以下に示すようにして作製した。まず、負極活物質として、ＭＣＭＢを２８００℃で焼成してなる黒鉛質炭素の表面が、水溶性ポリマーで被覆されてなり、水溶性ポリマーの被覆量が活物質あたり１重量％である活物質を調製した。ついで、この負極活物質を９０重量％と、結着剤としてポリフッ化ビニリデンを１０重量％とを混合した後、Ｎ−メチル−２−ピロリドン中に分散させてスラリー状の負極合剤を調製した。ついで、このスラリー状の正極合剤を、厚み１０μｍの銅箔の片面に均一に塗布して乾燥し、銅箔上に負極合剤層を形成した。さらにロールプレス機を用いて圧縮成形した後、セルの径に準じて円形に打ち抜くことで、負極を得た。
【０１５２】
ついで、電解質溶液を以下に示すようにして調製した。まず、エチレンカーボネートを４２．５重量％とγ−ブチロラクトンを４２．５重量％とを混合した混合溶媒に、ＬｉＰＦ_６を１５重量％として溶解してなる可塑剤を調製した。ついで、この可塑剤を３０重量％と、ブロック共重合ポリ（ビニリデンフルオロライド）を１０重量％と、ジメチルカーボネートを６０重量％とを混合溶解させてなる電解質溶液を調製した。
【０１５３】
ついで、上記電解質溶液を正極合剤層上および負極合剤層上に塗布して含浸させ、常温で８時間放置し、ジメチルカーボネートを気化、除去した。このようにして、正極合剤層上および負極合剤層上に、ゲル状電解質層を形成した。
【０１５４】
ついで、正極合剤層上に形成されたゲル状電解質層と、負極合剤層上に形成されたゲル状電解質層とを張り合わせて圧着し、電池素子を作製した。そして、この電池素子をラミネートフィルム中に収容し、縦幅２．５ｃｍ、横幅４．０ｃｍ、厚み０．３ｍｍの平板型のゲル状電解質電池を作製した。
【０１５５】
サンプル７−２
負極を作製する際、負極活物質としてＭＣＭＢを２８００℃で焼成してなる黒鉛質炭素を８９．１重量％と、結着剤としてポリフッ化ビニリデンを１０．９重量％とを混合した後、Ｎ−メチル−２−ピロリドン中に分散させてスラリー状の負極合剤を調製し、このスラリー状の負極合剤を銅箔の片面に均一に塗布して負極合剤層を形成する事以外はサンプル７−１と同様にして、ゲル状電解質電池を作製した。
【０１５６】
以上のようにして作製されたサンプル７−１，７−２のゲル状電解質電池に対して、以下に示す充放電試験を行い、サイクル特性を評価した。
【０１５７】
まず、開放電圧から１００ｍＡで４．２０Ｖまで定電流充電し、ついで、４．２０Ｖで電流値が２ｍＡになるまで定電圧充電を行った。ついで、５００ｍＡの定電流で、セル電圧が３．０Ｖになるまで放電した。この充放電サイクルを繰り返し行い、初期放電容量に対する各サイクル時点での放電容量の割合を求め、この割合を容量維持率（単位：％）とした。
【０１５８】
以上の測定結果を、図４に示す。
【０１５９】
図４から明らかなように、ポリマー被覆炭素粒子を負極活物質として含有するサンプル７−１のセルは、充放電サイクルを繰り返しても、安定した容量維持率を示している。これに対し、表面を水溶性ポリマーで被覆されてない炭素粒子を負極活物質として含有するサンプル７−２のセルは、充放電サイクルを繰り返すと、容量維持率が低下している。
【０１６０】
したがって、ポリマー被覆炭素粒子を負極活物質として含有することにより、安定したサイクル特性を有するゲル状電解質電池を実現できることがわかる。
【０１６１】
【発明の効果】
以上の説明から明らかなように、本発明では、活物質が、真密度が２．００ｇ／ｃｃ以上であり、且つ、Ｃ軸方向の平均面間隔ｄ（００２）が３．３９Å以下のメソフェーズピッチマイクロビーズを焼成してなる黒鉛質炭素の表面が０．０２重量％以上、１０重量％以下の範囲で水溶性ポリマーのカルボキシメチルセルロース又はその水溶性塩で被覆されているので、非水溶媒や電解質塩を含有する非水電解質や、バインダー等との反応性が抑制されている。したがって、この活物質によれば、非水電解質の分解反応が抑制されており、初期効率、サイクル特性、および大電流特性に優れた非水電解質二次電池を実現できる。
【０１６２】
本発明に係る非水電解質二次電池は、メソフェーズピッチマイクロビーズを焼成してなる黒鉛質炭素の表面が０．０２重量％以上、１０重量％以下の範囲で水溶性ポリマーのカルボキシメチルセルロース又はその水溶性塩で被覆されている活物質と、気相成長炭素繊維、アセチレンブラック、片状天然黒鉛、片状人造黒鉛及び繊維状人造黒鉛のうち少なくとも１種以上の炭素粒子と、ポリフッ化ビニリデン、ポリビニルアルコール、スチレン−ブタジエンゴムのうち少なくとも１種以上のバインダーとを負極に含有するので、非水電解質の分解反応が抑制され、初期効率、サイクル特性、および大電流特性に優れる。
【０１６３】
また、本発明に係る電極の製造方法によれば、炭素粒子の表面を被覆している水溶性ポリマーを破壊することなく、電極を製造することができる。
【図面の簡単な説明】
【図１】本発明を適用した非水電解液電池の一構成例を示す断面図である。
【図２】充放電サイクル数と電池効率との関係を示す特性図である。
【図３】充放電サイクル数と容量維持率との関係を示す特性図である。
【図４】充放電サイクル数と容量維持率との関係を示す特性図である。
【符号の説明】
１ 非水電解液電池、２ 負極、３ 正極、４ 負極缶、５ 正極缶、６ セパレータ、７ 絶縁ガスケット[0001]
BACKGROUND OF THE INVENTION
  The present invention relates to a non-aqueous electrolyte secondary battery andNegative electrode of non-aqueous electrolyte secondary batteryIt relates to the manufacturing method.
[0002]
[Prior art]
Carbon particles such as low crystalline carbon and graphitic carbon have the property of being able to occlude and release various compounds and ions such as lithium ions. Therefore, a non-aqueous electrolyte battery, a so-called lithium ion battery, has been realized that uses these carbon particles as an active material and utilizes the property of carbon particles that lithium ions can be occluded and released electrochemically.
[0003]
For example, in a lithium ion battery in which carbon particles are contained in the negative electrode and lithium-containing metal oxides are contained in the positive electrode, lithium is occluded in the carbon particles of the negative electrode by initial charging, and lithium is carbon in the negative electrode by discharge. The charge / discharge reaction proceeds by the movement of lithium ions released from the particles and between the electrodes.
[0004]
Such a lithium ion battery has an advantage that it has a high capacity and excellent cycle characteristics as compared with a conventional secondary battery such as a lead battery, a nickel cadmium battery, or a nickel metal hydride battery. Thus, lithium ion batteries having various advantages are expected as power sources for driving various electronic devices in various fields.
[0005]
For example, lithium ion batteries are used as power sources for driving portable electronic devices. It is also used for large EVs for pure EV (Electric Vehicle) and road leveling, lithium-ion batteries for assisting hybrid EVs and fuel cells, power supplies for electric bicycles and power tools, etc. Full-scale commercial use of ion secondary batteries is also near.
[0006]
However, the lithium-ion battery has (1) further increase in capacity, (2) improvement in deterioration due to high-temperature cycle, high-temperature storage, etc., (3) high performance, low cost, and high cost by using a high-degradable electrolyte. There are many points to be improved such as safety.
[0007]
In recent years, portable electronic devices have become multifunctional, and their power consumption is increasing. For this reason, for lithium ion batteries used as power sources for driving, it is possible to further reduce the capacity loss at the initial charge of graphitic carbon, which is the mainstream of the negative electrode active material, and realize further higher capacity. Longed for. In addition, the usage environment of lithium ion batteries has been diversified, but problems such as low capacity and high impedance at the time of high temperature use are still unresolved.
[0008]
[Problems to be solved by the invention]
By the way, in order to improve the safety and low temperature characteristics of a lithium ion battery, wide selectivity of a nonaqueous electrolyte composition containing a nonaqueous solvent and an electrolyte salt is important. However, when carbon particles are used as the active material of a non-aqueous electrolyte battery, there is a problem that the non-aqueous electrolyte is decomposed because the non-aqueous electrolyte containing the non-aqueous solvent and the electrolyte salt is highly reactive with the carbon particles. is there. As a result, in the nonaqueous electrolyte battery, battery characteristics such as cycle characteristics and large current characteristics are deteriorated.
[0009]
When carbon particles are used as the active material contained in the negative electrode, there is concern over continuous reductive decomposition on the negative electrode, even with non-aqueous solvents and electrolyte salts with good low-temperature characteristics and safety. Only nonaqueous electrolytes containing nonaqueous solvents and electrolyte salts can be used in actual use.
[0010]
In order to control the reactivity between the non-aqueous electrolyte and the carbon particles, researchers involved in lithium ion secondary batteries can control the reactivity of the non-aqueous electrolyte with the non-aqueous electrolyte or salt contained in the non-aqueous electrolyte. It has been proposed to use a method such as formation of a high-quality coating film, crystallinity of the carbon particles themselves, and carbon coating on a different surface.
[0011]
However, with all these methods, it is difficult to accurately predict the reactivity between carbon and the nonaqueous electrolyte at the time of initial charge. In an electrode mixture containing a large number of carbon particles, it is considered that a uniform reaction is unlikely to occur on the carbon surface due to the influence of variations such as the binder coating amount and potential distribution of each carbon, and the concentration gradient in the mixture.
[0012]
For example, in a negative electrode of a conventional nonaqueous electrolyte battery, a water-soluble polymer is added to the surface of carbon particles contained as an active material by adding a water-soluble polymer as a thickener or binder to the negative electrode mixture layer. It has been proposed to suppress the decomposition reaction between the active material and the non-aqueous electrolyte. However, although the water-soluble polymer is dispersed in the negative electrode mixture layer, it is not necessarily selectively deposited on the active material carbon surface.
[0013]
For this reason, in the negative electrode mixture layer containing a large number of carbon particles as an active material, variations such as the binder deposition amount and potential distribution of each carbon and the concentration gradient of the non-aqueous electrolyte in the negative electrode mixture are affected. In addition, a uniform oxidation reaction or reduction reaction hardly progresses on the surface of the carbon particles.
[0014]
In addition, for highly crystalline graphitic carbon active materials widely used as negative electrode active materials for lithium ion batteries, the decomposability of γ-butyrolactone, propylene carbonate, etc. can be achieved only by changing the crystallinity of the additive and carbon surface. It seems that there is still a need for improvement in battery systems such as for applications in which a high solvent is operated at a high temperature for a long time.
[0015]
In other words, when a carbon material is used as an active material for a non-aqueous electrolyte battery such as a lithium ion battery, oxidation and reduction reactions between the non-aqueous electrolyte containing a non-aqueous solvent and an electrolyte salt and the carbon material cannot be avoided. The initial capacity of the battery decreased, the cycle characteristics, and the large current characteristics deteriorated.
[0016]
  The present invention relates to a nonaqueous electrolyte that is excellent in initial efficiency, cycle characteristics, and large current characteristics by using an active material in which reactivity with a nonaqueous electrolyte containing a nonaqueous solvent and a nonaqueous electrolyte salt is suppressed.secondaryIt has been proposed for the purpose of providing a battery.
[0017]
[Means for Solving the Problems]
  In order to achieve the above object, a non-aqueous electrolyte secondary battery according to the present invention is a non-aqueous electrolyte battery including a positive electrode, a negative electrode, and a non-aqueous electrolyte.BakedAn active material whose surface of graphitic carbon is coated with a water-soluble polymer, and at least one carbon particle of vapor grown carbon fiber, acetylene black, flake natural graphite, flake artificial graphite and fibrous artificial graphite And at least one binder selected from the group consisting of polyvinylidene fluoride, polyvinyl alcohol, and styrene-butadiene rubber, and mesophase pitch microbeadsBakedGraphite carbon has a true density of 2.00 g / cc or more and an average interplanar spacing d (002) in the C-axis direction of 3.39 mm or less, and the water-soluble polymer is carboxymethyl cellulose or a water-soluble salt thereof. And the coating amount is in the range of 0.02 wt% or more and 10 wt% or less per the active material.
[0020]
  In the nonaqueous electrolyte secondary battery according to the present invention configured as described above, the true density is 2.00 g / cc or more, and the average interplanar spacing d (002) in the C-axis direction is 3.39 mm or less. Mesophase pitch microbeadsBakedSince the active material in which the surface of the graphitic carbon is previously coated with the water-soluble polymer carboxymethylcellulose or a water-soluble salt thereof in the range of 0.02 wt% or more and 10 wt% or less is contained in the negative electrode, The reactivity of the non-aqueous electrolyte containing a non-aqueous solvent or electrolyte salt and the active material surface is suppressed. Further, in the nonaqueous electrolyte secondary battery according to the present invention, the negative electrode includes at least one or more kinds of carbon particles among vapor-grown carbon fiber, acetylene black, flake natural graphite, flake artificial graphite, and fibrous artificial graphite; It contains at least one binder selected from the group consisting of polyvinylidene fluoride, polyvinyl alcohol, and styrene-butadiene rubber. Therefore, in this non-aqueous electrolyte secondary battery, the decomposition reaction of the non-aqueous electrolyte is suppressed. Conventionally, non-carbon electrolyte materials such as propylene carbonate and γ-butyrolactone, which are difficult to use because of high decomposability depending on the carbon material, are used. A non-aqueous electrolyte containing an aqueous solvent can be used, and battery characteristics can be improved.
[0021]
  Further, according to the present inventionNegative electrode of non-aqueous electrolyte secondary batteryThe mesophase pitch microbeads having a true density of 2.00 g / cc or more and an average surface spacing d (002) in the C-axis direction of 3.39 mm or lessBakedAn active material is prepared by coating the surface of graphitic carbon with a water-soluble polymer carboxymethyl cellulose or a water-soluble salt thereof in the range of 0.02 wt% to 10 wt%, and the active material and vapor grown carbon fiber At least one carbon particle of acetylene black, flake natural graphite, flake artificial graphite and fibrous artificial graphite, and at least one binder of polyvinylidene fluoride, polyvinyl alcohol, and styrene-butadiene rubber. A mixture is prepared by dispersing in a non-aqueous solvent, the mixture is applied onto a current collector to form a mixture layer, and the mixture layer is dried.
[0022]
  In the method for producing a negative electrode of a nonaqueous electrolyte secondary battery according to the present invention configured as described above, a mesophase pitch microbead is used.InSince the surface of the calcined graphitic carbon is coated with carboxymethylcellulose or a water-soluble salt thereof as a water-soluble polymer in a range of 0.02 wt% or more and 10 wt% or less, a non-aqueous solvent or an electrolyte salt containing non-aqueous solvent is contained. An electrode in which the reactivity between the water electrolyte and the active material surface is suppressed can be obtained. In addition, since the active material is dispersed in the non-aqueous solvent, the water-soluble polymer coated on the surface of the carbon particles is not destroyed. Further, in the method for producing a negative electrode for a non-aqueous electrolyte secondary battery according to the present invention, the negative electrode is made of vapor-grown carbon fiber, acetylene black, flake natural graphite, flake artificial graphite and fibrous artificial graphite together with an active material. Among these, at least one kind of carbon particles and at least one kind of binder among polyvinylidene fluoride, polyvinyl alcohol, and styrene-butadiene rubber are contained. Therefore, according to this electrode manufacturing method, the mixture containing the active material is applied onto the current collector without destroying the water-soluble polymer coated on the surfaces of the carbon particles, and the mixture layer is formed. And the characteristics of the electrode can be improved.
[0023]
DETAILED DESCRIPTION OF THE INVENTION
  Hereinafter, the non-aqueous electrolyte according to the present inventionsecondaryThe battery will be described in detail.
[0024]
A non-aqueous electrolyte battery to which the present invention is applied includes a positive electrode, a negative electrode, and a non-aqueous electrolyte as basic components. In this non-aqueous electrolyte battery, an active material (hereinafter referred to as polymer-coated carbon particles) in which the surface of carbon particles is coated with a water-soluble polymer is contained in the positive electrode and / or the negative electrode.
[0025]
By the way, in a conventional non-aqueous electrolyte battery, a water-soluble polymer is added to the surface of carbon particles contained as an active material by adding a water-soluble polymer as a thickener or binder into the negative electrode mixture layer. I was letting. However, although the water-soluble polymer is dispersed in the negative electrode mixture layer, it is not necessarily selectively deposited on the active material carbon surface, and the decomposition reaction between the active material and the non-aqueous electrolyte can be reliably suppressed. There wasn't.
[0026]
On the other hand, in the non-aqueous electrolyte battery to which the present invention is applied, the polymer-coated carbon particles, that is, the active material in which the water-soluble polymer is selectively supported on the surfaces of the carbon particles in advance are the positive electrode and / or the negative electrode. It is contained in. The polymer-coated carbon particles may have a water-soluble polymer supported on a part of the surface of the carbon particles, or the entire surface of the carbon particles may be coated with the water-soluble polymer.
[0027]
In this polymer-coated carbon particle, since the surface of the carbon particle is previously coated with a water-soluble polymer, the reactivity of the active material surface with a non-aqueous electrolyte containing a non-aqueous solvent or an electrolyte salt, a binder, etc. is suppressed. ing.
[0028]
Therefore, this non-aqueous electrolyte battery is excellent in initial efficiency, cycle characteristics, and large current characteristics because the decomposition reaction of the non-aqueous electrolyte is suppressed. In addition, in this non-aqueous electrolyte battery, a non-aqueous electrolyte containing a non-aqueous solvent such as propylene carbonate or γ-butyrolactone, which has been difficult to use because of its high decomposability depending on the carbon material, can be used. .
[0029]
The carbon particles coated with the water-soluble polymer are not particularly limited, and conventionally known carbon materials from conventionally known low crystalline carbon to graphitic carbon can be used. Particularly, the true density is 2.00 g / It is preferable to use carbon particles that are cc or more and that have an average interplanar spacing d (002) in the C-axis direction of 3.39 mm or less.
[0030]
Carbon particles having a true density of 2.00 g / cc or more and an average interplanar spacing d (002) in the C-axis direction of 3.39 mm or less are highly crystalline and have a decomposition property of the electrolyte. More intense. For example, when considering application to a negative electrode active material of a lithium ion secondary battery, a graphitic carbon negative electrode that is advantageous in terms of density and potential is the mainstream of batteries that are currently commercialized. If the active material of the present invention is introduced into this, cycle characteristics and large current characteristics can be greatly improved.
[0031]
Specific examples of the water-soluble polymer include polyacrylic acid, methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, carboxymethyl cellulose, polyvinyl alcohol, polyethylene oxide, and water-soluble salts thereof.
[0032]
Here, the solubility of the water-soluble polymer in water is preferably 1 g or more per 100 g of water. When it is slightly soluble in water, when some non-aqueous solvent is used as the electrolytic solution, the water-soluble polymer is dissolved and diffused in the electrolytic solution, and the effects of the present invention cannot be sufficiently obtained. Moreover, when it is insoluble in a non-aqueous solvent and hardly soluble in water, the production method of the active material itself is limited. Therefore, it is preferable that the polymer is moderately soluble in water and insoluble in a non-aqueous solvent.
[0033]
The coating amount with which the surface of the carbon particles is coated with the water-soluble polymer, that is, the coating amount of the water-soluble polymer is preferably in the range of 0.02 wt% or more and 10 wt% or less per active material. When the coating amount of the water-soluble polymer is less than 0.02% by weight per active material, the effects of the present invention may not be sufficiently obtained. On the other hand, when the coating amount of the water-soluble polymer exceeds 10% by weight per active material and the coating amount is too large, the water-soluble polymer is insulative, so that electrical contact between the carbon particles is hindered, resulting in a large electrode. There is a possibility that the current characteristics may be deteriorated. The coating amount of the water-soluble polymer is more preferably 0.1% by weight or more and 5% by weight or less per active material.
[0034]
The active material configured as described above is contained in the positive electrode and / or the negative electrode of the nonaqueous electrolyte battery, thereby realizing a nonaqueous electrolyte battery excellent in initial efficiency, cycle characteristics, and large current characteristics. In addition, the active material to which the present invention is applied may be contained only in the positive electrode of the nonaqueous electrolyte battery, may be contained only in the negative electrode, or may be contained in both electrodes.
[0035]
Hereinafter, an active material in which the surface of carbon particles is coated with a water-soluble polymer, that is, a nonaqueous electrolyte battery in which polymer-coated carbon particles are contained in a negative electrode will be described in detail with reference to the drawings.
[0036]
As shown in FIG. 1, a nonaqueous electrolyte battery 1 to which the present invention is applied includes a negative electrode 2, a negative electrode can 3 that contains the negative electrode 2, a positive electrode 4, and a positive electrode can 5 that contains the positive electrode 4, A separator 6 disposed between the negative electrode 2 and the positive electrode 4 and an insulating gasket 7 are provided, and the negative electrode can 3 and the positive electrode can 5 are filled with a non-aqueous electrolyte.
[0037]
The negative electrode 2 includes a negative electrode current collector and a negative electrode mixture layer formed by applying a negative electrode mixture containing a negative electrode active material on the negative electrode current collector. As the negative electrode current collector, for example, a copper foil or the like can be used.
[0038]
As a negative electrode active material, the active material by which the surface of carbon particle is coat | covered with the water-soluble polymer, ie, the polymer covering carbon particle mentioned above, is contained. In the polymer-coated carbon particles, since the surface of the carbon particles is previously coated with a water-soluble polymer, the reactivity between the non-aqueous solvent, the electrolyte salt, the binder and the active material surface is suppressed.
[0039]
When polymer-coated carbon particles are used as the negative electrode active material, the oxidation or reduction reaction that occurs on the surface of the carbon material at a specific potential, even if the binder has a non-uniform distribution in the negative electrode mixture layer, variation in the negative electrode potential or concentration gradient. Most substrates are water-soluble polymers that coat the carbon particle surface. That is, it is most important that a specific polymer is localized on the surface of the carbon particles, so that even if the potential in the electrode is not uniform, the microscopic nonaqueous electrolytic composition is not uniform. Even so, the reduced coating formed on the surface of the carbon particles during the initial charge is considered to be very homogeneous.
[0040]
Therefore, the nonaqueous electrolyte battery 1 containing polymer-coated carbon particles as the negative electrode active material is prevented from the decomposition reaction of the nonaqueous electrolyte, and is excellent in initial efficiency, cycle characteristics, and large current characteristics.
[0041]
In addition to the polymer-coated carbon particles, the negative electrode 2 preferably contains carbon particles whose surface is not coated with a water-soluble polymer (hereinafter simply referred to as carbon particles). The surface of the polymer-coated carbon particles is coated with an insulating water-soluble polymer. For this reason, the polymer-coated carbon particles have a lower surface electronic conductivity than carbon particles whose surfaces are not coated with a water-soluble polymer. Therefore, the large current characteristics of the nonaqueous electrolyte battery 1 can be improved by adding carbon particles to the negative electrode 2 containing polymer-coated carbon particles to compensate for the decrease in the electronic conductivity of the polymer-coated carbon particles. .
[0042]
Researchers have confirmed that the electron conductivity of the electrode itself is maintained by the contact between the carbon particles inside the active material during electrode pressing. However, when a negative electrode comprising only polymer-coated carbon particles is provided, the initial load characteristics may be lowered depending on the battery system.
[0043]
Then, the electronic conductivity in the negative electrode 2 can be improved by including the carbon particle by which the surface is not coat | covered with the water-soluble polymer. That is, the carbon particles whose surfaces are not coated with the water-soluble polymer function as a conductive agent in the non-aqueous electrolyte battery 1.
[0044]
The carbon particles are preferably at least one of vapor-grown carbon fiber, acetylene black, flake natural graphite, flake artificial graphite, and fibrous artificial graphite. These carbon particles are characterized by their own shape, particle size, conductivity and the like, and have a high effect of functioning as a conductive agent.
[0045]
The content of carbon particles is preferably in the range of 20% by weight or less in the negative electrode 2. When the content of the carbon particles in the negative electrode 2 exceeds 20% by weight, the reaction between the surface of the carbon particles and the non-aqueous electrolyte cannot be ignored, and the decomposition reaction of the non-aqueous electrolyte proceeds, leading to a decrease in battery performance. There is. Therefore, by setting the content of carbon particles to 20% by weight or less in the negative electrode 2, the large current characteristics of the nonaqueous electrolyte battery 1 and the electronic conductivity in the electrode can be reliably improved.
[0046]
Furthermore, it is preferable to add metal particles that do not form an alloy with lithium to the negative electrode 2 containing polymer-coated carbon particles. By adding metal particles that do not form an alloy with lithium, it is possible to improve conductivity and avoid deterioration of load characteristics. If a metal that is alloyed with lithium and decomposes the non-aqueous electrolyte as the charge / discharge reaction proceeds, the effects of the present invention may not be obtained. Examples of metal particles that do not form an alloy with lithium include copper, iron, Co, and stainless steel.
[0047]
The negative electrode can 3 accommodates the negative electrode 2 and serves as an external terminal (negative electrode) of the nonaqueous electrolyte battery 1.
[0048]
The positive electrode 4 includes a positive electrode current collector and a positive electrode mixture layer formed by applying a positive electrode mixture containing a positive electrode active material on the positive electrode current collector. As the positive electrode current collector, for example, an aluminum foil or the like can be used.
[0049]
The positive electrode active material contains a metal oxide, a metal sulfide, a specific polymer, or the like depending on the type of the target battery. For example, when constituting a lithium ion battery, a conventionally known positive electrode active material, for example, TiS₂, MoS₂, NbSe₂, V₂O₅, Polypyrrole, polyaniline, disulfide compounds, LiCoO₂And LiMn₂O₄A composite oxide of lithium and a transition metal that can occlude / release lithium ions such as can be used. Among these positive electrode active materials, in particular, LiCoO₂And LiMn₂O₄It is preferable to use a composite oxide of lithium and a transition metal that can occlude / release lithium ions.
[0050]
Further, when forming the positive electrode 4, it is possible to add a conventionally known conductive agent, binder or the like.
[0051]
The positive electrode can 5 accommodates the positive electrode 4 and serves as an external terminal (positive electrode) of the nonaqueous electrolyte battery 1.
[0052]
The separator 6 separates the negative electrode 2 and the positive electrode 4. As the separator 6, for example, a highly organic solvent resistant material such as a porous film such as polyethylene or polypropylene or a non-work cloth can be used.
[0053]
The insulating gasket 7 is incorporated in and integrated with the negative electrode can 3. The insulating gasket 7 is for preventing leakage of the non-aqueous electrolyte filled in the negative electrode can 3 and the positive electrode can 5.
[0054]
The nonaqueous electrolytic solution is prepared by dissolving an electrolyte salt in a nonaqueous solvent.
[0055]
Examples of the electrolyte salt include LiClO.₄And LiBF₄, LiPF₆, LiAsF₆, LiCF₃SO₃Etc. can be used.
[0056]
As the non-aqueous solvent, for example, any conventionally known organic solvent such as ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, dimethyl carbonate, ethyl methyl carbonate, γ-butyrolactone, dimethoxyethane, tetrahydrofuran, dioxolane and the like can be used. These nonaqueous solvents may be used alone, or at least two or more kinds may be mixed and used.
[0057]
  By the way, in the conventional lithium ion secondary battery, when γ-butyrolactone is contained in the non-aqueous electrolyte, if the carbon particles are used as the negative electrode active material, the non-aqueous electrolyte continues as the charge / discharge reaction is repeated. The battery characteristics were rapidly deteriorated due to a decrease in reversible lithium amount and electrode peeling. In addition, when propylene carbonate is contained in the non-aqueous electrolyte, if carbon particles are used as the negative electrode active material, the non-aqueous electrolyte is severely decomposed during the initial charge, resulting in a capacity loss during the initial charge. The battery capacity was reduced by the capacity loss. Furthermore, when the charge / discharge reaction was repeated, the nonaqueous electrolyte solution was continuously decomposed, and the battery performance was lowered. Furthermore, propylene carbonate and γ-butyrolactone have a high dielectric constant,polymerTherefore, there was a possibility that the surface film formed on the negative electrode 2 was dissolved during the initial charge or during the subsequent charge / discharge cycle.
[0058]
On the other hand, in the nonaqueous electrolyte battery to which the present invention is applied, the surface of carbon particles is coated with a water-soluble polymer even when a nonaqueous electrolytic solution containing propylene carbonate or γ-butyrolactone is used. Since the active material is used as the negative electrode active material, the decomposition reaction of the non-aqueous electrolyte is suppressed, and deterioration of battery characteristics and battery capacity are prevented.
[0059]
The nonaqueous electrolyte battery 1 configured as described above is manufactured as follows.
[0060]
First, the negative electrode 2 is produced. First, the surface of carbon particles is coated with a water-soluble polymer to prepare polymer-coated carbon particles.
[0061]
Examples of the method of coating the surface of the carbon particles with the water-soluble polymer include, for example, a method in which the water-soluble polymer and the carbon particles are dispersed in an appropriate solvent and dried in a spray state, or the carbon particles are dispersed in a polymer melt solution. A method of drying this in a sprayed state, a method of dispersing carbon particles in a polymer melting solution, solidifying it and then pulverizing it can be applied.
[0062]
Next, the polymer-coated carbon particles and the binder are dispersed in a non-aqueous solvent to prepare a slurry-like negative electrode mixture.
[0063]
When preparing a slurry-like negative electrode mixture, polymer-coated carbon particles are dispersed in a non-aqueous solvent. When polymer-coated carbon particles are dispersed in an aqueous system, the coated water-soluble polymer is destroyed, and the effects of the present invention cannot be obtained. Therefore, by dispersing polymer-coated carbon particles in a non-aqueous solvent and preparing a slurry-like negative electrode mixture, the negative electrode 2 can be produced without destroying the coated water-soluble polymer.
[0064]
As the non-aqueous solvent, for example, N-methyl-2-pyrrolidone, dimethyl sulfoxide, dimethyl sulfoamide, dichloromethane, cyclohexane, toluene, xylene and the like can be used.
[0065]
Next, this negative electrode mixture is uniformly applied onto the negative electrode current collector to form a negative electrode mixture layer.
[0066]
  Next, the negative electrode mixture layer is dried,furtherThe negative electrode 2 is obtained by pressing.
[0067]
Next, the positive electrode 4 is produced. First, a positive electrode active material and a binder are dispersed in a solvent to prepare a slurry-like positive electrode mixture. Next, the positive electrode mixture is uniformly applied onto the positive electrode current collector, and then pressed and dried to obtain the positive electrode 4.
[0068]
Next, the electrolyte salt is dissolved in a non-aqueous solvent to prepare a non-aqueous electrolyte.
[0069]
Next, the negative electrode 2 is accommodated in the negative electrode can 3, the positive electrode 4 is accommodated in the positive electrode can 5, and a separator 6 made of a polypropylene porous film or the like is disposed between the negative electrode 2 and the positive electrode 4. A coin-type nonaqueous electrolyte battery 1 is obtained by injecting a nonaqueous electrolyte into the negative electrode can 3 and the positive electrode can 5 and caulking and fixing the negative electrode can 3 and the positive electrode can 5 via the insulating gasket 7. .
[0070]
In addition, although the non-aqueous electrolyte battery 1 using the non-aqueous electrolyte was described as an example as the non-aqueous electrolyte battery to which the present invention is applied, the present invention is not limited to this, and the non-aqueous electrolyte is not limited thereto. As described above, the present invention can also be applied to a gel electrolyte battery using a gel electrolyte.
[0071]
By the way, in the gel electrolyte battery, the stability of the gel electrolyte depends on the compatibility between the matrix polymer and the nonaqueous solvent. For example, when polyvinylidene fluoride is used as the matrix polymer and a low-viscosity solvent such as dimethyl carbonate or diethyl carbonate is used as the non-aqueous solvent, a stable gel electrolyte is obtained because the compatibility between the matrix polymer and the non-aqueous solvent is low. I can't. In addition, when a mixed solvent such as ethylene carbonate or propylene carbonate is used as the non-aqueous solvent, if the carbon particles are used as the negative electrode active material, the decomposition reaction of the non-aqueous solvent is intense.
[0072]
Therefore, by using polymer-coated carbon particles as the active material of a non-aqueous electrolyte battery, a non-aqueous solvent system such as propylene carbonate and γ-butyrolactone, which has been difficult to use because of its high decomposability depending on the carbon material, has been used. A gel electrolyte battery can be realized.
[0073]
Each of the other matrix polymers also has an optimum non-aqueous electrolyte system, and the use of the active material, electrode or battery system of the present invention increases the degree of freedom in solvent selection.
[0074]
The configuration of the gel electrolyte is not particularly limited, but as the matrix polymer, for example, a polyether compound such as polyethylene oxide, polyacrylonitrile, polyvinylidene fluoride, polymethyl methacrylate, or the like can be used.
[0075]
Examples of non-aqueous solvents that are gelled by these matrix polymers include ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, γ-butyrolactone, and dimethoxyethane.
[0076]
Examples of the electrolyte salt include LiClO.₄And LiBF₄, LiPF₆, LiAsF₆, LiCF₃SO₃, LiN (C₂F₆SO₂)₂, LiN (CF₃SO₂)₂Etc. can be used.
[0077]
Moreover, although the nonaqueous electrolyte battery 1 in which the polymer-coated carbon particles are contained in the negative electrode has been described as an example of the nonaqueous electrolyte battery to which the present invention is applied, the present invention is not limited to this. A non-aqueous electrolyte battery in which polymer-coated carbon particles are contained in the positive electrode may be used.
[0078]
In the nonaqueous electrolyte battery in which the polymer-coated carbon particles are contained in the positive electrode, any conventionally known material can be used as the negative electrode active material contained in the negative electrode. For example, a non-graphitizable carbon material or a graphite carbon material can be used. Specifically, pyrolytically decomposed carbons and cokes (pitch coke, knee coke, petroleum coke), graphite, carbon on glass, organic polymer compound fired body (phenol resin, furan resin, etc.) at an appropriate temperature. Can be used, and carbon materials such as carbon fiber and activated carbon can be used. Other materials that can be doped / undoped with lithium include polymers such as polyacetylene and polypyrrole, SnO₂Etc. can be used.
[0079]
【Example】
Hereinafter, the present invention will be described in detail based on specific experimental results.
[0080]
<Experiment 1>
A non-aqueous electrolyte battery containing carbon particles as a negative electrode active material and a non-aqueous electrolyte battery containing carbon particles whose surfaces were coated with a water-soluble polymer were produced as a negative electrode active material.
[0081]
Sample 1-1
(Preparation of negative electrode active material)
First, natural graphite powder having an average particle size of 15 μm as carbon particles is dispersed in acetone, and this is put into an aqueous solution in which carboxymethyl cellulose (Na salt) is dissolved, and further stirred at 70 ° C. Sprayed in and dried. As a result, natural graphite having a surface coated with a water-soluble polymer was obtained as a negative electrode active material. The coating amount of the water-soluble polymer was 1% by weight per negative electrode active material. The negative electrode active material was used after being dried at 100 ° C. for 24 hours in a vacuum.
[0082]
[Production of cell]
95% by weight of the negative electrode active material prepared as described above and 5% by weight of polyvinylidene fluoride as a binder are dispersed in an N-methyl-2-pyrrolidone solution to prepare a slurry-like negative electrode mixture. did. Next, the slurry-like negative electrode mixture was applied on a copper foil having a thickness of 15 μm serving as a negative electrode current collector and dried at 70 ° C. for 3 hours to evaporate N-methyl-2-pyrrolidone. After being dried in a vacuum at 100 ° C. for 24 hours, it was punched into a size for a 2016 coin cell. Furthermore, it pressed with the hand press apparatus, and the negative electrode whose volume density of a negative mix layer was 1.6 g / cc was obtained.
[0083]
Subsequently, metallic lithium was punched out in substantially the same shape as the negative electrode to obtain a counter electrode.
[0084]
Next, LiPF as an electrolyte salt was added to a solution in which ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate were mixed at a weight ratio of 3: 3: 4.₆Was dissolved at a concentration of 1 mol / kg to prepare a non-aqueous electrolyte.
[0085]
Next, a 2016 type coin-type cell including a battery element in which a separator was disposed between the counter electrode and the negative electrode obtained as described above and filled with a non-aqueous electrolyte was produced.
[0086]
Sample 1-2
A cell was produced in the same manner as Sample 1-1 except that natural graphite was used as the negative electrode active material.
[0087]
Sample 1-3
Sample 1 except that a mesophase pitch microbead (hereinafter referred to as MCMB) is fired at 2800 ° C. as the negative electrode active material is an active material in which the surface of graphitic carbon is coated with a water-soluble polymer. A cell was produced in the same manner as in Example-1.
[0088]
Sample 1-4
A cell was fabricated in the same manner as Sample 1-1, except that graphitic carbon obtained by firing MCMB at 2800 ° C. was used as the negative electrode active material.
[0089]
Sample 1-5
A cell was fabricated in the same manner as Sample 1-1, except that an active material in which the surface of low crystalline carbon obtained by firing MCMB at 1200 ° C. was coated with a water-soluble polymer was used as the negative electrode active material. .
[0090]
Sample 1-6
A cell was fabricated in the same manner as Sample 1-1, except that graphitic carbon obtained by firing MCMB at 1200 ° C. was used as the negative electrode active material.
[0091]
Sample 1-7
A cell was prepared in the same manner as Sample 1-1, except that an active material in which the surface of low crystalline carbon obtained by firing a furfuryl alcohol resin at 1200 ° C. was coated with a water-soluble polymer was used as the negative electrode active material. .
[0092]
Sample 1-8
A cell was fabricated in the same manner as Sample 1-1 except that low crystalline carbon obtained by firing a furfuryl alcohol resin at 1200 ° C. was used as the negative electrode active material.
[0093]
For the cells of Sample 1-1 to Sample 1-8 produced as described above, the following charge / discharge test was performed to obtain the initial charge / discharge efficiency (initial battery efficiency).
[0094]
First, as initial charging, constant current charging was performed from the open voltage to 0 V at 1 mA, and then constant voltage charging was performed at 0 V until the current value reached 0.01 mA. Next, as an initial discharge, the battery was discharged at a constant current of 0.5 mA until the cell voltage reached 1.5V. And the ratio of the initial discharge capacity with respect to the initial charge capacity was calculated | required, and this ratio was made into initial stage battery efficiency (unit:%).
[0095]
The above measurement results are shown in Table 1 together with the intimacy of the carbon particles, the X-ray parameter d (002), and the water-soluble polymer coating amount.
[0096]
[Table 1]

[0097]
As is clear from Table 1, the cells of Samples 1-1, 1-3, 1-5, and 1-7 have very high initial battery efficiency, and all exceed 80%.
[0098]
On the other hand, the cells of Samples 1-2, 1-4, 1-6, and 1-8 have a large loss capacity that is used for the reductive decomposition of the nonaqueous electrolyte solution. Is less than practical.
[0099]
Therefore, it can be seen that a non-aqueous electrolyte battery excellent in initial battery efficiency can be realized by using carbon particles whose surfaces are coated with a water-soluble polymer as a negative electrode active material.
[0100]
  Also of carbon particlesTrue densityThe cells of Samples 1-1 and 1-3 with 2.0 g / cc are carbon particles.True densityAs compared with the cells of Samples 1-5 and 1-7, whose initial battery efficiency is less than 2.0 g / cc, the improvement range of the initial battery efficiency is larger. Therefore, it can be seen that by using a negative electrode active material in which the surface of carbon particles having high crystallinity is coated with a water-soluble polymer, a nonaqueous electrolyte battery having very excellent initial battery efficiency can be realized.
[0101]
<Experiment 2>
As the negative electrode active material, polymer-coated carbon particles having a different amount of water-soluble polymer were prepared, and a non-aqueous electrolyte battery containing this was prepared.
[0102]
Samples 2-1 to 2-9
Sample 1 except that the coating amount of the water-soluble polymer per active material was adjusted as shown in Table 2 below by appropriately adjusting the mixing conditions of the carbon particles and the water-soluble polymer when preparing the negative electrode active material. A cell was produced in the same manner as in Example-1.
[0103]
The charge / discharge test performed in Experiment 1 was performed in the same manner on the cells of Samples 2-1 to 2-9 produced as described above, and the initial battery efficiency was obtained. Furthermore, the following charge / discharge tests were performed on the cells of Samples 2-1 to 2-9 and the cells of Samples 1-1 and 1-2, and the large current characteristics were evaluated.
[0104]
First, the battery was charged to 0 V under the same conditions as the initial charge, discharged at a constant current of 6 mA, then charged to 0 V under the same conditions as the initial charge, and discharged at a constant current of 12 mA. Then, the ratio of the 6 mA discharge capacity to the previously measured 0.5 mA discharge capacity and the ratio of the 12 mA discharge capacity to the previously measured 0.5 mA discharge capacity were determined, and this ratio was determined as the 6 mA discharge capacity retention rate (unit:%). ), 12 mA discharge capacity retention rate (unit:%).
[0105]
The above measurement results are shown in Table 2 together with the weight ratio of the carbon particles in the negative electrode active material and the coating amount of the water-soluble polymer.
[0106]
[Table 2]

[0107]
The cell of Sample 2-2 in which the coating amount of the water-soluble polymer in the negative electrode active material is 0.02% by weight is the cell of Sample 2-1 in which the coating amount of the water-soluble polymer in the negative electrode active material is less than 0.02% by weight. It can be seen that the improvement range of the initial battery efficiency is larger than that of the cell.
[0108]
Further, the cell of Sample 2-7 in which the coating amount of the water-soluble polymer in the negative electrode active material is 10% by weight is compared with the cell of Sample 2-8 in which the coating amount of the water-soluble polymer in the negative electrode active material exceeds 10% by weight. Thus, although there is no difference in the improvement range of the initial battery efficiency, it can be seen that the 6 mA discharge capacity maintenance ratio and the 12 mA discharge capacity maintenance ratio are good.
[0109]
Therefore, when the surface of the carbon particles is coated with the water-soluble polymer, by preparing the negative electrode active material with the coating amount of the water-soluble polymer in the range of 0.02 wt% or more and 10 wt% or less per negative electrode active material, It can be seen that a nonaqueous electrolyte battery having excellent initial battery efficiency and excellent large current characteristics can be realized.
[0110]
<Experiment 3>
A negative electrode was produced by changing the solvent used in preparing the negative electrode mixture, and a non-aqueous electrolyte battery including this negative electrode was produced.
[0111]
Sample 3-1
When producing the negative electrode, a slurry-like negative electrode mixture was prepared by dispersing 95% by weight of the negative electrode active material, 3% by weight of polyvinyl alcohol, and 2% by weight of styrene-butadiene rubber in water. And after apply | coating this negative electrode mixture on the copper foil which is 15 micrometers in thickness used as a negative electrode collector, it dries and presses, and it punches out to the magnitude | size for 2016 type coin cells, and obtains a negative electrode. In the same manner as in Example 3, a cell was produced. As the negative electrode active material, similarly to Sample 1-3, the surface of graphitic carbon obtained by firing MCMB at 2800 ° C. is coated with a water-soluble polymer, and the coating amount of the water-soluble polymer is 1% by weight. An active material was used.
[0112]
Sample 3-2
When preparing the negative electrode, a slurry negative electrode mixture is prepared by dispersing 95% by weight of the negative electrode active material, 3% by weight of carboxymethylcellulose (Na salt), and 2% by weight of styrene-butadiene rubber in water. Was prepared. And after apply | coating this negative electrode mixture on the copper foil which is 15 micrometers in thickness used as a negative electrode collector, it dries and presses, and it punches out to the magnitude | size for 2016 type coin cells, and obtains a negative electrode. In the same manner as in Example 3, a cell was produced. As the negative electrode active material, similarly to Sample 1-3, the surface of graphitic carbon obtained by firing MCMB at 2800 ° C. is coated with a water-soluble polymer, and the coating amount of the water-soluble polymer is 1% by weight. I used what is.
[0113]
The charge / discharge test shown below was performed on the cells of Samples 3-1 and 3-2 and Sample 1-3 produced as described above, and the cycle characteristics were evaluated.
[0114]
First, constant current charging was performed from the open voltage to 0 V at 1 mA, and then constant voltage charging was performed until the current value became 0.01 mA at 0 V. Next, the battery was discharged at a constant current of 0.5 mA until the cell voltage reached 1.5V. The ratio of the discharge capacity to the charge capacity at this time was determined, and this was defined as the initial battery efficiency (unit:%). Subsequently, charge / discharge cycles were performed under the same conditions, and the battery efficiency in each cycle was determined.
[0115]
The measurement results of the battery efficiency in each cycle described above are shown in FIG.
[0116]
From FIG. 2, in the cell of Sample 1-3 comprising a negative electrode prepared using a negative electrode mixture obtained by dispersing a negative electrode active material in N-methyl-2-pyrrolidone, which is a nonaqueous solvent, the initial battery efficiency is It can be seen that it is very high and gives a high value as the initial capacity of the battery. In addition, the change in battery efficiency during the cycle also has a value close to 100%, which indicates that the cycle performance is good.
[0117]
On the other hand, in the cells of Samples 3-1 and 3-2 including a negative electrode prepared using a negative electrode mixture obtained by dispersing a negative electrode active material in water, the initial battery efficiency is low, and the battery efficiency during the cycle is low. Is also less than the change in battery efficiency of the cell of Sample 1-3. As a cause of this, it is considered that continuous decomposition of the nonaqueous electrolytic solution occurs in the cells of Samples 3-1 and 3-2. As a result, when a lithium ion secondary battery in combination with the negative electrode of Samples 3-1 and 3-2 and a lithium occlusion / discharge type positive electrode such as lithium cobaltate was prototyped, the capacity reduction associated with the charge / discharge cycle was further reduced. It is considered intense.
[0118]
Accordingly, a negative electrode mixture is prepared by selectively supporting a water-soluble polymer on the surface of the carbon particles and dispersing the polymer-coated carbon particles in a non-aqueous solvent so that the selectivity is not destroyed. It can be seen that a non-aqueous electrolyte battery with high initial efficiency, high capacity, and excellent cycle characteristics can be realized by manufacturing a cell using the above.
[0119]
<Experiment 4>
A non-aqueous electrolyte battery including a negative electrode containing polymer-coated carbon particles and a non-aqueous electrolyte battery including a negative electrode including polymer-coated carbon particles and carbon particles or metal particles functioning as a conductive agent were produced.
[0120]
Sample 4-1
In preparing the negative electrode, 94% by weight of the negative electrode active material, 5% by weight of polyvinylidene fluoride, and 1% by weight of graphitized vapor-grown carbon fiber were dispersed in N-methyl-2-pyrrolidone. Thus, a slurry-like negative electrode mixture was prepared. And after apply | coating this negative electrode mixture on the copper foil which is 15 micrometers in thickness used as a negative electrode collector, it dries and presses, and it punches out to the magnitude | size for 2016 type coin cells, and obtains a negative electrode. In the same manner as in Example 3, a cell was produced. As the negative electrode active material, similarly to Sample 1-3, the surface of graphitic carbon obtained by firing MCMB at 2800 ° C. is coated with a water-soluble polymer, and the coating amount of the water-soluble polymer is 1% by weight. An active material was used.
[0121]
Sample 4-2
In preparing the negative electrode, 94% by weight of the negative electrode active material, 5% by weight of polyvinylidene fluoride, and 1% by weight of acetylene black were dispersed in N-methyl-2-pyrrolidone to form a slurry-like negative electrode A mixture was prepared. And after apply | coating this negative electrode mixture on the copper foil which is 15 micrometers in thickness used as a negative electrode collector, it dries and presses, and it punches out to the magnitude | size for 2016 type coin cells, and obtains a negative electrode. In the same manner as in Example 3, a cell was produced. As the negative electrode active material, similarly to Sample 1-3, the surface of graphitic carbon obtained by firing MCMB at 2800 ° C. is coated with a water-soluble polymer, and the coating amount of the water-soluble polymer is 1% by weight. An active material was used.
[0122]
Sample 4-3
When preparing the negative electrode, a slurry-like negative electrode was prepared by dispersing 94% by weight of the negative electrode active material, 5% by weight of polyvinylidene fluoride, and 1% by weight of nickel fine particles in N-methyl-2-pyrrolidone. A mixture was prepared. And after apply | coating this negative electrode mixture on the copper foil which is 15 micrometers in thickness used as a negative electrode collector, it dries and presses, and it punches out to the magnitude | size for 2016 type coin cells, and obtains a negative electrode. In the same manner as in Example 3, a cell was produced. As the negative electrode active material, similarly to Sample 1-3, the surface of graphitic carbon obtained by firing MCMB at 2800 ° C. is coated with a water-soluble polymer, and the coating amount of the water-soluble polymer is 1% by weight. An active material was used.
[0123]
For the cells of Samples 4-1 to 4-3 and Sample 1-3 that were produced as described above, the charge / discharge test performed in Experiment 1 and Experiment 2 described above was performed in the same manner, and the initial battery The efficiency, the capacity retention rate during 6 mA discharge, and the capacity retention rate during 12 mA discharge were determined.
[0124]
The above measurement results are shown in Table 3.
[0125]
[Table 3]

[0126]
When comparing the cell of Sample 1-3 with a negative electrode not containing a conductive agent and the cells of Samples 4-1 to 4-3 with a negative electrode containing carbon particles or metal particles that function as a conductive agent, the initial battery efficiency is improved. Although no significant change is observed, it can be seen that the load characteristics are significantly improved in the cells of Samples 4-1 to 4-3.
[0127]
Since the surface of the polymer-coated carbon particles is widely coated with an insulating water-soluble polymer, the minute electrical contact between the negative electrode active material particles during electrode pressing or the like has a load characteristic in the case of a large current discharge application. A decrease may be seen.
[0128]
Therefore, by adding carbon particles or metal particles that function as a conductive agent to the negative electrode, it becomes a negative electrode that simultaneously satisfies the stability of the active material carbon surface and the current collection between the active materials, and has high initial efficiency and high capacity. In addition, it can be seen that a non-aqueous electrolyte battery having excellent cycle characteristics and large current characteristics can be realized.
[0129]
<Experiment 5>
A non-aqueous electrolyte battery comprising carbon particles or polymer-coated carbon particles as a negative electrode active material and a non-aqueous electrolyte solution containing a highly decomposable non-aqueous solvent was produced.
[0130]
Sample 5-1
When preparing a non-aqueous electrolyte, LiPF was used as an electrolyte salt in a solution in which ethylene carbonate and γ-butyrolactone were mixed at a weight ratio of 3: 7.₆A cell was prepared in the same manner as Sample 1-1 except that was dissolved at a concentration of 1 mol / kg.
[0131]
Sample 5-2
When preparing a non-aqueous electrolyte, LiPF was used as an electrolyte salt in a solution in which ethylene carbonate and γ-butyrolactone were mixed at a weight ratio of 3: 7.₆A cell was prepared in the same manner as Sample 1-2 except that was dissolved at a concentration of 1 mol / kg.
[0132]
The cells of Samples 5-1 and 5-2 produced as described above were subjected to the following charge / discharge test to evaluate the cycle characteristics.
[0133]
First, constant current charging was performed from the open voltage to 0 V at 1 mA, and then constant voltage charging was performed until the current value became 0.01 mA at 0 V. Next, the battery was discharged at a constant current of 3 mA until the cell voltage reached 1.5V. This charge / discharge cycle was repeated, the ratio of the discharge capacity at each cycle time to the initial discharge capacity was determined, and this ratio was defined as the capacity retention rate (%).
[0134]
The above measurement results are shown in FIG.
[0135]
From FIG. 3, in the cell of Sample 5-1 containing the polymer-coated carbon particles as the negative electrode active material, the capacity retention rate is drastically despite the use of a non-aqueous electrolyte having a high content of γ-butyrolactone. It can be seen that no deterioration was observed and stable cycle characteristics were exhibited.
[0136]
On the other hand, in the cell of Sample 5-2 that contains carbon particles whose surfaces are not coated with a water-soluble polymer as the negative electrode active material, it can be seen that the capacity retention rate is drastically reduced.
[0137]
Therefore, by including polymer-coated carbon particles as a negative electrode active material, a non-aqueous electrolyte battery having stable cycle characteristics even when a non-aqueous electrolyte containing a non-aqueous solvent having high decomposability is used. Can be realized.
[0138]
<Experiment 6>
A non-aqueous electrolyte battery comprising carbon particles or polymer-coated carbon particles as a negative electrode active material and a non-aqueous electrolyte solution containing a highly decomposable non-aqueous solvent was produced.
[0139]
Sample 6-1
When preparing the non-aqueous electrolyte, LiPF as an electrolyte salt was added to a solution in which ethylene carbonate and propylene carbonate were mixed at a weight ratio of 3: 7.₆A cell was prepared in the same manner as Sample 1-1 except that was dissolved at a concentration of 1 mol / kg.
[0140]
Sample 6-2
When preparing the non-aqueous electrolyte, LiPF as an electrolyte salt was added to a solution in which ethylene carbonate and propylene carbonate were mixed at a weight ratio of 3: 7.₆A cell was prepared in the same manner as Sample 1-3 except that was dissolved at a concentration of 1 mol / kg.
[0141]
Sample 6-3
When preparing the non-aqueous electrolyte, LiPF as an electrolyte salt was added to a solution in which ethylene carbonate and propylene carbonate were mixed at a weight ratio of 3: 7.₆A cell was prepared in the same manner as Sample 1-2 except that was dissolved at a concentration of 1 mol / kg.
[0142]
Sample 6-4
When preparing the non-aqueous electrolyte, LiPF as an electrolyte salt was added to a solution in which ethylene carbonate and propylene carbonate were mixed at a weight ratio of 3: 7.₆Was dissolved in a concentration of 1 mol / kg, and a cell was produced in the same manner as Sample 1-4.
[0143]
The charge / discharge test performed in Experiment 1 was similarly performed on the cells of Samples 6-1 to 6-4 produced as described above, and the initial battery efficiency was obtained.
[0144]
The above measurement results are shown in Table 4.
[0145]
[Table 4]

[0146]
In the cells of Samples 6-1 and 6-2 containing polymer-coated carbon particles as the negative electrode active material, the initial battery efficiency is very high despite using a non-aqueous electrolyte having a high propylene carbonate content. .
[0147]
On the other hand, in the cells of Samples 6-3 and 6-4 containing carbon particles whose surfaces are not coated with a water-soluble polymer as a negative electrode active material, the loss capacity used for the decomposition of the non-aqueous electrolyte is very high. Since it is large, the initial battery efficiency is low.
[0148]
Therefore, by including polymer-coated carbon particles as a negative electrode active material, a non-aqueous electrolyte battery excellent in initial battery efficiency even when a non-aqueous electrolyte containing a highly decomposable non-aqueous solvent is used. Can be realized.
[0149]
<Experiment 7>
A battery using a gel electrolyte was produced.
[0150]
Sample 7-1
First, the positive electrode was produced as follows. First, 91% by weight of lithium cobaltate as a positive electrode active material, 6% by weight of graphite as a conductive agent, and 10% by weight of polyvinylidene fluoride as a binder were mixed in N-methyl-2-pyrrolidone. To prepare a slurry-like positive electrode mixture. Next, this slurry-like positive electrode mixture was uniformly applied to one side of an aluminum foil having a thickness of 20 μm and dried to form a positive electrode mixture layer on the aluminum foil. Furthermore, after compression molding using a roll press machine, a positive electrode was obtained by punching into a circle according to the cell diameter.
[0151]
Next, a negative electrode was produced as shown below. First, as a negative electrode active material, an active material in which the surface of graphitic carbon formed by firing MCMB at 2800 ° C. is coated with a water-soluble polymer, and the amount of the water-soluble polymer coated is 1% by weight per active material. Prepared. Next, 90% by weight of this negative electrode active material and 10% by weight of polyvinylidene fluoride as a binder were mixed, and then dispersed in N-methyl-2-pyrrolidone to prepare a slurry-like negative electrode mixture. . Next, this slurry-like positive electrode mixture was uniformly applied to one side of a 10 μm thick copper foil and dried to form a negative electrode mixture layer on the copper foil. Furthermore, after compression molding using a roll press machine, a negative electrode was obtained by punching into a circle according to the cell diameter.
[0152]
Next, an electrolyte solution was prepared as shown below. First, LiPF was added to a mixed solvent in which 42.5% by weight of ethylene carbonate and 42.5% by weight of γ-butyrolactone were mixed.₆15% by weight of a plasticizer was prepared. Next, an electrolyte solution was prepared by mixing and dissolving 30% by weight of this plasticizer, 10% by weight of block copolymer poly (vinylidene fluoride), and 60% by weight of dimethyl carbonate.
[0153]
Next, the electrolyte solution was applied onto the positive electrode mixture layer and the negative electrode mixture layer and impregnated, and left at room temperature for 8 hours to vaporize and remove dimethyl carbonate. In this way, a gel electrolyte layer was formed on the positive electrode mixture layer and the negative electrode mixture layer.
[0154]
Next, the gel electrolyte layer formed on the positive electrode mixture layer and the gel electrolyte layer formed on the negative electrode mixture layer were bonded together and pressure-bonded to produce a battery element. And this battery element was accommodated in the laminate film, and the flat gel electrolyte battery of length 2.5cm, width 4.0cm, and thickness 0.3mm was produced.
[0155]
Sample 7-2
When producing the negative electrode, after mixing 89.1% by weight of graphitic carbon obtained by firing MCMB as a negative electrode active material at 2800 ° C. and 10.9% by weight of polyvinylidene fluoride as a binder, N -A sample except that a slurry-like negative electrode mixture is prepared by dispersing in methyl-2-pyrrolidone, and this slurry-like negative electrode mixture is uniformly applied to one surface of a copper foil to form a negative electrode mixture layer. A gel electrolyte battery was produced in the same manner as in Example 7-1.
[0156]
The following charge / discharge tests were performed on the gel electrolyte batteries of Samples 7-1 and 7-2 produced as described above, and the cycle characteristics were evaluated.
[0157]
First, constant current charging was performed from the open voltage to 4.20 V at 100 mA, and then constant voltage charging was performed at 4.20 V until the current value reached 2 mA. Next, the battery was discharged at a constant current of 500 mA until the cell voltage reached 3.0V. This charge / discharge cycle was repeated, and the ratio of the discharge capacity at each cycle relative to the initial discharge capacity was determined, and this ratio was defined as the capacity maintenance rate (unit:%).
[0158]
The above measurement results are shown in FIG.
[0159]
As is clear from FIG. 4, the cell of Sample 7-1 containing polymer-coated carbon particles as the negative electrode active material shows a stable capacity retention rate even when the charge / discharge cycle is repeated. On the other hand, the capacity maintenance rate of the cell of Sample 7-2 containing carbon particles whose surfaces are not coated with a water-soluble polymer as the negative electrode active material decreases when the charge / discharge cycle is repeated.
[0160]
Therefore, it can be seen that a gel electrolyte battery having stable cycle characteristics can be realized by including the polymer-coated carbon particles as the negative electrode active material.
[0161]
【The invention's effect】
  As is apparent from the above description, in the present invention, the active material has a true density of 2.00 g / cc or more and a mesophase pitch having an average interplanar distance d (002) in the C-axis direction of 3.39 mm or less. MicrobeadsBakedSince the surface of graphitic carbon is coated with carboxymethyl cellulose or its water-soluble salt as a water-soluble polymer in the range of 0.02 wt% or more and 10 wt% or less, a non-aqueous electrolyte containing a non-aqueous solvent or an electrolyte salt Moreover, the reactivity with a binder etc. is suppressed. Therefore, according to this active material, the decomposition reaction of the nonaqueous electrolyte is suppressed, and a nonaqueous electrolyte secondary battery excellent in initial efficiency, cycle characteristics, and large current characteristics can be realized.
[0162]
  The nonaqueous electrolyte secondary battery according to the present invention is a mesophase pitch microbead.BakedAn active material coated with a water-soluble polymer carboxymethyl cellulose or a water-soluble salt thereof in a range of 0.02 wt% or more and 10 wt% or less of the surface of graphitic carbon, vapor grown carbon fiber, acetylene black, piece Since the negative electrode contains at least one kind of carbon particles of flake shaped natural graphite, flake shaped artificial graphite and fibrous artificial graphite and at least one kind of binder of polyvinylidene fluoride, polyvinyl alcohol, and styrene-butadiene rubber. The decomposition reaction of the non-aqueous electrolyte is suppressed, and the initial efficiency, cycle characteristics, and large current characteristics are excellent.
[0163]
Moreover, according to the manufacturing method of the electrode which concerns on this invention, an electrode can be manufactured, without destroying the water-soluble polymer which coat | covers the surface of carbon particle.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing a configuration example of a non-aqueous electrolyte battery to which the present invention is applied.
FIG. 2 is a characteristic diagram showing the relationship between the number of charge / discharge cycles and battery efficiency.
FIG. 3 is a characteristic diagram showing the relationship between the number of charge / discharge cycles and the capacity retention rate.
FIG. 4 is a characteristic diagram showing the relationship between the number of charge / discharge cycles and the capacity retention rate.
[Explanation of symbols]
1 nonaqueous electrolyte battery, 2 negative electrode, 3 positive electrode, 4 negative electrode can, 5 positive electrode can, 6 separator, 7 insulating gasket

Claims (5)

In a non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode and a non-aqueous electrolyte,
An active material in which the surface of graphitic carbon formed by firing mesophase pitch microbeads on the negative electrode is coated with a water-soluble polymer, vapor-grown carbon fiber, acetylene black, flake natural graphite, flake artificial graphite, and At least one or more kinds of carbon particles in the fibrous artificial graphite, and at least one kind of binder of polyvinylidene fluoride, polyvinyl alcohol, and styrene-butadiene rubber are contained,
The graphitic carbon obtained by firing the mesophase pitch microbeads has a true density of 2.00 g / cc or more and an average interplanar spacing d (002) in the C-axis direction of 3.39 mm or less.
The water-soluble polymer is carboxymethyl cellulose or a water-soluble salt thereof, and the amount of coating is 0.02 wt% or more and 10 wt% or less per active material.   The nonaqueous electrolyte secondary battery according to claim 1, wherein the negative electrode containing the active material contains metal particles that do not form an alloy with lithium.   The nonaqueous electrolyte secondary battery according to claim 1 or 2, wherein γ-butyrolactone is contained in the nonaqueous electrolyte.   The nonaqueous electrolyte secondary battery according to claim 1 or 2, wherein the nonaqueous electrolyte contains propylene carbonate. An active material is prepared by coating the surface of graphitic carbon formed by firing mesophase pitch microbeads with a water-soluble polymer,
The above active material, vapor grown carbon fiber, acetylene black, flake natural graphite, flake artificial graphite and fibrous artificial graphite, at least one kind of carbon particles, polyvinylidene fluoride, polyvinyl alcohol, styrene-butadiene rubber At least one binder is dispersed in a non-aqueous solvent to prepare a mixture,
Apply the above mixture onto a current collector to form a mixture layer,
Dry the mixture layer,
The graphitic carbon obtained by firing the mesophase pitch microbeads has a true density of 2.00 g / cc or more and an average interplanar spacing d (002) in the C-axis direction of 3.39 mm or less.
The water-soluble polymer is carboxymethyl cellulose or a water-soluble salt thereof, and the method for producing a negative electrode of a non-aqueous electrolyte secondary battery in which the coating amount is in the range of 0.02 wt% or more and 10 wt% or less per the active material .

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