JP4292450B2

JP4292450B2 - Activated carbon for composite electrode and electrode material using the same

Info

Publication number: JP4292450B2
Application number: JP2001379087A
Authority: JP
Inventors: 誠井上; 真申小林; 季良潮見
Original assignee: Toyobo Co Ltd
Current assignee: Toyobo Co Ltd
Priority date: 2001-12-12
Filing date: 2001-12-12
Publication date: 2009-07-08
Anticipated expiration: 2021-12-12
Also published as: JP2003178761A

Description

【０００１】
【発明の属する技術分野】
本発明は複合電極用活性炭、特に亜鉛−臭素二次電池の正極即ち臭素極に使用される複合電極用活性炭とそれを用いる電極材に関するものである。
【０００２】
【従来技術】
金属−ハロゲン二次電池、例えば亜鉛−臭素二次電池は正極において、臭素イオンを臭素に酸化することによって充電し臭素を臭素イオンに還元し放電する。かかる二次電池において正極即ち臭素極は、電池のエネルギー効率に影響を与える放電時の臭素の還元反応を迅速に、かつ有効に反応させる反応場としての機能と電子を効率的に流通させる集電体としての機能を要求されている。従来、正極電極材料として白金が用いられてきたが高価であるために、導電性粉末カーボンと樹脂の混合物を加熱成形した導電性プラスチック板や炭素焼結板が用いられている。しかしこれらの電極では放電の電位が低く、放電時間が短くなるため充放電のエネルギー効率は低かった。白金電極は臭素の反応速度こそ速いものの反応場や集電体としての機能には不足していたためである。
【０００３】
この問題を解決する方法として、電極表面積を多くし臭素との反応面積を多くとり集電体としての導電性の機能を得るために導電性プラスチック板を電極基材とし、活性炭を表面に接合したり電極基材に練りこんで使用されている。これは複合電極と呼ばれ特開昭５９−２９３８５号には多孔質炭素繊維の織物、編地状布を電極基材に接合して使用する例が提案されている。また紙状の繊維状活性炭を接合して使用する例があり、特開昭５９−１６３７６５号においては繊維状活性炭の細孔、即ち細孔直径３０〜１０００オングストロームの細孔容積が０．１ｃｃ／ｇ以上である非常に細孔容積の大きい繊維状活性炭を紙状にし、電極基材に接合して使用されることが提案されている。また特開平０５−２３９７２０号には繊維状活性炭表面に窒素原子を含有した電極材を複合電極に用いることを提案している。
【０００４】
【発明が解決しようとする課題】
上記繊維状活性炭の紙状物は、繊維状活性炭の織布、編地に比べて安価に製造することが出来るので紙状物を電極基材に接合し正極として使用することは電池の価格を下げることからも有用である。しかしこうした紙状の電極材は上述の織布、編地に比べ依然として高電流密度での電位が低かった。これは基本的に紙状の電極材は電極基材との接合性が悪いため接触抵抗が増加しさらに反応場が織布、編地に比べ少ないことから分極値が増加するためである。
【０００５】
本発明者はかかる事情に鑑み、反応に寄与する活性炭の表面と臭素の吸着性やプラスチック電極との接着性について鋭意検討した結果、高電流密度でも高い放電電位を得ることができる金属−ハロゲン二次電池の電極材料を提供するに至った。
【０００６】
【課題を解決するための手段】
本発明は、
（１）水酸基（−ＯＨ）、カルボキシル基（−ＣＯＯＨ）、ヒドロキシアミノ基（−ＮＨ−ＯＨ）及びヒドロキシイミノ基（＝Ｎ−ＯＨ）のうちの１種以上からなる全酸性基量が０．２以上２．０ｍｅｑ／ｇ以下である活性炭であり、かつＸＰＳ表面分析より求めた酸素と二重結合した炭素原子数が全表面炭素原子数に対して２％以上７．３％以下であることを特徴とする複合電極用活性炭。
（２）活性炭が繊維状であることを特徴とする前記（１）記載の複合電極用活性炭。
（３）活性炭の比表面積は５００〜２０００ｍ²／ｇであることを特徴とする前記（１）または（２）記載の複合電極用活性炭。
（３）前記（１）〜（３）のいずれかに記載の活性炭を５０質量％以上含有し構成された紙状物であることを特徴とする電極材。
である。以後詳細に説明する。なお、以下において重量及び重量％の表記は、それぞれ質量及び質量％を意味する。
【０００７】
【発明の実施の形態】
本発明における活性炭は有機質を炭化、賦活して得られたものである。原料として使用される有機質とはおがくずなどの木質系、籾殻、豆類、やしがらなどの植物系、フェノール樹脂、石炭があり、また繊維状であればセルロース系、フェノールノボラック系、ポリアクリロニトリル系、芳香族ポリアミド系、ポリビニルアルコール系、ポリ塩化ビニル系、石油または石炭ピッチ系が用いられている。活性炭は電極との接触面積や活性炭同士の接触性から幾何表面積を広く出来る繊維状であることが好ましい。また炭化、および賦活の方法としては一般に公知である方法が使用できる。また場合によっては公知である賦活触媒を用いて賦活してもよい。繊維状活性炭の繊維直径は平均で１２μｍ以下、さらには１０μｍ以下がより好ましい。
【０００８】
本発明における酸性基とは活性炭表面の水酸基（−ＯＨ）、カルボキシル基（−ＣＯＯＨ）、ヒドロキシアミノ基（−ＮＨ−ＯＨ）、ヒドロキシイミノ基（＝Ｎ−ＯＨ）を意味する。本発明に使用される活性炭の酸性基の量は単位重量あたり０．２ｍｅｑ／ｇ以上２．０ｍｅｑ／ｇ以下であり、望ましくは０．３ｍｅｑ以上１．５ｍｅｑ／ｇ以下、さらに望ましくは０．４ｍｅｑ／ｇ以上１．０ｍｅｑ／ｇ以下のものである。これにより繊維状活性炭と電解液との濡れ性が向上し、繊維状活性炭の表面を有効に利用される。しかし単位重量当たり２．０ｍｅｑ／ｇ以上の活性炭を用いた場合、電極との接合時安定した接合がなされず接触抵抗が増加して電位の低下を招くため好ましくなく、反対に０．２ｍｅｑ／ｇ以下の場合繊維状活性炭と電解液との濡れ性が悪化し、実質的に反応に供する面積が減少してしまうため臭素を有効に吸着できず分極値が増加、電位が低下し好ましくない。
【０００９】
また本発明における酸素と二重結合した炭素原子数とはＸＰＳ表面分析（解析方法は後述する）によって検出される活性炭表面のキノン基を意味し、全表面炭素原子数に対する割合としてあらわす（％、以下Ｃ＝Ｏ／Ｃ比という）。活性炭の表面のＣ＝Ｏ基導入によって電極との接着性の向上が図られ電極との導電性が増加する。従ってＣ＝Ｏ／Ｃ比が２．０％以上、好ましくは２．２％以上より好ましくは２．５％以上の活性炭を用いることにより、電極との接触抵抗を低減し高い電流密度においても安定な電位を維持することが可能となる。しかし２．０％未満である場合、電極との接触性が低下し抵抗が高くなるため好ましくない。
【００１０】
上記した如き所定の酸性基量を有しかつＣ＝Ｏ／Ｃ比の高い活性炭は前記記載の原料を炭化、賦活した後、０．０１ｔｏｒｒ以上の酸素分圧を有する酸素雰囲気下で７００〜１０００℃の温度で重量収率にして５０〜９９％の範囲になるように酸化することによって得られる。重量収率が５０％未満になると表面のエッチングが進行し、接触抵抗の上昇をまねくので好ましくない。また、酸化方法としては７００℃以上の高い温度で短時間酸化処理することによって酸性基の生成を抑制しＣ＝Ｏ／Ｃ比の高い酸化処理を行うことが可能である。また７００℃未満の低い温度領域での酸化はＣ＝Ｏ基の生成に対して酸性基の生成が優先されるため好ましくない。また低温で酸化処理する場合活性炭中にアルカリ金属類あるいはアルカリ土類金属塩を数１００ｐｐｍ程度含有せしめることによってこの酸性基の生成を抑制することが出来る。このようにして得られた活性炭の比表面積は臭素の反応場を確保することから５００〜２２００ｍ²／ｇであることが望ましくさらには７００〜２０００ｍ²／ｇがより好ましい。
【００１１】
上述の如き作成された活性炭は紙層形成に一定の強度を得るため他の１種類以上の有機、無機材料と共に目付量が２５ｇ／ｍ²以上、厚みが０．１５ｍｍ以上になるように抄紙する。なお、特に強度を必要としないのであればこれに限定されるものではない。なお紙状物中の繊維状活性炭の含有量は５０重量％以上望ましくは５５重量％以上、より望ましくは６０重量％以上である。活性炭の含有率が５０％未満である場合臭素との反応面積が減少し高電流密度で安定した放電特性が得られないため好ましくない
【００１２】
紙状物として活性炭と同時に用いられる他の材料としてはパルプ、骨材の他、必要であればデンプン、ポリビニルアルコールのようなバインダーの他に粘剤、界面活性剤、離型剤、消泡剤、凝集剤等の各種添加剤を加えてもよい。使用されるパルプは耐水性、耐薬品性に優れるポリエチレン、ポリプロピレンの合成パルプが望ましいが再生セルロース系、アクリル系、ポリアミド系のパルプの他天然パルプを用いてもよい。骨材としては耐水性、耐薬品性に優れるポリエチレン、ポリプロピレンのチョップドファイバーやこれらの層状繊維（シースコア繊維）が望ましいが直鎖および／または芳香族ポリアミド系、ポリエステル、フェノールノボラック、ポリアクリロニトリル系の有機質繊維のほかガラス繊維、石綿、石英、アルミナの各種無機繊維が使用できる。これらパルプ、骨材は紙層形成後一定の強度が得られるものであればよく、先述に記載された素材に限定されない。
【００１３】
電極基材と紙状物との接合は、カーボンブラックや炭素繊維などのカーボンを主体とした導電性物質を３０重量％以上となるように、ポリエチレン樹脂粉末と均一に混合し、樹脂軟化点より１０℃高めに設定した金型の底に一定の厚みになるように敷いた後、熱プレスして厚さ１．０ｍｍ、大きさ１０ｃｍ平方の導電性電極基材として作成したものに加圧、加熱下で圧着する。
【００１４】
次に本発明において用いる酸性基量、比表面積、Ｃ＝Ｏ／Ｃ比、および電極電位の測定方法について述べる。
【００１５】
(1) 酸性基量：
酸性基を含有している活性炭を１２時間以上１規定の塩酸水溶液で洗浄し充分に水洗した後乾燥して約０．５ｇを採取し、１２０℃で１２時間真空乾燥して秤量し、６０ｍｌの１／１００ＮのＮａＯＨ水溶液に浸漬して２５℃で１０時間振とうした。この液をガラスろ過器でろ過しろ液を２５ｍｌ正確に分取して１／１００ＮのＨＣｌ標準液により逆滴定した。滴定の際にはフェノールフタレインを指示薬として用いた。空試験も同様にして行い、数式１により活性炭の単位重量当たりの酸性基量を求めた。
【００１６】
【数１】

【００１７】
式中Ｄは１／１００ＮのＨＣｌ標準液の滴定量から空試験での滴定量を引いた量（ｍｌ）、Ｋは１／１００ＮのＨＣｌ標準液の規定度、Ｗは活性炭の重量（ｇ）である。
【００１８】
(2) 比表面積：
１２時間以上１規定の塩酸水溶液で洗浄し充分に水洗し乾燥させた活性炭を約０．１ｇ採取し、１２０℃で１２時間乾燥して秤量し、液体窒素の沸点（−１９５．８℃）における窒素ガスの吸着量を相対圧を０．０から０．２の範囲で徐々に高めながら数点測定し、Ｂ．Ｅ．Ｔプロットにより単位重量当たりの比表面積（ｍ²／ｇ）を求めた。
【００１９】
(3) Ｃ＝Ｏ／Ｃ比：
ＥＳＣＡ、あるいはＸＰＳと略称されているＸ線光電子分光法により１２時間以上１規定の塩酸水溶液で洗浄し充分に水洗し乾燥せしめた活性炭表面のＣ＝Ｏ／Ｃ比を測定する。測定装置は島津ＥＳＣＡ７５０、解析にはＥＳＣＡＰＡＣ７６０を用いた。６ｍｍφに広げた導電性ペーストにサンプル活性炭を貼り付け加熱試料台に載せて試料を１２０℃で加熱しながら３時間以上真空脱気した後測定を行った。線源にはＭｇＫα線（１２５３．６ｅＶ）を用い、装置内真空度は１．３３×１０^-5Ｐａの条件で試料表面の分析を行った。なおここで言う表面とは試料の最外層から数十オングストロームまでの深さ領域を意味する。
【００２０】
測定はＣ１Ｓピークに対して行いＥＳＣＡＰＡＣ７６０を用いて各ピーク面積を求める。得られた面積をＪ．Ｈ．Ｓｃｏｆｉｅｌｄによる補正法に基づいて補正解析しピーク面積を求める。さらにＣ１Ｓピークに対してピーク形状が各構造におけるケミカルシフトになるように分離し、酸素と２重結合している炭素のピーク面積を決定し、全表面炭素に対する面積比を百分率（％）で算出する。
【００２１】
(4) 電極の電位：
本発明の複合電極用活性炭を実施例に基づいて湿式抄紙して電極材を得る。これを正極、即ち亜鉛−臭素電池の臭素極として充放電電位を評価する。電極材は５ｃｍにカットし５ｃｍ角厚み１．０ｍｍの電極基材の上に載せ、５ｃｍ角×１．１ｍｍ厚が成型可能な金型に入れ１６０℃にて５分間加圧接合する。出来上がった接合電極は直径１６ｍｍの打ち抜きポンチで打ち抜きリード線をつけて電位測定装置に設置する。このときの電極面積は打ち抜いた電極の幾何面積（２．０ｃｍ²）電解液は濃度３モル／リットルの臭化亜鉛溶液中に臭素０．２モルを溶解させたものであり、ゼロから１０ｍＡ／ｓｅｃの速度で５００ｍＡ（２５０ｍＡ／ｃｍ²）までプラス方向の電位をかけ−１０ｍＡ／ｓｅｃで放電電位が３００ｍＶになるまで放電した。対極には９９．９９％の圧延亜鉛板を使用し、測定温度は２５℃、参照極として飽和カロメル電極を用いた。
【００２２】
臭素極のゼロｍＡの時点の電位をＶopenとし、３００ｍＡ（１５０ｍＡ／ｃｍ²）のときの電位をＶｉとし、ＶｏｐｅｎとＶｉとの差を充電電位差とした。さらにマイナス３００ｍＡ（１５０ｍＡ／ｃｍ²）のときの電位をＶｉｉとし、ＶｏｐｅｎとＶｉｉとの差を放電電位差とした。充電電位差は臭化物イオンが臭素に変化する場合に生ずる電位差であり臭素イオンが過剰に供給されているのでこの電位差は基本的に電極の接触抵抗のみに影響する。放電の電位差は臭素が少ないので前記の接触抵抗に分極値が加算されたものである。
【００２３】
なお、上記電位の測定に用いた装置の説明図を図に示す。図において、１は臭素極であり、２は亜鉛板対極であり、３はルギンキャピラリーであり、４は電圧計であり、５は電源であり、６は電流計であり、７は電解液である。
【００２４】
【実施例】
以下に実施例をもって本発明を説明するがこれに限定されるものではない。
【００２５】
実施例１
単繊維繊度２．２ｄＴｅｘ、長さ８ｍｍの再生セルロース繊維にリン酸１水素アンモニウム１０重量％を添着し、空気中３５０℃で３０分加熱し炭化繊維を作製した。続いて窒素気流下で８５０℃まで約４００℃／時の速度で昇温し昇温後水蒸気濃度１５体積％の雰囲気で６０分間保持することによって賦活し繊維状活性炭を得た。さらに空気中、９００℃で３０秒間熱処理した。こうして得られた繊維状活性炭の酸性基量は０．８ｍｅｑ／ｇ、Ｃ＝Ｏ／Ｃ比は５．１％、比表面積は１２５０ｍ^２／ｇであった。
【００２６】
この繊維状活性炭を乾燥重量にして６７重量％分採取し、これに７重量％のポリプロピレン単繊維チョップドファイバー、２１重量％のポリエチレン製合成パルプ、５重量％のポリエチレン−ポリプロピレン芯鞘繊維を加えて湿式抄紙し目付量３３ｇ／ｍ²、厚み０．２５ｍｍの紙状物を作成した。この紙状物を先述のプラスチック電極基材と接合し電極を得た。この様にして得られた電極の充放電電位差を表１に示す。
【００２７】
実施例２
単繊維繊度２．２ｄＴｅｘ、長さ５４ｍｍのポリアクリロニトリル繊維を原料とし、空気中２５０℃で３０分加熱し耐炎化し炭化繊維を得た。続いて窒素気流下で９００℃まで４００℃／時の速度で昇温し昇温後水蒸気濃度１５体積％の雰囲気で６０分間保持することによって賦活し繊維状活性炭を得た。さらに空気中、９００℃で１分間熱処理した。こうして得られた繊維状活性炭の酸性基量は０．６ｍｅｑ／ｇ、Ｃ＝Ｏ／Ｃ比は２．８％、比表面積は７６５ｍ²／ｇであった。
【００２８】
この繊維状活性炭をカッターミルで粉砕した後、乾燥重量にして６７重量％分採取し、これに７重量％のポリプロピレン単繊維チョップドファイバー、２１重量％のポリエチレン製合成パルプ、５重量％のポリエチレン−ポリプロピレン芯鞘繊維を加えて湿式抄紙し目付量３１ｇ／ｍ²、厚み０．２２ｍｍの紙状物を作成した。この紙状物を先述のプラスチック電極基材と接合し電極を得た。この様にして得られた電極の充放電電位差を表１に示す。
【００２９】
実施例３
単繊維繊度２．２ｄＴｅｘ、長さ５１ｍｍの再生セルロース繊維にリン酸１水素カルシウム１０重量％を添着し、窒素気流下３５０℃で３０分加熱し炭化繊維を作製した。続いて窒素気流下で９２０℃まで約４００℃／時の速度で昇温し昇温後水蒸気濃度１５体積％の雰囲気で６０分間保持することによって賦活し繊維状活性炭を得た。さらに空気中、９００℃で２０秒間熱処理した。こうして得られた繊維状活性炭の酸性基量は１．０ｍｅｑ／ｇ、Ｃ＝Ｏ／Ｃ比は６．５％、比表面積は１６２０ｍ²／ｇであった。
【００３０】
この活性炭をミルで粉砕した後、これを乾燥重量にして６０重量％分採取し、これに１２重量％のポリプロピレン単繊維チョップドファイバー、２６重量％のポリエチレン製合成パルプ、２重量％のポリビニルアルコールのバインダーを加えて目付量３３ｇ／ｍ²、厚み０．２１ｍｍの紙状物を作成した。この紙状物を先述のプラスチック電極基材と接合し電極を得た。この様にして得られた電極の充放電電位差を表１に示す。
【００３１】
【表１】

【００３２】
実施例４
単繊維繊度２．２ｄＴｅｘ、長さ６２ｍｍのフェノールノボラック繊維を原料とし、リン酸１水素カルシウム１０重量％を添着し窒素気流下で８５０℃まで４００℃／時の速度で昇温し昇温後水蒸気濃度１５体積％の雰囲気で６０分間水蒸気賦活処理をおこない繊維状活性炭を得た。この活性炭を９００℃で４０秒間空気中で酸化処理した。こうして得られた活性炭の酸性基量は１．２ｍｅｑ／ｇ、Ｃ＝Ｏ／Ｃ比は７．３％、比表面積は１１５５ｍ²／ｇであった。
【００３３】
この繊維状活性炭をカッターミルで粉砕した後、これを乾燥重量にして８０重量％分採取し、これに１２重量％のポリプロピレン単繊維チョップドファイバー、６重量％のポリエチレン製合成パルプ、２重量％のポリビニルアルコールのバインダーを加えて目付量４２ｇ／ｍ²、厚み０．２２ｍｍの紙状物を作成した。この紙状物を先述のプラスチック電極基材と接合し電極を得た。この様にして得られた電極の充放電電位差を表１に示す。
【００３４】
比較例１
単繊維繊度２．２ｄＴｅｘ、長さ８ｍｍの再生セルロース繊維にリン酸１水素アンモニウムを１０重量添着し、空気中３５０℃で３０分加熱し炭化繊維を作製した。続いて窒素気流下で８５０℃まで約４００℃／時の速度で昇温し昇温後水蒸気濃度１５体積％の雰囲気で６０分間保持することによって賦活し繊維状活性炭を得た。こうして得られた繊維状活性炭の酸性基量は０．２ｍｅｑ／ｇ、Ｃ＝Ｏ／Ｃ比は．０．６％、比表面積は１１８８ｍ²／ｇであった。
【００３５】
この繊維状活性炭を乾燥重量にして６７重量％分採取し、これに７重量％のポリプロピレン単繊維チョップドファイバー、２１重量％のポリエチレン製合成パルプ、５重量％のポリエチレン−ポリプロピレン芯鞘繊維を加えて湿式抄紙し目付量３３ｇ／ｍ²、厚み０．２５ｍｍの紙状物を作成した。この紙状物を先述のプラスチック電極基材と接合し電極を得た。この様にして得られた電極の充放電電位差を表１に示す。
【００３６】
比較例２
単繊維繊度２．２ｄＴｅｘ、長さ８ｍｍの再生セルロース繊維にリン酸１水素アンモニウムを１０重量添着し、空気中３５０℃で３０分加熱し炭化繊維を作製した。続いて窒素気流下で８５０℃まで約４００℃／時の速度で昇温し昇温後水蒸気濃度１５体積％の雰囲気で６０分間保持することによって賦活し繊維状活性炭を得た。空気中、４５０℃で８分間熱処理した。こうして得られた繊維状活性炭の酸性基量は２．４ｍｅｑ／ｇ、Ｃ＝Ｏ／Ｃ比は５．４％、比表面積は１４５０ｍ²／ｇであった。
【００３７】
この繊維状活性炭を乾燥重量にして６７重量％分採取し、これに７重量％のポリプロピレン単繊維チョップドファイバー、２１重量％のポリエチレン製合成パルプ、５重量％のポリエチレン−ポリプロピレン芯鞘繊維を加えて湿式抄紙し目付量３３ｇ／ｍ²、厚み０．２５ｍｍの紙状物を作成した。この紙状物を先述のプラスチック電極基材と接合し電極を得た。この様にして得られた電極の充放電電位差を表１に示す。
【００３８】
【発明の効果】
以上説明したように本発明の活性炭および電極材料は活性炭の単位重量あたりの酸性基量を所定量に抑えつつかつＣ＝Ｏ基をを多く付与することによって集電板との接触性が向上し、かつ有効に臭素を吸着するので高電流密度においても安定した電圧を得ることのできる電極を得ることが出来る。
【図面の簡単な説明】
【図１】電極の電位特性に用いる装置の模式図
【図２】ＸＰＳ表面分析で測定されるＣ１Ｓピークの結合構造別分離図[0001]
BACKGROUND OF THE INVENTION
TECHNICAL FIELD The present invention relates to a composite electrode activated carbon, and more particularly to a composite electrode activated carbon used for a positive electrode of a zinc-bromine secondary battery, that is, a bromine electrode, and an electrode material using the same.
[0002]
[Prior art]
A metal-halogen secondary battery, for example, a zinc-bromine secondary battery, is charged by oxidizing bromine ions into bromine at the positive electrode and reducing bromine into bromine ions for discharge. In such a secondary battery, the positive electrode, that is, the bromine electrode, serves as a reaction field for reacting quickly and effectively the reduction reaction of bromine during discharge, which affects the energy efficiency of the battery, and a current collector that efficiently distributes electrons. Function as a body is required. Conventionally, platinum has been used as a positive electrode material, but since it is expensive, a conductive plastic plate or a sintered carbon plate obtained by thermoforming a mixture of conductive powder carbon and resin is used. However, in these electrodes, the discharge potential is low and the discharge time is shortened, so that the energy efficiency of charge and discharge is low. This is because the platinum electrode has a high bromine reaction speed but is insufficient for the function as a reaction field or a current collector.
[0003]
In order to solve this problem, in order to increase the electrode surface area, increase the reaction area with bromine, and obtain a conductive function as a current collector, a conductive plastic plate is used as an electrode base material, and activated carbon is bonded to the surface. Or kneaded into an electrode substrate. This is called a composite electrode, and Japanese Patent Laid-Open No. 59-29385 proposes an example in which a porous carbon fiber fabric or knitted fabric is joined to an electrode substrate. Also, there is an example in which paper-like fibrous activated carbon is joined and used. In JP-A-59-163765, the pores of fibrous activated carbon, that is, the pore volume of pore diameter of 30 to 1000 angstroms is 0.1 cc / It has been proposed that fibrous activated carbon having a very large pore volume of g or more is made into a paper shape and bonded to an electrode substrate. Japanese Patent Laid-Open No. 05-239720 proposes to use an electrode material containing nitrogen atoms on the surface of fibrous activated carbon for the composite electrode.
[0004]
[Problems to be solved by the invention]
Since the fibrous activated carbon paper can be manufactured at a lower cost than woven fabric and knitted fabric of fibrous activated carbon, joining the paper to the electrode substrate and using it as a positive electrode reduces the price of the battery. It is also useful from lowering. However, such a paper-like electrode material still has a low potential at a high current density as compared with the woven fabric and knitted fabric described above. This is because, basically, the paper-like electrode material has poor bondability with the electrode base material, so that the contact resistance is increased, and the polarization value is increased because the reaction field is smaller than that of the woven fabric or knitted fabric.
[0005]
In view of such circumstances, the present inventor has intensively studied the adsorption property of bromine and the adhesion between the surface of activated carbon and the plastic electrode that contribute to the reaction. As a result, the metal-halogen dioxide capable of obtaining a high discharge potential even at a high current density. It came to provide the electrode material of a secondary battery.
[0006]
[Means for Solving the Problems]
The present invention
(1) The total amount of acidic groups consisting of one or more of hydroxyl group (—OH), carboxyl group (—COOH), hydroxyamino group (—NH—OH) and hydroxyimino group (═N—OH) is 0.00. The activated carbon is 2 to 2.0 meq / g and the number of carbon atoms double-bonded to oxygen determined by XPS surface analysis is 2% to 7.3% with respect to the total surface carbon atoms. Activated carbon for composite electrodes.
(2) The activated carbon for a composite electrode according to (1), wherein the activated carbon is fibrous.
(3) The activated carbon for composite electrodes according to the above (1) or (2), wherein the activated carbon has a specific surface area of 500 to 2000 m ² / g.
(3) the (1) to (3) electrode material which is a paper-like material that is configured to contain activated carbon as claimed 50 mass% or more to any of the.
It is. This will be described in detail below. In the following, the notations of weight and weight% mean mass and mass%, respectively.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
The activated carbon in the present invention is obtained by carbonizing and activating organic matter. Organic materials used as raw materials include wood-based materials such as sawdust, plant-based materials such as rice husks, beans, and palms, phenolic resins, and coal, and if fibrous, cellulose-based, phenol novolac-based, polyacrylonitrile-based, Aromatic polyamides, polyvinyl alcohols, polyvinyl chlorides, petroleum or coal pitches are used . It is preferable activated carbon is widely capable fibrous geometric surface area of contact of the contact area and the activated carbon between the electrodes. Also, generally known methods can be used as carbonization and activation methods. Moreover, you may activate using a well-known activation catalyst depending on the case. The fiber diameter of the fibrous activated carbon is on average 12 μm or less, and more preferably 10 μm or less.
[0008]
The acidic group in the present invention means a hydroxyl group (—OH), a carboxyl group (—COOH), a hydroxyamino group (—NH—OH), or a hydroxyimino group (═N—OH) on the activated carbon surface. The amount of acidic groups in the activated carbon used in the present invention is 0.2 meq / g or more and 2.0 meq / g or less per unit weight, preferably 0.3 meq or more and 1.5 meq / g or less, more preferably 0.4 meq. / G or more and 1.0 meq / g or less. Thereby, the wettability between the fibrous activated carbon and the electrolyte is improved, and the surface of the fibrous activated carbon is effectively used. However, when activated carbon of 2.0 meq / g or more per unit weight is used, it is not preferable because stable bonding is not performed at the time of bonding with the electrode, and the contact resistance increases and the potential is lowered. On the contrary, 0.2 meq / g In the following cases, the wettability between the fibrous activated carbon and the electrolytic solution deteriorates, and the area used for the reaction is substantially reduced. Therefore, bromine cannot be effectively adsorbed, the polarization value increases, and the potential decreases, which is not preferable.
[0009]
The number of carbon atoms double-bonded to oxygen in the present invention means a quinone group on the surface of activated carbon detected by XPS surface analysis (analysis method will be described later), and is expressed as a ratio to the total number of carbon atoms (%, Hereinafter referred to as C = O / C ratio). By introducing the C═O group on the surface of the activated carbon, the adhesion with the electrode is improved and the conductivity with the electrode is increased. Therefore, by using activated carbon having a C = O / C ratio of 2.0% or more, preferably 2.2% or more, more preferably 2.5% or more, the contact resistance with the electrode is reduced and stable even at a high current density. It is possible to maintain a stable potential. However, if it is less than 2.0%, the contact property with the electrode decreases and the resistance increases, which is not preferable.
[0010]
Activated carbon having a predetermined acidic group amount and having a high C = O / C ratio as described above is 700 to 1000 in an oxygen atmosphere having an oxygen partial pressure of 0.01 torr or more after carbonizing and activating the raw materials described above. It is obtained by oxidizing to a weight yield in the range of 50-99% at a temperature of ° C. If the weight yield is less than 50%, etching of the surface proceeds to increase the contact resistance, which is not preferable. Further, as an oxidation method, it is possible to perform an oxidation treatment with a high C = O / C ratio by suppressing the formation of acidic groups by performing an oxidation treatment at a high temperature of 700 ° C. or higher for a short time. Further, oxidation in a low temperature range of less than 700 ° C. is not preferable because generation of acidic groups is given priority over generation of C═O groups. In addition, when oxidation treatment is performed at a low temperature, the generation of this acidic group can be suppressed by adding about several hundred ppm of alkali metal or alkaline earth metal salt in the activated carbon. The specific surface area of the activated carbon thus obtained is preferably 500 to 2200 m ² / g, more preferably 700 to 2000 m ² / g in order to secure a bromine reaction field.
[0011]
In order to obtain a certain strength in the paper layer formation, the activated carbon produced as described above is paper-made together with one or more other organic and inorganic materials so that the basis weight is 25 g / m ² or more and the thickness is 0.15 mm or more. . In addition, if intensity | strength is not required especially, it will not be limited to this. The content of fibrous activated carbon in the paper-like material is 50% by weight or more, desirably 55% by weight or more, and more desirably 60% by weight or more. When the activated carbon content is less than 50%, the reaction area with bromine is reduced, and stable discharge characteristics cannot be obtained at a high current density.
Other materials used simultaneously with activated carbon as paper-like materials include pulp, aggregate, and if necessary, binders such as starch and polyvinyl alcohol, as well as stickers, surfactants, mold release agents, antifoaming agents Various additives such as an aggregating agent may be added. The pulp used is preferably a synthetic pulp of polyethylene and polypropylene excellent in water resistance and chemical resistance, but natural pulp may be used in addition to regenerated cellulose, acrylic and polyamide pulps. As aggregates, polyethylene and polypropylene chopped fibers with excellent water resistance and chemical resistance and layered fibers (seascore fibers) are desirable, but linear and / or aromatic polyamides, polyesters, phenol novolacs, polyacrylonitriles are preferred. In addition to organic fibers, various inorganic fibers such as glass fibers, asbestos, quartz, and alumina can be used. These pulps and aggregates are not limited to the materials described above as long as they have a certain strength after the paper layer is formed.
[0013]
The electrode base material and the paper-like material are joined with a polyethylene resin powder uniformly so that a conductive material mainly composed of carbon such as carbon black or carbon fiber is 30% by weight or more. After laying on the bottom of the mold set to be higher by 10 ° C. so as to have a constant thickness, pressurize what was prepared as a conductive electrode substrate having a thickness of 1.0 mm and a size of 10 cm square by hot pressing, Crimp under heat.
[0014]
Next, a method for measuring the amount of acidic groups, specific surface area, C = O / C ratio, and electrode potential used in the present invention will be described.
[0015]
(1) Amount of acidic group:
Activated carbon containing acidic groups was washed with 1N aqueous hydrochloric acid solution for 12 hours or longer, thoroughly washed with water, dried, and about 0.5 g was collected, vacuum dried at 120 ° C. for 12 hours, weighed, 60 ml It was immersed in 1 / 100N NaOH aqueous solution and shaken at 25 ° C. for 10 hours. This solution was filtered with a glass filter, 25 ml of the filtrate was accurately collected, and back-titration was performed with a 1 / 100N HCl standard solution. In the titration, phenolphthalein was used as an indicator. The blank test was performed in the same manner, and the amount of acidic groups per unit weight of the activated carbon was determined by Equation 1.
[0016]
[Expression 1]

[0017]
In the formula, D is the amount obtained by subtracting the titration amount in the blank test from the titration amount of 1 / 100N HCl standard solution, K is the normality of 1 / 100N HCl standard solution, and W is the weight of activated carbon (g). It is.
[0018]
(2) Specific surface area:
About 0.1 g of activated carbon which has been washed with 1N hydrochloric acid solution for 12 hours or more, sufficiently washed with water and dried, dried at 120 ° C. for 12 hours and weighed, at the boiling point of liquid nitrogen (−195.8 ° C.) The nitrogen gas adsorption amount was measured at several points while gradually increasing the relative pressure in the range of 0.0 to 0.2. E. The specific surface area (m ² / g) per unit weight was determined by T plot.
[0019]
(3) C = O / C ratio:
The C = O / C ratio of the activated carbon surface washed with 1N hydrochloric acid aqueous solution for 12 hours or longer, thoroughly washed with water and dried by X-ray photoelectron spectroscopy abbreviated as ESCA or XPS is measured. Shimadzu ESCA750 was used as a measuring device, and ESCAPAC760 was used for analysis. A sample activated carbon was attached to a conductive paste spread to 6 mmφ, and the sample was placed on a heated sample stage and vacuum degassed for 3 hours or more while heating the sample at 120 ° C., and then the measurement was performed. An MgKα ray (1253.6 eV) was used as the radiation source, and the sample surface was analyzed under the condition that the in-device vacuum was 1.33 × 10 ⁻⁵ Pa. The surface mentioned here means a depth region from the outermost layer of the sample to several tens of angstroms.
[0020]
The measurement is performed on the C1S peak, and each peak area is obtained using ESCAPAC760. The obtained area was determined according to J.J. H. Correction analysis is performed based on the correction method by Scofield, and the peak area is obtained. Furthermore, separation is performed so that the peak shape is a chemical shift in each structure with respect to the C1S peak, the peak area of carbon double-bonded to oxygen is determined, and the area ratio to the total surface carbon is calculated as a percentage (%). To do.
[0021]
(4) Electrode potential:
The activated carbon for composite electrodes of the present invention is subjected to wet papermaking based on the examples to obtain an electrode material. The charge / discharge potential is evaluated using this as the positive electrode, that is, the bromine electrode of a zinc-bromine battery. The electrode material is cut into 5 cm, placed on an electrode base material having a 5 cm square thickness of 1.0 mm, and placed in a mold capable of molding a 5 cm square × 1.1 mm thickness and pressure bonded at 160 ° C. for 5 minutes. The completed joining electrode is punched with a punch having a diameter of 16 mm, attached with a lead wire, and installed in a potential measuring device. The electrode area at this time is the geometric area of the punched electrode (2.0 cm ² ). The electrolytic solution is obtained by dissolving 0.2 mol of bromine in a zinc bromide solution having a concentration of 3 mol / liter. A potential in the positive direction was applied to 500 mA (250 mA / cm ² ) at a rate of sec and discharged at −10 mA / sec until the discharge potential reached 300 mV. A 99.99% rolled zinc plate was used as the counter electrode, the measurement temperature was 25 ° C., and a saturated calomel electrode was used as the reference electrode.
[0022]
The potential at the time of zero mA of the bromine electrode was Vopen, the potential at 300 mA (150 mA / cm ² ) was Vi, and the difference between Vopen and Vi was the charging potential difference. Furthermore, the potential at minus 300 mA (150 mA / cm ² ) was defined as Vii, and the difference between Vopen and Vii was defined as the discharge potential difference. The charge potential difference is a potential difference generated when bromide ions are changed to bromine. Since the bromine ions are excessively supplied, this potential difference basically affects only the contact resistance of the electrode. Since the potential difference of the discharge is small in bromine, the polarization value is added to the contact resistance.
[0023]
An explanatory diagram of the apparatus used for measuring the potential is shown in the figure. In the figure, 1 is a bromine electrode, 2 is a zinc plate counter electrode, 3 is a lugin capillary, 4 is a voltmeter, 5 is a power source, 6 is an ammeter, and 7 is an electrolyte. is there.
[0024]
【Example】
Hereinafter, the present invention will be described with reference to examples, but is not limited thereto.
[0025]
Example 1
Single fiber fineness 2.2 dtex, impregnated with 1 0% by weight phosphoric acid monohydrogen ammonium beam to regenerated cellulose fibers of length 8 mm, to produce a 30-minute heating carbonized fiber at 350 ° C. in air. Subsequently, the temperature was raised to 850 ° C. at a rate of about 400 ° C./hour under a nitrogen stream, and after activation, the mixture was activated for 60 minutes in an atmosphere having a water vapor concentration of 15% by volume to obtain fibrous activated carbon. Further, heat treatment was performed in the air at 900 ° C. for 30 seconds. The thus obtained fibrous activated carbon had an acidic group content of 0.8 meq / g, a C═O / C ratio of 5.1%, and a specific surface area of 1250 m ² / g.
[0026]
67% by weight of this fibrous activated carbon was collected as a dry weight, and 7% by weight of polypropylene single fiber chopped fiber, 21% by weight of synthetic pulp made of polyethylene, and 5% by weight of polyethylene-polypropylene core-sheath fiber were added thereto. Wet paper was made to prepare a paper-like material having a basis weight of 33 g / m ² and a thickness of 0.25 mm. This paper was joined to the plastic electrode substrate described above to obtain an electrode. Table 1 shows the charge / discharge potential difference of the electrodes thus obtained.
[0027]
Example 2
A polyacrylonitrile fiber having a single fiber fineness of 2.2 dTex and a length of 54 mm was used as a raw material and heated in air at 250 ° C. for 30 minutes to make it flame resistant to obtain carbonized fiber. Subsequently, the temperature was raised to 900 ° C. at a rate of 400 ° C./hour under a nitrogen stream, and the temperature was raised and the mixture was held for 60 minutes in an atmosphere having a water vapor concentration of 15% by volume to obtain fibrous activated carbon. Furthermore, it heat-processed in the air at 900 degreeC for 1 minute. The fibrous activated carbon thus obtained had an acidic group content of 0.6 meq / g, a C═O / C ratio of 2.8%, and a specific surface area of 765 m ² / g.
[0028]
The fibrous activated carbon was pulverized with a cutter mill, and then collected in a dry weight of 67% by weight. To this, 7% by weight of polypropylene single fiber chopped fiber, 21% by weight of polyethylene synthetic pulp, 5% by weight of polyethylene- Polypropylene core-sheath fibers were added to make a wet paper to produce a paper-like material having a basis weight of 31 g / m ² and a thickness of 0.22 mm. This paper was joined to the plastic electrode substrate described above to obtain an electrode. Table 1 shows the charge / discharge potential difference of the electrodes thus obtained.
[0029]
Example 3
10% by weight of calcium monohydrogen phosphate was impregnated with regenerated cellulose fiber having a single fiber fineness of 2.2 dTex and a length of 51 mm, and heated at 350 ° C. for 30 minutes in a nitrogen stream to prepare carbonized fibers. Subsequently, the temperature was raised to 920 ° C. at a rate of about 400 ° C./hour under a nitrogen stream, and after activation, activation was carried out by holding in an atmosphere having a water vapor concentration of 15% by volume for 60 minutes to obtain fibrous activated carbon. Furthermore, it heat-processed in the air at 900 degreeC for 20 second. The thus obtained fibrous activated carbon had an acidic group content of 1.0 meq / g, a C═O / C ratio of 6.5%, and a specific surface area of 1620 m ² / g.
[0030]
After pulverizing this activated carbon with a mill, 60% by weight was collected as a dry weight, and 12% by weight of polypropylene monofilament chopped fiber, 26 % by weight of polyethylene synthetic pulp, and 2% by weight of polyvinyl alcohol. A paper-like material having a basis weight of 33 g / m ² and a thickness of 0.21 mm was prepared by adding a binder. This paper was joined to the plastic electrode substrate described above to obtain an electrode. Table 1 shows the charge / discharge potential difference of the electrodes thus obtained.
[0031]
[Table 1]

[0032]
Example 4
A phenol novolac fiber with a single fiber fineness of 2.2 dTex and a length of 62 mm is used as a raw material, and 10% by weight of calcium monohydrogen phosphate is added thereto. Steam activation treatment was performed for 60 minutes in an atmosphere having a concentration of 15% by volume to obtain fibrous activated carbon. This activated carbon was oxidized in air at 900 ° C. for 40 seconds. The activated group thus obtained had an acidic group content of 1.2 meq / g, a C═O / C ratio of 7.3%, and a specific surface area of 1155 m ² / g.
[0033]
After pulverizing this fibrous activated carbon with a cutter mill, 80 wt% was sampled as a dry weight, and 12 wt% polypropylene monofilament chopped fiber, 6 wt% polyethylene synthetic pulp, 2 wt% A binder of polyvinyl alcohol was added to prepare a paper-like material having a basis weight of 42 g / m ² and a thickness of 0.22 mm. This paper was joined to the plastic electrode substrate described above to obtain an electrode. Table 1 shows the charge / discharge potential difference of the electrodes thus obtained.
[0034]
Comparative Example 1
A regenerated cellulose fiber having a single fiber fineness of 2.2 dTex and a length of 8 mm was impregnated with 10 weights of ammonium monohydrogen phosphate, and heated in air at 350 ° C. for 30 minutes to produce a carbonized fiber. Subsequently, the temperature was raised to 850 ° C. at a rate of about 400 ° C./hour under a nitrogen stream, and after activation, activation was carried out by holding in an atmosphere having a water vapor concentration of 15% by volume for 60 minutes to obtain fibrous activated carbon. The fibrous activated carbon thus obtained had an acidic group content of 0.2 meq / g and a C = O / C ratio of. The specific surface area was 0.68% and 1188 m ² / g.
[0035]
67% by weight of this fibrous activated carbon was collected as a dry weight, and 7% by weight of polypropylene single fiber chopped fiber, 21% by weight of synthetic pulp made of polyethylene, and 5% by weight of polyethylene-polypropylene core-sheath fiber were added thereto. Wet paper was made to prepare a paper-like material having a basis weight of 33 g / m ² and a thickness of 0.25 mm. This paper was joined to the plastic electrode substrate described above to obtain an electrode. Table 1 shows the charge / discharge potential difference of the electrodes thus obtained.
[0036]
Comparative Example 2
A regenerated cellulose fiber having a single fiber fineness of 2.2 dTex and a length of 8 mm was impregnated with 10 weights of ammonium monohydrogen phosphate, and heated in air at 350 ° C. for 30 minutes to prepare a carbonized fiber. Subsequently, the temperature was raised to 850 ° C. at a rate of about 400 ° C./hour under a nitrogen stream, and after activation, activation was carried out by holding in an atmosphere having a water vapor concentration of 15% by volume for 60 minutes to obtain fibrous activated carbon. Heat treatment was performed in air at 450 ° C. for 8 minutes. The fibrous activated carbon thus obtained had an acidic group amount of 2.4 meq / g, a C═O / C ratio of 5.4%, and a specific surface area of 1450 m ² / g.
[0037]
67% by weight of this fibrous activated carbon was collected as a dry weight, and 7% by weight of polypropylene single fiber chopped fiber, 21% by weight of synthetic pulp made of polyethylene, and 5% by weight of polyethylene-polypropylene core-sheath fiber were added thereto. Wet paper was made to produce a paper-like material with a basis weight of 33 g / m ² and a thickness of 0.25 mm. This paper was joined to the plastic electrode substrate described above to obtain an electrode. The charge / discharge potential difference of the electrodes thus obtained is shown in Table 1.
[0038]
【The invention's effect】
As described above, the activated carbon and electrode material of the present invention improves the contact with the current collector plate by adding a large amount of C═O groups while keeping the amount of acidic groups per unit weight of the activated carbon to a predetermined amount. In addition, since bromine is effectively adsorbed, an electrode capable of obtaining a stable voltage even at a high current density can be obtained.
[Brief description of the drawings]
FIG. 1 is a schematic diagram of an apparatus used for electrode potential characteristics. FIG. 2 is a separation diagram of C1S peaks measured by XPS surface analysis according to bonding structure.

Claims

The total amount of acidic groups consisting of one or more of hydroxyl group (—OH), carboxyl group (—COOH), hydroxyamino group (—NH—OH) and hydroxyimino group (═N—OH) is 0.2 or more and 2 metal characterized in that .0meq / g or less and a carbon atom number of oxygen and the double bond determined from XPS surface analysis is not more than 7.3% over 2% of the total surface carbon atoms - halogen two Activated carbon for secondary battery composite electrodes.

The activated carbon for a metal-halogen secondary battery composite electrode according to claim 1, wherein the activated carbon is fibrous.

3. The activated carbon for a metal-halogen secondary battery composite electrode according to claim 1, wherein the activated carbon has a specific surface area of 500 to 2200 m ² / g.

Electrode material which is a halogen secondary battery composite electrode for the activated carbon contains more than 50 mass% configured paper-like material - claims 1 to metals according to any one of the three.