JP3851041B2 - Hydrogen storage alloy electrode - Google Patents
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- JP3851041B2 JP3851041B2 JP36548399A JP36548399A JP3851041B2 JP 3851041 B2 JP3851041 B2 JP 3851041B2 JP 36548399 A JP36548399 A JP 36548399A JP 36548399 A JP36548399 A JP 36548399A JP 3851041 B2 JP3851041 B2 JP 3851041B2
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
Description
【０００１】
【発明が属する技術分野】
本発明は、水素吸蔵合金電極に係わり、詳しくは、高率放電特性、充放電サイクル特性等の電池特性に優れる密閉型アルカリ蓄電池を与える水素吸蔵合金電極を提供することを目的とした、導電剤の改良に関する。
【０００２】
【従来の技術及び発明が解決しようとする課題】
近年、水素吸蔵合金電極を負極として使用した密閉型アルカリ蓄電池が、従前のカドミウム電極及び亜鉛電極を負極として使用したものに比べて、エネルギー密度が高いことから、注目されている。水素吸蔵合金電極は、集電体上に水素吸蔵合金を主材とする混合結着体からなる活物質層を形成することにより作製される。
【０００３】
水素吸蔵合金電極では、その活物質利用率及び電極容量を向上させるために、導電剤が水素吸蔵合金に添加される。
【０００４】
導電剤としては、アセチレンブラック等の炭素粉末、ニッケル粉末、ニッケルフレークなどが使用される。しかし、炭素粉末を使用した場合は、少量で導電性を付与することができるものの、水素吸蔵合金との均一な混合結着体を得ることが困難であるために、活物質利用率及び電極容量のいずれもさほど向上しない。一方、ニッケル粉末又はニッケルフレークを使用した場合には、活物質利用率は向上するものの、そのためにはこれらを多量に使用する必要があるので、水素吸蔵合金の充填量が減少し、そのため電極容量はさほど向上しない。
【０００５】
上記の問題を解決した水素吸蔵合金電極として、導電剤に炭素繊維を使用したものが提案されている（特開昭６３−１１０５５２号公報）。同公報によれば、導電剤として炭素繊維を使用することにより、導電性及び機械的強度に優れた水素吸蔵合金電極が得られるとのことである。
【０００６】
しかしながら、炭素繊維をそのまま使用した上記の水素吸蔵合金電極を使用した密閉型アルカリ蓄電池は、高率放電特性、充放電サイクル特性などが充分でなく、これらについての改良が望まれていた。
【０００７】
したがって、本発明は、高率放電特性、充放電サイクル特性等の電池特性が良い密閉型アルカリ蓄電池を与える水素吸蔵合金電極を提供することを目的とする。
【０００８】
【課題を解決するための手段】
上記目的を達成するための本発明に係る水素吸蔵合金電極（本発明電極）は、集電体と、当該集電体上に形成され、水素吸蔵合金と導電剤との混合結着体からなる活物質層とを備える水素吸蔵合金電極において、前記導電剤が、長さ方向に平行に走る多数の空孔を有する炭素繊維と、当該炭素繊維の表面を被覆する銅被覆層とからなり、その両端部が無被覆の銅被覆炭素繊維であることを特徴とする。
【０００９】
本発明電極は、導電剤として銅被覆炭素繊維を使用しているので、これを負極として使用することにより、炭素繊維をそのまま使用した従来の水素吸蔵合金電極を使用した場合に比べて、高率放電特性、充放電サイクル特性などが良い密閉型アルカリ蓄電池を得ることができる。高率放電特性が良い電池が得られるのは、銅の電導度が炭素（繊維）のそれに比べて高いからである。また、充放電サイクル特性が良い電池が得られるのは、銅の酸素過電圧が炭素（繊維）のそれに比べて小さいために、充電末期及び過充電時に正極で発生する酸素ガスが効率良く還元され、その結果、電池缶内の酸素分圧が低下して水素吸蔵合金の酸化劣化が抑制されるからである。
【００１０】
本発明における導電剤は、炭素繊維と、当該炭素繊維の表面を被覆する銅被覆層とからなる銅被覆炭素繊維である。炭素粉末ではなく、炭素繊維を使用することとしているのは、炭素繊維は導電剤として機能する外、電極の構造強化剤としても機能し得るからである。炭素繊維としては、繊維径が０．１〜１０μｍ程度、繊維長が０．０１〜１ｍｍ程度のものが好ましい。銅被覆層の厚みは、０．０５〜１．０μｍが好ましい。同厚みが０．０５μｍ未満の場合は、銅不足のため、一方同厚みが１．０μｍを越えた場合は、柔軟性が低下して銅被覆炭素繊維の分散性が低下するため、いずれの場合も導電性を充分に高めることができなくなる。本発明における銅被覆炭素繊維は、その両端部が無被覆のものである。両端部を露出させることにより、正極で発生した酸素ガスが、炭素繊維の長さ方向に平行に走る（すなわち炭素繊維の長さ方向に沿って走る）多数の空孔を通って水素吸蔵合金電極内に速やかに拡散し、効率良く還元されるからである。すなわち、炭素繊維の空孔が、酸素ガス拡散のための通路を提供する。銅被覆層の形成方法としては、めっき（電気めっき及び無電解めっき）及びスパッタリングが例示される。両端部が無被覆の銅被覆炭素繊維は、例えば、炭素繊維全体を銅めっきした後、所定寸法に切断して銅被覆炭素繊維の両端面を露出させることにより得ることができる。
【００１１】
本発明における活物質層は、水素吸蔵合金と上記の銅被覆炭素繊維との混合結着体からなる。水素吸蔵合金の種類は、本発明の性質上、特に限定されない。具体例としては、組成式ＭｍＮｉx Ｃｏy Ｍz 〔式中、Ｍｍはミッシュメタル（希土類元素の混合物）；ＭはＡｌ、Ｍｇ、Ｍｎ、Ｆｅ、Ｓｎ、Ｓｉ、Ｗ、Ｚｎ、Ｚｎ、Ｃｒ及びＣｕからなる群より選ばれた少なくとも一種の元素；２．８≦ｘ≦４．４、０≦ｙ≦１．０、０≦ｚ≦１．５、４．５≦ｘ＋ｙ＋ｚ≦５．８〕で表される、ＣａＣｕ5 型結晶構造を有する水素吸蔵合金が挙げられる。活物質層中の水素吸蔵合金に対する銅被覆炭素繊維の比率は、０．０５〜１０．０重量％が好ましい。同比率が０．０５重量％未満の場合は、導電性を充分に高めることができず、一方同比率が１０．０重量％を越えた場合は、水素吸蔵合金の充填量が減少するとともに、銅被覆炭素繊維と水素吸蔵合金との均一な混合結着体を得ることが困難になるために、活物質利用率は向上するものの、電極容量はさほど増大しない。
【００１２】
【実施例】
以下、本発明を実施例に基づいてさらに詳細に説明するが、本発明は下記実施例に何ら限定されるものではなく、その要旨を変更しない範囲において適宜変更して実施することが可能なものである。
【００１３】
（実験１）
本発明電極及び比較電極を作製し、それらを使用して密閉型アルカリ蓄電池を作製し、各電池の高率放電特性、過充電特性及び充放電サイクル特性を調べた。
【００１４】
（実施例１）
〔水素吸蔵合金粉末の作製〕
合金原料をアルゴン雰囲気のアーク溶解炉内で加熱溶解させて得た溶湯を、単ロール法により冷却して組成式ＭｍＮｉ4.0 Ｃｏ0.2 Ａｌ0.3 Ｍｎ0.5 で表される水素吸蔵合金片を作製し、この水素吸蔵合金片を粉砕して、平均粒径約４０μｍの水素吸蔵合金粉末を作製した。
【００１５】
〔銅被覆炭素繊維の作製〕
直径５μｍの炭素繊維に銅を電気めっきして直径５．４μｍの銅被覆炭素繊維を作製した。次いで、この銅被覆炭素繊維を切断して、両端部が無被覆の直径５．４μｍ、長さ０．１ｍｍ、銅被覆層の厚み０．２μｍの銅被覆炭素繊維を作製した。炭素繊維及び銅被覆炭素繊維の直径は、任意の３箇所に於ける走査型電子顕微鏡（ＳＥＭ）による測定値の平均値である（３点法）。また、銅被覆層の厚みは、銅被覆炭素繊維の直径（平均直径）と炭素繊維の直径（平均直径）との差に１／２を乗じて求めた計算値である。以下に登場する銅被覆炭素繊維の直径、炭素繊維の直径及び銅被覆層の厚みも、同様にして求めた値である。
【００１６】
〔水素吸蔵合金電極の作製〕
上記の水素吸蔵合金粉末と、上記の銅被覆炭素繊維とを、重量比１００：１．０で混合し、得られた混合物に結着剤としての５重量％ポリエチレンオキシド水溶液を２０重量％添加混合してスラリーを調製し、このスラリーを集電体としてのパンチングメタルに塗布し、乾燥し、圧延し、所定の大きさに切断して、水素吸蔵合金電極Ａ１（本発明電極）を作製した。
【００１７】
（参考例１）
直径５μｍの炭素繊維を切断して、長さ０．１ｍｍの炭素繊維を作製した。次いで、この炭素繊維に銅を電気めっきして、直径５．４μｍ、長さ０．１ｍｍ、銅被覆層の厚み０．２μｍの、全体が銅で被覆された銅被覆炭素繊維を作製した。
【００１８】
水素吸蔵合金粉末（実施例１で作製したものと同じもの）と、上記の銅被覆炭素繊維とを、重量比１００：１．０で混合し、得られた混合物に結着剤としての５重量％ポリエチレンオキシド水溶液を２０重量％添加混合してスラリーを調製し、このスラリーを集電体としてのパンチングメタルに塗布し、乾燥し、圧延し、所定の大きさに切断して、水素吸蔵合金電極Ａ２（参考電極）を作製した。
【００１９】
（比較例１）
水素吸蔵合金粉末（実施例１で作製したものと同じもの）と、直径５μｍ、長さ０．１ｍｍの炭素繊維とを、重量比１００：１．０で混合し、得られた混合物に結着剤としての５重量％ポリエチレンオキシド水溶液を２０重量％添加混合してスラリーを調製し、このスラリーを集電体としてのパンチングメタルに塗布し、乾燥し、圧延し、所定の大きさに切断して、水素吸蔵合金電極Ｘ１（比較電極）を作製した。
【００２０】
（比較例２）
水素吸蔵合金粉末（実施例１で作製したものと同じもの）と、平均粒径２０μｍの銅粉末とを、重量比１００：１．０で混合し、得られた混合物に結着剤としての５重量％ポリエチレンオキシド水溶液を２０重量％添加混合してスラリーを調製し、このスラリーを集電体としてのパンチングメタルに塗布し、乾燥し、圧延し、所定の大きさに切断して、水素吸蔵合金電極Ｘ２（比較電極）を作製した。
【００２１】
（比較例３）
水素吸蔵合金粉末（実施例１で作製したものと同じもの）と、直径５μｍ、長さ０．１ｍｍの炭素繊維と、平均粒径２０μｍの銅粉末とを、重量比１００：０．５：０．５で混合し、得られた混合物に結着剤としての５重量％ポリエチレンオキシド水溶液を２０重量％添加混合してスラリーを調製し、このスラリーを集電体としてのパンチングメタルに塗布し、乾燥し、圧延し、所定の大きさに切断して、水素吸蔵合金電極Ｘ３（比較電極）を作製した。
【００２２】
（比較例４）
水素吸蔵合金粉末（実施例１で作製したものと同じもの）と、直径５μｍ、長さ０．１ｍｍの炭素繊維と、平均粒径２０μｍのカーボンブラックとを、重量比１００：０．５：０．５で混合し、得られた混合物に結着剤としての５重量％ポリエチレンオキシド水溶液を２０重量％添加混合してスラリーを調製し、このスラリーを集電体としてのパンチングメタルに塗布し、乾燥し、圧延し、所定の大きさに切断して、水素吸蔵合金電極Ｘ４（比較電極）を作製した。
【００２３】
〔密閉型アルカリ蓄電池の作製〕
上記の各水素吸蔵合金電極（負極）と、水酸化ニッケルを活物質とする公知の焼結式ニッケル極（正極）と、３０重量％水酸化カリウム水溶液（アルカリ電解液）とを用いて、ＡＡサイズの密閉型アルカリ蓄電池Ａ１及びＡ２並びにＸ１〜Ｘ４（電池容量：１０００ｍＡｈ）を作製した（電池符号は、使用した水素吸蔵合金電極を示す。以下の電池も同様である。）。セパレータとして、耐アルカリ性の不織布を使用した。なお、正極の容量を負極の容量より小さくして、電池の容量が正極の容量により規制されるようにした。
【００２４】
１００ｍＡで充放電を３回繰り返して、各電池を活性化した。次いで、下記の３つの特性を調べた。結果を表１に示す。
【００２５】
〈高率放電特性〉
常温（２５°Ｃ）にて、１００ｍＡで１６時間充電した後、５０００ｍＡで電池電圧が１Ｖに低下するまで放電して、放電容量を求めた。
【００２６】
〈過充電特性〉
６０°Ｃにて、１００ｍＡで２週間充電し、常温にて１０００ｍＡで電池電圧が１Ｖに低下するまで放電した。次いで、常温にて、１００ｍＡで１６時間充電した後、１０００ｍＡで電池電圧が１Ｖに低下するまで放電して、過充電後の放電容量を調べた。
【００２７】
〈充放電サイクル特性〉
常温にて、１０００ｍＡで１．２時間充電した後、１０００ｍＡで電池電圧が１Ｖに低下するまで放電する充放電を３００サイクル繰り返して、１サイクル目の放電容量Ｃ1 （ｍＡｈ）に対する３００サイクル目の放電容量Ｃ300 （ｍＡｈ）の比率〔（Ｃ300 ／Ｃ1 ）×１００（％）〕を求めた。
【００２８】
【表１】
表１より、本発明電極を負極として使用することにより、高率放電特性、過充電特性及び充放電サイクル特性の良い密閉型アルカリ蓄電池を得ることができることが分かる。また、本発明電池Ａ１と参考電池Ａ２との比較から、高率放電特性、充放電サイクル特性等の電池特性が極めて良い密閉型アルカリ蓄電池を与える水素吸蔵合金電極を得るためには、導電剤として、両端部が無被覆の銅被覆炭素繊維を使用する必要があることが分かる。
【００３０】
（実験２）
集電体上に形成する活物質層中の水素吸蔵合金に対する銅被覆炭素繊維の好適な比率を調べた。
【００３１】
水素吸蔵合金粉末（実施例１で作製したものと同じもの）と、銅被覆炭素繊維（実施例１で作製したものと同じもの）とを、重量比１００：０．０３、１００：０．０５、１００：０．１、１００：０．５、１００：５．０、１００：１０．０又は１００：１２．０で混合し、得られた混合物に結着剤としての５重量％ポリエチレンオキシド水溶液を２０重量％添加混合してスラリーを調製し、このスラリーを集電体としてのパンチングメタルに塗布し、乾燥し、圧延し、所定の大きさに切断して、順に、水素吸蔵合金電極Ａ３〜Ａ９（本発明電極）及び密閉型アルカリ蓄電池Ａ３〜Ａ９を作製した。
【００３２】
各電池について、実験１で行ったものと同じ条件の３種の試験を行い、高率放電特性、過充電特性及び充放電サイクル特性を調べた。結果を表２に示す。表２には、電池Ａ１についての結果も表１より転記して示してある。
【００３３】
【表２】
表２より、活物質層中の水素吸蔵合金に対する銅被覆炭素繊維の比率は、０．０５〜１０．０重量％が好ましいことが分かる。
【００３５】
（実験３）
銅被覆層の好適な厚みを調べた。
【００３６】
銅被覆炭素繊維の作製において、電気めっきのめっき時間を種々変えたこと以外は実施例１と同様にして、両端部が無被覆である直径５．４μｍ、長さ０．１ｍｍ、銅被覆層の厚み０．０１μｍ、０．０５μｍ、０．１μｍ、０．５μｍ、１．０μｍ又は１．５μｍの銅被覆炭素繊維を作製し、各銅被覆炭素繊維を導電剤として使用して、順に、水素吸蔵合金電極Ｂ１〜Ｂ６（本発明電極）及び密閉型アルカリ蓄電池Ｂ１〜Ｂ６を作製した。
【００３７】
各電池について、実験１で行ったものと同じ条件の３種の試験を行い、高率放電特性、過充電特性及び充放電サイクル特性を調べた。結果を表３に示す。表３には、電池Ａ１についての結果も表１より転記して示してある。
【００３８】
【表３】
表３より、銅被覆層の厚みは、０．０５〜１．０μｍが好ましいことが分かる。
【００４０】
【発明の効果】
高率放電特性、充放電サイクル特性等の電池特性が良い密閉型アルカリ蓄電池を与える水素吸蔵合金電極が提供される。[0001]
[Technical field to which the invention belongs]
The present invention relates to a hydrogen storage alloy electrode, and more particularly, to provide a hydrogen storage alloy electrode that provides a sealed alkaline storage battery excellent in battery characteristics such as high rate discharge characteristics and charge / discharge cycle characteristics. Regarding improvements.
[0002]
[Prior art and problems to be solved by the invention]
In recent years, a sealed alkaline storage battery using a hydrogen storage alloy electrode as a negative electrode has attracted attention because it has a higher energy density than those using conventional cadmium electrodes and zinc electrodes as a negative electrode. The hydrogen storage alloy electrode is manufactured by forming an active material layer made of a mixed binder mainly composed of a hydrogen storage alloy on a current collector.
[0003]
In the hydrogen storage alloy electrode, a conductive agent is added to the hydrogen storage alloy in order to improve the utilization ratio of the active material and the electrode capacity.
[0004]
As the conductive agent, carbon powder such as acetylene black, nickel powder, nickel flakes and the like are used. However, when carbon powder is used, the conductivity can be imparted in a small amount, but it is difficult to obtain a uniform mixed binder with the hydrogen storage alloy. None of them improve so much. On the other hand, when nickel powder or nickel flakes are used, the active material utilization rate is improved, but in order to do so, it is necessary to use a large amount of these, so the filling amount of the hydrogen storage alloy is reduced, and therefore the electrode capacity is reduced. It does not improve much.
[0005]
As a hydrogen storage alloy electrode that solves the above problems, an electrode using carbon fiber as a conductive agent has been proposed (Japanese Patent Laid-Open No. 63-110552). According to the publication, by using carbon fiber as a conductive agent, a hydrogen storage alloy electrode excellent in conductivity and mechanical strength can be obtained.
[0006]
However, the sealed alkaline storage battery using the hydrogen storage alloy electrode using carbon fiber as it is does not have high rate discharge characteristics, charge / discharge cycle characteristics, and the like, and improvements for these have been desired.
[0007]
Accordingly, an object of the present invention is to provide a hydrogen storage alloy electrode that provides a sealed alkaline storage battery having good battery characteristics such as high rate discharge characteristics and charge / discharge cycle characteristics.
[0008]
[Means for Solving the Problems]
In order to achieve the above object, a hydrogen storage alloy electrode according to the present invention (electrode of the present invention) comprises a current collector and a mixed binder of a hydrogen storage alloy and a conductive agent formed on the current collector. in the hydrogen storage alloy electrode comprising an active material layer, the conductive agent, Ri Do from carbon fibers having a large number of holes running parallel to the length direction, and the copper coating layer covering the surface of the carbon fiber, Both ends are uncoated copper-coated carbon fibers.
[0009]
Since the present invention electrode uses copper-coated carbon fiber as a conductive agent, using this as a negative electrode has a higher rate than when using a conventional hydrogen storage alloy electrode using carbon fiber as it is. A sealed alkaline storage battery having good discharge characteristics, charge / discharge cycle characteristics, and the like can be obtained. The reason why a battery with good high rate discharge characteristics is obtained is that the conductivity of copper is higher than that of carbon (fiber). In addition, a battery with good charge / discharge cycle characteristics is obtained because the oxygen overvoltage of copper is smaller than that of carbon (fiber), so the oxygen gas generated at the positive electrode at the end of charge and overcharge is efficiently reduced, As a result, the oxygen partial pressure in the battery can decreases, and the oxidative deterioration of the hydrogen storage alloy is suppressed.
[0010]
The electrically conductive agent in this invention is a copper covering carbon fiber which consists of a carbon fiber and the copper coating layer which coat | covers the surface of the said carbon fiber. The reason why carbon fiber is used instead of carbon powder is that carbon fiber functions not only as a conductive agent but also as a structure reinforcing agent for electrodes. Carbon fibers having a fiber diameter of about 0.1 to 10 μm and a fiber length of about 0.01 to 1 mm are preferable. The thickness of the copper coating layer is preferably 0.05 to 1.0 μm. When the thickness is less than 0.05 μm, copper is insufficient. On the other hand, when the thickness exceeds 1.0 μm, the flexibility decreases and the dispersibility of the copper-coated carbon fiber decreases. However, the conductivity cannot be sufficiently increased. The copper-coated carbon fibers in the present invention are uncoated at both ends. By exposing both ends, the oxygen gas generated at the positive electrode runs in parallel to the length direction of the carbon fiber (that is , runs along the length direction of the carbon fiber) and passes through a number of pores. This is because it diffuses quickly and is efficiently reduced. That is, the carbon fiber vacancies provide a passage for oxygen gas diffusion. Examples of the method for forming the copper coating layer include plating (electroplating and electroless plating) and sputtering. The copper-coated carbon fiber having both ends uncoated can be obtained, for example, by copper-plating the entire carbon fiber and then cutting to a predetermined size to expose both end surfaces of the copper-coated carbon fiber.
[0011]
The active material layer in this invention consists of a mixed binding body of a hydrogen storage alloy and said copper covering carbon fiber. The kind of hydrogen storage alloy is not particularly limited due to the nature of the present invention. Specific examples, in the composition formula MmNi x Co y M z [wherein, Mm is the (mixture of rare earth elements) mischmetal; M is Al, Mg, Mn, Fe, Sn, Si, W, Zn, Zn, Cr and At least one element selected from the group consisting of Cu; 2.8 ≦ x ≦ 4.4, 0 ≦ y ≦ 1.0, 0 ≦ z ≦ 1.5, 4.5 ≦ x + y + z ≦ 5.8] Examples thereof include hydrogen storage alloys having a CaCu 5 type crystal structure. The ratio of the copper-coated carbon fiber to the hydrogen storage alloy in the active material layer is preferably 0.05 to 10.0% by weight. When the ratio is less than 0.05% by weight, the electrical conductivity cannot be sufficiently increased. On the other hand, when the ratio exceeds 10.0% by weight, the filling amount of the hydrogen storage alloy decreases, Since it becomes difficult to obtain a uniform mixed binder of copper-coated carbon fiber and hydrogen storage alloy, the active material utilization rate is improved, but the electrode capacity does not increase so much.
[0012]
【Example】
Hereinafter, the present invention will be described in more detail on the basis of examples. However, the present invention is not limited to the following examples, and can be implemented with appropriate modifications without departing from the scope of the present invention. It is.
[0013]
(Experiment 1)
The electrode of the present invention and the comparative electrode were produced, and sealed alkaline storage batteries were produced using them, and the high rate discharge characteristics, overcharge characteristics and charge / discharge cycle characteristics of each battery were examined.
[0014]
Example 1
[Production of hydrogen storage alloy powder]
A molten metal obtained by heating and melting the alloy raw material in an arc melting furnace in an argon atmosphere is cooled by a single roll method to produce a hydrogen storage alloy piece represented by the composition formula MmNi 4.0 Co 0.2 Al 0.3 Mn 0.5. The hydrogen storage alloy pieces were pulverized to produce hydrogen storage alloy powder having an average particle size of about 40 μm.
[0015]
[Preparation of copper-coated carbon fiber]
Copper was electroplated on a carbon fiber having a diameter of 5 μm to produce a copper-coated carbon fiber having a diameter of 5.4 μm. Next, this copper-coated carbon fiber was cut to produce a copper-coated carbon fiber having a diameter of 5.4 μm, a length of 0.1 mm, and a copper coating layer thickness of 0.2 μm at both ends. The diameters of the carbon fiber and the copper-coated carbon fiber are average values measured by a scanning electron microscope (SEM) at any three locations (three-point method). The thickness of the copper coating layer is a calculated value obtained by multiplying the difference between the diameter (average diameter) of the copper-coated carbon fiber and the diameter (average diameter) of the carbon fiber by 1/2. The diameter of the copper-coated carbon fiber, the diameter of the carbon fiber, and the thickness of the copper coating layer appearing below are values obtained in the same manner.
[0016]
[Production of hydrogen storage alloy electrode]
The above hydrogen storage alloy powder and the above copper-coated carbon fiber are mixed at a weight ratio of 100: 1.0, and 20% by weight of a 5% by weight polyethylene oxide aqueous solution as a binder is added to the resulting mixture. A slurry was prepared, and this slurry was applied to a punching metal as a current collector, dried, rolled, and cut into a predetermined size to produce a hydrogen storage alloy electrode A1 (electrode of the present invention).
[0017]
( Reference Example 1 )
A carbon fiber having a length of 0.1 mm was produced by cutting a carbon fiber having a diameter of 5 μm. Subsequently, copper was electroplated on the carbon fiber to produce a copper-coated carbon fiber having a diameter of 5.4 μm, a length of 0.1 mm, and a copper coating layer thickness of 0.2 μm, which was entirely coated with copper.
[0018]
Hydrogen storage alloy powder (the same as that prepared in Example 1) and the above-mentioned copper-coated carbon fiber were mixed at a weight ratio of 100: 1.0, and 5 wt. A 20 wt% aqueous solution of polyethylene oxide was added and mixed to prepare a slurry, which was applied to a punching metal as a current collector, dried, rolled, cut into a predetermined size, and a hydrogen storage alloy electrode A2 ( reference electrode ) was produced.
[0019]
(Comparative Example 1)
Hydrogen storage alloy powder (same as that prepared in Example 1) and carbon fiber having a diameter of 5 μm and a length of 0.1 mm were mixed at a weight ratio of 100: 1.0 and bound to the resulting mixture. A slurry is prepared by adding 20% by weight of a 5% by weight polyethylene oxide aqueous solution as an agent, and this slurry is applied to a punching metal as a current collector, dried, rolled, and cut into a predetermined size. A hydrogen storage alloy electrode X1 (comparative electrode) was produced.
[0020]
(Comparative Example 2)
Hydrogen storage alloy powder (the same as that prepared in Example 1) and copper powder having an average particle diameter of 20 μm were mixed at a weight ratio of 100: 1.0, and the resulting mixture had 5 as a binder. A 20% by weight aqueous solution of polyethylene oxide is added and mixed to prepare a slurry. The slurry is applied to a punching metal as a current collector, dried, rolled, cut into a predetermined size, and a hydrogen storage alloy. Electrode X2 (comparative electrode) was produced.
[0021]
(Comparative Example 3)
A hydrogen storage alloy powder (the same as that prepared in Example 1), carbon fiber having a diameter of 5 μm and a length of 0.1 mm, and copper powder having an average particle diameter of 20 μm are weight ratio of 100: 0.5: 0. The resulting mixture was mixed with 20 wt% of 5 wt% polyethylene oxide aqueous solution as a binder to prepare a slurry, and this slurry was applied to punching metal as a current collector and dried. And it rolled and cut | disconnected to the predetermined magnitude | size, and produced hydrogen storage alloy electrode X3 (comparative electrode).
[0022]
(Comparative Example 4)
A hydrogen storage alloy powder (the same as that prepared in Example 1), a carbon fiber having a diameter of 5 μm and a length of 0.1 mm, and a carbon black having an average particle diameter of 20 μm are weight ratio of 100: 0.5: 0. The resulting mixture was mixed with 20 wt% of 5 wt% polyethylene oxide aqueous solution as a binder to prepare a slurry, and this slurry was applied to punching metal as a current collector and dried. And it rolled and cut | disconnected to the predetermined magnitude | size, and produced hydrogen storage alloy electrode X4 (comparative electrode).
[0023]
(Production of sealed alkaline storage battery)
Using each of the above hydrogen storage alloy electrodes (negative electrode), a known sintered nickel electrode (positive electrode) using nickel hydroxide as an active material, and a 30 wt% aqueous potassium hydroxide solution (alkaline electrolyte), AA Size sealed alkaline storage batteries A1 and A2 and X1 to X4 (battery capacity: 1000 mAh) were produced (battery symbols indicate the hydrogen storage alloy electrodes used. The same applies to the following batteries). As the separator, an alkali-resistant non-woven fabric was used. In addition, the capacity of the positive electrode was made smaller than the capacity of the negative electrode so that the capacity of the battery was regulated by the capacity of the positive electrode.
[0024]
Charging / discharging was repeated 3 times at 100 mA to activate each battery. Next, the following three characteristics were examined. The results are shown in Table 1.
[0025]
<High rate discharge characteristics>
After charging at 100 mA for 16 hours at room temperature (25 ° C.), the battery was discharged at 5000 mA until the battery voltage dropped to 1 V, and the discharge capacity was determined.
[0026]
<Overcharge characteristics>
The battery was charged at 100 ° C. for 2 weeks at 60 ° C., and discharged at 1000 mA at room temperature until the battery voltage dropped to 1V. Next, after charging at 100 mA for 16 hours at room temperature, the battery was discharged at 1000 mA until the battery voltage dropped to 1 V, and the discharge capacity after overcharging was examined.
[0027]
<Charge / discharge cycle characteristics>
After charging at 1000 mA for 1.2 hours at room temperature, charging and discharging are repeated for 300 cycles until the battery voltage drops to 1 V at 1000 mA, and the 300th cycle with respect to the discharge capacity C 1 (mAh) of the first cycle is repeated. The ratio [(C 300 / C 1 ) × 100 (%)] of the discharge capacity C 300 (mAh) was determined.
[0028]
[Table 1]
From Table 1, it can be seen that by using the electrode of the present invention as a negative electrode, a sealed alkaline storage battery having good high rate discharge characteristics, overcharge characteristics and charge / discharge cycle characteristics can be obtained. In addition, in order to obtain a hydrogen storage alloy electrode that gives a sealed alkaline storage battery having extremely good battery characteristics such as high rate discharge characteristics and charge / discharge cycle characteristics from comparison between the present invention battery A1 and the reference battery A2 , as a conductive agent It can be seen that it is necessary to use copper-coated carbon fibers that are uncoated at both ends.
[0030]
(Experiment 2)
A suitable ratio of the copper-coated carbon fiber to the hydrogen storage alloy in the active material layer formed on the current collector was examined.
[0031]
Hydrogen storage alloy powder (same as that prepared in Example 1) and copper-coated carbon fiber (same as that prepared in Example 1) were in a weight ratio of 100: 0.03, 100: 0.05. , 100: 0.1, 100: 0.5, 100: 5.0, 100: 10.0 or 100: 12.0, and 5% by weight aqueous polyethylene oxide solution as a binder in the resulting mixture Is added to and mixed with 20% by weight of the slurry, and the slurry is applied to a punching metal as a current collector, dried, rolled, cut into a predetermined size, and sequentially filled with hydrogen storage alloy electrodes A3 to A3. A9 (electrode of the present invention) and sealed alkaline storage batteries A3 to A9 were produced.
[0032]
For each battery, three types of tests were performed under the same conditions as those performed in Experiment 1, and high-rate discharge characteristics, overcharge characteristics, and charge / discharge cycle characteristics were examined. The results are shown in Table 2. Table 2 also shows the results for battery A1 transcribed from Table 1.
[0033]
[Table 2]
From Table 2, it can be seen that the ratio of the copper-coated carbon fiber to the hydrogen storage alloy in the active material layer is preferably 0.05 to 10.0% by weight.
[0035]
(Experiment 3)
A suitable thickness of the copper coating layer was examined.
[0036]
In the production of the copper-coated carbon fiber, except that the electroplating time was variously changed, the diameter was 5.4 μm, the length was 0.1 mm, and the copper coating layer was uncoated at both ends in the same manner as Example 1. Fabricate copper-coated carbon fibers with a thickness of 0.01 μm, 0.05 μm, 0.1 μm, 0.5 μm, 1.0 μm, or 1.5 μm, and use each copper-coated carbon fiber as a conductive agent in order to store hydrogen. Alloy electrodes B1 to B6 (electrodes of the present invention) and sealed alkaline storage batteries B1 to B6 were produced.
[0037]
For each battery, three types of tests were performed under the same conditions as those performed in Experiment 1, and high-rate discharge characteristics, overcharge characteristics, and charge / discharge cycle characteristics were examined. The results are shown in Table 3. Table 3 also shows the results for battery A1 transcribed from Table 1.
[0038]
[Table 3]
From Table 3, it can be seen that the thickness of the copper coating layer is preferably 0.05 to 1.0 μm.
[0040]
【The invention's effect】
Provided is a hydrogen storage alloy electrode that provides a sealed alkaline storage battery having good battery characteristics such as high rate discharge characteristics and charge / discharge cycle characteristics.
Claims (4)
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| JP36548399A JP3851041B2 (en) | 1999-12-22 | 1999-12-22 | Hydrogen storage alloy electrode |
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