JP3695815B2

JP3695815B2 - Method for producing hydrogen storage alloy electrode

Info

Publication number: JP3695815B2
Application number: JP33856995A
Authority: JP
Inventors: 忠司伊勢
Original assignee: Sanyo Electric Co Ltd
Current assignee: Sanyo Electric Co Ltd
Priority date: 1995-12-26
Filing date: 1995-12-26
Publication date: 2005-09-14
Anticipated expiration: 2015-12-26
Also published as: JPH09180712A

Description

【０００１】
【発明の属する技術分野】
本発明は、水素吸蔵合金電極に関する。
【０００２】
【従来の技術】
負極活物質として水素を可逆的に吸蔵放出することができる水素吸蔵合金を用いたアルカリ蓄電池は、高エネルギー密度であり、過充電・過放電に強く、更に高率放電特性にも優れることから、携帯用電子機器等の駆動電源として近年、急速に需要が拡大している。そして、一層の高容量化により更なる用途の拡大が期待できる電池である。
【０００３】
ところで、水素吸蔵合金電極は、活物質である水素吸蔵合金粉末に合成繊維などの補強材や糊料を加えて混練しペースト状としたものを、パンチングメタルや発泡ニッケルなどの導電性基体に塗着・保持させる方法により製造される。したがって、導電性基体に対する充填密度の大小が、電極の単位体積当たりの電気容量を決定する要因となる。このため、従来より、導電性基体を高多孔度化して充填密度を高める方法や、水素吸蔵合金粉末の粒度を調整して充填密度を高める方法等の手段が採られてきた。
【０００４】
しかしながら、導電性基体の更なる高多孔度化は容易ではない。また水素吸蔵合金の粒度を調整する従来の方法は十分に効果を上げていない。他方、合金ペーストを導電性基体へ塗着・充填した後に、より大きい加圧力で圧延し充填密度を高める方法も考えられるが、水素吸蔵合金は基体を破壊しない範囲の加圧力では塑性変形を受けないため、この方法によって充填密度を高めることは困難である。更に、仮に高多孔度な基体を用いる場合であっても、合金粉末の充填性が悪ければ電極充填密度を高めることができない。したがって、合金粉末の充填性の良否は更なる高エネルギー密度化の重要な要素となる。しかし、従来、水素吸蔵合金においては充填密度を高める見地からする粉体工学的研究は殆どなされていない。
【０００５】
【発明が解決しようとする課題】
本発明は、上記に鑑みなされたものであって、粉体特性の面から電極基体に対する水素吸蔵合金の充填密度を高め得る簡易な手段を提供し、もってコストアップを伴うことなく高容量の水素吸蔵合金電極を得ようとするものである。
【０００６】
【課題を解決するための手段】
上記目的を達成するために、本発明第１の態様は、球状ないし略球状の水素吸蔵合金を作製する工程と、前記球状ないし略球状の水素吸蔵合金を粉砕して球状ないし略球状以外の水素吸蔵合金と成す工程と、安息角が２５度〜４０度になるように、前記球状ないし略球状の水素吸蔵合金と前記球状ないし略球状以外の水素吸蔵合金とを混合して、安息角が２５度〜４０度の水素吸蔵合金粉末を調製する工程と、前記水素吸蔵合金粉末を用いて活物質ペーストを調製する工程と、前記活物質ペーストを電極基体に保持させる工程と、前記活物質ペーストを保持させた電極基体を圧延する工程と、を備える水素吸蔵合金電極の製造方法であることを特徴とする。
【０００７】
本発明第２の態様は、球状ないし略球状の水素吸蔵合金と、球状ないし略球状以外の水素吸蔵合金とを、混合粉末の安息角が２５度〜４０度になるように混合調整する安息角調整工程と、安息角の調整された水素吸蔵合金粉末を用いて活物質ペーストを調製する活物質ペースト調製工程と、活物質ペーストを電極基体に充填する充填工程と、前記充填工程の後、電極基体を圧延して水素吸蔵合金粉末の充填密度が４．６ｇ／ｃｃ以上である水素吸蔵合金電極を作製する工程と、を備える水素吸蔵合金電極の製造方法であることを特徴とする。
【０００９】
ここで、上記における安息角とは、粉末堆積層の自由表面が静的平衡状態で水平面に対してなす角度を指し、より具体的には、図２に示すように、水素吸蔵合金粉末をロートを介して水平な平板上に落下させたときに形成される三角形状の堆積物の平均斜度θをいう。また、「球状ないし略球状」とは、最も広義の意味における球形や楕円形を指し、長径／短径比が３以下ほどで、角（鋭角）のない形状の粒子を意味する。他方、「球状及び略球状以外」とは「球状ないし略球状」以外の形状をした粒子を意味する。但し、これらは前者と後者の比較に基づく概念であり、粉流体全体をマクロ的に把握（粉体工学的に把握）した場合における概念である。したがって、例えば「球状及び略球状以外」の合金粉末には、「球状ないし略球状」の合金粒子が全く存在しないことを意味するものではない。
【００１０】
ところで、電極基体に対する水素吸蔵合金の充填密度を高めれば、その分電極の体積当たりの電気容量が高まるが、前述の如く電極基体の更なる高多孔度化は容易ではなく、その開発には多大なコストを要するとともに、例え高多孔度の基体を用いた場合であっても、水素吸蔵合金の充填特性が悪ければ高密度な充填を実現し得ない。したがって、水素吸蔵合金電極の容量を改善するためには、充填される側である電極基体の改良に加え、またはこれとは別個に、合金粉末自体の充填性を改善することが重要になる。
【００１１】
本発明者は、水素吸蔵合金電極の体積当たりの容量を向上させる目的で、電極基体に対する水素吸蔵合金粉末の充填特性を検討したところ、水素吸蔵合金電極においては、合金粉末のカサ密度を大きくしても、必ずしも高密度に充填できないということを知った。そこで、粉体特性をマクロ的に表現するもう一つの指数である安息角を用いて、安息角と電極充填密度の関係を検討したところ、電極充填密度と安息角には密接な関係があるという知見を得、本発明を完成させた。
【００１２】
即ち、安息角を一定範囲（２５度〜４０度）に規定することにより電極基体に対し高密度充填が可能になる。一方、カサ密度の大きい合金粉末を用いたとしても、確実かつ安定して電極充填密度を高めることができない（図１参照）。また、球状ないし略球状の水素吸蔵合金と球状及び略球状以外の水素吸蔵合金とを混合することにより、任意かつ容易に混合粉末の安息角を所定値に調整できる。そして、この方法により２５度〜４０度の安息角に調整した水素吸蔵合金粉末を用いて電極を作製すれば、電極の充填密度を確実に向上させることができる。つまり、この方法を適用すれば、新たに特別な製造装置を用意する必要がないので、低コストでエネルギー密度の高い水素吸蔵合金電極を得ることができる。
【００１３】
ところで、水素吸蔵合金粉末の安息角は、合金の形状や粒度などの他、合金の表面状態によっても大きく影響される。本発明では、これらの要因が互いに影響しあった結果現れるマクロ的な現象としての充填特性（粉体特性）を安息角で規定しようとするものである。したがって、安息角の調整手段は、機械的方法に限られるものではない。即ち、物理的手段や化学的手段によって合金表面の状態を変化させる方法で２５度〜４０度の安息角を有する合金粉末となし、これを用いて水素吸蔵合金電極を形成することも本発明が意図する範囲であり、また機械的手段と物理的手段や化学的手段を併用することも本発明の意図する範囲である。
【００１４】
合金表面の状態を変化させる物理的手段としては例えば熱処理法があり、化学的手段としては、例えばアルカリ表面処理法、酸表面処理法がある。なお、これらの手段で合金表面がすべり摩擦の小さくなるように改質された場合には、一般に安息角は減少し、すべり摩擦が大きくなるように改質された場合には、一般に安息角は大きくなる。
【００１５】
【実施の形態】
以下、本発明の実施の形態を具体的に説明する。
（水素吸蔵合金粉末の調製）
▲１▼市販のＭｍ（ミッシュメタル）、Ｎｉ、Ｃｏ、Ａｌ、Ｍｎを元素比で1：3.4：0.8：10.2：0.6 となるように秤量し、これら元素を不活性雰囲気下の高周波溶解炉で溶融混合した後、鋳型に流し込む方法により水素吸蔵合金鋳塊〔Ｘ₁〕を作製した。この製法で作製される合金は、角のある歪な形状をしたものとなる。
【００１６】
▲２▼上記と同様の組成および同様な方法で作製した合金溶融物を、アルゴンガス圧により細孔より噴霧し急冷するガスアトマイズ法を用い、１００μｍ前後の水素吸蔵合金〔Ｙ₁〕を作製した。この製法によると、球状ないし略球状の形状をした合金粒子が得られる。
【００１７】
▲３▼上記合金Ｘ₁を不活性ガス中でボールミルで粉砕して、粉砕合金〔Ｘ₂〕を作製した。なお、水素吸蔵合金は、ボールミルで機械的に粉砕した場合、合金粒子が割れて微細化するが、球状ないし略球状の形状に変化することはない。つまり、合金Ｘ₂は、角のある歪な形状をした合金（球状及び略球状以外の合金）となっている。
【００１８】
▲４▼上記合金Ｙ₁を不活性ガス中でボールミルで粉砕して、粉砕合金〔Ｙ₂〕を作製した。このボールミルによる機械的粉砕によって、球状ないし略球状の合金Ｙ₁が、粉砕されて球状及び略球状以外の形状に変化する。つまり、合金Ｙ₂は、角のある歪な形状をした合金（球状及び略球状以外の合金）となっている。
【００１９】
上記で作製した各合金を篩を用いて分級し、平均粒径５０μｍおよび３０μｍの合金を得、これらの合金粉末を所定割合で混合して、表１に示す１５通りの混合粉末を作製した。なお、説明の都合上、混合比率が０％のもの（単一合金粉末）についても混合粉末と称することにする。
【００２０】
上記１５通りの混合粉末（Ｎｏ. １〜１５）のタップカサ密度と安息角とを測定するとともに、これらの混合粉末を電極活物質として用いた水素吸蔵合金電極Ｎｏ. １〜１５を作製した。そして、混合粉末のタップカサ密度および安息角と電極充填密度との関係を調べた。
【００２１】
安息角の測定方法は次のようにした。合金粉末２００ｇを出口径５ｍｍのロートを通過させ、ロート出口より３ｃｍ下方にある平板上に落下し堆積させ、この堆積物を写真撮影して写真上で堆積物の平均的斜度θを測定し、これを安息角とした（図２参照）。また、タップカサ密度は、内径２０ｍｍ、容量５０ｃｃのメスシリンダーに１００ｇの合金粉末を入れて１００回上下方向に振動（タップ）する方法により求めた。
【００２２】
他方、水素吸蔵合金電極は、合金粉末に、５重量％のポリエチレンオキサイド水溶液（結着剤）を合金粉末重量に対して１０％加え、混練して合金ペーストとなし、この合金ペーストをパンチングメタルからなる集電体（電極基体）の両面に塗着し、乾燥した後、一定圧力でローラープレスする方法により作製した。そして、この電極の大きさ及び厚みと重量を測定し、これらの測定値から計算により電極中における合金の密度（電極充填密度とする）を算出した。
【００２３】
表１に混合粉末の混合比率、タップカサ密度、安息角および電極充填密度を一覧表示する。また、粉体特性値（安息角およびタップ密度）と電極充填密度の関係を判り易くするために、各特性値の大小関係と各混合粉末Ｎｏ. との相関を図１に示す。図１において破線で囲んだ部分が本発明で規定した範囲である。
【００２４】
【表１】

【００２５】
表１から次のことが明らかになる。球状及び略球状以外の合金粉末Ｘ₂、Ｙ₂のみからなるＮｏ. １、Ｎｏ. ３、及び球状ないし略球状合金粉末Ｙ₁のみからなるＮｏ. ２の比較から、平均粒径が同じであっても合金粉末の種類が異なるとタップカサ密度、安息角に大幅な差が生じることがわかる。一方、平均粒径が５０μｍのＮｏ. １と平均粒径が３０μｍのＮｏ. １０の各特性値の比較から、平均粒径を小さくしても必ずしも電極充填密度が大きくならないことがわかる。つまり、合金粉末の種類が異なると粉体特性が大きく異なるとともに、平均粒径の大小から予測される電極充填密度と実際の充填密度とに食い違いが生じる。よって、平均粒径を指標として電極充填密度を予測することは困難であることが理解できる。
【００２６】
混合粉末Ｎｏ. ４〜Ｎｏ. ９、Ｎｏ. １２〜Ｎｏ. １５において、各種合金粉末の混合比率と粉体特性の関係を見ると、使用する合金粉末の種類や混合比率により各特性値が変動し、好適な配合において電極充填特性が向上することが判る。即ち、球状及び略球状以外の合金粉末Ｘ₂のみからなるＮｏ. １およびＮｏ. １０や、平均粒径５０μｍの球状ないし略球状の合金粉末Ｙ₁のみからなるＮｏ. ２では、十分な電極充填密度が得られない。しかし、これらの合金粉末に逆の形状の合金粉末を適当な比率で混合した場合、電極充填密度を向上させることができる（Ｎｏ. ５〜Ｎｏ. ７、Ｎｏ. ９、Ｎｏ. １３〜Ｎｏ. １５を参照）。
【００２７】
次に、図１において、Ｎｏ. １〜Ｎｏ. １５の電極充填密度を大きい順に配列し、タップカサ密度および安息角との関係をみると、安息角が２５度以上、４０度以下の混合粉末で４．４ｇ／ｃｃ以上の電極充填密度が確保されていることがわかる。これに対し、タップカサ密度を指標として電極充填密度４．４ｇ／ｃｃ以上のＮｏ. を拾うと、その下限値はタップカサ密度４．１ｇ／ｃｃの点になる。しかし、タップカサ密度４．１ｇ／ｃｃ以上には、電極充填密度が４．４ｇ／ｃｃ以上でないＮｏ. ２、Ｎｏ. ８が含まれることになり、タップカサ密度では電極充填密度を信頼性をもって判断できないことがわかる。
【００２８】
以上の結果から、安息角は、合金粉末の種類等に影響されず、かつ一定以上の電極充填密度とできる合金粉末の特性を簡便に表すことのできる指標として有用であることが実証されるとともに、安息角が２５度〜４０度の合金粉末を用いて水素吸蔵合金電極を作製することにより、高密度に合金が充填された電極を得ることができることが証明される。また、異なる性状の合金粉末を適当な比率で混合すれば、簡易に安息角を２５度〜４０度に調整でき、このような混合粉末であっても、高い電極充填密度を確保できることが明らかとなる。
【００２９】
なお、安息角が小さくかつタップカサ密度の大きいＮｏ. ２において、電極充填密度が小さかったのは、次の理由によると考えれる。即ち、Ｎｏ. ２は球状ないし略球状合金の合金粉末のみで構成されているため、流動性が良すぎる。よって、電極の圧延工程において電極に対し垂直方向に加えられた力が水平方向に分散し、これに伴い合金粒子が水平方向に逃げて（移動）しまうためである。
【００３０】
【発明の効果】
上述からから明らかなように、安息角を電極充填特性の指標とすることにより、簡便に電極充填密度の高い合金粉末を調整できる。したがって、本発明によれば、電極の製造コストを殆ど上昇させることなく、単位体積当たりの電気容量が大きい水素吸蔵合金電極を得ることができる。
【図面の簡単な説明】
【図１】各粉体特性値の大小関係と混合粉末Ｎｏ.との関係を示す説明図である。
【図２】安息角の測定方法を示す説明図である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a hydrogen storage alloy electrode.
[0002]
[Prior art]
An alkaline storage battery using a hydrogen storage alloy capable of reversibly occluding and releasing hydrogen as a negative electrode active material has a high energy density, is resistant to overcharge / overdischarge, and is also excellent in high rate discharge characteristics. In recent years, the demand for driving power sources for portable electronic devices has been rapidly expanding. And it is a battery which can expect further expansion of use by further increase in capacity.
[0003]
By the way, a hydrogen storage alloy electrode is prepared by adding a reinforcing material such as synthetic fiber or a paste to a hydrogen storage alloy powder, which is an active material, and kneading it into a paste, which is applied to a conductive substrate such as punching metal or nickel foam. Manufactured by a method of wearing and holding. Therefore, the magnitude of the packing density with respect to the conductive substrate is a factor that determines the electric capacity per unit volume of the electrode. For this reason, conventionally, means such as a method of increasing the packing density by increasing the porosity of the conductive substrate and a method of increasing the packing density by adjusting the particle size of the hydrogen storage alloy powder have been adopted.
[0004]
However, further increasing the porosity of the conductive substrate is not easy. Further, the conventional method for adjusting the particle size of the hydrogen storage alloy has not been sufficiently effective. On the other hand, a method of increasing the packing density by applying and filling the alloy paste to the conductive substrate and then increasing the packing density is conceivable. However, hydrogen storage alloys are subject to plastic deformation at a pressure that does not destroy the substrate. Therefore, it is difficult to increase the packing density by this method. Furthermore, even if a highly porous substrate is used, the electrode packing density cannot be increased if the filling ability of the alloy powder is poor. Therefore, the quality of the filling of the alloy powder is an important factor for further increasing the energy density. Conventionally, however, little research has been conducted on powder engineering from the viewpoint of increasing the packing density of hydrogen storage alloys.
[0005]
[Problems to be solved by the invention]
The present invention has been made in view of the above, and provides a simple means capable of increasing the filling density of the hydrogen storage alloy with respect to the electrode substrate from the viewpoint of powder characteristics, and thus has a high capacity of hydrogen without increasing the cost. An object of the present invention is to obtain a storage alloy electrode.
[0006]
[Means for Solving the Problems]
In order to achieve the above object, the first aspect of the present invention includes a step of producing a spherical or substantially spherical hydrogen storage alloy, and a pulverization of the spherical or substantially spherical hydrogen storage alloy to hydrogen other than the spherical or substantially spherical shape. The step of forming the storage alloy and the spherical or substantially spherical hydrogen storage alloy and the hydrogen storage alloy other than the spherical or substantially spherical shape are mixed so that the repose angle is 25 to 40 degrees, and the repose angle is 25. A step of preparing a hydrogen storage alloy powder having a temperature of 40 degrees, a step of preparing an active material paste using the hydrogen storage alloy powder, a step of holding the active material paste on an electrode base, and the active material paste. And a step of rolling the held electrode substrate . A method for producing a hydrogen storage alloy electrode .
[0007]
The second aspect of the present invention is a repose angle in which a spherical or substantially spherical hydrogen storage alloy and a hydrogen storage alloy other than a spherical or substantially spherical shape are mixed and adjusted so that the repose angle of the mixed powder is 25 degrees to 40 degrees. An adjustment step, an active material paste preparation step for preparing an active material paste using a hydrogen storage alloy powder having an angle of repose adjusted, a filling step for filling the electrode substrate with the active material paste, and an electrode after the filling step And a step of rolling the substrate to produce a hydrogen storage alloy electrode having a filling density of the hydrogen storage alloy powder of 4.6 g / cc or more .
[0009]
Here, the angle of repose in the above refers to an angle formed by the free surface of the powder deposition layer with respect to the horizontal plane in a static equilibrium state. More specifically, as shown in FIG. The average slope θ of the triangular deposit formed when dropped on a horizontal flat plate via The term “spherical or substantially spherical” refers to a sphere or ellipse in the broadest sense, and means a particle having a major axis / minor axis ratio of about 3 or less and no corner (acute angle). On the other hand, “spherical and other than substantially spherical” means particles having a shape other than “spherical or substantially spherical”. However, these are concepts based on the comparison between the former and the latter, and are concepts when the entire powdered fluid is grasped macroscopically (powdered by powder engineering). Therefore, for example, it does not mean that “spherical or substantially spherical” alloy powder does not contain any “spherical or substantially spherical” alloy particles.
[0010]
By the way, if the filling density of the hydrogen storage alloy with respect to the electrode substrate is increased, the electric capacity per unit volume of the electrode is increased accordingly. However, as described above, it is not easy to further increase the porosity of the electrode substrate. Even when a high-porosity substrate is used, high-density filling cannot be realized if the filling properties of the hydrogen storage alloy are poor. Therefore, in order to improve the capacity of the hydrogen storage alloy electrode, it is important to improve the filling property of the alloy powder itself in addition to or separately from the improvement of the electrode substrate on the side to be filled.
[0011]
The present inventor examined the filling characteristics of the hydrogen storage alloy powder with respect to the electrode substrate for the purpose of improving the capacity per volume of the hydrogen storage alloy electrode. In the hydrogen storage alloy electrode, the bulk density of the alloy powder was increased. But I knew that I couldn't always fill with high density. So, using the angle of repose, which is another index that expresses powder characteristics in a macro manner, we examined the relationship between the angle of repose and the electrode packing density, and found that there was a close relationship between the electrode packing density and the angle of repose. Knowledge was obtained and the present invention was completed.
[0012]
That is, by defining the angle of repose within a certain range (25 degrees to 40 degrees), it is possible to fill the electrode substrate with high density. On the other hand, even if an alloy powder having a high bulk density is used, the electrode packing density cannot be reliably and stably increased (see FIG. 1). Moreover, the repose angle of the mixed powder can be adjusted to a predetermined value arbitrarily and easily by mixing a spherical or substantially spherical hydrogen storage alloy with a spherical or non-spherical hydrogen storage alloy. And if an electrode is produced using the hydrogen storage alloy powder adjusted to the repose angle of 25 degree-40 degree | times by this method, the filling density of an electrode can be improved reliably. That is, if this method is applied, it is not necessary to newly prepare a special manufacturing apparatus, so that a hydrogen storage alloy electrode with high energy density can be obtained at low cost.
[0013]
By the way, the angle of repose of the hydrogen storage alloy powder is greatly influenced not only by the shape and particle size of the alloy but also by the surface state of the alloy. In the present invention, the filling characteristic (powder characteristic) as a macroscopic phenomenon that appears as a result of these factors affecting each other is intended to be defined by the angle of repose. Therefore, the repose angle adjusting means is not limited to a mechanical method. That is, the present invention also forms an alloy powder having an angle of repose of 25 to 40 degrees by a method of changing the state of the alloy surface by physical means or chemical means, and using this to form a hydrogen storage alloy electrode. It is the intended range, and the combined use of mechanical means and physical means or chemical means is also the intended scope of the present invention.
[0014]
Examples of physical means for changing the state of the alloy surface include a heat treatment method, and examples of chemical means include an alkali surface treatment method and an acid surface treatment method. In addition, when the alloy surface is modified to reduce sliding friction by these means, the angle of repose generally decreases, and when the alloy surface is modified to increase sliding friction, the angle of repose generally growing.
[0015]
Embodiment
Hereinafter, embodiments of the present invention will be specifically described.
(Preparation of hydrogen storage alloy powder)
(1) Commercially available Mm (Misch metal), Ni, Co, Al, and Mn are weighed so that the element ratio is 1: 3.4: 0.8: 10.2: 0.6, and these elements are measured in a high-frequency melting furnace in an inert atmosphere. After melting and mixing, a hydrogen storage alloy ingot [X ₁ ] was produced by pouring into a mold. An alloy produced by this manufacturing method has an angular and distorted shape.
[0016]
{Circle around (2)} A hydrogen storage alloy [Y ₁ ] of about 100 μm was produced using a gas atomization method in which an alloy melt produced by the same composition and the same method as above was sprayed from the pores by argon gas pressure and rapidly cooled. According to this manufacturing method, alloy particles having a spherical or substantially spherical shape can be obtained.
[0017]
(3) The alloy X ₁ was pulverized with a ball mill in an inert gas to prepare a pulverized alloy [X ₂ ]. Note that when the hydrogen storage alloy is mechanically pulverized by a ball mill, the alloy particles are cracked and refined, but do not change to a spherical or substantially spherical shape. That is, the alloy X ₂ is an alloy having an angular distortion shape (alloy other than spherical and substantially spherical).
[0018]
(4) The alloy Y ₁ was pulverized with a ball mill in an inert gas to prepare a pulverized alloy [Y ₂ ]. By the mechanical pulverization by the ball mill, the spherical or substantially spherical alloy Y ₁ is pulverized to change into a spherical shape or a shape other than the substantially spherical shape. That is, the alloy Y ₂ is an alloy having an angular distortion shape (alloy other than spherical and substantially spherical).
[0019]
Each alloy produced above was classified using a sieve to obtain alloys having an average particle diameter of 50 μm and 30 μm, and these alloy powders were mixed at a predetermined ratio to produce 15 kinds of mixed powders shown in Table 1. For convenience of explanation, a powder having a mixing ratio of 0% (single alloy powder) is also referred to as a mixed powder.
[0020]
While measuring the tap bulk density and the angle of repose of the 15 mixed powders (No. 1-15), hydrogen storage alloy electrodes No. 1-15 using these mixed powders as electrode active materials were produced. Then, the relationship between the tap bulk density and repose angle of the mixed powder and the electrode packing density was examined.
[0021]
The angle of repose was measured as follows. 200 g of alloy powder is passed through a funnel having an outlet diameter of 5 mm, dropped and deposited on a flat plate 3 cm below the funnel outlet, and this deposit is photographed to measure the average inclination θ of the deposit on the photograph. This was taken as the angle of repose (see FIG. 2). Further, the tap bulk density was determined by a method in which 100 g of alloy powder was put into a measuring cylinder having an inner diameter of 20 mm and a capacity of 50 cc and vibrated (tapped) 100 times in the vertical direction.
[0022]
On the other hand, in the hydrogen storage alloy electrode, 5% by weight of a polyethylene oxide aqueous solution (binder) is added to the alloy powder in an amount of 10% with respect to the weight of the alloy powder, and kneaded to form an alloy paste. The current collector (electrode substrate) was coated on both sides, dried, and then roller-pressed at a constant pressure. Then, the size, thickness and weight of the electrode were measured, and the density of the alloy in the electrode (referred to as electrode filling density) was calculated from these measured values.
[0023]
Table 1 lists the mixing ratio, tap bulk density, angle of repose, and electrode packing density of the mixed powder. Further, in order to make it easy to understand the relationship between the powder characteristic values (the angle of repose and the tap density) and the electrode filling density, the correlation between the size relationship of each characteristic value and each mixed powder No. is shown in FIG. In FIG. 1, the portion surrounded by a broken line is the range defined by the present invention.
[0024]
[Table 1]

[0025]
From Table 1, the following becomes clear. From the comparison of No. 1 and No. 3 consisting only of spherical and non-spherical alloy powders X ₂ and Y ₂ and No. 2 consisting only of spherical or substantially spherical alloy powder Y ₁ , the average particle size was the same. However, it can be seen that when the type of the alloy powder is different, a large difference occurs in the tap bulk density and the angle of repose. On the other hand, comparing the characteristic values of No. 1 with an average particle diameter of 50 μm and No. 10 with an average particle diameter of 30 μm, it can be seen that the electrode packing density does not necessarily increase even if the average particle diameter is reduced. That is, when the type of alloy powder is different, the powder characteristics are greatly different, and there is a discrepancy between the electrode packing density predicted from the average particle size and the actual packing density. Therefore, it can be understood that it is difficult to predict the electrode packing density using the average particle diameter as an index.
[0026]
In the mixed powder No. 4 to No. 9 and No. 12 to No. 15, when the relationship between the mixing ratio of various alloy powders and the powder characteristics is observed, each characteristic value varies depending on the type and mixing ratio of the alloy powder used. And it turns out that an electrode filling characteristic improves in a suitable mixing | blending. That is, in No. 1 and No. 10 consisting only of spherical and non-spherical alloy powder X ₂ and No. ₂ consisting only of spherical or substantially spherical alloy powder Y _{1 having} an average particle diameter of 50 μm, sufficient electrode filling The density cannot be obtained. However, when an alloy powder having a reverse shape is mixed with these alloy powders at an appropriate ratio, the electrode packing density can be improved (No. 5 to No. 7, No. 9, No. 13 to No. 13). 15).
[0027]
Next, in FIG. 1, the electrode packing densities of No. 1 to No. 15 are arranged in descending order, and the relationship between the tap bulk density and the angle of repose is a mixed powder having an angle of repose of 25 degrees or more and 40 degrees or less. It can be seen that an electrode filling density of 4.4 g / cc or more is secured. On the other hand, when a No. with an electrode filling density of 4.4 g / cc or more is picked up using the tap bulk density as an index, the lower limit value becomes a point with a tap bulk density of 4.1 g / cc. However, the tap filler density of 4.1 g / cc or higher includes No. 2 and No. 8 where the electrode packing density is not 4.4 g / cc or higher, and the electrode filler density cannot be determined reliably with the tap filler density. I understand that.
[0028]
From the above results, it is demonstrated that the angle of repose is not affected by the type of alloy powder and the like, and is useful as an index that can easily represent the characteristics of the alloy powder that can be a certain density of electrode filling. It is proved that an electrode filled with an alloy can be obtained at a high density by producing a hydrogen storage alloy electrode using an alloy powder having an angle of repose of 25 degrees to 40 degrees. Moreover, if alloy powders having different properties are mixed at an appropriate ratio, the angle of repose can be easily adjusted to 25 to 40 degrees, and it is clear that even such a mixed powder can ensure a high electrode packing density. Become.
[0029]
In addition, in No. 2 with a small angle of repose and a large tap bulk density, the reason why the electrode packing density was small is considered to be as follows. That is, No. 2 is composed only of a spherical or substantially spherical alloy alloy powder, so that the fluidity is too good. Therefore, the force applied in the direction perpendicular to the electrode in the electrode rolling process is dispersed in the horizontal direction, and the alloy particles escape (move) in the horizontal direction accordingly.
[0030]
【The invention's effect】
As is apparent from the above, an alloy powder having a high electrode filling density can be easily adjusted by using the angle of repose as an index of electrode filling characteristics. Therefore, according to the present invention, a hydrogen storage alloy electrode having a large electric capacity per unit volume can be obtained without substantially increasing the production cost of the electrode.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram showing the relationship between the size relationship of each powder characteristic value and the mixed powder number.
FIG. 2 is an explanatory diagram showing a method for measuring an angle of repose.

Claims

Producing a spherical or substantially spherical hydrogen storage alloy;
Crushing the spherical or substantially spherical hydrogen storage alloy to form a spherical or substantially non-spherical hydrogen storage alloy;
The spherical or substantially spherical hydrogen storage alloy and the spherical or non-spherical hydrogen storage alloy are mixed so that the repose angle is 25 to 40 degrees , and the hydrogen storage angle is 25 to 40 degrees . Preparing an alloy powder;
Preparing an active material paste using the hydrogen storage alloy powder;
Holding the active material paste on an electrode substrate;
Rolling the electrode substrate holding the active material paste;
A method for producing a hydrogen storage alloy electrode, comprising:

A repose angle adjustment step of mixing and adjusting a spherical or substantially spherical hydrogen storage alloy and a spherical or substantially non-spherical hydrogen storage alloy so that the repose angle of the mixed powder is 25 degrees to 40 degrees ,
An active material paste preparation step of preparing an active material paste using a hydrogen storage alloy powder having an angle of repose adjusted;
A filling step of filling the electrode substrate with the active material paste;
After the filling step, rolling the electrode base to produce a hydrogen storage alloy electrode having a hydrogen storage alloy powder packing density of 4.6 g / cc or more;
A method for producing a hydrogen storage alloy electrode, comprising: